Abstract: p-Nitrophenyl N-(2-mercaptophenyl)-N-methylcarbamate cyclizes rapidly at 25'to N- methylbenzothiazolone with release of p-nitrophenol. The pH-rate constant profile is sigmoidal with pK,,,= 8.7. The effective molarity of the neighboring sulfhydryl group is 1.4 X los M in comparison with bimolecular attack of thiols on p-nitrophenyl N-methyl-N- phenylcarbamate. The pH-rate constant profile for cyclization of phenyl N-(2-aminophenyl) ...