Competitive addition of near-thermal fluorine-18 atoms to olefins

Abstract

Near-thermal lSF atoms, produced by the 19F(n,2n)18F nuclear reaction and moderated in kinetic energy by collisions with excess SFs, have been reacted with the fluorinated ethylenes. The radicals formed by '8F addition are predominantly collisionally stabilized at 5 atm of pressure and are identified after abstraction of H from HI as the corresponding fluoroalkane-l*F. In intermolecular competition, the 18F atoms react preferentially with less fluorinated positions. Intramolecularly, I8F addition is also preferred at the less fluorinated end of the molecule. The competitive reaction ratios per molecule are generally independent of olefin/HI ratios, as well as of the ratios of two competing olefinic substrate molecules. The decomposition by CF, loss of CHFI8FCF2* radicals from near-thermal addition of 18F to CHF==CF2 proceeds with a pressure for half stabilization of 45 i 5 Torr in CHF=CF2.he energetic 18F atoms formed by nuclear reactions

Reactions of fluorine-18 atoms with ethylene

“…At the same time, the total observed yield of 18F products has diminished markedly. The most probable sink for the "missing" 18F, unmeasured in these particular experiments, is through abstraction of H from C2H4, as in (7). Even in 95% SFe-moderated systems, abstraction from ethylene is competitive with addition to it as indicated in Table I by the maximum total observed yields of about 65%.…”

Spectroscopic studies of some laser dyes

“…carried out which unambiguously involve the reactions of atomic fluorine with aromatic systems despite the considerable interest in such reactions.2 345However, radioactive 1SF atoms (tv, = 110 min) can be produced by various nuclear reactions, including the 19F(n,2n)18F reaction with fast neutrons, and these atoms can be brought to thermal energies without bond formation by multiple collisions with suitable inert moderators. [3][4][5][6][7][8][9][10][11][12][13][14][15] In the last several years, research in this laboratory has utilized such thermal 18F atoms for reaction studies with olefins,6•7•9•10 acetylene,8 various RH compounds,11 and a variety of inorganic species.12•13…”

Relative rates of fluorination of fluorinated ethylenes

“…The fluoroalkyl radical formed in reaction I probably has the fluorine attached to the less fluorinated carbon atom, since this is the radical preferentially formed in the addition of near thermal 18F atoms to partly fluorinated ethylenes. 13 Stabilization of the excited radical formed in II• has been achieved by the nitrogen diluent present since no decomposition product was detected. Similar radicalchain mechanisms have been proposed for the fluorina-tion8 and bromination14 of ethylene.…”