Ketones, aldehydes and

Aldehydes are produced by the mild oxidation of primary alcohols—alcohols with the —OH group on an end carbon atom. 

The mild oxidation of a secondary alcohol (with the —OH group on a carbon atom connected to two other carbon atoms) produces a ketone. 

Each of these groups is characterized by having a carbonyl group, C=0, but the aldehyde has the C=0 group on one end of the carbon chain, and the ketone has the C=0 group on a carbon other than one on the end. Acetone is a familar solvent for varnishes and lacquers. As such, it is used as a nail polish remover. The systematic name ending for a/dehydes is -al that for ketones is -one. 

Aldehydes are usually called by their common names. These are derived from the name of the acid with the same number of C atoms (Table 2 3-9). The systematic (TUPAC) name is derived from the name of the parent hydrocarbon. The sufBx -al is added to the characteristic stem. The carbonyl group takes positional precedence over most other substituents. 

Unless otherwise noted, all content on this page is Cengage Learning. 

CHAPTER 23 ORGANIC CHEMISTRY I FORMULAS. NAMES. AND PROPERTIES 

Acetone Is the active Ingredient in some nail polish removers. 

Steroid molecnies have similar molecniar shapes hnt different hiochemical fnnctions. Progesterone [top), a female sex hormone, and testosterone [bottom), a male sex hormone. Both are ketones. 

In ketones this group is bonded to two carhon atoms an example is acetone  

In aldehydes the carbonyl group always appears at the end of the hydrocarbon chain. There is always at least one hydrogen bonded to the carbonyl carbon atom. An example of an aldehyde is acetaldehyde  

We often use compact formulas for aldehydes and ketones. For example, formaldehyde (where R = H) and acetaldehyde (where R = CH3) are usually represented as HCHO and CH3CHO, respectively. Acetone is often written as 

Many ketones have useful solvent properties (acetone is often found in nail polish remover, for example) and are frequently used in industry for this purpose. Aldehydes typically have strong odors. Vanillin is responsible for the pleasant odor of vanilla beans cinnamaldehyde produces the characteristic odor of cinnamon. On the other hand, the unpleasant odor of rancid butter arises from the presence of butyraldehyde and butyric acid. 

4- DNPHs and Celite 50 fil of the DNPH of butyraldehyde were added as an internal standard. An error of 10% was obtained in a quantitative evaluation. 

A standard mixture of aldehydes (1.7- 10 3 mol) was subjected to reaction with 

300 mg of Girard-T reagent (1.8 10 3 mol) in the presence of 250 mg of Rexyn 102 (H+) and 50 ml of tert. -butanol azeotropic solution. The mixture was refluxed at 80°C for 1 h, filtered through glass-wool and concentrated in Buchler rotational evaporator to ca. 5 ml at room temperature. The concentrated solution was transferred into a 25-ml volumetric flask and made up to the mark with tert. -butanol. Aliquots of 10 ml were pipetted into a 25-ml erlenmeyer flask and evaporated almost to dryness at 40°C in a stream of pure nitrogen. The residue was dissolved in 0.5 ml of tert.-butanol, transferred into a 1-ml volumetric tube and made up to the mark with tert.-butanol. Aliquots of 5 jul were transferred into a capillary (90 X 0.8 mm) with 5 jul of a solution of paraformaldehyde or methylolphthalimide. The capillary was sealed and heated at 200°C for 2 min, cooled and 2 /d were injected for GC analysis. 

More attention has been devoted, particularly in recent years, to the direct GC separation of hydrazones of carbonyl compounds. Phenylhydrazones of aldehydes can be separated successfully in a column packed with SE-30 on Chromosorb W at temperatures ranging from 120 to 190°C [50]. Korolczuk et al. [51] considered this problem in more detail. They described the separation of phenylhydrazones of 27 aldehydes and ketones using different temperature programmes and studied the influence of the initial temperature on the retention of the derivatives. The analysis time is less than 15 min for carbonyl compounds with up to 11 carbon atoms with programming at 10°C/min in the range 150—280°C. Some derivatives provide two peaks which can be ascribed to their syn—anti isomerism, although even the decomposition of the derivatives cannot be eliminated as a cause, particularly with the use of a metallic column. 

The GC separation of 2,4-dinitrophenylhydrazones has been studied by a number of workers [52-55], Non-polar stationary phases of the SE-30 and SF-96 type were utilized for this purpose at temperatures of 200—250°C, mostly with temperature programming. Retention indices of the 2,4-DNPHs of some carbonyl compounds on OV-type stationary phases are presented in Table 5.5. Using columns with a higher separation efficiency, some 2,4-DNPHs provide two peaks. The discussion of whether these artifacts are caused by thermal decomposition or syn-anti isomerization of the derivatives seems to favour the latter. The ratio of the areas of the peaks of the two derivatives depends on the polar- 

Formation and Properties of Formaldehyde (SECTIONS 176, 177).—(a) Prepare a dilute solution of formaldehyde by oxidizing methyl alcohol as directed in experiment 11b, page 55, and make the following tests  

—(b) In these teats very dilute solutions of formaldehyde should be used, since strong solutions give precipitates which obscure the colors that develop. 

Aldehyde and sodium hydrogen sulphite.—Shake under water 2 cc. of the aldehyde prepared in the experiment just described with 5 cc. of a saturated solution of sodium hydrogen sulphite. (.Eq.) Note the disappearance of the odor of aldehyde. Add 5 cc. of a strong solution of sodium carbonate and heat, noting the odor. (Eq.) 

Formation of Acetaldehyde from an Acetate (section 178).—Mix together 5 grams of sodium formate and 6 grams of anhydrous sodium acetate in an 8-inch test-tube. Place the tube in an inclined position and attach by means of a cork a delivery-tube which dips under water contained in a test-tube. Heat for a few minutes. Test the resulting solution of aldehyde with Schiffs reagent. 

—Sodium acetate is mixed with calcium acetate in this preparation in order to facilitate the formation of acetone. 

In 2010, Franz and co-workers found chiral pybox complex Sc Vl7 as an efficient catalyst for the direct addition of indoles to N-Me isatin 15 to afford 3-hydroxy-2-oxindole derivatives 16 (Table 6.1). This chiral catalytic system 

Aldehydes and Ketones. The best derivative from which an aldehyde can be recovered readily is its bisulphite addition compound, the main disadvantage being the lack of a sharp melting point. The aldehyde (sometimes in ethanol) is shaken with a cold saturated solution of sodium bisulphite until no more solid adduct separates. The adduct is filtered off, washed with a little water, then alcohol. A better reagent is freshly prepared saturated aqueous sodium bisulphite solution to which 75% ethanol is added to near-saturation. (Water may have to be added dropwise to render this solution clear.) With this reagent the aldehyde need not be dissolved separately in alcohol and the adduct is finally washed with alcohol. The aldehyde is recovered by dissolving the adduct in the least volume of water and adding an equivalent quantity of sodium carbonate (not sodium hydroxide) or concentrated hydrochloric acid to react with the bisulphite, followed by steam distillation or solvent extraction. 

