RADICAL CATIONS OF BENZO[A]PYRENE AND 6-SUBSTITUTED DERIVATIVES - SYNTHESIS AND REACTION WITH NUCLEOPHILES

Radical cations of benzo[a]pyrene (BP) and 6-substituted derivatives w ere synthesized by two methods: reaction of the hydrocarbon with I-2 a nd AgClO4 in benzene, and reaction of the hydrocarbon with NOBF4 in CH 3CN/CH2Cl2. Both the radical cation perchlorates and tetrafluoroborate s were stable for prolonged periods of time when stored under argon at subzero temperatures. The radical cations were reacted with nucleophi les of various strengths, namely H2O, AcO- and F-, as a means of best characterizing these intermediates, as well as determining their chemi cal properties. Reaction of BP, 6-FBP, 6-ClBP, and 6-BrBP radical cati on perchlorates with H2O produced BP 1,6- 3,6-, and 6,12-dione, wherea s the radical cation derived from 6-CH3BP yielded 6-CH2OHBP. When (BPC lO4-)-Cl-.+ and 6-(FBPClO4-)-Cl-.+ were reacted with NaOAc in H2O/CH3C N (9:1), 6-OAcBP was formed, in addition to the quinones. 6-(ClBPClO4- )-Cl-.+ formed a small amount of 1-OAc-6-ClBP and 3-OAc-6-ClBP, in add ition to the diones, whereas for 6-(BrBPClO4-)-Cl-.+ and 6-(CH3BPClO4- )-Cl-.+ the reaction products were BP diones and 6-CH2OHBP, respective ly. Reactions conducted under anhydrous conditions, using tetramethyla mmonium acetate in CH3CN, gave similar results, except that no quinone s were formed. These results confirm the reactivity of nucleophiles at the positions of high charge localization in the BP.+, i.e. C-6, foll owed by C-1 and C-3.