Eiben, K.

Guenther, K.

Louys, F.

Suarez, C.

English

KITopen

Februar 1970Institut für StrahlenchemieOH-Radical Induced Denitration of NitrophenolsG. Suarez, F. Louys, K. GÜnther,K. EibenKFK 1187M. 5. H.Tetrahedron Letters No.8, pp. 575-578, 1970. Pergamon Presso Printed in Great Britain.OH~Radical Induced Denitration of NitrophenolsC. Suarez 1), F. LoUYS2), K. Günther and K. EibenInstitut für Strahlenchemie, Kernforschungszentrum Karlsruhe, Germany(Received in UK 30 December 1969; accepted for pub1ication 16 January 1970)We wish to report that OH-radicals eliminate nitrous acid from 4-Nitrophenol to yield 1,4-Benzo-semi qui none as an intermediate , whi ch subsequently di sproportionates into 1,4-Hydrobenzoquinoneand 1,4-Benzoquione (1).OH6 °OB9 + OH ~ ----+ 1/2 0 + 1/2 0 (1)-HN02 "N02 ° 0 OBExperimental evi dence for reacti on (1) has been obtained from the ESR-detection of s emi qui noneradicals, as weIl as the analytical determination of Nitrite and 1,4-Benzoquinone.ESR measurementsTh . . . +) d . d . 3) .e l.nsltu ESR techmque was .employed as e sc r i be earller . A N20 saturated aque ous s o.Lut.ionof 3-Nitrophenol (2Xlo-4 molar) was investigated in the pH 'range 5 - 12. Radiation produceshydrated electrons, which in this solution are all converted into hydroxyl radicals (2)4,5) ..'ee aq + + OH(2)OHHelQ< .,pK = 4.0We observed a 1:4:6:4:1 ESR-quintet with hf-splitting of 2.35 Gauss and g = 2.0044. This radi-cal was unambigously identified as the radical anion of the 1,4-Benzosemiquinone (3)6).0-o (3)oWe obtained the same radical signal when 4-Nitrophenol reacted with OB-radicals, produced bymixing an aqueous solution of Ti 3+ (5~10-3 molar and complexed with EDTA7)) in the pB range6 - 9 with aqueous H202 (10-1 molar, containing 0.14% 4-Nitrophenol). Using 2-Nitrophenol inthe Ti/H202-system we obtained the ESR-spectrum of the 1,2-Benzosemiquinone radical, which ischaracterized by two triplets of a415= 3.6 and a3J6".,,,JI.-I0.76 Gauss6).576 NO o 8The irradiation of N2- or Ar-saturated 4-Nitrophenol solution yields a new ESR-spectrum whichis superimposed on, and approximately twice as intense as, the radical signal of the 1,4-Benzo-semi~uinone. The additional ESR-signal was identified as the anion radical of the 4-Nitrophe-no1 8), which is generated by the reaction of hydrated electrons with 4-Nitrophenol (4).N02Analytical and G""Value detern:drtatiönsOllQ e+ e aq (4)N20-or N2-saturated solutions of 4-Nitrophenol (2xl0-4 - 2xlo-2 molar) were irradiated in aCo-60-Gamma source with doses up to 5Xlü17 eV/ml. Nitrous acid was determined photometrically. "9) ("t"" " 9) Tusa ng the method of' Gr i es a-Tl.ovay . The test of' Nl rate w~th Br-ue i ne was negat i ve . he totalyield of Quinone - after aerial oxidation of the Hydroquinone in the irradiated solution - wasdetermined with 2,4-DinitroPhenylhydrazine10). The resulting blue coloured indophenone derivatewas measured photometrically.Corrections were applied to the Quinone yield because of the presence of 4-Aminophenol, a re-duced product in irradiated 4-Nitrophenol solutions4,5). 4-Nitropyrocatechol, the product ofhydroxylation of 4-Nitropheno14 ,5) , was determined in a'Lka.Li ne soluti ons, where a strong ab-sorption at 512 nm is obtained. The observed G-values are presented in table 1.Table 1 Yields of products of the OH induced denitration and hydroxylation of aqueous4-Nitrophenol (Dose: 5xlo17 eV/ml)pH Gas conc , (mol/l) GHNO2 Gl,4-Benzoquinone G4-Nitropyrocatechol5 N2-40.30 0.33 1.885xlo5 N:2 2xlo-20.39 2.42" N20-4 0.66 0.65 3.84.- 5xlo8 N2-4 0.68 0.70 1.505xlo8 N2-20·77 1.942xlo8 N205xlo-4 1.32 1.42 2.98No.8 577The yields of nitrous acid and 1,4-Benzoquinone are equal, within experimental error, demon-strating the validity of equation (1). The yields are doubled when N20 is used as electronscavenger (2) proving that OR radicals are the precursors of the reaction. In addition the re-sults show a remarkable dependence on the pR. At pR 5 the OH-induceddenitration amounts to14% while 86% of the OR radicals react to form 4-Nitropyrocatechol (5)4,5).+ OR - (5)In alkaline solution (pR 8) the yield öf denitration is more than doubled (31%) while thehydroxylated product decreases by the same amount. This pH-effect may be related to the acid-base equilibrium of 4-Ni trophenol (6) .°OS OH °6 0(&Q,IH0« ,. ---- (6)... --pK = 7.15" ,ISN02 N02 N02 N02HThe electronic structure of the 4-Nitrophenolate differs from the neutral molecule in so far asthe assumed electrophilic attack of the OR radical occurs with equal probability at the orthoand para positions of the molecula. In acid solutions OR-addition at the~ position of thering seems to be prefered.Evidence for OR-induced denitration has been obtained for NitrobenzeneIl) . We observed denitra-tion of Nitrobenzaldehydes and Nitrobenzoicacids. Thus this type of reaction seems to be ofgeneral importance duri ng the hydroxylati on of aromati c ni trocompounds.AcknowledgementsThe ESR measurements in part were made during a visiting fellowship of K.E. at the Mellon Insti-tute, Carnegie-Mellon-University in Pittsburgh, USA. We are grateful for the generous help ofProf. Dr. R.W. Fessenden and the technical assistence of A.E. Ulicny and R. Coleman.578Literature1) On leave from Junta de Energia Nuclear, Madrid, Spain2) Summer student of the Staatliche Ingenieurschule, Aalen, Germany3) K. Eiben and R.W. Fessenden, J. phys. Chem. 72,3387 (1968)4) D. Grässlin, F. Merger, D. Schulte-Frohlinde and O. Volkert, Z. physik. Chem. N.F.~, 84 (1966)5) O. Volkert, G. Termens and D. Schulte-Frohlinde, Z. physik. Chem. N.F., 56, 262 (1967)6) G. Vincow and G.K. Fraenkel, J. Chem: 'Phys., 34, 1333 (1961)7) S. Fujwara, K. Nagashima and M. Codel1, Bull. Chem. Söc. Japan, 37, 773 (1964)8) H. Piette, P. Ludwig and R.N. Adams, J. Aller. ehem. Soc., 84, 4212 (1962)9) D.F. Boltz, Ed. Cö10rmetric Determination of Non~etals, Interscience PublishersInc. New York 195810) D.P. Johnson and F.E. Critchfield, J. Anal. Chem., 33, 910 (1962)11) J.H. Fendler and G.L. Gasowski, J. Organic Chem., 33, 1865 (1968)

OH-Radical Induced Denitration of Nitrophenols

https://publikationen.bibliothek.kit.edu/270003433/3810285

OH-Radical Induced Denitration of Nitrophenols

Abstract

Similar works

Full text

Available Versions

KITopen