NUCLEOPHILICITY TOWARDS A SATURATED CARBON-ATOM - RATE CONSTANTS FOR THE AMINOLYSIS OF METHYL 4-NITROBENZENESULFONATE IN AQUEOUS-SOLUTION - A COMPARISON OF THE N AND N-+ PARAMETERS FOR AMINE NUCLEOPHILICITY

Second-order rate constants (k(Nu)) have been measured in aqueous solution (l = 0.1 mol dm(-3), 25 degrees C) for the S(N)2 reactions of methyl 4-nitrobenzenesulfonate with ammonia, 41 primary amines 20 secondary amines, 29 tertiary amines and 7 anionic nucleophiles. For the aminolysis reactions, Bronsted-type correlations of nucleophilicity with basicity require the classification of all amines in terms of strictly defined structural classes with beta(nuc) in the range 0.15-0.39. Swain-Scott plots indicate that simple amines, water and other light-atom nucleophiles (hydroxide; azide and cyanide anions) are five times more reactive than heavy-atom nucleophiles (thiosulfate, thiocyanate, iodide and bromide ions). For amine nucleophiles there is a close linear correlation (of slope 0.44, and including both primary and secondary amines) between log k(Nu) for the-aminolysis of methyl 4-nitrobenzenesulfonate and log k(Nu) for amine addition to the 1-methyl-4-vinylpyridinium cation. This correlation demonstrates a close linear relationship between the Swain-Scott n parameter and Ritchie's N-+ parameter for amine nucleophiles in aqueous solution (N-+ = 2.1n - 4.3).