Kinetics and mechanisms of the reactions of 9-substituted anthracene cation radicals with water or methanol in acetonitrile

The reactions of 9-substituted anthracene cation radicals (XA+s) with water and methanol in acetonitrile were analyzed using an electron transfer stopped-flow (ETSF) method. By adopting the tris(2,4-dibromophenyl)amine cation radical (TDBPA+) as a reaction initiator, five XA+s, i.e. phenyl, bromo, acetyl, benzyl, and methyl derivatives, could be generated quantitatively by mixing XA with TDBPA+, and the chemical reaction processes of XA+s with water or methanol (ROH) could then be followed by observing dynamic transformation processes of the absorption spectra. Consequently, the reaction orders of XA+ and ROH as well as the reaction rates could be determined. The order of the reactivity was anthracene+>9-methylanthracene+>9-benzylanthracene+>9-acetylanthracene+, 9-bromoanthracene+>9-phenylanthracene+, and diverse changes in the reaction orders of both XA+ and ROH were observed indicating some mechanistic changes. The order of the reactivity was difficult to explain only on the basis of the character of XAs or XA+s. However, as a hypothesis, it can be assumed that when the electron transfer between XA+ and XA(ROH)+ is favorable to formation of XA(ROH)2+, the reaction order of [XA+] is second, and the reaction rates become faster.