Catalytic Hydration of Olefins W. H. SHIFFLER, M. M. HOLM, AND L. F. BROOKE Standard Oil Company of California, San Francisco, Calif.
This paper presents the results of experimental work on the hydration of ethylene and propylene with a sulfuric acid catalyst. Sulfuric acid proved to be an active catalyst for the hydration of ethylene and propylene at relatively low temperatures where the equilibrium is favorable for high yields of alcohols. Typical acid concentrations and temperatures were, respectively, 7'0 per cent and 150' C. for ethylene hydration, and 55 per cent and 115"C. for propylene hydration. Measurement of the equilibrium constant for alcohol formation
T
HE method of producing alcohols by the absorption of olefins in acid and then hydrolyzing the acid liquor has been known for many years. The direct catalytic hydration of olefins, on the other hand, was not studied to any great extent until the 1920's. During the past ten years a number of papers and a larger number of patents have issued on various means for accomplishing the direct catalytic hydration reaction. With the exception of the most recent publications (2, 4, 7, IO), the literature on this subject was reviewed by Ellis (6). Probably the ideal method for hydrating a gaseous olefin, particularly ethylene, is to mix it with the proper amount of steam, pass the mixture over a catalyst, and then condense the hydration product. This method has been the goal of many investigators. However, the majority of the catalysts used have been active only at relatively high temperatures (ZOO" t o 500" C.) where the equilibrium is unfavorable for hydration. To obtain the high yields of product necessary for the commercial application of the process, the equilibrium of the reaction requires a catalyst that is active at low temperatures. Many investigators seem either to have failed to recognize this point or to have been misled by optimistic equilibrium calculations. I n any event, in spite of the recent extensive ljterature, particularly the patent literature, the general picture on practical operating conditions for catalytic hydration of ethylene and propylene is still rather confusing. Several years ago the authors made an experimental investigation of the hydration of ethylene and propylene, particularly on the use of sulfuric acid as the catalyst. Some of the principal conclusions resulting from this work have been outlined in issued patents (II), but practically no experimental support for the patent disclosures has been published. The primary object of the present paper is to report and discuss this experimental information. A secondary object is to review some of the recent articles and patents which appear pertinent t o commercial manufacture of ethyl and isopropyl alcohols by sulfuric acid catalysis. No attempt at a comprehensive literature survey on all hydration catalysts will
under these conditions gave ILp = 0.049 for ethylene hydration and ILp = 0.1 for propylene hydration. These values are in fair agreement with published data. Operation under pressure increased the rate of alcohol production and the concentration of alcohol i n the product, and decreased the amount of water required for maintaining the acid concentration constant. Pressure also increased the ratio of ether to alcohol in the product with ethylene but not with propylene. Some phases of commercial application of the process are considered briefly.
be made, and reference to literature that appears to be definitely out of line with the present experimental data purposely will be omitted.
Experimental Procedure Atmospheric pressure experiments were conducted in a 3 X 40 cm. vertical glass column packed with 0.3-cm. glass beads in the bottom half section. Sulfuric acid of the desired strength was charged in volume sufficient to cover the beads. Pure (99 per cent plus) olefin gas, either ethylene or propylene, was metered through a capillary flowmeter and bubbled up through the sulfuric acid. Water was added along with the olefin in volume sufficient to maintain the acid strength constant. The column was heated electrically, the temperature being measured by a thermometer immersed in the acid. The exit gaseous mixture of olefin, alcohol, ether, and water was conducted first through an iced condenser and then through a condenser cooled with an alcohol-solid carbon dioxide mixture. Refluxing of water and alcohol back to the acid was avoided by slight superheating of the va ors between the top of the acid and the downward turn of the &livery tube leading to the condensers, Analyses of the condensates for alcohol and ether were estimated from pycnometer specific gravity determinations and comparisons with established specific gravities for known solutions. In some cases the distribution of hydration product between ether and alcohol was neglected, and the lowering in specific gravity was assumed t o be due to alcohol only. In runs made with