Z-Methylbicy clo [ 2 o Z e l ] 5=heptene, 2-Methylbicyclo[2.2.1]heptane, and 2-Methylbicyclo[2e2.2]octane GEORGE CALINGAERT, HAROLD SOROOS, AND HYMIN S W I R O Ethyl Corporation, Detroit, Mich. 2-Methylbicyclo[2.2.11heptane and 2-methylbicyclo [2.2.2]octane were synthesized through Diels-Alder condensations of propylene with cyclopentadiene and l,3-cyclohexadiene to give, respectively, 2-methylbicyclo [2.2.1]5heptene and 2-methylbicyclo12.2.215-octene, followed by hydrogenation to the respective bicycloalkanes. The octane numbers of 2-methylbicyclo I2.2.115-heptene and the two bicycloalkanes were found to be 97,70, and 51, respectively. These octane numbers are compared with those of bicyclo [2.2.1]2-heptene, bicyclo 12.2.11 heptane, and several isomeric cycloparaflins.
Condensation of propylene with cyclopentadiene or its dimer dicyclopentadiene, gave 2-methylbicyclo[2.2.1] hheptene, and interaction of propylene with 1,3-cyclcrhexadiene gave 2-methyl' bicyclo[2.2.2] 5-octene. Both bicycloalkenes were readily converted t o the corresponding bicycloalkanes by hydrogenatioa with a nickel catalyst.
.
ANTIKNOCK RATMGS
YDROCARBONS of compact structure generally have higher antiknock values than the isomeric compounds of straight-chain or less highly compact structure (7). Models of the molecules of such compounds as bicyclo [2.2.1] h e p tane and bicyclo[2.2.2].,octane, having carbon skeletons I and 111,
H
fi mc C
'K
I11
\K IV
show that these compounds are very compact and, hence, might be expected to have high antiknock values. However, because of their high melting points (87" C. for the heptane and 169" for the octane) the antiknock evaluation of these two hydrocarbons is not of practical interest. The 2-methyl derivatives, however, which have carbon skeletons I1 and IV, have relatively low melting points and were deemed to be of interest for testing as high-antiknock fuels. These two bicyclic hydrocarbons, %rnethylbicyclo[2.2.l]hep tane and 2-methylbicyclo[2.2.2] octane, have been prepared previously only by Zelinskil and co-workers (6, IO) through DielsAlder reactions. Interaction of acrolein with cyclopentadiene and l,%cyclohexadiene, respectively, produced bicyclo[2.2.1]5heptene-%a1 and bicyclo[2.2.2] 5-octene-2-al. These compounds were converted to the respective hydrazones which were decomposed by heating with potassium hydroxide to give 2-methylbicycle[ 2.2.11 hheptene and 2-methylbicydo[2.2.2]5-octene.Hydrogenation of the olefins over platinum or palladium gave the corresponding bicycloalkanes. The recent work of Joshel and Butz (6),who prepared bicyclo[2.2.1]2-heptene by the interaction of ethylene and cyclopentadiene, suggested that the two methylbicyclo compounds might be prepared more directly through similar Diels-Alder condensations of propylene with cyclopentadiene and 1,3-cyclohexadiene, followed by hydrogenation of the resulting bicycloslkenes. This was found to be the case.
The two methylbicycloalkanes and 2-methylbicyclo[2.2.1] 5heptene were knock-rated in a nonsupercharged, variable-compression, single-cylinder engine. The results are given in Table I. Also included are the recently obtained ratings of bicyclo[2.2.l]%heptene and bicyclo[2.2.l]heptane (9) and the values given in the literature (1) for the isomeric hydrocarbons obtained by splitting one of the rings of the bicycloalkanes t o produce cycloparaffins. The antiknock values of the two bicycloalkanes were found t o be much lower than the structure of the two molecules had given reason to expect. Both have octane numbers somewhat lower than the better of the isomeric cycloparaffins listed but somewhat higher than the worse. Both show high susceptibility t o tetraethyllead. Substitution of a methyl group into the nucleus of bicyclo[2.2.1]heptane results in an increase in octane number while the symmetry of the molecule decreases. Both 2-methylbicyclo [2.2.1] bheptene and bicyclo [2.2.1 12-heptene have high antiknock values but low susceptibility toward tetraethyllead. I-METHY LBICYCU) 12.2.11 6-HEPTENE
I n a typical experiment 624 grams (4.7 moles) of 70% dicyclopentadiene (kindly supplied by United Gas Improvement Com-
TABLE I. ANTIKNOCK RATINGS OF CYCLOAND BICYCLOPARAFFINS --Octane Compound
Clear 61 b 18 63 64
Bicyclo 12.2.I]heptane Eth lcyclopentane 1 8-3;imethyloyclopentane dfethyloyclohexane
70 b 31 81 49
ai
66
62
O-.
