bromination of pmethoxybenzyl alcohol3 by the hydrogen bromide method,'Q followed by methanolysis with sodium methoxide. Benzyl alkyl ethers were obtained by the treatment of benzyl chloride with sodium alkoxide at the reflux temperature for 3-4 hr. The ethers were all purified by rectification under vacuum ( Table VIII).The other materials were the same with those described pre- viously. 3 (4 : 6 vol. %). The homogeneous reaction mixture was allowed to stand in a flask with a loosely held glass stopper without stirring; no difference in rates was observed between reactions with and without stirring. Aliquots were taken out at appropriate intervals of time, and the produced aldehyde was estimated by means of ultraviolet spectrophotometry after extracting with chloroform as reported previously. 3Materials. Substituted benzyl methyl ethers except the p methoxy derivative were prepared by way of the side-chain bromination of corresponding toluenes, followed by treatment with sodium methoxide. p-Methoxybenzyl ether was synthesized by the (19) R.Abstract: Rate constants for the bromination of several polynuclear aromatic hydrocarbons by molecular bromine were determined in aqueous acetic acid at 25 O. Partial rate factors were obtained from the rates and the major reaction products. The partial rate factors, and some obtained previously, were correlated with MO reactivity parameters and with the rates of other electrophilic substitution reactions. Addition accompanies substitution in the bromination of phenanthrene and anthracene.lthough interest in the reactivities of polynuclear A aromatic systems has increased as a result of the availability of various MO reactivity parameters with which the experimental reactivities can be compared, there are only very few reactions series in which these reactivities have been assessed in direct electrophilic substitution reactions. The studies that cover the largest number of compounds are those on n i t r a t i~n ,~ deuterio depr~tonation,~ the basicity toward hydrogen fluoride,6 and, to a lesser extent, chlorination.' To these we now add bromination. ResultsReactions were carried out in aqueous acetic acid. In acetic acid, as well as in other solvents of low dielectric constant, the kinetics of bromination is complicated by the intervention of terms which are of high order in bromine, and by the complexing of unreacted bromine with bromide ion which is formed as the reaction proceeds.* It is for this reason that investigations that did employ bromination for a comparison of relative rates have often relied on a comparison of time intervals required to reach a definite per cent of reaction, and rate constants were not determined. For instance, (1) Relative Reactivities of Polynuclear Aromatic Systems. (2) Taken from the Ph.D. thesis of L. Altschuler, Bryn Mawr Col-(3) To whom inquiries should be addressed. (4) M.in an earlier study of bromination, Mason compared the times for 5 and 10% bromination of hydrocarbons in 80% acetic acid.g Under these conditions, the bromination ...