Ortho ester

Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name 'ortho ester' is derived.

[1] Ortho esters can be prepared by the Pinner reaction, in which nitriles react with alcohols in the presence of one equivalent of hydrogen chloride.

The reaction proceeds by formation of imido ester hydrochloride: Upon standing in the presence of excess alcohol, this intermediate converts to the ortho ester: The reaction requires anhydrous conditions,[1] and ideally a nonpolar solvent.

[3]: 162 Carboxylic acids naturally form a trithio ortho ester when heated with a mercaptan of appropriate stoichiometry.

[4] The resulting compound undergoes transesterification to a traditional orthoester in the presence of zinc chloride.