Other derivatives that can be prepared are the Schiff bases and semicarbazones. Condensation of the aldehyde with an equivalent of primary aromatic amine yields the Schiff base, for example aniline at 100° for 10-30min. 

Semicarbazones are prepared by dissolving semicarbazide hydrochloride (ca Ig) and sodium acetate (ca 1.5g) in water (8-lOml) and adding the aldehyde or ketone (0.5-lg) and stirring. The semicarbazone crystallises out and is recrystallised from ethanol or aqueous ethanol. These are hydrolysed by steam distillation in the presence of oxalic acid or better by exchange with pyruvic acid (Hershberg dOC 13 542 1948). 

Aldehydes and ketones were also investigated by Hemptinne.2 

Acetaldehyde gives carbon monoxide, hydrogen, and methane. Paraldehyde.—The gaseous products formed are carbonic acid, 

Propylaldehyde breaks up in a different manner than the isomeric allyl alcohol. The gas, separated from the aldehyde, contained carbonic acid, methane, and ethane, hydrocarbons, CnH2n carbon monoxide, and hydrogen. 

Acetone, likewise isomeric with allyl alcohol, gives the same products as propyl aldehyde. As the quantity of carbon monoxide does not decrease in the presence of phosphorus, Hemp-tinne concludes that the following decomposition process occurs  

According to Maquenne1 acetone vapor is decomposed by the electric discharge into hydrogen, ethane, and carbon monoxide, a small quantity of acetylene and carbon dioxide being also formed. The quantity ratios are less dependent upon the pressure than in the case of methyl and ethyl alcohol  

Aldehydes and ketones are usually hydrogenated to the alcohol over platinum, rhodium or ruthenium catalysts at 25 -60°C and 1-5 atmospheres pressure. Platinum catalyzed hydrogenations are generally best run in acidic media while with rhodium or ruthenium neutral or basic solvents are preferred. Hydrogenations run over ruthenium catalysts are facilitated by the presence of water which makes ruthenium a particularly effective catalyst for the hydrogenation of sugars and other water soluble aldehydes and ketones.2 

50°C and 25-40 atmospheres of hydrogen (Eqn. 18.2). The use of the ftee base or other catalysts resulted in the production of varying amounts of the amine cleavage product. The presence of molybdenum or chromium increases the activity of a Raney nickel catalyst toward aldehyde and ketone hydrogenation. 

The hydrogenation of aryl aldehydes and ketones is complicated by the potential for the hydrogenolysis of the resulting benzyl alcohol as well as benzene ring hydrogenation (Eqn. 18.3). With the proper selection of reaction conditions 

Hydrogenolysis of the benzyl alcohol occurs readily during the hydrogenation of o- and p- hydroxyphenyl aldehydes and ketones, even over platinum and nickel catalysts. This can be minimized by using an activated Cu-CrO catalyst at 80°-90°C and 165-200 atmospheres of hydrogen. The catalyst was activated by refluxing it in cyclohexanol under nitrogen for four 

While the hydrogenation of unactivated aliphatic aldehydes and ketones does not generally take place over palladium, this catalyst readily promotes the hydrogenolysis of aryl aldehydes and ketones to the methylene at room temperature and 1-4 atmospheres pressure. The use of an acidic solvent facilitates this reaction2 -29 but is not essential for obtaining good to excellent yields of the desoxy product (Eqn. 18.8). 0 With a basic substrate such as a 2- or 4-acyl-pyridine, however, the alcohol product was obtained (Eqn. 18.9).31 

Aldehydes and ketones are generally reduced to primary and secondary alcohols by all the reagents studied with the following exceptions  

Although single-electron transfer is proposed in the reduction of aromatic ketones by AIH3, BH3, and LAH-pyridine [AG2], the reductions of aldehydes and ketones by alumino- and borohydrides and boranes occur mostly by nucleophilic attack of hydride on the carbonyl carbon. This process has been the subject of numerous theoretical [ESI, HWl, N2, W2] and mechanistic [CBl, N5, W2, W4] studies. 

In certain cases, the reduction can take place without electrophilic catalysis (n-BU4NBH4 or phase-transfer conditions), but most frequently it requires the coordination of the carbonyl group by a Lewis acid before nucleophilic attack [S2]. The Lewis acid may be the cation associated with the reagent, an added acid, or even the boron or aluminum atom of tricoordinate reagents (AIH3, DIBAH, boranes). The importance of this phenomenon has been shown by the introduction of coordinating macrocyclic molecules into solutions of LAH and LiBH4. This considerably retards the reduction of carbonyl compounds in an ether medium [DCl, HPl], Electrophilic catalysis is more important when the lowest unoccupied molecular orbital (LUMO) 

The reduction by alkaline cyanoborohydrides takes place at pH values less than 4 [LI]. The reduction of ketones by ZnlCNBHjlj is efficient only in EtjO [KK5] and 

LAH on silica gel reduces ketoesters to hydroxyesters in Et20 [KH3], The reduction of epoxy ketones to epoxy alcohols is easily accomplished by action of Zn(BH4)2 in Et20 or NaBH4 in MeOH, sometimes in the presence of CeClj. The stereoselectivity of the reaction is usually high [BB6, BC2, CP3, NTl] (Section 3.2.4). 

Aldehydes and ketones are compounds containing the acyl group. The carbonyl group present in them is polar because of the electronegativity of oxygen. It is noteworthy to mention that the carbonyl group in aldehydes and ketones are very reactive. 

The partial negative charge on the oxygen is because of its higher electronegativity compared to carbon. This gives the carbonyl carbon a partial positive charge. 

Aldehydes and ketones are a large family of organic compounds that permeate our everyday lives. They are responsible for the fragrant odors of many fruits and fine perfumes. For example, cinnamaldehyde (an aldehyde) provides the smell we associate with cinnamon, and civetone (a ketone) is used to provide the musky odor of many perfumes. Formaldehyde is a component of many building materials we use to construct our houses. The ketones testosterone and estrone are known to many as hormones responsible for our sexual characteristics. And the chemistry of aldehydes and ketones plays a role in how we digest food and even in how we can see the words on this page (see A Word About... The Chemistry of Vision on pages 76-77). So what are aldehydes and ketones  

Online homework for this chapter can be assigned in OWL, an online homework assessment tool. 

14 Keto-Enol Tautomerism A WORD ABOUT... Tautomerism and Photochromism 

The carbonyl group is a C=0 unit. Aldehydes have at ieast one hydrogen atom attached to the carbonyi carbon atom, in ketones, the carbonyi carbon atom is connected to two other carbon atoms. 

We will see that the carbonyl group appears in many other organic compounds, including carboxylic acids and their derivatives (Chapter 10). This chapter, however, will focus only on aldehydes and ketones. 

Aldehydes and ketones contain the same functional group, the so-called carbonyl group  

They differ only in the number of alkyl R or aryl groups Ar that surround them, or in the degree of substitution of the carbonyl group  

LEARHIHG GOAL Write the lUPAC and common names for alcohols, phenols, and ethers draw the condensed structural formulas when given their names. 