the object of measuring both ether and alcohol production, the specific gravity of the condensate was measured before and after complete extraction of the ether with petroleum naphtha. Under some conditions the' condensate separated into two phases, an upper ether phase and a lower aqueous phase. In such cases the volume of alcohol extracted by the ether was neglected, and the ether extracted from the aqueous phase by petroleum na htha was added to that which separated directly. The procefure in the pressure experiments was essentially the same except that glass-lined steel equipment of somewhat larger dimensions was used and that the rate of olefin feed was estimated from the exit gas rate and from the rates of production of alcohol and ether. Hydration of Ethylene Preliminary experiments at atmospheric pressure with different strength acids showed that a reasonably rapid rate of hydration was obtained at 150" C. with 70 per cent sulfuric 1099
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 31, NO. 9
TABLEI. HYDRATION OF ETHYLENE Product Water Moles Moles Moles Vol. % Vol.ethsr/ Charged CZH4 HzO alcohol alcohol vol. alcohol Effect of Acid Conceni;ration, Temperature, and Pressure 1.38 Pure 1.41 0.025 5.4 11 72 150 1.0 1.0 Pure 1.50 127 72 18 0.33 0.008 7.4 .. Pure 0.83 72 150 1.0 28 0.78 0.017 6.6 Pure 1.00 65 1.0 42 127 0.85 0.012 4.5 Pure 1.15 1.0 49 65 127 0.87 0.0052 1.9 1.0 Pure 0.99 65 127 0.76 0.0055 2.3 50 65 150 5 . 0 Pure 9 .5 0:i 73P Pure 65 150 6.4 10.6 0.45 74P 65 150 7 . 8 Pure . . . . 12.4 0.54 75P 3.0 Pure 2:is 70 150 . . ~ 0:25 0.032 29.1 0.54 1P Pure 2.50 70 150 3.0 0.32 0.0347 25.9 0.66 2P Pure 2.50 3.0 70 150 0.36 0.0316 21.8 3P Pure 1.04 65 150 3.0 0.51 0.014 8.3 5P Pure 1.35 160 3.0 0.51 0.014 8.1 65 6~ Pure 2 . 1 8 150 3 . 0 0.89 0 , 0 3 4 11.1 70 1 5 ~ Measurement of Kp 27 72 150 1.0 Pure 0.83 0.77 0.019 7.4 .. 28 72 150 1.0 0.83 0.78 0.017 6.6 29 72 150 0.57 0.014 7.4 0.46 30 72 150 0.011 7.4 .. 0.22 0.005 7.1 .. 31 72 150 Effect of Volume of Acid Pure 8 72 150 1.0 0.35 0.45 0.0043 3.1 Pure 9 72 150 1.0 0.26 0.72 0.0075 3.3 .. Pure 1.38 10 72 150 1.0 1.34 0.0157 3.6 11 72 150 1.0 Pure 1.38 1.41 0.0250 5.4 Volume alcohol per volume of apparatus per 24 hours. b 1100-00. packed tower: beads coated with acid. c 150-cc. packed tower; filled with acid.
Run NO.
Catalyst, Wt. % Has04
Tzmp., C.
Total Pressure, Atm.
Kp
.. ..
.. ..
.. ..
...
... ...
...
.. .. ....
.. ..
...
... ... ...
Kp =
pC2H60H (pressure in atmospheres) pHzO X pC&4
for several runs, in which the equilibrium was approached by means of both the synthesis and decomposition reactions, was 0.049. This value is in fair agreement with that shown by Sohumann and Aston (IO) in their plot of the equilibrium data obtained by several investigators. The results of five representative determinations are included in Table I. Tests were also carried out to determine the effect of pressure, since consideration of the equilibrium involved indicated that pressures above atmospheric would be beneficial.
1.8 0.6
0.124 0.038
1.2 0.5 0.5 0.2
0.062 0.022 0.028
1.5 1.4 1.3 1.4 1.0 1.6
0.12 0.27 0.25 0.24 0.20 0.27
....
...
... ...
...
0.049 0,043 0.051 0.046 0.057
... ... ...
... ... .. .. ..
1.2 2.9 1.1 1.8
.. .. ..
acid. With weaker acids the rate of production as well as concentration of alcohol in the products was lower. For example, a comparison of the results of runs 18 and 15p with runs 49 and 6p, respectively, in Table I demonstrates this point. The stronger acids tended to polymerize the ethylene and become charred if temperatures capable of giving a rapid rate of production were employed. The rate of production from an apparatus of given size was observed to vary with the volume of acid present. The hydration of the olefin is the result of two reactions occurring simultaneously; the first consists of absorption of the olefin in acid, and the second, the distillation (hydrolysis) of the alcohol from the acid. The slower reaction limits the rate of hydration. Under the particular conditions of acid strength, temperature, and degree of contacting reported here, the hydrolysis step was shown to be the limiting reaction. The heading "Effect of Volume of Acid" (Table I) gives the results of experiments with a n 1100-cc. bead-packed tower, in which the beads were coated only with a film of acid, and a 150-cc. tower in which the beads were covered with acid (approximately 50 cc.). I n spite of the greater volume, the rate of alcohol production in the larger apparatus was less than one tenth of that obtained with the smaller equipment in which there was more acid. With more dilute acid used as catalyst, it might be expected that the absorption step eventually would limit. This point has not been studied experimentally. The above procedure was used to measure the equilibrium in the hydration of ethylene to ethyl alcohol at 150' C. The ' average value of
Vol. Alco% CzH4 hol/Vol. Hydrated Acid/24 Hr.
