Generation of ground electronic state haloalkyl radicals in the gas phase

Abstract

Gaseous haloalkyl radicals were prepared by the photolysis of iodohaloalkanes in Pyrex vessels containing mercury (I) halides. Cleavage of the carbon‐iodine bond gave mercury (II) halide and a radical which was subsequently shown to react on the ground state electronic energy surface. The usefulness of this method for chemical activation rate constant studies is illustrated by measurement of unimolecular rate constants for decomposition of CH2ClCH2Cl and CF3CH3. Possible mechanisms for photodecomposition of iodoalkanes in the presence of mercury (I) halides are discussed.

Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals. II. Reactions of ?CF3 +CF3CH2CH2? and CF3CH2CH2? + CF3CH2CH2?

“…This technique would afford an assortment of substituted radicals by just varying the identity of the alkene; however, bromo-and chloro-alkenes could not be used because complicated reaction chemistry could result from any of the following: rupture of the C-X bond of the energized haloalkyl radical, abstraction of the halogen by the H atom, or production of halogen atoms by the Hg('PI). We have exploited [12] an efficient method for radical production, similar to the H + alkene procedure, that uses the rapid addition of trifluoromethyl radicals to alkenes to generate the radical of interest [ 13,141. The CFj radical is formed by the photodissociation of either hexafluoroacetone [ 15,161 or trifluoroacetic anhydride [ 171.…”

Reinvestigation of the Unimolecular Reactions of CHF2CHF2: Identification of the 1,1-HF Elimination Component from Addition of :CFCHF2 to trans-2-Butene

“…For all experiments a small amount of Hg 2 I 2 was added to control the free iodine. 12 Reagents were measured on a grease-free vacuum system and placed in Pyrex vessels of known volume to achieve the desired pressures. Irradiation times depended on vessel volume and were between 2 and 5 min using an Oriel 8510−4 high-pressure mercury lamp, which typically gave less than 10% conversion of the CHF 2 I to products.…”

“…The experimental measurements consisted of three series of photolytic experiments at room temperature, one with just CHF 2 I, the second with added trans -2-butene in a 1:2 ratio of trans -2-butene to CHF 2 I, and the third with a 10-fold excess of trans -2-butene relative to CHF 2 I. For all experiments a small amount of Hg 2 I 2 was added to control the free iodine . Reagents were measured on a grease-free vacuum system and placed in Pyrex vessels of known volume to achieve the desired pressures.…”

Substituent effects on the disproportionation—combination rate constant ratios for gas‐phase halocarbon radicals, Part 5: Reactions of CF3 + CF3CH2CHCH3 and CF3CH2CHCH3 + CF3CH2CHCH3

“…Commercial samples of CH 2 C(CF 3 )CH 3 and hexafluoroethane were purchased from PCR Inc. and CF 3 CH CHCH 3 (15% cis and 85% trans) was from Fluorochem Ltd. The CH 2 CHCH 2 CF 3 was prepared by photolysis [10] of CH 2 CHCH 2 I (Aldrich Chemical) and CF 3 I (PCR) in pyrex vessels containing Hg 2 I 2 , and the CH 3 CH(CF 3 )CH 3 was prepared by the photolysis of CF 3 I and CH 3 CHICH 3 (Aldrich Chemical). A sample of 1,1,1-trifluorobutane was prepared by two synthetic routes, from the photolysis of CF 3 CH 2 I (PCR) and CH 3 CH 2 I, and also from the photolysis of CF 3 I with CH 3 CH 2 CH 2 I (Aldrich).…”