The Effect of Aromatic Amines on the Catalyzed Decarboxylation of 3-Oxo-glutaric Acid

Abstract

Equilibrium constants have been measured for the formation of M A species, where M is divalent manganese, cobalt, nickel, or zinc, and A 2 -is the 3-0x0-glutarate ion. Equilibriumconstants havealso been measured for the reactions MB2' + A 2 -e M A B , where B is 2,2'-bipyridyl or 1,lO-phenanthroline. These constants were obtained by p H measurements at 25 "C and an ionic strength of 0.60. The results are compared with those for similar systems, especially as regards the tendency to form ternary mixed complexes of the type MAB.The rates of decarboxylation of the various M A and MAB species have been measured. The resulting rate constants follow the Irving-Williams order for stability constants, except that in both MAB species the cobalt compound decomposed slightly faster than the nickel compound. The aromatic base, which had been found earlier to have very little effect in copper complexes, increased the rate constants appreciably with other metals, especially with manganese and zinc. Usually 1,IO-phenanthroline has a larger effect than 2,2'-bipyridyl. Some possible explanations of the results are considered.Nous avons mesure les constantes d'equilibre dans la formation d'especes MA, ou M est le manganese, le cobalt, le nickel ou le zinc bivalents et A 2 -, I'ion 3-0x0-glutarate. Nous avons egalement mesure les constantes d'equilibre des reactions MB2' + A2-$MAB, oh B est le 2,2'-bipyridyl ou le 1 ,lo-phenanthroline. Ces constantes furent obtenues au moyen de mesures de p H a 25 "C et sous une force ionique de 0.60. Nous comparons les resultats Q ceux de systemes semblables, specialement en ce qui concerne la tendance a former des complexes ternaires mixtes du type MAB.Nous avons mesure les vitesses de dttcarboxylation des especes M A et MAB. Les constantes de vitesse obtenues suivent I'ordre d'Irving-Williams des constantes de stabilite, excepte que dans les deux especes MAB, le compose de cobalt se decompose Iegeremect plus vite que celui de nickel. La base aromatique, chez qui on a trouvk anterieurement tres peu d'effet dans les complexes de cuivre, augmente appreciablement les constantes de vitesse avec d'autres metaux, specialement le manganese et le zinc. La 1.10-phenanthroline possede un plus grand effet que le 7,2-bipyridyl. Nous considerons quelques explications possibles des rCsultats.[Traduit par le journal]Canadian Journal o f Chemistry, 50, 3573 (1972) In recent paper (I), the present authors reported experiments on the effect of two tertiary aromatic amines, 2,2'-bipyridyl and 1,lO-phenanthroline, on the decarboxylation of 3-0x0-glutaric acid, catalyzed by copper ions. It was found that complexes of formula CuAB, where A2-is the 3-0x0-glutarate ion and B is the aromatic amine, were responsible for the enhanced rates of decomposition. Kinetic and equilibrium measurements made it possible to compare the rate constants for decarboxylation of CuAB and CuA species. In fact the rate constants do not differ greatly, and the major enhancement of the rate arises from changes in the equilibria, and hence ...