1596
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
Vol. 43, No. 7
LITERATURE CITED
day without methionine, and run 5 shows the values when supplemented with methionine. These tests indicate that food-yeast protein and protein in Fusarium is deficient in methionine but when supplemented with methionine give weight gains equivalent to casein.
Frost, D. V., and Sandy, H. R., Federation Proc., 8 , 383 (1949). Frost, D. V., and Sandy, H. R., J . Nutrition, 39, 427 (1949). Harris, E. E., and Beglinger, E., IND.ENG. CHEM.,38, 890
CONCLUSIONS
Harris, E. E., Hannan, M. L., and Marquardt, R. R., Ibid., 40,
(1046). ~-_,. -.
Harris, E. E., Hajny, G. J., Hannan, M. L., and Rogers, 9. C., Ibid., 38, 896 (1946).
Six strains of food yeast have been grown continuously and rapidly in high yield and high protein content on wood hydrolyzate with almost complete utilization of sugar and volatile acids. The six yeasts, a sample of sulfite liquor food yeast, Fusarium grown on wood sugar, and casein were fed rotein-depleted adult rats to determine their repletion value. &he food yeasts were found t o have 50 t o 85% of the value of casein. Food yeast and Fusarium supplemented with methionine gave repletion values equivalent to casein and indicate a high value as a protein food. ACKNOWLEDGMENT
The authors acknowledge the assistance given them by H. T . Scott and Carl H. Krieger in planning the protein evaluations, in providing the space for the tests a t the Wisconsin Alumni Research Foundation laboratory, and in evaluating the information obtained. The authors wish t o thank A. J. Wiley of the Sulfite Pulp Manufacturers’ Research League, Inc., Appleton, Wis., for the sample of sulfite yeast, and D. K. Richardson of the Schlitz Brewing Co., Milwaukee, Wis., for the brewer’s yeast used in these testa. This experimental work was conducted with funds provided by the Research and Marketing Act.
2068 (1948).
Harris, E. E., Hannan, M. L., and Marquardt, R. R., Paper Trade J., 125, 34 (1947). Harris, E. E., Hannan, M. L., Marquardt, R. R., and Bubl, J. L., IND.EX+. CHEM.,40, 1216 (1948). Harris, E. E., Saeman, J. F., Marquardt, R. R., Hannan, M.L., and Rogers, S. C., Ibid., 40,1220 (1948). Johnson, M. C., and Harris, E. E., J . Am. Chem. SOC.,70, 2961 (1948).
Peterson, W. H., Snell, J. F., and Frazier, W. C . , IND. ENQ. CHEM.,37, 30 (1946).
Rose, W. C., Science, 86, 298 (1937). Saeman, J. F., A n a l . Chem., 19,913 (1947). Saeman, J. F., Harris, E. E., and Kline, A. A,, IND.ENQ.CHEM., ASAL. ED.,17, 95 (1945). Saeman, J. F., Locke, E. G., and Dickerman, G. K., U. S. Dept. Commerce, F I A T Rept., 499 (Nov. 14, 1945). Sohaffer, R. A., and Somogyi, N., J. Biol. Chem., 100, 695 (1933). RECEIVED September 5, 1950. Presented before the Division of Agrioultural and Food Chemistry at the 118th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
Catalytic Esterification of Olefins with Organic R. D. MORIN AND A. E. BEARSE BatteZle Memorial I n s t i t u t e , Columbws, Ohio T h e direct esterification of olefins with organic acids offers an attractive means of preparing many types of esters. I n order to obtain an efficient and practical process, a more active and effective catalyst was required than has previously been used, and the objective of this work was to find such a catalyst. Experimental results have shown that a mixed catalyst comprising boron fluoride and hydrogen fluoride is particularly effective in promoting the esterification of olefins with organic acids. Isopropyl acetate has been prepared from propylene and acetic acid in SOYO yield using this catalyst, and a number of other esters have also been pre-
pared in good yield from various olefins and organic acids by this method. Comparison of the boron fluoridehydrogen fluoride catalyst with other acid catalysts has shown i t to be superior for the catalytic esterification of olefins. Catalyst recovery and reactor corrosion were also studied. Etherification of olefins is also promoted by boron fluoride and hydrogen fluoride. Discovery of a novel and efficient catalyst, boron fluoride-hydrogen fluoride, for the direct esterification of olefins with *organic acids makes this process attractive for the preparation of esters from by-product refinery olefins.
