Alcoholysis of ester

The acyl carbon atom is also sp2-hybridised, much more electrophilic than an aryl carbon atom, and highly stabilised by the structure where the negative charge is on the oxygen atom (Figure 12.18). The acyl oxygen atom may, as in acid catalysed alcoholysis of esters, be protonated, before or after the formation of the new carbon-oxygen bond. 

Earlier work in this field has been thoroughly reviewed [1,2]. However, to illustrate in a sensible and logical way the evolution from simple metal ion promotion of acyl transfer in supramolecular complexes to supramolecular catalysts capable of turnover catalysis, an account of earlier work is appropriate. The following sections present a brief overview of our earlier observations related to the influence of alkaline-earth metal ions and their complexes with crown ethers on the alcoholysis of esters and of activated amides under basic conditions. 

Alcoholysis of ester and epoxide with various basic catalysts including alkaline earth metal oxides and hydroxides was reported recently by Hattori et alF61 Various alcohols were transesterified with ethyl acetate at 273 K. The results show that in the presence of strongly basic catalysts such as CaO, SrO and BaO, propan-2-ol reacted much faster than methanol, whereas in the presence of more weakly basic catalysts such as MgO, Sr(0H)2-8H20 and Ba(0H)28H20, methanol reacted faster than propan-2-ol. When the alcoholysis was performed with propene oxide, alkaline earth metal oxides were found to be more reactive than hydroxides the reactivity of the alcohols was in the order methanol > ethanol > propan-2-ol > 2-methylpropan-2-ol, regardless of the type of catalyst. 

Hattori, H., Shima, M. and Kabashima, H. Alcoholysis of ester and epoxide catalyzed by solid bases, Stud. Surf. Sci. Catal., 2000, 130D, 3507-3512. 

The experimental evidence obtained has shown that the reactivity of the estos of the aromatic and aliphatic carboxylic acids under study in the reaction of alcoholysis with cellulose changes substantially with changes in the chemical constitution of the acyl radical. According to existing con<%ptions (52), the alcoholysis of esters in the presence of an alkaline catalyst at the rate-determining step involves the attack of the alkoxy ion on the carbon atom erf the carbonyl group in the case of... 

Outside the scope of coverage of this work are synthetic systems involving the catalytic or stoichiometric alcoholysis of esters or amides promoted by zinc ions or complexes.172-177... 

Hydrolase-catalyzed enantiomer-differentiating alcoholysis of esters of racemic alcohols with achiral alcohols in organic solvents of low water content is a valuable alternative to hydrolysis (Table 11.1-22). 

As well as the above-described intermolecular alcoholysis of esters, the intramolecular version has been successfully utilized for the synthesis of lactones from racemic hydroxy carboxylic acid esters (25-41, 64—66) (Table 11.1-22). High selectivity in the pig pancreas lipase-catalyzed enantiomer-differentiating lactonization of y-hydroxy carboxylic acid esters with formation of butyrolactones substituted in... 

Table n.1-22. Lipase-catalyzed enantiomer- and enantiotopos-differentiating inter- and intramolecular alcoholysis of esters and lactones in organic solvents (PCL Pseudomonas cepacia lipase, PSL Pseudomonas sp. lipase, PPL pig pancreas lipase, MML Mucor miehei lipase, HLL, Humicola lanuginosa lipase, PFL Pseudomonasfluorescens lipase, CCL Candida cyiindracea lipase, CAL-B Candida antarctica B lipase, CRL Candida rugosa lipase, PRL Penicillium roquefbrti lipase, CAL-A+B Candida antarctica A+B lipase). 

Alkali metal alkoxides catalyse the alcoholysis of esters, by a mechanism analogous to basic hydrolysis. Additionally, alkoxides catalyse the reaction of alcohols with carbon monoxide to give formate esters ... 

Overall, the reactivity picture obtained with catalysts 1 Zn2, 2 Zn2, 24—Zn2, 25—Zn2, 14 Ba2, and 15—Ba2 in the basic alcoholysis of esters, shows that the order of catalytic efficiency 1,2-vicinal >> 1,3-distal is a substrate-independent feature of upper rim calix[4]arene-based bimetallic catalysts in the cleavage of esters provided with an anchoring group, which is unaffected by the nature of the metal ion and of the ligating unit. 

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