Dec., 1962
OXIDATION A S D REDUCTION REACT IONS
imperfectly understood. Water-soluble chlorophyll (potassium chlorophyllin) undergoes the Krasnovsky reaction in water with ascorbic acid when pyridine is present only to the extent of This reaction does not proceed, however, if the ascorbic acid is replaced by a secondary or tertiary amine. Hence we cannot at this time simply associate our yellow intermediate with the intermediate found by the Russian workers13for eosin. The intermediate apparently is not that observed for eosin by means of flash spectro~copy.'~~'~ The lifetimes of such, intermediates are of the order of one millisecond or less while ours has a lifetime some thousand times greater. Although a yellow intermediate absorbing a t 405 mp has been observed for eosin by flash spectroscopy,18this species was obtained only in the presence of phenol. I n common with species produced by high intensity flash our intermediate exhibits a shortened lifetime when oxygen is introduced. Furthermore, nitric oxide also decreases the lifetime of our intermediate without producing any over-all chemical change, thus indicating the paramagnetic nature of this intermediate. (16) G. Oster and S. B. Broyde, Nature, 192, 132 (1961).
(17) S. Kato, T. Watanabe, 8 . Kagalu, and M. Koizumi, Bull. Chem. SOC.J a p a n , 33, 262 (1960). (18) L. Grossweiner and E . Zwicker, J. Chem. Phys., 34, 1411 (1961).
O F AIAXGBNESE PHTHALOCYANINES
2217
The transient species decomposes to give what appears to be, in the case of rose bengal, a monodeiodinated species. The maximum in its absorption spectrum, namely, 540 mp, lies between that of the tetraiodinated species and the location where the diiodinated species should absorb. Due to overlapping spectra with the original dye the absorption a t 550 mp of this species appears as an apparent recovery of the original rose bengal. Continued irradiation of this triiodinated species leads to complete removal of the iodine atoms. Recently we have found that the yellow intermediate can be stabilized by carrying out the reaction in glycerol a t low temperatures where the systems form rigid glasses. Future experiments of this kind which have yielded intermediates in the photofading of visual purple1gand of thiobenzophenone*Gare contemplated to obtain more detailed spectra of the intermediates. We feel that this intermediate may play a role in dye-sensitized photopolymerization21since our dye-tertiary amine mixtures are photosensitizers for the initiation of polymerization of vinyl monomers. (19) G. Wald, J. Durell, and R. C. C. St. George, Science, 111, 179 (1950). (20) G. Oster, Ann. N . Y . Acad. Sci., 74, 305 (1958). (21) G. Oster, Nature, 173, 300 (1954); G. K. Oster, G. Oster, and G. Prati, J . A m . Chem. Sac., 79, 595 (1957).
THE EFFECT OF LIGHT OK OXIDATIOK AND BEDUCTION KEACTIOKS INVOLVING PHTHALOCYANINE AND ETIOPORPHYRIN I MANGANESE COMPLEXES BY
G. ENGELSMA,' AKIOYAMAMOTO,' E. MARKH.kM,3 9 N D MELVINCALVIN Department of Chemistry and Lawrence Radiation Laboratory,4 University of California, Berkeley 4, California Received M a y 66, 1966
A detailed study of the cheniistry and photochemistry of phthalocyanine manganese and a few metal derivatives of porphyrins has been made. It has been shown that the stable oxidation level of manganese may be shifted among the 11, 111,and IV oxidation states, depending on the nature of the fifth and sixth coordinating groups. Furthermore, photochemical oxidation as well as photochemical reduction of the phthalocyanine manganese( 111)has been observed, and photochemical reduction of the manganese( IV) compound demonstrated. Mn( 111), Fe( 111) and Go( 111), etioporphyrins also are photoreduced to the I1 state. The possible participation of such photochemical transformations in the oxygen evolution sequence of photosynthesis is indicated.
Introduction In particular, manganese seems to be essential Recent investigations have shown that manganese in the oxygen evolving systems.B Recently it was plays an important role in photosynthesi~.~-l~reported that a manganese chelate related to t'he porphyrins, namely, phthalocyaninemanganese, ap(1) The Pllilips' Research Laboratory, Eindhoven, The Netherparently formed a peroxide reversibly which, in lands, NATO Fellow, 1960-1961. turn, seemed to be capable of dissociating the (2) On leave from .:he Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Tokyo, Japan. oxygen-oxygen bond in a reversible fashion. l 2 (3) University Chemical Laboratory, Lensfield Road, Cambridge, This observation was so unusual that it attracted England. our attention immediately. It seemed possible (4) This work was supported, in part, by the U. S. Atomic Energy to incorporate such stages in the oxygen evolution Commission. (5) E . Kessler, Planta, 49, 435 (1957). scheme of photosynthesis with great ease. (6) E. Kessler, W. Arthur, and J. E. Brugger, Arch. Biochem. In order to determine the feasibility of using Biophys., 71, 326 (1957). (7) T. E. Brown, € I . C. Eyster, and H. A. Tanner, "Trace Elements," Academic Press, Inc., New York, N. Y., 1958, p. 135. ( 8 ) T. E. Brown, H. C . Eyster, and H. A. Tanner, ibid., p. 157. (9) H. A. Tanner, 1'.E. Brown, H. C. Eyster. and R. W. Treharne, Ohio J . Sei., 60, 231 (1960).
(10) R. mi. Treharne, T. E. Brown, H. C. Eyster, and H. A. Tanner, Biochem. Biophys. Res. Comm., 3, 119 (1960). (11) H. 4. Tanner, T. E. Browm, H. C . Eyster, and R. W. Treliarne. ibzd., 3 , 205 (1960). (12) J. A. Elvidge and .I. B. P. Lever, I'roc. Chem. Suc., 195 (1S.59).
2518
G. ENGELSMA, A. YAMAMOTO, E. MARKHAM, AND M. CALVIN PHTHALOCYANfNE MANGANESE (g) IN
WAVELENGTH
Fig. 1.-Spectrum
PYRIDINE
Vol. 66
I
ImJ)
of phthalocyaninemanganese(11) in pyridine.
phthalocyaiiinemanganese complexes as model compounds, a study was undertaken of the oxidation and reduction reactions of these complexes. The influence of light on these reactions was especially investigated. The basic compound of this series, phthalocyaninemanganese(I1) (I) is prepared from phthalonitrile and manganese dioxide l3 or manganese acetate.14 Elvidge and Lever12have reported that phthalocyaninemanganese(I1) in a pyridine solution has an absorption band a t 712.5 mp, whereas Rutter and ? \ / I ~ Q u e e nstated ~ ~ that its main absorption band in the visible region is a t 620 mp. We have found that these spectra belong to oxidized phthalocyaninemanganese compounds. A solution of phthalocyaninemanganese(I1) prepared in the absence of air has absorption peaks a t 880, 835, 660, 643, and 467 mp (Fig. 1). On introduction of air, these bands decreased and a new band a t 716 mp was observed. This band probably corresponds to Elvidge and Lever's band a t 712.5 mp. It gradually built up to a maximum and then decreased again, a band at 620 mp finally being formed (Fig. 2). On evaporation of a solution of phthalocyaninemanganese(I1) (I), prepared in the absence of air (660 mp), a green compound was obtained which changed in contact with the air. It probably is phthalocyaninedipyridinemanganese(11) (11) * From the completely oxidized solution (620 mp, (13) P. A. Biirrett, C. E. Dent, and R . P. Linstead, J . Chem. Sac.. 1719 (1936). (14) H.-1. Rutter. Jr., and J. D. JlcQueen, J . Inorg. Nucl. Chem., 12, 362 (1960).
