N. F. FOSTER AND R . J. CVETANOVI~
4274 [COKTRIRUlIOS FROM
THE
DIVISIONO F APPLIED CHEMISTRY, NATIONAL RESEARCH COUNCIL, OT.I.ATVA,
Vol. s2 CANADA
1
Stereoselective Catalytic Isomerization of n-Butenes B Y N. F. FOSTER' AND
R.J. CVETANOVI6
RECEIVEDOCTOBER 26, 1959 Following the recent observations of stereoselectivity in the catalytic isomerization of butene-1, the isomerization of nbutenes has been studied on a wide variety of catalysts. The stereoselective isomerization of butene-1 has been found t o occur t o a smaller or greater extent on all the catalysts studied. The highest selectivities were found on the basic catalysts and the smallest on some metals. The butene-2 isomerization has been observed to proceed by exclusive double bond shift (on some basic catalysts, e,f., KOH) or exclusive cisltvans conversion (on some acidic catalysts, e.g., I-12S0,)or by combination of the two processes,
Introduction cationic reaction was found difficult to rationalize. The isomerization reactions of the n-butenes The previous work in these laboratories using a have been the subject of study for many years,2 series of catalysts varying in composition from 0 to and both the therma13-6 and catalytice-10 processes. 100% NiO in Cr203showed that the stereoselectivity have been investigated. In the previous litera- was greatest on the catalysts containing approxture there have been some indications of a stereo- imately equimolar quantities of the two oxides and selectivity in the catalytic reaction of butene-1,11,12 consisting mainly of NiCr204, decreasing when a but only very recently has this aspect been studied. large excess of either oxide was present. The Three pieces of independent work on this subject impregnation of any of these catalysts with KOH have been reported in the last two years: (1) solution produced a highly selective catalyst. The present work was undertaken with the Lucchesi, et a1.,I3 using butene-1 on a silicaalumina catalyst; (2) Haag and Pines14 using object of establishing how general the selectivity butene-1, with some work with butene-2 isomers, on in the catalytic butene isomerization is and whether alkali metal and acidic catalysts; and (3) Cvet- a broad generalization can be drawn relating the anovik and FosterI6 using the three n-butene catalyst type and the extent of the selectivity. isomers on a series of NiO/Cr20s catalysts. Luc- For this purpose interconversions of the three nchesi, et al., found a very marked stereoselectivity butenes have been studied on a wide variety of favoring the formation of cis-butene-2 by a ratio catalysts. The work has been mainly limited to of 4 to 1 at 20% reaction, this ratio increasing small conversions in order that the initial ratios of rapidly a t lower conversions. This it was felt the isomers formed can be obtained by extrapolawas not consistent with the usually accepted tion. carbonium ion mechanism and the formation of a Experimental ir-complex between the double bond and the The apparatus used was a circulatory flow system with a surface proton was suggested. The results of total volume of approximately 1.5 1. and a catalyst cell volHaag and Pines show a similar marked selectivity ume of 20 cc. The flow rate throughout was 1.8 l./hr on supported alkali metal catalysts and a less a t N.T.P. and the initial butene pressure 10 cm. Most of the catalyst materials were formed into 0.25" cylindriral marked selectivity on the acid catalysts. cis- pellets and a charge of approximately 15 g. taken in e x h and trans-butene-2 were also used as initial reactant case.l6 Each catalyst was used a t the lowest possible in some cases and from the data obtained the temperature to obtain results at low 7 0 conversions. of the gas exiting from the reactor were w i t h d r a w relative rates of the six isomerization reactions aSamples t intervals and analyzed by gas chromatography, using a were calculated. The selectivity of the base- 50-ft. column of dimethylsulfolane on firebrick a t room catalyzed anionic reaction was attributed to a temperature. This gave a complete separation of the preferential attack on the cis form of the allylic (16) Some details of catalyst preparation are: K O H (AR grade) anion, but its occurrence in the acid-catalyzed (1) Xational Research Council Postdoctorate Fellow, 1957-1959.
Issued as N.R.C. Publication No. 5722. (2) H . N . Dunning, I n d E . E . Chem., 45, 551 (1953). (3) C. D. Hurd and A. S. Goldsby, THISJ O U R N A L , 56, 1812 (1934). (4) G . B . Kistiakowsky and W. R . Smith, i b i d . , 6 8 , 760 (1936). ( 5 ) W. F. Anderson, et al.. i b i d . , 80, 2884 (1958). (6) V. N. Ipatieff. H. Pines and R E. Schaad, i b i d . , 66, 2696 (1934). (7) G. H . Twigg, PVOC. Roy. SOC.( L o n d o n ) , 8178, 106 (1941). (8) W. W. McCarthy and J. Turkevich, J . Chem. Phys.. 12, 405 (1944). (9) J. Turkevich and R . R . Smith, ibid., 16, 466 (1948). (10) T . I. Taylor and V. H Diheler, J . Phys. C o l b i d Chem., 55, 1036 (1951). (11) H . H. Voge, G. M . Good and B. S. Greensfelder, I n d . E n s . Chem., 38, 1033 (1946). (12) M . H. Polley, W. D. Schaeffer and W. R. Smith, Can. J . Chem., 3 3 , 314 (1955). (13) P . J. Lucchesi, D. L . Baeder and J. P. Longwell, THISJ O U R N A L , 81, 3236 (1959). (14) H. Pines and W. 0 . Haag, J Org. Chem., 23,328 (19.58): W 0. Haag and H. Pines, Symposium on Isomerization and Related Processes, Am. Chem. Soc. Meeting, Boston, April 5-10, 1959. ( 1 5 ) R . J. Cvetanovik and N. F. cr, Disrrrsririns Fiiriidov .Sor., 2s. 201 (1959).
