Radical cations of benzo[a]pyrene (BP) and 6-substituted derivatives were synthesized by two methods: reaction of the hydrocarbon with I2 and AgClO4 in benzene, and reaction of the hydrocarbon with NOBF4 in CH3CN/CH2Cl2. Both the radical cation perchlorates and tetrafluoroborates were stable for prolonged periods of time when stored under argon at subzero temperatures. The radical cations were reacted with nucleophiles of various strengths, namely H2O, AcO- and F-, as a means of best characterizing these intermediates, as well as determining their chemical properties. Reaction of BP, 6-FBP, 6-ClBP, and 6-BrBP radical cation perchlorates with H2O produced BP 1,6- 3,6-, and 6,12-dione, whereas the radical cation derived from 6-CH3BP yielded 6-CH2OHBP. When BP•+ClO4- and 6-FBP·+ClO4- were reacted with NaOAc in H2O/CH3CN (9:1), 6-OAcBP was formed, in addition to the quinones. 6-ClBP•+ClO4- formed a small amount of 1-OAc- 6-C1BP and 3-OAc-6-ClBP, in addition to the diones, whereas for 6-BrBP•+ClO4- and 6-CH3BP•+ClO4- the reaction products were BP diones and 6-CH2OHBP, respectively. Reactions conducted under anhydrous conditions, using tetramethylammonium acetate in CH3CN, gave similar results, except that no quinones were formed. These results confirm the reactivity of nucleophiles at the positions of high charge localization in the BP•+, i.e. C-6, followed by C-1 and C-3.
ASJC Scopus subject areas
- Organic Chemistry