Xylene, flash pyrolysis

Further work to firmly establish which position loses a hydrogen atom in the gas-phase pyrolysis of a-chloro-u-xylene or omethylbenzyl chloride151 was undertaken by means of flash pyrolysis of o-methylbenzyl chloride-a,a-d2 at 750 °C152. The results as described in equation 66 indicated that the hydrogen atom is abstracted from the o-CH3 group. Consequently, the mechanism was rationalized in terms of a direct -elimination followed... 

This article surveys the polymerization of quinodimethanes including flash pyrolysis of p-xylene, the synthesis of poly-p-xylylene other than by flash pyrolysis, the vapor-coating process by Gorham, and the polymerizations of halo-p-xylylenes and electron-accepting quinodimethanes. 

No products could be identified when 3-alkyl- or 3-aryl-4-methylene-3,4-dihydro-l,2,3-benzotriazines were refluxed in ethanol or p-xylene (75CJC3714). Flash vacuum pyrolysis of 3-adamantyl-l,2,3-benzotriazin-4-one (79) led to the isolation of 1-adamantylbenzazet-2(l//)-one (80) (73JCS(P1)868>. In most other cases the isolation of the benzazetone failed. When l,2,3-benzotriazin-4-one (21) is heated in diethylene glycol dimethyl ether, quin-... 

In refluxing xylene (160 °C), fused Dewar s thiophene 40 mainly desulfurized to give cyclobutene 41 but under flash vacuum pyrolysis conditions, a mixture of isomeric dihydrothiophenes 42, 43, and 5H-benzocycloheptatriene 44 was formed (Scheme 9). Evidently the latter product derived from a formal electrocyclic ring opening of the cyclobutene intermediate 41 <1990H(31)1769>. 

Both 1,5- and 1,7-H shifts have been invdted in die thermal rearrangement of the diketone (38). In xylene (138 C, 24 h), (38) isomeiized quantitatively to the ( , )-trienedione (40), probably via intramolecular hydrogen transfer from (39). Under flash vacuum pyrolysis (FVP) conditions (740 C), the indan-l-one (43) was the only product observed. Its genesis may involve an initial 1,7-H sigmatropic shift to give (41) followed by cyclization to (42) and elimination of acetone to give (43). 

Pyridazinium A-ylide (213) underwent 1,3-dipolar cycloaddition with the perhalocyclopropene (214) to give the cycloadduct (215) which was thermolysed in refluxing xylene to give (128) <86CPB1023>. Flash vacuum pyrolysis, at temperatures between 450°C and 700°C, of the A-pyrazolyl derivative (216) gave a mixture of two products (217) and (218). The relative proportions of these two products were shown to be temperature dependent. The major product at higher temperature was shown to be (217), whereas at lower temperatures (218) predominated <93CC840>. 

When either the hydrocarbon (XLIX) or the diester (LI) is heated in boiling xylene the methyl group migrates to a peripheral bridgehead site [236,241]. The same product is obtained from (XLIX) on flash vacuum pyrolysis at 400° at higher temperatures alternative isomers result [236] ... 

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