27 Draw the condensed stractural formula for each of the following  

In the lUPAC system, an aldehyde is named by replacing the e in the corresponding alkane name with al. No number is needed for the aldehyde group because it always appears at the beginning of the chain. However, the aldehydes with carbon chains 

FIGURE 17.5 The carbonyl group is found in aldehydes and ketones. 0 If aldehydes and ketones both contain a carbonyl group, how can you differentiate between compounds from each family  

The two substitutive naming approaches for aldehydes are used exactly as in the case of carboxylic acides, nitriles, etc. 

For linear aldehydes bearing cyclic substituent groups, Chem. Abstr. again employs exclusively conjunctive names. 

H2C2 CH0 subst. 3-Chloro-3-[4-(2-Oxoethyl)-2-naphthyl] propanal 

The possibilities for naming ketones are manifold but not stringently delimited with regard to their respective areas of application. Nonetheless, is it again the rules of substitutive nomenclature that are most uniformly applicable here and should therefore be prefered. 

The substitutive method is also applied in a straightforward manner when the keto function is unilaterally attached to a cyclic component. To prevent breaking any rules, a nomenclatorial/semantic artifice is unavoidable here. This consists in the renaming of an alkanal, in principle not substitutable at its 1-position, as a fictive, substitutable, alkan-l-one. This leads to the 

This subject has been reviewed by Lecomte [82] and some very useful tables of typical carbonyl frequencies have been compiled by Jones and Sandorfy [83], Jones and Herling[84], Rao[178], Bellamy [179], and Renema[180] amongst others. The factors responsible for group frequency shifts have been considered by a 

Saturated open-chain ketones 0f 8-unsaturated ketones 

Six- and seven-mem-bered-ring ketones F ive-m emb ered-ring ketones 

There is, of course, a certain amount of overlapping between some of these frequency ranges and those arising from other types of carbonyl absorption, but in some cases this difficulty can be resolved 

Aldehydes have been less extensively studied, but there is a considerable body of evidence to show that the frequency shifts caused by environmental changes are closely parallel to those of ketones. The identification of aldehydes can usually be confirmed by a study of the C—H stretching frequency of the aldehydic group. By virtue of the strong influence of the carbonyl oxygen, this C—H frequency is virtually independent of the rest of the molecule, and is therefore highly characteristic. 

Numerous aldehydes and ketones, like the terpene alcohols, possess a characteristic odour. Some are easily accessible synthetically and are often used in the perfume industry. Commonly known examples are cinnamaldehyde with the typical smell of cinnamon vanillin with the vanilla odour and carvone smelling of caraway seed. 

Both the aldehydes and ketones directly and also their crystalline derivatives may be investigated chromatographically. 

Preparation.—The conversion of acid chlorides into ketones using lithium dialkyl cuprates has been studied by two groups the reagents are sufficiently 

Whereas platinum-catalysed reduction of acid chlorides with triethyl-silane gives aldehydes, Eaborn has shown that rhodium catalysis can give predominantly ketones. a-Ketophosphonate esters, readily available from the action of carboxylic acid chlorides on trialkyl phosphites, are reduced by sodium borohyffiride to the ester (123), which fragments to the 

Posner and C. E. Whitten, Tetrahedron Letters, 1970, 4647 J.-E. Dubois, M. Boussu, and C. Lion, Tetrahedron Letters, 1971, 829. 

Jallabert, N.-T. Luong-Thi, and H. Riviere, Bull. Soc. chim. France, 1970, 797. 

Mitsudo, T. Okajima, Y. Takegami, M. Tanaka, Y. Watanabe, and K. Yamamoto, Bull. Chem. Soc. Japan, 1971, 44, 2569. 

Review Comprehensive Organic Synthesis, Eds. B. M. Trost and I. Fleming, Pergamon, Oxford (1991), Vol 8, Parts 1.13 and 1.14, pp 307-362 

Also other reaction types have been dealt with in CHEC(1984) and CHEC-II(19%) like reduction to alcohols (e.g., sodium borohydride), Wolff Kishner reduction, nucleophilic addition via reaction with Grignard reagents or organo-lithium compounds, and formation of imine type functional groups (e.g., hydrazones). New examples are the reaction of 

FIGURE 4.24 Absorption cross section of S02 (adapted from Manatt and Lane, 1993). 

The absolute values of the absorption cross sections of HCHO have been somewhat controversial. This appears to be due to a lack of sufficient resolution in some studies as discussed in Chapter 3.B.2, if the spectral resolution is too low relative to the bandwidth, nonlinear Beer-Lambert plots result. The strongly banded structure means that calculations of the photolysis rate constant require actinic flux data that have much finer resolution than the 2- to 5-nm intervals for which these flux data are given in Chapter 3 or, alternatively, that the measured absorption cross sections must be appropriately averaged. One significant advantage of the highly structured absorption of HCHO is that it can be used to measure low concentrations of this important aldehyde in the atmosphere by UV absorption (see Sections A.ld and A.4f in Chapter 11.). 

TABLE 4-22 Absorption Cross Sections (Base e) for S03a 

Wavelength (nm) io2V (cni2 molecule 1) Wavelength (nm) to2V (cni2 molecule 1) 

FIGURE 4.25 Absorption spectra of H202 and CH,OOH at room temperature (data for H202 from DeMore et al., f997 recommendation, and for CH,OOH from Vaghjiani and Ravishankara, f989). 

Aldehydes appear as products of oxidation of primary alcohols while ketones are products of the oxidation of secondary alcohols. Since oxidation is recognized as the reaction in which hydrogen is removed from the molecule, the removal of a hydrogen molecule from the primary alcohol yields a compound that has historically been called alcohol dehydrogenatus. The word aldehyde is derived from the first few letters of this historic name. 

Besides being prepared by oxidation, aldehydes and ketones can also be prepared by reactions in which the first step includes the addition of water to the triple bond of the alkyne molecule. The first intermediate, the unsaturated alcohol (enol) is unstable and undergoes isomerization to the stable ketone. This type of reaction in which one isomer is transformed to another is called rearrangement. The older name for this molecular rearrangement is taulomerism and this special case is called the keto-enol tautomerism. 

The constitutional difference between aldehydes and ketones lies in the substituents at the carbonyl carbon atom. While in aldehydes one of the substituents is always hydrogen in ketones both substituents are alkyl groups. Therefore, the chemical properties of aldehydes and ketones, especially in nucleophilic addition reactions are similar. The simplest aldehyde is methanal or formaldehyde and the parent ketone is propan-2-one or acetone. 

Aldehide Ketone Methanal (Formaldehyde) Propan-2-one (2-Oxopropane) (Acetone) 

In the following scheme we list structures and the traditional names of some of the important and well-known aldehydes and ketones. Most of them are natural products, which shall be discussed in the subsequent chapters of this book. 

In addition to its uses in beverages, ethanol is used in organic solvents and in the preparation of various organic compounds such as chloroform and diethyl ether. Its production is also measured in the billions of pounds annually. 

18 Identify the sttuctural formulas of the functional groups that distinguish 

19 Given the name (or structural diagram) of an aldehyde or ketone, write the structural diagram (or name). 

20 Write structural diagrams to show how a specified aldehyde or ketone is prepared from an alcohol. 

If at least one hydrogen atom is bonded to the carbonyl carbon, the compound is an aldehyde, RCHO if two alkyl groups are attached, the compound is a ketone, R—CO—R.  

