Septiratioti of the C7FIi isomers by gas chromatography Fluorocarbons are difficult to prepare and are even more difficult to purify. &Gas chromatography seems the most practical approach to purifying fluorocarbons. GREENE AND WACNI~ have. separated low-molecular-weight fluorocarbons on a silica gel column and REED et al. 2~ have evaluated several liquid phases for the chromatographic separation of fluorocarbons. REED has separated the isomers of CDFIQ on a '~hexadecane substrate" and has done quantity purification of fluorocarbons on a preparative scale vz-hexadecane column 6. This paper describes the gas-liquid chromatographic separation of the perf-luoroheptane isomers.
Analytical. Gas chromatographic analysis of all samples ,was done with a Perkin-Elmer Model 154 vapor fractometer. The recording instrument was a I-mV full scale range Honeywell strip chart recorder. Peak areas were measured by a Perkin-Elmer Model rg4B printing integrator which gave 6000 c.p.m. at full scale deflection on the recorder, Gaseous samples were injected from a glass vacuum system through a gas sample valve.
The analytical column 'was a 1/4 in. x 50 ft. +hexadecane column, as described in Table . Appearance times and retention volumes of fluorocarbon compounds through the C,F,& isomers were determined by injecting known samples.
Prq!mratio~a of the C,F,, isomevs.
Radiolysis studies on fluorocarbonsa-8 show that products from irradiating a saturated perfluoroalkane are saturated per-fluoroilkane products with molecular weights above and below the parent compound, All df these products can be explained by a radical formation, radical propagation, and radical recombination mechanism involving abstraction reactions*. Because there are only certain radicals possible from a given parent the kind and distribution of radiolysis products from a given perfluoroalkane parent may be predicted@-*.
Using n-C,F,, as an example, the following scheme illustrates the' most probable C,FrB isomers obtainable from n-C,F,,.
Ru@we to jwodzcce radicals
n-cp,, -w -+ Cl?, ' + C1~,CF,CF&F~ l cp, ' + CF,CF,CF~' F -+ CF,CF,CF,CF&F, l F 9 + CF,CFCF,CF,CF, 1;. + (C,F,)&F* Ii-Abstraction to $rbdwe radicals R l -t_ ?a-C,F,, + R-F + CF,CF&F&F&F, l R. + ut-C,T(',, +