Preparation
Synthesis of 2,4-Dibromo-3-methylthiophene: A mixture of 3-methylthiphene (50.0 g, 0.509 mol), glacial AcOH (400 mL) and NaOAc (132 g, 1.60 mol) was stirred and heated to 60°C. Bromine (260 g, 1.63 mol) was then added dropwise at such a rate that kept the temperature below 85°C . The mixture was heated at 85°C for 5 h to complete the conversion to 2,4,5-tribromo-3-methylthiophene, then water (85 g) was added and the reaction temperature was dropped to 60°C. Zinc dust (48.1 g, 0.73 mol) was carefully added in 5-10 g portions so as to keep the temperature below 85°C. The mixture was heated to 100°C for 8 h, then cooled to 25°C. Water (350 mL) and hexanes (500 mL) were then added. The mixture was stirred for 30 min, the organic layer was separated, washed with water (150 mL), then saturated NaHCO3 solution (150 mL), then concentrated to give an orange oil. This oil was distilled (b.p. 80°C @ 0.3 mm Hg) through a 6” jacketed Vigreux column to give 107 g (82% wt.) of a yellow oil which slowly solidified. GC area % analysis showed the product to be a mixture of 2,4-dibromo-3-methylthiophene (89%), 4,5-dibromo-3-methylthiophene (9%), and 4-bromo-3-methylthiophene (2%).