Arylhydrazines (ArNHNH2), which include phenylhydrazine, 4-nitrophenylhy-drazine, and 2,4-dinitrophenylhydrazine, are commonly used to make crystalline derivatives of carbonyl compounds. The formation of a 2,4-dinitrophenylhydra-zone 3 is represented by Equation 25.9, and the mechanism of this transformation typifies that followed by a number of compounds, RNH2, that may be considered derivatives of ammonia. Thus, the overall reaction involves initial acid-catalyzed addition of the elements of N-H across the carbonyl Tr-bond to afford a tetrahedral intermediate, which subsequently dehydrates to the product (Eq. 25.9). 

The arylhydrazines are valuable reagents for both classifying and forming derivatives because the solid products of these test reactions may be used as derivatives of the aldehyde or ketone 2,4-dinitrophenylhydrazine is particularly useful in this regard. 

The arylhydrazines will give a positive test for either an aldehyde or a ketone. Schiff s and Tollens s tests given in Parts B and C, respectively, provide methods for distinguishing between these two types of compounds. 

This reaction work d best for aromatic aldehydes and for aliphatic chains up to seven carbons. 

The conversion of an acid chloride into the corresponding aldehyde requires the use of the reagent lithium aluminum trw-butoxy hydride (LiA]H[OC(CH )3 ] ) or LiAIH(0-f-Bu)3 

This reaction works on both aliphatic and aromatic acid chlorides. 

X-3 Chromium trioxide (CrOs ) and acetic anhydride (Ac, O) oxidation. This reaction is good only Tor the formation of aromatic aldehydes. This reaction requires a Cllj attached directly to the aromatic nucleus  

X-4 Oxidation of a secondary alcohol requires the use of 3 s r oxidizing agent, cither KMnO and OH or K2Cr,Oi 3,1 H,S04 (the latter is more frequently used). 

5 Reactions Common to Aldehydes And Ketones 3.15.5.1 Rednction to Alcohol 

To obtain derivatives of aldehydes and ketones for GC analysis the most widely used reaction is that of condensation with the corresponding amines, e.g., N-aminopiperidine, pentafluorophenylhydrazine or phenyUiydrazine [259]. The most popular reagent is 

4-dinitrophenylhydrazine, with the help of which carbonyl compounds can be 

LIMITS OF DETECTION IN THE GAS CHROMATOGRAPHIC ANALYSIS OF ELEMENTS IN THE FORM OF VOLATILE COMPLEXES AND COMPOUNDS 

Element Ligand (radical) Detection limit (g - 10 ) Reference 

The basic nomenclature for aldehydes and ketones follows that of other organic compounds. The following steps cire the keys  

Find the longest chain containing the carbonyl gronp to determine the parent name. 

Replace the final -e of the hydrocarbon with an -al for aldehydes or an -one for ketones. 

Number the longest chain so the carbonyl has the lowest number. 

Identify and name all substituents attached to the longest chain. 

The condensed structurai formuia for aide-hydes is RCHO, and for ketones it is RCOR. in ketones the R groups may be the same or different. 

Both aldehydes and ketones contain a carbonyl group (/ ). Ketones have an R group attached to both sides of the carbonyl group, while aldehydes have an R group on one side of the carbonyl group and a hydrogen atom on the other. (An exception is formaldehyde, which is an aldehyde with two H atoms attached to the carbonyl group.) 

Other common aldehydes and ketones are shown here. 

One way of naming amines is to name in alphabetical order the alkyl groups attached to the nitrogen atom, using the prefixes di- and tri- if the groups are the same. An example is isopropylamine whose formula is shown above. What are names for (a), (b), (c), and (d) Build handheld molecular models for the compounds in parts (a)-(d). 

Write bond-line formulas for (e) propylamine, (f) trimethylamine, and (g) ethylisopropyl-methylamine. 

Which amines in Review Problem 2.15 are (a) primary amines, (b) secondary amines, and (c) tertiary amines  

Amines are like ammonia in being weak bases. They do this by using their unshared electron pair to accept a proton, (a) Show the reaction that would take place between trimethylamine and HCI. (b) What hybridization state would you expect for the nitrogen atom in the product of this reaction  

Aldehydes and ketones both contain the carbonyl group—a group in which a carbon atom has a double bond to oxygen  

Principal component analysis of the aldehydes and the ketones, respectively, afforded two significant components which accounted for 78% (aldehydes) and 88% (ketones) of the total variance. A score plot of the ketones is shown in the example of the Fischer indole synthesis given in Sect. 5.3.2. For a score plot of the aldehydes, see [61]. 

I AIM To learn the general formulas for aldehydes and ketones and some of their uses. 

4 What Is the Most Common ReactionTheme of Aldehydes and Ketones  

5 What Are Grignard Reagents, and How DoThey React with Aldehydes and Ketones  

7 How Do Aldehydes and Ketones React with Ammonia and Amines  

2 How to Determine the Reactants Used to Synthesize a Hemiacetal or Acetal 

CHEMICAL CONNECTIONS 12A A Green Synthesis of Adipic Acid 

Electronically excited carbonyl compounds serve as versatile intermediates in countless reactions. They not only operate as reactive substrates for intra- and intermolecular hydrogen abstraction and cycloaddition reactions as well as C-C cleavage steps, but many of them also are useful sensitizers for the generation of triplet excited compounds. This variety of reaction possibilities makes carbonyl photochemistry sometimes very complex, 

In general electronically excited carbonyl compounds show five reaction types  

Norrish Type I cleavage reactions dominate in the gas phase photochemistry of many acyclic aldehydes and ketones, whereas in the liquid phase this process is less common and alternative pathways (ii, iii, v) dominate. When no suitable C-H bonds are present to allow hydrogen abstraction reactions, however, this process will also constitute an important synthetic method for the cleavage of a-C-C bonds in solution. One important subsequent reaction of the resulting acyl and alkyl radicals is carbon monoxide formation and radical combination. Overall CO extrusion results which represents a versatile method for the formation of C-C single bonds from ketones. When cyclic substrates (cycloalkanones but not conjugated cycloalkenones which exhibit a different photochemistry) are used, ring 

Beside carbon monoxide extrusion acyl radicals formed in a a-cleavage reaction can stabilize by subsequent hydrogen migration. Thus the a-trimethylsilylmethyl substituted cyclopentanone used by L. F. Tietze gives in a clean photochemical reaction the corresponding aldehyde with a vinylsilane moiety in its side chain. 

Three examples are given for the well-known Patemo-BUchi reaction, two intermolecular and one intramolecular version in the course of his studies on pharmaceutically active oxetanes, G. Just developed the [2+2]-cycloaddition of O-protected a-hydroxy acetic aldehyde to 2-methylfuran and an interesting further functionalization of the resulting oxetane. 

Aldehydes and ketones are most often produced commercially by the oxidation of alcohols. Oxidation of a primary alcohol gives the corresponding aldehyde, for example. 

This chapter will explore the reactivity of aldehydes and ketones. 

