Pyrolysis of olefins

Studies of the oxidation and pyrolysis of olefins show that the majority of the products are derived from reactions which involve the terminal carbon atom of the substituted allyl radical, R—CH=CH—CH2 (i.e. with the canonical form shown). It has been suggested that this is due to a higher spin density at this carbon atom than at the substituted end ofthe radical (Norrish and Porter, 1963 Bryce and Ruzicka, 1960). Thus the measurement of the spin density distribution in substituted allyl radicals would be of considerable interest. 

However, if this is the case the isomer 2b must be more stable or more reactive than isomer 2a, and there is no apparent reason why this should be so. Furthermore this conversion does not explain the results of the pyrolysis of olefins where peroxy-radicals are absent. 

The pyrolysis of olefins has not been as well studied as for paraffin pyrolysis. The lesser interest in olefins can be attributed to both more complex product mixtures and lower rates of pyrolysis for the olefins. 

Primary nitroparaffins react with two moles of formaldehyde and two moles of amines to yield 2-nitro-l,3-propanediamines. With excess formaldehyde, Mannich bases from primary nitroparaffins and primary amines can react further to give nitro-substituted cycHc derivatives, such as tetrahydro-l,3-oxa2iaes or hexahydropyrimidines (38,39). Pyrolysis of salts of Mannich bases, particularly of the boron trifluoride complex (40), yields nitro olefins by loss of the amine moiety. Closely related to the Mannich reaction is the formation of sodium 2-nitrobutane-1-sulfonate [76794-27-9] by warming 1-nitropropane with formaldehyde and sodium sulfite (41). 

Petroleum-derived benzene is commercially produced by reforming and separation, thermal or catalytic dealkylation of toluene, and disproportionation. Benzene is also obtained from pyrolysis gasoline formed ia the steam cracking of olefins (35). 

Pyrolysis. The pyrolysis of simple esters of the formula RCOOCR R CHR 2 to form the free acid and an alkene is a general reaction that is used for producing olefins ... 

Hexafluoropropylene oxide (HFPO), which decomposes reversibly to di-fluorocarbene and trifluoroacetyl fluonde with a half-life of about 6 h at 165 °C [30], is a versatile reagent. Its pyrolysis with olefins is normally carried out at 180-2(X) °C, and yields are usually good with either electron-nch or electron-poor olefins [31, 32, 33, 34, 35, 36, 37] (Table 2). The high reaction temperatures allow the eyclopropanation of very electron poor double bonds [58] (equation 10) but can result in rearranged products [39, 40, 41] (equations 11-13)... 

The pyrolysis of sodium chlorodinuoroacetate is still a widely used, classical method for generating difluorocarbene, especially with enol and allyl acetates [48, 49, 50, 51] (equation 21) A convenient alternative that avoids the hygroscopic salt uses methyl chlorodifluoroacetate with 2 equivalents of a lithium chlonde-hexa-methylphosphoric triamide complex at 75-80 °C in triglyme [52], Yields are excellent with electron-rich olefins but are less satisfactory with moderately nucleophilic alkenes (4-5% yields for 2-bulenes)... 

The pyrolysis of perfluoro carboxylic salts can result both in mono and bimolecular products At 210-220 °C, silver salts give mostly the coupled products, at 160-165 °C in A -methylpyrrolidinone, the corresponding copper salts also give the simple decarboxylated compounds in nearly equal amounts The decomposition of the copper salts m the presence of lodobenzene at 105-125 °C results m a phenyl derivative, in addition to the olefin and coupled product [94] (equations 60-62)... 

Catalytic reduction of thiophenes over cobalt catalysts leads to thiolane derivatives, or hydrocarbons. " Noncatalytic reductions of thiophenes by sodium or lithium in liquid ammonia leads, via the isomeric dihydrothiophenes, to complete destructions of the ring system, ultimately giving butenethiols and olefins. " Exhaustive chlorination of thiophene in the presence of iodine yields 2,2,3,4,5,5,-hexachloro-3-thiolene, Pyrolysis of thiophene at 850°C gives a... 

The same type of reaction occurs in the work of Hauptman (76T1293), who, studying the chemistry of diethynylcarbenes, found that the pyrolysis of the lithium salts of diethynylketone tosylhydrazones 5 (140-150°C) in the presence of olefins leads to cyclopropanes. This process results in the formation of the corresponding 3-ethynylpyrazoles. The formation of l-p-tolylsulfonyl-3-alkynylpyrazoles from hydrazone runs in milder conditions (50°C, 14 h) (Scheme 24). 

Homologous n-a-olefins by pyrolysis of high molecular weight C20-C30 n-alkanes (wax cracking)... 

