Alkyl nitrites, photolysis

TABLE 4. Parameters for Excited Alkoxyl Radical Production in Alkyl Nitrite Photolysis... 

Alkyl nitrites (RONO) absorb light strongly in the actinic region, dissociating to form RO + NO. Because of this rapid photolysis, other reactions such as that with OH cannot compete, and alkyl nitrites have not been generally observed in the troposphere at significant concentrations. 

Photolysis studies of alkyl nitrites in the vapor phase has been limited to the verification of the presence of a nitroso dimer moiety among the products by ultraviolet spectrophotometry. The principal product of photolysis of butyl nitrite in the vapor phase is the trans-isomer of the dimer of nitrosomethane43 86 87 281 286 the reaction has been explained by a mechanism involving fragmentation of alkoxy-radicals. 

Photolysis of primary, secondary, and tertiary alkyl nitrites in benzene indicated that a minimum chain length of five carbon atoms attached to the nitrite grouping is required for appreciable yields of secondary nitroso dimers via the Barton reaction. In the case of primary and secondary nitrites, a chain of length of four carbon atoms or more attached to the nitrite grouping is required for formation of the six-membered intermediate (e.g., A) involved in the Barton reaction.139140... 

Method (d), based on UV photolysis-TEA detection, seemed to give positive response to alkyl nitrites and C-nitroso compounds. In this respect, it is less specific than the preceding two HX-catalyzed denitrosation techniques, which give either negligible or no response for such compounds. Data on the actual use of the methods mentioned in Table 2 for the determination of NOC in foods is, however, limited. 

Halogens, alkyl nitrites and alkyl hypochlorites also undergo photolysis easily (Scheme 2.30). Alkyl nitrites and alkyl hypochlorites generate alkoxy radicals. 

Cekovic has examined the addition of electron-deficient olefins to 3-hydroxy radicals [164]. Addition to acrylonitrile of the carbon-centered radicals resulting from the Barton photolysis of alkyl nitrite 173 and subsequent 1,5-hydrogen transfer, yielded a-oximino nitrile 174 (63%, Scheme 57) [165]. 

The requirement of a six-membered ring cyclic transition state for the hydrogen abstraction dictates that in the photolysis of long chain alkyl nitrites, y-nitroso alcohols are produced, usually in the more stable form of the nitroso dimer, viz. 

Several procedures for remote alkylation at the < -carbon of alcohols have been reported. For instance, Cekovic has shown that photolysis of alkyl nitrites and/or benzenesulfenates in the presence of BusSnH and olefinic radical traps such as acrylate esters afforded the alkylated product in moderate yields (Scheme 10) [57, 58]. 

A novel procedure has been developed for the synthesis of phosphate esters of hindered alcohols, and was designed to avoid nucleophilic displacement reactions. It involves photolysis of the alkyl nitrite in the presence of a trialkyl phosphite and proceeds by addition of the alkoxyl radical to phosphorus followed by elimination of an alkyl group (Scheme 3). ... 

The photodecomposition pathways of alkyl nitrites have been reviewed by Calvert and Pitts (1966). Earlier a review of the photolysis of complex organic nitrites in solution was given by Akhtar (1964). Since the review of Calvert and Pitts... 

Excimer laser photolysis of ethyl nitrite was studied at 248 and 351 nm as a function of O2 pressure (Zellner). In contrast to methyl nitrite, the photolysis produced not only C2H5O radicals but also methyl radicals with high yield. This study indicates that photolysis of higher alkyl nitrites is not an appropriate source for the laboratory generation of alkoxy radicals. 

Nitrite photolysis as radical source 28,933 Nitrites s. Alkyl nitrite... 

Since these early studies on nitrite photolysis, a number of extensive synthetic and physicochemical studies on the photodissociation of steroidal alcohol nitrite esters and simple alkyl nitrites, such as t-butyl nitrite (as summarized by Calvert and Pitts, Ir. ), estabhshed that the primary reaction of the photolysis of nitrite esters in solution is the homolysis of the ONO bond of their nitrosoxy groups to give alkoxyl radicals and nitric oxide (Scheme 3). 

Gray, J.A. and Style, D.W.G., Photolysis of methyl nitrite, Trans. Faraday Soc., 48, 1137, 1952. Steacie, E.W.R. and Show, G.T., The homogeneous unimolecular decomposition of gaseous alkyl nitrites. II. The decomposition of ethyl nitrite, /. Chem. Phys., 2, 345, 1934. 

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