b FREER. 



THE COLORATION OF PHENOL, OF ANILINE, AND OF METHYL ALCOHOL IN 

 THE SUNLIGHT OF MANILA. 



All of us who have experience with laboratories in the Tropics pre- 

 sume, in a general way, that chemical reagents are much more subject 

 to deterioration and change in such regions than in temperate climates, 

 although the containers may be securely sealed from the air. Is this so, 

 or is it simply a hasty generalization, brought about by our personal 

 bias, driving us in the direction of thinking the phenomenon must really 

 exist because of preconceived notions of the influence of tropical en- 

 vironment ? 



Phenol is eminently fitted for study, because some data for comparison, 

 gathered in other climates, exist. Mr. H. D. Gibbs, 10 of the Bureau of 

 Science, has occupied himself with this subject for more than a year, 

 and I will give a brief summary of his results. 



The phenomenon of the coloration of phenol in the sunlight is one of oxidation, 

 it does not occur in an atmosphere of an indifferent gas such as hydrogen or 

 nitrogen. The change takes place even with absolutely pure, dry phenol and dry 

 oxygen, so that the presence of moisture is not necessary. The reaction, under 

 ordinary conditions, therefore, is inaugurated independently of the degree of 

 humidity of the atmosphere, although the water (or hydrogen-peroxide) produced 

 by the beginning reaction will undoubtedly have an accelerating effect on its 

 subsequent rate. Crystals of such pure, dry phenol, when sealed in a tube with 

 pure, dry oxygen and placed in the sunlight in Manila at a temperature of ap- 

 proximately 30°, color perceptibly after two hours and the entire mass changes 

 to a deep red liquid after five days. 



This rate of coloration probably varies with the seasons. When the sun is 

 directly overhead there is apparently a much more rapid production of color 

 than in December and January; and it is more rapid under quartz than when 

 the sample is exposed under soda glass. This latter difference would seem to 

 point to the fact that the change is inaugurated by and accelerated in a greater 

 degree by the ultra-violet portion of the spectrum, not absorbed by quartz glass, 

 than by the others, although the effect can be brought about by heat alone, but 

 much more slowly. 



The absorption spectuni of phenol " gives a broad absorption hand at X=272 p/i. 

 There is, therefore, according to Baly and Collie, 12 a condition of unstable 

 equilibrium of one hydrogen atom in each molecule of phenol, at a given tem- 

 perature in the dark. Therefore there would be a constant ratio between the 

 large proportion of phenol in the enol form and the minute quantity of the keto 

 ( quinone ) form. The action of light, especially of that of the ultra-violet portion 

 of the spectrum, would therefore be to change the equilibrium by increasing the 

 proportion of the latter present, and hence the rate of oxidation; it being 

 presumed that the enol form, the one ordinarily accepted for phenol, is not 

 attacked by the oxygen. No quinone form seems to be present in the crystals. 

 Anisol is not colored by oxygen or ozone in the presence of sunlight, hence it is 

 to be presumed that no such labile form exists in the latter. 



a This Journal, Sec. A (1908), 3, 361; Ibid. (1909), 4, 133. 

 "Hartley, Journ. Chern. Soc. (1902), 81, 929. 

 '-Ibid. (1905), 87, 1339. 



