2740
Vol.
i(j
Acknowledgments.-This study was aided in The analyses were carried out by Drs. G. \Vciler part by a grant from the Officeof Naval IZesearch.Ig and F. B. Strauss, Microanalytical Laboratory, (19) T h e authors wish tu express their gratitude t o Miss C Vitiello Oxford, England.
the Schering C o w . , Bloomfield, N. I.,for obtaining the infrared absorption d a t a and their interpretation.
of
[ CONTRIBUTIOS
FROM THE
SEIV YORKj8, SE\V YOKK
IPATIEFP HIGH P R E S S U R E A S D CATALYTIC LABORATORY, 1)EPAKTMEYT SORTHWESTERX UNIVERSITY]
UF
CHEMIS1.KY,
Studies in the Terpene Series. XIX. Hydroisomerization and Hydrogenolysis of Cyclohexene, Methylcyclohexene and p-Menthene in the Presence of Hydrogenation Catalysts BY HERMAN PIKES,ALFRED KUDIN,'G. 11. Bb3 A N D LT. N.IPATIEFF.' RECEIVEDDECEMBER7, 1953 The effect of hydrogcii pressure ~ t n dtemperature \vas studied upon cyclohexeiie, ~-1iiethy1cyclohexcri~ a i i t l /~.iiiciitlicriv ( l-incthyl-4-isopro~~ylcyclohexe1ie) in the presence of it nickel-Kieselguhr catalyst. At lower prcssurcs i t l i d highcr teriipcratures the cyclohexenes undergo hydrogenation arid hydrogenolysis accompanied by a skeletal isomerizatioii. A siiiiilnr reaction occurred when nickel-alumina or copper-alumina were used as catalysts.
The hydrogenolysis of pinane in a flow type apparatus in the presence of hydrogenation catalysts, such as nickel-Kieselguhr, nickel-alumina, copper-alumina and nickel, yielded tetramethylcyclohexanes, 0- and p-menthane and a substantial amount of alkylcyclopentanes admixed with bicyclic dihydr0terpenes.j The formation of the latter two types of compounds indicated that skeletal isomerization accompanied the hydrogenolysis of pinane. The formation of alkylcyclopentanes could have occurred through the isomeri-
pinane. A more detailed study was made of cyclohexane since i t was possible to determine the products of the reaction quantitatively by means of a mass spectrograph. Experimental Results Cyclohexene and Cyclohexane.-The exper'imental conditions and the composition of the product obtained from the interaction of cyclohexene and hydrogen over nickel-Kieselguhr catalyst arc' summarized in Table I. The extent of hydroisoiii 1.
TABLE 1 HYDROISOMERIZATION A N D HYDROGENOLYSIS OF CYCLOHEYESE OVER SICKEL-KIESELGUHR CA~ALYSI The molal ratio of hydrogen t o olefiiis used iti the experiinents was 4,3(=tI).3): I . The hourly liquid space velocity (nil. liquid per hour per ml. catalyst) was 0.49(10.05). T h e product withdrawn during the period of 1.5-3 hours was submitted for analysis. Values given in parentheses represent the coinposition of hydrogenolyzed and hydroisoinerized product. They were calculated on benzene and cyclohexnnc free b a & Experiment 9 I Y 1 8 3 G 4 Tetnp., "C. 285 265 2'33 262 230 "93 268 2i5 Pressure, a t i n -> 1.7 10 15 3 1 0 . 5 10 5 1 5 3 5 Product compositioii, mole -., Cyclohesarie 95.8 88 3 9ti.o 9 9 . 1 9s 2 1-3 1 Benzene 1.7 2.4 1.7 ... 0.1 IY 4 1 Cyclopentaiic K7(28) L.G(t'ii) 1 2(1'4) U.4 . . . -, hlethylcyclopentarie ti(24) 1.7(28) 3 2(26) .8 .I 9 .1 . , rz-Hexane ... . . . , 0.4(7) 0 5(6) .i(lG) 0.6(10) 1 7(20) .1 . . . .I 2-hlethylpentane 3-hlethylpentane ,3(20) 1 . 1 (18) 1 3(18) .3 . ;1 3 2,3-Dirnethylbutane .3(12) O.i(11J 1 U(12) .I .3 .B
-
i
"z'L
.i
.i
I
'' Analyzed by means of a mass spectrograph.