T
one of the raw materials. I n those cases where the alcohol ia derived from a n olefin by hydration, a processing step is eliminated. For example, in the preparation of isopropyl acetate from propylene by the usual method (7), isopropyl alcohol is obtained by the hydration of propylene with sulfuric acid and the ester is then formed by reaction of isopropyl alcohol with acetic acid in the presence of sulfuric acid.
HE production of esters by the catalytic esterification of olefins with organic acids offers a possibility of converting
by-product refinery olefins to more useful and valuable products. The esters t h a t can be prepared by this method have well established uses as solvents, plasticizers, and chemical intermediates. ilt the present time, nearly all commercially produced esters are obtained by the conventional esterification reaction of an alcohol with a n organic acid or anhydride in the presence of a mineral acid catalyst. This reaction is sometimes quite slow, and since it is reversible, some means of driving i t to completion usually must be employed. I n the majority of processes, this involves removal of water as it is formed. The direct esterification of olefins t o form organic esters offers many advantages over conventional esterification methods. I n the f i s t place, a cheap olefin replaces a more expensive alcohol as
CHaCH=CHs (CHa)GHOH
+ HzO -+ (CHa)&HOH &SO4
+ C H I C O OHzS04 H N CHaCOOCH(CHa)z + HzO
I n the direct catalytic olefb esterification process, the ester is obtained directly from propylene in one step. CHaCH=CH,
+ CHBCOOH + catalyst
CHaCOOCH(CH3)z
July 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
The direct esterification of olefins not only eliminates a process step but is a more rapid reaction under certain conditions, and, with a n efficient catalyst, goes essentially to completion without having to remove water of esterification. Furthermore, the desired ester is obtained directly, and recovery and purification of the product are readily accomplished. A final advantage is t h a t the catalyst can be recovered and reused for preparation of more ester from fresh olefin and organic acid. In spite of all of these advantages over conventional methods of esterification, the preparation of esters by reaction of olefins with organic acids has not been used extensively because of the inefficiency of most of the catalysts which have been tried for this reaction. The addition of organic acids to olefins in the presence of strong acid catalysts has been known for many years. The classical example of this reaction is the preparation of bornyl acetate from a terpene hydrocarbon, camphene or pinene, and acetic acid in the presence of sulfuric acid ( 2 ) or boron fluoride ( I d ) . Isobutylene has been converted to tert-butyl acetate in about 20y0 yield by reaction of isobutylene with acetic acid in the presence of zinc chloride (14). A number of processes and catalysts have been proposed for the direct combination of ethylene and secondary olefins with organic acids, but the yields were low and the catalysts were inefficient. Reaction of propylene with a mixture of sulfuric and acetic acids gave isopropyl acetate in 27% yield and isopropyl alcohol in 53y0yield (28). Nieuwland et al. (4) described the reaction of propylene with acetic, monoand dichloroacetic, and benzoic acids in the presence of boron fluoride. The reactions were carried out at atmospheric pressure, and in the case of isopropyl acetate the yield was about 7%. Schneider (23) also prepared esters of olefins by reaction with carboxylic acids in the presence of boron fluoride. secAmyl acetate was obtained in about 50% yield by this method. Preparation of ethyl acetate in unstated yield by reaction of acetic acid with ethylene in the presence of boron fluoride and hydrogen chloride a t 250" C. has been reported (IS). Preparation of esters by reaction of olefins with organic acids in the vapor phase over various catalysts a t elevated temperatures has not proved successful in obtaining high conversion to esters (5, 6, 16, 17, 20,35, 26). Among the many acid catalysts which have been suggested for the esterification of olefins with organic acids are sulfuric acid (8-10, 27), boron fluoride (S, 4 , 1.9, 2S), titanium chloride (2S), boron fluoride etherate ( 2 4 ) , boron fluoride dihydrate (19), and dihydroxyfluoboric acid (16, 2 2 ) . All of these catalysts will promote esterification of olefins to a certain extent, but the yield of ester is low, long reaction times or high reaction temperatures are required, and the amount of catalyst needed to effect reaction is large. In this paper, the use of a particularly efficient catalyst, boron fluoride-hydrogen fluoride ( I ) , for esterification of olefins is described. Many of the objections to the direct olefin esterification methods can be overcome by using this catalyst which is capable of promoting a high conversion of olefins to esters in a short time under mild operating conditions and in fairly low concentration. The results obtained in this investigation have demonstrated t h a t direct olefin esterification is potentially an efficient and economical means of obtaining esters from petroleum by-product olefins. EXPERIMENTAL TECHNIQUE
