Abstract:
This invention provides a novel process for preparing soluble phthalocyanines by microwave irradiation in the absence of any organic solvent. Three different starting materials, i.e. t-butylphthalic anhydride, t-butyl phthalonitrile and metal-free H 2 Pc (tetra-t-butylphthalocyanine) have been adopted , respectively. The starting material with proper metal compound, such as chloride or acetate were irradiated in a commercial microwave oven for a period of 1 to 30 minutes at a power of 200˜900 W. This process is noted to reduce drastically reaction time of MPc formation from 8˜24 hours to 10˜30 minutes due to its unique heating by microwave irradiation. Sandwiched type MPc 2 (such as Lu Pc 2 ) can be produced only through metal replacement from metal-free phthalocyanine by microwave irradiation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a novel process for preparing soluble phthalocyanines by microwave irradiating starting materials in the absence of any organic solvent.  
           [0003]    2. Description of the Related Prior Art  
           [0004]    Phthalocyanines exhibit extremely good stability and photoelectric properties due to its unique chemical structure, and hence have been used widely. They are currently the largest consumed dyes and/or pigments in the world, and have a role in application for the high technology industry.  
           [0005]    Phthlocyanines can be made into a film that in turn can be fabricated into to an element by means of a variety of methods. Among those methods, the spin-coating has the lowest cost (1-2) . Films made from phthalocyanines have been applied over various fields such as photo-recording materials (3-4) , gas sensors (5) , electrochromic elements (6) , non-linear optics (NLO) (7)  and photocells (8) .  
           [0006]    The structural formula of phthalocyanines is given in FIG. 1, wherein R represents alkyl, t-butyl , or alkoxy group like pentoxy , Mt represents central material of metal , like Co, Ni, Cu, Mg, Al, Pd, Sn, Tb, Ce, La, Zn, Lu or metal-free like H atom.  
           [0007]    Microwave had been developed from the radar during the Second World War. At that time, microwave emitted from the radar was found to be able to dry big ceramic objects. The application of microwave for the household electric commodities had been, however, since 1970. Nevertheless, in recent years, many studies have been devoted for exploring the feasibility of the application of microwave on the chemical reaction.  
           [0008]    Microwave is an energy in a form of electromagnetic wave. It is a non-ionization radiation that can induce the migration of electron and the rotation of dipole moment, and hence cause the motion of a molecule. Microwave heating is different from conventional heating method mostly in its mode of energy delivery. Traditional heating method delivers heat energy by conducting through a container containing the solution, and homogeneously distributes the heat to the solution and hence raises temperature thereof. On the contrary, microwave heating delivers heat by radiation, and therefore, can heat reactants directly and accordingly, promote its efficiency.  
           [0009]    Synthesis of phthalocyanine by microwave irradiation had been proposed firstly by Ahmad Shaabani (12)  in 1998 with phthalic anhydride having no side group as the starting material. This method had, however, a disadvantage in that the phthalocyanine thus synthesized had a poor solubility. It is insoluble in almost all solvent other than concentrated sulfuric acid. In 1999, Cezar Ungurenasu (13)  proposed a process for preparing phthalocyanine by microwave irradiation with phthalonitrile or diiminoisoindoline as the starting material. The product thus prepared had a defined solubility, however, it was disadvantageous in that a solvent must involve in the reaction, i.e., it was not a dry preparation, and hence was high in its production cost. Further, it differed from the scope claimed by the present invention.  
           [0010]    The traditional syntheses of phthalocyanine, no matter what starting material is used, all need a relatively long reaction time and a considerably high energy to provide sufficient kinetic energy to overcome the reaction kinetic barrier and hence promote the collision probability and energy of molecules, that results in low efficiency. Accordingly, the object of the present invention is to provide a novel process for preparing phthalocyanine by microwave irradiation that can eliminate the above-described disadvantage associated with the traditional process. Consequently, it is possible to shorten the reaction time, produce soluble phthalocyanines that can be used to fabricate elements avoiding expensive vacuum sputtering method by utilizing instead of the cheap spin-coating method, and thus increase its industrial practicability.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, the invention provides a novel process for preparing soluble phthalocyanines by microwave irradiation, characterized in that it involves no solvent so as to lower unnecessary heat consumption; increase collision frequency and effective collision probability of reacting molecules and hence increase the reaction yield and reaction rate; in which there are three different kinds of starting materials, i.e. (1) t-butyl-phthalic anhydride, (2) t-butyl-phthalonitrile, and (3) metal-free tetra-t-butyl-phthalocyanine H 2 Pc have been chosen for preparation of soluble metal containing tetra-t-butyl phthalocyanines.  
         DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
         [0012]    The novel process for preparing phthalocyanine according to the invention comprises reacting starting materials with various metal compounds in the absence of any solvent under microwave irradiation in a microwave oven. Metal chlorides and acetates are used as metal compounds.  
           [0013]    The starting materials used herein can be any conventional starting material useful for preparing phthalocyanine, for example, phthalic anhydride, phthalonitrile and metal-free phthalocyanine.  
           [0014]    In the process for preparing phthalocyanine by microwave irradiation, the starting reactants are placed in a heat-resistant quartz vessel of 10 ml. Then, the vessel is placed on the rotation table in the microwave oven. During the microwave irradiation, reactant molecules will have their dipole moments rotating in accordance with the change of the microwave field, and hence, increase collision frequency and effective collision probability, as described above. As the result, the reaction can be accelerated and the reaction yield can be promoted.  
           [0015]    Thus prepared phthalocyanine can be represented by the formula shown in in FIG. 1.  
           [0016]    wherein  
           [0017]    R is an alkyl group such as t-butyl, or an alkoxy group like pentoxy;  
           [0018]    Mt is metal or non-metal, like Co, Ni, Cu, Mg, Al, Pd, Sn, Tb, Lu, Dy, Ce, La, Zn or H atom.  
           [0019]    The invention will be further illustrated in more detailed by the following examples, but not limited by these descriptions. 
       
    
    
     EXAMPLES  
       [0020]    5 examples are provided for illustrating the preferred embodiment of the novel process according to the invention. The invention is, however, not limited by these examples. Among these, example 1 uses phthalic anhydride as the starting material; examples 2 and 3 employ phthalonitrile as the starting materials, wherein, the center in the ring of example 3 is a non-metal H atom; example 4 and 5 use H 2 Pc as the starting material, wherein, the central metal in the example 5 is a rare earth metal Lu, such that a sandwich type of phthalocyanine has been formed which can be identified by mass spectrometry. It should be noted Lu diphthalocyanine can only be prepared by using H 2 Pc as the starting material. All the examples are reacted in a microwave oven at a power of 200˜900 W for a period of 1 to 30 minutes.  
       Example 1  
       [0021]    Synthesis of Cu tetra-t-butyl-phthalocyanine using 4-tert-butyl-phthalic anhydride (4 g, 19.6 mmol), copper chloride (0.72 g, 5.45 mmol), urea (48 g, 0.8 mmol), ammonium chloride (4.048 g, 75.7 mmol) and ammonium molybdate (0.44 g, 2.23 mmol) were pulverized in a mortar and then, placed in a quartz vessel of 50 ml , and irradiated in a microwave oven at 440 W for 15 minutes. Thereafter, the reaction product was rinsed with an amount of demonized water, filtered under suction and the solid was dried under vacuum at 120° C.  
         [0022]    To the dried product, 500 ml of 2% HCl was added and the resulting mixture was heated to boil for several minutes. After filtering and drying, it was added into a 500 ml of 1% aqueous NaOH solution, boiled for several minutes and then filtered and dried. The acid/base washing was repeated several times. The oven-dried crude product was dissolved in dichloromethane, and filtered with suction. The filtrate was concentrated under reduced pressure and dried in vacuum to yield a bluish solid. The solid was recrystallized from ethanol and dichloromethane (5:1) to obtain Cu phthalocyanine with a yield of 47%.  
