Alkane decompositions photolysis

Radical Reactkms.— The reaction of a-chloro ethers with zinc in the presence of thiophen yields di-2-thienyl alkanes (106). Photolysis of 3-iodopyridine in the presence of thiophen yields a mixture of 3-(2-thienyl)-pyridine and 3-(3-thienyl)pyridine in a 7 1 ratio. The synthesis and rate of decomposition of 2- and 3-thenoyl peroxides and of mixed thenoylfuroyl peroxides have been described. " Aryl 2-thenoates were obtained in high yields by the reaction of substituted benzenes with 2-thenoyl peroxide in the... 

The photodecomposition of -alkanes at excitation energies slightly above the absorption onset involves both C-H and C-C bond decompositions [18]. The dominant process is the C-H scission, (H2) 0.8-0.9, and the contribution of C-C decomposition is small. In the photolysis of cyclohexane, cycloheptane, cyclooctane, and cyclodecane, however, only hydrogen evolution was observed [[Pg.375]

Alkane elimination has a low yield during the photolysis of liquid n-alkanes (e.g., n-pentane [104,106]). This reaction takes place with high yield only for branched alkanes where it is likely to be a main primary-decomposition step [105,107]. 

Similarly to the fluorescence quantum yields, the yields of individual primary decomposition steps generally show considerable excitation energy dependence the yields of the unimolecular H2 and alkane eliminations and also those of the radical-type decompositions show a continuous variation with photon energy [27,39,42,107,115]. In cyclohexane photolysis the sum of the quantum yields of the two primary decompositions described by Reactions (5) and (6) is practically unity between photon energies 7.6 and 11.6 eV yield decreases with the energy, [Pg.382]

Free radical mechanisms of the photolytic decomposition of R MCOR (M = Ge, Sn) were considered in a number of earlier fundamental studies30,31. The nature of the resulting reaction products identified in nonpolar (alkanes, benzene, either in the presence or in the absence of a radical trap) or polar (alcohols, pyridine) media has allowed the proposal of a generalized reaction mechanism of the photolysis of R GeCOR compounds (Scheme 2). 

The direct photolysis and benzophenone-sensitized decomposition of methyl diazomalonate has been shown to produce two different spin states of biscarbo-methoxycarbene. In the direct photolysis experiments stereospecific addition to olefins and a high yield of insertion products in the presence of alkanes demonstrate the singlet character of the carbene in the sensitized decomposition the yield of insertion products decreases, and addition to cis- or ra 5 -4-methyl-2-pentene yields about 88 % trnwj-cyclopropane. In this case, as with most carboalkoxy-carbenes, the addition reaction to olefins can proceed by two paths ... 

Relatively few rate constants are available for the alkyl homolysis reactions mainly because clean sources of the alkyl radical have proved difficult to find. Consequently, the data are not always reliable, but some check is available [64, 65] from thermochemical and kinetic data for the reverse reaction. Direct photolysis of azo-compounds and mercury-photosensitized decomposition of alkanes have so far provided the most reliable (although old) data [64]. For good results, the method depended on precise product analysis in the early stages of reaction, with equation (1.9) used to determine where Rabs and Rr r are the initial rates of formation... 

Photolysis (200-260 nm) of diazomethane (CH2N2) produces highly reactive methylene (rCHj), which can insert into primary, secondary, and tertiary C-H bonds of an alkane with almost equal ease, as well as undergo addition to double bonds. The eyclopropanation of alkenes can, however, be achieved by carrying out the photolytic decomposition of diazomethane in the presence of metal salts. Palladium(II) acetate has been reported to be a very effective catalyst for the eyclopropanation of alkenes using diazomethane vide infra). 

The explosion of gaseous mixtures of HN3 and alkanes, olefines, or arenes yields soot, unsaturated hydrocarbons, H2, N2, and small quantities of NH3 and HCN [3, 4]. The photolysis of HN3 and alkanes mainly leads to N2 and amines which form by insertion of the intermediate NH into C-H bonds. NH3 and H2 are minor products [5, 6]. The decomposition of HN3 to N2 and NH3 prevails in the copyrolysis with alkanes [7]. 

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