April, 1951
COMMUNICATIONS TO TNB EDITOR
1891
tions outlined will be discussed in a subsequent communication.
effecting the reduction of nitrobenzene without bringing about nuclear substitution. The presence of phenol along with biphenyl and terphenyl sugDEPARTMENT OF CHEMISTRY gests strongly that phenyl radicals axe also produced HARVARD UNIVERSITY HAROLD CONROY’ CAMBRIDGE 38, MASS. and that they, too, abstract oxygen rather than atRECEIVED JANUARY 29, 1951 tacking the nucleus of the nitro compounds. This 17) National T n s t i t i i t m of Health Postdoctoral Fellow is an entirely unexpected result in the light of previous work which indicates that phenyl radicals produced in the thermal decomposition of benzeneTHE REACTION OF TRIPHENYLMETHYL WITH diazoacetate6 and benzoyl peroxide6 attack nitroNITROBENZENE benzene to give p-nitrobiphenyl. This difference in Sir : behavior may be taken to indicate that pairs of It has been rather generally a c ~ e p t e d ’that ~ ~ ~ ~radicals produced in unimolecular decompositions aromatic nitro compounds are activated, relative are capable of making a concerted attack on solvent to their unsubstituted analogs, toward attack by molecules in the short time interval in which they free radicals leading to aromatic substitution. Re- are held in the same cavity in the solution. A simicent evidence concerning the inhibition of the per- lar discrepency involving the fate of benzoate radioxide induced polymerization of allyl acetate4 by cals? produced in different reactions has recently nitro compounds was taken to indicate that some been observed. other mode of reaction must be available to the This research was carried out under a contract growing chain radicals. A sequence of reactions involving attack on the nitro function was sug- with the Office of Naval Research. ( 5 ) W. S. M. Grieve and D . H . H e y , J . Chcm. SOC.,1803 (1934). gested as a likely alternative to nuclear substitution. D. F. DeTar and H . J. Scheifele, Absfructs, Chicago Mecling of We have undertaken a study of the reaction of tri- A m(6). Chcm. Soc., September, 1950. phenylmethyl with nitrobenzene in benzene solu(7) G. S Hammond, J. T Rudesill and F J Modic, THISTOURNAL, tion and find that this radical and others which may manuscript submitted. be formed in the course of the reaction react only by CHEMICAL LABORATORY abstracting oxygen from the nitro function. IOWA STATE COI,I.BC;E GEORGE S. HAMMOND ABRAHAM RAVVE When one mole equivalent of nitrobenzene is AMES, IOWA RECEIVED MARCH11,1951 added to a benzene solution of triphenylmethyl, the solution immediately develops a red color. If such a solution is allowed to stand exposed to dif- RADIATION CHEMISTRY OF FERROUS SULFATE fuse daylight for 24 hours, nearly a quantitative SOLUTIONS yield of triphenylcarbinol precipitates. The su- Sir: pernatant liquid is fractionated by adsorption on a Emphasis has been placed recently on R, the a 5 : 1 Magnesol-Celite mixture followed by elution yield ratio, Fe$$+/Fe;:+, obtained by X-ray or with mixtures of Skellysolve B, benzene and acetone or ethanol. Products isolated and characterized y-ray irradiation of dilute aqueous solutions of ferare unreacted nitrobenzene, azobenzene, azoxyben- rous sulfate in the presence and absence of air.lo2 zene, nitrosobenzene, biphenyl and p-terphenyl. These values vary from 2.55 to 4.0, as is shown in The nitrogen balance is quantitative but oxygen Table I.132J*4 The present communication demonand hydrogen have not been entirely accounted for. strates that theoretical values less than 4.0 are posPhenol is detected as its tribromo derivative in alka- sible on the basis of the accepted ferrous sulfate line extracts of the original solutions. When the oxidation mechanism. According to present concepts reaction (1) occurs reaction is carried out in the dark a slower reaction produces a quantitative yield of ditriphenylmethyl on the passage of ionizing particles through water. peroxide and the same nitrobenzene reduction Reaction ( 2 ) also proceeds through free radical inproducts. There is no evidence for attack on termediates and occurs where the rate of energy loss solvent in the dark reaction. Nitrosobenzene, is high and results from pairwise recombination of which is found only in small amounts, reacts rap- hydrogen atoms and hydroxyl radicals in zones of idly with triphenylmethyl, in separate experiments, high free radical concentration. The mechanism to produce azobenzene and a trace of azoxybenzene far ferrous sulfate oxidation is: (substantial amounts are produced from nitrobenH2O = H + OH (1) zene) along with triphenylcarbinol, biphenyl and €I20 = ‘/2H2 ‘/2H202 (2) terphenyl. Azoxybenzene does not react to any H + 0 2 = H01 (3) appreciable extent in 72 hours. Fe++ + OH = Fe++++ OH(4) It is not our intention to consider the mechanisms F e + + + H 0 2 = F e + + ++ €IOn(5) of these transformations in detail a t this time since Hot- + H + = H202 (6) further study is in progress. However, certain imFe + H202 = F e + + + + OH + OH- ( 7 ) portant conclusions are apparent. It is clear that I3 + H = Hz (8) a t least one radical, triphenylmethyl, is capable of In the absence of air the oxidation follows reac(1) W. A. Waters. “The Chemistry of Free Radicals,” Oxford Unitions (l),( 2 ) , (4), (7) and (8) and in the presence of versity Press, Oxford, 1946, p. 151.
+
(2) L. P. Hammett, “Physical Organic Chemistry,” McCraw-Hill C o . , New York, N. Y . , 1940, p. 383. (3) G. W. Wheland, “Advanced Organic Chemistry,” Jobn Wiley and Sons, Inc,, New York, N. Y . , 1949, p. 670. (4) G S. Hainrnond and P. D. Bartlett. J . Polymer Sci., in press.
(1) N. Miller, J . Chcm. Phys., 18, 79 (1950). (2) F. H. Krenz and H. A. Dewhurst, ibid., 11, 1337 (1949). (3) H.Fricke and S. Morse, Am. J . Roenf. a%d Rad, T h a . , 18, 430 (1927); H. Frickeand E. J. Hart, J . C k m . Phys., 8,60 (1986). (4) N. A. Shishacow, Phil. Mug., 14, 198 (1932).
