April 1950 0 ?F
n:
INDUSTRIAL AND ENGINEERING CHEMISTRY
= moles of Sa in the reaction mixture = moles of Se in the reaction mixture
(2) Bell, R. T., and Agruss, M. S., IND.ENG.CHEM.,ANAL.E D . , 13, 297-9 (1941). (3) Braune, H., and Peter, S., Nuturwissenschuften, 30, 607-8 (1942). (4) De Simo, M. (to Shell Development Co.), U. S. Patent 2,187,393 (Jan. 16, 1940). (5) Preuner, G., and Sohupp, W., 2.physik. Chem., 68, 129 (1909). (6) Reinhold, H., and Sohmitt, K., Ibid., B44, 98 (1939). (7) Thacker, C. M., and Miller, E . , IND. ENQ.CHEM.,36, 182-4 (1944).
= moles of Sa in the reaction mixture
A
= moles of methane in excess of the stoichiometric quan-
0'
= pseudoreaction
tity/mole of methane time, equal t o the reactor volume divided by the volumetric feed rate-i.e., 6' = VR/V' = hr. LITERATURE CITED
(1) Bacon, R. F., and Boe, E. (1945).
S.,IND. ENG.CHEW, 37, 469-74
709
'
RECEIVED August 15, 1949. Presented before the Division of Industrial and Engineering Chemistry at the 117th Meeting of the AMERICAN CHEMICAL SOCIETY,Houston, Tex.
Vitamin A Alcohol STABILITY AND ABSORPTION IN AQUEOUS AND OILY MEDIA C. J. KERN AND THOMAS ANTOSHKIW International Vitamin Division, Ives-Cameron Company, Inc., Brooklyn, N . Y .
~
T h e stability of vitamin A in aqueous dispersions (the media contained 20% of sorbitan monolaurate polyoxyalkylene derivative in water) was greatest a t pH 5, 7, and 9 and somewhat less at pH 3 and 4. Tocopherols enhanced the stability at pH 3 and 4 but had the reverse effect (to a mild degree) at pH 7 and 9. The vitamin A mixed with the dispersing agent alone was less stable than in aqueous media. The stability at all conditions was superior to vitamin A concentrate, diluted to the same degree (10,000 U.S.P. units per gram) in cottonseed oil. This was true
even in the presence of 2% tocopherol and 4 q lecithin, ~ which previous studies had shown to be the optimum antioxidant combination for oil. The stability was as good as or better than that shown by distilled vitamin A ester concentrate and distinctly superior to that shown by the distilled ester diluted in cottonseed oil. The absorption of vitamin A from aqueous media, as measured by vitamin A tolerances in humans, was better than that obtained with the same vitamin A diluted in oil. Tocopherol has no significant influence in this improvement.
THE
alone. As a secondary reference oil, natural distilled vitamin A esters (Distillation Products, Inc.) were employed because of their recognized stability. The concentrate (containing 200,000 U.S.P. units of vitamin A per gram) was studied, as well as a dilution with cottonseed oil (to contain approximately 10,000 U.S.P. units of vitamin A per gram). The studies were carried out at 40" C. for 17 days.
