CARBODIIMIDES AS IMPORTANT INTERMEDIATES IN THE REACTION OF ISOCYANATES WITH CARBOXYLIC-ACIDS

The reaction between isocyanates and carboxylic acids is known to lead to amides. We have studied the mechanism of catalysis of this reactio n by phospholene oxides. The reaction between phenyl isocyanates and b enzoic acid was monitored under various conditions using. High-Pressur e Liquid Chromatography. It was found that the catalyst reacts with th e isocyanate under formation of a carbodiimide. The carbodiimide react s with the carboxylic acid to form amide and isocyanate via an N-acylu rea as intermediate. The catalyst is partly deactivated by the acid. T he phospholene catalyst was only found effective in reactions with aro matic isocyanates.