The catalytic olefin esterification was carried out batchwise and on a small scale using pressure equipment. Use of the latter was necessary to contain the catalyst and the lower olefins at the reaction temperature, which varied from 60" to 150" C., depending on the olefin. The following procedure for the preparation of isopropyl acetate by reaction of propylene with acetic acid in the presence of boron fluoride and hydrogen fluoride is typical. A solution of boron fluoride in acetic acid was prepared by Fooling 480 grams (8 moles) of glacial acetic acid in an ice bath
1591
and allowing 25 grams (3% of weight of reactants) of gaseous boron fluoride from a cylinder t o be absorbed while swirling the solution. The heat of the reaction was dissipated with an ice bath. T o the ice cold solution were added cautiously 25 grams of ice cold liquid anhydrous hydrogen fluoride previously condensed from a cylinder of hydrogen fluoride. The solution of boron fluoride and hydrogen fluoride in acetic acid was charged t o a 3-liter Aminco high pressure bomb, which was quickly sealed, and a pressure valve was attached t o the head of the bomb. The propylene, 336 grams (8 moles) (Phillips C.P. grade), was charged as a liquid to the bomb from an inverted cylinder which had been previously pressured with nitrogen to about 250 pounds er square inch gage in order to force in the liquid propylene. %he amount of propylene charged was measured by weighing the bomb and its contents on a sensitive platform scale before and after charging. The charged bomb was placed in the heating shell of a rocking autoclave and heated to about 90' t o 100' C. without shaking. The temperature was peasured with a Chromel-Alumel thermocouple and a Leeds & Northru potentiometer. At a temperature of 90" t o 100' C., shafing was begun, and a rapid reaction ensued, as evidenced by a drop in pressure and a rise in temperature to about 110' C. The reaction was usually complete within 15 t o 30 minutes, at which time the pressure had dropped t o a constant value of about 75 pounds per square inch gage. The initial pressure a t around 100' C. was usually 350 to 400 pounds per square inch gage. When the bomb had cooled t o room tem erature, residual gases were bled off t o the atmosphere. The gomb was opened and the crude liquid product, consisting chiefly of isopropyl acetate, was removed. Two methods were used to recover the pure ester. I n the first, the crude product was treated with ice and 5Oj, sodium hydroxide, and the upper ester layer was separated, washed with aqueous 5% sodium carbonate and with water, dried over Drierite, and distilled. The fraction boiling at 87' t o 89' C. at 745 mm. was collected as isopropyl acetate; the yield was 610 to 655 grams (75 to 8070 of theoretical). An alternate procedure for recovery of pure isopropyl acetate was the direct fractional distillation of the crude reaction mixture. An all-copper fractionating assembly was used for this purpose. I n this distillation, a forerun consisting of unchanged propylene, isopropyl fluoride, and hydrogen fluoride was obtained. Isopropyl acetate boiling a t 87" t o 89" C. at 745 mm. was taken overhead next, leaving a residue of acetic acid and acetic acid-boron fluoride complex [(CH&OOH),.BF,] ( 2 1 ) . Obviously the latter method for recovering the ester would be used on a larger scale in order to conserve catalyst. The first mentioned procedure was used, with minor modifications, for all of the olefin esterification reactions. When ethylene was the olefin, more vigorous conditions were necessary. For the preparation of ethyl acetate from ethylene and acetic acid, a higher pressure (1750 pounds per square inch gage), higher temperature (150" C.), and a higher catalyst concentration (loyo each of boron fluoride and hydrogen fluoride) were required. For higher olefins, such as the butenes and pentenes, reaction temperatures of 50" to 60' C. sufficed. EXPERIMENTAL RESULTS
A number of esters of acetic acid were prepared by the catalytic esterification of various olefins with acetic acid in the presence of a boron fluoride-hydrogen fluoride catalyst. Table I shows the essential details.
