Mechanism of the Polymerization of Olefins by Acid Catalysts FRANKC. WHITMORE, T h e Pennsylvania State College, S t a t e College, Pa.
T
The polymerization of olefins is of considerable thus leaving the central carbon HE history of the polyof the isobutylene with only six merization of Olefins has industrial importance, This paper proposes a been t h o r o u g h l y reelectrons. Thus t h e p r o d u c t general theory f o r this type of process and illusviewed recently ( 1 ) . The poly(C) is positively charged. Its m e r i z a t i o n of s i m p l e olefins & aPP1ication to the pob'merization of carbon atom with only six elecisobutylene, a process of present industrial t r o n s c a n a t t r a c t a pair of takes place with acid catalysts. Those olefins which add a moleelectrons either from one of the signijicance. The theory is also used in prestructures 0 , certain unsolved OleJin adjacent methyl groups or from c u h HX, m o s t r e a d i l y also dieting polymerize most readily. I n the adjacent methylene group, mixlures. e a c h case the first step is the thus liberating a p r o t o n a n d addition of a hydrogen ion (a forming a double bond : proton) to the extra electron pair in the double bond: (C)= H e S\CH2=C(Me)-CH2-CMea hle&==CH-CMe, H (D) (E) :C::C: .. .. H e =: :C:C: *. .. It is important that the hydrogen ions regenerated in this type of change can add to the olefins present and start the By this process One carbon is left with Only six cycle of changes again, the process is catalyzed by It is thus positively charged and can undergo the changes any substance which givesThus hydrogen ions. which are characteristic of an atom with a deficiency of elecActually diisobutylene consists of 2,4,4-trimethyl-l-penikons (4). Among these are (l) union with a negative ion, tene (D) and 2,4,4-trimethyl-2-pentene (E) in the ratio 4 to 1 X, having a complete octet of electrons (this gives a simple (8)' Of the addition of HX to the bond); (2) At this stage the reaction mi&ure contains the three process by the loss Of the Same Or a different proton to give olefins, isobutylene (A) and the two diisobutylenes (D and E), the same Or a new Olefin;' (3) a rearrangement Of the and the p0sitit-e tert-butyl group (B), the positive group (C) skeleton followed by the loss of a proton to give a new olefin;' related to the diisobutylenes and positive hydrogen ions. (4) polymerization. This merely involves the addition of the The polymerization could continue by the addition of any Of Olefin in positive Organic to another of the three positive particles to any one of the three olefins. the same way that the positive proton added to the Thus a positive tert-butyl group (B) could add to the 2,4,4molecule of olefin. The result is a larger positive fragment trimethyl-l-pentene (D) to give the intermediate (F): which can undergo the changes indicated, including further polymerization. This may follow two courses: (1) The c3 (B) 4-(D) +M ~ ~ C C H Z - C ( M ~ ) - C H ~ - C M ~ ~(F) larger positive fragment may add to an olefin molecule, or (2) it may lose a proton to give a larger olefin molecule to which a posit.ve fragment may add. The same process Can The carbon left with only six electrons as the result of the continue until large inactive molecules are obtained. These addition is indicated with a @ sign. This unstable group could be stabilized by the loss of a proton from either of the predictions agree with the known experimental facts. The mechanism of the polymerization of olefins in the adjacent methylene groups Or from the adjacent presence of acid will be illustrated with isobutylene and its group: (F) a H e + Me3CCH=C(Me)-CH~-CMea polymers. The addition of a hydrogen ion to isobutylene (G) (A) gives a positively charged (4) tert-butyl group (B), This (MelCCH2)2C=CHz same product is obtained by treating tert-butyl alcohol with (H) acids: H H Me Triisobutylene has been found to contain 2,2,4,6,6-pentaMe:C::'C H e Me:C:'C:H t- Me:C:O:H methyl-3-heptene (G) and unsym-dineopentylethylene (H) Me H Me" Pie" (7). The addition of a positive tert-butyl group (B) to 2,4,4(A) (B) trimethyl-Zpentene (E) would place two tert-butyl groups Innthensameway that a positive hydrogen ion adds, the posi- on one carbon of a tetrasubstituted ethylene. No product tive tert-butyl group (B) can add to isobutylene (A) to give corresponding to such an addition can be found in triisobutyl&ne (2, 7 ) . The positive group (C), related to the two dithe intermediate ( C ) . isobutylenes, could also add to isobutylene (A) to give the H Me H Me intermediate (J). Me:C::'C C:Me + Me:C : C : C : M e (C) a3 MiH Me Me H Me (A) (C) ----f Me2CCHz-C(Me~)-CH2-CMe3 (J) The carbon atom with ohly six electrons in the positive tert- This could lose a proton in two ways: butyl group adds to the extra electron pair of the isobutylene, f CH1=C(Me)-CHz--C(Mez)--CI~pCMet Recently i t has been (J) S I Changes of t h e first type have long been known. found in this laboratory by K. C . Laughlin t h a t 3,3-dimethyl-l-butene with (K) Me&=CH-C(Mez)-CH-CMe, a n acid catalyst gives 2,3-dimethyl-2-butene and 2,3-dimethyl-l-butene in
+
+
+
+
+
+
+
(L)
yields of 60 and 30 per cent, reapeotively.
