Esters alcohol exchange reactions

A similar heterolytic cleavage reaction has been considered for diazoacetate esters to explain their alcoholic exchange reaction ". ... 

In general, the equilibrium in a base-catalyzed alcohol exchange reaction lies in the direction of incorporation of the less acidic alcohol in the ester. This is a reflection both of the kinetic factor, the more acidic alcohol being a better leaving group, and the greater stabilization provided to the carbonyl group by the more electron-rich alkoxy substituent. 

In general, the equilibrium in a base-catalyzed alcohol exchange reaction lies in the direction of incorporating the less acidic alcohol in the ester. 

The ring-opening process of Equation 8.45 is, of course, simply the reverse of the process by which oxiranes (oxacyclopropanes, epoxides) are formed from halohy-drins (e.g., see item 3,Table 7.6). Further, as written, the processes shown in Schemes 8.90-8.92 are reversible and thus, at least in principle, carbonyl compounds can be converted to enol ethers, acetals (and ketals), and orthoesters. However, while acetals and ketals readily form from alcohols and acids under dehydrating conditions (Chapter 9) and esters undergo exchange reactions with alcohols in the... 

Applications. Transesterifications via alcoholysis play a significant role in industry as well as in laboratory and in analytical chemistry. The reaction can be used to reduce the boiling point of esters by exchanging a long-chain alcohol group with a short one, eg, methanol, in the analysis of fats, oils, and waxes. For more details see References 7 and 68. A few examples are given below. 

In polyesterification media, alkoxytitaniums do not react with water but can undergo exchange reactions with alcohols, acids and, in some cases, with esters, e.g. ... 

Hence, enol esters such as isopropenyl acetate are good acylating agents for alcohols. Isopropenyl acetate can also be used to convert other ketones to the corresponding enol acetates in an exchange reaction ... 

Vardanyan [65,66] discovered the phenomenon of CL in the reaction of peroxyl radicals with the aminyl radical. In the process of liquid-phase oxidation, CL results from the disproportionation reactions of primary and secondary peroxyl radicals, giving rise to trip-let-excited carbonyl compounds (see Chapter 2). The addition of an inhibitor reduces the concentration of peroxyl radicals and, hence, the rate of R02 disproportionation and the intensity of CL. As the inhibitor is consumed in the oxidized hydrocarbon the initial level of CL is recovered. On the other hand, the addition of primary and secondary aromatic amines to chlorobenzene containing some amounts of alcohols, esters, ethers, or water enhances the CL by 1.5 to 7 times [66]. This effect is probably due to the reaction of peroxyl radicals with the aminyl radical, since the addition of phenol to the reaction mixture under these conditions must extinguish CL. Indeed, the fast exchange reaction... 

The first evidence that an elimination-addition mechanism could be important in nucleophilic substitution reactions of alkanesulfonyl derivatives was provided by the observation (Truce et al., 1964 Truce and Campbell, 1966 King and Durst, 1964, 1965) that when alkanesulfonyl chlorides RCH2S02C1 were treated in the presence of an alcohol R OD with a tertiary amine (usually Et3N) the product was a sulfonate ester RCHDS020R with exactly one atom of deuterium on the carbon alpha to the sulfonyl group. Had the ester been formed by a base-catalysed direct substitution reaction of R OD with the sulfonyl chloride there would have been no deuterium at the er-position. Had the deuterium been incorporated by a separate exchange reaction, either of the sulfonyl chloride before its reaction to form the ester, or of the ester subsequent to its formation, then the amount of deuterium incorporated would not have been uniformly one atom of D per molecule. The observed results are only consistent with the elimination-addition mechanism involving a sulfene intermediate shown in (201). Subsequent kinetic studies... 

A reaction which is related to the ortho ester Claisen rearrangement utilizes an amide acetal, such as dimethylacetamide dimethyl acetal, rather than an ortho ester in the exchange reaction with allylic alcohols.174 The stereochemistry of the reaction is analogous to that of the other variants of the Claisen rearrangement.175... 

The interpretation of the results of tracer experiments of this sort is sometimes complicated by, sO-exchange reactions. l80 from the solvent may be incorporated into the unreacted ester as hydrolysis proceeds (see below, p. 105), or into either or both of the products. The exchange reaction is significant with alcohols, such as triphenylmethyl alcohol, which give rise to relatively stable carbonium ions under acidic conditions (see, for example, refs. 67, 85), viz-... 

Two types of esterification reaction that can be studied with water as solvent are lactone formation, in which the alcohol is part of the same molecule as the acid, and the lsO-exchange reaction of carboxylic acids, which makes it possible to examine A-2 reactions of carboxylic acids under the conditions used for ester hydrolysis. Work in both these fields confirms the similarities between ester hydrolysis and formation. The hydrolysis and formation of y-butyrolactone have already been discussed (p. 109). We deal here with the lsO-exchange reactions of carboxylic acids. 

The first attempts to prepare cobalt and nickel ethoxides were reported in 1936 by Meerwein [1102] and Kandelaki [875]. Application ofNaOR in the exchange reactions could not, however lead to the obtaining of the pure products of purpose as they were insoluble in the parent alcohol. Application of LiOR for this purpose permitted Adams et al. in 1966 to obtain the individual M(OMe)2 — derivatives of id-transition elements in the series from Cr to Cu [6]. In the 1980s Mehrotra et al. have described the homologous series of Ni(OR)2 — from methoxide to r-hexyloxide [99], and also Co(OR)2, where R = Me,Et, Pr [1108]. On the alkoxylation of CoH(N2)(PPh3)3 by esters, phenol, or fluorinated ketones, Hayashi et al. [720] have obtained a series of tetrahedral [Co (OR)(PPh3)3] complexes. 

The ester exchange reactions of the oxyphosphoranes (285 R = R = Ph, Me, 4-nitrophenyl) with several alcohols, models for nucleosides, have been investigated.252 The oxidative hydrolysis of the phosphorus(V) esters of thiols such as (286)-(289) with... 

The hydrolysis reactions of A -phospho amino acids seen as models for protein dephosphorylation have been studied in Tris-HCl buffer (pH7.5)-DMSO. The reactions were first order and the rates were very much faster than those of simple phosphoamidates. A pentacoordinated phosphorus intermediate is proposed on the reaction pathway.265 The rates of ester exchange reactions of alcohols (nucleoside models) with the oxyphosphorane (299) have been studied and the rates of exchange are much faster for diols than for mono-alcohols.266... 

This reaction has now been applied to a very great number of substituted allylic alcohols, and the mechanistic and stereoisomeric features of the reaction are becoming clearer.11 In broad outline, it would appear that the initial step is an alkoxy-exchange reaction between two alkoxy residues in the titanium complex and the two hydroxyl groups in the tartrate ester, thus ... 

Transesterification [236] and the ester exchange reaction [237] were reported to be efficiently catalyzed (Eqs. 30 and 31). Either of the exchange reactions are sensitive to steric constraints of the substrates and to metal ion size. For example, transesterification is most applicable to primary alcohols. Increased catalytic activity in the presence of larger lanthanide centers is explained by enhanced coordinative unsaturation and increased basicity of the alkoxide complexes. Strong basicity of the lanthanide isopropoxides is considered to catalyze effectively the transhydrocyanation from acetone cyanohydrin to sev-... 

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