log E 4.94) a purple compound was obtained for which the elementary analysis was in approximate agreement with the formula given by Elvidge and Lever12: phthalocyanine-oxo-pyridinemanganese(TV) (111) .I4& Magnetic susceptibility measurement of this crystalline compound at room temperature showed that it is almost diamagnetic with a molar susceptibility of -270 X 10+ c.g.s., which, when adjusted by diamagnetic correction of phthalocyanine, pyridine, and oxygen, gives a slightly paramagnetic magnetic moment of 0.71 Bohr magneton. This would require some kind of electron pairing in the crystal, either by dimerization through two oxygen atoms (the peroxide which apparently is not present) or by metal-oxygenmetal interaction, or metal-metal interaction. Solubility limitations have so far prevented any reliable magnetic susceptibility measurement or molecular weight measurement in solution, and we tentatively assume the monomeric structure pht halocyanine-oxo-pyridinemanganese(IV) for this species (absorption maximum, 620 mp) in pyridine solution. In the absence of air the transient oxidation product (716 mp) is broken down under the influence of light to form phthalocyaninedipyridinemanganese(I1) and phthalocyanine-oxo-pyridinemanganese(1V). This appeared t o indicate that the 716 mp species might be the presumed reversible peroxide of phthalocyaninemanganese suggested by Elvidge and I,ever.12 They assume that the oxidation of phthalocyaninemanganese(I1) to phthalocyanine-oxo-pyridinemanganese(1V) and the reverse reaction, reduction to phthalocyaninemanganese(I1) by boiling a solution of phthalocyanine-oxo-pyridinemanganese(1V) in pyridine, have, as a common intermediate, a bis-(phthalocyanine pyridinemanganese) peroxide (PcMn-Py)zOz. The first part of this work is centered around the question of whether our photosensitive intermediate corresponds t o a dimanganese peroxy complex, and if so, whether oxygen is released on its decomposition. Isolation of Intermediate Oxidation Level Compounds A direct isolation of the intermediate from the (14a) The crystals as they originally come out of the pyridine solution at room temperature seem to have two molecules of pyridine per manganese atom. Removal of the pyridine by vacuum heating. reabsorption of pyridine, and removal of exceas or lightly bound pyridine leave behind crystals with only one molecule of pyridine per manganese atom.
Dec., 1962
O X I D A T I O N AND
*A"CLt*CI*
,
REDUCTION REACTIONS O F MANG.1NESE
" y
Fig. 4.-(a) Spectrum of a solution of phthalocyaninemanganese( 11), in 1-chloronaphthalene, prepared in the "absence" of air. (b) Spectrum of the same solution one hour after air had been admitted. The optical densities of the two curves are not necessarily comparable, since all of the compound may not have been dissolved in (a).
solution in pyridine is not feasible because of its equilibrium with the manganese(I1) and manganese(IV) compounds. A solution in which only the species absorbing a t 716 mp is present can be obtained by dissolving phthalocyaninemanganese(11) in a mixture of equal amounts of pyridine and water (in the presence of air). On evaporation of this solution i n vacuo a green compound precipitates. However, attempts to identify this compound failed, since in contact with the air it is converted rapidly to a violet compound which appeared to be identical with phthalocyanine-oxopyridinemanganese(1V) (111). A chart exhibiting the interrelationships to be described is shown in Fig. 3.
PHTHlLOCYANINES
2519
Solutions of phthalocyaninemanganese(I1) in l-chloronaphthalene, methanol, ethanol, chloroform, ethyl acetate, chlorobenzene, dimethylformamide, nitromethane, and acetic acid, prepared in the presence of air, have spectra which are very similar to the spectrum of the intermediate oxidation product in pyridine (716 mp). They have high absorption bands between 710 and 726 mp. In the case of l-chloronaphthalene it was shown that this spectrum belongs to an oxidized phthalocyaninemanganese. A solution prepared with exclusion of air as far as possible had a spectrum with peaks a t 878,726,682,654,598,532,494,473, and 440 mp. Except for the peak a t 726, this spectrum is very similar to the spectrum of phthalocyaninemanganese(I1) in pyridine. On introduction of air, the peak at 726 mp increased rapidly whereas all the other absorption bands decreased, indicating that the 726 mp band belongs to oxidized phthalocyanine manganese (Fig. 4). From the solutions in methanol and ethanol we isolated complexes to which, based on elementary analysis, we assigned the formulas phthalocyaninehydroxo-methanolmanganese(II1)(IV) and phthalocyanine-hydroxo-ethanolmanganese(II1) (V) , respectively. The magnetic moment of the compound (IV) was 4.87 Bohr magnetons (e, +17O K.) corresponding to four spin-free unpaired electrons of manganese(II1). A complex which according to the elementary analysis is phthalocyanine-chloro-methanolmanganese(II1) (VII) was obtained by extracting phthalocyaninemanganese(I1) with methanol saturated with sodium chloride and a trace of HC1. On evaporating a solution of this complex in pyridine, dark green crystals of phthalocyanine-chloropyridinemanganese(II1) (VIII) appeared. Phthal-
WAVELENGTH imp1
Fig. 5.-Reduction of phthalocyanine-oxo-pyridinemanganese( IV) in a pyridine-water 1: 1 mixture: freshly prepared solution; - - - -, spectra after 15,45, and 120 min., respectively.
-
n
I
WAVELENGTH( m y )
Fig. 6.-Photoreduction of phthalocyanine-chloro-pyridinemanganese(II1) in pyridine in the absence of air: , original solution; - - -, after illumination in the 8un for 10, 20, and 30 min., respectively.
-
ocyanine-chloro-methanolmanganese also could be prepared by adding sodium chloride to a methanolic solution of IV. Extracting phthalocyaninemanganese(I1) with glacial acetic acid containing 5% acetic anhydride resulted in a complex for which the elementary analysis was in agreement with phthalocyanineacetato-(acetic acid)-manganese(II1) (VI). Also starting with phthalocyanine-oxo-pyridinemanganese(1V) (111), it is possible to obtain complexes with absorption spectra which are very similar to the spectrum of the intermediate oxidation product seen in pyridine. When crystals of phthalocyanine-oxo-pyridinemanganese (IV) are dissolved in methanol, ethanol, or 1-chloronaphthalene the band a t 620 mp is observed first, but it soon disappears and exactly the same spectra are obtained as those that appear when phthalocyaninemanganese(I1) is dissolved in the same solvents in the presence of air. Also on addition of methanol to a solution of phthalocyanine-oxo-pyridinemanganese(1V) in pyridine,
the band a t 620 mp decreases slowly with an increase of the 716 mp band a t the same time. Adding sodium chloride to such a solution in which the 620 mp band had disappeared completely resulted in a precipitate of phthalocyanine-chloro-methanolmanganese(II1) (VII) . A similar spectral change corresponding to Mn(IV) reduction can be induced by adding water to a pyridine solution of manganese(1V). I n Fig. 5 the decrease of the peak a t 620 mp and the increase of the peak a t 716 mp can be followed for a pyridine solution of phthalocyanine-oxo-pyridinemanganese(1V) to which an equal volume of water had been added. Considerable bleaching of the solution takes place, possibly due to oxidation of the phthalocyanine ring. The reduction of the Mn(IV) complex is greatly accelerated by acids. On introduction of dry HC1 gas to the pyridine solution, the color changes from blue to green, and a dark green complex precipitates which according to the elementary analysis is phthalocyaninedipyridinemanganese(II1) dichloride or phthalocyanine-chloro-pyridinemanganese(II1) pyridine hydrochloride (VIIIa). When a small amount of pyridine hydrochloride is added to a solution of phthalocyanine-oxo-pyridinemanganese(1V) in pyridine, a complex slowly crystallizes for which the analysis corresponds to phthalocyanine-chloropyridinemanganese(II1) (VIII). Both complexes have an identical absorption spectrum in pyridine with a maximum a t 716 mp. We therefore assume that the comDlex first isolated is Dhthalocvaninechloro-pyridinkmanganese(II1) pyridine hychochloride (VIIIa). When a limited amount of glacial acetic acid is added to a pyridine solution of (111) the color changes from blue (620 mp) to green (713 mp) and green crystals slowly appear. They show analysis for phthalocyanine-acetat o-pyridinemanganese(II1) (IX). The magnetic moment of this compound was 4.76 Bohr magnetons (0, -40’ K.) corresponding to four spin-free unpaired electrons of manganese(II1). Thermal- and Photochemistry of Intermediate Oxidation Level Manganese Compounds.-Solutions in pyridine, prepared in the absence of air, of all these intermediate complexes obtained either from phthalocyaninemanganese(I1) or from phthalocyanine - oxo - pyridinemanganese(IV), have very similar spectra with a main absorption band around 716 mp. When these solutions, in the absence of air, are illuminated (GE Photospot RSP2 (DXB) at about 30 em., or sunlight) a reduction to phthalocyaninedipyridinemanganese(I1) (660 mp) takes place as shown in Fig. 6 for a solution of phthalocyanine-chloro-pyridinemanganese(II1)pyridine hydrochloride (VIIIa) . On the other hand, when air is admitted, oxidation to phthalocyanine-oxo-pyridinemanganese(1V) (620 mp) takes place. This reaction is fast in the case of the hydroxo complexes and relatively slow in the case of the chloro complexes. Light also accelerates the oxidation in the presence of oxygen. When pyridine is added t o a solution of a manganese(II1) complex in ethanol, methanol, or 1chloronaphthalene, this oxidation in air to a
J h . , l!)(i2
OXIDATIOIU A S D
REDUCTIOS REACTIONS O F AIANGASESE
PHTHALOCYASISGb
2321
TIME (min)
Fig. 7.--Effect of light of a specific wave length (720 mp) in the oxidation of a phthalocyanine-hydroxo-manganese (111) complex to a phthalocyanine-oxo-manganese( IV) complex in a mixture of 1-chloronaphthalene and pyridine 2 :1(by volume).