Preparing Aldehydes and Ketones A Review Introduction to Nucleophilic Addition Reactions Oxygen Nucleophiles Nitrogen Nucleophiles Mechanism Strategies Sulfur Nucleophiles Hydrogen Nucleophiles Carbon Nucleophiles Baeyer-Villiger Oxidation of Aldehydes and Ketones Synthesis Strategies 

Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter  

PLUS Visit www.wileyplus.com to check your understanding and for valuable practice. 

Aldehydes (RCHO) and ketones (R2CO) are similar in structure in that both classes of compounds possess a C=0 bond, called a carbonyl group  

Subsequent to the finding that the compounds Rh6(CO)i6 and Re2(CO)io will catalyze the autoxidation of ketones, it was also found that the phosphine complexes IrCl(CO)(PPh3)2 and Pt(PPh3)3 were effective catalysts for this oxidation.The organic oxidation products are carboxylic acids (Equations 24-27), but the phosphine compounds are not recovered unchanged. Inhibition by free-radical scavengers is observed, and a reaction pathway is followed whereby the phosphine complex acts to accelerate the conversion of preformed hydroperoxides and peracids to carboxylic acid.  

The compound Pd(PPh3)4 can be used as a liquid-phase autoxidation catalyst for cumene oxidation.It is again concluded that the role of the transition metal compound is in its reaction with preformed cumene hydroperoxides. 

Tertiary phosphines are among the easiest molecules to catalytically oxidize with molecular oxygen. The reactions can usually be effected under ambient temperature and pressure conditions. Metal complexes of both the platinum metal group and from the first row transition series have been used as catalysts, although in only a few cases have detailed mechanistic 

Complexes of cobalt have also been used as catalysts for the oxidation of tertiary phosphines with molecular oxygen. In methanol solvent the compound Co2(CN)4(PMe2Ph)502 reacts with PMe2Ph, converting it into the oxide.Since the oxygen compound is readily formed again from the product complex Co(CN)2(PMe2Ph)3, a catalytic cycle can be obtained (28, 29) for the phosphine oxidation. 

Studies on the reactions of CoCl2(PEr3)2/ and also on a mixture of Co(acac)2 and show the reactions to form only OPE s and 

3 Reduction of Carbonyl Compounds and Derivatives 3.23.1 Aldehydes and Ketones 

Of greater industrial interest is the possibility of converting carbonyl compounds into the corresponding hydrocarbons. The reaction requires strongly acidic electrolytes. Examples of this reaction are syntheses in the areas of carotenoids 463) and fragrances 4641  

The electrochemical reduction of carbonyl compounds can also be used for C—C coupling. An example of industrial interest is a new benzanthrone synthesis patented by Ciba 465). If anthraquinone is reduced in 85 % H2S04 in the presence of glycerol, the oxanthrone formed as an intermediate reacts with glycerol to form benzanthrone  

Since the reaction has to be carried out in a divided cell, the anode compartment can be used for a second reaction, for example, the oxidation of Mn(II) to Mn(III) sulfate 466). The Mn(III) solution can then be used for the synthesis of dioxoviolanthrone (intermediate for vat dyes). 

The electrochemical hydrodimerization of aromatic aldehydes is more familiar. The essential advantage of this electrosynthesis is the possibility to dispense with the use of metals as reducing agents. The reaction was investigated, for example, by Monsanto for the electrosynthesis of l,2-bis-(hydroxyphenyl)-ethanediol467 -4691  

The carbonyl group, C=0, is present in both aldehydes (RCH=0) and ketones (R2C=0). The IUPAC ending for naming aldehydes is -a/, and numbering begins with the carbonyl carbon. The ending for the names of ketones is -one, and the longest chain is numbered as usual. Common names are also widely used. Nomenclature is outlined in Sec. 9.1. 

The carbonyl group is planar, with the sp2 carbon trigonal planar. The C=0 bond is polarized, with C partially positive and O partially negative. Many carbonyl reactions are initiated by nucleophilic addition to the partially positive carbon and completed by addition of a proton to the oxygen. 

With acid catalysis, alcohols add to the carbonyl group of aldehydes to give hemiacetals [RCH(OH)OR ]. Further reaction with excess alcohol gives acetals [RCH(OR )2]- Ketones react similarly. These reactions are reversible that is, acetals can be readily hydrolyzed by aqueous acid to their alcohol and carbonyl components. Water adds similarly to the carbonyl group of certain aldehydes (for example, formaldehyde and chloral) to give hydrates. Hydrogen cyanide adds to carbonyl compounds as a carbon nucleophile to give cyanohydrins [R2C(OH)CN], 

Grignard reagents add to carbonyl compounds. The products, after hydrolysis, are alcohols whose structures depend on that of the starting carbonyl compound. Formaldehyde gives primary alcohols, other aldehydes give secondary alcohols, and ketones give tertiary alcohols. 

Nitrogen nucleophiles add to the carbonyl group. Often, addition is followed by elimination of water to give a product with a R2C=NR group in place of the R2C=0 group. 

The bond dissociation energy D[CFj-CX)—H] = 381 8 kJ mol at 298 K has been derived from data obtained in a study of the kinetics of thermal bromination of trifluoroacetaldehyde, and the results of a detailed study of the vibrational spectrum of the aldehyde have been presented. 2-Bromotetrafluoropropanal has been obtained by pyrolysis of the dibromide prepared from the ether (20-CF3-CF CH-OEt.  

The structures of hexafluoroacetone and its imine (CF ),C NH, together with that of the structurally related butene (CFs)2C CHj, have been determined by gas-phase electron difliraction comparison of the data obtained with those for the hydrocarbon counterparts indicates that replacement of CHj by CFg leads to a longer C—C bond (by 0.03—0.04 A) and a much longer multiple bond.  

The dielectric properties of hexafluoroacetone have been examined and compared with those of hexachloroacetone the dipole moments of the hexa- 

Studies on positive and negative ion formation as a result of the electron bombardment of hexafluoroacetone have provided the value 4.16 eV for the bond dissociation energy D[CF,—CO-CF,) this expm mental value is larger than the estimated value, and the difference, 0.46 eV, may represent the maximum activation energy for the decomposition CF -CO- CFs- CX .  

Hexafluoroacetone has been used as a photochemical source of trifluoro-methyl radicals in kinetic studies dealing with attack of the latter on ethylene, di-isopropyl ketone, methylchlorosilanes, the methylsilanes MejSi, MejSiF, MeaSiFj, and MeSiFj, methyl acetate and deuteriated methyl acetates, dimethyl and di-isopropyl ether, tetramethyltin (less precise data were obtained with McsB, Me Si, and Me Ge), methyl formate, and hydrogen sulphide, deuterium sulphide, hydrogen chloride, and deuterium chloride. The photolysis of hexafluoroacetone alone has received further detailed attention and trifluoromethyl radicals thus generated have been shown not to attack sulphur hexafluoride even at temperatures up to 36S °C.  

You should be able to recognize and give the common name for the simple aldehydes and ketones shown below. 

