Aldehydes mechanisms

In a preliminary consideration of the reaction mechanism, aldehydes and aldols seem to be logical intermediates. It was found that aldehydes undergo the same type of condensation, producing ketones in yields considerably superior to those obtained from the corresponding alcohol. When the aldols of n-butylaldehyde and n-heptaldehyde were subjected to the same reaction conditions, excellent yields of ketones were produced... 

Another class of transition-state inhibitors is the peptide aldehyde inhibitors (Fig. 7). Aldehydes inhibit cysteine, serine, and threonine proteases via a covalent, reversible mechanism, and metaUoproteases using an analogous but nonco-valent mechanism. Aldehydes were discovered in screens for protease inhibitors from microorganisms and generally consist of a peptidyl moiety that binds in the non-prime specificity sites with a C-terminal aldehyde group. These inhibitors are... 

This reaction, applicable only to the preparation of hydroxy-aldehydee, is alternative to the Gattermann aldehyde reaction (or the Adams modification of it) given under 4. The yields are usually smaller, but a large quantity of the phenol may be recovered. The following mechanism is consistent with the known facts ... 

The best results are obtained by conducting the steam distillation in a largo three-necked flask (compare Pig. 11,41, 1) provided with a glycorine-sealed mechanical stirrer in the central aperture the aldehyde distils slowly unless the mixture is well stirred. 

P-Hydroxy-a-naphthaldehyde, Equip a 1 litre three-necked flask with a separatory funnel, a mercury-sealed mechanical stirrer, and a long (double surface) reflux condenser. Place 50 g. of p-naphthol and 150 ml. of rectified spirit in the flask, start the stirrer, and rapidly add a solution of 100 g. of sodium hydroxide in 210 ml. of water. Heat the resulting solution to 70-80° on a water bath, and place 62 g. (42 ml.) of pure chloroform in the separatory funnel. Introduce the chloroform dropwise until reaction commences (indicated by the formation of a deep blue colour), remove the water bath, and continue the addition of the chloroform at such a rate that the mixture refluxes gently (about 1 5 hours). The sodium salt of the phenolic aldehyde separates near the end of the addition. Continue the stirring for a further 1 hour. Distil off the excess of chloroform and alcohol on a water bath use the apparatus shown in Fig. II, 41, 1, but retain the stirrer in the central aperture. Treat the residue, with stirring, dropwise with concentrated hydrochloric acid until... 

The mechanism of the reaction probably involves the production, by into -action of the aldehyde with hydroxide ions, of two reducing anions, the first (I) more easily than the second (II). Either of these anions may transfer a hydride ion to a carbonyl carbon atom in another aldehyde molecule ... 

The mechanism of the reaction, which is of the aldol type, involves the car-bonyl group of tlie aldehyde and an active methylene group of the anhydride the function of the basic catalyst B (acetate ion 0H3000 or triethylamine N(0,Hb)j) is to form the anion of the active hydrogen component, i.e., by the extraction of a proton from the anhydride ... 

The mechanism of the reaction between aromatic aldehydes and esters probably involves the intermediate formation of an aldol (hence the name— Claisen aldol condensation) ... 

An important general method of preparing indoles, known as the Fischer Indole synthesis, consists in heating the phenylhydrazone of an aldehyde, ketone or keto-acld in the presence of a catalyst such as zinc chloride, hydrochloric acid or glacial acetic acid. Thus acrtophenone phenylhydrazone (I) gives 2-phenyllndole (I V). The synthesis involves an intramolecular condensation with the elimination of ammonia. The following is a plausible mechanism of the reaction ... 

This is an example of the Doebner synthesis of quinoline-4-carboxylic acids (cinchoninic acids) the reaction consists in the condensation of an aromatic amine with pyruvic acid and an aldehj de. The mechanism is probably similar to that given for the Doebner-Miller sj nthesis of quinaldiiie (Section V,2), involving the intermediate formation of a dihydroquinoline derivative, which is subsequently dehydrogenated by the Schiff s base derived from the aromatic amine and aldehyde. 

Not-Strike may have seen. But what Dr. Quack did that SWINS did not was use the bisulfite test with positive results. What does that mean It means that some doublebonded oxygen was formed, unless Dr. Quack was fibbing to us, It cannot have been a propiophenone (don t ask) because propiophenones cannot form the bisulfite addition product. Could an aldehyde have formed (don t ask) Maybe. But highly unlikely considering the mechanism of the reaction. 

Stereoselectivities of 99% are also obtained by Mukaiyama type aldol reactions (cf. p. 58) of the titanium enolate of Masamune s chired a-silyloxy ketone with aldehydes. An excess of titanium reagent (s 2 mol) must be used to prevent interference by the lithium salt formed, when the titanium enolate is generated via the lithium enolate (C. Siegel, 1989). The mechanism and the stereochemistry are the same as with the boron enolate. 

From these facts, a mechanism of the Rosenmund reduction has been proposed, in which the formation of the acylpalladium species 893 is the first step of the aldehyde formation and also the decarbonylation, although the Rosenmund reduction proceeds under heterogeneous conditions[744]. 

The aldehyde or ketone is called the keto form and the keto enol equilibration referred to as keto-enol isomerism or keto-enol tautomerism Tautomers are constitu tional isomers that equilibrate by migration of an atom or group and their equilibration IS called tautomerism The mechanism of keto-enol isomerism involves the sequence of proton transfers shown m Figure 9 6... 

