function of Ni concentration using the analytical curve data from Figure 8b. In Figure 11, the intensity of the Co(1) 3453.5-8, line is plotted as a function of Pd concentration using the analytical curve data from Figure 9b. Here the Co line intensity decreases with increasing Pd concentration for Pd concentrations greater than about 0.5 pg. This suggests incomplete sample vaporization a t high Pd concentrations. The failure of line ratioing to completely linearize the Pd analytical curve (Figure 9b) further suggests that some thermal vapor fractionation occurred during sampling. This indicates that the convective heat-transfer model for shock-wave sampling suggested by Nicholls et al. (25) may be more important than the ablative or meteoric model (26)under the conditions reported here. Figure 12 shows the results of an independent study of the effect of Pd concentration on the intensity of Co, Ni,
and Zn neutral atom line radiation. In all systems, a nearly twofold decrease in intensity is observed with increasing P d concentration. Similar results were obtained using Alz(S04)3.18H20 as a matrix material. This substance decomposes to the very refractory A1203 a t 770 "C (27). These results suggest that matrix effects are very significant for refractory matrix materials, probably because the refractory matrix prevents complete sample' vaporization. More volatile matrix materials seem to be of less concern. In choosing an internal standard, matching bulk thermodynamic properties should not be necessary for relatively low boiling analytes, so long as the internal standard is present a t relatively low concentration. It may be possible to improve the linearity of the Pd analytical curve by using a more refractory internal standard material, thus reducing fractional vaporization. It is significant to note that linear analytical curves are obtained for Cd and Ni with no internal standard but only a t the price of a considerable loss in precision. While the excitation potentials for the analysis pairs reported here are fairly well matched, this should not be of prime importance in developing an analytical system because of the high degree of temperature control obtained with shock-tube excitation.
ACKNOWLEDGMENT The authors wish to thank Norman Johnston and Ernst Metzner for construction of much of the shock-tube hardware, Steven Rifkin for design of the gas handling system, and Richard Smiles (deceased) for the design and construction of the digital interface. Received for review July 30, 1973. Accepted December 6, 1973. This work was supported in part by the donors of the Petroleum Research Fund administered by the American Chemical Society.
(25) R . W. Nicholls, W . H. Parkinson, and H. Van der Lam, J. Appl. Phys., 30, 797 (1959).
Richards, "Aluminium.' 2nd ed , Henry Carey Balrd Co , Philadelphia, Pa , 1890
(27) J W
(26) R. N . Thomasand F. L. Whipple.Asfrophys.J., 114, 448 (1951).
New Spectrophotometric Reagent for the Determination of Osmium-2,3-Quinoxalinedithiol Harvey F. Janota and Sabrina B. Choy Department of Chemistry, California State University-Fullerton, Fullerton, Calif. 92634
Osmium(V1) reacts with excess 2,3-quinoxalinedithiol (QDT) in N, N'-dimethylformamide-water solutions acidified with hydrochloric acid to form a green complex with an absorption maximum at 560 nm. The color, which develops to maximum intensity within 1.5 hours, is stable for several hours. The system conforms to Beer's law. Optimum range for 1.00-cm optical path is 2 to 8 ppm of osmium, determined with a relative standard deviation of about 2%. The molar absorptivity at 560 nm is 1.73 X l o 4 , and sensitivity (for A = 0.001) is 0.011 gg cm-*. Platinum(lV), palladium(ll), nickel(ll), cobalt(ll), and copper(1I ) interfere so that separation is necessary. Reaction ratios of 1 to 2 and 1 to 4 for osmium to QDT have been deduced from spectrophotometric data. 670
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In the use of 2,3-quinoxalinedithiol (QDT) for the spectrophotometric determination of palladium ( I ) and platinum (2), the interference by osmium, which formed a colored product with the reagent, served as the basis for investigating the osmium-QDT complexes in detail.
