Thuya occidentalis(CHAPTER VII. Flavonol Group.)

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.

Thuya occidenlalis (Linn.). In 1858 Rochleder and Kawalier (Wien. akad. Ber., 29, 10) isolated from the green portions of the Thuya (Thuja) occidentalis a glucoside Thujin, which, when hydrolysed, gave a yellow colouring matter thujetin.

Thujin, C₂₀H₂₂O₁₂. The plant was extracted with alcohol, the extract when cold filtered from wax, and evaporated to a small bulk. The residue was diluted with water, a few drops of lead acetate solution added, the precipitated impurities removed, and the clear brown filtrate treated with lead acetate. The yellow lead compound was collected, extracted with dilute acetic acid, and basic lead acetate now added to the solution. The bright yellow precipitate was suspended in water, decomposed with sulphuretted hydrogen, the lead sulphide removed, the filtrate treated with carbon dioxide in order to free it from sulphuretted hydrogen and evaporated in vacua over sulphuric acid. Crystals gradually separated, and these were crystallised repeatedly from dilute alcohol until when treated with ammonia a green coloration was no longer produced.

Thujin is described by these authors as citron yellow microscopic prisms sparingly soluble in cold water. The alcoholic solution becomes yellow on treatment with alkalis, whereas with ferric chloride a dark green coloration is produced. When thujin is digested in alcoholic solution with dilute hydrochloric or sulphuric acid it is hydrolysed with formation of glucose and thujigenin, apparently an intermediate product, which readily takes up a molecule of water, with formation of thujetin
C₂₀H₂₂O₁₂ + H₂O = C₁₄H₁₂O₇(Thujigenin.) + C₆H₁₂O₆
C₁₄H₁₂O₇ (Thujigenin.) + H₂O = C₁₄H₁₄O₈ (Thujetin.)

Thujetin, C₁₄H₁₄O₈, forms yellow crystals, and is characterised by the fact that its alcoholic solution is coloured blue-green with ammonia, and green coloured by potassium hydroxide solution.

With lead acetate it gives a deep red precipitate. When thujetin is digested with boiling baryta water it is converted into thujetinic acid, C₂₈H₂₂O₁₃, which consists of yellow microscopic needles, sparingly soluble in water, readily soluble in alcohol.

Thujigenin, C₁₄H₁₂O₇, crystallises in fine yellow needles, soluble in alcoholic ammonia, with a blue-green coloration.

The quantity of thujin which is present in the plant is very small; thus, from 240 lbs. Rochleder and Kawalier were successful in isolating a few grams only.

Perkin (Chem. Soc. Trans., 1914, 105, 1408), who re-examined this subject and employed methods almost identical with those of Rochleder and Kawalier, found that the glucoside corresponding to thujin possessed the formula C₂₁H₂₀O₁₁, melted at 183-185°, and when hydrolysed gave rhamnose and quercetin and was identical with the quercitrln of quercitron bark. The plant also contained a small amount of quercetin, and this also, prepared by the hydrolysis of the glucoside which evidently corresponds to the thujetin of Rochleder and Kawalier, dissolved in alkaline solutions with a pale green tint, but failed to give the blue-green coloration with ammonia described by these authors. During a preliminary investigation of this plant (Chem. Soc. Trans., 1899, 75, 829), the sample then examined gave a trace of yellow colouring matter soluble in alkalis with a strong green coloration, the acetyl compound of which after frequent recrystallisation melted at 205-206°. It thus seems probable that the thujin of Rochleder and Kawalier consisted of quercitrin contaminated with a second glucoside, possibly that of myricetin. The quantity of this latter present in the plant may possibly vary according to its environment or with the season of the year.