Copper phthalocyanine polymorphic forms

However, there are metal complex pigments. Without doubt the most important metal complex pigment is copper phthalocyanine (4). The phthalocyanines were discovered by accident in 19286 and now represent the second most important class of colorants after the azo colorants. Copper phthalocyanine itself exists in several polymorphic forms and gives beautiful blue and cyan colors with outstanding fastness properties.5-7 Halogenated copper phthalocyanines provide green pigments (see Section 9.12.4.3). 

Quinacridone is the trivial name given to the five-ring heterocyclic system exemplified by the linear irani-quinacridone (2.69). The yellow-red to reddish-violet shade pigments based on this ring system show outstanding durability and are used in plastics, in industrial and automotive finishes and in exterior finishes. Like copper phthalocyanines the unsubstituted linear quinacridone exhibits polymorphism and two crystal forms, the reddish violet P-form and the red y-form, are commercially... 

Copper Phthalocyanine Blue. CPC blue exists in several polymorphic modifications, two of which, the red-shade blue alpha and greenshade blue beta form, are of great commercial significance. Beta is the thermodynamically more stable phase and is the product resulting from manufacture by the two basic processes using either phthalonitrilc or phthalic anhydride as starting materials. The alpha form is usually obtained by conversion from the beta form and has to be stabilized to prevent phase reconversion. 

Law (1993) has reviewed the widespread polymorphism in phthalocyanines and its relationship to their photoconductivity and use in xerographic applications. These are best demonstrated by the prototypical copper phthalocyanine CuPc (6-XIX, M = Cu), whose structural chemistry is discussed in detail in Section 8.3.3.1. The polarized absorption spectra of five forms are given in Fig. 6.9. One outstanding feature of these spectra is the rather intense red shifted band at 770 nm in the 5 and modifications compared to the solution absorption at 678nm (Law 1993). This... 

R = -C4H9) has been reported to crystallize in four polymorphic forms (Brandt et al. 1982). In the copper phthalocyanines Pigment Blue 15, containing no Cl, is isomorphous with Pigment Blue 15 1, which on an average contains 0.5-1.0 atoms of chlorine per molecule (Hao and Iqbal 1997). Recognition of this phenomenon can be useful, for instance, in attempting to work out the crystal structures of unknown polymorphic forms. 

The X-ray measurements of Robertson and his co-workers were in all cases carried out on the more stable /3 modification, which is also the more crystalline modification. The a modification is unstable to transition to the 8 form in aromatic solvents (335). Ebert and Gottlieb have published (81) detailed methods by which the different polymorphs of copper, nickel, zinc, and metal-free phthalocyanine may be isolated. Phthalonitrile condenses in hydrogen-donor solvents, such as cyclohexylamine, to form metal-free phthalocyanine. The a metal-free phthalocyanine may be obtained from this reaction by milling the product in the dry with sodium chloride, the 6 form by milling in the presence of xylene. Solutions of metal-free phthalocyanine in sulfuric acid precipitate the a modification upon dilution (172). This may be sublimed below 200°C in vacuo, but is converted to the j8 modification above this temperature. Copper phthalocyanine behaves similarly. The 6 phthalocyanine may be reconverted to the a form by milling in the dry with sodium chloride or sodium sulfate. The y metal-... 

In crystals of the copper phthalocyanine fairly rigid molecules can be packed in different arrangements giving rise to different polymorphs. In literature ten different polymorphic forms of copper phthalocyanine are described (Erk Hengelsberg, 2003). From all polymorphic forms commercial interest exhibits the first recognized a form and the most thermodynamically stable p form. 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

S compounds have also been made. Polymorphism has been widely recognised in these compounds with the discovery of various crystal forms of copper and other metal phthalocyanines however, few of these have found substantial use as pigments. Only the principal pigmentary forms are listed here. continued)... 

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