...
....
.... .... .... ....
....
0.001a9 b 0,020a,
0
0.0036Qrb 0.042"2 C
A marked effect was the increase in the ratio of ether to alcohol with increase in pressure. At 65 pounds gage pressure the product contained in some cases as much as 2 volumes of ether per volume of alcohol; a t atmospheric pressure the ratio of ether to alcohol varied from zero to about 0.5. Since the theoretical per cent conversion of ethylene to ethyl alcohol is practically independent of the ethylene pressure, the total conversion of ethylene may be increased appreciably by operation under pressure if a mixture of the two hydration products is desired. Since both the formation of alcohol and ether are equilibrium reactions, the process can be operated to produce only one of the hydration products by recycling the other. If alcohol is the desired product, the ether is recycled, and if ether is to be the product, the alcohol is recycled. The conflicting values given in the literature for the equilibrium constants for the formation of ether from ethyl alcohol prevent accurate calculation of the equilibrium conversion of ethylene to alcohol and ether a t different pressures for comparison with the results of this investigation. However, if the value of 6.2 for K p = (pC2H50C2H~X pHzO)/ (pCzH50H)2obtained by van Alphen (1) a t 160' C. for the conversion of ethyl alcohol to ether is assumed to be reasonably correct and to hold for a slightly lower temperature, the theoretical conversion of ethylene and the ratio of ether to alcohol in the product would approximate the values given in the following table when using 70 per cent sulfuric acid a t 150" C.: Total pressure, atm. Partial pressure, atm.: Water Alcohol Ethylene Ether yo conversion of ethylene: Total T o alcohol To ether Product: Vol. % alcohol (ether-free) Ratio ether alcohol
1
2
5
10
0.6 0.01137 0.3867 0,0013
0.6 0.03949 1.3432 0.0161
0.6 0.1213 4.1261 0.1522
0.6 0.2500 8.5033 0.6458
3.16 2.84 0.32
3.90 2.76 1.14
6.06 2.69 3.37
8.57 2.39 6.18
5.9 0.206
18.1 0.735
41.4 2.37
62.0 4.68
These calculated ratios of ether to alcohol in the product are slightly higher in general than those obtained experimentally. The calculated ratios and the volume per cent alcohol
SEPTEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
in the ether-free product are plotted against pressure in Figure 1. Experimental confirmation of the effect of pressure is shown in Table I. Experiments lp, 2p, and 3p produced solutions containing from 22-29 per cent alcohol as compared to 5-7 per cent for products made in atmospheric pressure runs 11 and 18.
-
p
0
2
4
B
6
IO
TOTAL PRESSURE- ATMOSPHERES
1101
The initial experiments consisted of determining the optimum acid strength and temperature for operation a t atmospheric pressure. An acid of less than 50 per cent concentration was found to be a relatively inactive catalyst. Solutions containing more than 60 per cent sulfuric acid caused appreciable polymer formation, resulting ultimately in a lower yield of alcohol. The optimum acid concentration was about 55 per cent sulfuric acid. With this strength of acid, 115" C. was selected as the optimum operating temperature, and it gave a clean reaction and no substantial reduction of the acid. The selection of this particular temperature was somewhat arbitrary since temperatures between 90" and 135" C. were satisfactory. The use of the higher temperature was considered unfavorable because of the decrease in the equilibrium conversion of propylene. At the lower temperatures the rate of alcohol production was decreased. The results of typical runs are given in Table 11. The effect of pressure on the hydration of propylene was much the same as with ethylene; increasing the pressure raised both the reaction rate and the concentration of alcohol in the product, Comparison of experiments 3 and 4 with 15 and 16 of Table I1 shows that raising the pressure from 1 to 3 atmospheres increased the concentration of alcohol in the product from 9-10 per cent to about 17 per cent. If
FIGURE 1. PRESSURE vs. CONCENTRATION OF ALCOHOL AND RATIOOF ETHERTO ALCOHOL IN PRODUCT FROM CATALYTIC HYDRATION OF ETHYL~NE WITH 70 PERCENTSULFURIC ACIDAT 150' C.