94
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1934
Triisobutylene is also found to contain 2,4,4,6,6-pentamethyl-1-heptene (K) and 2,4,4,6,6-pentamethyl-2-heptene (L) ( 7 ) . The unsolved tetraisobutylene mixture may be predicted to consist of olefins from the following combinations: (B) (H), (B) (K), (A) (F), and (A) (J). The less probable union of (C) and (D) would give the same products as (B) and (K). The determination of the structures of the hexadecenes in tetraisobutylene will throw light on such additions. The structures of the polyisoamylenes have also never been solved. Here the problem is complicated by the fact that catalysts for polymerization can also cause rearrangement of the olefin,’ thus increasing the number of substances to which the tert-amyl group can add. The most probable products in the diisoamylenes would be 3,5,5-trimethyl-Zheptene and -3-heptene, 2,3,4,4-tetramethyl-l-hexeneand -2-hexene, and 2-ethyl-4,4-dimethyl-l-hexene. Polymerization processes are complicated by the possible reversal of the addition of a positive tertiary group to an olefin (6). A further complication may be caused by re-
+
+
+
+
95
arrangements of the positive fragments formed by additions to the olefins (4). Such changes accompany the polymerization of tetramethylethylene ( 3 ) . I n conclusion it may be stated that the present theory is proving a valuable tool in laboratory studies of polymerieation.
LITERATURE CITED (1) Brooks, B. T., paper presented before Division of Organio Chemistry, 85th Meeting of American Chemical Society, Washington, D . C., March 26 to 31, 1933; Norris and Joubert, J. Am. Chem. SOC.,49, 879 (1927). (2) McCubbin, Zbid., 53, 356 (1931). (3) Meunier, P. L., unpublished data. (4) Whitmore, J. Am. Chem. SOC.,54, 3276 (1932). (5) Whitmore and Church, Ihid., 54, 3711 (1932). (6) Whitmore and Stahly, Ibid.. 55, 4153 (1933). (7) Wilson, C. D., unpublished data. RECEIVED December 6, 1933. This paper is a aummary of the address by the author aa retiring chairman of Section C at the meetinn of the American Association for the Advancement of Science, Boaton. Maes., December 29, 1933.
Fused Cobalt Oxide as a Water Gas Catalyst ERNESTC. WHITEAND J. F. SHULTZ, Bureau of Chemistry and Soils, Washington, D. C.
R
E C E N T years have witnessed a n increase in the number of industrial installations for the manufacture of hydrogen by the catalytic conversion of w a t e r g a s with steam according t o the wellknown reaction, CO
+ H20= COz 4-HZ (1)
Catalysts made by the fusion of cobalt oxide will, ulhen properly reduced in hydrogen, effeclively catalyze the water gas reaction to equilibrium at temperatures as low as 283” c. and space velocities as high as 1800. The addition of oarious promoters Seems capable of largely repressing the simultaneous formation of methane. Iron in quantities as high as 3 p e r cent appears to inhibit the formationof methane without cutting down appreciably the activity toward the water gas reaction. Copper as a promoter gives promising results. A cobalt catalyst containing38 per copper is particularly actiue as a water gas synthesizing sign*cant quantities of methane.
and the advantages of producing hydrogen-nitrogen mixtures by this method, especially for use in the direct synthesis of ammonia, h a v e s t i m u l a t e d the search for better catalysts than those originally employed in the Bosch process. Earlier studies in this laboratory have been reported by Evans and Newton (2) who prepared a number of precipitated metal oxides, with and without promoters, and noted the superior activity of cobalt when used with a sulfur-free gas. The known excellence of fused catalysts for ammonia synthesis and other reactions prompted the present authors to investigate the merits of fused cobalt oxide as a water gas catalyst and t o ascertain whether by proper addition of promoters the concomitant synthesis of methane according to the following reaction could be satisfactorily suppressed: CO
+ 3H2 = CH, + HzO
(2)
For extraneous reasons the investigation was interrupted before all of its objectives were attained. It is believed, however, that it contributes in a measure to the background of information useful to investigators in this field of catalysts.
PREPARATION OF MATERIALS CATALYSTS.In most cases cobalt oxide was prepared by ignition of cobaltous nitrate and was fused in an oxygen at-
mosphere by n ~ a n of s an OX!’hydrogen torch Playing directlv on the material contained in one of two s p e c i a l crucibles: The first was a 4-inch (10.2-cm.) iron crucible, t h e i n t e r i o r of which had been lined to a thickness O f a b o u t i n c h (1*27 cm.) with cobalt oxide by baking out a thick p a s t e of t h e ignited material. The second c r u c i b l e w a s m a d e from a casting of cobalt metal, the wall t h i c k n e s s being sufficient t o prevent melting by the flame used. Usually the minor components were added to the cobalt nitrate before i g n i t i o n in the form of nitrates or other suitable salts, but a few were introduced as oxide during the fusion. Two of the preparations (221 and 224) were made by burning cobalt metal. After the melt had cooled, it was crushed and screened to 10-14 mesh. I n Table I are shown the results of chemical analyses of the twenty-four preparations. It is worthy of note that nickel was never introduced purposely but appeared in association with the cobalt to an extent depending on the source of the latter, which is indicated in the final column. GAS. The water gas used in the tests was made in a semiworks generator, using a commercial coke. A regulated portion of the “blow” was introduced with the “run” so as to give a nitrogen content of about 25 per cent after removal of the carbon dioxide. After mixing in the holder, the gas was compressed and subjected to water scrubbing a t about 100 atmospheres t o remove carbon dioxide and hvdroeen sulfide. and Gas stored a t this pressure in cylinders. Analysis showed the percentage composition of the stored gas to be 32.6 carbon monoxide, 40.1 hydrogen, 26.1 nitrogen, 0.5 carbon dioxide, 0.5 oxygen, and 0.29 methane. O e 5
1
y
