ALDEHYDES, KETONES AND ACIDS

Most of the latest experimental techniques have been applied to the study of the photodissociation dynamics of these molecules. Part of the reason for the great interest in these molecules is a result of their long history in photochemistry and partly because there is a low lying absorption that is accessible to the available lasers. Formaldehyde is particularly important since it is the simplest molecules in the group and has been studied theoretically. 

Spectroscopy (39) and photochemistry (40) of formaldehyde have been extensively studied. The rotational analysis of the absorption spectrum of H2CO in the 250 to 360 nm region indicates that the transition is A(l-A2) X( Ap), which is 

This sequential process rather than the direct, - H2 + CO decay was invoked to explain the rapidly increasing decay rate with an increase of total energy. 

Bamford et al. (45) have recently studied the photolysis of H2CO near the S- origin. The complete rotational distribution has been obtained for CO, which was detected by vacuum ultraviolet laser induced fluorescence. The distribution has a peak at J = 42 and highly nonthermal, suggesting that energy randomization does not occur during dissociation. The population in CO J 20 is absent. The vibrational population of v = 1 is 14 5% as large as that of CO (v = 0). The C0(v = 1) has nearly the same rotational distribution as C0(v = 0). 

The photolysis of CH2C0 has been extensively studied The primary processes in the ultraviolet are  

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In the Fischer-Tropsch process, carbon monoxide reacts with hydrogen in the presence of a solid catalyst, with the formation of a mixture of hydrocarbons. The composition of the product varies considerably with the catalyst and the operating conditions. The mixture may include (in addition to hydrocarbons) alcohols, aldehydes, ketones, and acids. 

Figure 5.6 Alcohols, aldehydes, ketones and acids 15, ethylene glycol 16, vinyl alcohol 17, acetaldehyde 18, formaldehyde 19, glyoxal 20, propionaldehyde 21, propionaldehyde 22, acetone 23, ketene 24, formic acid 25, acetic acid 26, methyl formate. (Reproduced from Guillemin et at. 2004 by permission of Elsevier)...

The aldehydes, ketones and acid chlorides are reduced to alcohol. 

Arndt, F. Eistert, B. Ber. Dtsch. Chem. Ges. 1935, 68, 200. Fritz Arndt (1885—1969) was bom in Hamburg, Germany. He discovered the Arndt—Eistert homologation at the University of Breslau where he extensively investigated the synthesis of diazomethane and its reactions with aldehydes, ketones, and acid chlorides. Fritz Arndt s chain-smoking of cigars ensured that his presence in the laboratories was always well advertised. Bernd Eistert (1902-1978), bom in Ohlau, Silesia, was Arndt s Ph.D. student. Eistert later joined I. G. Earbenindustrie, which became BASE after the Allies broke the conglomerate up after WWII. 

REDUCTION OF SULFUR COMPOUNDS (EXCEPT SULFUR DERIVATIVES OF ALDEHYDES, KETONES AND ACIDS)... 

The volatile components from coal pyrolysis are primarily small hydrocarbons and oxygen-containing molecules. By adding H2O and limited O2 and while heating coal, these products incorporate considerable 0 atoms into the volatile products to form alcohols, aldehydes, ketones, and acids. However, these products consist of many molecules that... 

In addition to these larger VOCs, there are biogenic sources of a wide variety of small alcohols, aldehydes, ketones, and acids. For example, emissions of methanol and acetone have been reported from plant leaves, grass, and clover (e.g., MacDonald and Fall, 1993 Nemecek-Marshall et al., 1995 Fall and Benson, 1996 Kirstine et al., 1998). Table 6.25 shows some of the compounds measured in grass and clover emissions (Kirstine et al., 1998). Clearly, a wide variety of oxygen-containing species are emitted from this one source alone. Direct emissions of formaldehyde, ac-etaldehye, and formic and acetic acids have been observed from oaks and pines (Kesselmeier et al., 1997). 

Fleming and coworkers have developed a number of such multicomponent assembling reactions using alkyl halides, aldehydes, ketones and acid chlorides as electrophiles for post-functionalization of carbomagnesiation . The stereoselectivity of the reaction with electrophiles is not only generally high but also highly dependent on the nature of electrophiles. 

The relatively low molecular weight alcohols, aldehydes, ketones, and acids dissolved in the water stream condensed from the synthesis products can be separated into specification chemicals. Details concerning the production of these highly valuable by-products of the process have been given in recent publications (2,15). 

The production of water-soluble chemicals from several plants should not burden the market although it would be necessary to develop outlets for certain of the chemicals which are not now available in commercial quantities—for example, n-propyl alcohol and the higher molecular weight aldehydes, ketones, and acids. 

Thus, oxidation of paraffins yields alcohols, aldehydes, ketones and acids. The acids formed are vigorously corrosive to copper, lead and cadmium engine bearings. 

WATER-AIR EQUILIBRATION. McAuliffe (6) introduced a multiple phase equilibrium procedure for the qualitative separation of hydrocarbons from water-soluble organic compounds. For n-alkanes, more than 99% were found to partition in the gas phase after two equilibrations with equal volumes of gas and aqueous solution. Cycloalkanes require three equilibrations to be essentially completely removed, and oxygen-containing organic compounds (e.g., alcohols, aldehydes, ketones, and acids) remain in the aqueous layer. Thus, after equilibration with equal volumes of gas, an immediate clue is given regarding the identification of the compound. More details of this technique can be found in Chapter 7. 

