Cyclohexyl pyrolysis

The equation (conformational) for the pyrolysis of cyclohexyl acetate drawn and explained ... 

Figures 15-1 and 15-2 provide evidence for the extent to which transition states for closely-related reactions are very similar. Figure 15-1 compares the transition state for pyrolysis of ethyl formate (leading to formic acid and ethylene) with that for pyrolysis of cyclohexyl formate (leading to formic acid and cyclohexene). Figure 15-2 compares the transition state for Diels-Alder cycloaddition of cyclopentadiene and acrylonitrile with both syn and anti transition states for cycloaddition of...

The pyrolysis of (say) cyclohexyl chloride by the uni-molecular mechanism must involve. vvn-elimination (16 - 17) because the product is a cw-olefin. When I came across the pyrolysis of steroidal esters8,9 for the synthesis of olefins it seemed to me that sy/t-elimination (unimolecular mechanism)... 

Pyrolysis of cyclohexyl phenyl tellurium dibromide yielded 58% cyclohexyl bromide and 39% cyclohexene1. Bis[4-methoxyphenyl] tellurium dichloride under similar conditions gave 4-chloromethoxybenzene and tellurium as the main products2. 

Support for the c/j-nature of the elimination reaction has come from the work of Barton et on the pyrolysis of menthyl chloride, and the results of this study have recently been confirmed by Bamkole > who also examined the pyrolysis of neomenthyl chloride. The product ratio of menthene-3 to methene-2 is 3 1 in the case of menthyl chloride and 1 6 in the case of neomenthyl chloride, thus demonstrating a preference for m-elimination in each case. These two decompositions do, however, have some unusual characteristics the Arrhenius parameters are considerably lower than those reported for other secondary chlorides, and the rate of elimination of hydrogen chloride from each compound is appreciably faster than from cyclohexyl chloride . (The relative rate of pyrolysis of menthyl chloride and cyclohexyl chloride at 300 °C is about fifty.)... 

The same products, but in different ratios, occur in the gas phase eliminations of HCl from bornyl and isobornyl chlorides and from the pyrolysis reaction of bornyl and isobornyl benzoates and methyl xanthates . The isobornyl reaction is appreciably faster than that of the bornyl ester ((iso-B/B) = 6.8 at 345 °C), but proceeds at a slightly slower rate than that of cyclohexyl acetate, (CH/iso-B) = 2.1 at 600 °K. By analogy with the nonclassical carbonium ion interpretation of the solvolysis rates of bornyl and isobornyl chlorides, the participation of nonclassical carbonium ion intimate ion-pairs, e.g. 

If the alkyl group possesses any hydrogens, formation of alkene and alcohol predominates, whereas benzyl sulfite and like structures give the ether. Bordwell and Landis showed that the pyrolysis of methyl cyclohexyl sulfites parallels those of... 

Better yields have been obtained in the insertion reactions of car-boalkoxy nitrenes. Pyrolysis of -octadecylazidoformate (35) in cyclohexane gave 60% of (JV-cyclohexyl)-R-octadecyl carbamate (36) zilong with 23% of the abstraction product 37 . 

Alkyl phenyl telluroxides and cycloalkyl phenyl telluroxides, with the exception of cyclohexyl derivatives, are unstable compounds, suffering the elimination reaction at room temperature. In contrast, n-alkyl phenyl telluroxides and cyclohexyl phenyl telluroxide are stable compounds and undergo elimination only by prolonged heating in toluene or THF, or by pyrolysis at 200-240°C. 

Similarly, the cyclohexene 7.107 selectively loses the axial hydrogen from the allylic position with the C—H bond best aligned with the % bond, and the intermediate radical 7.108 selectively picks up the chlorine atom from the axial direction to give the less stable of the two possible diastereoisomers 7.109.1037 The cyclohexyl radical 7.111 derived from pyrolysis of the oxalate 7.110 again loses the axial hydrogen selectively to give the alkene 7.112, although the alternative 7.113 is the more stable isomer.1038... 

Pyrazoles (87) are also formed, by extrusion of SO2, on submitting 2-alkyl-3,5-dimethyl-l,2,6-thiadiazine 1,1-dioxides (86 R = Me or PhCHz) to flash vacuum pyrolysis at 700 °C (Equation (2)) <93CJC4io>. With 2-unsubstituted thiadiazine 1,1-dioxides (86 R = H) no pyrazoles are formed, whereas with the 2-cyclohexyl derivative (86 R = cyclohexyl) the reaction is more complex and yields, in addition to starting material, pyrazole (87 R = cyclohexyl 50%), the decycloalkylated thiadiazine 1,1-dioxide (86 R = H 35%), and cyclohexene. The last two products most probably arise by a retro-ene reaction. 

PRODUCTS OF PYROLYSIS OF cis- AND Ira i-2-S U BSTIT UTE D CYCLOHEXYL ESTERS AND XANTHATES... 

For four- or five-membered cyclic transition states, pyrolysis only leads to beta-elimination if the C -H and C -X bonds can eclipse so as to ensure the necessary proximity for reaction. The syn nature of the amine oxide decomposition has been demonstrated by elimination from the diastereoisomeric pairs of the 1,2-diphenylpropyl system. In the cyclohexyl series, an eclipsed transition state is only achieved if elimination proceeds through the boat conformer and consequently the pyrolysis of 1-methylcyclohexylamine oxide gives an almost quantitative yield of the less stable exo-olefin. This orientation contrasts markedly with that of the six-membered cyclic transition states of the corresponding esters and xanthates which yield predominantly the endo-olefin, syn-clinal stereochemistry being preferred. For all the other ring... 

The variability in the pyrolysis profiles of the different classes of coatings is self-evident. The interpretation of the composition revealed is as follows The acrylic lacquer (General Motors) is a methyl methacrylate/methacrylic acid copolymer plasticized with dibutyl-, butyl cyclohexyl-, and butyl benzyl phthalates. The acrylic enamel (Ford) is a styrene/ethylhexyl acrylale/methyl methacrylate terpolymer. The alkyd enamel (Honda) pyrolysis profile indicates that the paint resin is an orthoph-thaUc alkyd containing a butylated-amino resin cross-linking component. 

The disproportionation is also observed in high-boiling solvents (toluene, xylene, pyridine) and the order of decreasing ease of pyrolysis of the RjPba compounds has been reported (296) to be ethyl, methyl > w-tolyl, phenyl > p-tolyl, p-ethoxyphenyl, p-methoxyphenyl > o-tolyl, o-ethoxyphenyl, o-methoxyphenyl > cyclohexyl, mesityl, 1-naphthyl. 

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