Some kinetic and equilibrium studies of the reactions of carbonyl compounds with amines and/or sulfite

Abstract

Studies have been made of the reaction of several carbonyl compounds with sulfite in aqueous solution. (^1)H NMR results indicate the formation of hydroxyalkanesulfonates, HXS, of general structure, RR'C(0H)(S0(_3)Na). Equilibrium and kinetic studies of the decomposition reactions have been made making use of the rapid reaction of iodine with liberated sulfite. The decomposition shows an acidity dependence; above pH 3 reaction mainly involves the dianion, RR'C(0’)(S0(_3)"), while below pH 3 the monoanion, RR'(OH)(S0(_3)’) is involved. In the case of adducts from propanal values obtained for the rate constants for decomposition were 370 s(^-1) and 3.9x10(^-6) s(^-1) for the dianion and monoanion respectively. pK(_a) values for acid dissociation of several HXS compounds were measured and found to be in the range 9-12. The reactions of hydroxypropanesulfonate, HPS, with aniline and aniline derivatives have been studied. (^1)H NMR spectra accord with formation of anilinopropanesulfonates, APS, kinetic and equilibrium measurements were made spectrophotometrically in the presence of added sulfite ions. The overall equilibrium constant for the reaction with aniline was found to be 84 dm(^3) moI(^1) The mechanism of the reaction is thought to involve decomposition of HPS to yield propanal which reacts with the amine to yield a carbinolamine intermediate. This subsequently dehydrates giving an imine which reacts rapidly with free sulfite to give the product, APS. The results suggest a change in rate limiting step from the^reaction of aniline with propanal at low pH to carbinolamine dehydration at high pH, the change occurring at pH 6 -7, the effects of ring substituents in the aniline on reactivity have been examined. Reaction of propanal with aniline in acetonitrile yields the imine. Kinetic studies of its decomposition back to reactants in the presence of aqueous sulfite solutions confirm the conclusion reached from measurements on the forward reaction. Reactions of hydroxymethanesulfonate, HMS, with benzylamine and some derivatives were observed by (^1) H NMR spectroscopy. Equilibrium constants for the formation of 1:1 and 1:2 adducts were measured and the variations of values with pH were examined. Trimerisations of the imines formed from formaldehyde and benzylamine and its derivatives were successfully achieved.