Nitrites pyrolysis

Suggestions of untoward hazard inherent in the preparation of nitrosotrifluoro-methane by pyrolysis of trifluoroacetyl nitrite [1] are discounted in the later reference, which gives full details of the equipment and procedure that had been used uneventfully during the previous decade [2],... 

Nitrosomethane (1) is known to be less stable than its isomer formaldoxime 2 and original attempts to isolate this species failed owing to its facile isomerization to the oxime 2. Already Bamberger and Seligman considered in 1903 that it would be difficult to isolate nitrosomethane after oxidation of methylamine due to its rapid isomerization to 2. Hence, 2 is always present in the synthesis of the nitrosomethane. Nitrosomethane is produced in the pyrolysis or photolysis of tcrf-butyl nitrite and by the reaction of methyl radicals with nitric oxide. Early results were confusing since the final product obtained is dimeric nitrosomethane. It was first isolated in 1948 by Coe and Doumani from the photolysis of gaseous ferf-butyl nitrite according to the overall reaction shown in equation 2. 

Batt, Gowenlock and Trotman carried out a detailed study of the pyrolysis and photolysis of terf-butyl nitrite and established that dimeric nitrosomethane exists in two isomeric forms, cis and trans (Scheme 5). Monomeric nitrosomethane could be generated by heating the dimer in the gas phase (the activation energy for dissociation was found to be ca 90 kJmoH )". Also ultraviolet irradiation dissociates the dimer, leaving monomeric 1. Vibrational analysis of monomeric 1 is summarized in Table 4. 

Though much more stable than acetyl nitrite even at 100°C, the vapour of trifluoroacetyl nitrite will explode at 160—200°C unless diluted with inert gas to below about 50 vol% concentration. Higher perfluorohomologues are more stable [1], A detailed examination of the explosion parameters has been made [2]. This and higher polyfluoroacyl nitrites tend to explode above 140°C at ambient pressure, and handling of large quantities should be avoided [3], especially during pyrolysis [4],... 

My mind was prepared from my knowledge of the pyrolysis of chlorinated hydrocarbons (Chapter 1) and related subjects. The work of the late Professor E. W. R. Steacie, who eventually became Director of the National Research Council of Canada, had showed that the pyrolysis of alkyl nitrites in the gas phase gave NO and an alkoxy radical in a unimolecular reaction. The temperatures required for this reaction were much too high for... 

The book explores the invention of new chemical reactions for use in the synthesis of biologically and economically important compounds. It begins with a mechanistic study of the industrial importance of the pyrolysis of chlorinated alkanes. It continues with a theory on the biosynthesis of phenolate derived alkaloids involving phenolate radical coupling. Included in the book is a description of the work on nitrite photolysis (the Barton Reaction) which involved the invention of new radical chemistry leading to a simple synthesis of the hormone, aldosterone. In two final chapters Dr Shyamal Parekh views Professor Barton s pioneering work from the modern perspective, with a review of recent applications in industry and research. 

The alkyl nitrate and nitrite esters contain four different elements and as such may be expected to show a very complex kinetic behavior. This is certainly the case with the nitrate esters, the pyrolysis of which is accompanied by varying amounts of oxidation. For the nitrites, however, the pyrolysis seems to be less complex. The principal reaction products from the pyrolysis of C HsONO are CH3CHO + NO together with lesser amounts of N2O + H2O and much smaller amounts of C2H6OH, HCN, CO, and CII2O. 

Many of these reactions have been studied before in the section on NaOa and so will not be discussed again here. In excess NO, the rate becomes nearly first-order over most of the decomposition with a rate constant which is itself a function of the total pressure. NO2 is an inhibitor for the decomposition, and in consequence the reaction in the absence of added NO shows a steady fall in apparent first-order rate constant with continuing decomposition. In this respect the nitrates and nitrites all seem to have in common the feature that the pyrolysis products inhibit the rate of decomposition. Tliis is to be expected in systems decomposing via radical mechanisms when the products of the reaction include such efficient radical traps as NO and NO2. It is unfortunate that quantitative data on these systems are at present so sparse and in many cases disparate. This is to be expected for systems that are so complex and show such sensitivity to surface reactions. The free radical chemistry of these systems is, however, a very interesting and important one, and efforts to elucidate it will eventually turn out to be quite rewarding. 

Trifluoronitrosomethane may be obtained from photolysis of a mixture of trifluoroiodo-methane and nitric oxide [275, 276] or from pyrolysis of trifluoroacetyl nitrite [277, 278] (Figure 8.108). 

The use of the direct thermal decomposition method has been fairly widespread, and the values obtained by it will be discussed in the appropriate sections of this book. The O - N bond in alkyl nitrates and nitrites, and the G N bond in nitromethane are among those whose dissociation energy has been measured by this method, but in view of the possible kinetic complexities which may be encountered, such as those already mentioned in connection with the pyrolysis of organic iodides (see Section 4.2.4) the values obtained are often at best only tentative. 

Significant contribution towards elucidation of the overall mechanism comes from investigations of the pyrolysis on ethyl nitrite " . Arrhenius parameters for the pyrolysis of some alkyl nitrites are shown in Table In the... 

In one of the most elegant applications of gas-phase inhibition by nitric oxide, Birss, Danby and Hinshelwood have studied the thermal dissociation of r-butyl peroxide. The low temperatures required for pyrolysis permitted mass spectro-metric determination of t-butyl nitrite, and a fairly complete kinetic analysis of the system was possible. The rate of decomposition of peroxide was related to the consumption of nitric oxide and to the appearance of butyl nitrite during the inhibition period, and curves were obtained which showed the acetone and ethane concentrations as a function of time during and after inhibition. 

Photodissociation dynamics of alkyl nitrites adsorbed on Mgp2 surfaces and on the Ag(lll) surface have been studied. The laser photodissociation and thermal pyrolysis of poly(glycidyl nitrate) have been investigated. Such high-energy polymers have been proposed for use as binders in solid rocket motors. 

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