Stability of Carotene in Alfalfa Meal EFFECT OF ANTIOXIDANTS C. RAY- THOJIPSON Western Regional Research Laboratory, Albany, Calij.
Fit.tj-four compounds were tested as antioxidants for carotene in dehydrated alfalfa meal. Substituted phenylenediamines, amines, aminophenols, hydroquinones, sulfur compounds, and derivatives of 2,2,4-triniethyl1,Z-dihydroquinoline were applied with several solvent carriers. 2,5-Disubstituted hydroquinones, p-substituted phenylenediamines, and derivatives of 2,2,4- trimethyl1,Z-dihjdroquinoline were the most active compounds tested. Vegetable oils plus acetone were superior to alcohols, Cellosolve, or kerosene as carriers for 2,Sditert-butylhydroquinone. Combinations of certain antioxidants showed some synergistic effect. Metal deactivators failed to give increased stability. The addition of increasing amounts of antioxidant gave increased stability but approached a limit above which additional amounts gave no effect.
over-all dimensions were 20 cin. in diemeter and 25 em. i n length. During application of the spray, the open end was covered by it c o m e cloth with a hole large enough to admit, an air-brush sprayer nozzle. The solution was metered from a 25-ml. tall-form graduated cylinder. Four nil. of a solution conta,ining 0.25 gram of antioxidant were applied, resulting in a final antioxidant concentration of 0.123%. After spraying, the meal was mixed for about 1 minute, removed, and 2-gram samples were weighed into open shell vials (20 X 70 mm.) for storage at 65' C. for 7 and 14 days, respectively. Ensprayed controls w x e stored under the same conditions in each of a series of trials. Low temperature dehydrated alfalfa meal from a single lot containing about 200 p.p.m. of carot'ene mas used for all st'udies. I t was stored in friction-top cans at - 10" F. unt,il used. After storage the carotene content was determined ( I ) . \Then untreated controls were stored at 63' C. for 14 days t,he carotene content was reduced to about one fourth of the amount present originally. In a series of ten experiments the percentage of carotene remaining in controls varied from 22 to 27%. Samples treated with the more active antioxidants retained 50 to 65%, depending on the compound used. Twenty-five diff ercntly treated samples stored in duplicate under identical conditions had a maximum deviahion from the individual average of *3.1'%. The mean deviation was * 0.9%. The 7-day storage data m r e used as a preliminary check, but after 14 days t'he amount of carotene remaining in the treated samples, compared to that in the control, was determined and expressed as "percentage of control." I t is recognized that the use of 65' C. to obtain accelerated storage data may not give exactly the same results as lower commercial storage temperatures, depending on the antioxidant or the carrier used. Rowever, data presented herein confirm the findings of Bickoff and Williams (3) which indicated that antioxidants which are effective at 75" C. are also effective at 25" C.
T
H E use of antioxidants to stabilize easily oxidized materials such as gasoline, lubricating oils, rubber, and fats is well established. However, their use for preserving carotene in alfalfa meal has been limited by oral toxicity in many cases. M o s t edible compounds lack sufficient actiyity, since the conditions of exposure to oxygen in the finely divided material are severe. Silker and eo-workers (11) found that diphenylamine, thiourea, hydroquinone, and sodium cyanide inhibited the destruction of carotene, but the storage tests were conducted at 3" C. Mills and Hart (7) found diphenylamine to be an effective antioxidant a t room temperature. However, none of the antioxidants tested earlier found wide usage and the dehydrated alfalfa industry resorted to (a) storage under refrigeration, ( b ) storage in gastight bags or metal containers to exclude oxygen, or (e) storage in metal tanks in an inert atmosphere to preserve carotene. Careful control of moisture content during storage (1) aided carotene stability to some extent. Recently, Kephart (6) found that when alfalfa meal was sprayed with 0.1% of diphenyl-p-phenylenediamine, isopropoxydiphenylamine, or phydroxydiphenylamine, dissolved in either mineral or vegetable oil, a marked increase in stability was obtained during storage. Since little comparable information was available on the effect of a number of different antioxidants on carotene stability the following studies were carried out. Also, the effect of certain solvents, synergists, and metal deactivators was investigated.
