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The reaction of dl-and weio-2,3-dibromobutanes with tri-n-butyltin hydride gives 2-butenes as major products by a free-radical chain-debromination reaction in which anti elimination predominates. The stereospecificity increases with increased organotin hydride concentration and with decreasing temperature. The isomeric 2,3-dichlorobutanes give simple reduction as the major reaction with tri-n-butyltin hydride, and the same proportions of cis-and trans-butenes are formed from each isomeric chloride. 1,2-Dibromo-l -deuteriohexane gives preferred anti elimination, but the 2,3-dibromosuccinates and 1,2-dibromo-l ,2-dichloroethanes give nonspecific debrominations. 1 -Bromo-1 -phenyl-2-chloroethane reacts more slowly with tri-n-butyltin radicals than does 1,2-dibromo-1 -diphenylethane; m7/!ro-2-bromo-3-chlorobutane reacts more slowly than does meso-2,3-dibromobutane. These results are consistent with a reaction scheme involving open and halogen-bridged free-radical intermediates. The bridged radicals are destabilized by chlorine and by carbethoxy groups in the a positions.An investigation of the scope of the reaction of alkyl halides with organotin hydrides has revealed that geminal polyhalides undergo stepwise reduction to alkanes.1 On the other hand, propylene and mesostilbene dibromides do not undergo normal reduction to hydrocarbon upon reaction with tri-n-butyltin hydride. lb The major products of the reaction of 1 mol of the vicinal dibromide with 2 mol of the hydride were hydrogen, olefin, and tri-n-butyltin bromide.Since it had been demonstrated that the reduction of simple alkyl halides with organotin hydrides proceeds by a free radical chain mechanism,2 345it was of interest to determine some characteristics of this elimination, which might also be a free-radical process.Ionic eliminations have been extensively studied and results have been reviewed.3-5 Free-radical eliminations have received far less systematic investigation as shown in a recent summary by Kampmeier and coworkers.6 78910Such processes are generally regarded as involving formation of free radicals from which ß substituents can be lost, in turn, as free radicals. This is tantamount to reversibility in the first step of a freeradical addition to an olefin, a process which can be conveniently used as a means for isomerization of olefins, eq 1. Halogen atoms,7,8 thiyl radicals,9,10 and organotin radicals11 can function as X• in eq 1. The intermediate radical 1 may be formed from a saturated molecule by hydrogen abstraction as in the photochlorination of bromocyclopentane,12 by the reaction(1) (a) H. G.

Polyacrylamide gels have been used for some time to reduce water cut in production wells and control profiles in injectors. Formations up to 150°F have been treated rather routinely. Recently, interest has developed in using these gels at higher temperatures in formations containing relatively hard brines. We have investigated the changes in hydrolysis of polyacrylamide polymers and gels crosslinked with trivalent chromium with C-13 NMR. This method is a direct way to correlate changes in the gel composition with effectiveness under severe conditions. The carbonyl carbon of the amide group has a sharp resonance at 181 ppm. As the amide groups hydrolyze, the 181 ppm resonance decreases in intensity and a second resonance appears at 184 ppm. This resonance is due to the carbon in the carboxyl ate formed by hydrolysis of the amides. Of course, the resonance is already present in partially hydrolyzed polyacrylamides, but increases in intensity as hydrolysis progresses. In gels, crosslinked with paramagnetic ions such as chromium III, these resonance lines are broadened, but resolvable. Line shape analysis fits the spectra closely and allows integration of the intensity of each resonance. The degree of hydrolysis and changes in the degree of hydrolysis can be determined for the polyacrylamide chains comprising the gel. The increase in the degree of hydrolysis parallels the syneresis of the gels and their concommitant loss of effectiveness. The syneresis is caused by reaction of the newly created carboxylate groups with hardness ions in the brine leading to extensive over-crosslinking. This is a fundamental characteristic of polyacrylamide gels and will take place regardless of polymer source.