The Kinetics of the Incorporation of Metals into Tetraphenylporphyrin

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The Kinetics of the Incorporation of Metals into Tetraphenylporphyrin with Metal Salts in High-Temperature Water Takafumi Sato,† Katsutoshi Ebisawa,† Kiwamu Sue,‡ Satoshi Ito,† Takeru, Saito,† and Naotsugu Itoh†,* †

Department of Material and Environmental Chemistry, Utsunomiya University, 7-1-2, Yoto, Utsunomiya, 321-8585, Japan Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

‡

ABSTRACT: The incorporation of cobalt, nickel, copper, and oxovanadium(IV) into nonpolar 5,10,15,20-tetraphenyl21H,23H-porphyrin (H2TPP) occurred with their sulfates, nitrates, and chlorides in high-temperature water. The yield of metalloporphyrin significantly increased with increasing temperature for cobalt, nickel, and copper sulfates from 473 to 673 K, which means that the high temperature region was preferred for the incorporation of metals into the porphyrin structure. In hightemperature water, most of H2TPP dissolved, whereas almost all of metals probably existed in solid phase. The incorporation of metal into a porphyrin structure was almost first-order with respect to H2TPP and probably proceeded through the preequilibrium state between metal ion and H2TPP.

1. INTRODUCTION

Water can be used as a synthesis solvent for only polar porphyrins dissolved in water. The incorporation of metals into water-soluble porphyrins such as tetrapyridylporphyrine and porphyrin dimethyl ester proceeds in water,14−20 although most porphyrins are nonpolar and insoluble in water. The use of water makes this method environmentally friendly. Hightemperature water above 473 K has many favorable properties for chemical synthesis:21,22 it is a low-density liquid, and the dielectric constant of water at 573 K is around 20 compared with that of ambient water around 80, which makes hightemperature water have the characteristics of a polar organic solvent that dissolves organic compounds.21,22 After the synthesis of organic compounds, the separation of organic products from water can be easily done by cooling at ambient conditions. Further, high-temperature water dissolves inorganic species to some extent. For example, copper oxide and sodium salts slightly dissolved in high-temperature water.23,24 The concentration of inorganic species in the liquid phase greatly affects the inorganic reactions such as nucleation and growth in high-temperature water, and the calculation of the concentration of inorganic species helps to understand the reaction mechanism.25,26 The metal incorporation into organics in hightemperature water has been rarely reported, and the reaction fusing organics and inorganics will have a powerful impact on synthesis processes. In a preliminary communication, we reported that the incorporation of some metals in the porphyrin structure occurred in high-temperature water;27 however, the kinetics of the incorporation of metal into porphyrin structure has been in question. In this study, we examined the incorporation of metals in tetraphenylporphyrin in high-temperature water as shown in Figure 1. The metals we tested were cobalt, nickel, copper, and

Porphyrins have been key compounds for the chemical industry. Their photoelectro-properties such as strong absorption bands in the UV−visual region and a redox center opened a wide field of application. The incorporation of metal into porphyrin structure makes the properties of porphyrin change, which provides a variety of physical and chemical properties such as structure and absorption band.1 Porphyrins are used for source chemicals of solar battery, catalysts, and photosensitizers in photodynamic therapy. Recently, benzoporphyrins were used for an organic semiconductor as one of the important compounds of the organic electroluminescence display and organic transistor.2−4 Several methods to incorporate metals into the porphyrin structure have been reported. Metal-tetraphenylporphyrins are synthesized in organic acid and base medium.5−7 In these methods, the acid medium typically requires a large excess of metal salt to force the equilibrium to the product side, and base medium can make complexes with the metal ion to suppress the reaction between metal and porphyrin. The microwave heating of organic solvent also gives metalloporphyrin.8 On the other hand, these methods usually require undesirable expensive metal organics as a metal source. The syntheses in polar organic solvents such as dimethylformamide, dimethylsulfoxide, tetrafydrofuran, and methanol have been studied,9−13 and this technique has become a major synthesis method at present. Polar organic solvents have good solubility for both porphyrin and other species containing metals. In particular, aprotic organic solvents are useful because they enable the use of a large variety of porphyrin and metals.9 Both porphyrin and metal salts such as metal acetates, halides, hydroxides, and carbonates dissolve in polar organic solvents, and the solutions are refluxed to provide stoichiometric yield of metalloporphyrins.9 However, the aprotic organic solvents are difficult to remove after the reaction finishes because the high boiling point of solvent makes the distillation of solvent difficult. © 2012 American Chemical Society

