A-Bromo-»-butyric acid

In a SOO-ml. round-bottomed flask fitted with a calcium chloride drying tube are placed 226 g. (1.35 moles) of a-bromo- -butyric acid (Note 1) and 284 g. (175 ml., 2.39 moles) of thionyl chloride (Note 2). A small piece of porous plate is added, and the reaction mixture is allowed to stand at room temperature for 48 hours (Note 3). The excess thionyl chloride is removed by distillation, and the acid chloride is collected at 147-153° (Note 4). The yield of colorless product is 168-197 g. (67-78%). 

Bromobenzaldehyde, 100 Bromobenzene, 97 a-Bromo- -butyric acid, 62 a-Bromo- -butyryl chloride, 62 Butadiene, 93... 

The a-bromo-w-butyric acid obtained from the Eastman Kodak Company, which had a boiling range of 2°, proved to be satisfactory. 

Tetrahydrobenzo[6]thiophen-4-one (103) may be prepared from y-(2-thienyl)butyric acid by cyclization with phosphoric acid854 or by Friedel-Crafts cyclization of the corresponding acid chloride.194, 355.358 j s 5-methyl,357 2-ethyl,194 2-isopropyl,358 2- and 3-tert-butyl,359 2,3-dimethyl,360 2-ethyl-3-methyl,360 and 2-bromo 354 derivatives and diethyl 4,5,6,7-tetrahydrobenzo[6]thiophene-4,5-di-carboxylate861 may be prepared similarly. 4,5,6,7-Tetrahydrobenzo-[6]thiophen-7-one (104)357 362,863 and its 5- and 6-methyl 357 and 2-chloro 362 derivatives are obtained from the appropriately substituted y-(3-thienyl)butyric acid, A recent patent 364 describes the vapor phase cyclization of y-(2-thienyl)butyric acid to 103. Ketones (103 and 104) are useful intermediates for the synthesis of 4- and 7-substituted benzo[6]thiophenes, respectively their reactions are discussed in Section VI, B, 4. 

---