EXPERIMENTAL Apparatus. Absorbance measurements were made using a Cary Model 15 spectrophotometer in 1.00-cm optical path Pyrex cells. A Lauda-Thermostat Type WB 20 D was used to maintain temperatures within *1 " C for temperature effect studies. Measurements of pH were made with a Leeds and Northrup No. 7401 (1) G. ti. Ayres and ti. F. Janota, Anal. Chern., 31, 1985 (1959). (2) G. H . Ayres and R . W. McCrory, Anal. Chern., 36,133 (1964)
pH meter, using a glass-calomel electrode pair, and all analytical weighings were done on a Mettler Type H-15 balance. Reagents. QDT (Eastman No. 7317) was used to prepare fresh 0.2% (wjv) solutions in N,N'-dimethylformamide which were stored in nonactinic bottles protected from light and which were used in the standard procedure. A stock osmium solution, prepared according to the method of Ayres and Wells ( 3 ) , was standardized iodometrically by the method of Klobbie ( 4 ) and found to contain 738.3 ppm of osmium. Standards of lower concentration were prepared by volumetric dilution of the stock solution. Because of the volatility of osmium tetroxide, all osmium solutions were tightly sealed and exposed to air as briefly as possible. Potassium hexachloroosmate(1V) from A . D. Mackay, Inc. and N,N'-dimethylformamide (DMF) from Matheson, Coleman and Bell Manufacturing Chemists were used as received. Other reagents were ACS reagent grade. The cations in interference tests were used in the form of chlorides or nitrates, and the anions were added as sodium salts. Recommended Procedure. Into a 25-ml volumetric flask, transfer 10.0 ml of DMF and 1.0 ml of 1M hydrochloric acid. Mix and cool to room temperature. Then add 2.0 ml of 0.2% (w/v) QDT in DMF. Add 4.0 ml of the aqueous osmium solution, mix, and after cooling to room temperature, dilute to volume with DMF. Measure the absorbance after 1.5 hours, against a blank prepared similarly, at 560 nm.
RESULTS Spectral Characteristics. Figure 1 shows the visible absorption spectra of the QDT reagent (curve A ) , of the Os-QDT complex solution containing 8.00 ppm of osmium developed by the recommended procedure which contains dxcess QDT (curve B ) , and of the Os-QDT complex solution containing 8.00 ppm of osmium when the osmium is in excess (curve C). The Os-QDT complex formed in the recommended procedure has absorption peaks at 560 and 470 nm. Since the reagent has very strong absorption peaks from about 425 t o 350 n m which are in evidence at 470 nm, all subsequent measurements were made using the absorption peak a t the longer wavelength, where the QDT has negligible absorption. Solvent System. Burke and Yoe ( 5 ) , in a simultaneous determination of cobalt and nickel with QDT, have successfully used ethanol as a solvent. Ethanol has the advantages of being less expensive as well as less toxic than D M F which has been used commonly in other spectrophotometric methods involving QDT ( I , 2, 6, 7). Attempts to carry out the reaction in a n aqueous ethanol solution were unsuccessful. In one attempt, a 0.1% (w/v) QDT solution in D M F was used while all dilutions were made with ethanol. In another attempt dilutions were made with a 1:l DMF-ethanol solution. Both attempts resulted in precipitation of the complex. The use of D M F for dilutions so t h a t the water content did not exceed 20% (v/v) resulted in no turbidity formation for 78 hours and gave stable, reproducible absorbance values of the colored species a t 560 nm as the water content varied from 12 t o 20% (v/v). Subsequent studies of the osmium-QDT reaction were thus made in a 20% (v/v) aqueous-DMF solution. Effect of Amount of Hydrochloric Acid. Solutions containing 7.84 ppm of osmium were treated by the recommended procedure, except the amount of hydrochloric acid added varied from 0 t o 12.0 millimoles per 25 ml total volume. Full color development required a minimum of 0.25 millimole of hydrochloric acid. The absorbance and the wavelength of maximum absorption remained essentially constant from 0.25 to 4.0 millimoles of hydrochloric acid per 25 ml final volume. This corresponded to a p H range of 2.6 to 1.3. At 4.0 millimoles or above, a small decrease in absorbance at the absorption maximum (3) G .H . Ayres and W . N. Wells, Anal. C h e m . , 22, 317 (1950). (4) E. A . Klobbie. Chern. Zentr., 11, 65 (1898). (5) R. W . B u r k e and Y. H. Yoe, Anal. Chern., 34, 1378 (1962). (6)G. H. Ayres and H. F. Janota, Anal. Chem.. 36,138 (1964). (7) G. H. A y r e s and R. R . Annand. Ana/. Chem., 35, 33 (1963).
