Direct condensation of carboxylic acids with alcohols catalyzed by hafnium(IV) salts

In order to promote atom efficiency in synthesis and to avoid the generatio n of environmental waste, the use of stoichiometric amounts of condensing r eagents OF excess substrates should be avoided. In esterification, excesses of either carboxylic acids or alcohols are normally needed. We show that t he direct condensation of equimolar amounts of carboxylic acids and alcohol s can be achieved with the use of hafnium(IV) salts, such as commercially a vailable hafnium(IV) chloride and hafnium(IV) tert-butoxide. The present me thod can be applied to direct polyesterification and may be suitable for la rge-scale operations.