~ n d .Calcd. for C ~ ~ H , O ~ N A S CAS, I ~ : 20.95; CI, 19.83. Found: As, 21.05, 21.04; CI, 19.57, 19.61. Structure Proof.-An intimate mixture of 15 g. of Snitro-3-dibenzofuryldichloroanineand 15 g. of mercuric acetate was fused for ten minutes a t 350'. An acetic acid extract of this melt on dilution with water gave 1 g. of a yellow solid, m. p. 149" after crystallization from an alcoholacetone mixture. It wa.. identified as 2-nitrodibenzofuran by means of a mixed melting point.@ Reduction of this compound gave 2-aminodibenzofuran, I n . p. 125'. and acetylation of the amine producrd 2-acetaniinodibenzofuran, m. p. 162'. SNitro-3-dibenzofurylareine Oxide.-A quantitative yield of the oxide was obtained by the hydrolysis of 2 g, of 8-nitro3-dibenzofuryldichloroarsinewith boiling water for four hours; light orpage product alter crystallization from methyl cellosolve, not melted at 250° Anal. Calcd. for C&O+NAs: As, 24.75. Found: 24.87, 24.05. &hlao3-dibenzofufylmoupluronic Acid.-A pwtitatlvc yield of this acid was obtained by reducing an OlkPliOe aolution of 8-nitr0-3-dibenzofurylarsonicacid with hydrogen using the Raney catalyst.u Aci#ification to litmus with concd. hydrochloric acid produced a white precipitate of the amine which was recrystallized from dilute hydrochloric acid; not melted a t 250". A d . Calcd. for CltHlcO,NAs: As, 24.43. Found: As, 24.48, 24.44. Sulfo-3-dibenzofurylaraoni~Acid.-A suspension of 9 g. of 3-dibenzofurylarsonic acid in CiO cc. of concd. sulfuric acid was heated over a steam-bath for two hours. The - ..- .. (10) Haney, U. S. Patent 1,628,190 (1927).
[ CONTRlBUTION
FROM THE
solution was then cooled in a n ice-bath and diluted with water until a heavy white precipitate was formed; not melted a t 300' after recrystallization from water. The structure of this compound has not been proved but it is probably 8-su(fo-3-dibenzofurlarsonic acid. A d . Calcd. for CIIHOO7SAs:As, 20.16. Found: As, 20.30, 20.27. Sulfo-3-dibenzofuryline Oxide.-An 80% yield of the oxide was obtained by bubbling sulfur diox'ide through a solution of 0.5 g. of potassium iodide, und I g. of sulfo-3. dibenzofurylarwnic acid in 150 cc. of 2 iV hydrochloric) acid. At the end of twenty riiinutes the precipitated arsine oxide wag filtered out and purified by salting it out of a water solution, not melted 4t 275'. Anal. Calcd. for CltHtO'SAs: As, 22.18. Found;
As, 22.39, 22.37.
S m Direct arsonation of dibenzofuran
gives 2-dibenzofurylarsonic acid as shown by structure proof; its oxide is described. 2. 3-Dibenzofurylarsonic acid has been prepared through the diazo reaction and converted into the dichloroarsine and oxide by reduction. Nitration of 3-dibenzofuryluusonic acid gives the &nitro derivative and from this the corresponding amine compound has been obtained by catalytic reduction. 3. :3-Dibenzofurylarusoiiic acid has been sulfoliated directly. RECEIVED hfARCH 18, 1937 LINCOLN, NEBRASKA
1.
B~OCHEMICAL LABORATORY, STATE UNIVERSITY OF IOWA, TAL BIOLOGY, UNIVERSITY OF CALIFORNIA]
AND 1°K
INSTITUTE OF
EXPBRIYEN-
Antioxidants and the Autoxidation of Fats. M. The Antioxidant Properties of the Tocopherols BY H.S. O L ~ T AND T 0. H. EMERSON The unsaponifiable fraction of some vegetable oils exhibits marked antioxidant properties when small amounts are added to lard. Olcott aiid Mattill' have recorded some of the characteristics of the active principles which they called inhibitols. When wheat germ oil or cottonseed oil was used as the source, the inhibitol concentrates contained a large amount of vitamin E from which the inhibitols could not be separated. The successful isolation of three individual compounds possessing vitamin E activity from these oils by Evans, Emersori and Emerson2-' provided an (1) Olcott and Mattill. T H IJ ~ O I J ~ N A L .66, 1627 (1936). (2) Evan., Emerson and Emerson. I B i d C h r m , 111, 319 (1086). Emason, Emerson and Evans. .kiew.U,421 (1936).
