2.2- Dimethylbutane hydroxylation

Irradiation of hexafluorobiacetyl in the vapor phase produces a 2 1 mole ratio of carbon monoxide and hexafluoroethane, products consistent with an initial carbon-carbon bond cleavage.62 However, vapor phase irradiation of hexafluorobiacetyl in the presence of a large excess of 2,3-dimethylbutane vapor or in 2,3-dimethylbutane solution gave less than 1% carbon monoxide and trifluoromethane. No trifluoroacetaldehyde or hexafluoroacetone was produced in the latter reaction. Instead a complex mixture of products, which was not separated and identified but whose infrared showed the presence of a hydroxyl band and a diminished carbonyl band, was obtained. This observation is consistent with product formation via hydrogen abstraction. 

Hexafluorobiacetyl. In the gas phase, hexafluorobiacetyl behaved 169> in the same manner as biacetyl, affording carbon monoxide and hexa-fluoroethane in stoichiometric ratio. However, in the presence of hydrocarbon vapor or in hydrocarbon solution, the disappearance of dione was not accompanied by formation of cleavage products. For example, photolysis (A >3000 A, 65°) of hexafluorobiacetyl in 150 molar excess of 2,3-dimethylbutane until 84% of starting material had disappeared resulted in only 0.5% of carbon monoxide, an equivalent amount of trifluoromethane, and a complex mixture of other products. On the basis of carbonyl and hydroxyl absorption in the infrared, it was assumed that the excited dione abstracted hydrogen from hydrocarbons to give products of photoreduction, photoaddition, etc. Occurrence of H-abstraction in the gas phase is unique. 

A small fraction of the acidic hydroxyls interact with cyclohexane (592), W(CO)6 (204), and only a minor fraction of them are affected by toluene (331). Larger fractions are affected by benzene and p-xylene (311). 4-Methylquinoline affects about 35% of the acidic hydroxyls (591). 2,2-Dimethylbutane slowly accesses the pores and shifts the OH band from 3612 to 3485 cm (581). The residual OH groups are characterized by a band at 3619 cm. Although a relatively large molecule (with a kinetic diameter of 0.6 nm), 2,2-dimethylbutane interacts with acidic hydroxyls, thereby shifting the 3605 cm band to 3465 cm (333). Two types of... 

The Arrhenius parameters of the reactions of hydroxyl radicals with aromatic compounds, listed in Table 2, are based on the rate coefficients (cm molecules" s ) of the reference compounds taken from recent evaluations of OH radical reactions / (2,3-dimethylbutane) = 6.2 x 10" [1], independent of temperature / (diethyl ether) = 7.3 x 10" exp(158K/T), 242-440 K [3] ... 

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