The acid hdrolysis of methymalonamic acid (1953)
AuthorsStewart, B. L.show all
The acid hydrolysis of diamides of the malonic series is represented by the general equation: - [Diagram] where K₁ and K₂ are the specific rate constants for the hydrolysis of an amide group. In simplest principle, the reactions are third order, first with respect to the hydrogen ion and first with respect to each to each of the reactants, amide and water. In sufficient excess of acid and of water, the reaction is found to be pseudo-unimolecular and the kinetics reduced to those of first order. Thus the rate may be represented by the equation –dc/dt = kc, where c is the concentration of the amide and k the specific rate constant of the reaction. Integrating, the equation becomes 1n(c₁’-c) = kt, where c₁’ is the initial concentration of the amide. Thus the rate constant may be determined from a plot of the natural logarithm of the concentration of the unhydrolysed amide against the time, k being equal to the slope of the straight-line graph. Swain as analysed mathematically the kinetics of consecutive first-order reactions and has concluded that the initial slope of the graph on 1n(conc. of reactant) against time is equal to half the specific rate constant for the initial reaction (k₁ ) and the final slope is equal to the rate constant for the second reactions (k₂). This is,
[diagram] is the reaction rate for the overall rate and measure the rate of hydrolysis per amide group. When the electrode environment of the amide group is approximately the same at each step k₁’ = 1/2k#x2081; = k₂ and the graph should be linear throughout. The hydrolysis of substituted malonamides and of malonamic acid, in express acid, has been studies in the laboratory by Stone and McKenzie at 98±C and by Ivory at 80±C. At the higher temperature, graphs of 1n C against time were found to be linear for malonamide, methylmalonamide and nitromalonamide but not for aminomalonamide. Thus, in all but the latter, the rate of hydrolysis of an amide group was nearly the same in the two steps. In the case if malonamide this was confirmed by McKenzie by carrying out hydrolysis determinations on malonic acid, the intermediate in the formation of malonic acid from malonamide. He concluded that the rate of hydrolysis of one amide group was not markedly affected by a change, from amide to carboxyl, in the other functional group. In the case of aminomalonamide the curve bent downwards. This indicated an increase in the hydrolysis rate for the second amide group. At the lower temperature differences in the linearity of the curves were more marked. The rate of the second hydrolysis reaction was found to increase in the case of malonamide, amino – and nitromalonamide and decrease in methylmalonamide. The increase in the rate of hydrolysis of the amide group is appreciably less than that of the amide group in methylmalonamide, methyl-malonamic acid was prepared and a number of hydrolysis run carried out. The preparations of the acid and results obtained from its hydrolysis are described in this thesis.