         [0023]    IR (KBr); 2962, 2896, 2855, 1616, 1528, 1484, 1365, 1338, 1256, 1195, 1145, 1082, 1056, 923, 828, 745, 688, 553 cm −1 .  
         [0024]    MS: m/z 800(M + ).  
         [0025]    UV-Vis(n-hexane)□ max : 670 nm.  
       Example 2  
     Synthesis of Mg tetra-t-butyl-phthalocyanine Using 4-tert-butyl-phthalonitrile  
       [0026]    4-tert-butyl-phthalonitrile (0.5 g, 2.72 mmol) and magnesium chloride (0.0645 g, 1.36 mmol) were ground homogeneously and the resulting mixture was then placed in a quartz vessel. After addition of 5 ml 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), the quartz vessel was irradiated in a microwave oven at 440 W for 10 minutes. A mixture of toluene and water (1:2 v/v) was added to precipitate the product. After filtering and drying, the product was Soxhlet extracted with methanol. 0.4380 g of Mg phthalocyanine was obtained. The yield was 85%.  
         [0027]    IR(KBr); 2954, 1640, 1481, 1441, 1361, 1320, 1253, 1196, 1145, 1081, 1042, 916, 826, 751, 688, 538 cm − .  
         [0028]    MS: m/z 761(M + ).  
         [0029]    UV-Vis(methanol)□ max : 674 nm.  
       Example 3  
     Synthesis of Central Metal-free tetra-t-butyl-phthalocyanine Using 4-tert-butyl-phthalonitrile  
       [0030]    4-tert-butyl phthalonitrile (0.5 g, 2.72 mmol) was placed in a quartz vessel. After addition of 5 ml DBU, the quartz vessel was irradiated in a microwave oven at 440 W for 10 minutes, and a mixture of toluene and water (1:2 v/v) was added to precipitate the product. After filtering and drying, the product was Soxhlet extracted with methanol. 0.4144 g of central metal-free phthalocyanine (H 2 Pc) was obtained . The yield was 83%.  
         [0031]    IR (KBr); 2955, 1616, 1456, 1361, 1316, 1254, 1182, 1007, 869, 823, 743, 518 cm − .  
         [0032]    MS: m/z 740(M + ).  
         [0033]    UV-Vis(TUF)□ max : 696 nm.  
       Example 4  
     Synthesis of Zn-tetra-t-butyl-phthalocyanine through Metal Replacement  
       [0034]    Central metal-free tetra-t-butyl-phthalocyanine (0.02 g, 0.027 mmol) and zinc chloride (7.40×10 −3  g, 0.054 mmol) were ground homogeneously and the resulting mixture was then placed in a quartz vessel. The vessel was then irradiated in a microwave oven at 440 W for 10 minutes, and a mixture of toluene and water (1:2 v/v) was added to wash the product. After filtering and drying, 6.30×10 −3  g of zinc tetra-t-butylphthalocyanine was obtained. The yield was 29%.  
         [0035]    IR (KBr); 2953, 1611, 1485, 1441, 1389, 1328, 1277, 1253, 1215, 1186, 1146, 1084, 1043, 954, 917, 890, 823, 759, 743, 688, 667, 510 cm −1 .  
         [0036]    MS: m/z 801(M + ).  
         [0037]    UV-Vis(methanol)□ max  : 673 nm.  
       Example 5  
     Synthesis of Lu tetra-t-butyl-diphthalocyanine through Metal Replacement  
       [0038]    Central metal-free tetra-t-butylphthalonitrile (0.2 g, 0.27 mmol) and lutetium acetate (0.0953 g, 0.27 mmol) were ground homogeneously and the resulting mixture was placed in a quartz vessel. 3 ml of DBU was added to the vessel ,and the vessel was irradiated in a microwave oven at 440 W for 10 minutes. A mixture of methanol and water (1:2 v/v) was added to wash the product. After filtering and drying, 0.1581 g of Lu tetra-t-butylphthalocyanine was obtained. The yield was 71%.  
