Synthesis of 2,4-Dimethyl Benzoic Acid

dimethyl benzoic acid was synthesized as one medium of the acylphosphine oxid compound, which is an excellent photoinitiator used in UV-curing systems. In the first step, 2-chloro-2,4-dimethylacetophenone was synthesized from m -xylene and chloroacetyl chloride with Friedel-Crafts acylation. And in the scecond step the 2,4-Dimethyl Benzoic acid was synthesized through α-hydrogen halogenation , haloform reaction and acidification.The factors influencing the reactions were studied, such as the kind of the acylating reagent and the catalyst, the ratio between the reaction reagents, the optimum reaction time and reaction centigrade. And the concentration of the alkali solution used in the haloform reaction was also studied. The yield of acylation was 88%～91% when n (C 8H 10 )∶ n (ClCH 2COCl)∶ n (Fe 2O 3)=1∶(1.2～1.3)∶0.001, reaction centigrade being 100 ℃ and reaction time being 4 h. The total yield was 80% when the concentration of alkali solution was 40% which is strong enough to accelerate α-hydrogen halogenation and haloform reaction. After its recrystallisation, the compound was confirmed as 2,4-dimethyl benzoic acid by melting point, IR and 1 HNMR.