A small survey of the organic catalysts did not reveal any possible better candidates. However, as a byproduct, we found a mechanism of the reaction of PhCNO with the N-sulfinylaniline PhNSO that produces diphenyl carbodiimide (Ph-N--C --N-Ph). As it turns out, the reaction proceeds by a similar mechanism, through the formation of the fivemembered ring and then eliminating SO 2 upon PhNCNPh formation. The PhNSO-catalyzed conversion PhCNO --→ PhNCO is also a possible but less favorable reaction pathway, and it explains the found traces of PhNCO in the reaction mixture. In the end, we also surveyed the effect of phenyl ring substituents on the reaction kinetics. It turns out that such substitution slows down the reaction with respect to the unsubstituted PhCNO. The reaction seems to proceed slower with the increasing electron-withdrawing effect of the substituent.