Aliphatic esters ethyl formate

The major advantage of the seunpling technique developed, was that some trace chemicals could be trapped tind described for the first time as Black Truffle aroma constituents. In particular, some compounds, important flavor contributors, generally appearing in small concentrations, such as benzaldehyde, propanal, ethyl acetate, anisole or dimethyl disulfide - previously identified in Shiitake mushrooms (9) - could be characterized. This was also the case for three aromatic compounds, toluene, xylene and ethyl benzene, well known as raw vegetable constituents (1 ). In addition, two aliphatic esters, isopropyl and sec-butyl formates, and one cyclic sulfur compound (2-formyl thiophene) previously reported respectively in plums and apples (W) and in coffee and bread products (n) were identified. 

One effective technique for selective reaction is to employ one ester which possesses no a-hydrogen atoms. Simple aliphatic esters such as ethyl formate, diethyl oxalate and diethyl carbonate are commonly used while, among the aromatic esters, benzoic, substituted benzoic and furoic esters are commonly employed. Self-condensation of the ester providing the carbanion is not a major problem. Examples of this reaction are given in Scheme 4 further examples are listed in the reviews. Diethyl oxalate and ethyl formate react readily in this way, although forcing conditions are often necessary with diethyl carbonate and aromatic esters. 

Acyloin condensation. The usual preparation of acyloins from aliphatic esters is not applicable to aromatic esters. In this case the reaction with sodium results in formation of the sodium carboxylate and a radical from the R group which undergoes further reactions. However, benzoin can be prepared in moderate yield by treatment of the trimethylsilyl ester of benzoic acid with sodium or by treatment of ethyl benzoate with sodium naphthalenide in THF at room temperature (397 yield). ... 

The kinetics of the aminolysis (Et2NH) of ethyl formate at 45 °C in concentrated ethanol solutions have been described and a mechanism proposed. In kinetic studies on the aminolysis reactions of substituted aliphatic esters in a variety of apro-tic solvents, the reaction rate is strongly affected by inductive and steric effects of substituents in the acyl group, rising more than 10" -fold from cyanoacetate to trifluoroacetate. A study of the reactions between vinyl acetate (28) and diethylamine, piperidine, and morpholine in benzene and DMF has revealed that the corresponding enamines accompany the expected amides (29) secondary reactions, however, yielded a coloured oligomer. ... 

Low-molecular-weight esters react quite readily with hydrazine, but heavier ones must be coerced. Aromatic esters are less reactive than aliphatic esters toward hydrazine, and they and the more reristant aliphatic esters occasionally require prolonged heating with hydrazine at elevated temperatures in a se ed tube. Branching of the carbon chain alpha to the ester group retards hydrazide formation in contrast with ethyl acetate, which reacts spontaneously with hydrazine at room temperature, ethyl pivaJate (ethyl trimethylacetate) requires a temperar ture of 140 , And adamantane-l,3-dicarboxylic ester (I) failed to form a hydrazide under all conditions (imspecified) that were tried. 

The formation of acyloins (a-hydroxyketones of the general formula RCH(OH)COR, where R is an aliphatic residue) proceeds best by reaction between finely-divided sodium (2 atoms) and esters of aliphatic acids (1 mol) in anhydrous ether or in anhydrous benzene with exclusion of oxygen salts of enediols are produced, which are converted by hydrolysis into acyloins. The yield of acetoin from ethyl acetate is low (ca. 23 per cent, in ether) owing to the accompanying acetoacetic ester condensation the latter reaction is favoured when the ester is used as the solvent. Ethyl propionate and ethyl ji-butyrate give yields of 52 per cent, of propionoin and 72 per cent, of butyroin respectively in ether. 

The simple primary amines of the aliphatic series, then, do not form diazo-compounds because the reaction which would le, d to their formation only occurs at a temperature at which they are destroyed. The reactivity of the NH2-group can, however, be increased by a neighbouring carbonyl group. Thus we come to the case of the esters of the a-amino-carboxylic acids and of the a-amino-ketones. The ethyl ester of glycine can be diazotised even in the cold the diazo-compound which does not decompose under these conditions undergoes stabilisation by elimination of water and change into ethyl diazoacetate ... 

Although the present procedure illustrates the formation of the diazoacetic ester without isolation of the intermediate ester of glyoxylic acid />-toluenesulfonylhydrazone, the two geometric isomers of this hydrazone can be isolated if only one molar equivalent of triethylamine is used in the reaction of the acid chloride with the alcohol. The extremely mild conditions required for the further conversion of these hydrazones to the diazo esters should be noted. Other methods for decomposing arylsulfonyl-hydrazones to form diazocarbonyl compounds have included aqueous sodium hydroxide, sodium hydride in dimethoxyethane at 60°, and aluminum oxide in methylene chloride or ethyl acetate." Although the latter method competes in mildness and convenience with the procedure described here, it was found not to be applicable to the preparation of aliphatic diazoesters such as ethyl 2-diazopropionate. Hence the conditions used in the present procedure may offer a useful complement to the last-mentioned method when the appropriate arylsulfonylhydrazone is available. 

