ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 25, Number 2
JKCSEZ 25(2)
April 20, 1981 

Kinetics and mechanism for the reaction of substituted phenacyl bromides with substituted pyridines have been determined at 25, 35 and 45℃ in methanol and dimethylformamide by the conductivity method. The rate constants for the reaction of various pyridines with phenacyl bromide shown that electron-donating substituents in the pyridine increase the rate, while electron-attracting one decrease in both solvents. The effect of substituents in substrate, the rate being increased by electron-attracting substituents. This is as expected for nucleophilic attack of amines on the carbon atom. Isokinetic and Brψnsted linear relationship were shown in the reaction of phenacyl bromide with pyridines in both solvent in which isokinetic temperature were obtained 614, 202°K and β values were 0.29, 0.36 in methanol and dimethylformamide respectively. In the case of the reaction of substituted phenacyl bromide with pyridines, isokinetic temperature decreases with increasing electron-attracting ability of the substituents in the phenacyl bromide, while the β values were reverse. From the above results, it can be inferred that N…C bond formation decreases progressively from p-chloro- to p-methoxyphenacyl bromide and the bond formation predominates in DMF than methanol. The ρ values of Hammett equation of the reaction of phenacyl bromide with substituted pyridines are negative in both solvent, but its value was larger negative in DMF than methanol and the ρ value of that of substitutted substrates with pyridine was 0.3, the low value is ascribed to direct SN2 attack of the nitrogen atom in pyridine ring at the methylene carbon.