Pyrolysis of bis(trimethylsilyl)phenyl methanol 1668 at 500 °C leads, via elimination of trimethylsilanol 4, to the carbene intermediate 1669, which rearranges, via the carbene intermediate 1670, to give l,2-dimethyl-2,3-benzo-l-silacyclopent-2-ene 1671, in 25% yield, or rearranges via olefin 1672 and adds 4 to give the siloxane 1673 in 29% yield and smaller amounts of benzyltrimethylsilane 83 and styrene [43, 44]. Pyrolysis of l,l-bis(trimethylsilyl) cyclohexylalcohol 1674 furnishes, via the carbene intermediate 1675, 90% of olefin 1676 [43, 44] (Scheme 10.20). 

For a discussion of modern methods of olefin manufacture by pyrolysis, consult the paper by Ennis and co-workers (5). 

Chemical reactivity differences may be calculated if for the transition state of a rate-determining step of a reaction a structural model can be given which is describable by a force field with known constants. We give only two examples. Schleyer and coworkers were able to interpret quantitatively a multitude of carbonium-ion reactivities (63, 111) in this way. Adams and Kovacic studied the pyrolysis of 3-homoadamantylacetate (I) at 550 °C and considered as transition state models the two bridgehead olefins II and III (112). From kinetic data they estimated II to be about 2 kcal mole-1 more favourable than III. 

The first report of the cyclodimerization of fluorinated olefins was provided by Lewis and Naylor,3 working at E.I. DuPont de Nemours Co., in 1947. While studying the pyrolysis of polytetrafluoroethylene (PTFE), the compound octa-fluorocyclobutane was isolated from the pyrolysis off-gas stream. The researchers identified the product and speculated that it was formed by the cyclodimerization... 

Oligomeric products, obtaining, 16 106 Oligomeric titanates, pyrolysis of, 25 121 Oligomerization, 23 329 acetylene, 1 181 butadiene, 4 373-374 in higher olefins, 17 712 ionic liquids in, 26 885-887 olefin, 16 111... 

Oxidative damage, role of ascorbic acid in preventing, 25 769 Oxidative degradation, 70 682 of gasoline, 72 399-400 Oxidative dehydrogenation, 23 342-343 Oxidative pyrolysis, 27 466 Oxidative stability, of olefin fibers, 77 229 Oxidative stability test, 72 400 Oxide crystal glass-ceramics, 72 641 Oxide-dispersion-strengthened alloys, 77 103-104... 

Alkylphenols (AP) are produced by alkylation of phenol using either octene or nonene mixtures obtained from pyrolysis of gasoline and other petrochemical sources. These are highly branched olefins and consequently the corresponding final alkylated phenol is also a branched derivative. 

The primary products obtained from 2-butanol are of mechanistic. significance and may be compared with other eliminations in the sec-butyl system 87). The direction of elimination does not follow the Hofmann rule 88) nor is it governed by statistical factors. The latter would predict 60% 1-butene and 40% 2-butene. The greater amount of 2-alkene and especially the unusual predominance of the cis-olefin over the trans isomer rules out a concerted cis elimination, in which steric factors invariably hinder the formation of cis-olefin. For example, the following ratios oicisjtrans 2-butene are obtained on pyrolysis of 2-butyl compounds acetate, 0.53 89, 90) xanthate, 0.45 (S7) and amine oxide, 0.57 86) whereas dehydration of 2-butanol over the alkali-free alumina (P) gave a cisjtrans ratio of 4.3 (Fig. 3). 

The fuel oils coming out of olefin plants are also characterized by an abundance of polynuclear aromatic molecules, (Same definition as for Figure 2—1). They are sometimes inaccurately referred to as having a high aromatics content. Nomenclature aside, because of this, the burning characteristics of pyrolysis gas oil and pyrolysis pitch are poor. They are smoky, sooty, and gum formers they rend to be more viscous, and because of their polynuclear aromatic concent, they are suspected carcinogens. They are basically a witchs brew of unsavory hydrocarbons.. ... 

Method a + d. The tellnrinm dibromide is treated with 0.5 N NaOH at room temperatnre for 1 h. The mixtnre is dilnted with HjO and extracted with ether. The extracts are dried (MgS04), and evaporated nnder vacuum, furnishing the teUnroxide hydrate in a qnantita-tive yield. Pyrolysis of the telluroxide is performed in a Kiigelrohr apparatns at 200-240°C/760 torr, giving the olefin as an oil. 

One of the routes to epimestix>l begins with acylation of estradiol with benzoyl chloride to give the dibenzoate 5. Pyrolysis of the ester leads to formation of the 16,17-olefin. Hydroxylation by means of osmiiim tetroxide affords the cis-diol 7 due to the intermediacy of the cyclic osmate ester (6a)-, attack... 

In the 1930s it was discovered that the pyrolysis of alkanes produced large quantities of olefins. This pyrolysis process is not very selective, but the costs of separation were cheaper, and scaleup was simpler and safer in making ethylene rather than acetylene so during the 1940s ethylene and other small olefins replaced acetylene as the major building block in chemical synthesis. We will consider the reactions and reactors used in olefin synthesis from alkanes in the next chapter. 

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