stability of vitamin A has been the subject of numerous investigations (1-7, 9-14, 21, 22, 33, 29, 36-88), most of which were carried out with oily solutions. Recent investigations, however, indicate the importance of vitamin A in aqueous media. In various conditions where vitamin A is poorly absorbed when given in oily media, there is markedly improved absorption when the vitamin A is finely dispersed in aqueous media (8, 15, 16, 20, 94-97, $0-34,39). Prominent among these conditions are the celiac syndrome, liver disease, obliteration of the biliary tract, sprue, diarrhea, dermatologic disorders, prematurity, and the normal newborn (8, 15, 16, 17, 19, 20, f24-27, 28, 30-34, 39). Moreover, even in normal children, adults, and experimental animals, there is improved absorption of vitamin A in aqueous media (30,31, 34). The transfer of vitamin A to the milk of nursing mothers is superior when given aqueous dispersions (32, 33). I n view of the physiological importance of vitamin A in aqueous media the authors extended their studies of the factors influencing stability of vitamin A in oils ( 1 4 ) to vitamin A in aqueous media. The dispersing agent employed was the polyoxyalkylene derivative of sorbitan monolaurate, because most of the absorption studies with aqueous dispersions of A were carried out employing this compound. The source of vitamin A employed was the nonsaponifiable fraction of mixed fish liver oils saponified by the method of Marcus (18) (containing about 1,000,000 U.S.P. units of vitamin A per gram). The concentrate was diluted (to contain about 10,000 U.S.P. units per gram) with water containing 20% of the dispersing agent, a suitable buffer, and in some cases 0.3% of mixed tocopherols. The p H of these dispersions (which appear clear to the naked eye) ranged from 3 to 9. For comparison, the concentrate was diluted in the dispersing agent alone, in cottonseed oil containing 2% tocopherols and 4% lecithin (found to be the most effective antioxidant combination in previous studies, 1 4 ) , and in cottonseed oil
APPARATUS
The spectrophotometric data were obtained using a Beckman quartz spectrophotometer, Model DU, equipped with the ultraviolet accessory set. The wave-length scale setting was checked using several of the hydrogen lines emitted by the hydrogen discharge lamp. The colorimetric data were obtained using a Pfaultz and Bauer fluorophotometer Model B, equipped with a set of filters giving maximum transdttance at wave length 550 mp. The p H data were compiled using a Leeds & Northrup potentiometer, Catalog No. 7661, and a Beckman p H meter, Model G. REAGENTS AND PREPARATIONS EMPLOYED
Activated glycerol dichlorohydrin, obtained from J. B. Shohan Laboratories, 78 Wheeler Point Road, Newark 5, N. J. Chloroform, reagent grade. Citric acid, reagent grade. Cottonseed oil, U.S.P. grade, obtained from the Durkee Famous Foods Corporation. This oil was used as the standard diluent for all concentrates having a potency greater than 100,000 U.S.P. units of vitamin A per gram. Distilled natural vitamin A esters, obtained from Distillation Products, Inc. The material contained 200,000 U.S.P. units of vitamin A per gram. The vitamin A content of each specimen was checked spectrophotometrically. Isopropyl alcohol 99%, spectrophotometric grade, obtained from Carbide and darbon Chemicals Company. This material waB used as a standard solvent for all vitamin A samples to be assayed spectrophotometrically. Lecithin, obtained from Ross and Rowe, Inc. The material
710
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 4
DISCUSSION O F RESULTS
The results of the studies are given in Table I and Figures 1 to 5.
TIBLE I.
STABILITYOF VITAMINA ALCOHOL^ 3IED1.4 I N A I R AT 40" c.
IX
VARIOUS
(Value9 Expressed as % Vitamin A Remaining) Media Employed Cottomeed oil Cottonseed oil containing 4 % lecithin and 2% tocopherols Polyoxyalkylene sorbitan monolaurate .Iqiieous dispersion .\ h
I'olyoxyalkylene sosbitan monolanrated Uiatilled \,itamin A ester(200,OOO units/
2
6 8 IO I2 14 DAYS OF €XPOSURE IN AIR AT 40'C. 4
Figure 1. Effect of pII on Stttbility of Vitamin 4 Dispersed in Water Containing 20% Tween 20 1. p H 3 2.
pH 4a.
3.
4. plI 9
pH5 pH 7
is a regular commercial product and was used as received. The material is derived from soybean oil and contained a minimum of 62% lecithin. Satural mixed tocopherols, obtained from Distillation Products, Inc. The material is a distilled concent,rate of mixed t,ocopherols, Type IV,prepared from vegetable oils. Polyoxya1k;ylene sorbitan monolaurate, obtained from Atlas Powder Company, Inc., and commercially known as Tween 20. Sodium citrate, reagent grade. Sodium phosphate, t,ribasic, reagent grade. Vitamin A Alcohol C,oncentrate. Mixed fish liver oils were completely saponified with potassium hydroxide. The unsaponifiable fract,ion was extracted li-ith ethylene dichloride. The solvent was then removed by dist'illation a t reduced pressure, leaving the residue, which was used without further t'reatment. The vit,amin A content of the undiluted concentrate as measured spectrophotometrically was 1,020,500 U.S.P. units per gram.