The normal reactivity of carbonyl derivatives (e.g., hydrazone formation of aldehydes, Wolff-Kishner reduction of ketones to alkylpyridazines, sodium in ethanol reduction of ketones to alcohols) was very briefly discussed in CHEC-I 84CHEC-i(3B)l . Some examples of reactions are given here. 

and only traces of the 4-methyldihydropyridazine and its oxidation product were detected 

These compounds contain the carbonyl group (C=0), the frequencies of which are listed in Table 4.3g. The position of the C=0 stretching frequency within these ranges is dependent on both hydrogen bonding and conjugation. 

1780-1660 1740-1670 2900-2700 C=0 stretching, ketones C=0 stretching, aldehydes C—stretching, aldehydes 

In the discussion of alcohols it was noted that they are converted by active oxidation into acids. By careful regulation of the process, however, intermediate compounds are obtained in the case of primary and secondary alcohols. The reactions in the case of primary alcohols may be illustrated by the equations which express the oxidation of ethyl alcohol — 

The first change consists in the removal of two hydrogen atoms and the formation of a substance which is known as an aldehyde (from aZcohol de/ii/drogenatus). Addition of oxygen converts the aldehyde into an acid with the same number of carbon atoms. 

In the case of a secondary alcohol, the first step brings about a change similar to that which takes place when a primary alcohol is oxidized. The oxidation of isopropyl alcohol—the secondary alcohol which contains the smallest number of carbon atoms—is represented by the equation, — 

The substance formed in this case is called acetone, which belongs to the class of compounds known as ketones. Further oxidation of acetone and other ketones brings about a complete disintegration of the molecule and the formation of acids which contain a smaller number of carbon atoms than the ketone from which they were formed. 

In the formation of both aldehydes and ketones by oxidation, the change consists in the removal of two hydrogen atoms a similarity in structure of the two classes of compounds, and, as a consequence, in their reactions might be expected. Such similarity does exist. In the determination of the structure of 

Addition of a carbonyl group to an alkane lowers the ionization energy substantially typical values (Table A.3) of 9.4 to 9.8 eV are below those of the corresponding aliphatic alcohols. The molecular ion of even larger ketones with some degree of chain branching is usually of observable abundance. Molecular 

The latter two, spaced by 10 mass units, are especially prominent in the 12-eV mass spectra of straight-chain alkanals (Maccoll and Mruzek 1986). 

Aldehydes and ketones show the characteristic ion series 15,29,43, 51. due to both C H2 +iCO and C H2 +i ions. Although these are best distinguished by high-resolution data, the absence of a particular C H2 +i ion can sometimes be demonstrated by a low [(A -I- isotopic-abundance value 

Decompositions of low-energy, particularly metastable, ketone ions follow different pathways than those observed in the normal electron-impact-mass spectra (McAdoo 1988). For example, at 70 eV the 2-hexanone ion loses predominantly the C-1 methyl to give the stable acyl ion C HgCO however, metastable ions undergo a multistep rearrangement before finding the lowest- 

Sometimes displacement reactions (Section 8.11) appear to be possible at the carbonyl group such a reaction (Equation 9.29) accounts for the base peak corresponding to (M — CH3) in the spectrum of / -ionone (Unknown 4.13). 

As mentioned earlier [see reaction (6.43)], cyclic ketones undergo three distinct fragmentation pathways elimination of an alkene via cleavage of two 0-bonds in the ring, charge site-initiated reactions, and H-transfer reactions. 

The descriptors given below were used to characterize a set of 113 commercially available aldehydes, and a set of 79 available ketones. The data are siunmarized in Appendix 15A, Tables 15A.2 and 15A.3. 

molar mass (mm) 2, melting point (mp) 3, refractive index (ziq) 4, density ( f) 5, boiling point (bp) 6, wave number of infrared absorption (IR) 7, molar volume (mv). The symbols given within parentheses are used to identify the descriptors in the loading plot. 

The selection of these descriptors was based on an initial study of a smaller set of 

Principal components analysis of the set of 113 aldhydes (Table 15A.2) afforded two significant components according to cross validation. The model accounted for 

78 % of the total variance. For the set of 79 ketones (Table 15A.3), two significant components accounted for 88 % of the total variance. Fig. 15.20 shows the score and loading plots of the aldehydes, and Fig. 15.21, the corresponding ones for the ketones. The identification numbers are given in the tables in Appendix 15A. 

When treated with a hydride reducing agent, such as lithium aluminum hydride (LAH) or sodium borohydride (NaBH4), aldehydes and ketones are reduced to.  

The reduction of a carbonyl group with LAH orNaBHt is not a reversible process, because hydride does not 

When treated with a Grignard reagent, aldehydes and ketones are converted into alcohols, accompanied by the formation of a new bond. 

Grignard reactions are not reversible, because carbanions do not function as.  

Because the choice of metal depends upon the exact nature of the functional group, this chapter has been separated, as far as possible, into different classes of reactant. Although the literature contains reference to many supports, activated charcoal is normally the preferred choice because of its low cost, high surface area (typically greater than 900 m g ), chemical inertness, strength, and ease of burning during metal recovery. 

The specific example of sugar hydrogenation (e. g. glucose to sorbitol) has warranted an individual chapter in this book and so is excluded here. Reference to enantioselective hydrogenation of pro-chiral ketones is only included where appropriate, for the same reason. 

Excellent books by Augustine [1] and Rylander [2,3] are available to the interested reader for further reference. 

Cyclic terpene aldehydes occur in essential oils only in low concentration. These aldehydes are seldom used as single fragrance substances. A few of the cyclic terpene ketones are commercially important as fragrance and flavor substances, for example, menthone and carvone, which have the / -menthane skeleton, and the ionones, which have a (trimethylcyclohexenyl)alkenone skeleton. The ionones and 

CioHigO, Mr 154.25, exists as two stereoisomers, menthone and isomenthone, each of which occurs as a pair of enantiomers, due to the two asymmetric centers present in the molecule. 

Both stereoisomers occur in many essential oils, often as a single enantiomer species. A particularly high concentration (sometimes 50%) is found in oils from Mentha species. The menthones are colorless liquids that possess a typically minty odor the odor of isomenthone is slightly musty. They have a strong tendency to interconvert and are, therefore, difficult to obtain in high purity. Industrial products are mixtures of varying composition. Physical constants of industrially important menthone isomers are listed in Table 1. 

The menthones are converted into the corresponding menthols by means of hydrogenation for example, (—)-menthone yields (+)-neomenthol and (—)-menthol. 

Menthone and isomenthone are used for synthetic peppermint oils and bases. FCT 1976 (14) p.475 ( )-menthone. 

Interest in linkers for carbonyl compounds has only slowly emerged in recent years. The main driving force for the development of such linkers was the need for methods to prepare peptide aldehydes and related compounds (e.g. peptide trifluoromethyl ketones), which can be highly specific and valuable enzyme inhibitors [700,701], and are potentially useful for the treatment of various diseases. 

6-Tris(dimorpholinomethyl)-l,3,5-triazine (694, R = morpholino) can behave as a synthetic equivalent of the still unknown 1,3,5-triazinetricarbaldehyde. Trisphenylhydrazones, trioximes or trisemicarbazones of this tri-carbaldehyde have been obtained from (694) (87JHC793). 

