1911 Encyclopædia Britannica/Oxazoles

OXAZOLES, a group of organic compounds containing a ring complex (shown below) composed of three carbon atoms, and one oxygen and one nitrogen atom; they are isomeric with the isoxazoles (q.v.). They are obtained by condensing a halogen derivatives of ketones with acid-amides (M. Lewy, Ber. 1887, 20, p. 2576; 1888, 21, p. 2195)

R·C	NH	+	HO·C·R′	→R·C	N·CR′	;
	OH		Br ·C..H		O·C..H

by the action of concentrated sulphuric acid on nitriles and benzoin (F. Japp, Jour. Chem. Soc. 1893, 63, p. 469); and by passing hydrochloric acid gas into a mixture of aromatic aldehydes and their cyanhydrins (E. Fischer, Ber. 1896, 29, p. 205).

R·CH	CN	+OHC·R→R·C	CH·N
	OH		O – C..R

They are weak bases, and the ring system is readily split by evaporation with hydrochloric acid, or by the action of reducing and oxidizing agents.

The dihydro-oxazoles or oxazolines are similarly formed when β-halogen alkyl amides are condensed with alkali (S. Gabriel, Ber. 1889, 22, p. 2220), or by the action of alkali on the compounds formed by the interaction of ethylene chlorhydrin on nitriles. They are strong bases characterized by a quinoline-like smell. The amino-oxazolines are known as alkylene-ψ-areas and are formed by the action of potassium cyanate on the hydro bromides of the bromalkylamines (S. Gabriel, Ber. 1895, 28. p. 1899). They are strong bases. Tetrahydro-oxazoles or oxazolidines result from the action of aldehydes on amino-alcohols (L. Knorr, Ber. 1901, 34, p. 3484). The above types of compounds may be represented by the following formulae:—

N = CH	O,	N = CH	O,	N = C(NH2)	O,	NH – CH2	O
|		|		|		|
CH = CH		CH2·CH2		CH2 – CH2		CH2 – CH2
oxazole		oxazoline		amino-oxazoline		oxazolidines.

The benzoxazoles are formed when ortho-amino phenols are condensed with organic acids (A. Ladenburg, Ber. 1876, 9, p. 1524; 1877, 10, p. 1113), or by heating aldehydes and ortho-amino phenols to high temperature (G. Mazzara and A. Leonardi, Gazz. 1871, 21, p. 251). They are mostly crystalline solids which distil unchanged. When warmed with acids they split into their components. They behave as weak bases. By the condensation of ortho-amino phenols with phosgene or thiophosgene, oxy and thio-derivatives are obtained, the (OH) and (SH) groups being situated in the μ position, and these compounds on treatment with amines yield amino derivatives.