1732
NOTES
Vol. 64
lytic hydrogen was introduced to the cold adsorb- resonance irradiation restores the initial rate of ent, to give a pressure of 2 mm. During the first hydrogen adsorption. The presence of oxygen on seconds following the introduction of hydrogen a the surface of the catalyst is thus essential. This slight fall in pressure was observed owing to van is confirmed by the observation that thoria samder Waals adsorption. ples heated in hydrogen to 700-800° and then Irradiation of the system, after the pressure be- evacuated a t this temperature do not show hycomes constant, with the light from a mercury drogen adsorption on irradiation unless oxygen is lamp produces a regular and continuous decrease again introduced. Analysis of the gas desorbed of pressure, which could be followed by means of a after,either thermal or photoactivated adsorption McLeod gage, during several hours. In favorable shows the presence of oxygen only. cases an irradiation of ten hours results in pracWe have found an increase in the rate of thertically complete hydrogen adsorption. Further mally activated adsorption of hydrogen by chroadditions of hydrogen are adsorbed upon irradia- mium oxide and by reduced nickel when a certain tion. Rates up to 1 cc. of hydrogen a t 2.3 mm. amount of oxygen was introduced to the adsorbpressure per minute, for 40 sq. cm. of irradiated ent. surface and 18 g. of Thoz, have been observed. Hedvall uses the term photoactivation of adIn one case, niore than S cc. of hydrogen a t sorption when the light is absorbed by the crysN. T. P. was taken up by 100 g. of thoria. Ther- tals and their activity is changed by the irradimally activated adsorption on our thoria sample ation. We must consider, however, the cases in was observable a t 420”. which adsorbent and gas are both excited by irAdsorption is only observable with the irradia- radiation or the gas alone. In practice i t will not tion from a cold mercury lamp, which indicates be easy to decide between the several processes. that resonance radiation is involved and that it is We use the general term photo-activation of adatomic hydrogen which is taken up by the adsorb- sorption when we can measure an adsorption of ent. The formation of atomic hydrogen may occur gas by a surface owing to light irradiation. in the gas phase by the Frank-Cario mechanism INSTITUT D’AREMBERG UNIVERSITB DE LOWAIN with excited mercury atoms. We can also imagine LOUVAIN, RECEIVED MAY2, 1942 BELGIUM molecules adsorbed on the surface by van der Waals forces being dissociated by transference of On the Structure of Fucosterol energy from mercury atoms. We cannot yet decide between these alternatives. Comparison with B Y H. B. MACPHILLAMY the rate of reduction of tungstic oxide in the Fucosterol was first isolated from the alga, Frank-Cario experiment suggests a diffusion of Fucus vesiculosus, by Heilbron, Phipers and atomic hydrogen to the surface. Wright.’ These workers showed that the sterol At 20-30 mm. pressure no photoactivation is had the empirical formula C29H480and that it measurable. After subsequent lowering of the was a bond isomer of stigmasterol. They further pressure to 2 mm., photoactivation is again ob- stated that both double bonds were situated in the servable, but a t one-half to one-third the normal nucleus, since treatment with ozone failed to give rate, We interpret this as due to an adsorbed ethylisopropylacetaldeliyde. Additional evidence molecular layer of hydrogen protecting the adindicated the absence of a conjugated system, sorption centers. Lowering the pressure does not while the ease with which stigmastanol was formed uncover all such centers. Complete evacuation is on hydrogenation showed the lack of any “inert” necessary. When this is done the normal rate of double bonds. Later it was proved that one of the photoactivated adsorption at 2 mni. pressure is ethylenic linkages occupied the 5-6 position.2 In found. view of Sobotka’s3 suggestion that the second After many days of alternate irjadiation and double bond might be located in the 11-12 posievacuation a t 700” the rate of adsorption slowly tion, which would render the sterol a suitable decreases and falls to one-tenth of its initial value. starting material for the synthesis of cortical If after evacuation at 700’ air is introduced a t at(1) I . M. Heilbron, R. F. Phipers and H. R. Wright, Nature, 188, mospheric pressure and room temperature and 419 (1934); J. Chem. Soc.. 1572 (1934). (2) D. H. Coffey, I. M. Heilbron and F. S.Spring, ibid., 738 (1936). then evacuated at room temperature, introduc(3) H. Sobotka, “Chemistry of the Sterids,” Williams and Wilkins tion of hydrogen a t 2 mm. pressure followed by Company, Baltimore, Md , 1938, p. 240.
