Decomposition of 1-aryl-3-dimethylamino-1-propanone methobromides under weakly acidic conditions

Under basic conditions, some 1-aryl-3-dimethylamino-1-propanone methodbromides (2) were shown to decompose too readily to measure by the electronic absorption spectroscopy technique available. However, at pH = 5.9 and 20 degrees centigrade, the rate of deamination to the corresponding 1-aryl-2-propen-1-ones was able to be followed using Guggenheim's method and a Hammett plot showed that the rate of deamination correlated with the arly substituent constants (o). The rho value for this process was +1.00. In contrast the corresponding 1-arly-3-dimethylamino-1-propanone hybrobromides (1) did not decompose under simulated physiological conditions (pH = 7.4, 37 degrees centigrade). Neither 1 or 2 were active against P388 lymphocytic leukemia in mice but the methobromides displayed greater murine toxicity.