Days of Exposure 3 4 8
11
14
13.9
6.2
4.6
3.8
91.6
85.9 82.3
65.9
53.1
42.G
87.8
82.2
79.8
62.0
50.8
41.9
84.7 96.2 97.7 97.5 99.9
67.7 89.8 95.4 94.0 96.7
52.9 84.2 91.4 91.7 93.2
39.1 75.3 89.5 86.6 91.4
7.4 37.3 83.2 80.7 90.2
5.5 4 .5 15.5 7.8 74.7 66.0 7 6 . 8 70.0 88.1 83.8
3 . 0 87.9 4 . 0 96.2 5.0 94.7 7 . 0 85.5 9 . 0 86.0
78.8 92.9 92.1 75.3 76.5
75.9 87.7 89.5 68.0 67.4
67.7 83 6 85.6 60 1 62 1
56.9 74.0 80.5 49.3 49.8
51.3 67.6 69.5 42.9 39.5
47.1 62.8 63.0 39.0 35.3
93.6 91.3
89.5
82.9
76.3
72.0
67.8
PH
1
2
, .
79.5
R1.9
25,6
..
96.2
..
92.9
3.0 4.0 5.0 7.0 9.0
~.
%.,e . . 98.3 96 6 9 6 . 1 9 2 . 0 89.0 7 7 . 3 68.7 Distilled vitamin A ester (10,000 units/ g.)incottonseedoil . . 96.3 05.3 93 2 8 7 . 3 77.2 28.8 4.8 a Nonsaponifiable fraction extracted from fish liver oils, saponified by method of Marcus (IS),diluted o s dispersed in varioiis media t o about 10,000 U.8.P. units of vitamin A per gram. Before dilution, concentrate contained 1,020 500 U.S.P. units of vitamin A per Oram. 4 $itamin A alcohol concentrate dilnred, in a n aqueous media containing 20% polyoxyalkylene sorbitan monolaurate and sufficient amounts of apvsopriate buffer solution, t o about 10,000 U.S.P. units of vitamin A per gram. C Vitamin A alcohol concentrate diluted, in an aqueous media oontaininr: 2 0 7 olyoxyalkylene sorbitan monolaurate 0.3% mixed tocopherols, and suffi'cikt amount8 of appropriate buffer soiution, to about 10,000 U.S.P. unitn of vitamin A per gram. Polyoxyalkylene sorbitan monolaurate Containing 0.3% mixed tocopherols. e From Distillation I'roducts, Ino., used as obtained.
The stability of vitamin A dispprsed i l l water containing 20% 01 the dispersing agent was best a t p I i 9, clearly followed by the xtability at pII 7 and 5. Thew is a rapid decrease of stability at pH 4 and it is still poorer a t p l i 3.0 (Table I and Figure 1). The order of stability is changed in thc presence of 0.3% of' to-
METHODS
The experiments were conducted a t a temperature of 40 ', hich was maintained in a constant temperature oven. Standard conditions were set up for the samples by using 12.5 gram. of material contained in 100-ml. volumetric flasks. The neck\ of these flasks extended outside the constant, temperature oven, through holes bored in the top of the oven. I n this manneI, the necks of the flasks were utilized as air condensers, t o condense the slight ainount of moisture evaporated at this temperature from the aqueous dispersions of vitamin A under study. Constant temperature checks were made by means of a thermometer inserted into a blank oil sample subjected to the samr conditions as the test samples. The flasks were loosely stoppered with small plugs of cotton. I n the spectrophotometric determinations, approximately 0.5 gram of sample was diluted in isopropyl alcohol to give density readings from 0.2 to 0.5. The acid aqueous dispersions were buffered with an aqueous solution containing 5'% weight/volume of sodium citrate and 10% weight/volume of citric acid. The neutral (pH 7.0) and alkaline aqueous dispersions were buffered with an aqueous solution of 3% weight/volume tribasic sodium phosphate. Serum vitamin A was determined by the procedure of Sobel and Snow (85). The vitamin A samples were saponified according to the method of the U.S P X I I I . A
DAYS OF EXPOSURE IN AIR AT 40'C Figure 2. Effect of pH on Stability of Vitamin A Dispersed in Water Containing 200/0 Tween 20 and 0.3yo Mixed Tocopherols 1. p H 3 2*
""54.
3. 4.
pi1 9
pH 5 "€1 7
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
April 1 9 s
2
711
4 6 8 10 12 14 DAYS OF EXPOSURE IN AIR AT 40'C.
Figure 4. Stability of Vitamin A Dispersed in Water Containing 200/, Tween 20 a t pH 5, 7, and 9 with and without Added Mixed Tocopherols (0.3%) "
2
4 DAYS OF
1. pH 5 without added tocopherols pH 5 with added tocopherols 3. pH 7 without added tocopherole 4. pH 7 with added tocopherola
2.
