Coloured and colourless charge-transfer complexes of small and polymeric quaternary pyridinium bromides

Abstract

The products of quaternization reactions involving alkyl bromides are, under certain conditions, coloured, e.g. 4-methyl-N-n-propylpyridinium bromide is red and poly(4-vinyl-N-n-butylpyridinium bromide) is green when prepared in benzene, say, at 333 K. Neither are coloured, however, when heated in sulpholane. These and other products have been shown to be coloured due to charge-transfer bands; the possible involvement of impurities or side reactions has been eliminated: important in establishing the reliability of kinetic measurements by the authors. Comparison has been made with several iodides under varying conditions: these are invariably colourless in the solid and pale yellow in ethanol. They lack the low-energy charge-transfer bands (colours), but show charge-transfer bands in the u.v.