Reduction of halides.1 The reagent prepared from NaBH3CN and SnCl2 in a 2 1 ratio does not reduce primary or secondary alkyl halides or aryl halides in ether at 25°, but does reduce tertiary, allyl, and benzyl halides. It is thus comparable to NaBH3CN-ZnCl2 (12, 446). Aldehydes, ketones, and acid chlorides are reduced to alcohols, but esters and amides are inert. 

E. Burtschen, H. Binder, R. Concin, and O. Bobleter, Separation of phenols, phenolic aldehydes, ketones, and acids by HPLC, J. Chromatogr., 252 161 (1982). 

Amines will also react as nucleophiles with a wide range of electrophiles including alkyl halides, aldehydes, ketones, and acid chlorides. 

Identify whether oxidation or reduction is needed to interconvert alkanes, alcohols, aldehydes, ketones, and acids, and identify reagents that will accomplish the conversion. 

We make no apologies for the number of pages we have devoted to carbonyl chemistry. The first reactions you met, in Chapter 6, involved carbonyl compounds. Then in Chapters 9, 10, 12, and 14 we considered different aspects of nucleophilic attack on electrophilic carbonyl compounds. But carbonyl compounds have two opposed sides to their characters. They can be nucleophilic as well electrophilic attack on aldehydes, ketones, and acid derivatives is a useful reaction too. How can the same class of compound be subject both to nucleophilic and to electrophilic attack The resolution of this paradox is the subject of this chapter where we shall see that most carbonyl compounds exist in two forms—one electrophilic and one nucleophilic. The electrophilic form is the carbonyl compound itself and the nucleophilic form is called the enol. 

The best alternatives to enamines for conjugate addition of aldehyde, ketone, and acid derivative enols are silyl enol ethers, Their formation and some uses were discussed in Chapters 21 and 26-28, but these stable neutral nueleophiles also react very well with Michael acceptors either spontaneously or with Lewis acid catalysis at low temperature,... 

The Fischer-Tropsch process Reaction of carbon monoxide with hydro- 9,16.28, 32,44, gen in the presence of a solid catalyst to produce a mixture of 58,64.65,66. hydrocarbons, alcohols, aldehydes, ketones, and acids depending upon 67, 68. 69,85, operating conditions and the nature of the caialyst 105... 

In addition to the oxidative scission of 1,2-diols, the reaction can be extended to related 1,2-bifunc-tional compounds such as oxiranes, 1,2-dicarbonyl compounds, 2-hydroxy aldehydes, ketones and acids, a-amino alcohols, 1,2-diamines and also to polyols. LTA cleaves a-hydroxy acids much more readily than do periodates and both reagents oxidize 2-hydroxy aldehydes and 1,2-dicarbonyl compounds relatively slowly. Only periodic acid in water reacts with oxiranes via the corresponding diols. 

Fluorine-containing aldehydes, ketones and acid fluorides undergo photoinitiated cycloaddition reactions with fluorinated alkenes to give oxetanes.The addition of hexafluoroacetone... 

Example 5.5. Oxidation of paraffins to secondary alcohols. Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of boric-acid esters or boroxines [16-18], These intercept the alkyl peroxide, the first oxidation product, preventing it from generating free radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids (see also Section 9.6.2). The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. The reaction does not stop at... 

Fluorine-containing aldehydes, ketones and acid fluorides undergo photoinitiated cycloaddition reactions with fluorinated alkenes to give oxetanes.90 91 The addition of hexafluoroacetone (11) to fluoroalkenes can also be performed in the presence of the Lewis acid, aluminum chloride fluoride.92-1 22-1 23 Unlike the photochemical cycloaddition of hexafluoroacetone with trifluoroethene, the Lewis acid catalyzed addition is regioselective.92 Fluorooxetanes (c. g., 14) have also been synthesized by the addition of formaldehyde to fluoroalkenes in hydrogen fluoride.94 Examples of the formation of fluorooxetanes by [2 + 2]-cycloaddition reactions arc-given in Table 8. 

The iron cluster [Fe4S4(SPh)4] catalyzes the reduction of nitroarenes to arylamines. " A less hydridic nucleophile [HFe(CO)4] has also found application as a selective reducing agent for nitroarenes." Although [HFe(CO)4]"] is known to reduce aldehydes, ketones and acid halides," in THF solvent with tri-fluoroacetic acid, it selectively reduces nitrobenzenes to anilines in the presence of aldehyde and acid halide groups. 

Allylsilanes are easily protodesilylated, completing the reduction process. In the presence of Lewis acids, allylsilanes also react with electrophiles like aldehydes, ketones and acid halides through an Se2 mechanism involving anti stereochemistry. These reactions are extensively discussed in Volumes 2-4. 

In considering the aromatic aldehydes and ketones and later the aromatic acids it should be emphasized that the relationships discussed in Part I (p. 129) between alcohols, aldehydes, ketones and acids are general and apply just as truly to the aromatic compounds as to the aliphatic. The class characteristics of alcohols, aldehydes, ketones and acids are the same in both series. Thus the primary alcohols, on oxidation, always yield first aldehydes and then acids, while the secondary alcohols yield ketones. 

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