Sept., 1945
THE
CYCLIC DIMERIZATION OF
1455
ISOBUTYLENE
(CZH&N< NH3< (CzH&NH < C2HsNHz (curve D) ; and tri-t-butylboron, a reference acid with a high F-strain factor, yields the order (CzH5)3N< < C Z H ~ N H!I4 (lW!l).
liquid products contained the same main components regardless of the conditions under which they were prcpnretl. Typical detailed results of the examination of one liquid are shown in Table I11 and Fig. 1. In general, the product of the boiling range of fraction 4, the crude dimeric fraction, was made up largely of the cyclic dimer, but it contained a lesser amount of unsaturates and a small quantity of paraffins. Product of the boiling range of fraction 2 was mainly paraffinic, al(7) Zelinxky and Uspensky, tlcr., 46, 1 4 ~ 6(1018). ( 8 ) Dey and Linstead, J. ('hem. .Sot., 1063 (1935). (0) Zelinsky and Uspensky's preparation had a b. p. of 115-116' a t 7R0 mm., a d 2 0 1 of 0.770:$,and a 112011 of 1.4223. Dey a n d Linstead's product had a b. p . of 106- 107' a t 7ti7 m m . , a d % of 0.7764, and a n l b of 1.4240. (10) I n t h e bomb technique rmployed, t h e pressiire rnse t o ii ~ n i ~ x i m i i n:,nil i then fell lieritiise of reaction.
Sept., 1945
though a substantial amount of acyclic olefins was present. Material in the boiling range of fraction 5 contained mainly cyclic unsaturates, and that in the boiling range of fraction 7 was made up largely of cyclic saturates and' acyclic unsaturates, which were, most probably, trimers.
200
TABLE I11 EXAMINATION OF LIQUIDPRODUCED I N O N E HOURAT 400" UNDER 2050 LB. MAXIMUM PRESSURE"
160
Fraction
B. p . , 'C., 740 mm.
at
1457
THE CYCLIC DIMERIZATION OF.ISOBUTYLENE
Wt., %
n2%
d%
Rr. no.
to 75 0.9 1.3799 0.6672 51 75-85 5.4 1.3846 .6780 34 85-95 1.7 1.3919 ,6949 23 4 95-128 40.9 1.4101 .7389 38 5 128-150 3.6 1.4322 ,7711 121 6 150-175 2.6 1.4376 ,7789 104 7 175-195 14.3 1.4365 .7839 52 8 >195 30.6 1.4609 ,8292 ... 0 Gaseous product and experimental loss were 39.8 wt. % ' and 2.5 wt. %, respectively, of the isobutylene reacted. The analysis of the gas in wt. yo was methane, trace; propylene, 0.4; propane, 3.1 ; isobutylene, 91.2; isobutane, 2.7; Cg and higher (unsaturates), 2.3; CS and 'higher (saturates), 0.3. Analysis by E. H. Epprecht of Gulf Research and Developmetit Co. 1 2 3
180
f
-
ij
- 140 i
Y
2
8 120
G
100
80
2 ti0
I
20 40 60 80 Volume yo distilled. Fig. 1.-Distillation curve of the product described in Table 111. Arrows define fractions taken. 0
The effect (Table 11) of increasing either reaction time or maximum pressure was to increase the yield of total liquid product. The liquid yield also increased with increased temperatures up to 430°, but, when a substantially higher tempera- tetramethylcyclobutane (11). If (11) is formed, ture (460') was employed, it decreased because of thermal stress would be expected t o rupture one CHs excessive cracking of the product. The yield of 2 )C=CH, cyclic dimer showed the same general time ahd temperature dependence as did the total liquid ; CH, I however, it was relatively independent of maximum reaction pressure above 1280 lb./sq. in. The maximum yield of 23.4% resulted when the reaction was carried out under a maximum pressure of 2025 lb./sq. in. a t 430' for one hour. The percentage of cyclic dimer found in the various liquid products was independent of reaction time. This percentage decreased as the maximum reaction pressure was increased, but increased to a constant value of about 32% as the reaction temI perature \vas increased. The highest percentage C ' H? of cyclic dimer found in any liquid product was 45.9%, resulting when the reaction was carried out under a maximum pressure of 540 lb./sq. in. a t 400' for one hour. Mechanisms of Dimerization. -The mechanism by which the cyclic dimer forms is not known. It was found, however, t h a t the conipound could not be formed from the commonly occurring diisobutylene," an expected intermediate, under conditions suitable for the formation of the naphthene from isobutylexie. The hydrocarbon could form, however, in several other ways which are shown in the accompanying schematic diagram. For example, it is possible that two molecules of isobutylene (I) might polymerize to 1,1,3,3-
i
1
+
.1
(11) A mixture of f o u r parts of &,4.1-trimethylpentene-l and one 1mrt of L ' , - l , ~ - t r i m p t h ~ l * , ~ " t ~ n ~ - ~ .
j . B. MCKINLEY,D. 11. STEVENS .IND W. of the carbon-carbon bonds of the ring t o give the bivalent radical (111) which could isomerize to another bivalent radical (IV). The latter radical niight then cyclicize t o form the cyclic dimer (VII). I t is also conceivable that the dimerization involves the isomerization of isobutylene to the bivalent radical (VI), and the addition of (VI) to a normal isobutylene molecule. Alternatively, isobutylene might first form 2,5-diinethylhexene-l (V), which is postulated by McCubbin oxid AdkinsI2 as a possible acyclic dimer of isobutylene. This olefin, if formed, might cyclicize by a process of intraniolecular alkylation, involving the tertiary hydrogen, t o give (VII). These mechanisms support the structure assigned to the cyclic dimer, which is otherwise confirmed by the conventional synthesis.
