Reaction Product of Olefins with Sulfuric Acid RICHARD F. ROBEY Esso Laboratories, Standard Oil Development Company, Elizabeth, N. J.
A
PREPOKDERANCE of evidence exists to show that, in general, the primary reaction of sulfuric acid with the lower monoolefins results in the formation of the corresponding acid sulfate ester or alkylsulfuric acid. Thus, CnHzn
+ HzS04 e CnHen +
I
HSOc
(1)
or more explicitly, CvHzn
+ HSOd-
*=T
C n H z n + i SO,-
(2)
However, the ester may subsequently react with other constituents of the reaction mixture-the excess sulfuric acid, the olefin, or water, if present-or with itself; the direction and extent of these reactions depend on such conditions as the constitution, molecular weight, and concentration of the olefin, the concentration of the acid, and the temperature. In the industrial production of the lower alcohols and their derivatives, olefin polymers, and alkylates from hydrocarbon fractions resulting from petroleum refinery cracking operations, the reaction of the olefins with sulfuric acid plays a n important role. Under mild conditions, moderately stable acid reaction products are formed. This investigation is largely concerned with the composition of these acid liquors or extracts. The olefin content' of the acid liquors is generally supposed to exist largely in the form of the corresponding alkylsulfuric acid. However, when extracts of the n-butenes in 80 per cent sulfuric acid, for example, are analyzed for alkylsulfuric acid, relatively small concentrations are found. The remaining butene content might be visualized as being present in the form of the corresponding alcohol dissolved in the acid, but the presence of such a high concentration of alcohol seems unlikely since no alcohol can be extracted b y immiscible organic solvents. When the acid liquor is diluted with water, a considerable quantity of alcohol is almost instantaneously liberated, even in the cold, but the alcohol derived from the hydrolysis of the butylsulfuric acid is liberated only slowly, even a t considerably higher temperatures. To explain these observations Brooks (9) proposed that olefin is present in the acid extract largely in two formsnamely, anhydrous alkylsulfuric acid (RH304)and hydrated alkylsulfuric acid (RHS04.H20); the latter is presumably derived from the monohydrate of sulfuric acid. To the hydrated ester was ascribed the property of ready hydrolysis, which would account for the release of alcohol from the extract upon treatment with water in the cold. I n the present investigation data are presented which appear to be explained better b y the more modern theories of acid-catalyzed ester hydrolysis.
n-butenes in 80 per cent sulfuric acid. The homogeneous solutions were agitated out of contact with air, and the course of the reaction between the alcohol and the acid was followed over a considerable number of hours by eriodic withdrawal and analysis of small samples. N o detectabre quantity of gas was evolved from these solutions during this period. With olefin, acid extracts of the butenes were prepared by agitating portions of a liquefied refinery hydrocarbon mixture, consisting of 15 mole per cent of the n-butylenes and the remainder n-butane and isobutane, in a small turbomixer with 80 per cent sulfuric acid a t 35" C. under carefully controlled conditions. After the reaction the two liquid phases were separated under reflux and the acid extract was analyzed immediately as described later. The concentrations of acid and olefin in the resulting extract could be calculated from the analysis of the hydrocarbon phase and a careful material balance on the quantities of reactants and products. Final concentrations of butenes in these extracts were not exactly 15 and 25 per cent, respectively, but are believed close enough to be comparable.
The composition of the acid reaction product of n-butenes with sulfuric acid has been investigated. Only 30 to 40 per cent of the butene content of the reaction product with 80 per cent acid can be accounted for as alkylsulfuric acid. The remainder is believed to be present in the form of the alcoxonium ion, proposed by modern theories of acid-catalyzed ester hydrolysis. A value for the heat of the reaction reported in the literature is criticized briefly in the light of the conclusions.