10 12 14 EXPOSURE IN AIR AT 40'C. 6
8
5.
1. 2.
3. 4.
pH pH pH pH
pH 9 without added tocopherols
6. pH 9 with added tocopherols
Figure 3. Stability of Vitamin A Dispersed in Water, Containing 209%Tween 20 a t pH 3 and 4 with and without Added Mixed Tocopherol (0.3%)
.
3 without added tocopherols 3 with added tocopherols 4 without added tocopherols 4 with added tocopherols
z w
aL
-500 3 6 9 12 15 18 21 24 HOURS AFTER INGESTION O F 850 USP UNITS/LB. BODY WT
Figure 6. Serum Vitamin A Level Changes Following Administration of Vitamin A Alcohol in Aqueous and Oily Media Three adults -Vitamin A oil Vitamin A aqueous dispersion Vitamin A aqueous dispersion with 0.3% tocopherols
------- --
2 Figure 5.
4 6 8 IO 12 14 DAYS OF EXPOSURE IN AIR AT 40°C
Vitamin A Alcohol Stability in Aqueous and Oily Media
1. Vitamin A, 20% Tween 20 in water, pH 9 2. Distilled vitamin A ester, 200,000 unlts per gram 3. Vitamin A plus 0.3% tocopherols in Tween 20 4. Vitamin A plus 4 $6 lecithin plus 2 70 tocopherols in cottonseed oil 5. Vitamin A in Tween 20 6. Distilled vitamin A ester in cottonsced oil 7. Yitamin A in cottonseed oil
copherols. It is best at pH 5 and 4,intermediate at pH 3, and poorest a t p H 7 and 9 (Figure 2 and Table I). The influence of 0.3% tocopherols on the stability of aqueous dispersions of vitamin A is shown in Figures 3 and 4 and Table I. Tocopherols exert a distinct protective action against the deterioration of vitamin A a t pH 3 and 4. However, at p H 7 and 9 there is a decrease of vitamin A stability in the presence of tocopherols. This anomalous behavior should have further investigation. It is likely that the mechanism of oxidative destruction of vitamin A is different in aqueous media than in oily solutions. I n oily solutions the formation of peroxides is an important preliminary step in destruction of vitamin A. I n aqueous media, a t 40 O, however, one would not expect peroxides to be stable. I n fact, the destruction of peroxides already formed
INDUSTRIAL AND ENGINEERING CHEMISTRY
712
TABLE11. STABILITY Sample
Dispv$onAa, p H 8.0
DispersionBa, pH 3.0
Dispersion A n , pH 7.0
Initial Value, U.S.P. Units/G. After Before sap. sap. 12,000 12,100
0.742 0.994 0.552 12,100
0.741 0.992 0.553 12,000
0.802 0.992 0.540
0.804 0.990 0.548 11,600
0.671 0.990 0.506 11,600
.i A L C O H O L
I N AQCEOUS M E D I - 4 , I N h R AT
40'
%,Remain-
Before sap. 66.9
After sap. 63.7
Number of Days of Exposure at 40' C. 3 7 11 Before After Before After After Before sap. sap. sap. sap. sap. sap. 48.2 27.3 18.3 9.1 5.5 3.1
Eg%/328 E 320/328 E 350/328 %,Remain-
0.758 0.967 0.713 80.9
0.713 0,968 0.711 80.4
1.016 1.034 0.780 75.1
0,949 0.994 0.831 61.8
1.568 1.143 0.681 62.0
1.939 1.252 0.483 47.4
2.223 1.250 0.511 r74 4
EE%/328 E 320/328 E 350/328 %,Remain-
0.757 0.957 0.697 94.8
0.787 0.981 0.613 95.2
0.843 0.963 0.863 94.1
0.789 0.952 0.865 90.0
0.918 0.954 1.034 87.8
0.818 0.946 1,039 80.7
0.963 0.963 1.072 79.8
~-
11,700
O F IrITAMIN
Vol. 42, No. 4
1
14 __I__
Before sap. 4.2
After sap.
