Pyrolysis of N-oxides

Pyrolysis of N-oxides, 338 Pyrolytic elimination from esters, 334 3-(N-pyrrolidinyl) -androsta-3,5-diene-lla,17/3-diol, 410... 

An even milder cycloelimination uses a ring of five atoms 6.28 instead of six, but still involves six electrons. This is no longer a retro-ene reaction, but it is still a retro group transfer and it is allowed in the all-suprafacial mode 6.29. The pyrolysis of N-oxides 6.30 is called the Cope elimination, and typically takes place at 120°, the corresponding elimination of sulfoxides 6.31 (X=S) typically takes place at 80°, and, even easier, the elimination of selenoxides takes place at room temperature or below. All these reactions are affected by functionality making these numbers only rough guides, but they are all reliably syn stereospecific. 

The pyrolysis of N-oxides to yield alkenes proceeds at lower temperatures than the above reactions.20... 

Pyrolysis of N-oxides known as Cope elimination takes place at lower temperatures (100-150 °C). The pyrolysis of sulphoxides and selenoxides takes place easily below 100 °C because of weaker C-S and C-Se bonds. As for example, ery/firo-N-oxide 6 and eryT/iro-sulfoxide 7 on pyrolysis give cis and trans olefins as major product, respectively. 

The procedure is a modification of that published. Methylenecyclohexane has been prepared by the pyrolysis of N,N-dimethyl-l-methylcyclohexylamine oxide, N,N,N-trimethyl-l-methylcyclohexylammonium hydroxide, N,N-dimethylcyclo-hexylmethylamine oxide, and N,N,N-trimethylcyclohexylmethyl-ammoniumhydroxide. It has also been obtained from the pyrolysis of cyclohexylmethyl acetate and of cyclohexylideneacetic acid and from the dehydrohalogenation of cyclohexylmethyl iodide. ... 

Benzofurazan oxide is most conveniently prepared by the method herein described, which is adapted from the procedure of Green and Rowe.3 It has also been reported as an Organic Syntheses preparation 4 by way of the pyrolysis of n-nitrophenylazide. 

The principle of the method will be discussed for the pyrolysis of n-butane, then generalized for the oxidation of any alkane. 

Snlphinate Esters.—new preparation from disulphides involves chlorina-ti(m in alcohol solvents at -20 and a further new route is announced, in which N-alkyl-N -toluene-p-sulphonylhydrazines TolSOjNHNHCHi-CHjR give toluene-p-sulphinates TolSOOCHzCHzR and the alkene RCH==CH2 on oxidation with SeOz, C1O3, or HgO, probably via radical intermediates. Pyrolysis of n-butyl sulphoxylate Bu OSOBu is suggested to involve conversion into the sulphinate as first step, en route to SO2, S, Bu OH, and but-l-ene. Standard routes are illustrated in preparations of phenylmethanesulphinates and amides. ... 

Another important use of a-pinene is the hydrogenation to i j -pinane (21). One use of the i j -pinane is based on oxidation to cis- and /n j -pinane hydroperoxide and their subsequent catalytic reduction to cis- and /n j -pinanol (22 and 23) in about an 80 20 ratio (53,54). Pyrolysis of the i j -pinanol is an important route to linalool overall the yield of linalool (3) from a-pinene is about 30%. Linalool can be readily isomerized to nerol and geraniol using an ortho vanadate catalyst (55). Because the isomerization is an equiUbrium process, use of borate esters in the process improves the yield of nerol and geraniol to as high as 90% (56). 

Another important process for linalool manufacture is the pyrolysis of i j -pinanol, which is produced from a-pinene. The a-pinene is hydrogenated to (73 -pinane, which is then oxidized to cis- and /n j -pinane hydroperoxide. Catalytic reduction of the hydroperoxides gives cis- and /n j -pinanol, which are then fractionally distilled subsequendy the i j -pinanol is thermally isomerized to linalool. Overall, the yield of linalool from a-pinene is estimated to be about 30%. 

Attempts to prepare 1 from some other precursors were largely unsuccessful N, N , A,/-(cyclopropane-l,2,3-trimethyl)-tris(dimethylamine oxide) decomposed unspecifically above 250 °C3 and pyrolysis of l,2,3-tris(acetoxymethyl)cyclopropane gave mainly benzene3 its gas-phase pyrolysis at 570-580°C produced a mixture of at least fifteen compounds containing perhaps a small amount of l7. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

Pyrolysis of di-n-butylmercury in the presence of nitric oxide in a flow system produced mixtures of oximes and nitroso compounds [51]. 

Both NAT1 and NAT2 N-acetylate benzidine and O-acetylate the N-hydroxy metabolite. Because NAT2 and, to a lesser extent, NAT1 both show variation in the human population, this influences susceptibility to the carcinogenic effects of arylamines such as benzidine. With other aromatic amines, such as the heterocyclic amines found as food pyrolysis degradation products, N-acetylation is not favored, N-oxidation being the primary route followed by O-acetylation. This seems to take place in the colon. 

It was impossible to obtain naphtho[bc]azete on pyrolysis or on photolysis of N-substituted naphtho[cazete intermediates 29 from biradical 28 was not proved even indirectly, as was done, for instance, in the case of formation of the oxygen analogs 13, i.e., a substituent label was not introduced in the naphthalene nuclei of the initial compounds 26 and 27. 

N-Oxides 230 and 231 are stable benzo[o/]indazole derivatives. A mixture of these compounds was obtained on pyrolysis of l-azido-8-nitronaphthalene 228 or on oxidation of 1,8-naphthalenediamine 229. It... 

The products of the thermolysis of 3-phenyl-5-(arylamino)-l,2,4-oxadiazoles and thiazoles have been accounted for by a radical mechanism.266 Flash vacuum pyrolysis of 1,3-dithiolane-1-oxides has led to thiocarbonyl compounds, but the transformation is not general.267 hi an ongoing study of silacyclobutane pyrolysis, CASSF(4,4), MR-CI and CASSCF(4,4)+MP2 calculations using the 3-21G and 6-31G basis sets have modelled the reaction between silenes and ethylene, suggesting a cyclic transition state from which silacyclobutane or a trcins-biradical are formed.268 An AMI study of the thermolysis of 1,3,3-trinitroazacyclobutane and its derivatives has identified gem-dinitro C—N bond homolysis as the initial reaction.269 Similar AMI analysis has determined the activation energy of die formation of NCh from methyl nitrate.270 Thermal decomposition of nitromethane in a shock tube (1050-1400 K, 0.2-40 atm) was studied spectrophotometrically, allowing determination of rate constants.271... 

---