EXPERIMENTAL
Fifty-four compounds were evaluated in a series of experiments as antioxidants for stabilizing carotene in alfalfa meal. They included substituted phenylenediamines, amines, aminophenols, hydroquinones, sulfur compounds and derivatives of 2,2,4trimethyl-1,2-dihydroquinoline(Table I). In general, the disubstituted phenylenediamines, disubstituted hydroquinones, and the derivatives of 2,2,4-trimethyl-l,2dihydroquinoline were the most effective antioxidants. Compounds used for stabilizing lard such as nordihydroguaiaretic acid (KDGA), ethyl gallate, lauryl gallate, thiodipropionic acid, and lauryl thiodipropionate were low in activity, but 2-tertbutyl-4-methoxyphenol (butylated hydroxyanisole) was more effective. Although N,N'-di-sec-butyl-p-phenylenediamine and 6-ethoxy2,2,4-trimethyl-l,2-dihydroquinoline were the most active antioxidants tested, immediate further studies were delayed because
METHODS
To test the effect of a number of antioxidants on the stability of carotene in alfalfa meal, a rapid simple method of incorporating the antioxidant wm needed. This was accomplished by spraying a Cellosolve (ethylene glycol monoethyl ether) solution of the antioxidant on a 200-gram sample of meal while it was being tumbled a t 12 r.p.m. in a rotary mixer. The mixing chamber consisted of a hollow cylinder, closed a t one end and equipped with baffles similar in design to those of a concrete mixer. The 922
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
May 1950
TABLEI. COMPARISON OF ANTIOXIDANTS FOR CAROTENE IN ALFALFAMEAL Remaining, Carotene Antioxidant
% of
%
Control
66 50 51 45
280
Amine Type
N N’-di-sec-butyl-p-phenylenediamine
’
p-Isopropoxydiphenyl Diphenyl-*-phenylenediamine amine N-see-butyl-p-aminophenol p-HydroxydiDhenyl amine Phenyl-6-naphthylamine Diphenylamine N-phenyl- a-naphthylamine Phenothiazone Tetramethyldiaminodiphenylmethane Aminohydroquinone diethyl ether Phenothiazine Bp’-Diaminodiphenylmethane I tolyltriazine
46
3Y 36 35 33 33 30 29 25
ii:
195 191 168 I55 I48 142 142 128 125
The procedure with the alcohols was similar to that used to test the antioxidants, One gram of 2,5-di-tert-butylhydroquinone was dissolved in 16.0 ml. of an alcohol or kerosene and 4.0 ml. of the resulting solution were sprayed on 200 grams of meal, resulting in a final concentration of 0.125% antioxidant and about 1.7% of solvent. With the vegetable’oils alone, 8.0 ml. of oil were dissolved in 8.0 ml. of acetone and 4.0 ml. were applied. When 2,5-di-tert-butylhydroquinonewas applied with a vegetable oil, 1.0 gram was dissolved in 8.0 ml. of acetone, 8.0 ml. of oil were added, and 4.0 ml. were applied.
i;r
107
22
92
36 33 33 31 31 30 30 29 28 28 28 27 27 24 24 24 24 23 14
152 140 140 132 132 128 128 125 118 118 118 113 113 104 104 104 104 100
57
244
Phenolic Type a-Naphthol p-tert-Butylcatechol 2-tert-Butyl-4-methoxyphenol Pyrogallol Dibeneyloatechol 2 6-Di-tert.buty1-4-methylphenol datxlnmml -. _..____ _./
2 4 6-Trimethylphioroglucinol 2’4:Dimethyl-6-tert-butylphenol Bthyi hydrocaffeate imethylphlorobutyrylphenone atechol Lauryl gallate Ethyl gallate Nordih droguaiaretic acid (NDGA) 4,4’-Di~ydroxy-3-3’-dimethylbiphenyI Rutin Quercetin Di-tert-bu tylpyrogallol
8
Hydroquinone Type 2,5-Di-terl-butylhydroquinone 2,5-Di-tert-amylhydroquinone 2,5-Dibenzylhydroquinone Trichloroethylbenzenehydroquinone 1,2-Dihydroxynaphthalene Toluh droquirrone 2,7-Di%ydroxynaphthalene 2,5-DihydroxybiphenyI
50 46 38 32 32 30 28
Sulfur Compounds Di-(butyl-n-cresol) sulfide Bis-2-hydroxy-4-methylphenylsulfoxide Hydroquinone monomethyl ether Bis-2-hydroxy-4-methylphenyl sulfide Bis-2-hydroxy-4-chlorophenylsulfide Di-o-tolylthiourea Thiodipropionic acid Dilauryl thiodi ropionate N-phenyl-@-hyc%oxyethylthiourea
28 27 25 25 25 23 23 23
Substituted Dihydroquinolines 6-Ethoxy-2 2 4-trimethyl-1 2-dihydroquinoline 6-Phenyl-2 ’a 2-trimethyl-1 ’a-dihydroquinoline 2 2 I-Trim&hyl-l,2-dihyd~oquinoline Acid rearranged 2,2,4-trimethyl-1,2-dihydroquinoline Control
63 51 46 29 23.6
28 _.