Received: Revised: Accepted: Published: 13908

December 24, 2011 September 13, 2012 October 3, 2012 October 3, 2012 dx.doi.org/10.1021/ie2030294 | Ind. Eng. Chem. Res. 2012, 51, 13908−13914

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of H2TPP loaded basis: yield (%) = (moles of metal-TPP or H2TPP)/(moles of H2TPP loaded) × 100. 2.3. Observation of Dissolution of Porphyrin in Water. We observed the dissolution of H2TPP in water using a view cell for high pressure and high temperature conditions (Taiatsu Techno, Tokyo). Figure 2 shows the schematics of the cell. The Figure 1. Incorporation of metals into tetraphenylporphyrin in hightemperature water.

vanadium. We confirmed the effect of metal, counterion, and temperature, and estimated the state of porphyrin and inorganic species in the reaction field. Finally, we proposed the reaction model in high-temperature water by considering the reaction rate.

2. EXPERIMENTAL SECTION 2.1. Materials. We used 5,10,15,20-tetraphenyl-21H,23Hporphyrin (H2TPP: Wako Pure Chemical, Ltd.) as a porphyrin. This H2TPP had a purity of 96% by our analysis. Cobalt(II) sulfate heptahydrate (99.0%, purity), nickel(II) sulfate hexahydrate (over 99.0%), copper(II) sulfate pentahydrate (99.5%), cobalt(II) nitrate hexahydrate (98.0%), nickel(II) nitrate hexahydrate (98.0%), copper(II) nitrate trihydrate (99.9%), cobalt(II) chloride hexahydrate (99.0%), nickel(II) chloride hexahydrate (98.0%), copper(II) chloride dihydrate (99.0%), and sodium carbonate (99.5%) were purchased from Wako Pure Chemical Ltd. The oxovanadium(IV) sulfate n-hydrate (over 55.0% purity) was purchased from Kanto Chemical Co., Inc., as a vanadium salt. 2.2. Reaction Experiments. Reactions for the incorporation of metals to H2TPP were conducted with stainless steel (316) batch-type reactors whose internal volume was 6 cm3. The 0.02 g of H2TPP, 0.032 g of sodium carbonate, and a certain concentration of 3.0 g of metal salt aqueous solution were loaded into the reactors. Sodium carbonate was an additive used for the prevention of corrosion inside the reactor.28 The air in the reactors was purged with argon gas and the reactor was sealed. The molar amount of H2TPP and sodium carbonate were 3.3 × 10−5 mol and 3.0 × 10−4 mol, respectively. In the case of cobalt, nickel, and copper metal salts, the concentration of metal aqueous solution were 0.01, 0.1, and 0.5 mol/kg corresponding to 3.0 × 10−5, 3.0 × 10−4, and 1.5 × 10−3 mol, respectively. In a typical case, 3.0 × 10−4 mol of metal was loaded and the molar ratio of metal to H2TPP was 9:1. In the case of oxovanadium(IV) sulfate, the amount of vanadium was over 0.055 mol/kg, which corresponded to a molar ratio over 5.0 of vanadium to H2TPP. After loading the reactor, it was submerged into a sand bath that was controlled at the reaction temperature. The heat-up time was about 4 min. After the reaction time, the reactors were taken out of sand bath and rapidly quenched in the water bath to stop the reaction. The reaction time included the heat-up time. The inside of the reactor was rinsed with chloroform several times to recover the sample. The recovered samples were fractionated by silica gel column with a mixture of chloroform and n-hexane in a weight ratio of about 1:1 as a developing solvent. Each solution of product and reactant was evaporated and weighed. Qualitative analyses were conducted by UV−vis spectroscopy (V-560, JASCO Corporation) by comparing each spectra to literature values29,30 and by MALDITOF-MS (autoflex II, Bruker Daltonics Inc.) measuring the molecular weight. The product yield was defined on 96% purity

Figure 2. The schematics of a view cell for high-pressure and hightemperature conditions.