' 1
0'
1
550
WAVELENGTH
500 ~ r n
550
7W'
Figure 1. Spectral curves A. QDT, 4.1 X 10-5M.B . Osmium, 4.1 X' 10-5M,and excess QDT, 4.2 X 10-4M.C. QDT, 1.0 X 10-4M.and excess osmium, 4.1 X 1 O - w
wavelength and a shift of the absorption maximum from 560 n m t o 550 n m were observed. The acidity in the recommended procedure was therefore set a t 1.0 millimole of hydrochloric acid per 25 ml total volume. Stability of the Colored Species. The stability of the osmium complex was examined with freshly prepared QDT solution and with a QDT solution t h a t was 1 day old. Solutions containing 7.88 ppm of osmium were prepared according to the recommended procedure and the absorbances were measured a t 560 n m from 0.5 to 25.5 hours after the addition of the osmium to the QDT reagent. The color developed rapidly, and a stable color with maximum intensity was obtained 1.5 hours after addition of the reactants. Absorbance was constant for a t least 6 hours after preparation, after which the absorbance decreased slowly. The intensity of the color was slightly dependent on the age of the QDT reagent. Reagent 1-day old gave a n absorbance about 4% less than freshly prepared reagent. Freshly prepared reagent solutions were used for all other studies. Effect of Heating. In order to possibly increase the rate of formation of the complex, the effect of heating was studied. The recommended procedure, using solutions of 7.84 ppm osmium, was followed except the various solutions were heated in a constant temperature bath for 15 and 30 minutes at temperatures of 40, 50, 60, and 70 "C. Comparison of the spectral curves of the non-heated solutions and the various heated solutions showed them to be essentially the same. Temperatures higher than 70 "C were not attempted since heating a t 70 "C produced a decrease in absorbance a t 560 nm. Heating the solutions at 60 "C resulted in only a 5% increase in sensitivity. No appreciable increase in rate of formation of the complex was observed. All subsequent measurements were therefore made a t room temperature. Effect of Reagent Concentration. The amount of QDr was varied in a series of solutions prepared by the recommended procedure. while the osmium concentration was kept constant a t 7.88 ppm. As t h e amount of QDT was increased, the reaction product turned from brown to green. The absorbance a t 560 nm, the absorption maximum for the green complex, was essentially independent of the amount of QDT added if the QDT/Os molar ratio was between 10 and 20. Immediate precipitation of the QDT ocmole per 25 curred if the QDT added exceeded 8.2 x 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
671
Table I. Tolerance of Foreign Ions Tolerance concentration, ppm Foreign ions
Platinum (IV) Rhodium (111) Ruthenium (111) Iridium(1V) Palladium (11) Nickel(I1) Cobalt (11) Copper(I1) Iron (11) Iron(II1) Manganese(I1) Chromium(II1) Zinc(I1) Mercury(I1) Lead(I1) Nitritea Nitrate Sulfate Phosphate
Os, 3.928 ppm Os, 5.862 ppm
0.2 13 2 2.5
0.2 18 2 2.4
0.1 0.1 0.06 0.12 15 9 50 50
0.09 0.1 0.06 0.16 9 15 50 50
Average
0.2 16
2 2.4 0.1
necessary. Well established procedures for the separation of osmium by distillation of osmium tetroxide from various oxidants such as nitric acid, hydrogen peroxide, or perchloric acid are available (11) have been carried out successfully and routinely by many workers (12-15). STUDY OF THE REACTIONS Mole Ratio Method. For one application of this method (16, 13, a series of solutions was prepared of final osmium
