Orthoester

A ball-and-stick model of ethyl orthoacetate, an orthoester.

In organic chemistry, an orthoester is a functional group containing three alkoxy groups attached to one carbon atom. The name can also refer to any organic compound that contains this functional group. An example of an orthoester is ethyl orthoacetate, CH₃C(OCH₂CH₃)₃, more correctly known as 1,1,1-triethoxyethane. Orthoesters are used in organic synthesis as protecting groups for esters. Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids (the products of hydration of carboxylic acids; see also acetal).^[1]

Reactions

Preparation

Orthoesters can be prepared by the reaction of nitriles with alcohols under acid catalysis:

RCN + 3 R’OH → RC(OR’)₃ + NH₃

Hydrolysis

Orthoesters are readily hydrolyzed in mild aqueous acid to form esters:

RC(OR’) ₃ + H₂O → RCO₂R’ + 2 R’OH

For example, trimethyl orthoformate [CH(OCH₃)₃] may be hydrolyzed (under acidic conditions) to methylformate and methanol^[2]; and may be further hydrolyzed (under alkaline conditions) to salts of formic acid and methanol^[3].

References

1. ^ David A. Shirley, Organic Chemistry (1968).
2. ^ J. P. Clayden, N. Greeves, S. G. Warren, P. D. Wothers (2000), Organic Chemistry (1st ed.), Oxford: Oxford University Press, p. 345, ISBN 978-0-19-850346-0 
3. ^ United States Patent Application 20070049501, Saini; Rajesh K.; and Savery; Karen, March 1, 2007