manganese(1V) complex also can be observed. Figure 7 shows the effect of light of a specific wave length (720 mp) on the growth of the 620 mp band for a solution of manganese(II1) complex in 2.0 ml. of 1-chloronaphthalene to which 1.0 ml. of pyridine has been added (original spectrum has only the 723 mp band). Illumination with light of 620 mp had no effect on the rate of disappearance of the 723 mp band. When a pyridine solution of phthalocyaninemanganese(II1) complex, in the absence of air, is kept in the dark a t room temperature, a slow disproportionation into manganese(I1) and manganese(IV) complexes takes place. This is shown in Fig. 8, where a solution of phthalocyanine-acetato-(acetic acid)-manganese(II1) (VI) in pyridine in the presence of air is compared with a solution of the same concentration from which the air has been carefully evacuated. Both solutions were kept in the dark for 12 hours. The spectrum of the first solution (exposed to air) shows that the manganese(II1) complex after 12 hours is largely oxidized to the N!n(IV) complex (620 mp). During the same time in the second solution (evacuated) both llIn(1V) (620 mp) and ?(h(II) complexes (6GO and 880 mp) have been formed. The rate of this disproportionation is increased by heating. Also, illumination of a manganese(II1) complex other than the chloride in pyridine appears to accelerate this disproportionation. Here it is accompanied by a direct photoreduction of the manganese(II1) complex so that more manganese(11) than manganese(1V) complex is formed. The further increase of both the 620 and 660 mp bands when the second sample (evacuated) was kept in the light is shown in Fig. 9. With continued illumination the 620 mp peak decreased, the final spectrum being the spectrum of phthalocyaninedipyridinemanganese (11). This experiment shows that not only phthalocyanine manganese(II1) complexes but also a phthalocyaninemanganese (IV) complex in pyridine is “photosensitive.” I n Fig. 10 it is shown that a solution of phthalocyanine-oxo-pyridinemanganese(1V) in pyridine, in the absence of air, is reduced rapidly to phthalocyaninedipyridinemanganese(I1) in the sunlight. An intermediate Mn(111) complex (7 16 mp) is not observed in this case.
Fig. 8.-Disproportionation in the dark of phthalocyanineacetato-(acetic acid)-manganese(111) in pyridine in the absence of air. The original solution showed only a very high peak at 716 mp: -, after 12 hours in contact with the air; - -, after 12 hours in the absence of air.
Elvidge and Lever’? have reported that a solution of phthalocyanine-oxo-pyridinemanganese(IV) in pyridine was reduced when the solution was boiled. From their publication it is not clear whether they obtained phthalocyaninemanganese(11) or (111). We found that a solution of phthalocyanine-oxo-pyridinemanganese (IV) in “dry” pyridine, from which the air had been carefully removed, kept in the dark a t 75” for three days was reduced completely to phthalocyaninemanganese(I1). The rate of this reduction is much faster when the pyridine contains a small amount of water. More careful “drying” has inhibited not only the thermal
2522
G. EXGELSBIA, A. YAMAMOTO, E. MARKHAhI,
AND
&I. CALVIN OH
PY
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IN PYRIDINE ( V A C )
(E)
I!
I
I
I
I
500
1
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I
I
I
I
I
700 800 WAVELENGTH (my)
I
930
3
I
Fig. 9.-Disproportionation and photoreduction of phthalocyanine-acetate(acetic acid)-manganese( 111)in pyridine in the absence of air. The sample was kept in the dark for 12 hours (), then exposed to diffuse light for one hour ( . . . ), and finally illuminated in the sun for a total of 20 min.: (- after 10 min., after 20 min.).
...
-
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1 : : I
$"%
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1
PY PY IN PYRIDINE I V A C )
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Fig. ll.-Scheme of oxidation and reduction of phthalocyaninemanganese complexes in pyridine.
,
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Vol. 66
,.,ORIGINAL
I
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SOLUTION
l
7co
,
l
800
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900
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WAVELENGTH ( m y )
Fig. 10.-Photoreduction of phthalocyanine-oxo-pyridinemanganese(1V) in pyridine in the absence of air: -, original solution; - -, after illumination in the sun for 8, 16, and 24 rnin., respectively.
reduction of the phthalocyanine-oxo-pyridinemanganese(1V) but the photoreduction as well. The Intermediate Oxidation Level Manganese Complex in Pyridine.-As we have seen, the stable complex in weakly donating solvents (methanol, ethanol, chloroform, 1-chloronaphthalene) is a phthalocyanine-hydroxo-manganese(II1) com-
plex. This is obtained on dissolving in the presence of air either a phthalocyaninemanganese(I1) or a manganese(1V) complex, in such a solvent. I n a strongly donating solvent or solvent system, such as pyridine, diethylamine, quinoline, or ammonia in methanol, the stable oxidation level in the presence of oxygen is manganese(1V). However, when excess chloride or acetate is present, the stable complex in pyridine is a chloro- or acetatopyridinemanganese (111) complex even in the presence of air. Based on these observations we are now able to suggest a structure for the intermediate oxidation product which was called a peroxide by Elvidge and Lever.'* By analogy with the complexes isolated, we assign to the intermediate the formula phthalocyanine - hydroxo - pyridinemanganese(II1) (X). This makes our scheme of oxidation and reduction in pyridine as shown in Fig. 11. The chemistry of the intermediate dissolved in pyridine can be summarized as follows: In the presence of oxygen it is oxidized slowly to phthalocyanine-oxo-pyridinemanganese(1V) . This oxidation is accelerated by light. I n the absence of oxygen a disproportionation into phthalocyaninedipyridinemanganese(I1) and phthalocyanine-oxopyridinemanganese (IV) takes place. On illumination the rate of this disproportionation is increased and at the same time a rapid reduction of the manganese(II1) complex to the manganese(J.1) complex takes place. It should be mentioned here that there are evidences that the 716 mp band is a composite one, indicating the possibility of another intermediate manganese(II1) complex. In the course of the decrease of the 716 mp band on illumination of the hydroxomanganese(II1) complex in pyridine in the absence of air, a slight shift from 716 mp to longer wave length takes place (reaching to about 730 mp). When air is introduced to a solution of phthalocyaninedipyridinemanganese(I1)in pyridine (660 mp) the 716 mp band builds up in a reverse order. A peak a t 730 mp appears first; on further increase of the band intensity its peak shifts to 716 mp. Photoreductions in Solvents Other Than Pyridine.-In order to determine whether pyridine is essential for the photoreductions, we dissolved phthalocyaninemanganese(I1) in methanol, ethanol, or 1-chloronaphthalene and obtained manganese(111) compounds absorbing in the 716 mp region. The air was removed from the solutions and they were illuminated for a prolonged time. No changes in the spectra could be observed. Only when pyridine was present (20% by volume of the solution) did the reduction to phthalocyanine-
nec., 1962
OXIDATIOV AND
REDUCTIONREACTIOVS O F 1'r.41'GhUESE
