SOLVOLYTIC REACTIVITY OF 6-(CHLOROMETHYL)BENZO[A]PYRENE AND SELECTIVITY OF TRAPPING OF THE ARYLMETHYL CATION BY ADDED NUCLEOPHILES

The rate of solvolysis of the chemical carcinogen 6- (chloromethyl) benzo [a] pyrene in aqueous organic solvents is first order and independent of the presence of added nucleophiles, as expected for a carbonium ion reaction. The solvolytic reactivity of this arylmethyl chloride is comparable to that of compounds, such ap, p'-dimethylbenzhydryl chloride, which are known to form relatively stable carbonium ions. Evidence for the formation of a relatively stable carbonium ion in the solvolysis of 6-(chloromethyl)benzo[o]pyrene was obtained from the activation parameters (ΔSǂ = -4.6 eu) and from the presence of a marked common-ion effect when the solvolysis proceeded in the presence of LiCl. The nucleophilicities of a number of nucleophiles were measured kinetically in the presence of LiCl by their abilities to inhibit the common-ion effect in the solvolysis reaction. The selectivity of trapping of the arylmethyl cation shows the following order: aniline > N3- > Cl- > N-acetylcysteine ≃ pyridine > n-propylamine > hydroxide > diethylamine > water. This set of nucleophiles ranges in nucleophilic strength (kNu/kH2O) from 3 for diethylamine to 1.7 ˟ 103 for aniline. The products of trapping from the solvolysis of 6-(chloromethyl)benzo[a]pyrene enriched in carbon-13 at the methyl carbon were analyzed by 13C NMR. There is a good correlation of chemical shifts of carbon in 6- (substituted-methyl) benzo [a ] pyrenes and 1-substituted alkanes. © 1979, American Chemical Society. All rights reserved.