Plua 3 oc. EhPb/gal. 66 a
.. ..
..
68
74 '2-Methylbioyclo12.2. llheptane Propylcyclopentane Is0 ro ylcyclopentane l-hfe)ef&lJathylc clopentane 1.2-Dimethylcyclo~elsne
No.
+6O
72 76
.. ..* .
86 b
.. .. .... .. ..
2-Methylbioyclo f2.2.116-heptene 97 6 99 b Bicyclo[2.!2. 1]2-heptene 9.5 6O 0 Except as otherwise noted, ratin n were obtained from Doss (I). b Measured by a modified Resear% Method, at 360° F. intake temperature. 0 Measured by A.S.T.M. Procedure D367-41T on a 20% blend in 60% iso-octan&O% n-heptane (9).
1055
+
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
1056
pany) and 646 grams (15.4 InoIcs) of propylene were charged into an autoclave (2). (Cyclopentadiene and dicyrlopentadienc were used in this condensation reaction with equally good results. The mechanism of thc dicyclopentadiene-propylene reaction probably involves the prcliminary dissociation of the dimer to the monomer, which then reacts with the propylene.) Rocking of the autoclave was started, and its temperature was raised to 228" C. and maintained for 2.5 hours. The maximum pressure attained was 2530 pounds per square inch a t 175" C.; this dropped t o 1500bounds at 228' C. at the end of the run. After cooling the autorlave and venting the excess propylene, distillation of the product yielded 543 grams of crude methylbicycloheptene, distilling at 95-128" C. (mainly at 114-116"). The yield of crude product was 73%, based on the diene content of the dicyclopentadiene charged. Seven runs made in thir manner gave 3423 grams of this product. Fractional distillation of 1458 grams of the crude bicycloheptene through an efficient column yielded 1156 grams of material having a boiling range of 115.9-116.3° C. (760 mm.); d,:' 0.8653-6; and n2:, 1.4598. The literature values for 2methylbicyclo[2.2.1] 5-heptene (10) are: boiling point (750 mm.), 115.5-117.0" C; d:,' 0.8668; n1,8,1.4606. 2-METHY LBICYCLO 12.2.11 HEPTANE
The remainder of the crude methylbicycloheptene (1965 grams) was hydrogenated in a n autoclave a t 100" C. over nickel catalyst. The product, after separation from the catalyst by distillation, was shaken with concentrated sulfuric acid, washed with sodium bicarbonate solution, and refluxed overmetallic sodium. Fractional distillation of the chemically purified material through an efficient column yielded 1710 grams of product boiling a t 126.9127.3" C. (760 mm.); dpo, 0.8544; and n2t, 1.4540. The literature values (10) for 2-methylbicyclo[2.2.l]heptaneare: boiling point (745mm.), 124.5-126.0' C.; di6 0.8561; n'," ', 1.4553.
',
2-METHYLBICYCLO 12.2.21 OCTANE O F 1,3-CYCLOHEXADIENE. l,2-Dibromocyclohexane was prepared by bromination of cyclohexene (Eastman Kodak Company) following the method of Greengard (a). The yields of crude product from individual batches varied from 76% to 99%. 1,2-Dibromocyclohexane was dehydrobrominated to 1,3oyclohexadiene by passage over calcium oxide a t 375-400' C. under a pressure of approximately 10 mm., following the general method of Schmidt, Hochschwender, and Eichler (8). The yield of crude product, distilling at 80-81" C. a t 760 mm., was 467,, A sample of this product was separated by fractional distillation into twelve fractions. These fractions varied in refractive index from ' 2 n 1.3770 to 1.4731, and in density from d:' 0.8594 to 0.8393, an indication that the cyclohexadiene contained appreciable amounts of other compounds. The latter were probably benzene, cyclohexene, and cyclohcxanc, all of which boil in the temperature range 80-83' C. CONDENSATION O F 1,3-CYCLOHEXADIENE WITH PROPYLEXE. The condensation of propylene with 1,3-cyclohexadiene to yield 2-methylbicyclo[2.2.2]5-octene was considerably more sluggish than the dicyclopentadiene-propylene condensation, required a higher temperature, and was accompanied by considerable polymerization of the propylene, apparently because of the high temperature ( 4 ) . I n order to speed up condensation and minimize polymerization, the method ultimately employed consisted of pumping the cyclohexadiene slowly into an excess of propylene a t 300" C . This gave considerably better yields than the method of simply charging the reactants into the autoclave and heating the mixture to the desired temperature; but even so, the product contained considerable amounts of propylene polymerizat!on products, largely nonenes, as shown by fractional distillation of the crude product after hydrogenation. I n a typical run the autorlave was evacuated and charged PREPARATION
