SolutionsAlpha Halogenation
1. An amino acid from an acid
Which product does 3-methylbutanoic acid give in the Hell-Volhard-Zelinsky reaction (Br2, red P, then H2O)? And if that product is treated with an excess of ammonia?
2-Bromo-3-methylbutanoic acid, (CH3)2CH–CHBr–COOH. With excess ammonia, the bromine is replaced by NH2 to give 2-amino-3-methylbutanoic acid: the amino acid valine.
2. An acid that does not react
Why does 2,2-dimethylpropanoic acid not undergo the Hell-Volhard-Zelinsky reaction?
Because it has no α-hydrogens: its acid bromide cannot enolize, and it is the enol that reacts with bromine.