manganese(I1) take place on illumination of these solutions. Apparently the amount of pyridine needed is much smaller. A solution of phthalocyanine-c hloro-pyridinemanganese (111) pyridine hydrochloride in ethanol is reduced slowly in the sunlight in the absence of air, as can be seen in Fig. 12. Cyano Complexes.-A potent donor group which might be expected to affect the oxidation-reduction relationships among the manganese levels is CN-. Figure 13 shows the interrelationships of the cyanomangrinese complexes with other phthalocyaninemanganese complexes which will be discussed in this section. Manganese(I1) Complexes.-The spectrum of a freshly prepared solution of phthalocyaninemanganese(I1) (I) in ethanol saturated with sodium cyanide shows absorption maxima a t 824, 660, 598, 533, 464, and 373 mp (Fig. 14). On evaporation of the solvent we obtained green crystals for which the elementary analysis corresponded to phthalocyanine-cyano-ethanolmanganese(I1j sodium (XI). A solution prepared by dissolving this complex in pyridine, in the absence of air, showed the spectrum of phthalocyaninedipyridinemanganese (11). This proves that the cyano complex is a manganese(I1) complex. When sodium cyanide is added to a solution of phthalocyanineinanganese(I1) in pyridine containing 5% water, the spectrum is very similar to the spectrum of phthalocyanine-cyano-ethanolmanganese(I1) sodium (XI) in ethanol (Fig. 15). This solution of what is probably phthalocyaninecyano-pyridinernanganese(I1) sodium (XII) is very stable in air. Only after long standing does a small peak at 620 mp i@!In(IV))sometimes appear. Manganese(1II) Complexes.-In air, phthalocyanine-cyano-ethanolmanganese(I1)sodium (XI) dissolved in ethanol, containing excess sodium cyanide, is slowly oxidized, as can be seen in Fig. 16. The final spectrum has maxima a t (892), 752, 669, 636, 614, 557, and 385 mp. On evaporation of the ethanol, a complex crystallized which according to the elementary analysis is phthalocyaninedicyanommganese(II1) sodium (XIII). On addition of a methanol solution of sodium cyanide to a solution of phthalocyanine-hydroxo-methanolmanganese(II1) (IT3 in methanol, the same complex is formed. Figure 17 shows that with a small amount of sodium cyanide a complex which has a main absorption band a t 701 mp is formed. With more sodium cyanide, the spectrum ascribed to phthalocyaninedicyanomanganese(II1)sodium (as in Fig. 16) is obtained. Attempts to isolate the intermediate absorbing a t 701 mp have failed so far. Phthalocyaninedicyanomanganese(II1) sodium (XII) also can be prepared from phthalocyanineoxo-pyridinemanganese(1V) (111). I n the previous section it was mentioned that on dissolving phthalocyanine-oxo-pyridinemanganese(1V)in ethanol it is reduced very rapidly to what is probably a phthalocyanine-hydroxo-manganese(II1)complex (716 mp). A solution prepared by dissolving phthalocyanine-oxo-pyridinemanganese(1V) in ethanol saturated with sodium cyanide is more stable (620 mp). It it; not known whether the complex in
4cO
?CC,
500
2523
PHTH4LOCYASIUES
603
702
NAVELENGTrl
8ccI
90.3
1
(my)
Fig. 12.-Photoreduction of phthalocyanine-chloro-pyridinemanganese( 111)pyridine hydrochloride in ethanol in the absence of air: -, original solution; - -, after 1, 2, and 5 hours in the sunlight, respectively.
m
i
1-
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Fig. 13.-Phthalocyaninecyanomanganese complexes.
solution is phthalocyaninedicyanomanganese(1V) (XIV). On standing, the manganese(1V) complex is slowly reduced to the dicyanomanganese(II1) complex (669 mp), as can be seen in Fig. 18. Also, by addition of sodium cyanide to a solution of phthalocyanine-chloro-pyridinemanganese (111) (VIII) in pyridine containing 5y0 water, phthalocyaninedicyanomanganese(II1) sodium (XIII) is formed, as can be seen from the spectral change of the solution. The reaction is reversed by addition of hydrogen chloride. With this solvent system the
G. ENGELSMA, A. YAMIIBIOTO, E. I\~ARKH.W,ASD
2524
313
300
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Fig. 14.-Spectrum of phthalocyanine-cyano-ethanolmanganese(1V) sodium in ethanol containing sodium cyanide. PY
Tnl. RR
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WAVELENGTH i m y l
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;I[.CALVIN
1-
Fig. 16.-Oxidation of phthalocyanine-cyano-ethanolmanganese(11)sodium to phthalocyaninedicyanomanganese( 111) sodium a t room temperature in the dark: -, solution freshly prepared by dissolving phthalocyaninemanganese(11) in ethanol saturated with sodium cyanide; - -, after standing in contact with the air for 1. 14, and 72 hours, respectively.
58641660
6co
m
8Cc
9J)
WAVELENGTH im9)
Fig. 15.- -, spectrum of phthalocyaninedipyridinemanganese(I1) in pyridine with 5 7 , water; - -, spectrum after addition of sodium cyanide (in vacuo).
intermediate absorbing at 701 mp is not observed. At room temperature in the dark in contact with air, phthalocyaninedicyanomanganese(II1) sodium (XIII) dissolved in pyridine with 5% water saturated with sodium cyanide is reduced slowly to the cyanomanganese(I1) (XII) complex absorbing at 660, 816 mp (Fig. 19). The solution obtained by dissolving phthalocyaninedicyanomanganese(II1) sodium (XIII) in pyridine, in the absence of air, has a main absorption peak a t 716 mp, indicating that one or both cyano groups have been replaced. The complex thus obtained undergoes the same reactions as the manganese(II1) complexes described in the previous section: disproportionation on standing in the dark, complete reduction on keeping the sample in the dark a t an elevated temperature, and a disproportionation followed by reduction on illumination of the sample a t room temperature. X o change in the spectrum can be observed when a solution obtained by dissolving phthalo-
V.i.VEI.EhG'H
r p ~
Fig. 17.-Spectral changes on addition of sodium cyanide to a solution of phthalocyanine-hydroxo-methanolmanganese(II1) in methanol. The final curve is the spectrum ascribed to phthalocyaninedicyanomanganese(II1) sodium.
cyaninedicyanomanganese(II1) sodium (XIII) in ethanol (713 mp), from which the air has been removed, is illuminated in the sun. However, when excess sodium cyanide is added so that the phthalocyaninemanganese(II1) is present as the dicyano complex (669 mp) in the solution, a reduction to phthalocyanine-cyano-ethanolmanganese(I1) sodium (XI) takes place in the evacuated system on illumination (Fig. 20). We also found that the manganese(IT7) complex (620 mp) obtained by dissolving phthalocyanine-oxo-pyridinemanganese(IV) in the absence of air in ethanol saturated with sodium cyanide is reduced to a manganese(I1) complex in the sunlight, as can be seen in Fig. 21. The final solution obtained shows the spectrum of phthalocyanine-cyano-ethanolmanganese(I1)sodium (XI) (824, 660 mp).
?3 AAVELENGTH ( m y 1
Fig. 18.-Reduction of phthalocyaninedicyanomanganese(IV) (XIV) to phthalocyaninedicyanomanganese(II1) sodium in ethanol saturated with sodium cyanide: -, phthalocyanine-oxo-pyridinemanganese( IV) dissolved in ethanol saturated with sodium cyanide; - -, after standing in the dark for 3, 18, and 100 min., respectively.
1
Fig. 20.-Photoreduction of phthalocyaninedicyanomanganese( 111)sodium to phthalocyanine-cyano-ethanolmanganese(I1) sodium in ethanol saturated with sodium cyanide in original solution; - -, after illuthe absence of air: -, mination in the sun for 30 and 60 min., respectively.