1.175 1.185 0.620 43.2
2.397 1.270 0,494 49.4
1.700 1.115 0.654 37.2
0.838 0.952 1.095 76.9
1,021 0.977 1.079 73.5
0.866 0.953 1.119 69.0
2.0
0.677 0.986
E%/328 0.691 0.703 0.698 0.717 0.730 0.736 0.777 0.733 0.805 0,751 E 320/328 0.969 0.981 0.985 0.991 0,995 0,994 0.996 0,990 1.002 0.995 E350/328 0.512 0.513 0,516 0.513 0.523 0.517 0.533 0.525 0.533 0.518 Dispersion Bb 11,600 %Remain87.8 81.1 70.0 66.8 56.7 51.1 49,l 46.1 45.4 41.9 ing E 300/328 0.785 0.808 0.899 0.854 1.019 0,988 1.113 0.976 0.750 0.749 1.165 1.036 0.978 0.955 0.955 E320/328 0.996 1,007 1.011 1.022 1.031 1,017 1.024 1.041 1,051 0.495 0.497 E 350/328 0.535 0.534 0.691 0.551 0.642 0.675 0.668 0.568 0.694 0.586 a Vitamin A alcohol concentrate diluted, in aqueous media containing 20% polyoxyalkylene sorbitan monolaurate and sufficient amounts of appropriate buffer solution to about 10,000 U.S.P. units of vitamin A per gram. b Vitamin A alcohol concentrate diluted, in aqneous media containing 20% polyoxyalkylene sorbitan monolaurate, 0.3% mixed tocopherols, and sufficient amounts of appropriate buffer solution, t o about 10,000 U.S.P. units of vitamin A per gram. 0.500
appears to take place. After a vitamin concentiate high in peroxides had been dispersed in water and heated a t 40" for 24 hours, there was no evidence of peroxides remaining. The mechanism of protection must be different. I n such aqueous dispersions, each suspended particle is surrounded by the dispersant. Oxygen must penetrate this layer in order to reach the vitamin A particle. The protection to oxygen penetration probably varies with p H because of changes in the manner in which the dispersant surrounds the oil particle. The presence of tocopherols may influence this in such a inanner that a t high p H oxygen penetration is increased, whereas a t low p H it is decreased. Careful investigations are needed to clarify the mechanics of vitamin A destruction in such systems. On comparing the stability of vitamin A in different media (Figure 5 and Table I ) one is immediately impressed by the stability of the aqueous dispersion compared to the stability of the same vitamin 9diluted with cottonseed oil. Merely changing from oil t o an aqueous dispersion a t p H 9 caused this difference. I n these studies only the stability of vitamin A in the distilled esters concentrate was of the same order of magnitude, and only for the first 8 dags. After this the vitamin A content of the distilled esters fell off more rapidly, until a t the end of 17 days it was 59.5% of the original value compared to 82.0% in the aqueous dispersion a t p H 9. The stability of the vitamin A with distilled esters diluted with cottonseed oil was still less; it was 77% of the original value on the eighth day, and after this it dragged very sharply. The distilled ester was more stable than the alcohol concentrate diluted in cottonseed oil containing antioxidants (4% lecithin and 2oj, tocopherols). However, the distilled ester diluted in cottonseed oil was more stable only for the first 8 days. After 8 days the vitamin A content dropped sharply, whereas in the A alcohol concentrate the rate of deterioration was about constant. Thus a t the end of 17 days the alcohol concentrate in oil had appreciable vitamin A, whereas the diluted esters had only negligible amounts. The stability of A in the aqueous dispersion was greater than in the pure dispersing agent [curves 1, 3, and 5 (Figure 5 ) ] . Tocopherols had a distinct protective action when the oily dispersing agent alone was used as the solvent. To supplement the stability results obtained, a study was undertaken to determine the vitamin A values before and after saponification of the samples under study. Several samples of aqueous dispersions with and without added tocopherols a t p H 3.0 and 7.0 were subjected to the same rigid conditions as before. However, a new sample of vitamin A alcohol concen-
trate was used in the preparation of the various dispersiorib In addition, the absorption spectra of the various samples wrw studied before and after saponification. The results obtained appear in Table 11. The essential conclusions were not altered. Where stability was high-i.e., aqueous dispersion without added tocopherols a t p H 7.0-the values obtained before and after saponification were essentially the same and the changes between the E 300/328, E 320/328, and E 350/328 ratios are small. When the destruction was more than SO%, the differences between the whole and saponified values are great and this occurs when the E 300/328 changes are the greatest. A further study to amplify these results will he undertaken in the near future. INFLUENCE OF VITAMIN E ON ABSORPTION OF VITAMIN A IN AQUEOUS MEDIA
The superior absorption of aqueous dispersions of vitamin A as compared to oily preparations is well known (8, 15, 26, 17, 20, 21, 22, 24, 50-34, 39). The authors were interested to determine the effect of the addition of o.3y0of mixed tocopherols on this absorption in normal. adults. Figure 6 s h o w distinctly the improved absorption as measured by vitamin A tolerance of tho concentrate in mater compared to the same vitamin A dissolved in cottonseed oil (both 10,000 U.S.P. units per gram). Thc further enhancing effect of vitamin E is not statistically significant and is certainly nowhere near the same order of magnitudc as the difference between aqueous and oily preparations. LITERATURE CITED
Bisceglie, U., Boll. soc. ita2. biot. sper., 22, 1116 (1948). Bolomey, R. A., J. B i d . Chem., 169,323 (1947). Buxton, L. O., IND. ENG.CHGM.,39,225 (1947). Ibid., p. 1171. Buxton, L. O., U. S.Patent 2,396,681 ( M a r c h 19, 1946). Buxton, L. O., and Dryden, C. E., Ibid., 2,426,486 (-4ug. 26. 1947).
