Reaction of dibutyltin oxide with amides in presence of traces of water:: multinuclear NMR study and mechanism

The product of the reaction of primary and secondary amides with dibutyltin oxide is shown to be a dimeric 1,3-diacyloxytetrabutyldistannoxane. The reaction was studied in hulk with model amides at 180 degrees C, avoiding perfect anhydrous conditions, in view to be transposable to transamidification with reactive extrusion process. The formation of an intermediate compound of the type 1-acyloxy-3-alkylaminotetrabutyldistannoxane is pointed out. With an excess of amide, the presence of water leads to the dimeric 1,3-diacyloxytetrabutyldistannoxane. Without an excess of amide, the hydrolysis of this intermediate leads to a more complex tetrastannoxane structure associated in a more or less perfect ladder-like structure including partially hydrolyzed and condensed forms of the distannoxane. The dimeric 1-acyloxy-3-alkoxytetrabutyldistannoxane resulting from the reaction of esters with dibutyltin oxide are shown to give a similar stannoxane structure after hydrolysis. All the products were characterized in solution by H-1-, C-13- and Sn-119-NMR spectroscopy. On the basis of the spectroscopic analysis, a mechanism of the reaction is proposed and discussed. (C) 1999 Elsevier Science S.A. All rights reserved.