cell was a horizontal cylindrical shape (i.d. 14 mm) made from inconel alloy-22, and sapphire windows were embedded at each end to enable the observation of inside. The internal volume of cell was 11.5 cm3, and a thermocouple was inserted and a magnetic stirrer was placed inside the cell. The body of the cell contained four cartridge heaters, was placed on magnetic stirrer controller (C-MAG HS 7, IKA) that can heat, and was covered with a heat insulator jacket. The pressure gauge (GC61, Nagano Keiki Co., Ltd.), high-pressure valve (SS-ORS2, Swagelok), and relief valve (SS-4R5A, Swagelok) were attached to the upper side of view cell and the volume of this space was about 3.5 cm3. In this study, 5.0 g of water and 0.033 g of H2TPP were introduced into the view cell, which corresponded to almost the same ratio of H2TPP and water in the reaction experiments described above. After the loading, heating was started and the inside of the cell was sometimes stirred. The inside of the cell was continuously observed with a video camera, and the temperature and pressure in the reactor were also monitored.

3. RESULTS 3.1. Incorporation of Metal into Porphyrin Structure with Various Metal Salts. Figure 3 shows the yield of H2TPP remaining, CuTPP, and others versus reaction time at 623 K for CuSO4 as a metal salt. We evaluated others by using the sum of

Figure 3. The yield of CuTPP, H2TPP, and others with reaction time with 0.1 mol/kg CuSO4 aqueous solution at 623 K: (○) H2TPP, (Δ) CuTPP, (□) others. 13909

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the yield of H2TPP and CuTPP and subtracting from 100%. The main product was CuTPP, and the yield of CuTPP increased while the yield of H 2 TPP decreased. The incorporation of copper into the porphyrin structure proceeded in high-temperature water. The yield of others slightly increased with reaction time, indicating that the side reaction proceeded to a small extent. However, the maximal yield of others was only below 5%, which means that porphyrin structure was almost stable and the main reaction selectively proceeded by using CuSO4. Figure 4 shows the yield of metal-TPP for metal sulfate, nitrate, and chloride salts at 623 K. Cobalt, nickel, and

Figure 5. Effect of temperature on the yield of metal-TPP with 0.1 mol/kg metal sulfate aqueous solutions for 60 min: (a) CoSO4 aq., (b) NiSO4 aq., (c) CuSO4 aq.; (○) H2TPP, (Δ) metal-TPP, (□) others.

the incorporation of metals into the porphyrin structure, and the porphyrin structure was relatively stable in metal sulfate aqueous solutions. We evaluated the stability of H2TPP in the absence of any reagents in supercritical water for 60 min. The framework structure of H2TPP was stable, although 90% of H2TPP decomposed, and metal containing compounds related to the metal in stainless steel were produced at 673 K. In the presence of sodium carbonate and metal salts, the effect of stainless steel should be small because a high yield of the metalTPP was obtained at 673 K. Figure 6 shows the observation of the dissolution of H2TPP in water for the H2TPP−water system. Moles of water are extremely larger than those of H2TPP, and the pressure in the cell is dependent on the partial pressure of water. There were two phases in the reactor below the critical temperature of water. The saturated vapor pressure of water increases with temperature and the calculated value are 4.0, 8.6, 12.0, and 16.5 MPa at 523, 573, 598, and 623 K, respectively.31 The 0.44 g/ cm3 of water density corresponds to the amount of loaded water and provides 22.7 MPa at 648 K in the supercritical state.31 The pressure inside the reactor should almost obey the theoretical behavior of pure water, although the pressure in the cell was slightly lower than those of the calculated values due to the effect of dead space of the cell. The water density of gas phase and liquid phase changes with temperature. Those (liquid phase g/cm3, gas phase g/cm3) are (0.99, 8.3 × 10−5), (0.79, 0.03), (0.71, 0.05), (0.65, 0.07), and (0.58, 0.11) at 323, 523, 573, 598, and 623 K, respectively.31 The water density of liquid phase decreases with increasing temperature while that of gas phase increases. At 323 K, H2TPP is seen as a solid phase above water. H2TPP was insoluble in water around ambient conditions. The color of liquid phase became darker with increasing temperature from 523 to 598 K, while the color of gas phase was transparent. At 623 K, the color of liquid phase was black and that of gas phase was light black. H2TPP mainly dissolved in the liquid phase. The increase in temperature makes the dielectric constant of water decrease so that organics can dissolve in

Figure 4. The yield of metal-TPP for metal sulfate, nitrate, and chloride salts (623 K, 60 min, 0.1 mol/kg for cobalt, nickel, and copper salts, over 0.055 mol/kg for oxovanadium(IV) sulfate).