AFTER 18 h r i
lY . A F T E R
6 hrr
300
4CO
500
600
700
600
3Cc
WAVELENGTH Imp1 WAVELENGTH I m y )
Fig. 19.-Reduc&tion of phthalocyaninedicyanomanganese(111) sodium in ,pyridine with 575 water, saturated with directly after addition of sodium sodium cyanide: -, cyanide to a solution of phthalocyanine-hydroxo-methanolmanganese(II1) in pyridine with 5y0 water; - -, after 3, 6, and 18 hours, ri?spectively, in the dark.
Fig. 21.-Photoreduction of phthalocyaninedicyanomanganese(1V) (XIV) to phthalocyanine-cyano-ethanolmanganese(I1) sodium in ethanol saturated with sodium cyanide: -, original solution obtained by dissolving phthalocyanine-oxo-pyridinemanganese(1V) in ethanol saturated with sodium cyanide in the absence of air; - -, after illumination in the sun for 12 and 24 min., respectively.
Preliminary Experiments with Phthalocyanine Hydroxo Manganese Complexes Manganese(II1) Complex.-When an aqueous methanol solution of phthalocyanine-hydroxomethanolmang:tnese(III) (IV) is titrated with a dilute sodium hydroxide solution, the bands a t 716 and 513 mp disappear and a new band a t 702 mp appears a t pH 10.0. Above p H 11.3 this band decreases and a spectrum with a high band at 678 mp and a smaller band a t 625 mp is now obtained (Fig. 22). These changes are reversible. The solution which is obtained when phthalocyaninemanganese(I1) is extracted in air with methanol containing sodium hydroxide has the same spectrum (678 mp). On evaporating the solvent,
a blue-green compound crystallizes. The elementary analysis for this complex varies. After prolonged washing with water it comes close to what is calculated for phthalocyaninedihydroxymanganese(II1) sodium (XV). Partial formation of a di- or trisodium salt may be the reason for the varying composition of this complex. In the absence of air this complex gives a green solution in pyridine with a main absorption peak at 716 mp, indicating that it is a manganese(II1) complex. The rate of oxidation of phthalocyanine-hydroxopyridinemanganese(II1) (716 mp) to phthalocyanine-oxo-pyridinemanganese(1V) (620 mp) in pyridine with 10% water is much increased by the addition of a small amount of sodium hydroxide.
G. ENGELSJI.4, Ai.~ A M A b l O T O ,E. ATARKHAM,
2526
AST)
hI. CALVIN
T'ol. GB
1.0
P c Mn"
/N MeOH
A-pH
E-.
76 pH I O 0
I
WAVELENGTH (rn))
Fig. 22.-Phthalocyaninemanganese( 111) complexes in methanol containing sodium hydroxide a t pH 7.6, 10.0, and 11.3, respectively. IC
1I Ii >
t
However, when excess sodium hydroxide is added rapidly, the complex absorbing a t 678 mp is formed, which on standing in contact with the air is oxidized slo~vlyto a Mn(1V) complex (620 mp), as can he seen in Fig. 23. In the absence of air, in the dark, disproportionation, then complete reduction, takes place a t room temperature (Fig. 24). We have tried to obtain a photoreduction similar to that obtained with the cyano complexes. Although photoinduced spectral changes can be observed in the evacuated ethanolic solutions, the identity of the products is as yet undetermined.
Studies with Etioporphyrin Complexes The translation of the results of the phthalocyanine studies into porphyrin complexes more J O closely related to natural products has only just 2 Ibegun. But a few observations of considerable n 0 relevance can already be reported. The etioporphyrin I complexes of the metallic ions Mn(III), Fe(III), and Co(I1) have been prepared. We have observed the photoreduction of the higher oxidation level and the reoxidation by O2 of the lower oxidation level in each case. Figure 25 shows the change in absorption spectrum on illumination in the sun of an etioporphyrin I manganese(II1) complex, prepared by dissolving etioporphyrin I acetato-(acetic acid) -manganese(111) in pyridine in the absence of air. The final spectrum with absorption bands a t 550 and 584 mp I I is similar t o the spectra in pyridine of the copper600 700 E (11), nickel(II), and zinc(I1) complexes of etioWAVELENGTH ( m y ) porphyrin I, indicating that a manganese(I1) comFig. 23.-Oxidation in air of phthalocyaninedihydroxo- plex has been formed. The reoxidation to the manganese(II1) sodium to phthalocyanine-oxo-pyridine- original manganese(II1) complex on introduction mangmese(1V) in pyridine (10% water) saturated with of air is very fast (Fig. 26). freshly prepared solution; - -, sodium hydroxide: The cyano complex of etioporphyrin I manganeseafter standing in the dark in contact with the air for 15, 30, (111) prepared by dissolving etioporphyrin I 45, 60, and 180 min., respectiveIy. Lo
2
W 0
-
OXIDATIONAND REDUCTION REACTIONS OF X~SGANESE PHTHALOCYASISES2527
Dec., 1962
>k
z Ln 0 W _I
a
0 c
0 a
' A' I
0
5co
600
1
I
1
I
I
'
900
800
700
I
3 i l 3 9 5 427 471 494
WAVELENGTH (my)
Fig. 24.-Disproportionation and reduction in the dark at room- temperature-of phthalocyaninedihydroxomanganese(111) sodium in pyridine with 575 water, saturated with sodium hydroxide: -, original solution prepared in the absence of air; - -, after 1, 4,and 30 hours in the dark, respectively.
10
m
4co
752
530533584 6Zj
6co
797
802
702
WAVELENGTh im )I)
Fig. 26.-Oxidation with oxygen (2 mm.) of photoreduced etioporphyrin I acetato-(acetic acid)-manganese(111) in pyridine: -, before admission of oxygen; - -, 2, 4,6, and 8 min., respectively, after admission of oxygen.
I.
'TI#
I 4'
MnmEtp
f",
I\ [,
ComEtp
min SUNLIGHT
hY
MnnEfp
PYA'DINE I VAG I
; e 7 mln SUNLIGHT
t
cLn
a
J
a 0
0.
cL l0
t cn z
w n -J
0
5 I-
n 0
518 547
4aJ
500
600
WAVELENGTH (mp)
Fig. 29.-Photoreductioii of etioporphyrin I chloroiron(111) in pyridine in the absence of air and reoxidation with air in the dark: -,original solution in the absence of air; -, after 15 min. in the sun; - - -, 2 hours after air has been admitted (in the dark).
-
cytochrome-c. After introduction of oxygen the 518 and 547 mp bands slowly decrease. The Oxidized Products Reduction of manganese complexes is observed on changing the medium, on heating, and on illumination. We have tried to establish the nature of the oxidation products which these reactions produce. The photoreduction of a number of transition element complexes has been reported.'j When the complex involves cyanide, it has been presumed that cyanogen is formed; when the complex is hydroxy or aquo, i t is presumed that peroxide is formed. I n neither case were these oxidized products firmly established, and in all these cases the light used to perform the reduction was in the near ultraviolet or ultraviolet, the so-called chargetransfer absorption. In order to determine whether oxygen is formed on reduction of a phthalocyanine-hydroxo or oxomanganese complex, the following experiments were carried out: A concentrated solution of phthalocyanine-oxopyridinemanganese(1V) from which the air had been evacuated carefully was heated until the reduction to phthalocyaninemanganese (11) was completed. The liquid phase was frozen in a Dry Ice-acetone bath and the gas phase was analyzed with a mass spectrometer. S o oxygen could be detected. Infrared examination of the residue obtained upon cold evaporation of the solvent showed the material to be largely phthalocyaninemanganese(I1). In another experiment a mixture of phthalocyanine-hydroxo-pyridinemanganese(II1) and phthalocyanine-oxo-pyridinemanganese(1V) in pyridine with 1% water containing 0l8 (30.2% 0l8)in a closed system containing a small amount of oxygen gas ( 2 mm.) was illuminated in the sun under continuous stirring. After illumination for three hours the oxygen isotope ratio of the gaseous oxygen was determined. S o enrichment was found. In a similar experiment with a pyridine solution of an etioporphyrin I manganese (111) complex we found that all the oxygen had been used up during the illumination, nith a concomitant destruction of the etioporphyrin ring. When, after a photoreduction, a phthalocyaninemanganese complex is reoxidized with oxygen, the extinction of the resulting absorption bands is in many cases slightly lower than before the photoreduction. A solution of phthalocyanine-oxo-pyridinemanganese(1T') is bleached slowly in the sunlight in the presence of oxygen. Also in some cases, where by a change in the medium a reduction was forced upon a phthalocyaninemanganese complex, considerable bleaching could be observed. All this indicates that the phthalocyanine ring system is oxidized. A preliminary attempt to find oxidation products has beeii made. The aqueous pyridine solution of phthalocyaninemanganese in any initial oxidation level mas boiled (open to air) until most of the phthalocyanine was bleached. Infrared examination of the residue upon evaporation (15) r. Basolo a n d R. J. Pearson, "LIeclianlsrns of Inorganic Reactions: A Study of l f e t a l Complexes in Solution ' John Riley and Sons, Inc., Nca Yuck, N. T.,1958, p. 374.
