:254 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS II. COOH I (•HBr CHq. CH2 I CHBr I COOH (meso-form) COONHa CHSNH4 I I ] CHSNH4 COONH4 (meso-form) COOH ! CHSH I CHs 1 CH2 CHSH COOH (meso-form) COOH I CH--S CH• I CH• I CH---S ! COOH (dl-mixture) KSSC(OC,,Ha) Na:•COo H•SO• FeCI., + H.,.O= NH•OH Zn dust H2SO4 - ) NH•OH scheme 1 COOH CHSSC(OCsHa) ] NH4OH CH• - j N. CH• CHSSC(OC.oH.•) COOH (meso-form) COOH CHSH CH: I CH, CHSH COOH (meso-form) COOH CH--S ] heat CH• ] 220øC. CH2 CH--S COOH (meso-form) COOH CHSH I CH• - CH• CHSH COOH (dl-mixture) The recovery was approximately 80 per cent. A further amount could be obtained by concentrating the mother liquors. The acid had a melting point of 191-193øC., corresponding to the literature value for the melting point of the meso-form (7). B. 2,5-Xanthogenoadipic /lcid (meso-form). Dibromoadipic acid (30 •, gin. 1 mole) was added to two liters of water contained in a four liter beaker. To the well-stirred mixture, solid sodium carbonate (106 gm. 1 mole) was added in small portions. In order to minimize foaming, approximately 1 ml. of octyl alcohol was added. After addition of the

HAIR WAVING PROPERTIES OF 2,5-DIMERCAPTOADIPIC ACID 255 sodium carbonate was complete, stirring was continued until solution was complete. The reaction mixture was neutral at this time. Potassium ethyl xanthate (320 gin. 2 moles), which had been previously recrystal- lized from alcohol, was added over a period of ten minutes. Stirring was continued until solution was complete. This required approximately one hour. The reaction mixture after standing at room temperature for twenty-four hours was acidified with 50 per cent sulfuric acid to Congo Red. The dixanthogenoadipic acid separated as an oil, which soon solid- ified. By maintaining good agitation during this time, a granular solid was obtained, which was removed by suction filtration and washed with water until free of mineral acid as indicated by Congo Red paper. The product thus obtained was air dried. The yield of crude product was 80-85 per cent. Upon recrystallization of a small amount from ethyl acetate, it had a melting point of 163-164øC. C. 2,5-Dimercaptoadipic Atcid (meso-form). Crude 1,4-dixanthogeno- adipic acid (386 gm. 1 mole) was dissolved in 500 mi. of methanol con- tained in a two-liter round-bottom flask. While the solution was slowly stirred with a magnetic stirrer and externally cooled, concentrated aqua ammonia (500 ml.) was slowly added over a period of thirty minutes. An atmosphere of nitrogen was maintained during this time. The reaction vessel was stoppered and allowed to stand for forty-eight hours at room temperature. At the end of this time, most of the methanol and ammonia were re- moved under reduced pressure. The residue was made distinctly alkaline with ammonia and extracted twice with 100 mi. portions of di-isopropyl ether in order to remove some ethyl thionocarbamate (xanthogenamide), which is formed during the reaction. The ether extracts were discarded. The aqueous phase was acidified with 50 per cent sulfuric acid to Congo Red. The dimercapto acid separated as a light brown solid. It was removed by suction filtration and washed free of mineral acid with water as indicated by Congo Red paper. The yield of crude product was 80-85 per cent. The crude dimercaptoadipic acid was purified by dissolving it in hot glacial acetic acid, treating with decolorizing charcoal, and filtering through a hot funnel. The recovery was 80-90 per cent. The recrystallized product had a melting point of 186-188øC. (with moderate decomposition). D. 2,5-Dimercaptoadipic Atcid (dl-mixture). The dl-mixture of DMA was prepared from the meso cyclic disulfide by heating it at 220øC. for seven minutes, followed by reduction (2). An aqueous slurry of meso-DMA (105 gm. 0.5 moles) was adjusted to pH 8 with ammonium hydroxide. Fifteen drops of 1 per cent ferric chloride were added and the solution cooled in an ice bath, while 15 per cent hydrogen peroxide was added dropwise with stirring until the violet