A-Bromobutyric acid bromide

The reported analyses of the products suggested that the COOCH2CH3 substituent provided anchimeric assistance for the reaction paths 2 and 3. The mechanism was explained in terms of an intramolecular solvation of the bromide ion through an intimate ion-pair intermediate which decomposes in two different directions (equation 74, where X = Br and CH3CH2 replaces CH3). The formation of bromobutyric acid and ethylene (path 3) indicated a normal six-membered transition state for their formation as found in primary ethyl esters pyrolyses in the gas phase. Bromobutyric acid, which is known to be unstable at room temperature, rapidly produced butyrolactone. The consecutive reaction of path 4, under the experimental conditions, was ascribed to a similar mechanism where an intimate ion-pair intermediate is formed through COOH participation (equation 76). 

Bromobutyric acid (100 g) was boiled for 5-6 h with an equivalent amount (83 g) of potassium carbonate in water (500 ml). The solution was then evaporated, the residue was treated with the calculated amount of hydrochloric acid, and the viscous solution was filtered from the precipitated mixture of potassium chloride and bromide and extracted with ether. Drying of the extract over sodium sulfate, removal of the ether, and several fractionations in a vacuum gave 2-hydroxybutyric acid, m.p. 42°, b.p. 140°/12 mm. The yields were not stated. 

The alcoholic solution of the product is kept for 24 hours at 0° and then poured into 1 1. of ice-cold water. The oily layer is separated, and the aqueous layer is extracted with two 100-ml. portions of ethyl bromide (Note 4). The combined oil and extracts is washed with ice-cold 2% potassium hydroxide solution, then with very dilute hydrochloric acid, and finally with water. The organic layer is dried over sodium sulfate, the solvent is removed imder reduced pressure, and the residual crude ester is purified by distillation. The yield of ethyl 7-bromobutyrate, obtained as a colorless oil, b.p. 97-99° (25 mm.), 1.4543, is... 

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