concentration of 4.13 X lO-5M and varying QDT concentration. These solutions were measured against simulta0.14 neously prepared blanks, containing the corresponding 12 amounts of QDT. Figure 2 shows the plots of absorbance 12 us. mole ratio of QDT to osmium. At all three wave50 lengths plotted, marked changes of slope occurred a t mole 50 ratios of 4:1and 2:1. 42 21 32 39 50 28 Alternatively, another series of solutions was prepared 50 50 50 of final QDT concentration pf 1.04 x 10-4M varying os2 1 3 mium concentrations, which were measured us. a simulta200 200 200 neously prepared QDT blank. A plot of absorbance us. 200 200 200 mole ratio of osmium to QDT in Figure 3 shows marked 200 200 200 changes of slope at mole ratios of 0.25 and 0.50. The mole a Nitrite caused precipitate formation. ratio plots, therefore, indicate successive formation of two QDT:Os complexes: a 2 : l complex with absorption maximum at 475 nm and a 4:l complex with absorption maximl. Since no turbidity was observed with 2.06 X ma a t 560 and 460 nm shown as curves C and B, respecmole of QDT, which was about a 20-fold excess of the tively, in Figure 1. The 4:l complex is the absorbing amount of osmium, this amount was used in the recomspecies in the proposed method. mended procedure. Isolation of the 4:1 QDT-to-Osmium Complex. One Beer's Law, Range, Sensitivity, and Precision. Three millimole of osmium, originally as 0 ~ 0 4 ,in 60 ml of standard series of 7 samples each, ranging in concentra0.045M aqueous solution of sodium hydroxide was added tion from 1.96 to 11.78 ppm osmium, were treated by the dropwise with constant stirring to 4.5 millimoles of QDT recommended procedure. Conformity to Beer's law was dissolved in 25 ml of DMF that had been acidified with 26 obtained in each case. Optimum concentration range for ml of 1M HC1. A dark, colloidal precipitate formed immemeasurement a t 560 nm and 1.00-cm optical path is about diately. After standing for 25 hours in the dark, the mix2 to 8 pprn of osmium. The molar absorptivity a t 560 nm ture was filtered, washed thoroughly with small amounts is 1.73 x l o 4 liter mole-1 cm-1, and the sensitivity (for A of 5:l DMF-water mixture and afterwards with water, = 0.001) is 0.011 Fg cm-2. The relative standard deviation and dried under vacuum at 40 "C for 3 hours. The final of the calculated absorptivities of the 21 samples in the product was green-black, shiny material which dissolved three standard series is 4.1%. The relative standard deviain aqueous solutions of alkalies to give a yellow solution. tion of the calculated absorptivities of the 15 samples in Isolation of the 2:l QDT-to-Osmium Complex. Two the optimum concentration range is 2.1%. millimoles of QDT dissolved in 114 ml of DMF were Effect of Foreign Ions. Varying amounts of foreign ion added dropwise with constant stirring to 49 ml of a soluwere taken with fixed amounts of osmium (3.92 and 5.86 tion containing 1.15 millimoles of osmium, originally as ppm) and the color was developed according to the recom0 9 0 4 , and 8.2 millimoles of HC1. A dark colloidal precipimended procedure. Spectral curves from 700 to 450 nm tate formed immediately. After standing in the dark for were obtained. Initially, the foreign ion was added to the 24 hours, the precipitate was filtered, washed thoroughly osmium solution in large excess: 50 pprn for cations and with small amounts of 5 1 DMF-water mixture and then 200 ppm for anions. When the interference was extensive, with water, and dried under vacuum at 40 "C for 3 hours. the tests were repeated with successively smaller amounts The final product was a black, finely divided, apparently of foreign ion. Tolerance