Preparation of a-Bromopropionic Acid

Place 37 g of pure propionic acid in the flask, add 84 g of bromine, and connect with the reflux condenser. Raise the stopper connecting the top of the condenser with the absorption line, add rapidly 1-2 ml of phosphorus trichloride, and replace the stopper securely. Warm the water bath under the flask slowly until the reaction begins (40-50 ). Adjust the flame so that the evolution of hydrogen bromide is not so vigorous as to carry any considerable vapor of bromine into the absorption bottles. The reaction proceeds smoothly without a great deal of watching. When bromine vapor no longer appears in the condenser tube, the reaction is completed. 

The crude acid is transferred to a 125 or 250 ml Claisen flask and distilled at ordinary pressure until the temperature of the vapor rises to 160 . The apparatus is arranged for vacuum distillation (pages 238-239). The fraction which boils at 95-100 /10 mm is collected. The yield is 60-65 g. 

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B) Preparation of a-Bromopropionic Acid (M.). Arrange a 500-ml Florence flask as shown in Figure 46, without the dropping funnel the absorption train is the same as used in the preparation of chloroacetic acid (page 225). The rubber stopper which connects the reflux condenser to the flask is painted with sodium silicate twice, and allowed to dry each time. 

Zelinsky, N. A convenient preparation of a-bromopropionic acid ester. Ber. 1887, 20, 2026. 

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