TABLEI. ESTERIFICATION O F LOWEROLEFINS ACIDIN
WITH
ACETIC
THE PRESENCE OF BORON FLUORIDE-HYDROGEN FLUORIDE
Catalyst Reaction Reaction Concn., Temp., Time, %" C. Hours 10 150 3 3 90-100 0.5 3 60 1 3 BO 1 3 100 1 6 150 2
Yield, Ester Formed % Ethyl acetate 50 Isopropyl acetate 80 sec-butyl acetate 50 sec-amyl acetate 52 Cyolohexyl acetate 62 0-Chloroisopropyl 32 acetate a Catalyst concentration is expressed as per cent each of BFs and H F based on the total weight of olefin and acetic acid. Olefin Ethylene Propylene 1-Butene 1-Pentene C clohexena A 6yl chloride
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INDUSTRIAL AND ENGINEERING CHEMISTRY
In these experiments the molar ratio oi olefin to acetic acid was unity. A chlorinated olefin, allyl chloride, was more difficult to esterify than were simple olefins. In all cases of esterification of olefins, the ester formed was the product expected from Markownikoff's rule. Thus, propylene formed isopropyl acetate, and 1-butene formed seobutyl acetate. The products obtained by this method were all water-white, pleasant-smelling liquids, distilling over a narrow range, and in all respects identical with the esters formed by conventional esterification methods. Table I1 illustrates the applicability of the olefln esterification reaction to a number of different organic acids. Propylene was the olefin used and the catalyst was boron fluoride-hydrogen fluoride.
Vol. 43, No. 7
TABLE It'. COI\IPBRISOP\' O F BORON FLUORIDE-HYDROGEN FLUORIDE WITH OTHER -kCIIlIC CATALYSTS FOR ESTERIFICATION OF PROPYLENE WITH ACETIC ACID Yield of Catalyst Reaction Reaction Isopropyl Concn., Tfmp., Time, Acetate, %" C. Hours % 6 150 2 5 6 100 5 0 6 100 3 0
Catalyst Zinc chloride Aluminum chloride Aluminum chloride-hvdroaen . chloride Sulfuric acid 6 150 5 1 Fluosulfonic acid 3 100 2 5 Fluoboric acid 3 100 1.5 40 Boron firnoride-sulfuric acid 3 150 5 60 Boron fluoride-hydrogen 3 100 0.5 64 chloride Boron fluoride-hydrogen 3 100 0.5 80 fluoride Boron fluoride 100 0.5 57 Hydrogen fluoride a Catalyst concentration is expressed as s e r cent of each component TABLE11. ESTERIFICATIOX O F P R O P k E N E WITH ORGlNlC ACIDSI N THE PRESENCE OF A BORON FLUORIDE-HYDROGEN based on total weight of propylene and acetic acid.
7)
FLUORIDE CATALYST
Catalyst Reaction Reaction Time, Concn., Temp., yoa C. Hours 0.3 3 100 0.5 90-100 3 1 3 100
Yield, Ester Formed % Xsopropyl formate 70 Isopropyl acetate 80 Isoprepyl chloro84 acetate 2 Diisopropyl 60 3 100 hlonoisopropyl phthalate phthalate 1 Monoisopropyl 22 3 120 Phthalic phthalate Diisopropyl 63 phthalate Per cent each of BF1 and H F based on total weight of propylene and organic acid.