Caspe, S., and Hadjopoules, L. G., Am. J . Pharm., 110, 533 (1938).
Davidson, D., and Sobel, A. E., J. Investigative DermatoE., accepted for publication. Dubouloa, P., and Hedde, &I. F., Trav. msmbres soc. chim. bid., 24, 1137 (1942).
Dubouloa, P., Hedde, M. F., and Rousset, F., Compt. r e n d .
soc.
bioZ., 137,457 (1943). Feigenbaum, J., Nature, 157, 770 (1946). Fiedler, H., Fette u. Seifen,45,638 (1938). Govindarajan, S.V., and Bannerjee, B. K . , I n d i a n J . Vet. Sci.. 10, 335 (1940).
April 1950
I
I
INDUSTRIAL A N D ENGINEERING CHEMISTRY
(14) Kern, C. J., Antoshkiw, T., and Maiese, M. R., I N D . ENQ. CHEW,41, 2849 (1949). (15) Kramer. B., Sobel, A. E., and Gottfried, S. P., Am. J . Diseases Children, 73, 543 (1947). (16) Lewis, J. M., Bodansky, O., Birmingham, J., and Cohlan, S. Q., J . Pediat., 31, 496 (1947). (17) McCoord and Breeze, cited by Clausen, S. W., Harvey Lectures, 19&-43, 38, 199, 216 (1943). (18) Marcus, J . K., J . Biol. Chem., 80, 9 (1928). (19) May, C. D., Blackfan, K. D., MoCreary, J. F., and Allen, F. H., Am. J . Diseases Children, 59, 1167 (1940). (20) May, C. D., and Lowe, C. U., J . Clin. Invest., 27, 226 (1948). (21) National Oil Products Co., Brit. Patents 589,273 (June 16, 1947); 590,090 (July 8, 1947). (22) Olcott, H. S., Oiland Soap, 1 8 , 7 7 (1941). (23) Parker, W. E., Neish, A. C., and McFarlane, W. D., Can. J . Research, 19B, 17 (1947). (24) Popper, H., Steigmann, F., Dubin, A., Dyniewicz, H. A., and Hesser, F. P., Proc. SOC.Exptl. Biol.Med., 68,676 (1948). (25) Popper, H., Steigmann, F., and Dyniewicz, H. A., Gastroenterology, 10, 987 (1945). (26) . . Popuer. H.. Steiamann. F.,and Dvniewicz, H. A,, J . Lab. Clin. Med:, 32, 1403 (1947). (27) Popper, ~. H., and Volk, B. W., PYOC.SOC.Exptl. Biol. Med., 68, 562 (1948).
