Hexaalkylguanidinium chlorides

Xie H, Duan H, Li S et al (2005) The effective synthesis of propylene carbonate catalyzed by silica-supported hexaalkylguanidinium chloride. New J Chem 29(9) 1199-1203... 

Zeolites have been employed to shift the equilibrium in transesterifica-tions by absorbing smaller molecules [57]. For example, the methyl ester of benzoic acid can be converted into the tertiary-butyl ester by refluxing in tertiary-butanol in the presence of zeolite 5A. Selective esterification of sterically hindered carboxylic acids with alkyl chloroformates over silica bound hexaalkylguanidinium chloride achieves high yields [58]. For example, benzyl 2,4,6-trimethylbenzoate was synthesised from the carboxylic acid and benzyl chloroformate in 96% yield at 120°C. 

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