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

The mechanism of lithium aluminum hydride reduction of aldehydes and ketones IS analogous to that of sodium borohydride except that the reduction and hydrolysis... 

FIGURE 15 2 Mechanism of sodium borohydnde reduction of an aldehyde or ketone... 

The mechanisms by which transition metal oxidizing agents convert alcohols to aldehydes and ketones are complicated with respect to their inorganic chemistry The organic chemistry is clearer and one possible mechanism is outlined m Figure 15 4 The... 

The next section explores the mechanism of nucleophilic addition to aldehydes and ketones There we 11 discuss their hydration a reaction m which water adds to the C=0 group After we use this reaction to develop some general principles we 11 then survey a number of related reactions of synthetic mechanistic or biological interest... 

Hydration of aldehydes and ketones is a rapid reaction quickly reaching equilibrium but faster in acid or base than in neutral solution Thus instead of a single mechanism for hydration we 11 look at two mechanisms one for basic and the other for acidic solution... 

A number of compounds of the general type H2NZ react with aldehydes and ketones m a manner analogous to that of primary amines The carbonyl group (C=0) IS converted to C=NZ and a molecule of water is formed Table 17 4 presents exam pies of some of these reactions The mechanism by which each proceeds is similar to the nucleophilic addition-elimination mechanism described for the reaction of primary amines with aldehydes and ketones... 

You have had earlier experience with enols m their role as intermediates m the hydration of alkynes (Section 9 12) The mechanism of enolization of aldehydes and ketones is precisely the reverse of the mechanism by which an enol is converted to a carbonyl compound... 

FIGURE 18 1 Mechanism of acid catalyzed enolization of an aldehyde or ketone in aqueous solution... 

The simplest a 3 unsaturated aldehyde acrolein is prepared by heating glycerol with an acid catalyst Suggest a mechanism for this reaction... 

The first stage of the mechanism is exactly the same as for nucleophilic addition to the carbonyl group of an aldehyde or ketone Many of the same nucleophiles that add to aldehydes and ketones—water (Section 17 6) alcohols (Section 17 8) amines (Sections 17 10-17 11)—add to the carbonyl groups of carboxylic acid derivatives... 

In the first stage of the hydrolysis mechanism water undergoes nucleophilic addi tion to the carbonyl group to form a tetrahedral intermediate This stage of the process IS analogous to the hydration of aldehydes and ketones discussed m Section 17 6... 

Elimination unimolecular (El) mechanism (Section 5 17) Mechanism for elimination characterized by the slow for mation of a carbocation intermediate followed by rapid loss of a proton from the carbocation to form the alkene Enamine (Section 17 11) Product of the reaction of a second ary amine and an aldehyde or a ketone Enamines are char actenzed by the general structure... 

The amount of a particular component in a sample can be monitored by examining the height of a spectral absorption peak The reduction of an aldehyde to an alcohol would show up as a decrease in line intensity for the carbonyl and an increase for the hydroxyl peaks in the spectrum. Changes in the relative importance of different relaxation modes in a polymer can also be followed by the corresponding changes in a mechanical spectrum. 

Furfural—acetone resins have been used to form resin-aggregate mixtures referred to as organic concretes. Despite the reportedly excellent properties, there has been virtually no commercial use of such resins outside the former Soviet Union. The stmctures and polymerization mechanisms of these furfural—aldehyde—ketone polymers are discussed in a review (6). 

Under acidic conditions, furfuryl alcohol polymerizes to black polymers, which eventually become crosslinked and insoluble in the reaction medium. The reaction can be very violent and extreme care must be taken when furfuryl alcohol is mixed with any strong Lewis acid or Brn nstad acid. Copolymer resins are formed with phenoHc compounds, formaldehyde and/or other aldehydes. In dilute aqueous acid, the predominant reaction is a ring opening hydrolysis to form levulinic acid [123-76-2] (52). In acidic alcohoHc media, levulinic esters are formed. The mechanism for this unusual reaction in which the hydroxymethyl group of furfuryl alcohol is converted to the terminal methyl group of levulinic acid has recendy been elucidated (53). 

Chemical Properties. A combination of excellent chemical and mechanical properties at elevated temperatures result in high performance service in the chemical processing industry. Teflon PEA resins have been exposed to a variety of organic and inorganic compounds commonly encountered in chemical service (26). They are not attacked by inorganic acids, bases, halogens, metal salt solutions, organic acids, and anhydrides. Aromatic and ahphatic hydrocarbons, alcohols, aldehydes, ketones, ethers, amines, esters, chlorinated compounds, and other polymer solvents have Httle effect. However, like other perfluorinated polymers,they react with alkah metals and elemental fluorine. 

Synthesis from Aldehydes and Ketones. Treatment of aldehydes and ketones with potassium cyanide and ammonium carbonate gives hydantoias ia a oae-pot procedure (Bucherer-Bergs reactioa) that proceeds through a complex mechanism (69). Some derivatives, like oximes, semicarbazones, thiosemicarbazones, and others, are also suitable startiag materials. The Bucherer-Bergs and Read hydantoia syntheses give epimeric products when appHed to cycloalkanones, which is of importance ia the stereoselective syathesis of amino acids (69,70). 

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