AMINOLYSIS AND HYDROLYSIS OF SULFAMATE ESTERS - SUBSTANTIAL N=S BONDING IN THE TRANSITION-STATE LEADING TO N=SULFONYLAMINES

The aminolysis and hydrolysis of several sulphamate esters, RNHSO(2)ONp (R=PhCH(2), Ph, 4-MeC(6)H(4),4, 3-MeC(6)H(4), 4-FC6H4, 4-ClC6H4, 3-ClC6H4, H; Np=4-NO2C6H4) were been studied in 50% (v/v) aqueous acetonitrile at various temperatures. Reaction at the esters with an amine (R(1)NH(2)) gives (ONp)-O-- and both sulphamide, (RNHSO(2)NHR(1)) and sulphamate (RNHSO(2)O-R(1)NH(3)(+)) products. First-order rates were determined by the appearance of (ONp)-O-- and sometimes also by the disappearance of ester. The reaction was found to be independent of amine type and concentration and at the high pHs that obtain the substrate esters are fully ionized. A Hammett rho(acyl) of -1.8 was obtained for the decomposition of the sulphamate anions and this is consistent with substantial N=S bonding in the transition state leading to N-sulphonylamine, RN=SO2. This intermediate then partitions very rapidly, reacting with R(1)NH(2) and H2O respectively. Delta H-+(+), Delta S-+(+) and a deuterium solvent isotope effect were determined and were also interpreted in favour of the proposed mechanism, The dimethyl sulphamate ester (Me(2)NSO(2)ONp) does not react under the conditions used.