The rate of reaction also increased with increase of pressure, the rate of ethylene absorption being approximately proportional to the ethylene pressure. With 70 per cent acid a t 150" C. and 65 pounds gage pressure, the rate of reaction corresponded to about one volume of hydration products (alcohol and ether) per volume of acid per 24 hours. I n the runs a t 150" C. and higher there was some reduction of the acid to sulfur dioxide. The following table gives the results of several quantitative measurements of sulfur dioxide formation. The acid consumption is expressed as volume per cent of original acid charged and as volume consumed per volume of alcohol produced : % HzSO4 Temp.
Pressure
c.
Atm.
179 182 181 181 150 150 165
5.0 5.0 6.5 7.8 3.0 5.5 5.5
Charged 64.5 64.5 64.5 64.5 70.0 70.0 70.0
Vol. Acid Consumed Vol. Alcohol Reduced/24 Hr.
Vol. % ' Acid 1.3 1.1 1.2 6.7
... ... ...
0.040 0.017 0.020 0.131 0.012 0.035 0.120
On the basis of these data it was concluded that a t temperatures above 180" C. with 65 per cent acid and above 165" C. with 70 per cent acid the reduction of acid becomes appreciable. Increased pressure also tends to increase the acid consumption. Although no quantitative measurements were made, the amount of acid consumed appeared to decrease with continued use of the acid. Except in the most severe cases the reduction of acid was so small that it would not influence appreciably the cost of commercial production of alcohol by sulfuric acid catalysis.
Hydration of Propylene The experimental work on propylene hydration was carried out in the same equipment used for ethylene. The ethylene experiments provided a useful background which facilitated the tests with propylene.
1000 T"H .
FIGURE2. EQUILIBRIUM DATAFOR HYDRATION OF PROPYLENE TO ISOPROPYL ALCOHOL
equilibrium had been reached in each case, the difference in alcohol concentration would have been greater, as will be shown later. A distinct difference between the hydration of ethylene and propylene was the effect of pressure on ether production. Raising the pressure did not produce noticeable quantities of ether, as was the case with ethylene. The equilibrium constant for the hydration of propylene to isopropyl alcohol was measured a t 115" and 127" C. Approaching equilibrium from both the synthesis and decomposition sides gave average values of 0.104 and 0.052 for K p a t 115" and 127" C., respectively. These values, as Figure 2 shows, correlate fairly well with the values obtained a t higher temperatures by Stanley, Youell, and Dymock (15). The pertinent data on the runs for determining the equilibrium constants are also included in Table 11. On the basis of the equilibrium data the maximum conversion of propylene under the optimum operating conditions (55 per cent acid a t 115" C.) is 5.6 per cent. For the same conditions the effect of pressure on the concentration of alcohol in the product is shown graphically by Figure 3. The maximum concentration of alcohol in the product for operation a t 1, 5, and 10 atmospheres total pressure is, respectively, 15,59, and 82 per cent by volume.
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TABLE11. HYDRATION OF PROPYLENE Run No.
Catalyst,
Temp.,
Total Pressure, Atm. 1 1 1 1 1
Water
OC. Charged 115 Pure 3 55 115 Pure 4 55 115 50 Pure 5 115 50 6 Pure 55 115 7 Pure 115 1 20 vol alcohol 55 8 15 vol: 55 115 1 9 128 8 . 8 vol. 1 59 13b 128 1 4 . 4 vol. alcohol 14C 59 121 Pure 55 3 15 I21 Pure 55 3 16 a Volume of ether per volume of alcohol nil in each case. b 0.0122 mole inert. C 0.0112 mole inert'.
89 %
%$c
Moles
CsHs 0.46 0.42 0.21 0.50 0.412 0,213 0.380 0.222 0.213
... ...
The hydration of propylene was a much faster reaction than the hydration of ethylene, although the equilibrium is more favorable for the ethylene. The following representative examples a t one atmosphere pressure illustrate this point : Olefin
Temp.
c.
%
Ethylene Propylene
127 115
72 56
Acid Strength
Vol. Alcohol/Vol. Acid/24 Hr. 0.038 0.32
Even though the temperature and the strength were more favorable for the ethylene, the rate of ethyl alcohol production was only about one eighth that of isopropyl alcohol.
ProductQ
Moles Hz0
0.61 0.61 0.47 0.57 0.400 0.240 0.370 0.360 0.363
... ...
