Butenes, addition photolysis

Photolysis of the parent compound (44) yields singlet methylene, as evidenced by its stereospecific addition to ( )-butene. The cyclopropane is formed together with the characteristic insertion products of methylene (62MI50800, 64PAC(9)527)... 

The photolysis of a-diazosulfones dissolved in alkenes provides sulfonyl-substituted cyclopropanes in high yields. This is exemplified by the preparation of l-(p-methoxyphenylsulfonyl)-2,2,3,3-tetra-methylcyclopropane in 75% yield from -methoxybenzenesulfonyl-diazomethane and 2,3-dimethyl-2-butene. A similar addition to [Pg.101]

Enhancement of the total butene yield is observed when various additives whose ionization potential falls below about 9.4 e.v. are present during ethylene radiolysis (35). This is consistent with the above interpretation (Figure 2). In the vacuum ultraviolet photolysis of cyclobutane the yield of butenes varies with the ionization potential of the additives in the same way as observed here (12). The maximum enhancement corresponds closely to the yield of C4H8+, as expected from our mechanism. 

The addition of carbenes is also a stereospecific reaction, each geometrical isomer forms the cis addition product. Thus carbene generated from the photolysis of diazomethane adds in a cis manner to both cis and trans butene-2. 

The addition of the diphenylcarbene, generated by the photolysis of diazo-diphenylcarbene, to cis- or trans-butene gives mostly the abstraction product, and a small amount of the addition product. However, the abstraction processes are... 

This technique has been repeatedly utilized. Photolysis of diazomethane in the liquid phase yields methylene in the singlet state, as is shown by the practically stereospecific addition to cis- or trans-butene. Dilution with perfiuoropropane reduces the degree of stereospecifity as well as the amount of C—H-insertion, indicating that triplet methylene is involved A similar effect has been reported for CF3CH which, on dilution with perfluoro-diethylether (in the gas phase), adds in a non-stereospecific manner owing to the presence of the triplet... 

In the photolysis of diphenyl-diazo-methane in olefins the ratio cyclopro-pane/abstraction products depends on the structure of the olefin. The nonstereospecific addition of diphenylcarbene to cis-2-butene is temperature-dependent i8b) ... 

Loss of stereospecifity on dilution with cyclohexane also occurs in the otherwise stereospecific addition of the biscarbene 55 by photolysis of 55 in cis-2-butene i ). 

Thermolysis and/or photolysis of 4 in aliphatic halides resulted in the formation of the corresponding 1,2-addition products (73JA2695). Photolysis in cyclohexene gave the 2-cyclohexenylimidazole by allylic insertion, whereas insubstituted butenes it led to no isolable products [80DIS(B)(40)3747],... 

Little evidence is available to determine whether aromatic ketones can act as singlet sensitizers. If they can do so, it will be only at high acceptor concentrations because the lifetime of benzophenone singlets,154 for example, is less than 2 x 10-10 sec and that of several other aromatic ketones is estimated to be less than 10 10 sec.155 Yang231 has noticed that the photochemical addition of benzophenone to 2,3-dimethyl-2-butene is less efficient in neat olefin than in 4M olefin, which may indicate deactivation of benzophenone singlets. Golub218 has mentioned that benzophenone is a singlet sensitizer in the photolysis of 1,4-dichlorobutane. 

The two-step deoxygenation of benzoyl cyanide to phenylcyanocarbene, which added quickly to alkenes via photolysis of the appropriate 2,2-dihydro-1,3,2,-dioxaphos-pholanes, has been performed70. A homolytic fragmentation mechanism was assumed. When the 1,3,2-dioxaphospholane 36 in trans-butene was irradiated, the range of observed substances included 37 and 38 as the major products, in addition to fluorenone and bifluorenylidene (equation 16)70. 

An added complication in the interpretation of long-wavelength ketene photolysis is demonstrated by Cundall s discovery of ketene sensitized cis-trans isomerization of the 2-butenes.33 As the pressure of olefin increases, the rate of ketene decomposition decreases and the rate of olefin isomerization increases. At high olefin concentrations part of the apparent nonstereospecificity of cyclopropane formation can thus result from stereospecific singlet addition to already isomerized olefin. 

Likewise, 03 reacts with hydrocarbons to produce unknown numbers of H02 and R02 (or RC002) [see below]. From the computer analysis of simulated smog formation involving the hypothetical illumination of N0-N02-H20-butene-aldehydes-C0-CH4 mixtures in air, Calvert and McQuigg (184) estimate that H02 and R02 radicals, formed mainly by the addition of OH to butene, account for 10% of NO to N02 conversion. The H02 and R02 radicals formed from the photolysis of aldehydes and OH reactions with aldehydes are responsible for 25% of the conversion. Carbon monoxide is only 5% effective for the NO to N02 conversion. The effect of paraffins on the NO to N02 conversion rate is very small. 

Our several attempted additions of CH3S CH3 to CF =CFCF=CF reactions by photolysis alone with prior emuls1rication, solution photolysis, sonolysls singly, and thermolysis up to 230°C for 24 hours were unsuccessful but the combined photolysis and ultrasound provided a convenient path to synthesize the trans-l,4-bis(methylthio)hexafluoro-2-butene (I, the trans-1, 4-adduct) as the major product in the presence of trace amount of the other 1 1 adducts and minor quantity of oligomers (Eq. 4)... 

The flash-photolysis study revealed that the vinyl radicals produced in process (3) can be stabilized at higher pressures. Butene-1 and propylene, which are attributed to the combination of vinyl radicals with ethyl and methyl radicals respectively, were found to be absent at low ethylene pressure but became significant at 10-20 torr. Furthermore the addition of 600 torr N2 sharply increased the butene-1... 

Studies on the photolysis of butene-1 at 1849 A have been made by Harumiya et and by Borrell and Cashmore . Ethane and 1,5-hexadiene are the most important products. Borrell and Cashmore report a total of twenty-five products which in addition to the ethane and 1,5-hexadiene include methane, ethylene, acetylene, propene, propane, allene, cis- and franj-butene-2, 3-methylbutene, n- and isopentane, cis- and fra j-pentene-2, pentene-1, as well as various Cg, C and Cg compounds. The following reactions explain these products. 

The photolysis and pyrolysis of difluorodiazirine has been shown to involve difluoromethylene and stereospecific addition to 2-butene indicates that it is probably in a singlet state. In argon or nitrogen matrices, Cp2 has been detected by spectroscopic measurements . Products arising from the thermolysis or photolysis of fluoromethoxydiazirine, cyanofluorodiazirine, difluoroaminodiazirine and chlorofluorodiazirine have been reported the main feature of these reactions is that the intermediate carbene in all cases can be trapped by olefin reagents, whereas fluorocarbenes from other sources are quite unreactive. 

As the two components do not react in the dark, a triazoline intermediate is not probable. Other A -carbethoxyaziridines were formed via carbethoxy nitrene when ethyl azidoformate was irradiated in dihydropyran and in enolacetates . The stereospecificity of the addition is high. The photolysis of cis and trans 2-butene at — 20° yielded mainly the cis (130) and trans (131) aziridines respectively This stereospecificity has been found to diminish upon dilution... 

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