Dec. 5, 1964
DIHYDRAZYL.SYNTHESIS A X D MAGXETIC PROPERTIES
cal run is shown in Table IV. Since this run contained 81 points, only every fifth point is reproduced. The equilibrium constant was determined by adding a solution of hydrochloric acid in 80% aqueous acetone to weighed amounts of benzhydrol. The resistance of the acid solution was taken before and after the addition using equilibrium values in the 25.00' thermostat. The depression of the hydrochloric acid concentration was taken as the equilibrium concentration of benzhydryl chloride.
tivity cell of conventional design. Resistance measurements were taken at 1-2-min. intervals with an Electro-Measurements, Inc., impedance bridge, Model 250-Dh. A variable capacitor attached to the capacitance terminals of the bridge was used to maximize the sensitivity of the bridge. Infinity points were taken after a t least 10 half-lives. Rate constants were calculated for each point using the usual integrated first-order rate equation with hydrochloric acid concentrations derived from the resistance measurements and previously determined calibrations. A typi-
[CONTRIBUTION FROM THE CHEMISTRY
5173
DIVISIOX,ARGONNEXATIONAL LABORATORY, ARGOXNE,ILLINOIS]
Dihydrazyl. Synthesis and Magnetic Properties] BY JOACHIM HE ID BERG^
AND JOHN
A. WEIL
RECEIVED J U N E 1, 1964 Synthesis and characterization of the previously undescribed 1,3-bis(l,l-diphenylhydrazyl)-2,4,6-trinitrobenzene is described Removal of the two hydrazinic hydrogen atoms by oxidation with PbOs proceeds in two steps, leading first to an unstable radical very similar to DPPH (e.p.r., color) and then yielding the (very unstable) "dihydrazyl" molecule. The latter was shown, by e.p.r. and n.m.r. measurements below -30", t o be a diamagnetic, spin-paired species.
in benzene using a glass electrode as indicator and a Recently, a number of studies on the synthesis and calomel electrode as reference4; mol. wt. calcd. 578, magnetic properties of triplet molecules and biradicals have yielded detailed information about the electron found 567 and 592. Further evidence for the struccorrelation in these systems. Herein, an investigation ture of I was obtained by means of high-resolution proof the potentially paramagnetic molecule 1,3-bis(l>l- ton magnetic resonance studies in methylene chloride a t diphenylhydrazylene)-2,4,6-trinitrobenzene(111, dihy60 Mc./sec. employing a Varian -4-60 instrument. The drazyl) will be reported. weak peaks5 a t 314 and 240 c.,'sec. are attributed to the N H and picryl proton, respectively, and the strong doublet a t 113 and 108 c.!sec. to the phenyl protons. There is ample analogy for these assignments.6 Oxidation of I in methylene chloride or 2-methyltetrahydrofuran solution was effected by PbOs (well washed with acetone, then with the solvent to be used) freshly prepared by hydrolysis of P b ( C H 3 C 0 0 ) 4 in glacial acetic acid in the presence of CHC13.7 Since the oxidation products I1 and I11 were found to be unstable a t room temperature, all preparations and experiments with these were carried out a t temperatures below -30'. The oxidation was followed by recording the e.p.r. spectra of the radical produced. The clearly I11 resolved five-line spectrum of a deeply violet (mono) radical I1 appeared immediately; its intensity increased T h e previously undescribed substance 1,3-bis(1,l-dias the oxidation proceeded and then decreased markedly phenylhydrazyl)-2,4,6-trinitrobenzene (I), precursor to but could not be made to vanish entirely without irformation of the dihydrazyl, was prepared as follows. reversible decomposition. The g-value, nitrogen hyCondensation of pyridinium styphnate with phosgene in acetone a t 35' gave 1,3-dichlor0-2,4,6-trinitro- perfine-coupling constants ,-1 and .I I , and line-widths A measured in degassed 2-methyltetrahydrofuran solubenzene (IV) in 9Oy0yield, m.p. 129'. 1,l-Diphenyltion a t - 50' were found to be very similar for the radihydrazine (4.4 moles), m.p. 35', which had been purical I1 (g = 2.0035 + 0.0003,-4 = 8.5 f 0.3 oe. (oersted), fied immediately before the reaction, and IV (1 mole) -4'= 8.9+0.3oe., A = 5 . 5 0.1 oe.) and l,1-diphenylin boiling ethanol in 2 hr. yielded the dark red, crystal2-picrylhydrazyl ( D P P H ). 8 line dihydrazine I (yield 90%). Recrystallization from When the PbOs was removed by centrifugation from ethyl acetate and subsequent drying in vacuo a t 60' the oxidized solution and an excess of dihydrazine (I) afforded the pure product; I undergoes color changes was added, the intensity of the e.p.r. signal from I1 inwhen heated and melts with decomposition a t 164'. creased to more than twice the maximum intensity ob-4nal. Calcd.: C, 62.4; H, 4.0; N , 17,O. Found: served during the course of the oxidation, whereas the C , 62.5; H , 4.0; N , 16.6. Compound I contains two spectral pattern remained unchanged. acidic hydrogens and its molecular weight could be determined by potentiometric titration in pyridine with a (4) J , A. Weil and G. A Janusonis, J . Ore. Chem., 27, 1248 (1962). ( 5 ) Spectrum taken a t -60'. Peak positions are relative t o t h e CH2C11 0.1 -11 solution of triethyl-n-butylamrnonium hydroxide
*
(1) Based on work performed under the auspices of t h e U. S . Atomic Energy Commission. (2) Please address reprint requests t o J . A. Weil. J. Heidberg on leave of absence f r o m I n s t i t u t f u r Physikalische Chemie, F r a n k f u r t a m Main. (3) H. B. Hass, H. Feuer, and A. A. H a r b a n , J . A m . Chem. Soc., 71, 2282 (1950).
peak. Conversion t o t h e iscale can be made using T (CHsC12) = 1 67 (6) J . Heidberg, J. A. Weil, G . A. Janusonis, a n d J. K . Anderson, J Chem. Phys , 41, 1033 (1964). ( 7 ) W. K . Wilmarth and N. Schwartz, J . A m . Chem. SOL., 77, 4.543 (19.55J . (8) 14.hl. C h e n , K. V. Sane, R.I. Walter, and J . A. Weil, J . Phys Chem., 66, 713 (1961).
