Dolbier HW Solutions 661

Dolbier HW Solutions 661 - 755 AMINO ACIDS, PEPTIDES, AND...

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Valine has been prepared by this method. The Hell Volhard Zelinsky reaction was carried out in 88% yield, but reaction of the a -bromo acid with ammonia was not very ef f cient, valine being isolated in only 48% yield in this step. 27.6 In the Strecker synthesis an aldehyde is treated with ammonia and a source of cyanide ion. The resulting amino nitrile is hydrolyzed to an amino acid. As actually carried out, the aldehyde was converted to the amino nitrile by treatment with an aque- ous solution containing ammonium chloride and potassium cyanide. Hydrolysis was achieved in aqueous hydrochloric acid and gave valine as its hydrochloride salt in 65% overall yield. 27.7 The alkyl halide with which the anion of diethyl acetamidomalonate is treated is 2-bromopropane. This is the dif f cult step in the synthesis; it requires a nucleophilic substitution of the S N 2 type in- volving a secondary alkyl halide. Competition of elimination with substitution results in only a 37% observed yield of alkylated diethyl acetamidomalonate. Hydrolysis and decarboxylation of the alkylated derivative are straightforward and proceed in
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