Anthranilic acid

Anthranilic acid (or o-amino-benzoic acid) is an aromatic acid with the formula C6H4(NH2)(CO2H). The molecule consists of a substituted benzene ring, hence is classed as aromatic, with two adjacent, or "ortho-" functional groups, a carboxylic acid and an amine. The compound is consequently amphoteric. In appearance, anthranilic acid is a white solid when pure, although commercial samples may appear yellow. It is sometimes referred to as vitamin L1 and has a sweetish taste. The anion [C6H4(NH2)(CO2)]-, obtained by the deprotonation of anthranilic acid, is called anthranilate.

Structure
Although not usually referred to as such, it is an amino acid. Solid anthranilic acid consists of both the amino-carboxylic acid and the zwitterionic ammonium carboxylate forms.

Production
Many routes to anthranilic acid have been described. Industrially it is produced from phthalic anhydride, beginning with amination:
 * C6H4(CO)2O +  NH3  +  NaOH  →   C6H4(C(O)NH2)CO2Na  +  H2O

The resulting sodium salt of phthalamic acid is decarbonylated via a Hofmann rearrangement of the amide group, induced by hypochlorite:
 * C6H4(C(O)NH2)CO2Na +  HOCl   →  C6H4NH2CO2H  +  NaCl  +  CO2

A related method involves treating phthalimide with sodium hypobromite in aqueous sodium hydroxide, followed by neutralization. In the era when indigo dye was obtained from plants, it was degraded to give anthranilic acid.

Biosynthesis
Anthranilic acid is biosynthesized from chorismic acid. It is the precursor to the amino acid tryptophan via the attachment of phosphoribosyl pyrophosphate to the amine group.

Uses
Industrially, anthranilic acid is an intermediate in the production of azo dyes and saccharin. It and its esters are used in preparing perfumes to imitate jasmine and orange, pharmaceuticals (loop diuretics e.g. furosemide) and UV-absorber as well as corrosion inhibitors for metals and mold inhibitors in soya sauce.

Anthranilic acid can be used in organic synthesis to generate benzyne.

It is also a DEA List I Chemical because of its use in making the now-widely outlawed euphoric sedative drug methaqualone (Quaalude, Mandrax).

It has been suggested that anthranilate esters could be efficient insect repellents, replacing DEET.