Reactivity of sulfur nucleophiles with N-methyl-N-nitroso-p-toluenesulfonamide

Abstract

The transfer of the nitroso group from N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) to cysteine (CYS) and 2-aminoethanethiol (AET) has been studied in a pH range between pH = 7 and pH = 13. Kinetic results clearly indicate that both nucleophiles react through the corresponding thiolate to give the corresponding nitrosothiol. The existence of two (AET) or three (CYS) macroscopic acidity constants has been kinetically evidenced and the nitrosation rates of the corresponding bases have been identified. Nitrosation rate constants of the different species present in the reaction medium have been determined and a Brønsted-type plot has been established giving a β_nuc value ≅ 0.08 clearly different from the values of β_nuc ≅ 0.7 obtained in the nitrosation of primary and secondary amines by MNTS. The low β_nuc value has been attributed to the need for previous desolvation of the nucleophile.