vanadium as well as copper were incorporated into the porphyrin structure. In the case of chloride salts, the yield of CoTPP, NiTPP, and CuTPP were constantly over 60%. The chloride salts were favorable for the synthesis of metalloporphyrin regardless of metals. In the case of sulfate salts, the yield of NiTPP was lower than those of CoTPP and CuTPP. In literature, the apparent incorporation rate constant of copper and cobalt into the porphyrin structure was larger than that of nickel in polar organic solvent with Metal(ClO4)211 and water with Metal(NO3)2.14,20 A similar trend was observed in this system. In the case of nitrate salts, the yields of metalTPP were lower than those of other salts and the yield of CuTPP was the lowest. The reaction with cobalt nitrate and copper nitrate gave many unidentified compounds. The existence of NaNO3 rather than NaCl makes the reaction rate slower in the incorporation of copper into the porphyrin structure in aqueous solution.17 Both the side reaction and the suppression effect of nitrate salt in aqueous solution probably led to the small yield of metal-TPP by using nitrate salt in hightemperature water. 3.2. Effect of Temperature. Figure 5 shows the effect of temperature on the incorporation of cobalt, nickel, and copper into a porphyrin structure with metal sulfate aqueous solutions. The yield of metal-TPP increased with increasing temperature and significantly rose around 600 K for all metals, while the residual yield of H2TPP decreased. At 673 K, the yield of metalTPP was more than 86% in all cases. The maximal yield of others was 14% and usually below 10% regardless of temperature. The high-temperature region was preferred for 13910

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Figure 7. The calculated concentration of main species containing metal in the solid phase and the liquid phase against temperature for 0.1 mol/kg metal−SO4 and 0.1 mol/kg of Na2CO3 aqueous solution. Co-S, cobalt in solid phase: (○) Co(OH)2, (Δ) CoO. Co-L, cobalt in liquid phase: (○) Co2+, (Δ) CoOH+. Ni-S, nickel in solid phase: (○) Ni(OH)2, (Δ) NiO, (□) NiCO3. Ni-L, nickel in liquid phase: (○) NiSO4,aq, (Δ) Ni2+. Cu-S, copper in solid phase: (○) Cu(OH)2, (Δ) Cu2(OH)2CO3, (□) CuO. Cu-L, copper in liquid phase: (○) Cu2+, (Δ) CuCO3,aq.

Figure 6. The observation of the dissolution of H2TPP in hightemperature water: (a) 323 K, 0.1 MPa; (b) 523 K, 3.4 MPa; (c) 573 K 7.8 MPa; (d) 598 K, 11.2 MPa; (e) 623 K, 16.0 MPa; (f) 648 K, 21.3 MPa.

water easier. The entire inside of the cell became black at 648 K in a supercritical state of water, indicating that H2TPP dissolved into supercritical water. These observation results clearly show that the dissolution of H2TPP was enhanced in high temperature region. Here, we calculated the concentration of inorganic species in the gas, liquid, and solid phases. The concentration of inorganic species in the gas, liquid, and solid phases up to 623 K were calculated by the OLI Analyzer studio 3.1 from OLI systems, Inc.32 The initial concentration of CoSO4, NiSO4, CuSO4 was 0.1 mol/kg and that of Na2CO3 was 0.1 mol/kg. Figure 7 shows the calculated concentration of the main species containing cobalt, nickel, and copper in the solid and liquid phase with temperature; the minor species are not shown in this figure. The concentration of the species containing metals in the gas phase was negligible. In the case of cobalt, the main species in the solid phase was CoO above 398 K. In the liquid phase, the main species were Co2+ and Co(OH)+, and the concentration of those decreased with increasing temperature. The minor species were Co(OH)2,aq, CoOH+, Co(OH)42− and Co(OH)3−. Above 498 K, over 99.9% of cobalt existed in the solid phase. In the case of nickel, the main species in the solid phase were NiCO3 and Ni(OH)2 below 418 K and NiO over 418 K. The main species in the liquid phase were NiSO4,aq, and Ni2+, and