Analysis The acid extracts were analyzed for free, titratable, and total sulfuric acid. The free sulfuric acid-that is, uncombined HnSOd-was determined by the method of Bacon (1). It is based on the principle that a solution of aniline in chloroform precipitates the free acid as insoluble aniline sulfate, while the aniline salts of the alkylsulfuric acids, and any alkanesulfonic acids, remain in solution. The sudden reduction of acidity on introduction of the aniline does not permit appreciable hydrolysis of the ester. The titratable acid was determined, as recommended by Suter and Oberg ( 6 ) ,by titrating a sample of extract immediately after it has been diluted with ice water. The alkylsulfuric acid hydrolyzes only negligibly under these conditions and the Experimental Details resulting,acidity is due to the free plus the alkylsulfuric acid, the latter being a monobasic acid. Acid liquors of known composition were prepared from alThe total acidity was determined by titration after diluting the cohol and from olefin and sulfuric acid. With alcohol, weighed extract and completelv hydrolyzing it. This gives the acidity quantities of c. P. acid, redistilled sec-butyl alcohol, and distilled derived from the free acid, H2804,from alkylsulfuric acid, RHwater were mixed in proportions to simulate, in ultimate comSOa, and from any dialkyl sulfate, R280a. Fortunately the conposition, 15 and 25 weight per cent solutions, respectively, of the 1076
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1941
siderations of this investigation were simplified by the presence of no appreciable concentration of the dialkyl compound in 80 per cent acid extracts.
Results and Discussion The results of the experiments are summarized in Table
I. Data on the mixtures of alcohol and acid show the state of the reaction between these two compounds at various times and the approach t o the equilibrium concentrations. For present purposes the concentration of alkylsulfuric acid is calculated from twice the difference between the total and the titratable acidities, or 2(C B). Other calculations, 2(B - A ) and C - A , give substantially the same results. From these the percentage of the total olefin present as alkylsulfuric acid has been derived. Comparison of the final values for the alcohol-acid mixtures with those of the freshly prepared reaction product of the olefin with acid shows them t o be approximately equal. This amounts t o approaching the equilibrium mixture from two directions. A more ready comparison of the values may be made from Figure 1; the free acidity and the titratable acidity, as percentages of the total acidity, are plotted against time. The curves represent the course of the reaction in the synthetic acid extracts prepared with alcohol, while the points on the ordinate and the extensions in the form of the three horizontal broken lines represent the composition of actual acid extracts prepared with the olefin. The free acidity of one olefin extract was not determined. The slight rise in the curve for the synthetic 15 per cent extract after the minimum is believed due to the formation of olefin polymer which became apparent by visual inspection of this mixture after a time. Presumably the increase of acidity is due to the conversion of alkylsulfuric acid t o polymer and free acid. I n any case, it is apparent from these data that only 30 to 40 per cent of the reacted butene content of an extract in 80 per cent sulfuric acid can be accounted for as the alkyl-
-
100 4
sulfuric acid (BuHS04). The observation t h a t no appreciable amount of alcohol can be extracted from the undiluted extract by an immiscible organic solvent was also confirmed. Some light is thrown on the compositions of the acid extracts by the work of Goldschmidt on esterification of alcohols catalyzed by acids, briefly described by Smith (6). I n these investigations considerable evidence was uncovered which seems t o show t h a t the hydrogen ions from the catalytic acid form complexes with alcohol molecules, which is interpreted for the present reaction in the form of the following equation: RSO;
+ H80+ e ROH; + HSOT
(3)
TABLEI. COMPOSITION OF ACID EXTRACTS OF BUTENES IN 80 PERCENTSULFURIC ACID Moles per Kilogram
Time, Hr.
0.0 0.5 2.3 4.0 22.0
.. 0.0 0.5 2.0 3.5 21.5 47.0
..
Total olefin CrHs'
A. free acidity,
Hisor
B
C,
titr&,ble total acidity 2(C B), Per Cent acidity H&Oa HzS04 $ ester CaHa as 1/iBuHSOi BuHSOi BuHSbr BuHSOi
4
-
.. .. ..
