The mechanisms of the hydrolyses of N-nitrobenzenesulfonamides, N-nitrobenzamides and some other N-nitro amides in aqueous sulfuric acid1

Abstract

The mechanisms of the hydrolysis reactions of some N-nitrobenzenesulfonamides (YC₆H₄SO₂NHNO₂), N-nitrobenzamides (YC₆H₄CONHNO₂) and N-methyl-N-nitrobenzamides (YC₆H₄CON(CH₃)NO₂) have been determined in aqueous sulfuric acid using the excess acidity method. Also studied were N-methyl-N-nitroacetamide and nitrourea, with N,N-dinitromethylamine for comparison. N-Nitrobenzenesulfonamides give either YC₆H₄SO₂⁺ and NH₂NO₂ (electron-donating Y) or YC₆H₄SO₂NH₂ and NO₂⁺ (electron-withdrawing Y) in A1 processes; the change in product is reflected in the different ρ⁺ values found for the two modes of cleavage. N-Nitrobenzamides behave similarly in strong acid, with an A1 reaction following presumed O-protonation, but in more moderate acid they exhibit a neutral water-catalysed hydrolysis mechanism, and in dilute acid the parent N-nitrobenzamides actually show hydroxide catalysis. N-Methyl-N-nitroacetamide shows only the neutral water-catalysed process. Nitrourea has an A1 acid-catalysed hydrolysis reaction in acid, analogous to the known B1 mechanism in base (also visible in dilute sulfuric acid), but has no water reaction; the pH-rate profile for the hydrolysis of this substance is here extended into the non-ideal acid region. N,N-Dinitromethylamine loses NO₂⁺ in an A1 process following initial nitro-group protonation, giving N-nitromethylamine which is identifiable by its known hydrolysis rate. Activation parameters, m*m^‡ slopes and ρ⁺ values given by the excess acidity analysis are shown to be compatible with the postulated mechanisms.