[CONTRIBUTION FROM
THE
SCHOOL OF CHEMICAL TECHNOLOGY OF NORTH DAKOTA AGRICULTURAL COLLEGE ]
CATALYTIC DEHYDROGENATION OF PRIMARY AND SECONDARY ALCOHOLS WITH COPPER-CHROMIUM OXIDE RALPH E. DUNBAR
AND
MELVIN R. ARNOLD'
Received April lY, 1940
The results obtained in a previous study (1) of the dehydrogenation of butanol1 with copper-chromium oxide catalyst, precipitated upon inert porous materials,
prompted this additional investigation with other primary and also secondary alcohols. It was hoped that satisfactory laboratory methods might be found for the production of numerous aldehydes and ketones. It seemed probable, in addition, that certain tendencies might evolve which could be correlated with the type or structure of the alcohols undergoing dehydrogenation. Significant contributions in the dehydrogenation of various alcohols have been made over a period of years (2, 3, 4, 5, 6, 7, 8). Various workers have tested, studied, and developed suitable catalysts for these investigations. (1,9, 10, 11, 12, 13, 14, 15). EXPERIMENTAL
Catalyst and equipment. Copper-chromium oxide catalyst which had been previously precipitated and decomposed on Johns-Manville Celite C-12,212, Type IX, 6- t o 10-mesh screen size, was used in the dehydrogenation of the sixteen alcohols. The method for the preparation of the catalyst was identical with that previously described (1). A fresh portion of catalyst was used for each determination with the several alcohols, The general procedure for the dehydrogenation was essentially the same as that previously described (1). For the successful dehydrogenation of alcohols with boiling points of 125" or higher it is advantageous to use an electrically heated Widmer fractionating column on the dehydrogenation equipment a t the point where the aldehydes or ketones are separated from the unreacted alcohol. The temperature within the Widmer was never allowed to exceed the boiling point of the aldehyde or ketone being produced. Sources of alcohols. The Sharples Solvents Corporation kindly supplied generoussamples of pentanol-1, 3-methylbutanol-1, 2-methylbutanol-1, pentanol-3, and pentanold. The Carbide and Carbon Chemicals Corporation generously furnished samples of hexanol-l,4methyI-pentanol-2,2ethylbutanol-l,2ethylhexanol-l,and heptanol-2. The butanol-2, hexanol-2, and propanol-2 were of Eastman Organic Chemicals grade. The propanol-1 and butanol-1 were of the usual commercial grade. All these alcohols were dried, fractionated through an 8-inch Widmer column, and only that portion of the alcohol was retained which distilled within a 1" range. The octanol-2 was prepared according to accepted procedure (16). Procedure. For the dehydrogenation of the various alcohols, temperatures for the catalyst chamber ranging from 250-350" have been used both with different portions of the 8ame and with different alcohols. Intervals of approximately 25" were used in locating the optimum temperatures for the subsequent dehydrogenations. I n the majority of instances temperatures of 300-325" have been found to be most satisfactory. As a check on the general efficiency of the catalyst a t the temperature used, the total hydrogen evolved was collected and the volume recorded a t fifteen minute intervals. A close correlation was found in every case between the amount of gas evolved and the amount of aldehyde or ketone produced. 1
Present address: E. I. duPont de Nemours and Co., Charleston, Indiana. 501
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R. E. DUNBAR AND M. R . ARNOLD
The distillate in each case was dried with anhydrous sodium sulfate, combined with the residue from the reaction flask, and fractionated through an 8-inch Widmer Column t o separate the various products. In those instances where the boiling points of the original alcohol and the corresponding ketone were too close for efficient separation by fractionation, titration (17) was used to determine the amount of ketone produced. The reliability of this analytical method, as applied to this problem, was checked by titrating known samples of ketones. The results were found to agree within experimental limits. Results. Average values for representative dehydrogenations for the sixteen alcohols studied are included in Table I. One hundred-gram samples of all alcohols were used. All values included in Table I are the average of several determinations, and represent normal yields under the operating conditions. Optimum temperatures for the catalyst TABLE I PERCENTAGE CONVERSION OF SIXTEEN ALCOHOLS TO ALDEHYDES OB KETONES BY DEHYDROQENATION
I
ALCOHOL DEHYDROGENATED
OPTIh(UY TEYPEPATUPE,
Propanol-I.. . . . . . . . . . . . . . . . . . . .* . . . . . . . . . . . . . . Butanol-I . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pentanol-I.. .......................... Hexanol-1 . . . . . . . .
OC
300-320
Pentanol-3. . . . . . . . . . . . . . . . . 4-Methylpentanol-2 ............................
OX KETONE
67 62 58
3-Methylbutanol-l .
......... ......... ...........................