Roberts269 has studied the hydrolysis of series of ethyl esters271 272 and alkyl benzoates273 in a limited range of water-dimethyl sulphoxide mixtures in some detail, and finds that the data for the hydrolysis of aliphatic ethyl esters (at 35°C in 85% dimethyl sulphoxide-water) fit the modified Taft equation (eqn. 5, p. 132). The values of p = 1.88 and 8 = 0.88 can be compared with p = 2.39 and 8 = 1.04 for 85% EtOH-water at the same temperature. The polar reaction constant is reduced in the dipolar aprotic solvent, consistent with a reduced degree of bond formation in the transition state, expected if the activity of the hydroxide ion is increased. However, Roberts considers that the sensitivity to steric effects, as measured by 8, would be reduced more substantially if bond formation were less advanced. It is difficult to accept this argument, since we... 

A quantitative assessment of the effects of head group bulk on, S k2 and E2 reactions in cationic micelles has been made.148 The kinetics of the acid-catalysed hydrolysis of methyl acetate in the presence of cationic, anionic, and non-ionic surfactants has been reported on.149 The alkaline hydrolysis of -butyl acetate with cetyltrimethylammonium bromide has also been investigated.150 The alkaline hydrolysis of aromatic and aliphatic ethyl esters in anionic and non-ionic surfactants has been studied.151 Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of /j-nitrophenyl alkanoates (185 n = 2-16) catalysed by the 4-(dialkylamino)pyridine-fimctionalized polymer (186) in aqueous Tris buffer solution at pH 8 and 30 °C. The formation of a reactive catalyst-substrate complex, (185)-(186), seems to be promoted by the presence of tris(hydroxymethyl)methylammonium ion.152... 

The preparation of (83) (Expt 8.29) is an example of the Hantzsch pyridine synthesis. This is a widely used general procedure since considerable structural variation in the aldehydic compound (aliphatic or aromatic) and in the 1,3-dicarbonyl component (fi-keto ester or /J-diketone) is possible, leading to the synthesis of a great range of pyridine derivatives. The precise mechanistic sequence of ring formation may depend on the reaction conditions employed. Thus if, as implied in the retrosynthetic analysis above, ethyl acetoacetate and the aldehyde are first allowed to react in the presence of a base catalyst (as in Expt 8.29), a bis-keto ester [e.g. (88)] is formed by successive Knoevenagel and Michael reactions (Section 5.11.6, p. 681). Cyclisation of this 1,5-dione with ammonia then gives the dihydropyridine derivative. Under different reaction conditions condensation between an aminocrotonic ester and an alkylidene acetoacetate may be involved. 

Aliphatic olefins and (z-btoraocarboxylic esters yield y-bromo esters in good yields, as illustrated by the formation of ethyl y-bromocapoate from 1-octene and ethyl bromoacetate (57%). ... 

Aliphatic carboxylic esters have been reduced to produce simple primary alcohols (84-92%) via Cp2TiCl2-catalyzed reaction with Bu MgBr. Additionally, hydrosilylation of aliphatic and aromatic carboxylic esters using Ph2SiH2, (EtO)2Si(Me)H, (EtO)3SiH or MeSiO[Si(Me)H—0]nSiMe3 has been used to produce simple primary alcohols (50-100%). In contrast, the photolytic reactions of esters with HSiCb produces ethers. For example, l-dodecyl acetate was converted into l-dodecyl ethyl ether in this way. Competitive deoxygenation complicates ether formation particularly with secondary and tertiary alkyl esters. All these exotic methods have little synthetic merit. 

A study of Rh2Ln4-catalyzed decomposition of 2-diazo-A-phenylmalo-namic acid ethyl ester 128 (R = C02Et) showed, that with perfluorocarbox-amides as catalyst ligands, the aromatic C—H insertion giving rise to oxindoles 129 occurs in preference to aliphatic C—H insertion, addition to C=C and C=C bonds, O—H insertion, and ylide formation, all of which are observed simply by switching to a carboxylate-based rhodium catalyst (94JOC2447). 

Unsaturated Lignin Model Compounds Double bonds in lignin model compounds are attacked by peracetate ions. Dehydro-di-woeugenol (XXI, Figure 12.9) reacted with epoxidation of the aliphatic double bond and formation of the diol. The double bonds in stilbenes [59] and coniferaldehyde [90] are also cleaved. FemUc acid (IVa) and its ethyl ester reacted slowly at 50°C the methyl ether, 3,4-dimethoxy cinnamic acid, was much less reactive and was almost quantitatively recovered [55]. The reactions of ferulic acid and its ethyl ester (both in the trans form) were accompanied by trans-cis isomerization, perhaps an indication of reversible phenoxy radical formation. HomovanilUc acid (XXXa) was also formed the proposed mechanism involved epoxidation of the a-P double bonds followed by decarboxylation. 

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