NOTES
July, 1 9 6
1733
hormones, the complete elucidation of its structure Over-ozonization had to be avoided as it results in low if not negligible yields, The reaction mixture, combined seemed desirable. with the wash water, was distilled through an efficient fracIt was decided, first of all, to reinvestigate the tionating column. After approximately 20 cc. of distillate ozonization reaction. The failure of Heilbron, had been collected, the receiver was removed, and a soluet al., to isolate ethylisopropylacetaldehyde can- tion of 500 mg. of recrystallized p-nitrophenylhydrazine in not be considered conclusive evidence for the lack 20 cc. of 50% acetic acid was gradually added. The hydraof unsaturation in the side chain, since the later zone crystallized out immediately. It was filtered, washed work of this author on zymostero14has shown that with cold water, and after drying weighed 175 mg. (33.6%) ; m. p. 124-125'. After three recrystallizations from dilute side chain double bonds in sterols may occupy po- alcohol the substance had a constant m. p. of 128-129'. sitions other than 22-23. The result of our study The melting point of a mixture with authentic acetaldeshowed that fucosterol indeed presents a similar hyde fi-nitrophenylhydrazone showed no depression. Anal. Calcd. for CsHcNsOa: C, 53.63; H, 6.06; N, case. In two separate experiments acetaldehyde could be isolated as the p-nitrophenylhydrazone 23.45. Found: C, 53.58; H, 4.89; N, 23.69. from the products of the ozonolysis. The yield of The author wishes to thank Dr. 0. Winteraldehyde was over 30% in both cases, which pre- steiner for his interest and advice during this includes the possibility that it may have been de- vestigation. rived from an impurity or formed in a secondary THESQUIBBINSTITUTE FOR MEDICAL RESEARCH OF ORGANIC CHEMISTRY reaction. Since position 24-28 for the double DIVISION NEWBRUNSWICK, N. J. RECEIVED MAY20, 1942 bond in question is the only one which would account for the formation of acetaldehyde by ozonolysis, is it suggested that the structure of fucos- O l e h Rearrangements. The Equilibrium of terol is best represented by the accompanying Olefins from Pinacolyl Alcohol' formula. BY ROBERT KINSELSMITH CHs flTCH I L!H.CCHCHa
II
CH 1
CH,
I
CH,
Experimental Isolation of Fucostero1.-The material used for this work was obtained from a quantity of Fucus vesiculosus gathered along the New Jersey coast. About 22.5 kg. of the dried sea weed was ground and percolated thoroughly with ether. After evaporation of the solvent 650 g. of extracted material remained. The residue was saponified overnight at room temperature and on purification yielded 40 g. (0.18%) of sterol. Several recrystallizations from methanol gave pure fucosterol, the physical properties of which agreed quite closely with those given by Heilbron,' as shown in the following table M y Phillamy M. P., [a]D
c.
Sterol Acetate Benzoate
124 118 121
-41 -45 -16
Heilbron
M. P., ''2.
DI.[
124 118-119 120
-38.4 -43.8
..
Ozonization of Fucostero1.-A finely divided suspension of 1.15 g. of fucosterol in 12 cc. of glacial acetic acid was ozonized for one-half hour at an ozone concentration of about 274, the exit gases-being led through 50 cc. of water. (4) B. Heath-Brown, 1. M. Heilbron and E. R . H. Jones, J . Chew. SOC.,1482 (1940).
The dehydration of saturated alcohols and the attendant rearrangement of olefins formed during the reaction have long been investigated experimentally. The mechanisms of these rearrangements have been studied intensively on the basis of experimental results. The absence of thermodynamical data has in general prevented the calculation of equilibrium constants for the ratios of different olefins obtained from a particular dehydration. Recently, thermal data have been published21aconcerning the heats of hydrogenation of 2,3-dimethyl-l-butene, 2,3-dimethyl-2-butene and 3,3-dimethyl-l-butene and the relative heat contents of 2,2-dimethylbutane and 2,3-dimethylbutane. These provide a basis for the calculation of the equilibrium mixture of these olefins produced in the dehydration of methyl-t-butylcarbinol. The equilibrium values for the ratios of the olefins obtained in this reaction are of importance because widely variant results are obtained through the use of different catalysts to effect the dehydration. Meunier and Whitmore4 dehydrated methyl-tbutylcarbinol with phosphoric acid on silica gel (1) Original manuscript received August 7, 1941. (2) (a) Dolliver, Gresham, Kistiakowsky and Vaughan, T H I ~ JOURNAL, 69, 831 (1937); (b) Kistiakowsky, Ruhoff, Smith and Vaughan, ibid., 68, 142 (1936). (3) Rossini and Prosen, ibid., 69, 2250 (1940). (4) Meunier and Whitmore, i b i d . , 65, 3721( 1933).
