INDUSTRIAL A N D ENGINEERING CHEMISTRY
474
Vol. 20, No. 5
Preparation of Butadiene' Stanley Francis Birch T H E ANGLO-PERSIAN OIL Co.,LID., MEADERRST. SUNBURY-ON-THAMBS, ENGLAND
F THE numerous methods available for the prepara-
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tion of butadiene in the laboratory, those described by Thielel and by Ostr~muislenskii~ are probably the most convenient. Both, however, suffer from the disadvantages which usually characterize operations a t comparatively high temperatures; the exact conditions are difficult to find, the process is long and tedious, and finally involves the separation of the required material from a complex mixture. It has long been known that butadiene occurs in the various products obtained when oils are heated to a high temperature. Caventou4 first isolated butadiene in the form of its tetrabromide from illuminating gas, and Armstrong and Millerb definitely established the presence of butadiene in the liquid obtained by compressing oil gas. The work of numerous later investigators has confirmed their results and has shown that the more drastic the heat treatment to which the oil is submitted the greater is the tendency for butadiene to be formed. For this reason vapor-phase cracking of petroleum, which is carried out a t a much higher temperature than liquid-phase cracking, yields products specially rich in butadiene. Indeed, a patent6 for the preparation of butadiene and isoprene by the pyrolysis of petroleum oils at about 700" C., particularly under reduced pressure, has actually been taken out. It was therefore surprising to note the opinion expressed by Brooks' that the isolation of butadiene from the low fractions of the liquid obtained by compressing oil gas or Pintsch gas was particularly due to the skill of the chemists, since this material might well be expected to be comparatively rich in the more volatile diolefins. I n fact, a reinvestigation of this material has shown it to be a convenient and inexpensive source of butadiene, which can be readily isolated from it in the form of its tetrabromides. Owing to the cheapness of the material and the simplicity of the method of separation, it is an easy matter to prepare as large a quantity of the tetrabromides as may be desired. Preparation of Butadiene Tetrabromide
"Railway hydrocarbon," the liquid produced during the preparation of oil gas, was distilled from a copper can in 2-gallon (9.1-liter) batches, through a 6-foot (1.8-meter) column, packed with metal rings and attached to a Liebig's condenser. The uncondensed vapors from the receiver were led into bromine (250 cc.) which was initially mixed with ice, The evolution of gas commenced long before any condensable distillate came over and was practically complete when the stillhead temperature reached 60-70" C. Decoloration of the bromine took place rapidly. Considerable heat was evolved; judicious cooling was employed, but towards the end of the experiment the reaction mixture was allowed to become sufficiently warm to prevent the solidification of the butadiene tetrabromide. To avoid loss of butadiene the bromine taken represented a slight excess. When evolution of gas had ceased, the excess of bromine Received November 21, 1927. * Ann., 308, 337 (1899). a J . Russ. Phys.-Chem. Soc., 47, 1494 (1915). 4 Ber., 6, 70 (1873). 5 J . Chem. Sor. (London),49, 80 (1886). E Engler and Staudinger, D. R. P. 265,172 (1912). 7 "Non-Benzenoid Hydrocarbons," p. 216. 1
was destroyed by sulfur dioxide and the bromides were washed twice with hot water. After separation of the water, the product was cooled in ice, when the whole set to a semisolid mass. As much of the liquid as possible was then separated a t the pump, the residual solid was washed with a small quantity of petroleum ether (60-80" C.) and finally crystallized from the same solvent. The solid butadiene tetrabromide separated in small, glistening, colorless plates melting, after a second recrystallization, a t 117" C. The yield from 2 gallons (9.1 liters) of starting material was 200 to 210 grams; a further small crop separated from the liquid bromides and petroleum ether mother liquors on standing. The liquid bromides were freed from solid tetrabromide as completely as possible and fractionated under reduced pressure. The fraction boiling above 150" C. at 42 mm. deposited on cooling a further crop of the solid tetrabromide (about 12 grams); this was removed and the residue refractionated. The fraction boiling a t 169" C. and 30 mm. appeared to be mainly liquid tetrabromide but still contained some of the solid isomer, which again separated on cooling. The yield was about 80 grams. When treated with zinc dust and alcohol in the manner described by Thiele,l it gave a colorless gas which, on passing into bromine, yielded a further quantity of the solid tetrabromide. Further quantities of both liquid and solid tetrabromides were obtained by distilling the low-boiling hydrocarbons which collected in the receiver when the starting material was distilled. Eight gallons (36 liters) of the railway hydrocarbon gave a little over a liter of these hydrocarbons, from which about 200 grams of the crude solid tetrabromide and 145 grams of the liquid tetrabromides were obtained. Besides butadiene tetrabromide, about 500 grams of bromides boiling from 65" to 150' C. and 42 mm. were obtained. These probably consisted mainly of isobutylene dibromide and were not further treated. Using the method described, it is possible to distil four 2-gallon (9.1-liter) batches in one day and thus produce about 800 grams of the solid tetrabromide. Redistillation of the condensate and fractionation of the combined liquid bromides takes another day and produces a further 250 grams of the solid and 560 grams of the liquid tetrabromide. Preparation of Pure Butadiene
Pure butadiene can be readily and conveniently prepared from the solid tetrabromide by the method described by Thiele.2 For most purposes the once-crystallized material is pure enough. Butadiene prepared from the liquid tetrabromides is probably contaminated with traces of highboiling olefins. It is interesting to note that, in spite of its high boiling point, the solid tetrabromide has an appreciable vapor pressure a t ordinary temperature. Hence loss by volatilization must be guarded against in attempting to dry the material in a steam oven, particularly as the vapor is lachrymatory. Attempt to Isolate Isoprene
An attempt to isolate isoprene from the low-boiling hydrocarbons in the form of j3-methyl-p,6-dichlorobutane8led to the formation of a small quantity of liquid dichloride of indefinite boiling range, which was not further investigated. 8
Ostromuislenskii, J . Russ. P h y s L h c m . Soc., 47, 1983 (1915).
