Benzene, 99%
Anhydrous aluminium chloride, Lab reagent
3-methyl acrylic acid, Lab reagent
Hydrochloric acid, concentrated, commercial
Sodium hydroxide, commercial

In a 2 Lt four necked round bottom flask (assembly was set up in cooling tub) equipped with a mechanical stirrer, 500 mL dropping funnel, thermometer, calcium chloride guard tube, was charged benzene (550 mL). This slurry was cooled to about 5 oC and added anhydrous aluminium chloride (543 g, 4.06 mol ). Methacrylic acid (100 g, 1.31 mol) was slowly added keeping the reaction temperature below 8oC over a period of 1 h. Cooling removed and allowed to come to room temperature over a period of 2-3h. The reaction mixture thus obtained was heated to 50-50 oC and maintained at this temperature for 2 h. Further the reaction mixture was cooled and added to ice concentrated HCl ( ~500 g + 500 mL). The Product gets extracted in benzene. Benzene layer thus obtained was washed with water ( 250 mL) and then extracted with 15% sodium hydroxide solution (400 mL). This extraction brings the product to water layer. Aqueous alkaline solution was acidified to pH-2 with concentrated hydrochloric acid. The white crystals thus separated was washed with water (~250 mL) and dried at 70-75 oC for 8 h to get 2,2-dimethyl phenyl acetic acid as almost white crystalline solid (115 g, 53.5% based on methacrylic acid ).

1. Reaction and workup should be done under efficient hood  to take care of HCl gas and benzene.
2. Methylacrylic acid should be added to benzene and aluminium chloride. Addition of aluminium chloride to the reaction mizxture do not give any product.
3. This is the best procedure for the preperation of dimethyl phenylacetic acid compared to the other known  procedure in the lab scale.

See attached spectra

Slightly modified procedure of - Prijs, V. B, Helv. Chemica Acta, 1952, 35(98), 780-782

 

Shabanov, A. L., Seidov, N. M, Gasanova, U. A, kakhramanova, Z. O, Gasanova, M. M. Russian Journal of Organic Chemistry, 2009, 45(1), 26-29.