CRESOLS or METHYL PHENOLS. The three isomeric cresols are found in the tar obtained in the destructive distilla tion of coal, beech-wood and pine. The crude cresol obtained from tar boils from 185 to 205° and constitutes the "cresylic acid" of commerce (see COAL TAR). The formula is and the proportions of the three isomerides are approximately 35% ortho-, 40% meta- and 2 5 % para-cresol.
Ortho-cresol, , may be prepared by fusion of ortho-toluene-sulphonic acid with potash ; by the action of phosphoric oxide on carvacrol ; or by the action of zinc chloride on camphor. It is a crystalline solid, which melts at 3o° C. and boils at 19o.8 ° C. Being more volatile than the other two cresols it may be separated by fractional distillation.
Meta-cresol, is formed when thymol (para-isopropyl-meta-cresol) is heated with phosphoric oxide. Propylene is liberated during the reaction, and the phosphoric acid ester of meta-cresol which is formed is then fused with pot ash. It solidifies in a freezing mixture, on the addition of a crys tal 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. The mixture of meta- and para-cresols is converted by 94% sulphuric acid into monosulphonic acids, when the p-sulphonate or its sodium salt is separated by crystallization, after which the two cresols are regenerated by hydrolysing their respective sul phonic acids with superheated steam.
Para-cresol, 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-hydroxy phenylacetic 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. Para cresol is produced during the putrefaction of albumen, and occurs as sulphate in the urine of the horse.