E F F E C T O N T H E N O R M A L A G I N G P R O C E S S
J. P. HOLLIIIAN AND SANFORD A . M O SS, JR.A m erican Viscose C orporation, M arcus H ook, Pa.
D
URING the aging of viscose, the cellulose xanthate becomes steadily more precipitable; this behavior is probably due largely to the gradual loss of the solubilizing xanthate groupstermined by standard tests involving a salting out of the cellulose
xanthate, the results being expressed as salt index, Hottenroth number, etc. A number of substances are known which, when added to viscose, substantially affect the rate of aging (9).
The effect of these compounds, however, is entirely a retardation of the normal rate of aging, and no immediate increase or change in the salt index is observed when they are added. In contrast, acrylonitrile and certain related compounds (4) have a marked solubilizing action and cause an immediate rise in salt test, as indicated by the data of Tables I and II.
February 1947 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 223 difficultly precipitable, and 2.0 w ou ld represent one that is easily precipitable and has aged con sidera b ly past the optim u m spinning con dition . pounds cause an im m ed ia te increase in salt index, w h ich can be explained by the follow in g m ech a n ism : W hen acrylonitrile is nddcd to viscose, it reacts rapidly w ith the principal b y -p rod u ct sulfur con stitu en ts; the latter are converted in to organic sulfides, and carbon disulfide is released.
T b e carbon disulfide evolved causes further
An explanation for the solubilizing action of acrylonitrile could possibly be given on the basis of a colloidal protective mechanism.
Thus Scherer and Leonards (I f) explain the lowering of the viscosity when pyridine is added to viscose on the basis of a selective adsorption of the pyridine. Alternatively, a second possible explanation for the solubilizing action of acrylonitrile could be given on a purely chemical basis, if we assume that a reaction takes place between the cellulose and the acrylonitrile with the formation of a more soluble cellulosic derivative. A third possible mechanism would involve interaction between the acrylonitrile and the by-product sulfur, the net result being a re- xanthation of the cellulose xanthate. (Viscose solution contains sodium sulfide, sodium thiocarbonate, sodium perthiocarbonate, and related compounds. This group is spoken of as by-product sulfur and arises in part during the xanthation of the alkali cellu
lose. Additional by-product sulfur is also formed during the aging process, since the sulfur released by the decomposition of.
the cellulose xanthate reacts with the “ free” sodium hydroxide to form these compounds. For practical purposes the by-product sulfur may be considered to be composed entirely of sodium sul
fide and sodium thiocarbonate.)
As a first attack on the problem, the sulfur relations shown in Table III were determined. The total and by-product sulfur decrease some 12 and 45%, respectively, whereas the xanthate sulfur increases some 25%. These data point at once to a purely chemical mechanism for the solubilizing, since it is known that the salt index increases with increasing xanthate sulfur content.
Specifically, it is clear from these data that a part of the by
product sulfur has reacted with the acrylonitrile and has been transformed into xanthate sulfur or into some sulfur-containing derivative similar in solubilizing action to the xanthate group.
Further, from the decrease in total sulfur it is clear that some volatile sulfur compound must have been formed and subse
quently lost to the atmosphere. As a first assumption it seems reasonable to suppose that this volatile substance is carbon disulfide, particularly since it is known that, when carbon disul
fide is added to viscose, a further xanthation of the cellulose xanthate is readily effected (3, 9, 10, 12).
The next step in the study was the elimination of effects which might be due to the presence of cellulose. This was accomplished by reacting the acrylonitrile with an artificial by-product solution prepared by shaking carbon disulfide with sodium hydroxide.
Such a solution apparently contains the sulfur entirely as sodium thiocarbonate {13) and does not contain the sodium sulfide, poly
sulfide, and the like which are normally present in viscose. How
ever, since viscose by-product sulfur is largely sodium thiocar
bonate, the artificial by-product solution is a reasonable simula
tion of the conditions actually encountered in viscose. When acrylonitrile is added to this artificial solution, the same sequence of events occur as with viscose. In this case, however, the drop
lets which form during the opaque stage can be separated by centrifuging. They were found to be nonvolatile and quite viscous, and to have a strong sulfurous odor. Since the proper
ties of the separated droplets were similar to those of an organic sulfide, the following equations were proposed to account both for their formation and for their subsequent disappearance with time: the nitrile to the water-soluble 0,0 '-sodium thiodiproprionate, as in reaction 2.
To test the mechanism further, reaction products in quantities large enough to identify were prepared by reacting acrylonitrile with sodium sulfide, sodium thiocarbonate, and sodium hy
droxide. The general appearance and properties of the reaction.
224 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 39, No. 2 monosulfide or the disulfide, further experimentation (described later in the paper) showed that the thionitrile is always present essentially in the monosulfide form, as required by Equation 1.
