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INDUSTRIAL AND ENGIKEERING CHElIISTRY
VOL. 12, NO. 12
presence of such compounds in the dianilinogossypol-dipyridine complex by washing with water, aqueous solutions of alcohol, and pyridine. Moreover, Smith in his revised method for the determination of gossypol in cottonseed meal (4) specifies a n alcohol and water wash, and owing to the chance of water-soluble meal extractives being present in crude oil, a similar washing treatment was tested in the present method. However, reference to Table V indicates that neither water, alcohol, nor pyridine washes change the weight of the precipitate to any significant degree. The effect of adding purified gossypol to a crude oil prior to analysis is shown by samples 96 and 97, to which 0.2 per cent of gossypol was added. Taking 0.128 per cent as the average amount of gossypol found in the crude oil, samples 96 and 97 would be expected to return 0.328 per cent, whereas the actual recovery was 0.343 per cent. This increase in recovery may be explained b y the seeding action of the added gossypol, whereby precipitation of dianilinogossypol is brought about soon after addition of the reagents, and a large number of crystal nuclei are formed to act as centers of subsequent crystal growth. I n the absence of this added gossypol, precipitation does not start for several days after the addition of the pyridine-aniline, and even after the first appearance of the precipitate, crystal nuclei are not numerous enough to bring the precipitation to completion in 7 days. Precipitation is hastened by agitating the samples for a brief period each day after the initial appearance of crystals. On the basis of the results of the foregoing experiments, the following revision of the pyridine-aniline method for the determination of gossypol in crude cottonseed oil is outlined.
The above method will recover 95 to 98 per cent of the gossypol from a 0.1 per cent oil solution, which is about the average gossypol concentration encountered in analysis of hotpressed cottonseed oils. The reproducibility of results is fairly good for this type of analysis, as shown by the results obtained on two commercial samples of hot-pressed oil, an expeller oil, and a stock solution of 0.1 per cent gossypol in refined cottonseed oil (Table VI). Referring to sample 1, it mill be noted that the results are not closely reproducible on oils containing less than 0.01 per cent of gossypol, because precipitation is relatively blow and incomplete. At 0.1 per cent and higher concentrations the method is satisfactory. Sample 4 indicates that better checks can be obtained on stock solutions of purified gossypol in refined oil than on corresponding concentrations of gossypol in crude oil (sample a ) , probably because of the presence of gossypol degradation products and other nonfats in the crude oil. As recommended in an earlier paper ( 2 ) accuracy and reproducibility of results on oil samples containing less than 0.01 per cent of gossypol are improved b y the addition of a known amount of pure gossypol to the oil being analyzed.
Proposed LVodificationof Pyridine-Aniline lMethod
Literature Cited
Summary
A mixture of pyridine and aniline is more effective than aniline alone in precipitating gossypol from crude cottonseed oil. A modification of the pyridine-aniline method, which recovers up to 98 per cent of gossypol from a 0.2 per cent solution in oil, is described. The pyridine-aniline reagent precipitates dianilinogossypol containing 2 molecules of pyridine of crystallization. The pyridine is removed quantitatively, without decomposition of the residual dianilinogossypol, by heating the precipitate 1 OF DETERMINATIONS AT VARIOUS TABLE VI. REPRODUCIBILITY hour a t 160 O C. The dianilinogossypol-dipyridinecomplex GOSSYPOL CONCENTRATIONS is fairly stable at 60" C., and after heating for 2 hours a t this Percentage temperature, its composition corresponds closely to the forGossypol Deviation Found Mean from Mean Sample mula C42H40N206.2C6H6X. % % The addition of a small amount of pyridine to the petroleum 0.0036 0.0039 7.7 1 Hot-pressed oil A ether used for washing the dianilinogossypol precipitate de0.0042 creases the solubility of the precipitate, and gives higher re2 Hot-pressed oil B 0.110 0.1115 1.4 0.113 covery of gossypol from dilute oil solutions. 3 Expeller oil E 1.370 1.386 1.1 Pyridine alone will not precipitate gossypol from crude 1.402 cottonseed oil. The solubility of gossypol in pyridine was 4 Stock solution of, 0.1% gossypol in cottonseed oil 0.095 0.0955 0.5 found to be 13.3 per cent by weight a t 25' C. A pyridine0.096 is gossypol complex having the formula 2C30H~008.5C5H6N described.
Weigh 50 grams of filtered crude cottonseed oil in a 200-ml. wide-mouthed extraction flask and dilute to 110 to 130 ml. with petroleum ether (Skellysolve F). Add 10 ml. of a mixture of 4 parts pyridine and 1 part aniline, mix well by swirling, stopper loosely, and store in a warm place (35' to 40" C.) for several hours. Replace any solvent lost by evaporation, and hold the samples at room temperature for 7 to 14 days. To prevent undue loss of solvent during the precipitation period, tight-fitting stoppers provided with a capillary vent may be employed. In any case maintain the solvent volume close to its original value throughout the precipitationand agitate the samples once each day after precipitation has begun. Oils containing less than 0.1 per cent of gossypol should be allowed 14 days to precipitate. Filter under suction on tared crucibles provided with medium asbestos mat, washing the crystals of dianilinogossypol-dipyridine onto the filter with petroleum ether containing 1 to 3 per cent of pyridine. Wash the crystals free from oil with this solvent mixture, keeping the total volume of wash below 100 ml. Drive off the pyridine of crystallization by heating the precipitate 1 hour a t 160" C., and weigh as dianilinogossypol. If it is desired to weigh the precipitate as dianilinogossypol-dipyridine, heat 2 hours at 60" C. The factors for converting weights of dianilinogossypol and dianilinogossypol-dipyridine to gossypol are 0.775 and 0.627, respectively.
(1) Campbell, Morris, and Adarns, J . Am. Chem. Soc., 59, 1723 (1937). (2) Royce, Oil & Soap, 10, 183 (1933). (3) Royce and Kibler, Ibid., 11, 116 (1934). (4) Smith, F. H., IND. EVG.CHEX, Anal. Ed., 9, 517 (1937). (5) Smith and Halverson, Ibid., 11, 476 (1939).
Jacketed Receiver for Vacuum Distillation Our attention has been called by Baird and Tatlock (London),
Ltd., to the similarity between the jacketed receiver for vacuum distillation described by J. B. Cloke [IND.ESG. CHEY.,Anal. Ed., 12, 329 (1940)], and a receiver designed by Dr. Linnell of the Pharmaceutical Society of Great Britain. The Linnell type, described in a bulletin of the manufacturer, differs mainly from that suggested by Cloke in that it is not graduated, has no "dripper", has a simplified stopcock arrangement, and has proportionately more condenser surface between the side entry and the vacuum connection. The receiver is a modification of the Perkin vacuum triangle. Both receivers may be used advantageously with the new jacketed Pyrex flasks made by the Corning Glass Co.
