The kinetics of quaternization of a series of 5-aryl- and 5-heteroarylpyrimidines with phenacyl bromide in acetonitrile have been studied in order to assess the electronic effects of the 5-substituent. The observed order of reactivity is 5-(1-methylpyrrol-2-yl) > 5-panisyl >5-(2-furyl) >5-p-tolyl > 5-(2-thienyl) >phenyl > 5-(m-chlorophenyl). The reactions are enthalpy controlled and the rate data can be accounted for in terms of the electronwithdrawing or donating ability of the 5-substituent. The substituent effects of the 2-fury 1- and 2-thienyl groups in the above reaction are significantly different from those observed in the piperidinolysis of 2-chloro-5(2-heteroaryl)pyrimidines.
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