for a foreign ion was taken as the non-crystalline material which dissolved in aqueous solulargest amount that could be present to give an absorbtions of alkalies to give a brown solution. ance error of 0.020 a t 560 nm. This difference is approxiIon Exchange Behavior, The isolated 4 : l and 2:l commately twice the average deviation for the osmium deterplexes dissolved in 1M aqueous NaOH solutions were not mination. Tolerances for the ions tested are shown in retained on Dowex 50W-X4 cation exchange resin in the Table I. hydrogen form. Each colored species was retained, howIt was noted that nitrite caused precipitation, probably ever, on Dowex l-X8 anion exchange resin in the chloride due to complex formation with osmium. The ligand NOzform. Elution with acidified DMF gave solutions that had is ambidentate in the same sense as NCS- (8). Osmium identical spectra to curves B and C of Figure 1 for the 4 : l may form a nitro complex similar to [ O s 0 ~ ( 0 H ) z ( N O z ) z ] ~ the i:1 QDT-to-osmium complexes, respectively. which is formed by the action of an aqueous solution of nitrite on osmium tetroxide (9, 10) rather than the Os-QDT F. E. Beamish. "The Analytical Chemistry of the Noble Metals," Pergamon Press, Oxford, 1966, pp 39-56. absorbing species. R. Gilchrist, J . Res. Nat. Bur. Stand.. 6, 421 (1931). Table I shows that platinum(IV), palladium(II), nickelA. D. Westland and F. E. Beamish. Anal. Chem.. 26, 739 (1954). (11), cobalt(II), and copper(I1) interfere seriously. Prior C. V . Banks and J. W. O'Laughlin,Anal. Chem., 29, 1412 (1957). G . H . Ayres and C. W . McDonald, Anal. Chim. Acta., 30, 40 separation of osmium from these elements is, therefore, 0.1
0.06
(8) C. K . Jorgensen, "Inorganic Complexes," Academic Press. New York, N . Y . . 1963, Chap. 5, p 83. (9) L. Winterbert, Ann. Chim. Phys., 28, 15 (1903). (10) W. P. Griffith. J. Chem. SOC., 1964, 245.
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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 1 9 7 4
(1964). J. H . Yoe and A. L. Jones, Ind. Eng. Chem., Anal. Ed., 16, 111 (1944). A. S. Meyer. J r . , and G. H. Ayres. J. Amer. Chem. SOC., 79, 49 (1957).
I
I I
0
I
1 02
I ~
,
I
1
1
04 06 M O L E S OSMIUM / MOLES Q D T
I
1 08
1
I ? !
Figure 3. M o l e ratio plot QDT concentration constant (1 04 X 10-4M) and osmium concentration varied
MOLES QDT / MOLES OSMIUM
Figure 2. M o l e ratio plot Osmium concentration constant (4 13 X 10-5M) and QDT concentration varied
Each complex appears, therefore, to be a weak acid that is readily neutralized with NaOH to give colored anions. T h e Oxidation S t a t e of the Reactive Osmium. ACcording to Majumdar and Sen Gupta ( I 8 ) , the standard osmium solution prepared should contain osmium in its octavalent state. It is known, that the octavalent species are all easily reduced to the hexavalent or lower states (19). In order to determine the oxidation state in which osmium complexes with QDT, the absorption spectra of osmium solutions of oxidation states VIII, VI, and IV, which had been treated by the recommended procedure, were obtained. The Os(VII1) solution was obtained by dilution of the standard solution prepared previously from OSOS; the Os(VI) solution was prepared according to the method of Majumdar and Sen Gupta (18); and the Os(1V) solution was obtained by dissolving KzOsC16 in 1M hydrochloric acid. The data revealed that osmium(1V) does not react with QDT. The osmium(VII1) and osmium(VI) solutions, when treated by the recommended procedure, gave identical absorption spectra which are the same as that of the 4:l complex.