Vol. 36, No. 11
with 421 grams (10 moles) of propylene. Rocking and heating were started, and when the temperature had reached 300' C., 168 grams (2.1 moles) of crude cyclohexadicne were pumped into the autoclavc a t a uniform rate during a period of 2 hours. Thib was accomplished by means of a piston-type hydraulic pump fitted with a double-ball check valve on the exit side. When the addition was completed, heating and rocking were continued for 3 hours. During the addition and subsequent heating period, the pressure fell from 2280 pounds per square inch at the start to 1525 pounds at the end. Distillation of the product removed aftcr venting the excess propylene gave 95 grams of low-boiling material (boiling point, 110" C., 106 grams of crude methylbicyclo-octene (boiling at 110-145" C., mainly at 144145") and 137 grams of residue. The yield of crude methylbicyclo-octene was 4170 based on the cyclohexadiene and 19% based on the cyclohexene. A total of 2042 grams of crude product waa prepared in this manner. Redistillation of the low-boiling material gave largely material boiling at 80-81' C., which on systematic recrystallization gave both benzene and 1,3-~yclohexadiene. When the low-boiling material was rerun with propylene, very low yields of the desired adduct were obtained. HYDROGENATION AND PURIFICATION OF PRODUCT. The crude rnethylbicyclo-octene was hydrogenated over nickel catalysi at 100" C. in the autoclave, and the product was treated chemically as described above for methylbicycloheptane. Fractional distillation of 1828 grams of the chemically purified product through an efficient column gave 109 grams of material boiling at 70.3-88.0' C. (760 mm.) with n2$ of 1.4462-1.4204 (largely cyclohexane); 528 grams of material boiling a t 88.0-157.0' C . with nzz of 1.3994-1.4615 (largely branched-chain nonanes resulting from hydrogenation of the nonenes formed by polymerization of propylene) ; 938 grams of 2-methylbicyclo[2.2.2]octanr boiling at 157.0-160.1' C., freezing at 6" C., n2: of 1.46541.4690 and d:' of 0.8780. The literature values (6) for the compound are: boiling point (761 mm.), 157-158.5' C.; freeaing point, 33-34' C.; n4,0.6,1.4613; d:0.6, 0.8674. Attempts to purify the methylbicyclo-octane by fractional crystallization were unsuccessful. Analyses of the first and last fractions of the methylbicyclo-octane gave hydrogen to carbon ratios of 1.801 and 1.789, respectively; from these values the compositions of the fractions were calculated to be, respectively, C4Hla.2 and CSH,~.~.Assuming the impurity to be Cg paraffins, the amounts of impurity in the two fractions were calculated to be 5.5 and 2.5 mole yo,respectively. These figures are in good agreement with those based on the refractive index and density data, using the literature values (6) for methylbicyclo-octane and the values n2j 1.4030 and d:' 0.7120 for the C9 impurities. Hence the combined methylbicyclo-octane was judged to have a purity of at least 95 mole %. ACKNOWLEDGMENT
The authors wish t o thank Wheeler G . Lovell and Basil A. D'Alleva of the General Motors Research Laboratories for the octane number determinations. LITERATURE CITED
(1) Doss, "Physical Constants of Principal Hydrocarbons", 4tb ed., New York, Texas Co., 1943. (2) Dykstra and Calingaert, IND.ENQ.CHEM.,ANAL.ED., 6, 383 (1934). (3) Greengard, Org. Syntheses, XII, 26 (1932). (4) Ipatieff and Pines, IND.ENG.CHEM.,28, 684 (1936). (5) Joshel and Butz, J. Am. Chem. Soc., 63,3350 (1941). (6) Kazanskii and Plate, Ber.. 68B, 1259 (1935). (7) Lovell and Campbell, in "Science of Petroleum", Vol. IV, p 3004, London, Oxford Univ. Press, 1938. ( 8 ) Schmidt, Hochschwender, and Eichler, U. S. Patent 1,221,382 (1917). (9) Thomas, IND. ENG.CREM.,36,310 (1944). (10) Zelinskii, KazanskiI, and Plate, Ber., 66B, 1415 (1933). PREUENTED before the Division ofl'etroleum Chemistry at the 107th Meetin@ of the AHERICANCHEMICAL SOCIETYat Cleveland. Ohio.
