butanone, dipentyl ether, or isoamyl alcohol (sensitivity decreases from 0.0085 to 0.12 pg cm-2 through the series) (28); 3-mercapto-5-hydroxy-1,2,4-triazine in aqueous solution with sensitivity = 0.0129 pg cm-2 (29). The present method is intermediate in the sensitivity range, 0.011 pg cm-2 ( c = 1.73 x lo4). The procedure is (28) J. H.Wiersma and P. F. Lott, Anal. Chem., 39,674 (1967). (29) C. Lazar, G. Popa. and C . Cristescu, Anal. Chim. Acta, 47, 166 (1969).
simple; it does not require rigid control of pH, heating, or any reducing agents. The color development is moderately rapid, and absorbance is stable for several hours. In common with other methods for osmium, this method is subject to interference from several elements which, if present, would require the separation of osmium by the usual distillation procedure. Received for review October 4, 1973. Accepted December 7. 1973.
Secondary Photolysis Products David M. Hercules and Steven A. Carlson Department of Chemistry. University of Georgia, Athens, Ga. 30602
Prolonged photolysis of 9,10-anthraquinone in ethanol produces a variety of blue fluorescing species. These are derived from the photolysis of oxanthrone, a tautomeric form of 9,lO-dihydroxyanthracene. These products include 9-anthranol, anthrone, 9-anthanol photodimer, anthrapinacol, and a "362 intermediate," tentatively identified as 7,16-dihydrodibenzo[a,o]perylene. Phototautomerization of anthrone to 9-anthranol also occurs. Other products are produced from photochemical and thermal reactions which include 9,lO-dihydroanthracene and anthracene. A variety of pathways involving several of the observed species, and 9-anthranol have been observed and are discussed. Absorption and fluorescence spectra are compared for 9-anthrol and bi-9-anthrol anions. The former fluoresces strongly, the latter very weakly.
The photochemical conversion of anthraquinone (AQ) to 9,10-dihydroxyanthracene (9,lO-DHA) is well known. Under continued photolysis 9,lO-DHA is photolyzed to produce a variety of blue fluorescing products. This phenomenon has been referred to as photoinduced luminescence ( I ) . Gorsuch e t al. (a),attempted to identify the blue fluorescing species, particularly to determine whether or not the sequence of photoproducts paralleled that of the products formed in the chemical reduction of anthraquinone. Recently we have studied ( 3 ) the photoinduced luminescence of 9,lO-anthraquinone in greater detail and have identified some of the products. We also observed that blue fluorescing species arose from primary photolysis of 9,lO-dihydroxyanthraceneas well as from secondary reactions. The primary photolysis was the topic of the earlier paper ( 3 ) . The present paper is concerned with the secondary photolysis products giving rise to blue fluorescence. Even when all of the 9,lO-DHA has disappeared during prolonged photoreduction of AQ, a compound which fluoresces blue continues to be formed ( 3 ) . The structured ( 1 ) D. M. Hercules and J. J. Surash, Spectrochirn. Acta. 19, 788 (1963). (2) J. D. Gorsuch, J. P. Paris, and D. M. Hercules, 144th National Meeting. American Chemical Society, Los Angeles. Calif.. April 1963. (3) S. A. Carlson and D.M. Hercules, Ana/. Chern., 45, 1794 (1973).
674
A N A L Y T I C A L C H E M I S T R Y . VOL. 46, NO. 6, M A Y 1974
fluorescence and photostability of this compound make it observable long after the other blue-fluorescing products have been photolyzed. It was of interest to' determine where this photoproduct (to be called the 362 intermediate in reference to its 0-0 band of fluorescence) fits into the sequence of AQ photoreduction. Two approaches were taken to find the precursor to the 362 intermediate. First, compounds known or thought to be products of 9,lO-DHA photolysis were photolyzed to see if they produced any of the 362 intermediate. Second, 9,9',10,10'-tetrahydrobianthryl (THB) derivatives were examined. One of the derivatives (R. = OH, R' = H) is
g
THB
R, R' = H
or
OH
derivatives
known ( 4 ) to be formed by photoreduction of anthrone indicating that THB derivatives are possibly produced by AQ photolysis. Since this type of compound does not absorb at wavelengths greater than 300 nm, it could contribute to the higher yield of blue-fluorescing photoproducts with 253.7 nm irradiation ( 3 ) .
