The colouring matter of cotton seed.CHAPTER XVIII. Colouring Matters of Unknown Constitution.(Osa artikkelista)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Cotton seeds contain, in addition to cotton-seed oilx a phenolic substance gossypol, which remains dissolved in the oil when this is expressed.

By extracting the oil with caustic soda and neutralising the solution thus obtained a voluminous precipitate separates which consists of the colouring matter admixed with fatty acids, and the products of its own oxidation. For the isolation of gossypol Marchlewski (J, pr. Chem., 1899, 60, 84) employed a partially purified preparation of this character from which the main bulk of the fatty acids had been eliminated. By extraction with ether, repeated crystallisation from glacial acetic acid, and from a mixture of alcohol and 50 per cent, acetic acid, it was isolated in the form of small yellow prisms.

As the result of analyses of this substance dried in vacua over sulphuric acid, Marchlewski suggested two formulæ, C₁₃H₁₄O₄ and C₃₂H₃₄O₁₀, and of these the first is considered preferable. Preparations dried at higher temperatures appeared to suffer alteration as they thus became darker, and had then a lower melting-point.

Thus the gossypol when quickly heated melted at 188°, but when previously dried at 125-130°, at 179-180°. It is easily soluble in the usual organic solvents, and dissolves in sulphuric acid with a cherry-red coloration, a reaction by which its presence in cotton-seed oil can be detected. In alkalis, gossypol dissolves with a yellow coloration which rapidly changes to violet, and then slowly fades. The ready susceptibility of alkaline gossypol solutions to air oxidation accounts largely for the impure nature of the crude colouring matter isolated by such reagents from the oil, and it appears that if care is taken in the process, it is possible to obtain a much cleaner material in the first instance. An alcoholic solution of gossypol gives with ferric chloride a dark green coloration and with the neutral and basic acetates of lead a deep yellow precipitate. The analysis of the lead salt corresponded to C₁₃H₁₂O₄Pb. According to Marchlewski, gossypol yields amorphous acetyl and benzoyl derivatives and appears to possess two hydroxyl groups. It contains no methoxy groups, and is not a glucoside. It dyes iron mordanted material a grey shade, but the product obtained by a careful oxidation of its alkaline solution possesses, it is stated, tinctorial properties of greater importance. Gossypol can be employed on cotton fabrics as a mordant for the basic colouring matters.

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