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COLOUR AND CHEMICAL CONSTITUTION. 
Part III. — Derivatives of the Unknown Ortho-para- 
PHENOLPHTHALEIN. 
By James Moir, M.A., D.Sc, F.I.C. 
Ordinary phenolphthalein is a dioxy-derivative of diplienylphtlialide, 
both —OH groups being pam to the central carbon-atom. Fluorane, on 
the other hand, is the anhydride of an unstable dioxydiphenylplithalide in 
which both —OH groups are ortho to the central carbon. There should, 
therefore, exist a third dioxydiphenylplithalide in which one of the —OH 
groups is ortlio and the other para, to the central carbon, and this, not being 
capable of forming an anhydride, should be soluble in alkali and should 
exhibit all the phthalein properties. This paper describes derivatives of 
this substance, including an attempt to make the substance itself from one 
of these derivatives. It should be noted that another or^Ao-^am-dioxy- 
diphenylphthalide was described in Part I, isomeric with the above but 
having both —OH groups in the same ring, viz. phenylresorcinolphthalein. 
For convenience of nomenclature, the new substance, in which the ortho and 
para —OH groups are in different rings, will be called o-|)-phenolphthalein. 
Preparatio7i ofm^-methyl-o-'p-phenolphthalein {phenolparacresolphthalein) . 
— Zinc chloride is melted in a round-bottomed flask and distributed in a 
thin layer by rotation and allowed to solidify. Equal parts of paracresol 
and ^-oxybenzoylbenzoic acid are added and the mixture heated in an oil- 
bath, slowly raising the temperature until the zinc chloride has melted and 
the whole become a uniform brown gum. On cooling, the zinc chloride is 
got rid of by digesting with a small quantity of dilute HCl on the steam - 
bath, cooling and decanting, whereon the organic product is dissolved in 
dilute caustic soda and reprecipitated with acid, this process eliminating any 
of the original ingredients which may have escaped reaction. The following 
are the reactions involved : 
* These refer to the central carbon, not to the OH as in Parts I and II. 