As a further test of the mechanism, a direct determination was made for any carbon disulfide which might be evolved (Equation 1). The diethylamine method (5, 7) was used, which is extremely sensitive for carbon disulfide. The general procedure followed was to pass a stream of air, which had been carefully cleaned of hydrogen sulfide and carbon disulfide, through artificial by
product sulfur solution until all of the carbon disulfide which is normally present in the solution had been swept out. Acrylo- nitrile is then added, and the air stream is tested on continued sweeping for the presence of carbon disulfide. It was found possible to demonstrate by this procedure that large quantities of carbon disulfide are evolved on the addition of the acrylonitrile.
E X P E R IM E N T A L P R O C ED U R E
Reaction products were prepared by reacting acrylonitrile with (a) artificial by-product sulfur solution, (b) 10% sodium sulfide solution, and (c) 6% sodium hydroxide solution. The artificial by-product solution, a, is essentially sodium thiocarbo- nate and was selected to afford a test of Equation 1. The reac
tion with sodium sulfide, 6, was included since viscose contains considerable sodium sulfide in addition to sodium thiocarbonatc.
The reaction with sodium hydroxide, c, was included to permit a comparison of the sulfur-containing reaction products from a and b with those of the ether, CNCH2CH2OCH2CH2CN, which might be expected to form to some extent when acrylonitrile is added to the alkaline viscose (t).
Re a c t i o n w i t h By-p r o d u c t Su l f u r So l u t i o n. Three hundred milliliters of 6.0% sodium hydroxide were shaken with 25 ml. of carbon disulfide and a few drops of sulfonated castor oil for 4 hours. The mixture was centrifuged, and 50 ml. of acrylo
nitrile were added to 200 ml. of the clear solution. The red color changed to a yellowish green in a few minutes. The reaction products and the unreacted acrylonitrile were extracted with ethyl ether. Anhydrous sodium sulfate was added to the ether solution, and after filtration the solution was vacuum-distilled.
The oily fraction distilled over at 10-15 mm. pressure; the temperature was not determined but was estimated to be about 130° C. About 10 ml. of a yellow oil were obtained. It was immiscible with water and fairly viscous, and had an unpleasant odor resembling hydrogen sulfide.
Re a c t i o n w i t h So d i u m Su l f i d e. Three hundred milliliters of 10% sodium sulfide solution were shaken with 50 ml. of acrylo
nitrile for several hours. The mixture was extracted with ethyl ether, and the extract treated as in step a. The distillation characteristics and physical appearance of the product were iden
tical with a. About 5 ml. of product were obtained.
Re a c t i o n w i t h So d i u m Hy d r o x i d e. The preparation of the product was carried out as in step b. The product is a fairly viscous oil and is water clear, but becomes slightly yellow near the end of the distillation. The distillation behavior is the same as in step a. About 3 ml. of product were obtained.
Co m p a r i s o n o f Pr o d u c t s f r o m a , b, a n d c. The general appearance of the products from a and b were similar and quite different from that of c. The refractive indices of the products from a and c at 23° C. were 1.4903 and 1.4389, respectively.
Recrystallizations from water were not carried out, but the prod
uct from step a was comparable in general properties to the mono
sulfide, (CNCH2CH2)2S, as described by . Nekrasov (<?). The nitrogen content of the product from a was found to be 19.8%.
Since the theoretical nitrogen content of the monosulfide is 20.0%
and the disulfide 16.3%, the reaction product appears to be the ether. In carrying out the analyses, a moderately strong stream
of cleaned air is bubbled through 10 ml. of the by-product solu
tion, followed by passage through 20 ml. of diethylamine test reagent. The procedure used for cleaning the air and the details of the reaction train are those of Hunter (5). Samples were withdrawn from the diethylamine test solution and diluted 1 to 10, and the transmission was observed in the Evelyn colorimeter.
The method is extremely sensitive, and considerable difficulty was encountered at first in obtaining a satisfactory blank. Satis
factory results were later obtained with the construction of an required to make any one determination). A transmission read
ing of 74.5 was obtained. After 30 minutes of additional sweeping, a reading of 76.5 was obtained; and after 30 more minutes of sweeping, 77.0. Hence it is clear that fairly large quantities of carbon disulfide are developed.
S U M M A R Y
When acrylonitrile is added to viscose, it reacts rapidly with the principal by-product sulfur constituents; they are converted into identical organic sulfides, and carbon disulfide is released as shown: Interscien ce Publishers, In c., 1943.
(10) R ussian Organic Chem. In d ., 3, N o . 12, 693 (1 937).
(11) Scherer, P . C ., Jr., and L eonards, J. R ., R a yon Textile M onthly, 23, 6 0 7 -9 (1942).
(12) V ita le, T om a sso, G iorn. chim. ind. applicata, 13, 4 7 6 -9 (1931).
(13) W eeld en b u rg , J. G ., R ec. trav. chim ., 47, 4 9 6 -5 1 2 (1 928).
Tocopherols as Antioxidants for
destruction and peroxidation. No difference was observed between th e antioxidant characteristics o f pure natural 7-tocopherol and those o f pure syn th etic 7-tocop h erol.T
HE inherent resistance of natural glyceride oils to oxidative changes is due primarily to the presence in the oils of varying quantities of substances commonly termed antioxidants. Many natural oils, particularly fish liver oils, are notoriously easy prey to oxidative changes, regardless of the fact that they also contain some natural antioxidants. Fish liver oils are our most valuable source of vitamin A; because of the lability of vitamin A to oxidative changes, it is important that oxidation be inhibited to the fullest degree.