Experimental Detailsi3 l-Chloro-l,3-dimethylcyclopentane.--A method which i i esseiitially that of Chavaiiiie14 was used to prepare a \tack of 1,3-dimethylcyclopentanol (ti. p. 59.8-60.Oo a t 20 trim., d2O40.8903, n% 1.14201. I n a sample experiment, the cyclopeiitariol (132.4 g.) reacted with 57.6 g. of dry hydrogen chloride a t 2'. The crude product was washed n ith water, then with saturated sodium bicarbonate solution, again with water, aiid filially dried with calcium chloride. The preparation was fractionated through a 20-plate coluirin a t 15 mm. pressure using a reflux ratio of 20 : I . Super1ieati:ig atid dccompositioii during fractionation were avoided by immersing the still pot in a water bath a t 45-60". 'Thc coilstant boiling product (b. p . :i3.2'" a t 15 mm.,d2", (J,9347, ? i Z " 1,4406) ~ weighed 11'8.9 g . ; yield, 83.8';. .lnul. Calcd. for C ~ H U C ~C,: (3.39; H, 9.88; C1, 2ii.;:i. Found: C, 034fi; H , I[J.W; CI, 26.37. 1,1,3-Trimethylcyclopentane. A. By Zinc Dimethyl Methylation.--A solution of 53 g. of l-chloro-l,3-dimethylcyclopentanc in 53 g. of dry sylcne was added, in one hour, t o a stirred solution of 20 g. of ziiic dimethyl (Eastina!i Kodak Co.) in 150 g. o f dry xylene, keeping the teniperature a t 2t5".i6The rcaction mixture was slowly heated to aiitl maintained a t 40' for one-half hour. The cooled product was treated with 20 nil. of concentrated hydrochloric acid in 8U ml. of water to decompose zinc dimethyl. I t was washed with saturated sodium bicarbonate solution and with water, dried over calcium chloride, and finally refluxed over sodium. The product was combined with other similarly prepared material and the composite was fractionated to obtain 90 g. of product, boiling from 90.5 to 139.5' at 760 mrii., which \vas free froin the bulk of the solvent xyleiie. Fractionatioii of This concentrate a t 735 mm. through a ti2-platc columii using a reflus ratio of 30: 1 with detcrmination of the bromine nuinhers16of the frarrions, showed that it consisted of urisaturates (b. 11. 91--92', d2", 0.7696, broniiiie number 1491, a solvent and haturated, product. Except for the small amount (10 ml.) contained in transition fractions, all of this haturated product (50 1111.) boiled a t 103.i O . l O , showing the isolation of a pure compound. A 10-ml. middle fractiou was filtered through silica gel" to remove tr of lo\ver-l)oiling unsaturates f
-
i l 2 ) hlcCubbin and Adkins. 'l'rrrs Jurmsar., 62, 23-17 (193U). (13) Microanalyses by Ralph 0 Clark and I.incoln T. J e n k i n s of Gulf Research and Development Co. (14) Chavanne, BILII.:iic chiin. B e k . , 35, 283 i1026). (15) l h e zinc dimethyl solution W A S made up in a n atmosphere of d r y carbon Jioxide and t h c reaction w a s carried o u t in such an atmosphere ( 1 0 ) Alulliken and V-alreman. i i i d E,ig. Cherir , "Ilrn!. Ed.. 7, 2'9 (1',1:3.?),
6~17) >lair :inti n ' h i t i . , .7
< 103.?1.
R ~ ~ t i i i r \h
ii.1,
S/niiJni.dc, 15,
il
E.R.II,DWIN
I-01. 67
and solvent xylene. Properties of the purified product arc given in Table I. The total yield of the naphthene was :i4.i'ni; of the theoretical, based on the chloride reacted. .lnul. Calcd. for C Y H , ~C,: 85.633; H, 14.37; mol. wt., 112.2. Found: C, 85.55; H, 14.44; mol. wt., 112. B. By Methylmagnesium Iodide Methylation.Methylmagtiesiurn iodide was prepared in 1030 ml. of dibutyl ether at 35-39' from 60.9 g. of magnesium and 356 g. of methyl iodide. Three hundred and eight grams of l-chloro-1,3-dimethylcyclopentanewas added to the stirred Grigiiard reagent in forty minutes. The temperature was not controlled during this operation; the heat geiierated caused i t to rise gradually to 70". Stirring was continued for an additional one hundred and thirty-five minutes while the reaction mixture cooled to 2.5'. T h r Grignard reagent was decomposed with water acetic acid. The oily layer was washed with 10 hydroxide solution and with water and finally drieci with anhydrous potassium carbonate. It was fractionated through a 15-plate column to obtain 100 ml. of product boiling from 90.8-129.0" (740 mm.). This fraction was cornbincd with 50 nil. of xylene, refluxed over sodium, and refractionated (reflux ratio 30: 1) through a 62-plate column. The data showed the production of 50.3 g. (19.37; yield) of the desired naphthene. A 15-mi. middle fraction of the naphtheriic material (b. p. 104.0-104.1" a t 745 tniii.) was further purified by filtration through silica gel. I t s properties were idcritical with those of the I,i$ triniethylcyclopentane prepared using ziiic dimethyl.