5174
JOACHIM
HEIDBERG AND
JOHN
A. WEIL
VOl. 86
Although the hydrazyl hydrogen atom is known to Two resonance lines were observed from the protons of be labile, presence of excess diphenylpicrylhydrazine in CHzClz in the two solutions because of the difference in D P P H solutions does not affect the e.p.r.spectrum, inditheir volume susceptibilities, the broader line from the cating t h a t the rate of the proton transfer from hydraparamagnetic solution lying a t higher field. The frezine to hydrazyl is small compared to the hyperfine quency separation AV of the two lines is given by AV splitting. The great similarity of the e.p.r. spectra = ( 2 ~ / 3 ) v A x . The observed A V corresponded quan( e . g . , line-widths) of D P P H and radical I1 suggests titatively ( * 2 ( 1 7 ~ )to the concentration of 11, as measthat, in the latter case, the effects of intramolecular ured by e.p.r. Addition of 1,l-diphenyl-2-picrylhydrahydrogen transfer are also not appreciable. zine to the dihydrazyl solution caused an upfield shift of the broad line and an increase of A V by the same factor Even after prolonged oxidation no e.p.r. signal at(2 to 3 corresponding to 1-4 c./sec. a t v = 60 Mc.;sec.) tributable to biradical I11 was observed and there was as for the increase of the intensity of the e.p.r. signal no absorption in rigid 2-methyltetrahydrofuran solution under the same conditions. Also the magnitude, 8 . 3 (2 X 1 0 - 3 M ) a t -170' other than one a t g = 2, X I O F , of the mass susceptibility of D P P H derived which was assigned to the monoradical I1 However, from these measurements was in agreement with literait was possible to show t h a t the oxidation had effected ture values.8 If dihydrazyl were a diradical with two the removal of the hydrogen atom of the second hyindependent unpaired spins, there should have been no drazyl group to yield a mesomeric or tautomeric form of change in AV on addition of the hydrazine; if it were a 111. a'hen a standardized solution of I was fully ground-state triplet molecule, AV should have become oxidized and treated with an excess of l,l-diphenyl-2smaller. picrylhydrazine after removal of the PbOs by centriAssociation of dihydrazyl molecules cannot be ruled fugation, the small five-line e.p.r. signal a t g = 2 imout but appears improbable for structure 111, since mediately increased to an intensity corresponding to D P P H does not dimerize. T h e only known reaction of 1.5 to 2 moles of D P P H per mole of I, as revealed by D P P H with radicals is their addition to the para carcomparison of its e.p.r. spectrum with that of a standbon atom of the phenyl ring with formation of the corardized D P P H solution in the same solvent (CH,Cl,, responding hydrazine.1° A single linking in this manCHC13, 2-methyltetrahydrofuran). Moreover, it could ner of two dihydrazyl molecules followed by re-oxidabe confirmed t h a t the nuclear framework of dihydrazyl tion would lead to a paramagnetic species with two or was not fragmented during oxidation, since its reductive four unpaired electrons, contrary to observation. titration with hydroquinone caused first an increase by The two zwitterion structures of type I I I a , as well as a factor 2-3 of the intensity of the e.p.r. signal of the always present monoradical, then a decrease, and finally 0(-) the disappearance of the spectrum, demonstrating t h a t (+) the first reduction product of I11 is the monoradical 11, n / h ' y y N 0 2 which is further reduced to the diamagnetic dihydra' \ zine I. I n accord with the nonobservability of an e.p.r. CeHs spectrum attributable to 111, the ground state of I11 IIIa proved to be diamagnetic. Since the application of IIIb conventional methods to measure the static susceptibility x of I11 in diluted solution [c(saturation) 5 quinoid ionic structures invoking charge withdrawal 10-2 M ] in the presence of the paramagnetic monoby the nitro groups (similar to those used to describe radical I1 appeared to be difficult, proton magnetic the salts of 1,l-diphenyl-2-pi~rylhydrazine~), may be resonance was employed for the determination of x . ~ important in describing the singlet ground state of A capillary, 0.d. -2.5 mm., containing a solution of 1 , l monomeric dihydrazyl. T h e latter may also be stabilidiphenyl-2-picrylhydrazine in CH& was placed into zed by the formation of a dihydrofurazan ring," as in the standard n.m.r. sample tube which was filled with a structure IIIb. methylene chloride solution of about the same concen(10) S. Goldschmidt and K . R e n n , Be?., 88, 628 (1922); J . A . TXTeil, K . Y , Sane, and J. M. Kinkade, J r . , J . P h y r . Chem., 66, 710 (l!361). tration of dihydrazyl, accompanied as usual by 11.
7'
(9) D F Evans, J Chem S o c , 1959. 2003.
(11) P. K a r r e r , "Organic Chemistry," 1st E d . , Elsevier Press, S e w Y o r k , N. Y . , 1938, p. 731.
