1911 Encyclopædia Britannica/Imidazoles

IMIDAZOLES, or Glyoxalines, organic chemical compounds containing the ring system HN	CH = CH	.
	|
	CH = N

Imidazole itself was first prepared by H. Debus (Ann. 1858, 107, p. 254) by the action of ammonia on glyoxal, 2C₂H₂O₂ + 2NH₃ = C₃H₄N₂ + H₂CO₂ + 2H₂O. The compounds of this series may be prepared by the condensation of ortho-diketones with ammonia and aldehydes

R⋅CO⋅CO⋅R+2NH3+R′⋅CHO=3H2O+	R⋅C–N	C⋅R′;
	‖
	R⋅C–NH

from thioimidazolones by oxidation with dilute nitric acid (W. Marckwald, Ber., 1892, 25, p. 2361); by distillation of hydrobenzamide and similarly constituted bodies; and by the action of phosphorus pentachloride on symmetrical dimethyloxamide, a methylchlorglyoxaline being formed (O. Wallach, Ann., 1877, 184, p. 500).

The glyoxalines are basic in character, and the imide hydrogen is replaceable by metals and alkyl groups. They are stable towards reducing agents, and acidyl groups are only introduced with difficulty.

Imidazole (glyoxaline), C₃H₄N₂, crystallizes in thick prisms which melt at 88-89° C. and boil at 253° C., and are readily soluble in alcohol and in water. It is unaffected by chromic acid, but potassium permanganate oxidizes it to formic acid. It forms salts with acids.

Lophine (triphenylglyoxaline),	C6H5⋅C–N	C⋅C6H5;
	‖
	C6H5⋅C–NH

is formed by the dry distillation of hydrobenzamide, or by saturating an alcoholic solution of benzil and benzaldehyde (at a temperature of 40° C.) with ammonia. It crystallizes in needles which melt at 275° C. It is a weak base. When heated to 300° C. with hydriodic acid and hydrochloric acid, in the presence of some red phosphorus, it yields benzoic acid.

The keto-glyoxalines are known as imidazolones and are prepared by the action of acids on acetalyl thioureas (W. Marckwald, Ber., 1892, 25, p. 2357). Benzimidazole, C₆H₄N
NHCH, is the simplest representative of the benzoglyoxalines and is prepared by the condensation of formic acid with ortho-phenylene diamine. It forms rhombic crystals which melt at 170° C. It is basic in character, and on oxidation with potassium permanganate yields a

small amount of glyoxaline dicarboxylic acid,

HOOC⋅C–N	CH; (E. Bamberger, Ann., 1893, 273, p. 338).
‖
HOOC⋅C–NH