number of other catalysts. The common strong acid catalysts were quite ineffective for olefin esterification a t the concentrations used. Hydrogen fluoride and bo1 011 fluoride separately were effective only in high concentrations and with longer reaction times. Use of equal parts by neight of boron fluoride and hydrogen fluoride-i.e., 3% of each-as a catalyst gave a higher conversion t o isopropyl acetate than did an equimolar ratio of boron fluoride and hydrogen fluoride (3% boron fluoride and 1 % hydrogen fluoride). The fluoboric acid used was a 42% aqueous solution, and the water was removed by reaction with acetic anhydride to obtain an essentially anhydrous system. With solid organic acids, such as chloroacetic acid and phthalic The presence of water during the esteiification of olefins with acid, some modification of the experimental procedure x-as the boron fluoride-hydrogen fluoride catalyst reduces the yield necessary. The boron fluoride was introduced as its complex materially. Only 1% of water in the reaction mixture lowered with acetic acid, (CH,COOH),.BFa, and a n inert liquid, such as the yield of isopropyl acetate obtained from esterification of pentane or the ester to be prepared, was added as a suspension propylene with acetic acid from the u ~ u a l80 to 56%. Thus, medium for the reaction. The hydrogen fluoride was charged to it is important to carry out the boron fluoride-hydrogen fluoride the bomb in the liquid state just before the olefin was introduced. catalyzed olefin esterification under essentially anhydrous condiThe reaction was then carried out and the esters were recovered tions. in the usual manner. It was necessary to introduce the boron The order of addition of the reactants and catalyst is important fluoride in the form of a complex with a polar organic compound in obtaining a high yield of ester and minimizing side reaction8 such as acetic acid, since the presence of free boron fluoride in the such as polymerization of the olefin. For example, if boron reaction zone caused polymerization of the olefin before esterificafluoride is added to a mixture of acetic acid, hydrogen fluoride, tion could occur. and propylene, a rapid exothermic reaction occurs resulting in polymerization of the propylene to an oil. No isopropyl acetate is formed. The recommended procedure is to dissolve the boron TABLE111. COMPARISONOF BORON FLUORIDE-HYDROGEN fluoride-hydrogen fluoride catalyst in the organic acid before FLUORIDE CATALYSTWITH BORONFLUORIDE A N D HYDROQEN contacting with the olefin. 9 high yield of ester is obtained, FLUORIDE ALONE FOR ESTERIFICATION OF PROPYLENE WITH ACETICACID and virtually no polymerization of the olefin OCCWE. Addition of Yield of hydrogen fluoride t o a mixture of the organic acid, boron fluoride Catalyst Reaction Reaction Isopropyl Concn., TeomE:, Time, Acetate, (previously dissolved in the organic acid), and an olefin is satisCatalyst % Hours % factory, and a good yield of the desired ester can be obtained in this way. However, there is usually no advantage to this proc d u r e . The important point is to prevent free boron fluoride from contacting the olefin. Acid Formic Acetic Chloroacetio
Table I11 shows the synergistic effect of boron fluoride and hydrogen fluoride when used jointly as a catalyst in olefin esterification. The practical lower limit of the catalyst concentration has been found to be about 3% each of boron fluoride and hydrogen fluoride, based on total weight of olefin plus organic acid. At concentrations of less than 1%each, virtually no reaction occurred at temperatures of looo to 170" C. Concentrations of boron fluoride and hydrogen fluoride between 1 and 3% promoted olefin esterification, but the yield of ester was diminished. Except in the case of esterification of ethylene, there was no advantage in using catalyst concentrations of over 3%Table I V shows that the boron fluoride-hydrogen fluoride catalyst is much more effective for olefin esterification than are a
LIMITATIONS OF THE REACTION