Acyl groups adjacent to a quatemized pyridinium nitrogen atom (e.g. 695) are susceptible to removal by nucleophilic attack via (696) and the ylide (697). 

/J-unsaturated carbonyl compounds [282, 283], carbonyl carbons are shielded relative to those in comparable saturated compounds. Electron withdrawal of the carbonyl oxygen at the carbonyl carbon is attenuated by electron donation of the double bond. This, in turn, generates a positively charged [1 carbon atom which is deshielded as a result  

Carbon-13 chemical shifts of representative aldehydes [284] and ketones [285-288] are collected in Tables 4.27 and 4.28. Inspection of the data shows that a, / , and y effects are up to 7, 2, and — 1 ppm, respectively. These increments are significantly smaller compared with those reported for alkyl carbons. Obviously, the electron releasing effect of alkyl groups (( +(-/-effect) slightly attenuates positive polarization of the carbonyl carbons. 

Particularly large carbonyl shifts (215-218 ppm) are measured for 2,4-dimethyl-, 

4- trimethyl- and 2,2,4,4-tetramethyl-3-pentanone (di-t-butyl ketone). Strong steric repulsion of the bulky alkyl groups which spreads the bond angle from 115° in acetone to 130° in di-t-butyl ketone is assumed to be responsible for these deviations from increment additivity [285] the IR and UV spectra of di-f-butyl ketone also exhibit anomalies. 

It has been demonstrated for a series of cyclic and acyclic ketones that there is a correlation between the 13C chemical shifts of carbonyl groups and their n -+ n transition energy, as is expressed by eq. (4.9) [289], 

Show the resonance structures for the conjugate base of phenol. 

The pATa for phenol is 10, the pA for ethanol is 16, and the p/Q for carbonic acid (H2C03) is 6.35. Complete these equations and predict whether the reactants or the products are favored at equilibrium. 

Phenol is an important industrial chemical. More than 3 billion pounds are produced each year. The major uses of phenol are as a disinfectant and in the production of polymers. Complex phenols, with multiple substituents and functional groups, are common in nature, although the simple phenols are seldom encountered. 

Common names for simple aldehydes are frequently encountered. These common names are derived from the common names for the related carboxylic acid (see Section 12.4) by replacing the suffix -ic acid with the suffix -aldehyde. Thus, the aldehyde related to acetic acid is acetaldehyde. If the carbonyl group of an aldehyde is attached to a ring system, the compound can be named as a hydrocarbon with the suffix -carbaldehyde. (Some sources use -carboxaldehyde.) 

4-Lthyl-4-pentenal (The longest chain containing the carbonyl carbon and the carbon-carbon double bond is chosen as the root. Again, numbering begins with the carbonyl carbon.) 

Rates of decompositions of the molecular ions of hexanal [234, 632], hexanal-3, 3-d2 [234], hexanal-4,4-d2 [230, 234], hexanal-5, 5-d2 

The rates of a number of decompositions of molecular ions of specifically deuterated phenylhexanones have been determined [355]. 

The doubly charged molecular ion of acetophenone has been observed to decompose in short times at room temperature giving (C6H5)+ and (CH3CO)+ [44], 

Prelab Exercise Outline a logical series of experiments designed to identify an unknown aldehyde or ketone with the least effort. Consider the time required to complete each identification reaction. 

The carbonyl group occupies a central place in organic chemistry. Aldehydes and ketones—compounds such as formaldehyde, acetaldehyde, acetone, and 2-butanone—are very important industrial chemicals used by themselves and as starting materials for a host of other substances. For example, in 1985 8.2 billion lb of formaldehyde-containing plastics were produced in the United States. 

The carbonyl carbon is sp hybridized, the bond angles between adjacent groups are 120°, and the four atoms R, R, C, and O lie in one plane  

The electronegative oxygen polarizes the carbon-oxygen bond, rendering the carbon electron deficient and hence subject to nucleophilic substitution. 

Attack on the sp hybridized carbon occurs via the ir-electron cloud above or below the plane of the carbonyl group  

All these compounds are considered in the final library of UV spectra (Chapter 11). 

In general, carbonyl compounds (aldehydes, ketones) present a poor absorption in the UV region, except benzaldehyde (Table 2). 

As previously noted, formaldehyde does not present a significant absorption spectrum (without derivatives, see Section 4.1). On the contrary, acetaldehyde, butyraldehyde and benzaldehyde show absorption maxima of different intensities according to absorptivities (Fig. 30). For benzaldehyde, the peak position is close to the one of aromatic rings. 

Like aldehydes, ketones generally present an absorption in the UV region due to the carbonyl group. For example, acetone and butanone have an absorption maximum at 

266 nm and 268 nm, respectively (Fig. 31). The difference between the absorption peak position of diisobutylketone (ramified ketone) and butanone is approximately 20 nm. 

7-hydrogen rearrangement for formation of (C4H7D) is strong it is conceivable that the formation of (C2H3DO)t is a concerted process. 

The kinetics of the McLafferty rearrangement have been investigated in a number of other ketone molecular ions, viz. specifically deuterated octan-2-one [235], 1-phenylpentan-l-one (valerophenone) [522] and 

2-isopropyl-5-methylcyclohexanone (menthone) [522] using doublefocussing mass spectrometers and 1-phenylbutan-l-one (butyrophenone), 

1-phenylpentan-l-one, 1-phenylhexan-l-one (caprophenone), 1-phenyl-octan-l-one, 2-isopropyl-5-methylcyclohexanone and 1-phenyltetradecan- 

1-one using single-focussing mass spectrometers [518—520]. It has been reported that the molecular ion of 1-phenylpentan-l-one formed 

For an alcohol, such as methanol, the anion RO has the electronic structure H jC—O . For phenol, however, the phenolate ion can be assigned a structure that is the hybrid of several valence-bond structures  

The resonance energy for these five structures stabilizes the phenolate ion more than the amount by which the undissociated phenol molecule is stabilized by resonance between the two Kekule structures (with only small contributions by the other three, which involve a separation of charges). The extra stabilization of the anion increases the acid constant the observed factor 10 corresponds to the reasonable value 33 kJ moIe for the extra resonance energy of the phenolate ion. 

The alcohols and ethers (Section 8-6) represent the first stage of oxidation of hydrocarbons. Further oxidation leads to substances called aldehydes and ketones. The aldehydes have the formula 

Formaldehyde is a gas with a sharp irritating odor. It is used as a disinfectant and antiseptic, and in the manufacture of plastics and of leather and artificial silk. 

A cetaldehyde, CH3CHO, is a similar substance made from ethyl alcohol. The ketones are effective solvents for organic compounds, and are extensively used in chemical industry for this pwvposc. Acetone, (CH3)2CO, which is dimethyl ketone, is the simplest and most important of these substances. It is a good solvent for nitrocellulose. 

The aldehyde group may be written as separate atoms or as —CHO, with the double bond understood. In a ketone, the carbonyl group is bonded to two alkyl groups or aromatic rings. The keto group (C=0) can sometimes be written as CO. A skeletal formula may also be used to represent an aldehyde or ketone. 

Write the lUPAC and common names for aldehydes and ketones draw the condensed stmctural formulas. Describe the solubility of aldehydes and ketones in water. 