EXPERIMENTAL C h e m i c a l s . Anthrone ( E a s t m a n Organic) was recrystallized three t i m e s f r o m benzene: p e t r o l e u m ether (bp 40-60 "C), mp 154-155 "C lit ( 5 ) . 154 " C ; UV (cyclohexane) l o g t 260(4.29),
ZgZ(3.58)304(3.60),348(1.81),363(1.76),379(1.51). 9, IO-Diphen).lphenanthrene was p r e p a r e d f r o m t e t r a p h e n y l e t h ylene ( E a s t m a n Organic) b y t h e m e t h o d of Sargent a n d T i m m o n s (6). 9,9', 10,I O ' - T e t r a h y d r o b i a n t h ~(THB) ~ was synthesized accordi n g t o t h e procedure of W i n k l e r a n d W i n k l e r (7)in 62% yield, mp N. Kanamaru and S. Nagakura, J . Amer. Chern. Soc.. 90, 6905 (1968). "Encyclopedia of Organic Chemistry," E. Josephy and F. Radt. Ed., Vol. 13, Series I l l , Elsevier, New York, N . Y . , 1946. M . V . Sargent and C. J. Timrnons, J. Chern. SOC. Suppl.. 1, 5544 (1964). H.J. S. Winkler and H. Winkler, J. Org. Chem.. 32, 1695 (1967).
251 "C (dec.) lit. (8) 255 "C; UV(ethano1) log t 266(3.42), 273(3.41) ; IR(KBr) 3055(w), 3010(m), 29oO(w), 2865(w), 2815(w), 1575(w), 1476(s), 1452(s), 1419(s), 774(vs), 757(s), 738(s), 724cm-'(vs). T H B was also prepared by adding 0.4 gram of LiAlH4 in 40 ml of ether to a solution of 0.70 gram of 10,10'-bianthronyl in 100 ml of benzene. The mixture was refluxed for 2.5 hours with continuous stirring in a Nz atmosphere. The product was isolated by acidification with a dilute HC1:ice mixture, extraction with ether, evaporation to dryness, and crystallization from benzene. This yielded 0.35 gram of fine, colorless needles, m p 248-249 "C. Its UV and IR spectra matched that of the compound prepared by the method of Winkler and Winkler. 10,10'-Dih~droxy-9,9',lO,IO'-tetrah~drobianthryl (2) was prepared by adding 0.22 gram of LiA1H4 in 75 ml of ether to 0.863 gram of 10,lO'-bianthronyl in 300 ml of 1:l ether:benzene. The reaction mixture was kept under a Nz atmosphere and at 10 "C. After stirring for 1 hour, ethanol, water, and dilute acid were added in succession. Collection of the organic layer, evaporation, and crystallization from benene yielded 0.44 gram (51%) of 2, m p 184-187 "C (dec.) lit. ( 9 ) 193 "C; UV(ethano1) log t 264(3.18), 272(:3.11) ; IR(KBr) 3160(vs), 3060(w), 3020(w), 2920(w), 2865(m), 1602(w). l573(w), 1472(s), 1450(s), 1044(vs), 765(s), 721(s); NMR(DMS0) multiplet (16H) 6 6.60-7.78, doublet (2H) ( J = 10 cps) 6 5.79, singlet (2H) 6 4.41, doublet (2H) ( J = 10 cps) 6 3.82; NMR(DMS0:trace of Dz0) spectrum identical .to that in DMSO except that the doublet at 6 5.79 disappeared and the doublet a t 6 3.82 became a singlet. 9, IO-Dihydrodroanthracene (Eastman Organic) was recrystallized four times from ethanol. Anthracene (Pilot Corp., scintillation grade) was used without further purification. lO,IO'-Bianthron.vl was prepared according to the method of Dimroth (10) and recrystallized three times from benzene before use; UV(ethano1) log t 266 (4.41), 305 shoulder (3.86), 350(2.48), 366(2.19), 383(1.61). 9-Anthrol was formed by dissolving anthrone in ethanol. Adding 10-3M NaOH gave the 9-anthrol anion. Bi-9-anthrol was prepared according to Schonberg and Ismail ( Z l ) , yield 6670, m p 222-225 "C (dec) lit. ( 1 1 ) ca. 230 "C (dec); UV(ethano1) log c 371 (4.021, 402(4.14), 421(4.07); IR(KBr) 3430(vs. broad) 3060(w), 3020(w), 1615(m), 1075(s). The bi-9-anthrol dianion was prepared by adding lO-3M NaOH to a solution of bi-9-anthrol or 10,lO'-bianthronyl in ethanol. The bi-9-anthrol monoanion could not be prepared by adding lesser amounts of base to hi-9-anthrol or 10,lO-bianthronyl in ethanol. Instrumentation a n d Procedures. Instrumentation and procedures were the same as those reported earlier (3).