the minor ones were NiOH+, Ni2OH3+, Ni4(OH)44+, Ni(OH)2,aq, and Ni(OH)3−. The concentration of metals in the liquid phase decreased with increasing temperature, and over 99.9% of the nickel containing species was NiO in the solid phase above 513 K. In the case of copper, the main species in the solid phase changed in the order of Cu2(OH)2CO3, Cu(OH)2, and CuO with increasing temperature. In the liquid phase, the main species were Cu2+ and CuCO3,aq, and the concentration of these species decreased with increasing temperature over 450 K. The minor species were Cu+, Cu(OH)+, Cu(OH)3−, Cu(CO3)22−, and Cu(OH)42−. For all temperature ranges, the concentration of species containing copper in the solid phase was almost 0.1 mol/kg, which corresponded to the initial amount of copper, whereas the concentrations of species containing copper in the liquid phase were significantly lower than those in solid phase. In all cases, almost all of metals existed in the solid phase and a very small amount of metal was in the liquid phase in hightemperature water. Considering the incorporation of metals into the porphyrin structure should occur in the liquid phase, the reaction probably proceeded in the liquid phase in which most of the H2TPP and a very small amount of species 13911

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containing metal dissolved. At 623 K, the main species containing metal in the liquid phase were CoOH+, NiSO4,aq, and CuCO3,aq, and the concentrations of these were 6.12 × 10−8, 4.24 × 10−8, and 2.97 × 10−6 mol/kg, respectively. In the presence of metal sulfate, the yield of Cu-TPP was higher than those of Co-TPP and Ni-TPP as shown in Figure 4, which is probably due to a higher concentration of CuCO3,aq than of CoOH+ and NiSO4,aq. 3.3. Reaction Kinetics. We conducted a series of experiments with CuSO4 and H2TPP over a range of initial concentrations of CuSO4 from 0.01 to 0.5 mol/kg at 623 K. In these experiments, the main product was CuTPP only. Here, we assumed that the initial concentration of H2TPP in the reactor represented the concentration of initial H2TPP in liquid phase, because both H2TPP and metal-TPP would be always in the liquid phase at 623 K by considering that the reaction occurred in the liquid phase, the solubility of H2TPP and metalTPP in liquid phase was probably similar, and above 80% of H2TPP reacted with copper to form CuTPP in liquid phase at 623 K. Figure 8 shows a plot of −ln(CH2TPP/CH2TPP,initial) versus

Cu 2 + + H 2TPP ⇌ Cu 2 +; H 2TPP

(1)

k2

Cu 2 +; H 2TPP → CuTPP + 2H+

(2)

2+

where Cu ;H2TPP is the intermediate of the reaction. We calculated the existence form of copper for a wide range of initial concentration of CuSO4 in high-temperature water by changing the initial concentration of CuSO4 and using the same method described above. Table 1 shows the calculated concentration of the main species containing copper against the initial concentration of CuSO4 at 623 K. The concentration of Cu2+ in the liquid phase remarkably increased about 1016 times with increasing initial concentration of CuSO4 from 0.01 to 0.5 mol/kg. The first-order reaction with respect to H2TPP clearly shows that the reaction rate was insensitive to Cu2+. For the reaction mechanism including the pre-equilibrium reaction expressed as eq 1 and 2, the overall reaction rate constant for H2TPP is expressed as kall = k 2K1[Cu 2 +]/(1 + K1[Cu 2 +])

(3)

where k2 is the first-order rate constant for eq 2 and K1 is the stability constant of the pre-equilibrium reaction as eq 1. We fit the models to the all experimental data of Figure 8, and obtained k1 = 3.38 × 10−4 s and K1 = 2.16 × 1017 kg/mol. The straight line going through the origin in Figure 8 shows the concentration of H2TPP calculated from eq 3 by using these parameters, which suggests that the reaction rate can be expressed by using eq 1 and eq 2. The magnitude of K1 should be reasonable because a stability constant of metal complexes can be over 1010 in aqueous solution in general, although K1 for the incorporation of copper into porphyrins in dimethyl sulfoxide and water at ambient condition is several tens in magnitude.10,13,14 The dielectric constant of water at 623 K is about 10 compared with 41.9 for dimethyl sulfoxide at 328 K and 60.9 for water at 353 K.22,33 The polarity of solvent affects the reaction by the solvation of both reactant and product sides, including transition state to stabilize their forms.22,34,35 In the reaction of eq 1 and 2, Cu2+;H2TPP can be considered as an intermediate. The very low dielectric constant would make ionic species such as Cu2+ itself unstable and probably causes the shift of equilibrium of eq 1 to the formation of Cu2+;H2TPP to reduce the density of electric charge of copper ion, which may be one of the reasons for a large K1 value compared to that in dimethyl sulfoxide and water at ambient conditions. The Cu2+ being consumed for the reaction to form CuTPP that dissolved in the liquid phase should be replaced by the dissolution of Cu species to the liquid phase from CuO in the solid phase. Further, high temperature accelerates all reactions. By considering these facts, the incorporation of copper into

