Methyl group, pyrolysis

The ketone (738) on treatment with KOBu at 185 °C undergoes rearrangement to (739) and deuterium exchange at C-1, C-7, and the methyl groups. Pyrolysis of... 

The 1-azirines obtained from the vapor phase pyrolysis of 4,5-disubstituted 1-phthalimido-1,2,3-triazoles (157) have been found to undergo further thermal reactions (71CC1S18). Those azirines which contain a methyl group in the 2-position of the ring are cleaved to nitriles and phthalimidocarbenes, whereas those azirines which possess a phenyl substituent in the 2-position rearrange to indoles. 

Recently, Stair and coworkers [10, 11] developed a method to produce gas-phase methyl radicals, and used this to study reactions of methyl groups on Pt surfaces [12] and on molybdenum oxide thin films [13]. In this approach, methyl radicals are produced by pyrolysis of azomethane in a tubular reactor locat inside an ulttahigh vacuum chamber. This method avoids the complications of co-adsorbcd halide atoms, it allows higher covraages to be reached, and it allows tiie study of reactions on oxide and other surfaces that do not dissociate methyl halides effectively. 

Cyclohexadienylidenes, disubstituted at the 4-position are expected to be kinetically more stable than the parent carbene, however, the rearrangement to benzene derivatives is still very exothermic. The gas phase chemistry of 4,4-dimethyl-2,5-cyclohexadienylidene Is was investigated by Jones et al.100,101 The gas phase pyrolysis of the diazo compound 2s produces a mixture of p-xylene and toluene, and by crossover experiments it was demonstrated that the methyl group transfer occurs intermolecularly via free radicals. Thus, the pyrolysis of a mixture of the dimethyl and the diethyl derivative 2s and 2t... 

When dimethyl-2,2-dioxo-5-methyl-177,377-pyrrolo[l,2-r-][l,3]thiazole-6,7-dicarboxylate was heated under flash vacuum pyrolysis at 700°C/10 3mmHg, sulfur dioxide was eliminated and the vinylpyrrole 391 was obtained, which can be explained by allowed suprafacial [1,8]H shifts in the 871 1,7-dipolar system 390. Concerted sigmatropic shifts can only occur when the methyl groups adopt an inward (Z)-conformation (Scheme 57) <2002J(P1)1795, 2004TL3889, 2005JOC6629>. 

The pyrolysis of this compound at around 490° in a stream of nitrogen yields 1,2,3-trimethylbuta-l,3-diene. Unlike the parent compound, it does not yield a substituted acetylene (Stechl, 1964). It is thus apparent that the movement of a hydrogen atom is much easier than that of a methyl group. It is possible that the isomerization involves a five-membered ring, viz. ... 

It is also almost certain that the methyl groups are completely eliminated during pyrolysis at 600°C. Infrared (7) and chemical studies (24) on semicoke indicate that semicoke is about 1009 aromatic in character and hence contains no methyl carbon. 

Bhupendra K. Mazumdar We have not worked on the nature of the methyl groups in coal but have sought to assess the total methyl content by interpreting the sources of methane formation during low temperature (600°C.) pyrolysis. 

Thus, by shifting a methyl group from Si to N, the mechanism of transformation has been changed entirely. The products from pyrolysis of — [ NMe] — and —[MeHSiNHR— are quite different as clearly seen in Figure 4, which compares the 29Si NMR spectra for both materials pyrolyzed to 1000 °C. This is proof that polymer architecture can strongly influence the type of ceramic material produced on pyrolysis. 

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