DISCUSSION Burke and Yoe ( 5 ) assumed QDT to undergo the following tautomeric equilibria,
;\ci
H
and the semi-aci form was proposed as the reactive species which formed the metal complexes. QDT and related substances have been reported to exist largely in the thione form (20) which indicates the possibility of the lig(18) A. K. Majumdar and J. G . Sen Gupta, Anal. Chim. Acta., 21, 260 (1959). (19) W. P. Griffith, "The Chemistry of the Rarer Platinum Metals (Os, Ru, Ir and Rh)," lnterscience Publishers, London, 1967,pp 64-66. (20) G. W. H. Cheesman, "Advances in Heterocyclic Chemistry," Vol. 2, A. R. Katritsky, Ed., Academic Press, New York, N.Y., 1963, pp 231-234.
and acting as a coordinating agent. Studies of QDT in aqueous DMF solutions (21) showed that it is a dibasic acid with dissociation constants of pK1 = 6.94 f 0.05 and pK2 = 9.91 f 0.08. In a study of the QDT complexes of nickel(II), cobalt(11), and palladium(I1) in alkaline solution, Stevancevic and Drazic (22) concluded that the complexes had the following structure:
They assumed that the QDT behaves as a bidentate ligand with two anionic groups. This assumption seems to be consistent with the findings in the present work as this would account for the anionic character of both the 4:l and 2:l complexes when dissolved in basic media. The semi-aci form of QDT, however, would imply that the bonding between the sulfur atoms and the osmium is coordinate covalent which would not account for the anionic character. It has been reported ( 2 ) that QDT has reducing properties. Since osmium in either the VI11 or VI oxidation state gives the same QDT complex, it would seem that the osmium is first reduced to the VI state, after which it complexes with QDT. If osmium is in the VI state, the 4:l complex would be dianionic in basic solution and could add two protons to precipitate as a neutral species. This is consistent with ion exchange observations, ease of solubility in aqueous basic solutions, and different spectral characteristics in acid and basic DMF solutions. Beamish et al. have critically evaluated the spectrophotometric methods for the determination of osmium up to 1964 in several reviews (23-26). Subsequently, over 20 spectrophotometric methods for osmium have been reported with molar absorptivities that range from about 4 x lo2 to 2.4 x lo4 liter mole-I cm-l; this corresponds to sensitivities ( A = 0.001) of about 0.48 to 0.0079 kg cm-*. The more sensitive reagents recently reported include 3nitroso-2,6-pyridinediolin aqueous solution with sensitivit y = 0.0079 gg cm-* (27); thiocyanate extracted into diethyl ether, 2-heptanone, 2-octanone, cyclohexanone, 2(21) L. I . Chernomorchenko, A. G. Akhmetshin, and V . T.Chuiko, Zh. Anal. Khim., 25,231 (1970). (22) D. V . Stevancevic and V. G. Drazic, Bul. lnst. Nucl. Sci. "Boris Kidrich" (Belgrade), 9,69 (1959). (23) F. E. Beamish and W . A. E. McBryde, Anal. Chim. Acta, 9, 349 (1953). (24) F. E. Beamish, "The Analytical Chemistry of the Noble Metals," Pergamon Press, Oxford, 1966,pp 393-408. (25) F. E. Beamish and W . A. E. McBryde, Anal. Chim. Acta, 18, 551 (1958). (26) F. E. Beamish, Taianta. 12, 789 (1965) (27) C. W . McDonald and R . Carter, Jr., Anal. Chem..41, 1478 (1969). A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO.
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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).
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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).
