Butenes, thermal reactions

Unusual sources for nitrogen-substituted carbenes are 1,3,4-oxadiazolines such as 6. Thermal reaction of 6 with 4-bromo-l-butene furnishes only one diastereomer of spiro-fused /1-lactam cyclopropane 76. However, precursors similar to 6 react less selectively with other olefins. 

Figure 2. Selectivities of ethane and 1-butene in the thermal reaction of ethylene...

Thermal Reaction of Ethylene. Dahlgren and Douglas (5) reported that the primary products of the reaction were propylene, butenes, butadiene, and ethane at temperatures ranging from 480° to 582°C and at pressures from 9 to 137 mm Hg. However, analyses of reaction products were incomplete, and the primary products were not distinguished from the secondary ones. 

Thermal Reaction of Propylene. Thermal reaction of propylene has been studied extensively. Laidler and Wojciechowski (16) reported that main products were ethylene, methane, and hydrogen and that minor ones were ethane, propane, butenes, cyclopentadiene, cyclohexadiene, benzene, toluene, and diallyl at temperatures from 580° to 640°C pressures from 40 to 400 mm Hg in a static system. No allene was detected, which is in contrast to the results obtained at higher temperatures by Szwarc (21) and by Sakakibara (19). Reaction order was determined as 3/2, and the A-factor and activation energy were reported as 1013 34 ml1/2 mole"1/2 sec"1 and 56.7 kcal/mole, respectively. Kallend et ah (9) carried out a detailed analysis of the reaction product at 555° -— 640°C and pressures 7 300 mm Hg. The main C6 compounds present were 1,3-and 1,4-hexadiene. Methylcyclohexene and cyclohexadienes were not found. 

Figure 8. Selectivities of hydrogen and butenes in the thermal reaction of propylene...

Thermal Reactions of Butenes. Among the C4 olefins, 1-butene has been studied most extensively. Bryce and Kebarle (2) pyrolyzed 1-butene at 490° 560°C in a static system, and the main gaseous products were methane, propylene, ethylene, and ethane. The main liquid products were cyclohexadiene, benzene, cyclopentene, cyclopentadiene, and toluene. The rates of formation of methane, propylene, ethylene, and ethane showed first-order dependence on the initial butene concentration. The activation energy for 1-butene disappearance was ca. 66 kcal/mole. 

In the thermal reaction of 1-butene, considerable amounts of liquid hydrocarbons were produced at 700°C and at conversion levels around 30 mole % (13), whereas 2-butene isomers did not give significant yields of liquid hydrocarbons at comparable pyrolysis conditions. Thermal reaction of 1-butene is mainly the scission of the C-C bond that proceeds by a radical mechanism, while reaction of cis- and frans-2-butene involves isomerization that proceeds by a molecular mechanism (6, 17). 

Figure 14. Product yields in the thermal reaction of butadiene at 650°C. Feed butadiene contains 0.55% mole % butenes as impurity.

Thermal Reactions of Olefins with Butadiene. The rate constant of the reaction of ethylene with butadiene was reported by Rowley and Steiner (18), whereas that of propylene or butenes with butadiene has not been reported. Tarasenkova (22) reported that the thermal reaction of propylene with butadiene at 600°C gave toluene, the yield of which was twice as large as the yield of benzene plus xylenes. Moreover, the thermal reactions of 1-butene with butadiene and 2-butene with butadiene at 500° — 550°C gave as main products ethylbenzene and o-xylene, respectively. The ratio of ethylbenzene to total xylenes was close to the ratio of 1-butene to 2-butene in the feed. 

Thermal reaction of 1-butene, cis- and trans-2-butene or isobutylene with butadiene yielded 4-ethylcyclohexene, cis- and transA,5-dimethyl-cyclohexene, or 4,4-dimethylcyclohexene, respectively, accompanied by a larger amount of 4-vinylcyclohexene. Rate constants of these respective reactions were calculated by the method above. 