         [0039]    IR(KBr): 2956, 1637, 1608, 1482, 1455, 1362, 1315, 1275, 1253 ,1223, 1194, 1140, 1077, 1043, 1023, 915, 822, 749, 673, 531, 505 cm −1 .  
         [0040]    MS: m/z 1649(M + ).  
         [0041]    UV-Vis(n-hexane)□ max : 676 nm.  
         [0042]    Spectra of Various Phthalocyanines  
         [0043]    Table 1 exhibits characteristic absorption peaks in Uv/Vis spectra of various mentioned above phthalocyanines obtained in examples mentioned above. Owing to the unique chemical structure, phthalocyanine exhibits specific optical characteristics. From the UV/Vis spectra, it is clear that two main strong absorption regions were present, namely, Q regions around 670 nm and B region around 340 nm. Both of the two regions are related to □−□* transition and the resonance on their rings.  
                                                     TABLE 1                           Characteristic absorption peaks in UV/Vis spectra of various lab-       made phthalocyanines            Name   Q region   B region   Name   Q region   B region   Name   Q region   B region               CoPc   664   331   ZnPc   673   337   TbPc 2     684   347       NiPc   665   332   DyPc 2     675   346   LuPc 2     676   346       CuPc   670   334   PdPc   657   329   LaPc 2     647   334       MgPc   674   348   SnPc   684   341   H 2 Pc   696, 659   340                  
 
         [0044]    Solubilities of Various Phthalocyanines  
                                         TABLE 2                           displays solubility of various lab-made phthalocyanines, wherein: ⊚,       soluble (&gt;3 wt. %); ◯, slightly soluble (1 wt. % ˜ 3 wt. %); Δ, hardly       soluble (&lt;1 wt. %).            Name   toluene   THF   n-hexane   acetone   methanol               H 2 Pc   Δ   Δ   Δ   Δ   Δ       ZnPc   ⊚   ⊚   ◯   Δ   Δ       MgPc   ⊚   ⊚   ◯   ◯   Δ       CoPc   ◯   ◯   Δ   ◯   Δ       CuPc   ◯   ◯   Δ   Δ   Δ       NiPc   ◯   ◯   Δ   ◯   Δ       TbPc 2     ◯   ◯   Δ   ◯   Δ       LaPc 2     ⊚   ⊚   ⊚   ⊚   Δ                  
 
         [0045]    The Correlation of Reaction Condition with Yield of Phthalocyanine  
         [0046]    Table 3 sets forth the reaction condition used in various example and yields of phthalocyanine prepared.  
                                     TABLE 3                           The correlation of reaction condition with yield of phthalocyanine                        Reaction                   Microwave   time   Yield       Name   Starting material   power (W)   (minute)   (%)               CuPc   t-butyl phthalic anhydride   440   10   47       MgPc   t-butyl phthalonitrile   440   10   85       H 2 Pc   t-butyl phthalonitrile   440   10   83       ZnPc   tetra-t-butylphthalocyanine   440   10   29           (H 2 Pc)       LuPc 2     tetra-t-butylphthalocyanine   440   10   71           (H 2 Pc)                  
 
         [0047]    Advantages of the Invention  
         [0048]    The invention provides several advantages as follows:  
         [0049]    1. Due to the unique property of heating associated with microwave irradiation itself instead of heating in condition and convection fashion involved in conventional synthesis, undue heat energy consumption can be lowered;  
         [0050]    2. Since the operation of microwave field may cause dipolar rotation of reacting molecules and hence increase the collision frequency and the effective collision probability, the reaction time can be reduced drastically from 8˜24 hours to 10˜30 minutes and the yield can be raised;  
         [0051]    3. It can produce phthalocyanine that is soluble in organic solvent and can be used to fabricate elements by utilizing the convenient spin-coating method instead of expensive vacuum sputtering method, and thus increase its industrial practicability; and  
         [0052]    4. Since none of any organic solvent is involved in the reaction according to the invention, the disposal of the organic waste can be greatly reduced and the impact onto environment can be largely avoided.  
         [0053]    Many changes and modifications in the above-described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to be limited only by the scope of the appended claims.  
         [0054]    References:  
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