X(nrn)
Figure 1. Fluorescence and excitation spectra of the 362 intermediate and 9,10-diphenylphenanthrene in ethanol 362 Intermediate, ---;
9,lO-diphenylphenanthrene.
------
tolysis, the only blue-fluorescing compound produced by photolyzing anthrone was in the 362 intermediate. It was found for photolyses in both ethanol and cyclohexane. but the yield was about a factor of 10 greater than ethanol. Figure 1 shows the fluorescence and excitation spectra of the 362 intermediate compared to those of 9,lO-diphenylphenanthrene. The close agreement between these two compounds supports 1 as a tentative structure for the 362
fFWY-7 A
RESULTS When anthrone is dissolved in ethanol, absorption peaks due to tautomerization to 9-anthrol were immediately observed along with the blue fluorescence (A, 454 nm) of 9-anthrol. The equilibrium ratio of tautomers was 92% anthrone and 8% 9-ant,hrol. Conversely, a solution of anthrone in cyclohexane was unchanged after sitting in the dark for a week. A deoxygenated 10--2Msolution of anthrone in ethanol was photolyzed a t 300 nm until the yellow color of 9-anthrol had almost completely disappeared. Evaporation to dryness and crystallization from benzene gave a white compound, mp 166-167 "C (dec). The IR of this photoproduct was similar to that of anthrapinacol (AP); but several peaks not seen in A P were present. The UV of the photoproduct had the same peaks as in AP, but absorption extended to longer wavelengths than in AP. The absorption and fluorescence changes for anthrone in ethanol and hexane upon 300-nm irradiation were followed as function of time. For photolysis in ethanol, the absorption due to 9-anthrol a t no time exceeded its initial value; whereas, in hexane, there was no 9-anthrol absorption initially, but it appeared upon photolysis. Other than 9-anthrol, which disappeared after a few minutes of pho(8) J. W. Cook, J. Chem. SOC.,London, 1926, 1677. (9) F. Bell and D. H . Waring, J. Chem. Soc.. London. 1949, 267. (10) 0. Dimroth, Ber.. 34, 219 (1901). (11) A . Schonberg and A . Isrnail. J. Chern. Soc.. London, 1944, 307.
1
intermediate. Assuming identical molar absorptivities (12,500) for 9,10-diphenylphenanthrene and the 362 intermediate a t their 300-nm peak, the photolysis of anthrone in ethanol gives ea. 7% 1. To check the effect of irradiating wavelength on the yield of the 362 intermediate, a lO-4M solution of anthrone in ethanol was photolyzed at wavelengths longer than 290 nm (Pyrex reaction vessel) until the fluorescence due to the 362 intermediate had reached a steady-state. Transferring the solution in a N2-filled glove bag to a quartz cell and irradiating at 253.7 nm produced a 50% increase of the 362 intermediate fluorescence. Isolation of the 362 intermediate was not achieved by column chromatography. Elution with ethyl acetate gave fractions containing the 362 structured fluorescence, but the yield was small and contaminated with yellow material. Sublimation was not practical since the temperatures required (110 "C) also caused the thermal decomposition and sublimation of other photoproducts. The thermal decomposition of 9,9', lO,lO'-tetrahydrobianthryl (THB) in a degassed sealed tube held a t 250 "C in an oil bath gave 50% yields of 9,lO-dihydroanthracene and anthracene (from UV and fluorescence analysis). When 8 x 10-5M T H B is deoxygenated ethanol was photolyzed a t 253.7 nm, equal amounts (ea. 10% yield) of 9,lO-dihydroanthracene and anthracene were formed along with comA N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 6, M A Y 1974
675
/ ’-\
/
\I
/
Lz
‘
/ \
350
400
450
500
550
X(nm)
Absorption of fluorescence spectra of 9-anthrol anion and bi-9-anthrol dianion 9-Anthrol anion, absorption, : fluorescence, -.-.-.-. Bi-9-anFigure 2.