..
6.94a 6.65 6.05 6.06 6.23
Alcohol and Acid 6.940 6.940 6.79 7.10 6.59 7.10 6.60 7.08 6.63 7.08
0 0.62 1.02 0.96 0.90
23.1 38.0 35.8 33.6
2.95a
5.83
Olefin Extract 6.24 6.69
0.90
30.5
6.12a 5.66 5.08 4.76 4.66 4.59
Alcohol and Acid 6.120 6.12" 5.84 5.98 5.52 5.90 5.35 5.90 5.27 5.91 5.24 5.92
0 0.28 0.76 1.10 1.28 1.36
6.3 17.0 24.6 28.7 30.4
..
Olefin Extract 5.87 6.54
1.34
34.5
2.68'
4.47a
.... .... ..
3.880 a Calculated from synthesis.
0
0
Thus the alkylsulfuric acid formed as indicated by Equation 2 is visualized as hydrolyzing rapidly in the presence of strong acid (the reaction is much slower in dilute acid) to form the alcohol complex and free acid so t h a t equilibrium values are maintained. This readily accounts for the concentrations of free acid found in the mixtures as well as other properties of the extracts. The fact that alcohol is not readily removed under ordinary conditions without dilution of the extract is explained by the presence of the alcohol in the form of a n ion. The alcoxonium ion is readily decomposed by the addition of water, however, t o liberate the alcohol in the proton exchange reaction, ROH;
0
1077
10
2'0 5b TIME,HOURS
40
FIGURE 1. COMPOSITION OF THE PRODUCT OF REACTION OF Sec-BUTYL ALCOHOL AND OF THE 12-BUTYLENES WITH SULFURIC ACIDAS A FUNCTION OF TIME A Titratable acidity of reaction product containing 15 per cent butenes.
A Same, 25 per cent butenes. 0 Free acidity of reaction product,
15 per cent butenes.
0 Same, 25 per cent butenes. Unbroken curves, reaction product prepared with alcohol; broken curves, reaction product prepared with olefin.
+ HzO e ROH + HaO+
Further, Ogg (4) pointed out that the characteristics of the hydrolysis of alkyl halides are best explained by assumption of the existence of the alcoxonium ion and t h a t the existence of this ion is entirely feasible from a thermochemical point of view. The relative proportions of olefin sulfated and hydrated depend largely on the strength of acid used. As shown above, 30 to 40 per cent of the olefin is sulfated in 80 per cent acid; this would be expected to increase t o 100 per cent sulfation in 100 per cent acid.
Heat of Reaction The conclusions reached in this study may have considerable bearing on those of others. For example, a direct determination of the heat of reaction of the n-butenes with
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INDUSTRIAL AND ENGINEERING CHEMISTRY
75 per cent sulfuric acid in the liquid phase was made a few years ago (S), and the value 34.15 kg.-cal. per mole of acid reacted at 60” C. to form butylsulfuric acid (as determined in the acid reaction product) was reported. Review of the data, however, shows that an assumption was made which probably is not justified, particularly in light of the above findings. It was assumed that all of the butenes reacting with 75 per cent sulfuric acid form butylsulfuric acid. The present investigation shows that acid extracts of the butenes prepared with 75 per cent acid would undoubtedly contain less than 30 per cent of the butenes as products of sulfation. The calculated heat value, therefore, is probably several hundred per cent too high.
Vol. 33, No. 8
Acknowledgment The writer tenders his thanks to the Standard Oil Development Company for permission to publish this work, to Ralph F. Howe for assisting in the analytical work involved here, and to others among his colleagues who offered kind criticism.
Literature Cited (1) Bacon, IND. E N G .CHEM., Anal. Ed., 1,89(1929). (2) Brooks, IND. ENQ.CHEM.,27, 278 (1935). (3) Khokhlovkin et al., Sintet. Kauohulo, 1936,No.2, 12. (4) Ogg, J . Am. Chem. SOC.,61,1946 (1939). (5) Smith, I b i d . , 61,254 (1939). (6) Suter and Oberg, Ibid., 56, 677 (1934).