Figure 8. The concentration of H2TPP against reaction time at 623 K and 0.1 mol/kg of Na2CO3 aqueous solution. Initial concentration of CuSO4: (○) 0.01 mol/kg, (Δ) 0.1 mol/kg, (□) 0.5 mol/kg, (solid line) calculation according to eq 3.

reaction time within 1800 s in the region of early reaction stage. All the plots were in a similar level and tended to increase with reaction time regardless of initial concentration of CuSO4, which means that the reaction was almost first-order with respect to H2TPP. The kinetics of the incorporation of metals into porphyrin structure has been studied. In polar organic solvent and aqueous solution, the major reaction mechanism includes a preequilibrium reaction.10,13,14,19,20 This mechanism can be simply expressed as follows:10,13

Table 1. The Calculated Concentration of Main Species Containing Copper for Different Initial Concentration of CuSO4 at 623 Ka concentration of species containing copper liquid phase [×10−7 mol/kg] initial concentration of CuSO4 [mol/kg] 0.01 0.1 0.5 a

solid phase [mol/kg] CuO >0.00999 >0.0999 0.350

CuCO3,aq 0.974 29.7 30.2

Cu2+

Cu(OH)2,aq 1.06 1.07 1.07

Cu+ −10

2.96 × 10 1.24 × 10−3 1.49 × 106

Cu(OH)+ −3

5.23 × 10 2.43 7560

−12

5.81 × 10 0.124 2870

Cu(OH)3−

Cu(CO3)22−

Cu(OH)42−

5.42 2.37 × 10−3 3.98 × 10−7

0.342 5.41 × 10−5 1.50 × 10−12

1.61 2.70 × 10−7 3.3 × 10−14

Initial concentration of sodium carbonate was 0.1 mol/kg. 13912

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(8) Dean, M. L.; Schmink, J. R.; Leadbeater, N. E.; Brückner, C. Microwave-promoted insertion of group 10 metals into free-base porphyrins and chlorins: Scope and limitations. Dalton. Trans. 2008, 1341−1345. (9) Adler, A. D.; Longo, F. R.; Kampas, F.; Kim, J. On the preparation of metalloporphyrins. J. Inorg. Nucl. Chem. 1970, 32, 2443−2445. (10) Pasternack, R. F.; Vogel, G. C.; Skowronek, C. A.; Harris, R. K.; Miller, J. G. Copper(II) incorporation into tetraphenylporphine in dimethyl sulfoxide. Inorg. Chem. 1981, 20, 3763−3765. (11) Bain-Ackerman, M. J.; Lavallee, D. K. Kinetics of metal-ion complexation with n-methyltetraphenylporphyrin. Evidence concerning a general mechanism of porphyrin metalation. Inorg. Chem. 1979, 18, 3358−3364. (12) Baum, S. J.; Plane, R. A. Kinetics of the incorporation of magnesium(II) into porphyrin. J. Am. Chem. Soc. 1966, 88, 910−913. (13) Bhyrappa, P.; Nethaji, M.; Krishnan, V. Structure of nonpolar octabromotetraphenyl porphyrin and kinetics of rapid metalation reactions. Chem. Lett. 1993, 22, 869−872. (14) Fleischer, E. B.; Choi, E. I.; Hambright, P.; Stone, A. Porphyrin studies: Kinetics of metalloporphyrin formation. Inorg. Chem. 1964, 3, 1284−1287. (15) Plane, R. A.; Stein, T. P. The incorporation of zinc ion into a synthetic water-soluble porphyrin. J. Am. Chem. Soc. 1969, 91, 607− 610. (16) Hambright, P.; Fleischer, E. B. The acid-base equilibria, kinetics of copper ion incorporation, and acid-catalyzed zinc ion displacement from the water-soluble porphyrin α,β,γ,δ-tetra(4-n-methylpyridyl)porphyrine. Inorg. Chem. 1970, 9, 1757−1761. (17) Baker, H.; Hambright, P.; Wanger, L. Metal ion porphyrin interactions. II. Evidence for the nonexistence of sitting atop complexes in aqueous solution. J. Am. Chem. Soc. 1973, 95, 5942− 5946. (18) Baker, H.; Hambright, P.; Wanger, L.; Ross., L. Metal ion intereactions with porphyrins. I. Exchange and substitution reactions. Inorg. Chem. 1973, 12, 2200−2202. (19) Hambright, P.; Chock, P. B. Metal−porphyrin interactions. III. A dissociative-interchange mechanism for metal ion incorporation into porphyrin molecules. J. Am. Chem. Soc. 1974, 96, 3123−3131. (20) Turay, J.; Hambright, P. Activation parameters and a mechanism for metal−porphyrin