Hofmann and Schotensack decompose a mixture of phenol (3 molecules) and sodium carbonate (4 mols.) with carbonyl chloride at 140-zoo° C. When 90% of the phenol has distilled over, the residue is dissolved and hydrochloric acid added, any phenol remaining is blown over in a current of steam, and the salicylic acid finally precipitated by hydrochloric acid.
Other reactions which introduce carboxyl groups into aromatic groups are: the action of carbonyl chloride on aromatic hydrocarbons in the presence of aluminium chloride, acid-chlorides being formed which are readily decomposed by water to give the acid; the action of urea chloride Clï¿½COï¿½NH 2, cyanuric acid (CONH) 3, nascent cyanic acid, or carbanile on hydrocarbons in the presence of aluminium chloride, acid-amides being obtained which are readily decomposed to give the acid.
Urea chlorides are formed by the action of carbonyl chloride on ammonium chloride (at 400° C.), or on salts of primary amines.
Alkyl ureas are formed by the action of primary or secondary amines on isocyanic acid or its esters: [[Conh+Nh2r= R Nhc0nh]] 2 i [[Conr+Nhr 2 =Nr 2 Co Nhr]]; by the action of carbonyl chloride on amines: COC12+2NHR2=C0(NR2)2+2HC1; and in the hydrolysis of many ureides.
Those containing more than one acyl group are formed by the action of carbonyl chloride on acid amides: COC1 2 +2CH 3 Conh 2 = Co(NHCOCH3)2+2HC1.