Investigation of dialkyltin compounds as catalysts for the synthesis of dialkyl carbonates from alkyl carbamates

Abstract

New syntheses for dibutyldimethoxytin, dibutyldiisocyanatotin and 1,1,3,3-tetrabutyl-1,3-diisocyanatodistannoxane as well as the novel compounds dibutylisocyanatomethoxytin and 1,1,3,3-tetrabutyl-1-methoxy-3-isocyanatodistannoxane are described. These compounds were characterized by elemental analyses as well as 119Sn, 13C, and proton NMR, FTIR, MS and HPLC. They were found to have good catalytic activity for the synthesis of symmetrical dialkyl carbonates from alkyl carbamates and the corresponding alcohols. Extensive NMR and IR data indicate that tin compounds containing both an alkoxy and an isocyanato moiety bounded to tin are reaction intermediates in the synthesis of dialkyl carbonate and their formation is a key step in this catalytic process. The mechanism of carbonate synthesis involves the interconversion of the various tin species present in the reaction mixture to these reaction intermediates. Dibutyldimethoxytin, dibutylisocyanatomethoxytin and 1,1,3,3-tetrabutyl-1-methoxy-3-isocyanatodistannoxane have similar activity and are more active (10–14%) than dibutyloxotin for the synthesis of symmetrical dialkyl carbonates.