Ionic and radical processes in the .gamma. radiolysis of tetrahalomethane-arene gaseous mixtures

Abstract

The reactivity and selectivity of radiolytically (60Co y rays) generated unsolvated trifluoromethylium (CF3+) ions toward selected aromatic substrates have been measured under conditions where nonionic processes can be safely ruled out. The same situation could not be attained for the trichloromethylium (CC13+) ion, owing to the overwhelming interference of CC13 radicals, by far the major reactive species produced by the y radiolysis of gaseous carbon tetrachloride. The unsolvated CF3+ ion is a moderate electrophile, whose attack on differently substituted aromatic substrates is rather indiscriminate; its positional selectivity toward a toluene molecule (para/0.5 meta = 4.3) appears intermediate between the one of t-C3H7+ ions (para/0.5 meta = 2.7) and that displayed by the very mild t-C4H9+ cation (para/0.5 meta = 35).Publication costs assisted by Consigno Nazionale deile Ricerche, RomaThe triplet state lifetime for 3-benzoylpyridine has been determined in aqueous solution at different pH values. The lifetime was found to decrease with decreasing pH and with increasing concentration of 3-benzoylpyridine. These findings are interpreted in terms of a complex formation with hydroxonium ion and of self-quenching of the triplet. Kinetic parameters for these interactions have been determined. The results obtained are compared with those of benzophenone.

Hot Atom Chemistry of 18F in Liquid Substituted Benzenes

“…This is in accordance with the generally accepted hot' ® F-for-H replacement in (fluoro-) alkanes [12]. Also the very low yield -if any -of C^ Hs CH2 F as a product of radiolysis in the CsHsCHj /CF4 system [11] indicates that thermal radiolytic F atoms do not readily lead to F-for-Hbenz substitution. c) As in the case of fluorobenzenes [1 ], addition of I2 generally tends to lower the total organic yield (Table 1).…”

“…This is particularly true for aromatic Compounds because of the intrinsic reactivity of the usual radical source Fj. More recently distinct positional selectivity has been reported for homolytic bromination [6,7] and fluorination [8,9,10,11 ] of halobenzenes by non-nuclear techniques. The use of nucleogenic atoms conceivably could shed more light on the role and nature of the attacking halogen atoms as well as on the particular effects displayed by different substituents in the aromatic target molecule.…”

Reactions of 34mCI Recoil Atoms with Liquid Mixtures of CCl4 and C6H6

“…-thermal radicals (CI and CC1 3 ) formed by the decomposition of excited CC1 4 molecules -singlet and triplet excited C 6 H 6 molecules, leading to polymerisation reactions -Cr.CClJ andC 6 [10] found no evidence for reactions of Cl-ions in radiolysis experiments of gaseous mixtures of of CC1 4 and arenes. A similar conclusion was derived by MASCOTTE etal.…”

“…and C 6 H 6 . C 6 H 5 CC1 3 has also been observed in the radiolysis of gaseous mixtures of CC1 4 and C 6 H 6 (G = 0.2, about half the yield of C 6 H S C1), but no CH 3 C 6 H 4 CC1 3 have been found in the radiolysis of mixtures of CC1 4 and C 6 H S CH 3 [10]. This proves that a CC1 3 radical is involved in the reaction leading to C 6 H S CC1 3 in CC1 4 /C 6 H 6 mixtures, because these radicals will preferentially abstract a side-chain Η-atom from C 6 H S CH 3 [10].…”

The gas phase reactions of the trichloromethylium ion with alkyl aromatics, studied by high pressure mass spectrometry

“…It is therefore surprising that no chlorinated aromatic products are ascribed to the reactions of CC13+ in y-irradiated CCl,/aromatic (100: 2) mixtures at total pressures from 100 to 760 Torr and ambient temperature (6,7). The reported yields of chlorinated benzene and toluene products are very low, the sum of G values (molecules of product formed per 100 eV of energy absorbed by the system) being in no system greater than 1, whereas G (ions) in gases is -4 (8).…”