THE AMINOLYSIS AND HYDROLYSIS OF N-(4,6-DIPHENOXY-1,3,5-TRIAZIN-2-YL)SUBSTITUTED PYRIDINIUM SALTS - CONCERTED DISPLACEMENT MECHANISM

Reaction of the title pyridinium salts in aqueous buffers containing a mines involves nucleophilic displacement of the pyridine by the amine nitrogen in addition to background hydrolysis. The second-order rate c onstants for attack of a series of unhindered primary amines on the (4 ,6-diphenoxy-1,3,5-triazin-2-yl)pyridinium cation obey a Bronsted-like equation with slope beta(nuc) = 0.68. Six-membered-ring cyclic second ary amines have a similar Bronsted selectivity but are approximately 1 0-fold more reactive than primary amines of similar pK(a). The reactiv ity of ethanolamine against the title pyridinium salts obeys a Bronste d-like equation with beta(1g) = -0.47. In aminolysis of the triazinyl pyridinium salts the changes in bond fission and bond formation signal led by the polar substituent effects give Leffler alpha(1g) and alpha( nuc) values of 0.38 and 0.54, respectively, which indicate strong coup ling between the bonding changes consistent with a concerted process f or the displacement reaction. The adduct in the putative stepwise mech anism is considered too reactive to possess a significant barrier for it to exist as a discrete molecule.