Thionyl Chloride → (3,5-Dimethylphenoxy)acetyl chloride

To a solution of 3,5-dimethylphenoxyacetic acid (9.0 g, 50 mmole) in benzene (100 mL) was added thionyl chloride (10.89 mL). The resulting mixture was refluxed for 2 hr, then the benzene was removed by distillation. The residual material was dried in vacuo to give 3,5-dimethylphenoxyacetyl chloride, which was dissolved in 20 ml of acetonitrile and used in situ. L-Glutamic acid (8.8 g, 60 mmole) was dissolved in a solution of sodium carbonate (12.72 g, 150 mL, 120 mmole) and the 3,5-dimethylphenoxyacetyl chloride in the acetonitrile solution was slowly added while the pH 8 was adjusted from time-to-time by adding sodium carbonate solution. The reaction mixture was stirred at room temperature for 2 hr, and acidified to pH 2 to give a solid precipitate. The solid precipitate was collected by filtration, treated with hot benzene, filtered, again and washed again with benzene to give Intermediate 31 (9.2 g).