Pyrolytic cleavage

VDP processes using means other than the pyrolytic cleavage of DPX (Gorham process) to generate the reactive monomer are also known, although none are practiced commercially at the time of this writing (ca 1997). 

Although DPXC and DPXD prepared by the chlorination of DPXN are relatively complex mixtures, after pyrolytic cleavage the resulting mixture... 

Reactions of alkyl halides with alkaU metal phosphides [39-41], addition reactions of olefins with PHj [42] or the pyrolytic cleavage of P-0 bonds in RPO2H2 [43] are also reported for the preparation of alkyl/aryl functionalized primary... 

The initiation step in the high-temperature oxidation of toluene is the pyrolytic cleavage of a hydrogen atom from the methyl side chain, and at lower temperatures it is 02 abstraction of an H from the side chain, namely... 

The first step of other high-order alkylated aromatics proceeds through pyrolytic cleavage of a CC bond. The radicals formed soon decay to give H atoms that initiate the H2—02 radical pool. The decay of the initial fuel is dominated by radical attack by OH and H, or possibly O and H02, which abstract an H from the side chain. The benzylic H atoms (those attached to the carbon next to the ring) are somewhat easier to remove because of their lower... 

Pinene is similar to a-pinene in its reactions. Pyrolytic cleavage to myrcene, the starting material for acyclic terpenes, is used on an industrial scale. Addition of formaldehyde results in the formation of nopol nopyl acetate is used as a fragrance material. /3-Pinene is produced in large quantities by distillation of turpentine oils. It is used as a fragrance material in household perfumery. However, most /3-pinene is used in the production of myrcene. 

Isopulegol can be isolated from this mixture and hydrogenated to (-)-menthol. The remaining isopulegol stereoisomers can be partly reconverted into (+)-citronellal by pyrolytic cleavage and reused in the cyclization procedure [79]. 

The concerted nature of these reactions is also supported by the pyrolytic cleavage of cis-2,3-dimethylcyclobutanone and rra i-2,3-dimethylcyclobutanone at a temperature of 325 °C under a pressure of 10 Torr, from which approximately 99% retention of configuration in the resulting but-2-enes is observed.92,93 Moreover, the results obtained from the thermolysis of cis- and m -2,4-dimethylcyclobutanone also lend support to the concertedness of this reaction.92,93 However, as substantiated by Arrhenius parameters, a diradical pathway is the most likely competing reaction in the pyrolysis of 2-chlorocyclobutanone.94 On the other hand, the kinetics of the gas-phase pyrolysis of bicyclo[3.2.0]hept-2-en-6-one (14),95 bicyclo[3.2.0]heptan-6-one (IS)96 and 2,2-dimethyl-3-ethoxycyclobutanone (16)97 are commensurate with a concerted cycloreversion mechanism involving four-center auasi-zwitterionic transition structures. 

A number of papers report investigations of the pyrolytic cleavage of aromatic hydrocarbons. The oxidation and pyrolysis of anisole at 1000 K have revealed first-order decay in oxygen exclusively via homolysis of the O—CH3 bond to afford phenol, cresols, methylcyclopentadiene, and CO as the major products.256 A study of PAH radical anion salts revealed that CH4 and H2 are evolved from carbene formation and anionic polymerization of the radical species, respectively.257 Pyrolysis of allylpropar-gyltosylamine was studied at temperatures of 460-500 °C and pressures of 10-16 Torr. The product mixture was dominated by hydrocarbon fragments but also contained SO2 from a proposed thermolysis of an intermediate aldimine by radical processes.258... 

In the thermolysis of 2,2-dichloro-l,3-diphenylaziridine, the increased polarisation of the bonds adjacent to the CCI2 group results in the opposite (carbon-nitrogen) bond in the ring undergoing pyrolytic cleavage viz. 

Another common type of mechanism found to operate in pyrolytic eliminations involves free radicals. Initiation occurs by pyrolytic cleavage. A schematic example of this type of reaction is... 

In an elimination reaction, fragments of a molecule are removed and form a new molecule. Elimination involving a free radical mechanism operates in many pyrolytic reactions. First, an initiation occurs by pyrolytic cleavage, followed by... 

The other reaction is pyrolytic cleavage (via a retro-ene reaction) of a fatty acid containing a homoallylic alcohol in the chain. This is used to produce two important feedstocks, heptanal and undecylenic acid, from ricinoleic acid, the major fatty acid component of castor oil. The mechanism of this reaction is shown in Scheme 4.61. 

Fig. 8 Mechanism for ultrasound-induced polymta- chain scission (a) gradual bubble formation results from pressure variations induced by the acoustic field (b) rapid bubble collapse genc tes solvodynamic shear (c) small molecules pyrolyze to form radical byproducts up

Pyrolysis of bicyclopentanes usually leads to the cleavage of the central C—C bond to give a vibrationally excited diradical, which suffers a consecutive 1,2-H shift (Table 8 entries Ic, 4b, 6b) or subsequent C—C bond cleavage (Table 8 entries 5b, 6b, 9, 10a, b, 12b, 13a, 14, 16). In other cases syn/anti isomerizations of the substrates are observed (Table 8 entries 2e, 4a, 10c). The higher annulated syn/anti-pentacyclo[5.3.0.0 . 0 . 0 ]-decanes (Table 8 entry 18) react preferably by pyrolytic cleavage of the cyclobutane unit, whereas the cyclopropane ring is not affected. 

Yajima discovered that heating polydimethylsilane at 400" °C leads to pyrolytic cleavage of Si-Si bonds and subsequent reaction of the generated radicals, as seen in Scheme I ... 

Kawamoto H, Ryoritani M, Saka S. Different pyrolytic cleavage mechanisms of (3-ether bond depending on the side-chain structure of lignin dimers. J Anal Appl Pyrol. 2008 81 88-94. 

---