The greatest success has been obtained in the esterification of secondary olefins, such afi propylene, 1- and 2-butene, 1- and 2pentene, etc., with lower aliphatic acids, such as formic and acetic acids. Ethylene can be esterified jn the presence of the boron fluoride-hydrogen fluoride catalyst, but, as shown previously, the conditions required are much more vigorous, and the yield of ester is somewhat lower. Tertiary olefins tend to polymerize in the presence of boron fluoride, hydrogen fluoride, and acetic acid. Isobutylene forms an oily polymer when i t is added to a solution of boron fluoride and hydrogen fluoride in acetic acid; tert-butyl acetate does not form under these conditions. The same effect was observed when a conjugated diolefin, 1,3-butadiene, was added to'a mixture ?f
July 1951
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
acetic acid, boron fluoride, and hydrogen fluoride. Presumably, nonconjugated diolefins, such as I,.i-pentadiene, would react in much the same way as secondary olefins, and would yield the dienter of the corresponding diol. Most of the carboxylic acids which can be esterified by conventional means can also be used in the catalytic olefin esterification process. An extensive study of this point was not made, but it has been shown that the lower aliphatic acids (formic and acetic acids), a halogenated aliphatic acid (chloroacetic acid), and an aromatic acid (phthalic acid) were readily esterified with propylene in the presence of boron fluoride-hydrogen fluoride catalysts. CATALYST RECOVERY
Experiments designed to determine the fate of the boron fluoride-hydrogen fluoride catalyst during the olefin esterification reaction showed that the hydrogen fluoride largely reacted with the olefin, and could be recovered as an alkyl fluoride. The boron fluoride combined with the organic acid to form a complex of the type (RCOOH)2.BF8. In the case of esterification of propylene with acetic acid in the presence of boron fluoride and hydrogen fluoride, isopropyl fluoride, boiling point of - 10" C., was formed. Theisopropyl fluoride was recovered by condensing out the off-gases in a dry ice trap. The boron fluoride remained as a high boiling complex with acetic acid, (CH&OOH)2.BFa, in the distillation residue. Another experiment showed that it was possible to esterify propylene with acetic acid in the presence of boron fluoride and isopropyl fluoride. Since alkyl fluorides are largely dissociated into olefin and free hydrogen fluoride at temperatures of 100' C. (II),the hydrogen fluoride was available to act in its role of esterification catalyst along with the boron fluoride. Additional experiments showed that the still residue, obtained after recovery of tfie isopropyl acetate by direct reduced-pressure distillation of the crude reaction mixture, retained its catalytic activity, and could be used in the esterification of additional quantities of propylene and acetic acid. Thus, the still residue from a typical run, in which the yield of isopropyl acetate was 77%, was used as the source of boron fluoride for a second run without the addition of any fresh boron fluoride. The yield of isopropyl acetate from the second run was 79%. A system for recovery of both components of the boron fluoride-hydrogen fluoride catalyst was devised and proved by experiment. The low boiling fraction obtained by direct reducedpressure distillation of the reaction mixture, consisting chiefly of iaopropyl fluoride, was condensed out and used as the source of hydrogen fluoride for a later run. The high boiling residue from the same distillation served as the source of boron fluoride in a subsequent run. Then a reaction of propylene with acetic acid waa carried out in which no fresh catalyst was added, but only catalyst recovered as described was used. The result was an 8770 yield of isopropyl acetate, showing t h a t the catalyst had been effectively recovered. Table V summarizes the results on catalyst recovery, REACTOR CORROSION
Early in this work, it was observed that pressure reactors constructed of mild steel were seriously attacked by the acid mixture of boron fluoride, hydrogen fluoride, and acetic acid. The corroaion damaged the bombs and also resulted in a serious loss of catalyst. I n one experiment over 90% of the boron fluoride was converted to metallic (chiefly iron) fluoborates. Corrosion tests on a number of common metals and alloys ahowed that nearly all are seriously attacked by a mixture of boron fluoride, hydrogen fluoride, and acetic acid. These included copper, Monel, nickel, Hastelloys A, B, and C, 18-8stainless steel, lead, and tin. The only metal which apparently re-
1599
TABLEv. CATALYSTRECOVERY FROM ESTERIFICATION OF PROPYLENE WITH ACETICACIDIN PRESENCE OF BORON FLUORIDE AND HYDROQEN FLUORIDE Recovered Catalyst Used HF BFI HF and BFn