N 0
I
0’
118 118 113 108 108 108 100 100
I 02
03
ANTIOXIDANT,%
d4
&,
Figure 1. Effect of Increasing Concentrations of 2,5-Di-tert-butylhydroquinone on Stability of Carotene in Alfalfa Meal
59
213 196 161 137 137 126 118
923
The results (Table 11) showed that the alcohols were slightly better than Cellosolveas a carrier of the antioxidant. Propyleneglycol was poorer. Vegetable oils plus acetone were somewhat better as carriers than the alcohols. Some of the vegetable oils alone had a small effect, except refined coconut oil, which gave increased stability, probably because of the low unsaturation of the oil. The dustiness of the meal was reduced markedly by the oils and the green color was enhanced.
100
268 218 195 123 100
of some brown color given to the meal by these compounds and the irritating action of the former on the skin. Instead, 2 , 5 di-tert-butylhydroquinone was selected as more promising for further evaluation because of its shelf stability, lack of discoloration of meal, and reported lack of skin toxicity ( l a ) . It is also easily synthesized and is inexpensive and commercially available in large quantity. Since the effect of increasing concentrations of antioxidant on the stability of carotene was undetermined, samples of meal were sprayed with increasing concentrations of 2,5-di-tertbutylhydroquinone from 0 to 0.5%. The samples were stored as indicated previously. ’ When the percentage of carotene remaining against the amount of antioxidant added was plotted (Figure l), it was apparent that increasing amounts up to 0.125% were increasingly effective. Above this level the additional antioxidant gave proportionately smaller effects. To determine the effect of solvent carriers, alone and with an antioxidant, on the stability of carotene, several alcohols, vegetable oils, and odorless kerosene were compared with Cellosolve.
TABLE 11. EFFECT OF SOLVENT ON ANTIOXIDANT ACTIVITYOF 2,5-DI-tert-BUTYLHYDROQUINONE
Solvent Carrier Cellosolve (ethylene glycol monoethyl ether) 95% ethanol Isopropanol n-Pmnannl
&fi;i&iPropylene glycol Crude cottonseed oil acetone acetone Crude soybean oil Refined coconut oil acetone Crude corn oil acetone Refined peanut oil acetone Crude sesame oil acetone Odorless kerosene acetone
+++ + + ++
% of Control With Without antiantioxidant oxidant 222 113 241 ... . . 241 ... 922 ---
229 211 310 3130 277 291
309
300 286
...
......
110 100 145 110 I15 110 100
The effect of adding a large amount of a volatile solvent, followed by subsequent removal, was determined. The addition of an antioxidant with the solvent was studied also. One hundred grams of alfalfa meal were stirred with 200 ml. of petroleum ether (boiling point, 30” to 60’ C.) in an evaporating dish. After soaking for several minutes the petroleum ether was removed before a fan. Another sample was treated similarly, except that 0.125% of 2,5-di-tertbutylhydroquinonewas added to the meal. The addition to and removal of solvent from the meal reduced the car,otene about 9%. The sample treated with the solvent plw an antioxidant was reduced about 5% (Table 111).
