10-Methylacridine derivatives acting as efficient and stable photocatalysts in reductive dehalogenation of halogenated compounds with sodium borohydride via photoinduced electron transfer

Abstract

10-Methylacridine derivatives, 9,10-dihydro-10-methylacridine (AcrH{sub 2}) and acriflavine (AFH{sup +}), act as efficient and stable photocatalysts in reductive dechlorination of p-chlorobiphenyl (ClBP) as well as dehalogenation of other halogenated compounds with sodium borohydride (NaBH{sub 4}) in a mixture of acetonitrile and H{sub 2}O (9:1 v/v) at 298 K. The reductive dechlorination proceeds via the reduction of ClBP by the singlet excited state ({sup 1}AcrH{sub 2}*) to yield dechlorinated product (biphenyl) and 10-methylacridinium ion (AcrH{sup +}), followed by the facile reduction of AcrH{sup +} with NaBH{sub 4} to regenerate AcrH{sub 2}. The absence of the primary kinetic isotope effect as well as the comparison of the observed rate constants with those predicted by using the Marcus theory of electron transfer indicates that the reduction of halogenated compounds (RX) by the singlet excited state ({sup 1}AcrH{sub 2}*) proceeds via photoinduced electron transfer from {sup 1}AcrH{sub 2}* to RX, which results in the cleavage of C-X bonds.