Isopropyl Isopropyl Acetate Yield, Acetate Yield, Initial Run Subse uent (Fresh Run ?ReCatalyst), covered % Catalyst), % 78 82 77 79 80 87
Over-all Yield, Both Runs,
*
%
80
78 83.5
sisted attack completely was fine silver. However, No. 316 stainless steel (3% molybdenum) withstood corrosion to a greater extent than did other common metals and alloys. A bomb constructed of No. 316 stainless steel was used in all catalyst recovery work. Experimental results showed that only about 15% of the boron fluoride was lost as metallic fluoroborates when this alloy was employed as a reactor for the olefin esterification reaction. ETHERIFICATION O F OLEFINS IN PRESENCE O F BORON FLUORIDE AND HYDROGEN FLUORIDE
Ethers of secondary and tertiary olefins can be prepared by reaction of a n olefin with an alcohol in the presence of boron fluoride and hydrogen fluoride (18). I n general, the yields are lower than in the esterification of olefins with the same catalyst mixture, and more vigorous reaction conditions are required. The experimental technique for the preparation of ethers by this method was similar to the catalytic olefin esterification. The boron fluoride-hydrogen fluoride catalyst was f i s t dissolved in the desired alcohol, and the resulting mixture was contacted with the olefin in a pressure reactor. Ethyl isopropyl ether was prepared in 17% yield by reaction of propylene with ethyl alcohol in the presence of 30/, each of boron fluoride and hydrogen fluoride at 150' C. for 3.5 hours. By increasing the catalyst concentration to 5y0,a 34% yield of ethyl isopropyl ether was obtained in a reaction time of 2 hours at 150' C. . Methyl tertbutyl ether was readily obtained in 86% yield by reaction of isobutylene with methanol for 0.5 hour at 100" C. in the presence of 3% each of boron fluoride and hydrogen fluoride. CONCLUSIONS
The catalytic esterification of olefins with organic acids is a simple and effective means of converting olefins to esters of organic acids. The discovery of a very effective catalyst, boron fluoride-hydrogen fluoride, for $his reaction makes this process attractive for the preparation of esters from by-product refinery olefins. Because of the greater efficiency of the boron fluoride-hydrogen fluoride catalyst, the direct esterification method of producing esters shows more promise than earlier published work has indicated. Results of the present study show t h a t the method is applicable to a number of olefins and organic acids, making possible the production of a wide variety of esters. Since the boron fluoride-hydrogen fluoride catalyst can be recovered, the catalyst cost is low. Reactor corrosion by the boron fluoride, hydrogen fluoride, and organic acid mixture is one disadvantage to the esterification of olefins with a boron fluoride-hydrogen fluoride catalyst. This has largely been overcome by use of a pressure reactor constructed of No. 316 stainless steel, the corrosion of which is not serious under the usual reaction conditions. Ethers can be prepared by reaction of olefins with alcohols in the presence of a boron fluoride-hydrogen fluoride catalyst. However, the yields are generally lower than for the esterification reaction.
1600
INDUSTRIAL AND ENGINEERING CHEMISTRY ACKNOWLEDGMEKT
This investigation was carried out under the sponsorship of the Standard Oil Co. (Indiana), and the results are published with their permission. The authors are indebt,ed t o F. IT. Fink of the Battelle staff for his assistance in connection 73-ith the korrosion problem. LITERATURE CITED (1) Bearse, A. E., and hlorin, R. D., U. 8.Patents 2,414,999 and 2,415,000 (Jan. 28, 1947). (2) Bouchardat and Lafont, Compt. r e n d . , 113, 551 (1891). (3) Dorris, T. B.. and Sowa, F. J . , J . Am. Chem. S o c . , 60, 358 (1938). (4) Dorris, T. B . , Sowa, F. tJ., and Kieurrland, J . d.,I b i d . , 56, 2689 (1934). (5) Dreyfus, H., Brit. Patent 485,108 (May 16, 1938). (6) Dreyfus, H., U. 5 . Patent 2,083,693 (June 15, 1937). (7) Ellis, C., “The Chemistry of Petroleum Derivatives,” Tal. I, p p ~348-58, 372, Nevi York, Chemical Catalog Co., 1934. (8) Ellis. C., U . S. Patents 1,365,050 and 1,365,052 (,Jan. 11, 1921). (9) E n n s , T. W,, Edlund, K. R., and Taylor, M. D., ISD. ESG. CHEM.,30, 55 (1938). (10) Frolich, P . K . , and Young, P . L., 1;. 6 . Patent 1,877,291 (Sept. 13, 1933).