INDUSTRIAL AND ENGINEERING CHEMISTRY
924
TABLE111. EFFECT O F ADDIXG L.4RGE h f O U S T O F ETHER AND SUBSEQUENT Rl?:\%Ov.4J,
Carotene Remaininn Carotene after before Storage, % 7 14 Storage, P P 11 days day3
Antioxidant Control 0 . i2.570 2,5-di-fert-butylhydroquinonein 1.7% Cellosolre Petroleum ether Petrqleum ether 0.12.57, 2,5-di-rrrt-butylhydroquinone 75 parts alfalfa 25 parts rice bran 180% petroleum ether 73 parts alfalfa 25 parts crude rice bran 0.125% 2,5-di-te~t-butylhydroquiiione
+ + +
PETROLEUM
+
+
201
45
23
196 183
72 50
62
192
76
64
150
53
28
133
82
69
TABLEIV. EFFECTO F SYNERGISTIC COMBINATIONS
24
OF
.kNTIOXIDAXTS WITH
2,~-DJ-tWt-BUTYLHYDROQ~INONE Carotene 70 of Remaining, Synergist Control 70
Control 1, 0.125cI, 2,5-di-tert-butylhydroquinone Contro: 2, 0,2570 2,5-di-tert-butylhydroquinone S-sec-butyl-p-aminophenol M,.V'-di-sec-butyl-p-phenylenediamine 2-tert-butyl-4-methoxyphenol p-Isopropoxydiphenylamine
Ethyl hydrocaffeate p-Hydroxydiphenylamine Lauryl gallate Thiodipropionic acid 5.0% crude cottonseed oil 0.017, citric acid 0.01% HIPO; Control
233 2.54 282 318 268 343 250 267 244 233 313 237 233 100
63 69 76 86 72 93 67 72 66 63 85 64 63 27
These samples were stored a t 65" C. When they were compared with a stored control and a sample sprayed with antioxidant in 1.7% Cellosolve, a small increase in stability was shown by the samples treated with excess solvent. The untreated control was reduced to 23% of the original carotene present, n hereas the petroleum ether-treated sample contained 29%. Kith the antioxidant in 180% petroleum ether, 64% of the carotene remained; with 1.7% Cellosolve, 62% remained. Two samples of a mixture of 75 parts of alfalfa meal plus 25 parts of crude rice bran meal were treated with petroleum ether and with antioxidant in the same way as the alfalfa meal and n ere stored under identical conditions. The carotene remaining was about the same with petroleum ether alone (28%). The sample with the antioxidant gave 69y0 retention of carotene. which seemed to indicate a small amount of additive effect 11-ithwhatever was contained in the rice bran meal. Since some antioxidants react synergistically with other compounds to give marked increases in activity (4, C), several antioxidants were added a t a level of 0.125% to an equal amount of 2,5-di-tert-butylhydroquinone,and the results were compared n.ith double the amount (0.25%) of the substituted hydroquinone (Table IV). The effect of 0 01% of citric or phosphoric acid and 5.0% of crude cottonseed oil was determined also. The results showed that p-isopropoxydiphenylamine, S,S'di-sec-butyl-p-phenylenediamine,S-sec-butyl-p-aminophenol, 2tert-butyl-4-methoxyphenol,lauryl gallate, and p-hydroxydiphenylamine were quite effective as synergists, but the other compounds had little effect. Five per cent of crude cottonseed oil with the hydroquinone gave increased stability, probably because of naturally contained antiouidants. To further evaluate some of these compounds a t lower concentrations, seven samples were sprayed with 0.01% of the compounds in 1.8% Cellosolve. 2,5-Di-tert-butylhydroquinone, diphenyl-p-phenylenediamine, p-isopropoxydiphenylamine, and p-hydroxydiphenylamine were used alone. k o , the last three mentioned x-ere tried individually in combination with 2,5-di-tert-butylhydroquinone. The results (Table V) showed that this concentration of a single antioxidant gave a small but significant stabili-
Vol. 42, No. 5
zation of carotene Combinations of the antioxidants were additive, but little synergistic activity mas demonstrated. Metal ions, especially copper and iron, have been shown to catalyze the oxidation of unsaturated hydrocarbons and vitamins to a marked extent (8, I O ) . Since alfalfa contains appreciable amounts of these metals (2, 9) and all antioxidants, despite the use of high concentrations of synergists, had failed to give 100% stability of carotene, the effect of adding metal deactivators with an antioxidant \vas tried. The metal deactivators were dissolved in Cellosolve in amounts equal to the antioxidants (0.125%) and were sprayed on alfalfa meal as indicated previously (Table VI). The results showd that none of the metal deactivators gave increased stability of carotene with the antioxidants. Those tried with 2,5-di-tert-butylhydroquinonewere slightly prooxidant, whereas with the S,S'-di-sec-butyl-p-phenylenediamine, thenoyltrifluoroacetone gave some pro-oxidant effect. Apparently metals are not active in catalyzing the oxidation of carotene in dried alfalfa under these conditions. Since the accelerated storage tests a t 65" C. may not give results comparable t o those obtained in commercial storage a comparison was made between results obtained at 65' and 25 O C. Five lots of alfalfa meal were treated with 0.125% of antioxidant and were stored a t the indicated temperatures. The samples stored a t 65" C. were run for 5 and 10 days and those at 25" C. were kept for 112 and 224 days. The results (Table TIL) showed that some compounds are relatively more effective at 25" C. than at 65" C. However, the data are considered comparable enough to warrant the w e of the higher temperature for screening a number of compounds for antioxidant activity prior to more exhaustive tests.