Dec., 1962
O X I D A T I O N AND
REDUCTION REACTIOKS OF hhXGhSESE
1'HTHALOCYASISES
2529
of the solvent shows that the phthalocyanine has been largely converted into phthalimide. This should not be construed as evidence of the source of the electrons :required in the cold vacuum photoreduction of manganese(II1) or manganese (IV) to manganese(1I).
Experimental Spectra in the visible region were measured with a Cary recording spectrophotometer, Model 14, and a Beckman Model DK-2 spect.rophotometer. All the quantitative data were obtained with the Cary. Infrared spectra were measured with a Beckman IR-7 spectrophotometer. For the mass spectra we used a Consolidated Electrodynamics Corp. Model 21-130 mass spectrometer. Magnetic susceptibility measurements were carried out by a Faraday method, using an apparatus developed by Cunningham.l6 The measurements were carried out at room temperature, liquid Freon temperature (230" K.), and liquid nitrogen temperature (77' K.). The diamagnetic corrections applied were as follows: pyridine, -49 X 10+ c.g.s.; phthalocyanine, -422 X 10-6 c.g.s. (obtained by averaging the values for the, t,hree crystal axes determined by Lonsdalei7i. Diamagnetic corrections for other groups were obtained from tables of Pascal's constants. These solvents were used for the spectrophotometric measurements: pyridine distilled from barium oxide, 1chloronaphthalene distilled under reduced pressure, chloroform, methanol, and absolute ethanol, all redistilled under normal pressure. I n order to study reactions in the absence of air spectrophotometrically, a special cell was constructed (Fig. 30). The cell consists of a small flask of about 15 to 20 ml. capacity connected by a side arm, which can be closed with a stopcock, to a 1 cni. optical cell (Pyrex). The flask can be connected at the top to a vacuum line. A Typical Illumination Experiment .-A small amount of the solid compound t o be studied was put into the optical cell. The cell was connected with a high vacuum line and evacuated to 10-5 mm. The st,opcock in the side arm was then closed, and 10 to 15 ml. of solvent was introduced into the flask. The vacuum cell was again connected with the vacuum line and the solvent was frozen with liquid nitrogen. After evacuation of the system, the stopcock connecting the reaction vessel with the vacuum line was closed and the solvent allowed to thaw and degas. The system then was evacuated again with the solvent frozen in liquid nitrogen. This process was repeated at least five times until the final pressure (with the solvent frozen) was less than mm. After disconnecting the closed vacuum cell from the vacuum line, the solvent was poured over into the optical cell and the compound was allowed t o dissolve. The light reactions were carried out in the sunlight or with one or two GE Photospot RSPZ lamps at a distance of 30 cm. When lamps were used, an infrared absorbing screen which was cooled with water was placed between the lamp and the sample. For most dark reactions in the absence of air, we used the same vacuum cells, wrapped in aluminum foil. For experiments lasting longer than two days, the optical cell containing the solution was glass-sealed off from the rest of the system in order to avoid any possibility of air leakage. Oxygen Exchange Experiment.-Phthalocyaninemanganrse(I1) ( 2 5 mg.) was dissolved in50ml. of pyridine t'o which 0.5 ml. of HzO (30.2% 018)had been added. After allowing the solution to stand in contact ait,h the air for 15 minutes, so that both hIn(II1) and RIn(1T') complexes were formed, the system was evacuated as above. After the air had been removed, oxygen gas was introduced slowly to a pressure of 2 mm. The system was glass-sealed off and under continnous stirring with it magnetic stirrer it was illuniinated in the sun for 3 hours. The liquid phase then was frozen in liyuid nitrogen and the isotope distribution of the uxygeri wit8 measured with the mass spectrometer: Before illuminntion: 0 2 3 4 / 0 2 3 2 X 100 = 0.395 0 2 3 4 / 0 2 3 2 X 100 = 0.397 -4fter illumination: Experiments to Identify the Oxidation Product.---PhthRIocyanine-oxo-pyridinenlanganese(IT') (10-20 1ng.1 wxs placed
Y
lcm %
OPTICAL CELL Fig. 30.-Vacuum
WREACTION VESSEL
cell used for experiments in the absence of air.
in a cell with a breakable tip and the cell was evacuated to 10-5 mm. Pyridine (10-20 nil.) was distilled into the cell in vacuo, and the cell was sealed off. The solution was illuminated by sunlight, or heated at 70" in the dark to reduce Mn(IV) t o Mn(I1). The reduction was faster when the pyridine contained a small amount of water. After the reduction was complete, all the volatile materials condensable at the temperature of liquid nitrogen in vacuo were collected in a side arm with a breakable tip and sealed off. This cell was attached to the mass spectrometer. After the solution was frozen with a Dry Ice-acetone bath, a mass spectrum of the gas phase wits taken. This showed that no oxygen was present. The residue was examined with the infrared spectrophotometer. The spectrum was similar to that of phthalocyaninemanganese(I1) except that sometimes a band at 1740 ern.-' appeared. This band is considered t o be due to the C=O stretching vibration and probably belongs to some oxidation product of the pht'halocyanine ring. When phthalocyanineoxo-pyridinemanganese( IV ) was refluxed in pyridine containing ZdL,i, water in contact with air, the blue color readily disappeared. After prolonged boiling, t,he formation of phthalimide having t,he strong C=O band around 1750 an.-' could be shown kiy comparing the infrared spectrum of the residue with the infrared spectrum of an authentic sample of phthaliniide. Synthesis: a. Phthalocyaninemanganese(11)(I).-This compound was prepared according to the method of Itutter and RIcQueeni4from manganese acetate and phthalonitrile. The product (yield; 527%) was purified by vacuum sublimation at 420" mm.). It also was prepared by the method of Barrett, Dent, and LinsteadI3by fusing manganese dioxide and phthalonitrile together. The chloronaphthalene extraction was omitted. The crude material was sublimed as above and long, fibrous black needles were obtained. The visible and infrared spectra for both samples were identical. The magnetic moment of this compound was 4.33 Bohr magnetons (8, +20° K.) corresponding to about 3 unpaired electrons with some orbital contributions. .lnnl. Calcd. for C32HIR?ITRRln: C, 6i.73; H, 2.84; S , 19.iS. Found: C, 67.7; H, 2.99; Y,19.7. b, Attempts to Prepare Phthalocyaninedipyridinemanganese (11)(II).-Sublimed phthalocyaninemanganese(11)was dissolved in t'he absence of air in pyridine which had been freshly distilled from barium oxide. The pyridine was distilled off in a vacuum rot,ating evaporator. In contact with thc air the green precipitate slowly became brown. A wliitioii in pyridine prepared in tht: absence of air showed 716 aiid 620 nip bitiids, indicating that oxidation had taken place. c. Phthalocyanine-oxo-pyridinemanganese(1V) (III).Sublimed phthalocyaninemanganese( 11) (-50 mg.) was dissolved in pyridine ( -100 ml.) at room temperature. The solritioii W:IS :~llowedt o stand for :I few days exposed t o the air :ind concentrated (cold). The product crystallized as large purple rhombs with a metallic luster. After washing threr times with pyridine and oncc with water they mere dried in a vacuuni desiccator. The complex gives off pyri-