was heated above its melting point t o remove the water; it was then allowed t o solidify and was broken into fragments (approximately 0.25'' diameter) which a e r e placed in t h e reactor a t 320" and pumped i m mediately t o minimize mater uptake. An almost saturated solution of AR grade NaOH in distilled water was poured into a reaction cell packed with glass beads and then allowed t o drain off until n o more liquid dripped out; the cell was then attached t o t h e apparatus, heated and pumped t o remove excess water. LiOH and CaO powders (AR grade) were compressed into 0.25" cylindrical pellets. KnCrO4 was pelleted similarly b u t with the addition of a few per cent. graphite as binding agent which was subsequently burned off by heating in a muffle furnace t o just below t h e melting point of K2CrOP. T h e carbon used n a s "Carbon Decolorizing" from Fisher Scientific Co. which was compressed into 0.25" pellets. Concentrated phosphoric and sulfuric acids were poured over glass beads packed in t h e reactor and time allowed for drainage as in t h e case of R'aOH, with subsequent heating and pumping. Kickel (powder) and silver (shot) were compressed into 0.25" pellets. CrzOa (AR grade), ZnO (AR grade) and Firebrick powder were each mixed with a few per cent. graphite and compressed into 0.25" pellets which were then fired a t 900" for 3-4 hours t u burn off the carbon. T h e remaining catalysts (Clay, Rsso, Davison and Alcoa) were obtained already activated and were formed into 0.25'' pellets without t h e addition of graphite and used nithrmt any pretreatment other than the usual pumping overnight (the ? t m d a r d pr~icrdure with all cntalvsts) prior t o doing a rim.
CATALYTIC ISOMERIZATION OF %-BUTENES
Aug. 20, 1960
n-butene isomers. T h e butene isomers used were Phillips research grade.
Results The data given in the accompanying tables were obtained from analyses of samples containing only the n-butenes, i.e., from runs in which isomerization was the only reaction. The ratio between the two isomers produced by the reaction was calculated for each sample and plotted against the corresponding conversion of the react antisomer. The ratio a t zero conversion was obtained by extrapolation, giving the relative reaction rates for the formation of the two isomers." In Table I the observed ratios and 70conversions are given for some of the more interesting catalysts. RATIOSOF
THE
TABLE I ISOMERS FORMED AT DIFFERENTCONVERSIOSS
Catalyst K O H (320")
LiOH (440')
Alcoa (300')
Activated clay (400)
Artivnted clay
(200")
Nickel (300")
d
a Percentage &/butene-1.
-Butene-1%a Ratiob 1 . 5 0 11 1 77 ,086 2.2 236 6.0 .3i 5,35 .35 12.7 .33 13.7 33 26.1 .51 41.3 .50 64.9 .66 72.2 1.04 2.16 0.98 7.3 1.06 1 8 . 1 1.07
3.12 0.6 4.02 .51 17.95 .59 34.8 .64 2.73 .86 5.15 .96 10.0 1.23 4 . 5 1 0.86 6.73 .98 22.0 .95 45.5 .92 50 .98 78.3 1.2 11.8 1.25 32.7 1.41 63.8 1.43 78 1.57 9.8 1.49 17 1.49 30 1.51
Reactant cis-Butene-2 RatioC 0 1.3 0 1.7 2 2 0 5.6 0,037 15 7 .l9 22.3 .21 40.5 .44 56.5 1.06 %a
2.6 5.11 14.2 19.2 4.2 12.9 23.0
4.53 4.5 4.38 4.5 0.075 .11
.18
13.4 22.4 43.4 52.5 6.91 9.47
112 50 26 19 1.37 1.65
9.€6 21.5 41.6 61.7 3.1 4.13 9.25
2.68 2.61 2.9 3.4 1.82 1.3 0.88
conversion.
trans/&.
trans-Butene-2 %a Ratiod 0 0.08 0 1.23 2.75 0 5.03 0.23 11.3 ,49 25.8 .8 39.8 1.1
2.0 7.3 13.8
7.2 4.15 3.96
2.14 9.1 12.7
0.09 .17 .21
Q . 2 5 150 16.25
169
35.5 39.3 7.35 16.02 20.4
30 20 2.15 3.37 4.1
7.37 15.47 26.7 48.1 2 0 2.76 5.62 10.74
2.03 1.74 2.7 2.4