TABLE V. EFFECT OF Low COXCENTRATIONS OF ANTIOXIDANTS 03' C.4ROTESE STABILITY Caiotene Remaining, %_ 7 days 14 days
Antioxidant
51
Control
0.01 702,5-di-tert-butylhydioquinone 0.01 c/, dtohenvl-a-ohenvlenediamiiie
pro oxydiphenylamine 0.01$2,5-d' 1-tert-butylhydroquinone hy &oxy diphenylamine
52 50
23 2s 27 30 27
63
35
60
29
56
33
54 54
+ 0.01&!
p-
TABLEVI. EFFECTOF METAL DEACTIVATORS PLVS AXTJOXID.4WTS ON ST.4BILITY OF CAROTESE IS ALFALFA h r E A L Carotene Remaining, ?,5-Di-tert-butylhydroquinone 2 5-Di-tert-butylhydroquinone benzidine 2:5-Di-tert-butylhydro~uinone anthranillic acid 2,5-Di-tert-butylhydroquinone 8-hydroxyquinoline 2,5-Di-tert-butylhydroquinone salicylaldoxime iV V'-di-sec-butyl-p-phenylenediamjne N~i\"-di-sec-butyl-p-phenglenediamine thenoyltrifluoroacetone Control
+ +++
+
TABLEVII.
% of Control
59 51 66 47 46 61
244 213 229 196 192 256
54 24
224 (100)
COMPARISON OF RESULTSOF STORAGE TESTSAT 65' A N D 25" C. At 25" c., % .It 65' C., 70"
Antioxidant (0.125%) Control N , N'-di-sec-butyl-p-phenylene diamine 2-tert-Butyl-4-methoxyphenol p-Isopropoxydiphenylamine 2,5-Di-tert-butylhydroquinone a
%
Per cent remaining.
5 days
10 days
57
36
82 61 76
75 43 63 70
81
112 days 224 d a y s 54 36 86 72
s,?
t O
67 47 69 72
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY DISCUSSION
*
The structure of compounds is apparently correlated with their antioxidant activities. The presence of a tertiary alkyl group in the 2,5 positions on hydroquinone results in increased activity. The benzyl group also serves to give comparable stabilization. With p-phenylenediamines either a secondary butyl or a phenyl group serves to give high antioxidant activity. Insufficient data are available on the 1,2-dihydroquinolinesJ but additional work ivith these three groups and others might provide a basis for predictions of antioxidant activity from their chemical structure. Solubility and consequent penetration of the antioxidant into the site of carotene occurrence may be of extreme importance, especially since the water-soluble compounds such as catechol and pyrogallol are relatively ineffective. Why complete stabilization of carotene with increasing amounts of antioxidant is not achieved is not apparent. The occurrence of carotene in two forms as shown by Weier (IS) in carrots, one of which is more readily stabilized, would explain the anomaly to some extent.
*
CONCLUSIONS
AXTIOXIDLVTS. 2,5-Disubstituted hydroquinones, p-substituted phenylenediamines, and derivatives of 2,2,4trimethyI-1,2dihydroquinoline were the most active compounds tested for stabilizing carotene in alfalfa. SOLVENTS.Vegetable oils plus acetone were superior to alcohols, Cellosolve, or kerosene as carriers for 2,5-di-tert-butylhydroquinone. The addition and subsequent removal of a large amount of volatile solvent were not particularly beneficial.
