[CONTRIBVTION FROM THE STERLING CHEMISTaY LABORATORT, YALE UNIYEBBITY]
CONTRIBUTIONS TO THE STUDY OF MARINE PRODUCTS. VI. THE OCCURRENCE OF CETYL PALMITATE I N CORALS DAVID LESTER
AND
WERNER BERGMANN
Received September 6, 1940
Corals occur in almost unlimited quantities in the coastal waters of the tropical regions of the globe. In spite of their abundance, however, little if anything is known about the nature of their organic constituents. Silliman (l),in his classical study on the composition of corals, was the first to point out that in spite of their principally inorganic appearance the stony- or reef-corals contain considerable amounts of organic material. He found that the organic matter of a number of corals amounted to from four to eight per cent of the total, and that it was intimately united with inorganic material throughout the structure of the coral. Silliman’s observations have been verified by the more recent studies of Clarke and Wheeler (2), who estimated from two to seven per cent of organicmaterial in twenty-eight species of corals. Silliman also observed that corals contained some wax-like material which was separated from its inorganic surroundings by boiling the corals with water. It was found floating on the surface of the water in “transparent jelly-like masses of yellowish color.” Silliman stated that “it was insoluble in alcohol, but readily so in ether, and the ethereal solution yielded a yellow solid resembling wax. It fuses below 200°F.’’ The only other publications which contain some reference to organic constituents of stony corals are those of Montignie (3), who found the presence of sterol-like material indicated by certain color reactions, and of Yonge and collaborators (4), who demonstrated the presence of certain enzymes. No other information concerning the nature of the organic constituents of corals appears to be available a t present. During an investigation of the sterols of corals which is in progress at this laboratory it was found that corals contain significant quantities of wax-like material similar to that described by Silliman. As a rule it can be isolated in a crystalline form by concentrating the acetone extract of the crushed corals. From the staghorn coral, Madrepora CervicoTnis, the wax was obtained in a yield of 0.25%. The recrystallized product melted at 50-50.5”, and its composition and physical properties indicated that it was cetyl palmitate. This was borne out by the fact that saponification 120
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led to the isolation of cetyl alcohol and palmitic acid. Similar results were obtained with the coral Meundru areolufa. Data so far available indicate that the average content of cetyl palmitate of the stony- or reef-corals is from 0 . 2 5 4 5 % . EXPERIMENTAL
All melting points are corrected. Isolation of cetyl palmitate from Madrepora cervicornis. Two thousand eight hundred and fifty grams of crushed corals was placed in a large Soxhlet apparatus and extracted with acetone for 24 hours. The acetone extract was then concentrated to about 300 cc. and cooled, whereby a copious crystalline precipitate was formed. After filtering, washing with dilute acetone, and drying i n vacuo, i t weighed 6.85 g. and hence represented 0.25% of the total. It was recrystallized six times from acetone. During the last recrystallizations the melting point remained constant at 50.0-50.5". The refractive index waa n)oDo1.4414; Whitby's (5) value for cetyl palmitate is n'z 1.4429. Anal. Calc'd for CtnHstO2: C, 79.93; H, 13.42. C, 79.33; H, 13.26. Found: Cetyl alcohol. A 1.0823 g. sample of the wax was refluxed for two hours with an excess of a 1% solution of potassium hydroxide in ethanol. The saponificationmixture was then separated in the usual manner into an alcohol and an acid fraction. The alcohol fraction, weighing 0.47 g., showed a constant m.p. 47.447.5" after three recrystallizations from acetone. A larger quantity of the alcohol was fractionally distilled in Vacuo from a small flask with a built-in Widmer column. Practically all the material distilled at constant temperature. The distillate melted a t 49.2". Recrystallizations from acetone did not raise this melting point. When mixed with a n authentic sample of cetyl alcohol of m.p. 49.349.5" and setting point 48.6', the alcohol melted at 49.5' and set at 48.6" AnaE. Calc'd for ClsHstO: C, 79.25; H, 14.14. C, 79.17; H. 14.10. Found: Cetyl S,b-dinitrobenzoate. A 0.5 g. sample of authentic cetyl alcohol and 0.8 g. of 3,5-dinitrobenzoyl chloride were dissolved in 25 cc. of dry pyridine and the mixture heated on the steam-bath for two hours. After cooling, the mixture was poured into a separatory funnel and diluted with 400 cc. of ether. Dilute sulfuric acid was then added to remove the pyridine, and the ether layer was washed first with a solution of sodium bicarbonate and then with water. After drying over anhydrous sodium sulfate, the ether was evaporated and the residue recrystallized twice from petroleum ether. The product showed a constant melting point of 72.3'. The 3,5dinitrobenzoate of the coral alcohol was prepared in the same manner. It melted at 72.2" and gave no depression of the melting point when mixed with cetyl-3,5dinitrobenzoate. Anal. Calc'd for C z ~ H ~ N a OC, s : 63.28; H, 8.31. Found : C, 63.47; H, 8.24. Palmitic acid. The acid obtained by the saponification of 1.0823 g. of coral wax weighed 0.650 g. Its molecular weight as determined by titration was 253.1; palmitic acid 256. After five recrystallizations from acetone the acid melted at 62.5-62.6'. When mixed with an authentic sample of palmitic acid of the same melting point, no depression of the melting point was obtained.
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DAVID LESTER AND WERNER BERGMANN
To complete the identification of the acid a larger sample was changed into the methyl ester which was then subjected to fractional distillation i n vacuo in a flask with a built-in Widmer column. Practically all the material distilled a t constant temperature. The distillate melted a t 28.2’. Upon hydrolysis of the ester, palmitic acid was obtained which after recrystallization from acetone melted a t 62.4-82.5”. Anal. Calc’d for ClsH*~O,:C, 74.95; H, 12.57. Found: C, 75.26; H, 12.49. SUMMARY
The staghorn coral, Madrepora cervicornis, contains between 0.25 and 0.5% of cetyl palmitate. NEW HAVEN,CONN. REFERENCES (1) SILLIMAN, A n . J. Sci., (2) 1, 189 (1846). (2) CLARKE AND WHEELER, U. S. Geol. Survey Paper No. 124. G.P.O. Washington (1922). (3) MONTIGNIE,Bull. soc. chim., (5) 4, 2086 (1937). (4) YONGE,et al., “Great Barrier Reef Expedition” Vol. I, No. 3 (1931). (5) WEITBY,J . Chem. Soc., 1926, 1458.