2530
G. ENGELSMA, A. YAMAMOTO, E. MARKHAM, AKD AI. CALVIN
dine on heating in vacuo a t 190" aa detected with a mass spectrometer. On heating the crystals a t 420" in vacuo, phthalocyaninemanganese( 11)was obtained aa sublimate and COz gas was formed. The spectrum in pyridine haa a maxi-mum-at 620 mp with a log of 4.94. Anal. Calcd. for C3,HnN90Mn: C , 67.07; H, 3.19; N, 19.03. Found: C. 67.34: H. 3.38: N. 18.92. d Phthalocyanine-hydroxo-methanolmanganese(111) (IV).-Phthalocyaninemanganese(I1) was extracted in a Soxhlet extractor with methanol. The complex crystallized as dark needles in the boiler. They were filtered off, washed with methanol, and dried in a vacuum desiccator. The com lex gives off the methanol on heating in uacuo at 70" aa c o d be shown with the mass spectrometer. At 190" in uucuo, the formation of COZalso was observed. On heating the crystals to about 400" in vacuo, we obtained a sublimate for which the solid spectrum was identical with the solid spectrum of phthalocyaninernanganese(11). A n d . Calcd. for C33H21N802Mn:C, 64.29; H , 3.43; li, 18.18: illn.8.91. Found: C,64.30; H.3.39; N, 18.44; h h , 8.94 (calcd. for residue). e. Phthalocyanine-hydroxo-ethanolmanganese(II1) (V).-Phthalocyaninemanganese(I1) waa extracted in a Soxhlet apparatus with ethanol. The dark een crystals were washed with ethanol and ether and d r i e 8 n a vacuum dpnirrxtor -__. - - - -. . C, 64.69; H , 3.67; N, Anal. Calcd. for C34H2SN80zMn: 17.85. Found: C. 64.75; H, 3.58; N, 17.87. Phthalocvanine-acetat04 acetic acid )-manganese(II1) f (VI).-Phthaloiyaninemanganese( 11) ( I ) was ex6acted in a Soxhlet extractor with glacial acetic acid containing 5% acetic anhydride. The dark green crystals were washed with acetic acid and ether and dried in a desiccator. And. Calcd. for C3eH23Ns04Mn:C, 63.01; H, 3.23; N , 16.42. Found: C, 63.24; H, 3.45; N, 16.51. g. Phthalocyanine-chloro-methanolmanganese(II1) (VII).-Methanol was saturated in the cold with sodium chloride and a trace of hydrochloric acid was added. With this solution, phthalocyaninemanganese( 11) was extracted in a Soxhlet apparatus. The dark green crystals were washed with methanol and ether and dried in a desiccator. Anal. Calcd. for CaaHzoNsOMnCl:C, 62.46; H, 3.02; 9, 17.75; C1, 5.59. Found: C , 62.74; H, 3.09; N, 17.72; C1, 5.83. This complex was also prepared from phthalocyanine-oxopyridinemanganese(1V) (111). Three volumes of methanol were added to one volume of a solution of phthalocyanineoxo-pyridinemanganese( IV) in pyridine. After one hour the solution waa saturated with sodium chloride. The dark green precipitate waa filtered off after 12 hours, washed three times with water. and then with acetone. It waa dried in a desiccator, Anal. Found: C, 62.63; H,.2.74; N, 17.64; C1, 5.43. h. Phthalocyanine-chloro-pyndmemanganese(111)(VIII). -A solution of phthalocyanine-oxo-pyridinemanganese(IV) was prepared by dissolving 50 mg. of sublimed phthalocyaninemanganese(I1) in 200 ml. of pyridine and allowing the solution to stand in contact with the air for 24 hours. Fifty mg. of pyridine hydrochloride then was added. The blue solution gradually turned to green and fine crystals separated out. After two days the crystals were filtered off, washed with pyridine and anhydrous diethyl ether, and dried in a vacuum desiccator over potassium hydroxide. Anal. Calcd. for Cs7HzlN9MnC1: C, 65.16; H, 3.10; Mn. 8.05:. C1,. 5.20. Found: C , 64.49; H , 3.30; Mn, 7.92; c1, 6.00. The same complex was obtained on dissolving phthalocyanine-chloro-rnethanolmanganese(111) (VII) in pyridine in the cold and concentrating the solution in vucuo. i. Phthalocyanine-chloro-pyridinemanganese(II1) Pyridine Hydrochloride (XIIIa).-Dry HCl gas was passed into a solution of phthalocyanine-oxo-pyridinemanganese(I V ) in pyridine, prepared as above, until the color changed to green. After one hour the dark green precipitate of the manganese( 111) complex was separated from the solution by centrifugation. It waa washed n;ith pyridine and ether, and dried in a vacuum desiccator. Anal. Calcd. for CaHnNloMnClt: C, 63.29; H, 3.29; N,I;.C,T; CI, 8.90. Found: C, G3.01; H, 3.27; N, 17.00; c1: 8.54. J. Phthalocyanine-acetato-pyridinemangmese(111)(IX). -One ml. of glacial acetic acid was added to 100 ml. of it pyridine solution of phthalocyanine-oxo-pyridinemanganese-
.
.
Vol. 66
(IV) prepared from 80 mg. of phthalocyaninemanganese( 11). The blue solution turned gradually to green and fine crystals were formed slowly. They were filtered off after two days, washed with pyridine and diethyl ether, and dried in a vacuum desiccator over potassium hydroxide. And. Calcd. for Ca8Hz1NeOzMn:C, 66.09; H, 3.07; N, 18.26; Mn, 7.95. Found: C , 66.40; H, 3.41; N, 18.29; Mn, 7.85. k. Attempted Preparation of Phthalocyanine-hydroxopyridinemanganese( 111) (X) .-Phthalocyaninemanganese(11) waa dissolved in a mixture of equal amounts of pyridine and water. The solution was filtered and then evaporated to dryness in a vacuum type rotating evaporator. The green residue became violet on contact with the air. A solution in pyridine, prepared in the absence of air, showed the 620 mp (Mn(1V)) band. 1. Phthalocyanine-cyano-ethanolmanganese( 11) Sodium (XI).--Phthalocyaninemanganese( 11) (I) waa dissolved in the cold in ethanol saturated with sodium cyanide. During this process the solution waa swept with nitrogen. The solution was filtered, after which the solvent waa distilled off in vacuo. The green residue was washed three times with water to remove the excess sodium cyanide. After washing with acetone, the compound was dried in a desiccator. Anal. Calcd. for C S H B N ~ O M ~ NC, ~ :63.44; H, 3.35; N, 19.04. Found: C, 63.14; H, 3.22; N, 19.32. m. Phthalocyaninedicyanomanganese(II1) Sodium (XIII).-Phthalocyaninemanganese(I1) ( I ) waa dissolved in boiling ethanol which waa saturated in the cold with sodium cyanide. After refluxing for two hours, all the manganese(I1) complex was oxidized as could be seen from the disappearance of the 827 mp band in the spectrum. On cooling, the manganese( 111) complex crystallized aa green needles, After washing three times with water and once with acetone, they were dried in a desiccator. Anal. Calcd. for Ca4Hl8NloMnNa: C, 63.52; H, 2.51; N, 21.79. Found: C, 63.52; H, 2.66; N, 21.31.
