pH Control in Aqueous Processes: N-4-Methylsulfonylphenylguanidine

The kinetics and mechanism of the synthesis of the sulfonylguanidine 2 by reaction of the corresponding aniline, 1, with cyanamide have been investigated in aqueous acid solution. The reaction is acid-catalysed, but at low pH, where substantial protonation of 1 occurs, the dominant reaction occurring is a competing hydrolysis of cyanamide to urea. It is shown that reactions run under pH control in the region of pH 2 achieve close to maximum selectivity with respect to the desired guanidine formation, whilst still occurring at a practical rate.