thranol dianion, absorption, - - - - - - -
pounds having fluorescence peaks a t 326, 350, and 366 nm . Similar studies on anthrapinacol (AP) and 10,lO’-dihydroxy-9,9,10,10’-tetrahydrobianthryl(2) showed that they thermally decomposed a t their melting points. AP thermal decomposition gave anthrone, 9-anthrol, and anthracene; 2 thermal decomposition gave anthracene, anthrone, and possible other products. The photolysis of AP in ethanol a t 253.7 nm gave fluorescence peaks attributable to 9-anthrol, a small amount of anthracene, and the 362 intermediate. The same fluorescence peaks, with a larger amount of anthracene present, were found in the photolysis of 2 a t 253.7 nm. The photolysis of 6 x IO-SM 10,lO’-bianthronyl in deoxygenated ethanol a t 350 nm gave a high initial yield of 9-anthrol and anthrone from UV and fluorescence measurements. Continued photolysis produced the 362 intermediate. Both anthrone and 10,lO‘-bianthronyl had phosphorescence spectra in EPA a t 77 OK. similar to oxanthrone (3). Phosphorescence decay measurements gave values of T~ for anthrone and 10,lO’-bianthronyl of 1.5 and 0.9 msec, respectively. 9-Anthrol and bi-9-anthrol would be expected to have similar spectral properties since the anthracene rings in a bianthryl derivative are a t right angles (12). Their anionic forms should also give similar spectra. Both 9-anthrol and bi-9-anthrol are possible photoproducts in 9,lO-anthraquinone (AQ) photoreduction; their anions could be formed in alkaline AQ photoreduction. As part of our study of the photoinduced luminescence in the AQ system, it was necessary to distinguish between them. 9-Anthrol and bi-9-anthrol are best differentiated by their fluorescence spectra since their absorption spectra are very similar. 9-Anthrol in ethanol showed a strong fluorescence with a maximum a t 454 nm. On the other hand, bi-9-anthrol is weakly fluorescent (q5f < 0.005) with a maximum near 475 nm. The shift to longer wavelengths in bi-9-anthrol is due to the “methyl-substitution’’ effect of each anthracene system on the other. The low intensity of fluorescence in bi-9-anthrol can be attributed to the nonrigidity of the molecule with its ability to rotate around the 9,9‘-bond. By comparison, 9-anthrol is a rigid and planar molecule. Figure 2 shows the absorption and fluorescence spectra of the anions of 9-anthrol (AO-) and bi-9-anthrol (biAO-). I t can be seen that the anions can be differentiated (12) H Weiler-Feilchenfeld. E D Bergmann, and A Hirschfeld, Tetrahedron Lett, 1965, 4129
676
ANALYTICAL CHEMISTRY, VOL. 46, NO. 6, M A Y 1974
either by UV or fluorescence. The absorption peak positions are different in the two anions, and the intensity ratios of the anthracene-like transition (ca.380 nm) and the broad charge-transfer band (ca. 450 nm) are also different. As in the undissociated forms, AO- fluoresces strongly and bi-AO- showed little or no fluorescence. Using these spectral criteria, no evidence was found for the presence of lO,lO’,bianthronyl or bi-9-anthrol in the AQ photoreduction. Bi-9-anthrol was also eliminated on the basis of its photochemistry. Photolysis in ethanol with 350 nm radiation proceeded slowly (& < 0.01) to give a compound with strong absorption around 300 and 380 nm 478 nm). and a fluorescence of medium intensity (A, The spectral properties are compatible with the following change,
*-* ?H
OH
0
but the major point is that no products characteristic of AQ photoreduction are formed.
DISCUSSION In contrast to the slow tautomerization of oxanthrone and 9,lO-DHA ( 3 ) ,anthrone and 9-anthrol in ethanol approach equilibrium within the time it takes to prepare a solution and measure its absorption. In hydrocarbon solvents, there is no ground-state tautomerization. Baba and Takemura (13) have studied the keto-enol tautomerization of anthrone and 9-anthrol. The presence of the enol form in alcoholic solvents was explained as due to hydrogen bonding between 9-anthrol and the solvent. The photochemistry of anthrone in ethyl ether has been examined by Kanamaru and Nagakura ( 4 ) . The two main photoproducts were found to be anthrapinacol (AP) and the photodimer of 9-anthrol. By comparing their IR and UV data with those from this study, the photoproduct from the 10-2M anthrone in ethanol photolysis is seen to be composed of approximately equal amounts of AP and 9-anthrol photodimer. Kanamaru and Nagakura also observed the phototautomerization of anthrone to 9-anthrol in ethyl ether. The slow tautomerization rate in ether enables the 9-anthrol formed by photolysis to be observed. A similar result was obtained in this study for anthrone in hexane. For anthrone in ethanol, the lack of increased 9-anthrol absorption upon photolysis can be attributed to the fast tautomerization rate in this solvent. Thus, the concentration of 9-anthrol a t any time approaches a constant fraction (ca. 8%) of the anthrone concentration, which is a t its maximum before photolysis is begun. Since both anthrone and 9-anthrol are produced during the extended photolysis of AQ in ethanol, their respective major photoproducts, AP and 9-anthrol photodimer, would be expected. Besides the two main products, Kanamaru and Nagakura ( 4 ) also observed a small amount (