Evidence to date has established that tocopherols and allied substances in association with phosphatidic materials are largely responsible for the stability exhibited by natural vegetable oils.
Olcott and Emmerson (5) were the first to show that the tocoph
erols are increasingly effective as antioxidants in lard in the or
der alpha, beta, and gamma. The gamma form was found to have about three times the antioxygenic index of a-tocopherol, and the activity of 5-tocopherol was intermediate between the other two. Esters of the tocopherols were ineffective as antioxi
dants. Olcott and Mattill (7) showed that the antioxidants or inhibitols present in the lipid fractions of vegetables and in vege
table oils are so similar to vitamin E (tocopherols) that it was impossible to fractionate them.
In a paper on the use of natural as well as synthetic a-tocoph- erol as an antioxidant in cottonseed oil, Swift, Rose, and Jamieson (11) demonstrated that the «-tocopherols function most effectively at lower levels of concentration. These authors also showed that a cephalin fraction from cottonseed oil greatly en
hanced the antioxygenic activity of a-tocopherol. Certain acids also increase the antioxygenic activity of tocopherols and of the corresponding quin ones in autoxidizing fats (5). Published data on the antioxidant activity of phosphatides in oils as a whole is conflicting. It has been the author’s experience that, when rela
tively pure phosphatides alone are added to antioxidant-free fish liver oils, they have no antioxidant activity for inhibiting either peroxide formation or vitamin A destruction, even at concentra
tions as high as 5% . When relatively pure phosphatides are added to crude fish liver oils, they may or may not exhibit an an
tioxidant effect, depending upon whether the crude oils contain natural antioxidant principles which may act synergistically with
the added phosphatides to enchance the stability of the oils.
Golumbic (4) reported that the antioxygenic o-quinones present in vegetable fats but not in animal fats retarded peroxide accu
mulation in the former type of oils after the complete disappear
ance of the tocopherols. Riemenschneider (S) showed that various vegetable oils added to lard in amounts of 1 to 10% ap
preciably increase its stability and that the increase is related to the tocopherol content of the oils.
Robeson and Baxter (9) isolated a-tocopherol from Mangona shark liver oil and from soup-fin shark liver oil by distillation and concluded that the a-tocopherol found in the soup-fin shark liver oil was about 0.04%. The Mangona shark liver oil was found to contain about 0.01% and was the major antioxidant present in the oil. Bird (5) concluded that the natural antioxidants in fish oils probably involve several types of compounds. Using halibut liver oil, he showed that exhaustive extraction with 80% metha
nol removed only part of the antioxidants, whereas with water or dilute aqueous alkali, complete extraction or destruction of the antioxidant fraction occurred. It was also reported that a-tocoph
erol at high concentrations is an effective antioxidant for vitamin A.
In another report from these laboratories (3) it was shown that the natural antioxidants present in various types of fish liver oils were either completely removed or destroyed when the oils were treated with activated carbon in the presence of a solvent for the oil. The present investigation reports the effect of the pure a-, 5-, and 7-tocopherol isomers, alone and in combination with vege
table oil lecithin, on vitamin A destruction and peroxidation in soup-fin shark and halibut liver oils. It was postulated that such studies on the relation between the destruction of vitamin A and the rate and extent of peroxidation, with and without the added tocopherols or tocopherols plus lecithin, should bring to light any similarity between the action of the latter type of antioxidants and those naturally occurring in the crude fish liver oils. Further- more, to date the literature is lacking in information on the ef
fectiveness of a-, 5-, and 7-tocopherols as antioxidants for vitamin A as it exists naturally in fish liver oils. This work is not con
cerned with the merits of tocopherols or tocopherols plus lecithin as antioxidants for the alcohol form of vitamin A.
M A T E R IA L S
Cr u d e Oi l s. The samples of crude soup^fin shark and halibut liver oils used in this work were of known origin and of the highest quality. They were filtered before using and were dry and free from foreign matter. It was established by numerous stability studies, under analogous storage conditions on other comparable lots of soup-fin shark and halibut liver oils, that the oils used in this investigation behaved in a manner quite representative of this type of oil, both as to the rate and extent of peroxidation and the rate of vitamin A destruction. The crude oils used can be considered as being relatively stable, in so far as fish liver oils are concerned. Their analysis is given in Table I.
Ca r b o n- Tr e a t e d Oi l s. The samples of crude soup-fin shark and halibut liver oils were treated with 20% (based on oil weight) of activated carbon (Nuchar X X X ), using cyclohexane as the sol
vent (20% solution of oil in solvent) by the process reported pre
viously (3). The cyclohexane used was a special grade sold by The Barrett Company and was devoid of unsaturates, as determined spectrophotometrically. The carbpn-treated oil samples were 225