925
SYNERGISTIC COMBINATIONS. Combinations of antioxidants were synergistic to some extent. The addition of metal deactivators METALDEACTIVATORS. failed to give increased stability. ACKNOWLEDGMENT
The author gratefully acknowledges the analytical assistance of E. M. Bickoff and I. V. Ford. L l T E R A T U R E CITED
G. F., A t k i n s , M. E., a n d Biokoff, E. M., IND.ENQ. CHEM.,41,2033 (1949). Bailey, L, F., a n d M c H a r g u e , J . S., Plant Physiol., 20, 79 (1945). Bickoff, E. M., and Williams, K. T., Oil & Soap, 23,65 (1946). Calkins, V.P., J . Am. Chem. SOC.,69,384 (1947). Clausen, D. F., L u n d b e r g , W . 0.. and Burr, G. O., J . Am. Oil Chem4ts' Soc., 24, 403 (1947). K e p h a r t , J. C. (to N a t i o n a l Alfalfa D e h y d r a t i n g a n d Milling Co.), U. 8. P a t e n t 2,474,182 (June 21, 1949). Mills, R. C., and H a r t , E. B., J . Dairy Sci., 28, 1 (1945). R a o , S. D a t t a t r e y a , Indian J . Med. Research, 33, 63 (1945). S h e r m a n , W. C., E l v e h j e m , C. A,, a n d H a r t , E. B., J . Riol. Chem., 107, 383 (1934). Sieffert, L., 2.Vitaminforsch., 17, 52 (1946). Silker, R. E., Sohrenk, W. G., and King, H. H., INDENQ. CHEM.,36,831 (1944). Bailey,
Tennessee E a s t m a n Corp., communication. Weier, T. E., Am. J . Rot., 29,35 (1942).
RECEIVED January 20, 1950. Report of a study made under the Research and Marketing Act of 1946 a t the Western Regional Research Laboratory, Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.
.
Desulfurization of Heptane Solutions of Organic Sulfur tornpounds J. R . MEADOW
AND T. A. WHITE' C'niversity of Kentucky, Lexington, Ky.
Quantitative data have been presented to show *e desulfurizing action, at room temperature, of 95qo sulfuric acid, concentrated sulfuric acid saturated with nitrogen dioxide, anhydrous aluminum chloride and bromide, anhydrous hydrogen fluoride, and aqueous solutions of hydrofluoric acid on various organic sulfur compounds dissolved in n-heptane. The results show that for the amounts of the reagents used concentrated sulfuric acid, nitrogen dioxide dissolved in 95% sulfuric acid, and anhydrous hydrogen fluoride were generally the most effective desulfurizing agents studied. The latter agent would have certain economic advantages in recovery and re-use. The sulfuric acid-nitrogen dioxide mixture was quite effective in removing alkyl disulfides which were relatively unaffected by the other desulfurizing agents,
The present study has extended the observations of some of these investigators to include higher molecular weight organic sulfur compounds, and also furnishes quantitative data on the removal of these compounds by desulfurizing agents about which more information seems desirable. In order to study the effect of a desulfurizing agent on a particular organic sulfur compound, solutions were made in which a known amount of the pure sulfur compound was dissolved in n-heptane, an inert hydrocarbon diluent of known specifications and purity. MATERIALS AND R E A G E N T S
The following desulfurizing agents were used in this rork: Concd. Has04 (95 5 % ) sp. gr. 1.84 Concd. H1SO4. sp.' gr. i.84,saturated with KO2 a t 20° C. AlCla C.P anhydrous AIBri, c.;; anhydrous HF, acid (52%) HF, anhydrous
.
P
REVIOUS work by Wood and co-workers (27,288)showedthe effect of petroleum refining agents on certain organic sulfur compounds dissolved in naphtha. Reduction in sulfur content of naphtha solutions by treatment with silica gel, bauxite, copper oxide, zinc oxide, and fuller's earth a t elevated temperatures has been reported by various authors (8, IS, 86-89), 1
Present address. Esso Standard Oil Company, Baltimore, Md.
Normal heptane, A.S.T.M. reference fuel, was selected as the solvent for the sulfur compounds listed in Table I. Some of its physical properties are given below: Purity mole 0 Refrao'tive i n g x a t 20' C. Freezing point, O C. Sulfur content, %
99.5 1.3878 -90.68 Less than , 0 . 0 1