Moles
alcohol 0.016 0.0150.006+ o.o09+ 0.010f
0.011+ 0.017+ 0.0067 0.007+
.... ..
Vol o/
alcdho? 10.2 9.3 5.3 6.5 9.8 16.6 16.6 7.3 7.6 16.9 17.3
KP
... ... ... 0 : io8
0.101 0.0493 0,0547 ,.
VOl. Alcohol/ C&a Vol. Acid/ Hvdrated 24 Hr. 0.32 3.5 0.32 3.6 0.28 3.0 0.17 1.9 2.5 5.3 4.6
... ... ... ...
.... .. ..
0:25 0.30
An important objection to the attainment of high olefin conversion per pass is that the alcohol content of the condensate is relatively low unless enormous pressures are used or a further compromise is made in temperature and acid strength. Thus, in the example just cited, the alcohol content of the condensate was reported as only about 10 per cent by volume, necessitating vaporization and condensation of about 9 gallons of water per gallon of alcohol made. I n order to minimize this objection, the use of indirect heat exchange between gases entering and leaving the reaction vessel has been proposed (8). Similarly, an ingenious cycle which eliminates the indirect feature of the heat exchange has been described by Rowland and Wallin (9).
Hydration of Higher Olefins The catalytic conversion of normal butenes to secondary butyl alcohol was tested briefly with temperatures from 25 to 115" C. and acid strengths from 30 to 55 per cent. The results of these preliminary experiments indicated that this reaction was not feasible with a sulfuric acid catalyst because of the excessive losses of butenes by polymerization. On this account the catalytic hydration of isobutene was not attempted. No experimental work was done with olefins higher than butene.
Commercial Applications
As far as we are aware, no applications of sulfuric acid catalysis to commercial synthesis of ethyl and isopropyl alcohols from the corresponding olefins have been reported. However, numerous patents (3, 4, 6-9) directed to specific practical phases demonstrate the general interest in the subject. One of the principal problems is the attainment of a reasonably high conversion of olefin per pass. Equilibrium considerations show that conversion per pass may be increased b y decreasing temperature and decreasing acid strength (increasing water vapor pressure), but is practically independent of olefin pressure. On the other hand, the attainment of a high rate of reaction forces the operation to be conducted under conditions of moderately high temperature and acid strength. The obvious preferred procedure is to compromise o n temperature and acid strength and to increase the rate of reaction by operating under relatively high pressure. Metzger (8) reports that in operation a t 250" C. and 600 pounds per square inch gage pressure, with an acid strength of 41 per cent, a 10 per cent conversion of ethylene to ethyl alcohol is attained a t a rate corresponding to production of 12 volumes of absolute alcohol per volume of acid catalyst per 24-hour day. When operating for production of alcohol only, an added advantage of using such relatively weak acid as catalyst is the fact that practically no ether is formed.
TOTAL PRESSURE-ATMOSPHERES
FIGURE 3. EFFECTOF PRESSURE ON THE CONCENTRATION OF ALCOHOL IN THE CATALYTIC HYDRATION OF PROPYLENE T O ISOPROPYL ALCOHOL WITH 55 PER CENTSULFURIC ACID AT 115" C.
Under the preferred operating conditions of temperature and acid strength, sulfuric acid is highly corrosive to the metal equipment required for high-pressure operation. An expedient for minimizing this objection has been described (8); the principle is to maintain the metal shell of the reaction vessel at a temperature much lower than that of the acid catalyst by loosely inserting insulating bricks of silica or other acid-resistant material. The temperature of the shell may thus be lowered to the point where a simple lead lining suffices for protection of the steel. One of the chief uses of the processes described above is the conversion of the ethylene and propylene in petroleum gases to the corresponding alcohols. The Czfraction of such gases normally contains both ethylene and ethane; the CBfraction contains both propylene and propane. In cyclic operation the paraffin builds up, and either a rejection of some olefin or a pre-separation of olefin from paraffin is required. I n the classical two-step absorption and hydrolysis sequence, complete utilization of the olefin may be attained without preseparation from paraffin. Economic calculations which need
SEPTEMBER, 1939
INDIJSTRIAL AND ENGINEERING CHEMISTRY
not be detailed here have shown that in the case of ethylene hydration the cost of acid concentration in the two-step process far more than offsets the cost of gas purification for the catalytic operation. On the other hand, in the erne of propylene hydration the authors are inclined to favor the two-step absorption and hydrolysis, particularly when the absorption step is accomplished by liquid-phase reaction (f8).
