The regio-selective anodic chlorination of some benzene derivatives with an α-cyclodextrin (α-CD-) chemically modified graphite electrode via “ester bonding” (α-CD-CME) and with an α-CD adsorbed graphite (α-CD-AE) was studied. In the C Is ESCA spectrum of the α-CD-CME, a small peak which is considered to be based on carbon atoms in α-CD appeared at a higher binding energy side of the main peak, indicating that a-CD can be immobilized on the electrode surface. The immobilized α-CD as well as the adsorbed α-CD had a pronounced effect on the para-position selective chlorination of anisole and toluene, but such an effect could not be observed in the chlorination of chlorobenzene. Increasing the conversion of a substrate resulted in a decrease in the ratio of para- to ortho-chlorination product, p/o ratio, since the products have an inhibition effect on the inclusion of the substrate in α-CD's cavity. Although the homogeneous chlorination by NaOCI in the presence of α-CD in solution also showed a relatively high p/o ratio, it revealed that the ratio observed in the electrochemical method was slightly higher than that observed in the homogeneous method. The α-CD-CME used repeatedly showed relatively high regio-selectivity even after a month of immersion of the electrode in water, whereas the α-CD-AE showed decrease of the p/o ratio with increasing immersion time.
- anodic chlorination
- chemically modified electrode