(a)
(0 Emermb, Bmerbon. Mohnmmcd m d Evnna, in pfw.
opportunity for ascertaining the relationship between the inhibitols and tocopherols. The three tocopherols and their allophaiiates were assayed for antioxidant activity by the oxygen absorption method previously described.5 The tocopherols were effective antioxidants i n lard and oleo oil, but had no activity iii esters prepared from hydrogenated cottonseed oil (Table I ) . Since the inhibitol concentrates from wheat germ oil and cottonseed oil behave similarly,' it seems apparent that they owe a t least part, and possibly all, of their antioxidant activity to the tocopherols. However, the inhibitols obtained C k m , ST, 724 (1936). (5) French, OIcott and Mattill. l w d (6) olcotl sod Mattill, Tntr J O I J ~ N A L , U, 2204 (1936).
ANTIOXIDANT PROPERTIES OF THE TOCOPHEROLS
June, 1937
from lettuce' and tomatoess in the methanol fraction after distribution between petroleum ether and 92% methanol are presumably not tocopherols, since the latter, on distribution between these solvents, are found in the petroleum ether phase, and have, moreover, appreciably higher boiling points. TABLEI
ANTIOXIDANTPROPERTIES OF THEIR
THE TOCOPHEROLS AND ALLOPHANATES
% Qsgd
Added antioxidant
a-Tocopherol"
Substrate fat: Lard 0 01
Induotion period O t 75 Exptl Cwtrcd
36
,oi
ao
,Oa
60
02 -02
74 62
8-Tocopherol
.01 -02
y-Tocopherolb
.01 .01 02 .02 02 02 02 02 02 02
61 96 99 96
02
a-Tocopherol allophanate' ,%Tocopherol allophanated 7-Tocopherol allophanate'
18 15 15 13
1K 14 14
85 114 132 166 156 172
15 10 11 10 11 20 17 20 17 20 17
32 110 360
12 12 12
107 150 166
Oleo oil a-Tocopherol 7-Tocopherol
01 01 02
Crude esters hydrogenated cottonseed oil a-Tocopherol 0 01 2.5 2 5 02 2 0 2 0 Approximate minimum effective dose when administered to vitamin E deficient female rats; a-tocopherol, 1-3 mg.; @-tocopherol,3-5 mg.; y-tocopherol, 1-3 mg Biological assays from the two laboratories showed reasonable agreement. The y-tocopherol and its allophanate used in these tests contained some a-tocoDhero1. M. D. 157158'. M. p. 138'. M. p. 135-135.5'.
1009
hand, as vitamin E, fi is less effective than a or y . This lack of correlation between the antioxidant and vitamin properties of the pure substances offers an explanation for the previously observed lack of direct relationship in the concentrates. l S 6 Vitamin E concentrates virtually free from antioxidant activity have been described. A possible explanation of these results may be based on the assumption that the preparations were not completely hydrolyzed. Simple esters of the tocopherols are effective as the vitamin, but in. effective as antioxidants, The possibility that vitamin E may occur in nature in the form of an ester has been suggested previous1y.O The antioxidant activity of the tocopherol allophanates (Table I) was unexpected, inasmuch as previous observations had indicated that the activity of inhibitols and of antioxidants of known structure depended on the presence of a free hydroxyl group.li10 However, the fact that anaphthol allophanate'l is also an effective antioxidant while cholesterol allophanate is not, suggests that the activity of the allophanates parallels that of the parent compounds. Since antioxidants of known structure are phenolic in nature,1° the antioxygenic activity of the tocopherols suggests that they map belong to this class of substances. The absorption spectrum of the tocopherols resembles that of hydroquinone; however, the tocopherols differ from most phenols in having little or no acidic properties. Acknowledgment.-One of us (H. S. 0.) is indebted to Lever Brothers Cnmpany for a grant in support of this work. Summary
(I
The tocopherols are increasingly effective as antioxidants in the order a, p, y. On the other (7) Olcott and Mattill, J . Biol. Chem., 98, 59, 65 (1931). (8) Bradway and Mattill, THISJOURNAL, 18, 2405 (1934).
a, /3 and y tocopherols and their allophanates are effective antioxidants in lard. The degree of protection afforded by the tocopherols is not proportional to their vitamin E activity. IOWACITY,IOWA BERKELEY, CALIF.
RECEIVED APRIL7, 1937
(9) Olcott, J . Bioi. Chem 110, 695 (1935) (10) Olcott, THISJOURNAL, 56, 2492 (1934). (11) The preparation and properties of this compound will be described in another place. 9
