3-methyl-2-butanone, photolysis

The reaction of OH with 3-methyl-butanone has been studied by Le Calvd et al. (1998). The measurements are given in table V-B-9. They used pulsed laser photolysis with LIF detection of OH radicals and found a small negative temperature dependence, with some evidence of curvature in the Arrhenius plot the rate coefficient was essentially independent of temperature above room temperature. Calvert et al. (2008) fitted the Arrhenius expression to the data from Le Calve et al. (1998), obtaining the relation k = 1.45x 10 exp(219/r)cm molecule" s for use in atmospheric models, with A (298) = 3.0 x 10 cm molecule" s In the absence of conhrmatory measurements the uncertainty is estimated to be 40%. 

The methylethylcarbene which is formed thermally from methyl-ethyldiazirine at 160°C gives the same products as that from butanone p-toluenesulfonylhydrazone and bases in aprotic solvents." However, photolysis of the same diazirine gives a different mixture of C4H8 hydrocarbons. Considerable amounts of 1-butene are formed, the trans-butene content is reduced by half, and the amount of methyl cyclopropane increased fivefold. ... 

The Norrish type I process is considered to be the mechanism by which radicals are formed. The regio-chemical outcome of Norrish type I cleavage depends on the wavelength of light employed. For example, photolysis of 2-butanone at 313 nm (91.4 kcal moT, 382.5 kJ mol" ) gave a 40 1 mixture of 40 and ethyl radical (CH3CH2 ). Irradiation at 253.7 nm (112.7 kcal mok 471.9 kJ moT ), however, gave a 2.4 1 mixture of methyl radical and acyl radical 21. 

The 24 hour photolysis of chlorendic anhydride (III) in acetone in the presence of diethoxyacetophene (IV) yielded at least twelve measurable products as observed by the GC/MS procedure (Table I). Some of the products observed, i.e. 4-methyl-4-hydroxy-2-pentanone, biacetal, 4-methyl-3-pentene-2-one, ethyl acetate, 3-methyl-3-hy-droxy-2-butanone, 4-methyl-2-pentanone, and 2,4-pentane-dlone, are clearly derived from the photochemically induced decomposition of acetone and/or dlethoxyacetophe-none. 

The reaction of OH with 3,3-dimethyl-2-butanone has been studied by Wallington and Kurylo (1987a), who used flash photolysis with resonanee fluorescence detection. They determined a rate coefficient of (1.21 0.05) x 10" cm molecule" s" at 298 3 K. In the absence of other measurements, we recommend this rate coefficient, but with an increased uncertainty of 40%. The reaction probably has a negative temperature dependence similar to that of 4-methyl-2-pentanone. Most of the reaction... 

The total quantum yield of decomposition of 3-methyl-2-butanone as estimated by Lissi et al. (1973/1974) from an extrapolation of the product yields to zero absorbed light intensity gave 0.75. This is in good agreement with that derived from co = 0.78 estimated by Zahra and Noyes (1965) in photolysis at 127°C. 

Zahra and Noyes found that at 313 nm the addition of small amounts of oxygen (0.03-0.14 Torr) to 26 Torr of ketone (27°C) lowered the emission yield from 3-methyl-2-butanone by 21%, comparable to the effect seen in other small ketones. The emission yields observed by Zahra and Noyes in photolyses of pure ketone and in 2,3-butanedione-ketone mixtures, indicate clearly that the triplet state plays an important role in the photolysis of 3-methyl-2-butanone at 313 nm. There was no evidence of the triplet excited state observed in experiments at 253.7 nm. Lissi et al. (1973/1974) carried out experiments at 313 nm both with added 2,3-butanedione and with added cfi-l,3-pentadiene. These experiments confirm the importance of the triplet precursor to products for photolysis at 313 nm. 

The data available are insufficient to allow a definitive estimate of the quantum efficiencies as a function of wavelength for photolysis of 3-methyl-2-butanone in air that are required to define y-values. The photochemistry of 3-methyl-2-butanone may be similar to that observed for 2-butanone and 3-pentanone (section IX-D-2 and IX-D-3). However, the CH3C(0)—CH(CH3)2 bond is somewhat weaker than the CH3C(0)—C2H5 bond, and it seems reasonable that the y-values for use with 3-methyl-2-butanone should be somewhat greater than those of acetone and 2-butanone. 

Signicant new information related to the photodecomposition of some bifiinctional alkyl nitrates has been reported. In addition to absorption spectra of many alkyl nitrates, Roberts and Fajer (1989) also measured the spectra for the bifiinctional 2-nitrooxyethanol. Bames et al. (1993) studied the absorption spectra and photolysis products of several dinitrates 1,2-propandiol dinitrate, 1,2-butandiol dinitrate, 2,3-butandiol dinitrate, l,4-dinitrooxy-2-butene, 3,4-dinitrooxy-l-butene, as well as several bifiinctional nitrates a-nitrooxyacetone, l-nitrooxy-2-butanone, and 3-nitrooxy-2-butanone. Wangberg et al. (1996) reported on the the atmospheric chemistry of the bifiinctional cycloalkyl nitrates 2-hydroxy-cyclopentyl-l-nitrate, 2-oxo-cyclohexyl-1-nitrate, and frans -l-methyl-cycto-l,2-dinitrate. In this section, we will review the findings related to the tropospheric photodecomposition of these multifunctional nitrates. 

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