zation of alkylcyclohexanes duririg the hydrogenolysis of pinane. In order to test this hypothesis the reactions of several monocyclic hydrocarbons were investigated under experimental conditions similar to those used in the study of the hydrogenolysis (1) V. N . (2) 1952. (3) T,pon,
For Paper XVIII of this series see H. Pines, E. F. Jenkins and Ipatieff, THISJ O U R N A L , 76, 6226 (1953). Universal Oil Products Company Predoctoral Fellow IU;iO--
On leave of ahsence from Societe Chimique RhOne-Pnulenc, France. ) Deceased, Sovernber 29, l E 2 . . Ipatieff, I?. J . Pavlik ancl H. Pine, T H I SJ O I J R N A I . , 7 6 ,
erizatioii decreases sharply with the incrcusc of pressure (Fig. l), and increases with the temperature of reaction (Fig. 2). The formation of cyclopentane most probably from methylcyclopentane, during hydrogenolysis is of interest in view of the work of Haensel and I~atieff,~.' who found that a methyl group linked to a tertiary carbon atom is removed less readily than a methyl group on a secondary carbon. Thus the paraffins, namely, pz-hexane and methylcyclopentanes found i n the reaction product would be expected to lose a methyl !li) V. Haensel and V h-.Ipatieff, ibid., 68, :34j ( I W f i ) . f7) V l f x e r i w l . i i i r l V N. Ipatieff. I i i d E I I X ('kriir , 39, h;:!
I
I!) 17)
May 20, 195-1 HYDROISOMERIZATION OF CYCLOIIEXENE, NETHYLCYCLOHEXENE AND ~ ~ I E N T I I E 27-11 NE group with more facility than methylcyclopentane, and yield n- and isopentane, respectively, none of which was found. The results obtained presently cannot be accounted for without the assumption of skeletal rearrangement; this is significant since in the study reported by Haensel and Ipatieff none of the hydrogenolyzed hydrocarbons underwent rearrangement. At atmospheric pressure part of the cyclohexene undergoes dehydrogenation to benzene. In all the experiments listed previously unused catalyst was used and the sample was withdrawn during the period of 1.5-3.5 hours although i t was found that the activity of the nickel-Kieselguhr catalyst did not change much over a period of 12 hours. Duplicate runs were made in many instances and i t was found that the results were reproducible. I n order to determine whether the hydroisomerization reaction applies also to saturated hydrocarbons, the effect of hydrogen upon cyclohexane was investigated under conditions described for experiment 4. The results were identical with these obtained with cyclohexene. The effect of copper-alumina and nickel-alumina upon the hydrogenolysis and hydroisomerization of cyclohexene was studied (Table 11). The extent of isomerization in the presence of nickel-alumina catalyst was more pronounced than in the case of the copper catalyst. It was found that the prevailing reactions were general for all the three hydrogenation catalysts, although the extent of the various reactions were different.
6 -
5 -
a W
6
12
PRESSURE
18
24
30
- ATMOSPHERES.
36
42
Fig. 1.-Effect of pressure upon hydroisornerization and hydrogenolysis of cyclohexane in presence of nickel-Kieselguhr a t 270 ( h 5 " ) .
9r
TABLE I1 HYDROISOMERIZATION AXD HYDROGENOLYSIS OF CYCLOHEXENE IN THE PRESENCE OF COPPER-ALUMINAA N D NICKEL-ALUMINA CATALYST The experiments were made at 290" and a t 5.5 atmospheres of pressure. The molal ratio of hydrogen t o cyclohexane used was 4.4 and the hourly liquid space velocity was 0.45. Experiment Catalyst Product compositiori, mole Cyclohexane Benzene Cyclopentane 3-Methylpentane 2,3-Dimethylbutane Methylcyclopentane n-Hexane 2-Methylpentane
9 Cu-AlsOa
10 Si-AlZOa
90.7 8.6
94.9 1.5 0.5 .8
% .. 0.1
.1 .5
..
..
.5 1.6 0.1 0.1
2. Methylcyc1ohexene.-The experimental conditions and the composition of the products obtained from the interaction of methylcyclohexene and hydrogen over nickel-Kieselguhr catalyst are summarized in Table 111. The composition of the product was determined by selective dehydrogenation and chromatographic separation as described p r e v i ~ u s l y . ~The product which did not undergo dehydrogenation consisted of alkylcyclopentanes which resulted from hydroisomerization and of paraffins which were formed by the hydrogenolysis of the cycloparaffins. The composition of these hydrocarbons was determined by means of infrared
I 230
I
245
I
I
260
275
290
TEMPERATURE 'C. Fig. 2.-Effect of temperature upon hS'droisoiiierizatioii and hydrogenolysis of cyclohexene in presence of nickelKieselguhr.
spectral analyses.8 The data obtained indicate that the extent of hydrogenolysis and hydroisomerization is greater in the case of methylcyclohexene than in the case of cyclohexene. 3. p-Menthene (1-Methyl-4-isopropylcyclohexene) .-The extent of hydroisomerization and hydrogenolysis of p-menthene (Table IV) was about the same as that of methylcyclohexene. ( 8 ) T h e authors are indebted to Mr. Edmond Baclawski of the Physics Department, Universal Oil Prodilcts Company, for the inlrnred spectral analyses.
