A-Bromocaproic acid

Place 425 ml. of concentrated ammonia solution (sp. gr. 0-88) in a 500 ml. round-bottomed flask and add slowly 75 g. of a-bromocaproic acid (Section 111,126). Stopper the flask tightly and allow it to stand in a warm place (50-55°) for 30 hours. Filter the amino acid at the pump and keep the filtrate A) separately. Wash the amino acid (ca. 26 g.) well with methyl alcohol to remove the ammonium bromide present. Evaporate the aqueous filtrate (A) almost to dryness on a steam bath. 

In a i-l. round-bottom flask is placed 760 g. of concentrated ammonium hydroxide (sp. gr. 0.9) and to this is slowly added 150 g. of a-bromocaproic acid (Note 1). The flask is well stoppered and allowed to stand in a warm place (50-55°) for twenty to thirty hours. The amino acid separates and is filtered off with suction and washed with methyl alcohol (Note 2). This crop of crystals weighs 51-56 g. The aqueous filtrate is evaporated nearly to dryness on a steam bath and then treated with about 250 cc. of methyl alcohol. This precipitates a second crop of amino acid contaminated with ammonium bromide. On washing with methyl alcohol and recrystallizing from water, there is obtained 10—15 g. more of pure product. The total yield is 63-68 g. (62-67 per cent of the theoretical amount). 

A) dl-t-Benzoyllysine.—A solution of 180 g. (0.57 mole) of e-benzoylamino-a-bromocaproic acid (p. 18) in 2 1. of aqueous ammonia (sp. gr. 0.9) is filtered into a 5-I. flask and allowed to stand for two days. The crystals formed at the end of this time are filtered (Note 1) and the filtrate evaporated on a steam bath at reduced pressure to about 1 1. The crystals are filtered, combined with the first crop, and washed with 100 cc. of alcohol and finally with 100 cc. of ether. The aqueous filtrate is evaporated under reduced pressure to dryness and the residue washed with two 100-cc. portions of water to remove the ammonium bromide, and then with 50 cc. of alcohol followed by 50 cc. of ether. The total yield of e-benzoyllysine, melting at 265-270°, is 100-116 g. (70-81 per cent of the calculated amount). 

Fig. 4, Dependence of slope (a) and half-wave potential (b) of reduction wave of a-bromocaproic acid on its concentration [22] with various drop times 1) 0. 3 sec 2) 0.6 sec 3) 1.2 see 4) 2.4 sec.

Bromohexanoic acid (6-bromocaproic acid) [4224-70-8] M 195.1, m 32-33", 35", 34-36", b 129-130"/5mm. It has been prepared by the oxidation of 6-bromohexanol with concentrated HNO3 (sp. gr. 1.42, one hour for addition at 25-30°, stir at 25° for 4 hours then at 100° for 45 minutes) pegering Boatright J Am Chem Soc 72 5137]. It is made more conveniently by oxidation of cyclohexanone (174 g) with Caro s acid (using a mixture prepared from 919g of potassium persulfate for 10-15 minutes as in Barger et al. J Chem Soc... 

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