JOURNAL O F CHEMICAL EDUCATION
PREPARATION OF CARBONYL COMPOUNDS BY CATALYTIC DEHYDROGENATION IN LIQUID PHASE A. HALASZ University of Montreal, Montreal, Canada A L ~ ~ U G theHpreparation
of carbonyl compounds by catalytic dehydrogenation of the corresponding alcohols in the gaseous phase is mentioned briefly in most textbooks, little, if anything, is written about dehydrogenation in the liquid phase. Actually, dehydrogenation in the liquid phase ( 1 , d ) is an excellent method for demonstrating reactions of the following general t,vnm. -.Jr--.
RXHOH-R' R-CH20H
--
R-CO-R'
R-CHO
+ Ha
+ Hz
This process avoids cumbersome adjustmeut and regulation of apparatus (3) necessary for a gaseousphase operation. It can be applied successfully even with alcohols which are too high boiling to he readily distillable. The required apparatus consists simply of a flask with reflux condenser, and an oil bath the temperature of which can be easily regulated. An apparatus for collecting and measuring evolved hydrogen may be added if desired. Many metals have been used as dehydrogenation catalysts (4). Most suitable are Raney nickel, reduced nickel, copper, and copper chromite. Example. To 100 g. of dodecanol, 5-10 g. of copper chromite, prepared as described in "Organic Syntheses" (5),is added. The mass is heated to 250°C. Reaction sets in immediately with evolution of hydrogen. After 30 minutee the reaction is stopped in order to avoid decomposition of the aldehyde product. The yield of aldehyde is about 40 per cent, and the unreacted alcohol can be recovered. The aldehyde may be isolated conveniently by dissolving the mass in ether, followed by filtration and shaking of the filtrate with a solution
of sodium bisulfite. The bisulfite addition complex is washed with ether and decomposed in the usual way by a solution of sodium carbonate. Other saturated high molecular-weight alcohols such as cetyl or octadecyl can be used with similar results. With ethylenic alcohols, such as 9-octadecen-1-01, saturation of the double bond takes place and stearaldehvdeis obtained. Secondary alcohols are much more easily dehydrogenated and the yield of ketone is often in the range of 8C-100 per cent. Even mild catalysts, such as copper powder, give excellent results. Borneo1 when refluxed carefully (to avoid clogging of the reflux condenser) with copper powder until evolution of hydrogen ceases gives a theoretical yield of camphor of high purity. Primary glycols likewise can be dehydrogenated easily hut secondary reactions often occur. Thus, 1,4-hutanediol yields y-butyrolactone (6):
-
HO-CH-CH-CH-CH2-OH
yHaCH2-CH2-CO
-
+ 2H2
1,5-Pentanediol gives 6-valerolactone:
HO-CH2-CHaCHrCH2-CH-OH CH1- CH2-CHn-CHn-CO
+ 2H1
'A
0
Cyclic glycols may react abnormally. Thus 1,2cyclohexanediol yields 2-hydrox~cyclohexanone:
+ H2
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625
l,3-Cyclohexanediol gives cyclohexanone. 1,4-Cyclohexanediol yields the expected 1,4-cyclohexanedione. Primary secondary glycols also react unpredictably. 1,4-Pentanediol affords -y-valerolactone (7):
-
HO-CH2-CH2-CH1-CHOH-CHs
CHp-CH2
CH,-&I
&O
+ 2H1
0 ''
Styrene glycol yields acetophenone: C.H,-CIIOH-CHIOH
-
CsHs--CO-CH,
It can be seen that the distance between the alcohol group exerts a decided influence on the course of the reaction. These examples will point up the simplicity of the
reaction and should suggest many other interesting possibilities. If convenient the reaction can be carried out also in the presence of a solvent, such as xylene. I n this case, however, a t the lower temperature the reaction rate is slower, hut even this may often be compensated for by use of a more active catalyst, Raney nickel. LITERATURE CITED (1) PAUL, R.,Bull. sac. ehim., 5, 1053 (1938). A,, Ann. chim., 14, 318 (1940). (2) HALASZ, (3) BOUVEAULT, L., Bull. SOC. chim., 3, 50 (1908). Can. J. Chem., 31, 297 (1953). (4) HALASZ, (5) BLAIT,A. H., Editor, "Organic Syntheses," Collective Vol. 2,John Wiley & Sons, Inc., New York, 1943,p. 142. (6) KYRIDES, L. P., AND F. B. ZIENTY,J . Am. Chem. Soe., 68, 1385 (1946). (7)SCHNIEPP, L. E.,AND H. H. GELLER,J. Am. Chem. Soe., 69, 1545 (1947).
