1911 Encyclopædia Britannica/Cresols
CRESOLS or Methyl Phenols, C7H8O or C6H4·CH3·OH. The three isomeric cresols are found in the tar obtained in the destructive distillation of coal, beech-wood and pine. The crude cresol obtained from tar cannot be separated into its different constituents by fractional distillation, since the boiling points of the three isomers are very close together. The pure substances are best obtained by fusion of the corresponding toluene sulphonic acids with potash.
Ortho-cresol, CH3(1)·C6H4·OH(2), occurs as sulphate in the urine of the horse. It may be prepared by fusion of ortho-toluene sulphonic acid with potash; by the action of phosphorus pentoxide on carvacrol; or by the action of zinc chloride on camphor. It is a crystalline solid, which melts at 30° C. and boils at 190.8° C. Fusion with alkalis converts it into salicylic acid.
Meta-cresol, CH3(1)·C6H4·OH(3), is formed when thymol (para-isopropyl-meta-cresol) is heated with phosphorus pentoxide. Propylene is liberated during the reaction, and the phosphoric acid ester of meta-cresol which is formed is then fused with potash. It can also be prepared by distilling meta-oxyuvitic acid with lime, or by the action of air on boiling toluene in the presence of aluminium chloride (C. Friedel and J. M. Crafts, Ann. Chim. Phys., 1888 , 14, p. 436). It solidifies in a freezing mixture, on the addition of a crystal of phenol, and then melts at 3°-4° C. It boils at 202°.8 C. Its aqueous solution is coloured bluish-violet by ferric chloride.
Para-cresol, CH3(1)·C6H4·OH(4), occurs as sulphate in the urine of the horse. It is also found in horse’s liver, being one of the putrefaction products of tyrosine. It may be prepared by the fusion of para-toluene sulphonic acid with potash; by the action of nitrous acid on para-toluidine; or by heating para-oxyphenyl acetic acid with lime. It crystallizes in prisms which melt at 36° C. and boil at 201°.8 C. It is soluble in water, and the aqueous solution gives a blue coloration with ferric chloride. When treated with hydrochloric acid and potassium chlorate, no chlorinated quinones are obtained (M. S. Southworth, Ann. (1873), 168, p. 271), a behaviour which distinguishes it from ortho- and meta-cresol.
On the composition of commercial cresylic acid see A. H. Allen, Jour. Soc. Chem. Industry (1890), 9, p. 141. See also Creosote.