PEPCENTACE CONYBPSION
r o ALDEEYLIE
300-325 300-310 300-325
300-310
53 63 55 58 61 71 68 53 20*
30 37* 70 80
)EHYDXOGENATION TIME IN
HOUXS
1.5 2.5 4.5 2.5 3.6 2.3 3.3 4.0
1.7 2.9 2.0 3.5 4.0 3.8 2.0 2.6
* Percentage conversion determined by titration. chamber are those that have been found by variation of temperature to give the most satisfactory results. All values, for percentage conversion t o aldehydes or ketones, recorded in Table I, represent actual amounts of materials recovered by fractionation, with the exception of hexanol-2, and octanol-2. The average time required for a complete dehydrogenation of a 100-gram sample of the alcohols is included. DISCUSSION
An examination of the results summarized in Table I indicates several tendencies where the type, structure, and molecular weights of the alcohols may be correlated with their ease of dehydrogenation over copper-chromium oxide catalyst. The percentage conversion of normal primary alcohols to aldehydes, under comparable conditions, decreases with increasing molecular weight. It is also advantageous to increase temperatures from 300-320" for propanol-1 t o 335345" for hexanol-1 in order t o obtain efficient operation. While it is rec-
DEHYDROGENATION O F ALCOHOLS
503
ognized that an increase in temperature increases slightly dehydration a t the expense of dehydrogenation, yet experience has shown that dehydration has never been a troublesome factor with the sixteen alcohols studied at temperatures below 350". Any increase in dehydration can not alone account for the 14% decrease from propanol-1 to hexanol-1. It is also interesting to note that Komarewsky and co-workers (4,5,6,7) have observed a marked tendency for various primary, secondary, and branched alcohols not only to dehydrogenate but to condense, dehydrate, dehydrocyclize, and decarbonylate but such reactions occured at temperatures of 350" to 525" which are far in excess of those used in this study. Likewise distinctly different catalysts were employed. Little if any such tendencies were observed under these operating -conditions. The time required, with one exception, for the successful dehydrogenation of 100 grams of normal primary alcohol and the separation of the alcohol and aldehyde increased with increasing molecular weight. However, the time is also influenced by the difference between the boiling point of the alcohol and aldehyde, and temperatures maintained throughout the system. Branching in the carbon chain, either on the second or third carbon atom, with primary alcohols, favors dehydrogenation to the corresponding aldehyde. The two branched chain pentanols, 2-methylbutanol-1, and 3-methylbutanol-1, gave conversions of 63% and 6101, respectively as compared to 58% for pentanol-1. The percentage yield for 2-ethylbutanol-1, is higher than that for hexanol-1 and that for 2-ethylhexanol-1, namely 58% is higher than that which would be expected for octanol-1, in view of percentage conversions of the normal alcohols. The simpler secondary alcohols, such as propanol-2, and butanol-2, gave higher conversions to ketones than the corresponding normal primary alcohols to aldehydes. The decrease in percentage conversion is rapid with increasing molecular weight and decrease in symmetry of the molecule, until the minimum is reached with hexanol-2, and then the values increase with increasing molecular weight. The percentage conversion of octanol-2 is lower than that for 2ethylhexanol-1, which again illustrates the effect of branching and primary or secondary nature of the alcohol on the ease of dehydrogenation. Pentanol-2 produces results which are only slightly lower than those for pentanol-1 ,yet pentanol-3 shows the highest percentage conversion of these three pentanols. Propanol-2 and pentanol-3, both represent balanced configurations in terms of alkyl radicals. These two alcohols, with the exception of 4-methylpentanol-2, gave the highest percentage conversions of all of the alcohols used. It appears that balanced structures and branching of the carbon chain are conducive to high conversions in such dehydrogenations. Finally, 4-methylpentanol-2 gave at low temperatures the highest percentage conversion of any of the sixteen alcohols studied. The secondary nature of the alcohol and the branching of the carbon chain are perhaps responsible for this high conversion. The data reported in Table I do not necessarily represent maximum or minimum conversion or equilibrium values, but average values under comparable conditions, and are representative of what logically might be expected under
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like conditions and can, therefore, be used in noting certain tendencies and predicting probable results with other related alcohols. SUMMARY
1. The effectiveness of copper-chromium oxide, when precipitated and decomposed upon Celite, as a dehydrogenation catalyst for primary and secondary alcohols has been further demonstrated. 2. Satisfactory laboratory methods have been outlined for the production of eight aldehydes and eight ketones in yields ranging from 20 to SOT0by the direct dehydrogenation of the corresponding primary and secondary alcohols. 3. Certain tendencies regarding the type, structure, and molecular weight of the alcohol, with the ease of dehydrogenation over copper-chromium oxide catalyst have been discussed. FARGO,NORTHDAKOTA REFERENCES (1) DUNBAR, J . Ofg. Chem., S, 242 (1938). (2) BERTHELOT AND JUNQFLEISCH, “Trait6 614m. de C h i d e Org.,” I, 2nd ed., Paris,1888, p. 256. (3) KNOEVENAGEL AND HECPEL, Bef., 36,2816 (1903). RIESZ,AND THODOS, J. Am. Chem. Soc., 61,2525 (1939). (4) KOMAREWSPY, (5) KOMAREWSKY AND COLEY, J . Am. Chem. Soc., 63,700 (1941). (6) KOMAREWSXY AND COLEY, J. Am. Chem. Soc., 63, 3269 (1941). AND SMITH, J . Am. Chem. SOC.,66,1116 (1944). (7) KOMAREWSKY (8) BADINAND PACSU,J.Am. Chem. SOC.,66,1963 (1944). AND MAILHE, Ann. Chim. Phys., [8], 20,289,341 (1910). (9) SABATIER (10) IPATIEFF, Ber.,S4,3589(1901);36,1047(1902);J.Russ.Phys.-Chem.S0~.,34,182 (1902); 40, 500 (1908). (11) SABATIER AND MAILHE, Bull. soc. chini., [4]1, 107, 341, 524,733 (1907);Compt. rend., 146, 1376 (1908);147, 16, 106 (1909);148, 1734 (1909). (12) CONNOR, FOLPERS, AND ADPINS,J . Am. Chem. Soc., 54, 1138 (1932). J . Am. Chem. SOC.,64,3080 (1932). (13) LAZIERAND VAUGHEN, Ind. Eng. Chem., 26, 54 (1933). (14) FREYAND HUPPKE, AND ARNOLD, Ind. Eng. Chem., Anal. Ed., 16,441 (1944). (15) DUNBAR (16) ADAMSAND MARVEL, “Organic Syntheses,’’ Vol. 1, John Wiley and Sow, Inc., New York, N.Y.,1921,p.61. (17) BRYANT AND SMITH, J . Am. Chem. SOC.,67, 57 (1935).
