The decarboxylation of methylmalonic acid and n-octadecylmalonic acid in normal alkanols

Rate constants and activation parameters are reported for the decarboxylation of methylmalonic acid and n-octadecylmalonic acid in three normal alkanols (hexanol-1, octanol-1, and decanol-1). Enthalpies of activation for both substrates in the various solvents are found to be a linear function of the number of carbon atoms or methylene groups in the hydrocarbon chain of the solvent. For both reaction series the isokinetic temperature is found to be equal to the melting point of the substrate. The free energy of activation at the isokinetic temperature in kcal/mole is 29.0 for n-octadecylmalonic acid and 29.4 for methylmalonic acid. Based on the results of the present investigation as well as on previously reported data in the case of malonic acid and n-butylmalonic acid, an empirical method of calculating the rate of reaction for the decarboxylation of malonic acid and its n-alkyl derivatives in normal alkanols is proposed. As a further test of the method of calculation the decarboxylation of n-dodecylmalonic acid in heptanol-1 at 110.30°C was studied. The calculated value of the pseudo-first-order specific reaction velocity constant of the reaction agreed with the experimental value to within about 0.1 percent.