Literature Cited (1) Alphen. J. YSO, Rec. tmu. chim.,49,754 (1930). (2) Applehy. Glass. and Horsley, J . SOC. C h m . Id.. 56, 279T
1103
Ellis, "Chemistry 01 Petroleum Derivatives," Vol. 2.. pp. 28S97, New York, Reinhold Publishing Corp., 1937. Frenois, U. S. Patent 2,055,720 (1936). Lewis. I M . ,2,130,669 (1938). Metsar. Ibid., 2,021,564 (19351; 2,050,442,Reissue 20,505 (1937): 2,050,443, Reissue 20,474 (1937): 2,087.290 (1937): and 2,050.445, Reissue 20,739 (1938). Rowisnd and Wallin, Ibid.. 2.142.036 (1938). Sohumann and Aaton, J . Chem. Phw., 6,480 (1938). Shifflerand Holm,Jbid., 1351,740 (1934) and 2,052,806 (1936). Shiffler,Holm, and Anderson, Ibid.. 1,988,611 (1935). Stanley, Youcll. and Dymock, J . Soc. C h m . Id., 53, 205T (1934).
,109n l_"-.,.
(3) Bdoar, U. S. Patent2.044.417 (1936). (4) Dreyfus, Ibid.. 2.a45.842 (1936)arid 2,093,426 (1937).
P~EJ~NT boioie E D the Division of Petroleum Chemistry at the 97th Meeting of the American Ciiemical Society, Baltimore, Md.
ANTIOXIDANTS FOR CASTOR OIL GERALD 0. INMAN Rock Island ilrsenal, Rock Island, Ill.
C
ASTOR oil as a lubricant in ordnance niatdriel has proved very advantageous in certain instances, since it can be used in contact with rubber packings with no harmful effects on the latter. A disadvantage frequently encountered, however, is that, witlh age, the castor oil becomes oxidized, attacks brass parts, and causes undesirable corrosion. It is not nnconnnon for castor oil which bas been applied to a lubricator of a mechanism in storage to increase in acidity from a value of 2 to above 35 in two years. The green color which develops in the oil and on the lubricators is evidence of corrosion. These brass parts are attacked more rapidly by castor oil of high acidity than by oil of low acidity. It was with the hope of finding an inhibitor which would prevent the oxidation of castor oil that this work was nndertaken. Yamaguchi (4)subjected olive oil and castor oil to oxidation. Progress of the reaction via8 followed by the determination of the iodine number. He showed that the addition of minut.e amounts of diphenylhydrazine greatly prolonged the latent period and that the length of the latent period was approximately proportional to the quantity of diphenylhydrazine added. KO subsequent work has been reported on antioxidants for castor oil. However, considerable investigative work has been done by Tariaka arid Nakamura (8) on antioxidants of classes of oils such as linseed, soybean, cottonseed, and others. Phenols were arranged by tliesc authorsaccording to their antioxygenic activity as follows: pyrogallol, hydroquinone, catechol, anhydrous phloroglucinol, resorcinol, phloroglucinol dihydrate, and phenol. With nitro- and chlorophenol the activity depends upon the position of the group or atom. The action of aniline and its methyl, nitro, and chloro snbstitution products upon the oxidation of linseed oil was examined. The changes in properties were det,erinined by comparing the specific gravity, index of refraction, iodine number, and viscosity before and after treatment. Aniline, xylidine, 0- and ptoluidine are ant.ioxidants or pro-oxidants, meording to conditions.
The effect oi antioxidants on the autoxidation of fats has also been studied by Mattill (8). He st,udied the rate of oxygen uptake by a standard mixture of lard and cod liver oil in the presence of various aromatic hydroxyl derivatives. He observed that if there are two hydroxyl groups in the ortho or para position, the antioxygenic activity is high; that the meta compounds are inactive; and that alphanaphthol is a much more effective antioxidant than the beta derivative.
Experimental Procedure In this work the antioxygenic activity of the various compounds towards castor oil was measured by following the rise in acidity of the oil. The action was accelerated by passing oxygen through tho oil held a t an elevated temperature. The general layout of tlie apparttt~usis shown in Figure 1. The apparatus consists of two main parts-the gas measuring device which regulates the amount of oxygen going to each sample of oil and the constnnt.teniperature bath which holds tlie oil sample tubes. This apparatus is capable of handling six samples of oil at one time. The oxygen is drawn from a commercial cylinder of oxygen through the pressurereducing valve, shown at the left of Figure 1. From here the oxygen