CH3 H Aldehyde FIGURE 12.3 The carbonyl group is found in aldehydes and ketones. 

Conunon (formaldehyde) (acetaldehyde) (propionaldehyde) (butyr aldehyde) 

FIGURE 12.4 In the structures of aldehydes, the carbonyl group is always the end carbon. 

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Brady s reagent A solution of 2,4-dinitro-phenylhydrazine sulphate in methanol. Gives characteristic crystalline yellow to deep red 2,4-dinitrophenylhydrazone products with aldehydes and ketones. 

Clemmensen reduction Aldehydes and ketones may generally be reduced to the corresponding hydrocarbons by healing with amalgamated zinc and hydrochloric acid. 

Girard s reagents Quaternary ammonium salts of the type Me3NCH2CONHNH2 X which form water-soluble compounds with aldehydes and ketones, and are therefore separable from other neutral compounds the aldehyde or ketone may be subsequently regenerated after separation. 

Reformatski reaction Aldehydes and ketones react with a-bromo- fatty acid esters in the presence of zinc powder to give -hydroxy-esters which may be dehydrated to give a-, 0-unsaturated esters. a-Chloroesters will react if copper powder is used in conjunction with the zinc. 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

NH2-C0-NH NH2,CH5N30. Colourless crystalline substance m.p. 96" C. Prepared by the electrolytic reduction of nitrourea in 20% sulphuric acid at 10 "C. Forms crystalline salts with acids. Reacts with aldehydes and ketones to give semicarbazones. Used for the isolation and identification of aldehydes and ketones. 

Hydrazine and its alkylated derivatives are used as rocket fuels in organic chemistry, substituted phenylhydrazines are important in the characterisation of sugars and other compounds, for example aldehydes and ketones containing the carbonyl group C=0. 

Both aldehydes and ketones usually condense readily with free hydroxyl-amine, HONHj, to give crystalline oximes ... 

Being crystalline compounds which usually have sharp melting-points, they are used to characterise the parent aldehydes and ketones. 

Impure aldehydes and ketones are sometimes purified by conversion into the corresponding oximes, and the latter after recrystallisation are then hydrolysed by boiling with dilute sulphuric acid ... 

By (he direct addition of hydrogen cyanide to aldehydes and ketones, giving cyanhydrins ... 

Phenylhydrazine on exposure to light slowly darkens and eventually becomes deep red in colour salts of the base share this property but to a lesser degree, the sulphate and acetate (of the common salts) being most stable to light. Phenylhydrazine is largely used in organic chemistry to characterise aldehydes and ketones as their phenyl-hydrazones (pp. 342, 345), and carbohydrates as their osazones (pp. 136-140). It is readily reduced thus in the process of osazone formation some of the phenylhydrazine is reduced to aniline and ammonia. On the... 

Aldehydes and ketones may be converted into the corresponding primary amines by reduction of their oximes or hydrazones (p. 93). A method of more limited application, known as the Leuckart Reaction, consists of heating the carbonyl compound with ammonium formate, whereby the formyLamino derivative is formed, and can be readily hydrolysed by acids to the amine. Thus acetophenone gives the i-phenylethylformamide, which without isolation can be hydrolysed to i-phenylethylamine. 

Phenyl hydrazine condenses readily with aldehydes and ketones to give phenylhydrazonesy which, being usually crystalline compounds of sharp... 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Dinitrophenylhydrazine is a very important reagent for the identification of aldehydes and ketones (pp. 342, 346). It is readily prepared from chloro-2,4-dinitrobenzene (I). In the latter compound the chlorine is very reactive in... 

Reagent A is particularly useful for the treatment of the lower aliphatic aldehydes and ketones which are soluble in water cf. acetaldehyde, p. 342 acetone, p. 346). The Recent is a very dilute solution of the dinitrophenylhydrazine, and therefore is used more to detect the presence of a carbonyl group in a compound than to isolate sufficient of the hydrazone for effective recrystallisation and melting-point determination. 

Dinitrophenylhydra2ones usually separate in well-formed crystals. These can be filtered at the pump, washed with a diluted sample of the acid in the reagent used, then with water, and then (when the solubility allows) with a small quantity of ethanol the dried specimen is then usually pure. It should, however, be recrystallised from a suitable solvent, a process which can usually be carried out with the dinitrophenylhydrazones of the simpler aldehydes and ketones. Many other hydrazones have a very low solubility in most solvents, and a recrystallisation which involves prolonged boiling with a large volume of solvent may be accompanied by partial decomposition, and with the ultimate deposition of a sample less pure than the above washed, dried and unrecrystal-lised sample. 

The term Knoevenagel Condensation was originally applied to the base-catalysed condensation of the carbonyl ( CO) group of aldehydes and ketones with the reactive methylene group of malonic acid, with loss of w ater ... 

Many aldehydes and ketones can be reduced directly by Clenimemen s method, in which the aldehyde or ketone is boiled with dilute hydrochloric acid and amalgamated zinc. />-Methylacetophenone (or methyl />-tolyl ketone) is reduced under these conditions to />-ethyltoluene. An excess of the reducing agent is employed in order to pre ent the formation of unsaturated hydrocarbons. 

This is a test for the >C = 0 group. Most aldehydes and ketones readily condense with this reagent giving yello v- or orange-coloured precipitates. 

Note. The 2,4-dinitrophenylhydrazones of many higher aldehydes and ketones may be insoluble in most solvents. In this case, Mter them off, wash with ethanol, dry and take the m.p. attempted recrystallisation may cause partial decomposition. (M.ps., pp. 530-540.)... 

K. Treat with 2,4-dinitrophenylhydrazine reagent (pp. 263, 334). Yellow or orange-yellow precipitates given by most aldehydes and ketones. 

Clemmensen reduction of aldehydes and ketones. Upon reducing aldehydes or ketones with amalgamated zinc and concentrated hydrochloric acid, the main products are the hydrocarbons (>C=0 —> >CHj), but variable quantities of the secondary alcohols (in the case of ketones) and unsaturated substances are also formed. Examples are ... 

Wolff - Kishner reduction of aldehydes and ketones. Upon heating the hydrazoiie or semicarbazone of an aldehyde or ketone with potassium hydroxide or with sodium ethoxide solution (sealed tube), the corresponding hydrocarbon is obtained ... 

Phenylhydrazones (compare Section III,74,C). Dissolve 0-5 g, of colourless phenylhydrazine hydrochloride and 0 8 g. of sodium acetate in 5 ml. of water, and add a solution of 0-2-0-4 g. of the aldehyde (or ketone) in a little alcohol (free from aldehydes and ketones). Shake the mixture until a clear solution is obtained and add a little more alcohol, if necessary. Warm on a water bath for 10-15 minutes and cool. Filter ofiF the crystalline derivative, and recrystalhse it from dilute alcohol or water sometimes benzene or light petroleum (b.p. 60-80°) may be used. 

Aldehydes and ketones can be reduced smoothly to the corresponding alcohols by aluminium alkoxides. The most satisfactory alkoxlde for general use Is aluminium tsopropoxide ... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars)... 

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