How is 2,2',4-Trichlorobiphenyl (CAS: 37680-66-3) typically synthesized?

2,2',4-Trichlorobiphenyl is typically synthesized through a Friedel-Crafts alkylation reaction of biphenyl with chlorine gas in the presence of a Lewis acid catalyst like aluminum chloride. The reaction requires strict control of temperature and pressure to achieve high selectivity and yield. This method ensures that the chlorine atoms are added preferentially to the 2,2', and 4-positions of the biphenyl, leading to a high purity product.