Mechanistic studies on the photohydrolysis of 4-chlorobiphenyl

Because PCBs are environmental pollutants, many researchers are concerned about their fate in the environment. The photochemistry of 4-chlorobiphenyl in water was studied in this project.

Previous experiments in the photohydrolysis of 4-chlorobiphenyl indicated that 4-chlorobiphenyl proceeds through an intermediate aryl cation. Photohydrolysis of 4-chlorobiphenyl was suppressed by added chloride ion, which indicated an aryl cation intermediate.

Both hydrochloric acid and sodium chloride were shown to quench the excited state of 4-chlorobiphenyl. Spin orbit effects and ionic strength effects were not involved in the rate suppression. Hydrochloric acid was shown to quench the photohydrolysis of 4-chlorobiphenyl beyond the quenching seen by sodium chloride. However, experiments showed that protonation does not take place on the biphenyl ring.

These results represent the first example of a common ion effect in a photochemical reaction.