formation reactions. Inorg. Chem. 1980, 19, 562− 564. (21) Eckert, C. A.; Bush, D.; Brown, J. S.; Liotta, C. L. Tuning solvents for sustainable technology. Ind. Eng. Chem. Res. 2000, 39, 4615−4621. (22) Akiya, N.; Savage, P. E. Roles of water for chemical reactions in high-temperature water. Chem. Rev. 2002, 102, 2725−2750. (23) Sue, K.; Hakuta, Y.; Smith, R. L., Jr.; Adschiri, T.; Arai, K. Solubility of lead (II) oxide and copper (II) oxide in subcritical and supercritical water. J. Chem. Eng. Data 1999, 44, 1422−1426. (24) Leusbrock, I.; Metz, S. J.; Rexwinkel, G.; Versteeg, G. F. Quantitative approaches for the description of solubilities of inorganic compounds in near-critical and supercritical water. J. Supercrit. Fluids 2008, 47, 117−127. (25) Sato, T.; Sue, K.; Suzuki, W.; Suzuki, M.; Matsui, K.; Hakuta, Y.; Hayashi, H.; Arai, K.; Kawasaki, S.; Kawai-Nakamura, A.; Hiaki, T. Rapid and continuous production of ferrite nanoparticles by hydrothermal synthesis at 673 K and 30 MPa. Ind. Eng. Chem. Res. 2008, 474, 1855−1860. (26) Sue, K.; Sato, T.; Kawasaki, S.; Takebayashi, Y.; Yoda, S.; Furuya, T.; Hiaki, T. Continuoous hydrothermal synthesis of Fe2O3 nanoparticles using a central collision-type micromixer for rapid and homogeneous nucleation at 673 K and 30 MPa. Ind. Eng. Chem. Res. 2010, 49, 8841−8846. (27) Sato, T.; Ebisawa, K.; Ito, S.; Sue, K.; Itoh, N. Novel synthetic method for metalloporphyrins with inorganic metal salts in hightemperature water. Chem. Lett. 2011, 40, 1414−1416.

porphyrin structure in high-temperature water occurred due to the positive effect for the formation of the intermediate in low dielectric constant region and the rapid deprotonation from the intermediate due to high temperature condition.

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CONCLUSION The incorporation of cobalt, nickel, and copper into 5,10,15,20tetraphenyl-21H,23H-porphyrin (H2TPP) occurred by using their sulfates, nitrates, and chlorides in high-temperature water. The yield of metal-TPP for nitrate salts was lower than those for sulfate and chloride salts at 623 K. The incorporation of oxovanadium(IV) into H2TPP also occurred with its sulfate at 623 K. The time profile of the reaction of H2TPP and copper sulfate indicated that the metal incorporation proceeded in tens of minutes. The yield of metal-TPP significantly increased for cobalt, nickel, and copper sulfate aqueous solutions with increasing temperature from 473 to 673 K. The high temperature region was preferred for the incorporation of metals into the porphyrin structure. We observed phase behavior of the H2TPP−water system and found that H2TPP dissolved easier in water with increasing temperature. The calculation of the concentration of inorganic species for cobalt, nickel, and copper sulfate aqueous solution in high-temperature water revealed that almost all of metals existed in the solid phase and a very small amount of metal was in the liquid phase regardless of temperature. Next, we determined the dependence of the concentration of copper sulfate on the reaction rate and found that the reaction was almost first-order with respect to H2TPP. The reaction model containing pre-equilibrium between Cu2+ and H2TPP expressed the reaction kinetics. In high-temperature water, both the positive effect for the formation of the intermediate containing metal ion and H2TPP and the rapid deprotonation from the intermediate in high temperature probably promoted the incorporation of metal into porphyrin structure.

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*Tel.: +81-28-689-6178. Fax: +81-28-689-6159. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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