n. Phthalocyaninedihydroxomanganese(II1) Sodium (XV).-Phthalocyaninemanganese( 11) waa extracted in the cold with a strong solution of sodium hydroxide in ethanol. .4fter filtration, the extract was evaporated to a small volume zn vacuo. After standing for one night, the blue-green precipitate waa filtered off and extracted three times with water. It then waa waahed with acetone and dried in a desiccator. Anal. Calcd. for CstHtsN802MnNa: C, 61.59; H, 2.91; N, 17.95. Found: C, 62.13; H , 3.74; N, 17.83. 0 . Etio orphyrin 1.-Twenty g. of 5-bromo-4,3'-dimethyl-5'-~romomethyl-3,4'-diethylpyrromethane hydrobromide (made by bromination of cryptopyrrole according to Fischer and Orth)18 was heated in 80 g. of succinic acid a t 190-200" for one hour. After cooling, the hard cake was powdered and the succinic acid waa extracted with a 10% NaOH solution. The residue then waa treated with chloroform to dissolve the etioporphyrin I. This solution was purified by chromatography over an aluminum oxide (Merck) column. The chloroform solution then was concentrated in uacuo and methanol was added to crystallize the etioporphyrin I. The spectrum in pyridine shows maxima a t 376 mp (log e 4.90), 399 mp (log e 5.15), 471 mp (a shoulder, log E 3.43), 498 mp (log E 4.10), 503 mp (a shoulder, log e 4.06), 532 mp (log E 3.95), 558 mp (a shoulder, log E 3.31), 568 mp (log E 3.77), 576 mp (a shoulder, log e 3.66), 596 mp (log e 3.091, 611 mp (a shoulder, log e 3.16), 622 mp (log e 3.69), and 652 mp (log e 3.38). Anal. Calcd. for C32H3SN4: C, 80.3; H, 8.0; N,11.7. Found: C,80.2; H , 7.8; N, 11.9. p. Etioporphyrin I Acetato-(acetic acid)-manganese(II1). -Five hundred mg. of etioporphyrin I was extracted from an extraction thimble into 100 ml. of glacial acetic acid containing 500 mg. of manganese chloride and 500 mg. of sodium acetate. The solution was concentrated to 25 ml. and the product which separated was washed with water and dried. To purify the product it was sublimed under high vacuum a t
x w ..
Anal. Calcd. for C36H43N404Mn:C, 66.4; H, 6 . 7 ; N, 8.6. Found: C , 67.5; H, 6.5; X , 8.5. The absorption curve in pyridine has maxima at: 371 mp (log e 4.75), 395 mp (a shoulder, log e 4.51), 471 mp (log e 4.51), 547 mp (log e 4.02), 580 nip (a shoulder, log e 3.721, (18) 13. Fisolier and 11. O r t h , "Die Cheiriie des Pyrrols," Band 11, 1. Halfte, 106 (1937).
Dec., 1962
PHOTOREDUCTION OF UROPORPHYRIN
653 mp (log e 3.44), 675 mfi (log c 3.45), 742 mp (log e 3.49), and 797 mp (log e 3.26). a. Etiooomhvrin I CobaltlII).-This and the iron compl& were 'prepared according to Fischer and Orth.19 Five hundred mg. of etioporphyrin I waa extracted from a thimble into 100 ml. of glacial acetic acid containing 600 mg. of CoC12.6H20 and 600 mg. of sodium acetate. The product waa purified by vacuum sublimation at 350'. (19) H. Fischer and H. Orth, "Die Chemie des Pyrrola," Band 11, 1. Hblfte, 193 (1937).
2531
A n d . Calcd. for CsHaNaCo: C, 71.7; H, 6.8; N, 10.5. Found: C, 71.5; H,6.8; N, 10.8. r. Etioporphyrin I Chloroiron(III).-Five hundred mg. of etioporphyrin I waa extracted from a thimble into 100 ml. of glacial acetic acid containing 500 mg. of ferric chloride and 500 mg. of sodium acetate. The precipitate was filtered off and extracted with water. After washing with methanol the product waa dried in a desiccator. Anal. Calcd. for ClzHzsN4FeCl: c1, 6.24. Found: c1, 6.87.
THE PHOTOREDUCTION OF UROPORPHYRIN: EFFECT OF pH O N THE REACTION WITH EDTA BY D. MAUZERALL The Rockefeller Institute, New York 81, N . Y . Received May
106.9
The quantum yield of the photoreduction of uroporphyrin to the dihydroporphyrin in 0.1 i b' EDTA reaches a maximum of 0.4 a t pH 5.7, and is independent of the wave length of the exciting light and of temperature between 3 and 56". The
data are consistent with the reaction of the free amine with the protonated, excited porphyrin.
Introduction The photoreduction of porphyrins leads to dihydro- and tetrahydroporphyrins in which the hydrogens are added to the methine bridges. A variety of evidence for these structures has been obtained.' Bis-tertiary amines were very useful as mild reducing agents in this work. However, the pH dependence of the reaction of porphyrins with ethylenediaminetebraacetic acid (EDTA) was different from that found with most other dyes. Since these differences may give direct evidence concerning the reactive photo-excited state of the porphyrin, they were investigated in detail. Experimental Uroporphyrin isomer I11 was isolated from feathers of the Turaco bird, The porphyrin and other materials and most of the experimental methods have been described previously.' A braas block with suitable windows served both to define the area of the photochemical light beam and to act as a thermostat in the cell compartment of the spectrophotometer. Heating or cooling fluid was circulated through channels in the block. For experiments at very low temperatures the whole block waa suspended in a dewar flask with three windows. Oxygen was removed by either freeae-thawing the solution in Vacuo (0.01 mm.) with intermittent flushing with repurified nitrogen and sealing off the cell, or by bubbling Relium through the solution. Diffusion of oxygen through the Teflon capillary tubing was greatly reduced by using concentric tubes, m t h helium flowing through both. The inner tubing used for deoxygenation was thus in an atmosphere of almost pure helium. The amount of residual oxygen in the solution was estimated by measuring both the (very slow) rate and the extent of reoxidation of the reduced porphyrin or other dye. With allowance for the disproportionation of the dihydroporphyrin' the average oxygen concentration was about 5 X 10-7 M . Monochromatic light was obtained from a 500-w. tun sten projection lamp and interference filters of average f a l f band width of 5 mp, and suitable blocking filters. Over the range of wave lengths absorbed by the porphyrin in the Pyrex cell, 300 to 650 mp, these filters transmitted less than 0.1% of light of wave lengths outaide the band pass. The energy of this light beam waa measured with a thermopile (Eppley) and a microvoltmeter (Keithle 150 A). The accuracy was &3%. The intensity of t l e 398 mp (1) D. Maueerall, J . Am. Chem. SOC.,84, 2437 (lg62).
light also waa determined with the ferric oxalate actinometer,Z and agreement within 10% was obtained. The average light intensities ranged from 0.16 to 5.0 X einstein sec.-l at 398 and 605 mp, respectively. The fraction of light absorbed by the solution varied from complete absorption a t the Soret band, 398 mp, to 10% a t 605 mp a t the usual concentration, 2 X 10-6 M. The number of molecules converted per short, usually lo-sec., illumination period waa calculated from changes in the absorption of the dihydroporphyrin a t 440 or 735 mp and the known extinction coefficients of the porphyrin and phlorin and the volume of the solution. These changes were a t least 20 times the photometric error, f0.001 A. The quanta absorbed were calculated from the measured absorption spectra of the porphyrin under these conditions and the percentage of reaction which had occurred. An average of only 3% reaction per illumination period allowed linear corrections for changes in light absorption, back reflection, and screening to be made with small error. The illuminating wave length waa changed after measuring the photoreaction rate over a range of two to sixteen in light intensity by the use of neutral density filters. An average of six measurements at each wave length was made. When a sealed cell was used for the experiments a t various temperatures, the solution was not stirred, and the illumination waa confined to wave lengths where low (10%) absorption of light occurred. The helium bubbling technique allowed stirring during and/or after illumination. There waa ood agreement between the results obtained by the two met%ods (Table I, sealed tubes, and Fig. 1, helium). The over-all accuracy of the quantum yield determinations is f10%.
TABLE I EFFECTOF TEMPERATURE ON THE QUANTUMYIELD OF FORMATION OF UROPHLORIN FROM UROPORPHYRIN (2 x lod M) IN EDTA (0.1 M,pH 5.9, 25") Temp., OC.
-Quantum
2.8 25.5 56.4 86.0
0.41
605 rnr
.38 .36 .20
yield-
502 m p
0.37 .37 .40 .15
Results The quantum yield of the photoreduction of uroporphyrin I11 to the dihydroporphyrin, uro(2) C. G . Hatahard and C. A. Parker, Proc. Row. SOC. (London), AP86, 618 (1956).
