Nitrosation by alkyl nitrites. Part 4. S-nitrosation in acidic alcohol solvents

Abstract

Both isopropyl nitrite (IPN) and t-butyl nitrite (TBN) react rapidly with thiourea (TU) and thioglycolic acid (TGA) in isopropyl and t-butyl alcohol, respectively, containing an acid catalyst, to give the corresponding S-nitroso derivatives, contrasting with the behaviour of aromatic amines under the same conditions. The thiourea reaction is reversible and thiourea itself is significantly protonated under the experimental conditions. A kinetic analysis reveals that both alkyl nitrites are of comparable reactivity and also that TU is significantly more reactive than TGA. The reactive species is probably the protonated form of the alkyl nitrite. Catalysis by added Et₄NCl and Et₄NBr is interpreted in terms of ClNO and BrNO formation, but there may be a contribution due to general acid catalysis by HCl or HBr. The reaction rate is much reduced by the addition of small amounts of water.