2742 TABLE I11 catalyst is accompanied, especially at the lower HYDROISOMERIZATION A N D HYDROGEXOLYSIS OF METHYL- hydrogen pressures, by a skeletal isomerization. This type of isomerization was not noticed during CYCLOHEXENE OVER NICKEL-KIESELGUHR CATAL the selective demethanation of paraffinic hydroAND UNDER 6 ATMOSPHERES PRESSURE carbons.61~ The difference in the behavior of The experiment was made at 266" and 5.5 atmospheres nickel-Kieselguhr catalyst could probably be of pressure. The molal ratio of hydrogen to methylcyclohexene used Kas 4,and the hourly liquid space velocity was attributed to the fact that Haensel and Ipatieff 0.50. in their studies partially deactivated the catalyst Experinmi t 11 by heating i t in a stream of hydrogen at 538" for Product composition, F'c 12 hours prior to its use, and thereby probably 1. Toluene 4 destroying the acidic properties of the catalyst. 3. hlethylcyclohexane 88 The skeletal isomerization accompanying the 3. Saturated C; hydrocarbons other than hydrogenation and hydrogenolysis of cyclohexenes methylcyclohexane s implies that the reaction proceeds probably via Composition of fraction 3," an ionic mechanism. This may occur either trans-1,2-Dimetliylcyclo~~e1it3lie 0--5 through a presence of source of protons on the nickel cij- and trans-1,3-dinietliylcy~lo~~ci1t~11e 25-3C -Kieselguhr catalyst or through a formation of a Ethylcyclopentaiic 0-5 polar bond between the hydrocarbon and the n-Heptane 16-20 catalyst. :3-hlethylhesane 13-20 The extent of hydroisomerization of p-menthene 2-Methylhexane CM is much less than that observed for inane.^ I t 2,3-Dimethylpexitane 0-4 appears therefore that the hydroisomerization of a
The composition of fraction 3 was determined by nieaiis
of infrared analysis. TABLE I\' HYDROISOMERIZA.TIOK A N D HYDROGEXOLYSIS OF ,!-A\IEIvTHEiYE ( l - ~ ~ E r H . i L - 4 - l S O P R O P . i L C Y C l . ~ € t E X E S E )
Experinlent" 12 Catalyst ?;i(K) Temp., ' C . 262 5 5 Pressure. a t m . Product composition, wt. Yo: 5 1. Aromaticsb 0 2. p-Menthane 88 3. Paraffins and alkylcyclopentanes' 8 Anal. and composition oi 3 ,
13 Si(K) 202 1.5 6
..
14 Xi-AlsOa 290
7.5
15 Cu-AIIOI 289 6.5
26
pinarie does not proceed through alkylcyclohexanes but probably through the formation of bicyclic hydrocarbons of the type of bornylane. These hydrocarbons on liydrogenolysis would form alkylcyclopentanes. The presence of bicyclic hydrocarbons, others than pinane, was observed in the reaction products obtained from pinane. Materials
a The molal ratio of hydrogen p-menthane = 5 . 5 . * Composed of over 90% p-cymene. c Hydrocarbons which did not undergo dehydrogenation when passed over platinumalumina catalyst at 290'. Calculated from the carbon and hydrogen analysis with % C and % H corrected to 100 .O%.
Cyclohexene was prepared by $hydration of cyclohexanol over activated a l y i n a a t 420 , It distilled at 82.2" a t 750 mm., n a 4 ~1.4462 . 4-Methylcyclohexene was prepared by dehydration of 4methylcy~lohexanol.~ p-Menthene ( 1-Methyl-4-isopropyl-x-cyclohexene) .-1Menthol (Eastman Kodak t o m p a n y ) was dissolved in equal volume of n-hexane and dehydrated at 425" by passing it over activated alumina. The p-menthene distilled a t 167-169", ?ZZ1D 1.4618, [ ~ Y ] ~ 57'. . ~ D Nickel-Kieselguhr was obtained from Universal Oil Products Company.1c Copper-alumina contained 13 parts by weight of copper oxide per 100 parts of a l ~ m i n a . ~ Nickel-alumina was composed of 75y0nickel and 25% by weight of alumina.6 Apparatus and procedure were the same as described previously.5 Ii VANSTOS, I r,r.tNoIs
Discussion of Results The hydrogenation of cyclohcxcne and alkylcxyclohexenes in the prcscnce of nickel-Kiesclgullr
(9) V. S. Ipztieff, E , E. Meisinger a n d H. Pines, THISJ O U R N A I L 7 2 , 2772 (1030) (10) V . N. Ij),i:icfi and I i . :1. C o h n n , l i d . Eng. Chcin., 26, 1888 (1!13 1).
98
7 88.5
26 70
2
4.5
4
70 Carbon Hydrogen Refractive index, n% Alkylcy~lopentanes~ Paraffinsd Paraffinsd
85 30 86.21 14 72 14.00 1.4215 1 4427 72 60 28 40 28
X.5 3 I 14 62 1 4:i:$Y 80
20
83.58 14.68 1 4311 80 20
