KINETICS OF THE HYDROLYSIS OF CYCLIC N-SUBSTITUTED SULFAMIDES - O-2-CYCLOHEXYL-2,3-DIHYDRO-3-OXO-1,2,5-THIADIAZOLE 1,1-DIOXIDES AND NO-2-PHENETHYL-2,3-DIHYDRO-3-OXO-1,2,5-THIADIAZOLE 1,1-DIOXIDES

The hydrolysis reactions of 4-amino-2-phenethyl- and 4-amino-2-cyclohe xyl-2,3-dihydro-3-oxo-1,2,5 thiadiazole 1,1-dioxide (Ia and Ib) were i nvestigated in the range 24-73 degrees C in buffered aqueous solutions . The observed rate constants (k(obs)) are independent of pH in the ra nge ca 1-4 pH, but increase with increase in pH above ca 4. A linear l og k(obs) vs pH profile with unit slope is observed from pH ca 4 up to the highest experimental pH (ca 10). The products are the correspondi ng new compounds: 2-amino-2-[(N-substituted-sulfamoyl)imino]acetic aci d salts. The C=N bond of these compounds hydrolyses further, in a slow reaction, to the sulfamide and oxalic acid derivatives. The substrate s decompose to the final products without accumulation of the acetic a cid derivatives under these experimental conditions. A mechanism is pr oposed. Rate constants and activation parameters are given for the fir st reaction step. Owing to steric effects, the reaction rate is higher for the N-phenethyl-substituted derivative than for the 2-cyclohexyl- substituted derivative. (C) 1998 John Wiley & Sons, Ltd.