Butvl-Acetonic Fermentation of Jerusalem Artichokes J
RAY T. WEiVDLAND, ELLIS I. FULMER, AND L. A. UNDERKOFLER Iowa State College, Ames, Iowa
HE so-called Jerusalem artichoke or girasole (Helianthus tuberosus) is a native plant of this country, and because
T
of its ability to produce high yields of tubers, increasing attention has been given to its possible value as a new farm crop. B u t as repeatedly pointed out, this new crop can become profitable only when proper methods for its industrial utilization have been worked out. At present a farmer would be justified in raising only as many girasoles as he could use directly on the farm as feed for hogs or cattle. One suggested commercial outlet is the production of levulose. The artichoke tubers are rich in levulans which are easily hydrolyzed to levulose by mild acid treatment. The Sugar Section of the Sational Bureau of Standards (1, 6 ) has contributed to the development of this possible use. Independently a semicommercial plant, capable of producing 22 pounds of crystalline levulose per batch run, was developed and operated continuously by the Chemistry Department of Iowa State College in 1931 and 1932. A second large-scale use which has been contemplated is in the manufacture of ind, stria1 alcohol. The tubers have long been recognized as a possible raw material for this purpose and have actually been employed to a limited extent in Germany and France. A report, based on work a t Iowa State College, was published on the alcoholic fermentation of Jerusalem artichokes in 1937 (18). A fermentation process which is second only to alcoholic fermentation in industrial importance, is that in which butanol, acetone, and ethanol are produced. This process employs a bacterium now most generally designated as Clostridium acetobutylicum, the name proposed by McCoy, Fred, Peterson, and Hastings ( 7 ) . I n this butyl-acetonic fermentation the organism, acting on the usual raw materials, produces the sohents in the approximate ratio of 60 parts butanol, 30 parts acetone, and 10 parts ethanol, along with large amounts of carbon dioxide and hydrogen. The weight of gases formed is about one and a half times that of the sol-
vents, the carbon dioxide representing about 60 per cent of the gas by volume. Industrially the by-product gases are employed for the synthesis of methanol and for the production of solid carbon dioxide. In the commercial fermentation corn has been largely used as the raw material. Recently molasses has also become an important raw material for the production of the solvents mentioned, the process employing a different organism from that named above. I n view of the commercial importance of this fermentation, i t was believed that an exhaustive investigation of the butyl-acetonic fermentation of the Jerusalem artichoke should prove of considerable interest. The only investigators mho have reported attempts to subject Jerusalem artichokes to the butyl-acetonic fermentation have been Thaysen and Green ( I S ) and Reynolds and Werkman (11). The latter workers reported merely that “the carbohydrates of the artichoke tuber are not readily available to attack by C1. acetobutylicum”. Thaysen and Green employed fresh tubers. They were steamed until soft and the juice was removed by pressing. It was found that the sterilized juice did not ferment, but the juice fermented readily after acid hydrolysis. The juice was hydrolyzed by adding sulfuric acid to 0.2 per cent concentration and heating for 1 hour a t 15 pounds steam pressure; the acid was then neutralized by calcium carbonate. The hydrolyzed juice was diluted to several concentrations and inoculated with 2 per cent of fresh maize culture of Weizmann’s butyl-acetone organism. The results of the fermentations shon ed that the optimum concentration for best fermentation \\as about 3 per cent of total sugar. Yields of solvents dropped off rapidly, with sugar concentrations lower than 2 or higher than 4 per cent. The best yields obtained were in the neighborhood of 33 to 36 per cent of carbohydrate present. Fermentations were conducted on a semitechnical scale with properly diluted hydrolyzed artichoke mashes in 20- and 500-gallon tanks. The concentration of sugar before fermentation va-