Chlorobutanes. Chlorobutanes can be obtained by diverse procedures, such as (1) the liquid-phase or thermal chlorination of butane, (2) addition of chlorine or hydrogen chloride to butenes, (3) reaction of hydrochloric acid with butanols and butylene glycols, (4) chlorination of chlorobutenes and chlorobutadienes, and (5) hydrochlorination of tetramethylene oxide (tetrahydrofuran) and butadiene. 

For the pyrolysis of paraffinic hydrocarbons at 700- 800 C, yields of olefins such as ethylene, propylene, butenes, butadiene and cycloolefins increase during the initial stage of the reaction, pass through their maxima, and later decrease yields of aromatics, hydrogen and methane however increase monotonically throughout the reaction course. Sakai et al. (1 ) reported previously the result of a kinetic study on thermal reactions of ethylene, propylene, butenes, butadiene and these respective olefins with butadiene at the conditions similar to those of paraffin pyrolysis, directing their attention on the rates of formation of cyclic compounds. Kinetic features of the thermal reactions of these olefins are sunnnarized in Table I combined with the results obtained in later investigations for thermal reactions of cycloolefins ( 2) and benzene O). 

Thermal reactions of ethylene (A>A) require higher temperatures (750- 800 C) than the other olefins. Initial reaction products are butadiene, 1-butene, propylene, ethane and acetylene. 

As the yields of these initial products decrease with increased residence times, cyclic compounds such as cyclopentene, cyclopen tadiene, cyclohexene and benzene are produced. In the case of propylene (, 7 ), the reaction proceeds 2-4 times faster than that of ethylene and ethylene, methane, butadiene, butenes, acetylene, and methylcyclopentene are the main products during the initial step cyclopentadiene, cyclopentene, benzene, toluene and polycyclic compounds higher than or equal to naphthalene are products of secondary reactions. A remarkable fact for the thermal reaction of propylene is that the yields of five membered ring compounds are larger than those in the case of ethylene. 

Different features were observed between the thermal reaction of 1-butene and those of cis- and trans-2-butenes at 640- 680 C (1 ). In the former case, the reaction proceeded mainly in three ways these were pyrolysis to methane and propylene, dehydrogenation to butadiene, and pyrolysis to two moles of ethylene the ratio of rates for these three reactions are 4 3 1, respectively. In the latter cases, the main reaction was isomerization between... 

Cyclization proceeded in nearly 100% selectivity in the case of thermal reaction of butadiene (1 ), yielding 4-vinylcyclohexene (VCH) for the first step and ethylene, cyclohexene, cyclohexa-diene, and benzene in the secondary steps. Similar highly selective cyclizations were observed for the reactions between butadiene and ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene or isobutylene (1), yielding cyclohexene (HCH), 4-methyl-cyclohexene (MCH), 4-ethylcyclohexene, cis-4,5-dimethylcyclo-hexene, trans-4,5-dimethyIcyclohexene or 4,4-dimethylcyclohexene, respectively. Based on the above information, it can be said that butadiene plays an important role in the formation of cyclic compounds in pyrolysis conditions. 

From Figure 1, it is clear that the primary products of the thermal reaction of diallyl are ethylene, propylene, 1-butene, butadiene, 1-pentene, cyclopentene, cyclopentadiene, and 1,3,5-hexatriene, and the secondary products are 1,3-cyclohexadiene and benzene. Trace amounts of methane, propane, and 1,4-pentadiene were also found in some experiments. No hydrogen was detected by a nitrogen carrier gas chromatograph with MS 5A column. The formation of C 2 compounds was noticed at low temperatures. A small amount of liquid product was found in the separator tube after 50 or more experimental runs. The average molecular weight of the liquid product was 428 based on the method of Hill (15). 

Thermal Reaction of DAO in Excess Ethylene. To get better knowledge about the formation of cyclopentene and 1-pentene, DAO was employed as another source material for allyl radicals. In the case of the pyrolysis of DAO in excess ethylene, the reaction temperature was considerably lowered, and a large amount of diallyl was produced, accompanied with cyclopentene, 1-pentene, propylene, 1-butene, butadiene and cyclopentadiene. All of these except diallyl were the same main products as obtained in the pyrolysis of diallyl in excess ethylene. In other words, the same mechanism regulate both the reactions of DAO and those of diallyl in the presence of ethylene. 

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