Vol. 43, No. 7
(11) Grosse, A. V., and Linn, C. R.. J . Org. C h e m . , 3, 26 (1938). (12) Hilcken, V., U. S. Patent 1,902,364 (March 21, 1933). (13) Hofmann, F., and Wulff, C., I h i d . , 1,898,627 (Feb. 21, 1933). (14)Kondakow. J . prakt. Chem., 48,479 (1893). (15) Kroeger, J. W., Sowa, F. J., and Nieuviland A c u d . Sci., 46,115 (1937). (16) Larson, A. T., U. S.P a t e n t 2,093,695 (Sept. 21, 1937). (17) Lazier, W. A . , I b i d . , 2,174,895 (Oct. 3, 1940). (18) Lien, A. E’., Ihid., 2,399,126 (April 23. 1946). (19) Loder, D. J.. I b i d . , 2,253,525 (Aug. 26, 1940). (20) I b i d . , 2,265,946 (Dec. 9, 1941). (21) Meerwein, H., Be?., 66B,411-14 (1933). (22) Nieuwland, J. A., and Sow-a, F. .J.. U. 8. Patent 2,192,015 (Feb. 27, 1940). (23) Schneider, H . G., I b i d . , 2,065,540 (Dec. 29, 1936). (24) Spring, F. S.,Ann. R e p t s . o n Progress C k e m . , 39, 129 (1942). (25) Stanley, H. XI., and Youell. J. E., Rrit. Patent 641,056 (SOT-. 11, 1941). (26) Strange. E. H., and Kane, T., C . 8 . Patent 2,014,850 ( S e p t . 17, 1935). (27) Suida, H., E. S.P a t e n t 1,536,135 (Doc. 15, 1932). (28) Woolcock, J. W., Brit. P a t e n t 334,228 (April 30, 1929).
RECEIVED October 31, 1Q.50. Presented hefore the Division of Potro!cuni Chemistry at the 117th Meeting of rhe . i \ r x a i c . ~ s C:HW\IICAI. S o c r m y , Houston, Tex.
GR-S Aging in Solution GIFFIN D. JOSES ~ N RALPH D E. FRIEDRICN Dow Chemical Co., Midland, Mich.
T h e degradation and oxygen absorption of solutions of GR-S have been studied in an effort to explain the failure of antioxidants under ultraviolet light. It has been found that the photodegradation of GR-S in solution occurs only if oxygen is present. Two types of peroxide can be formed, a stable peroxide at elevated temperatures and a labile one, which may be polymeric, at room temperature. These peroxides can be differentiated by the use of aliphatic amines which cleave the latter an’d produce thereby a viscosity decrease. Aliphatic amines are shown to be good antioxidants for GR-S at 90” C. but poor antioxidants under ultraviolet light. The work has led to a better understanding of the viscosity changes which occur in GR-S solutions on standing and the mechanism of light stabilizer action.
I
T HAS long been recognized (1) that the viscosity changes in
rubber solutions under light depend in a complicated way on oxygen and on the effect of various promoters, retarders, and modifiers on the autoxidation and polymerization reactions involved. Stevens (10) has shown that a number of substances drawn from both pro- and antioxidant types have the effect of promoting photogelation when used in low concentration and retarding photogelation when used in high concentration. h partial answer to this seeming paradox appears to be in the discoveries connected with redox systems of polymerization. The use of aliphatic amines, for example, to initiate cold polymerization (9, 11) gives confirmation of the view (7) that the induced decomposition of a peroxide gives a free radical as a by-product. This free radical may be the cause of subsequent polymerization or autoxidation steps before it, too, interacts with the amine and presumably dehydrogenates the amine to form a nitrogen radical. This nitrogen radical attacks the peroxide and a new cycle of the chain reaction ensues. If an amine, such as n-butylamine is added portionwise to a solution of peroxidic GR-S, there is a nearly instantaneous decrease in viscosity. Equilibrium is reached within a few minuteq,
and a further decrease results aiter another portion OS aiiiiiie is added until an end point is reached; after this the further atidit,iou of amine produces little effect,. Figure 1 shdws amine titmtion curves for solutions (in ethylbenzene) of aged and unaged (;It-S. EXPERIMENTAL
9 107, solution of soluble GR-S (X274) in ethylbenzenc was prepared and precipitated in ethanol by means of a \\-&ring Blendor. The precipitated GR-S was then redissolved without drying, and the residual alcohol was distilled off under reducwl pressure. The operations were conducted under nitrogen containing less than O.OlYc oxygen and at room temperature or below. The final concentration of GR-S in ethylbenzene was -t.5cc. The intrinsic viscosity of thc GR-S in ethylbenzene was 2.1.
The GR-S solutions were nged by exposure to air a t various temperatures in diffuse daylight. The duration of exposure is indicated iri the key to Figure 5 and the peroxide content in Talde I10
, TITRATION OF 4 . 5 % G R - S SOLUTION IN ETHYLBENZENE W I T H
50 0
ti-BUTYL
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4
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10
M I L L I M O L E S n - B U T Y L AMINE
Figure 1
