Lead phthalocyanine preparation

Lead(II) phthalocyanine can be prepared by heating lead(II) oxide with the respective phthalonitrile without solvent150-159 or in 1-chloronaphthatene.154 Addition of anhydrous lead(II) acetate to a solution of dilithium phthalocyanine in anhydrous alcohol gives a precipitate of lead phthalocyanine.59 Lead phthalocyanine can also be obtained by electrosynthesis.160... 

In the following example, the low stability of lead phthalocyanines is used to prepare a metal-free 4,5-tetrabridged phthalocyanine 4 as the decomposition product. 

Silver phthalocyanine may be prepared by the action of silver nitrate on dilithium phthalocyanine in absolute alcohol at room temperature, or by the action of silver sulfate upon lead phthalocyanine in boiling chloronaphthalene (11). It is rapidly decomposed by sulfuric acid (11, 26), and... 

A second reaction which is very often used for the preparation of phthalonitriles, although the yields are usually not reproducible, is the Rosenmund-von Braun reaction (see Houben-Weyl, Vol. E5, p 1460).106 107 Herein, a benzene derivative with a 1,2-dibromidc or 1,2-dich-loride unit is treated with copper(I) cyanide in dimethylformamidc or pyridine. During this reaction the formation of the respective copper phthalocyanine often occurs. This can be used as an easy procedure for the exclusive synthesis of copper phthalocyanines (see Section 2.1.1.7.),1 os-109 but can also lead to problems if the phthalonitrile is required as the product. For example, if l,2-dibromo-4-trifluoromethyl-benzene is subjected to a Rosenmund-von Braun reaction no 4-trifluoromethylphthalonitrile but only copper tetra(tri-fluoromethyljphthalocyanine is isolated.110... 

Usually metal-free phthalocyanine (PcH2) can be prepared from phthalonitrile with or without a solvent. Hydrogen-donor solvents such as pentan-l-ol and 2-(dimethylamino)ethanol are most often used for the preparation.113,127 128 To increase the yield of the product, some basic catalyst can be added (e.g., DBU, anhyd NH3). When lithium or sodium alkoxides are used as a base the reaction leads to the respective alkali-metal phthalocyanine, which can easily be converted into the free base by treatment with acid and water.129 The solvent-free preparation is carried out in a melt of the phthalonitrile and the reductive agent hydroquinone at ca. 200 C.130 Besides these and various other conventional chemical synthetic methods, PcH2 can also be prepared electrochemically.79... 

In abroad sense, the model developed for the cobaloxime(II)-catalyzed reactions seems to be valid also for the autoxidation of the alkyl mercaptan to disulfides in the presence of cobalt(II) phthalocyanine tetra-sodium sulfonate in reverse micelles (142). It was assumed that the rate-determining electron transfer within the catalyst-substrate-dioxygen complex leads to the formation of the final products via the RS and O - radicals. The yield of the disulfide product was higher in water-oil microemulsions prepared from a cationic surfactant than in the presence of an anionic surfactant. This difference is probably due to the stabilization of the monomeric form of the catalyst in the former environment. 

In an interesting study, phthalocyanine complexes containing four anthraquinone nuclei (5.34) were synthesised and evaluated as potential vat dyes and pigments [18]. Anthraquinone-1,2-dicarbonitrile or the corresponding dicarboxylic anhydride was reacted with a transition-metal salt, namely vanadium, chromium, iron, cobalt, nickel, copper, tin, platinum or lead (Scheme 5.6). Substituted analogues were also prepared from amino, chloro or nitro derivatives of anthraquinone-l,2-dicarboxylic anhydride. 

In 1929, Linsted obtained samples of this complex from ICI chemists (Scottish Dyes Ltd was now owned by ICI). ICI had developed two routes leading to the phthalocyanine iron complex. One method started from phthalic anhydride, iron, and ammonia, while the second pathway proceeded from phthalimide, iron sulfide, and ammonia. In 1933/34, elucidation of the phthalocyanine structure was credited to Linstead. The corresponding copper and nickel phthalocyanines had been prepared in the meantime. ICI introduced the first Copper Phthalocyanine Blue to the market as early as 1935, and the Ludwigshafen subsidiary of the IG Farben-industrie followed suit with a corresponding product. 

Pyromellitic derivatives can also be used to prepare phthalocyanins, which have been proposed as pigments(36-38) and as oxidation catalysts(38,39). The use of PMDA in place of phthalic anhydride leads to the formation of large sheet-like molecules, or phthalocyanins with external carboxylic groups. In the latter case, the sodium salts are quite water soluble, which may be of importance for homogeneous catalytic applications. Apart from that, however, they offer few advantages and are a little more difficult to make. However, phthalocyanins have been advocated for use in high performance greases, and in this context, the sheet-like structures of the PMDA phthalocyanins may be of benefit. 

Characterization of conjugated metallopolymers can be difficult. When the metals are paramagnetic, very broad NMR spectra are obtained. Also, many metal complexes, particularly porphyrins and phthalocyanines, aggregate in solution. This leads to broad NMR spectra and can lower solubility. Some researchers have used bulky substituents to disrupt cofacial stacking, but this can add several synthetic steps to the polymer preparation. It is often difficult to obtain clear, unequivocal characterization of the structures of metallopolymers. 

In some cases it has been possible to prepare LB films from porphyrin and phthalocyanine containing fourfold symmetry. However, it is not entirely clear how such materials can be deposited by the LB technique. A nttmber of studies deals with LB films made of non-amphiphilic phthalocyanines. However, it is very difficult to form LB films from symmetric porphyrins [67]. True LB deposition of such compounds leads to an edge-on structirre, whereas related techniques can lead to a structure in which the molecular planes lie parallel to the substrate [68. 69. 70, 71, 72, 73, 74, 75, 76, 77, 78 and 79]. 

Treatment of Lu(0Ac)3-nH20 with phthalonitrile in the presence of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) in 1-hexanol gives the sandwich compound Lu(Pc)2 and the half-sandwich complex Lu(Pc)(0Ac)(H20)2 (De Cian et al. 1985). Both compounds were structurally characterized and the latter was believed to be an intermediate in the formation of the former complex. A solid-state reaction of Lu(OAc)3 and phthalonitrile may also lead to the formation of Lu(Pc)(OAc) and Lu(Pc)2, along with the metal-free phthalocyanine H2(Pc). The ratio of these products depends on the reaction temperature and reaction time (Clarisse andRiou 1987). The 1,2-naphthalocyanine analog Lu(l,2-Nc)(OAc) has recently been prepared in 56% yield by treating Lu(OAc)3 with Li2(l,2-Nc) in 1,2,4-trichlorobenzene (Guyon et al. 1998). 

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