__
713
(28) Ruch, D. M., Brunsting, L. A,, and Osterberg, A. E;.,PIOC. Staff Meetings, Mayo Clinic, 21, 209 (1946). (29) Sandell, E., Farm. Revy, 45, 697 (1946). (30) Sobel, A. E . , Besman, L., and Kramer, B., Federation Proc., 7, 189 (1948); Am. J . Diseases Children, 77, 576 (1949). (31) Sobel, A. E., Gottfried, S. P., and Kramer, B., Abstracts of 110th meeting, AM.CHEM.SOC., Division of Biological Chemistry, Chicago, Ill., Sept. 11, 1946. (32) Sobel, A. E . , Rosenberg, A,, Geduldig, R., Engel, E., West, %I., and Kramer, B., Federation Proc., 8,253 (1949). (33) Sobel, A. E., Rosenberg, A., and Kramer, B., Abstracts of 114th meeting, AM. CHEM.SOC., Division of Biological Chemistry, Washington, D. C., Aug. 30, 1948. (34) Sobel, A. E . , Sherman, M., Lichtblau, O., Snow, S.,and Kramer, B., J . Nutrition, 35, 225 (1948). (35) Sobel, A. E . , and Snow, S., J . Biol. Chem., 171, 617 (1947). (36) Stern, M. H., Robeson, C. D., Weisler, L., and Baxter, J. G., J . Am. Chem. SOC.,69,689 (1947). (37) Thurman, B. H., U. S. Patent 2,201,062 (May 14, 1940). (38) U. S. Rubber Co., Brit. Patent 560,958 (April 28, 1944). (39) Weick, G., and Tsao, M., Univ. Mich. Hosp. Bull., Ann Arbor, 13, 114 (1947). RECEIVED June 16, 1949. Presented before the Division of Biological Chemistry e t the 114th Meeting of the AMERICAN CHEMICAL SOCIETY, Washington, D . C.
Thermodynamic Properties of Sulfur JAMES R. WEST Mellon Institute, P i t t s b u r g h , Pa. Data on the critical properties, the vapor pressure, and the molecular species present in sulfur vapor were compiled by calculation. Enthalpy and entropy computations were made for the saturated liquid, for the vaporization process, for the saturated vapor, and for the superheated vapor with allowances for dissociation. Similar calculations were made on the volume. The results are shown in tabular and graphical form.
S
ULFUR has been known since antiquity; much knowledge of i t has been acquired since then, but as much or more re-
I
mains unknown. Data relating t o the solid, the liquid, and the vapor forms of sulfur have been published, but the literature has not disclosed any compilation of thermodynamic properties or any Mollier chart. This article describes the computations used t o prepare tables and a chart for sulfur. Rhombic sulfur a t 20" C. and 1 atmosphere w&s taken as the reference state. It is hoped that this work will prove useful t o industrial users of sulfur and will stimulate experimental research on its thermodynamic properties. CRITICAL PROPERTIES OF SULFUR
Temperature. I n the literature the accepted value of the critical temperature is 1040" C. (6). This property was also computed, from the equation for all elements given in the article published by Meissner and Redding (IO),t o be 936" C. The estimated temperature is 10% less than the accepted one. Pressure. Values of the critical pressure of sulfur, with water and mercury as reference materials, were estimated from Duhring lines (2). The method of Calingaert and Davis (9) was next applied. Then, using the procedure described by Othmer ( I I ) , values were found using water, sulfur dioxide, and ammonia, respectively, as reference substances. I n each case the critical temperature reported in the literature was employed. The results are compared in Table I.
The arithmetic average of the values shown in Table I is 116 atmospheres. It is quite apparent t h a t there is considerable deviation in the critical pressure determined by these different methods. This average value may serve estimation purposes in the absence of any other data. Density and Volume. Based on the assumptions that sulfur is diatomic a t the critical state, t h a t the critical pressure is 116 atm., and that the critical temperature is 1040" C., the critical density was calculated from the method of Meissner and Paddison (9) to be 0.393 gram per ml. (24.5 pounds per cubic foot). The reciprocal, or critical volume; is 2.64 ml. per gram (0.041 cubic foot per pound). Based on the assumption that the sulfur molecule a t the critical point is diatomic, the critical volume was estimated from the parachor by the method of Meissner and Redding (IO)t o be 2.42 ml. per gram (0.039 cubic foot per pound). The reciprocal, or critical density, is 0.413 gram per ml. (25.8 pounds per cubic foot). If the unassociated sulfur molecule a t the critical state is considered as monatomic, use of the parachor gives 2.11 ml. per gram (0.034 cubic foot per pound). No value is recorded in the literature for the critical density or the critical volume. It is suggested that the averages of the values for diatomic molecules be used for estimation work. For the critical density the average is 0.403 gram per ml. (25.1 pounds per cubic foot); for the critical volume, 2.48 ml. per gram (0.040 cubic foot per pound).
TABLE I. CRITICALPRESSURE OF SULFUR Method Duhring line (3) Calingaert and Davis (3) Othmer (11)
Reference Substance Water Mercury None Water Sulfur dioxide Ammonia
Critical Pressure, Atm. 163 138 123 92 85
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