Phthalocyanine modifications

There are other metal complexes, such as tin, aluminum, magnesium, iron, cobalt, titanium, and vanadium complexes, which are similarly useful in stabilizing a particular phthalocyanine modification. Moreover, carboxy, carbonamido, sulfo, or phosphono-copper phthalocyanine may be admixed during fine dispersion of the pigment. 

Industrial research in this area is devoted mainly to the synthesis of Pc or PcM (M = Cu, Ni, Fe, Al, etc.) starting from urea and phthalic anhydride (or its derivatives) as the most cheap precursors. A survey of the literature shows that most of the articles and patents (among them Refs. 40 49) in the phthalocyanine area during the last 15 years are devoted to searching for the optimal conditions for Pc or PcM (M = Cu, Fe, Al, etc.) preparation, as well as the study and applications of different phthalocyanine modifications [50-56], synthesis of various Pc-substituted derivatives [57 66], study of reaction mechanisms of Pc formation [9,10,18,19,29,30], and much more relevant information generalized in a recent book [67]. 

The cmde copper phthalocyanine must be treated to obtain a satisfactory pigment in regard to the crystal modification and optimal particle size... 

Very unstable modifications, like the reddish, chlorine-free a-copper phthalocyanine, can be stabilized with amides or salts of copper phthalocyanine sulfonic acids (59—63). Mixture with other metal phthalocyanines, eg, tin, vanadium, aluminum, or magnesium, also inhibits crystallization change and poor performance in binders and prints (flocculation) due to the hydrophobic character of unsubstituted phthalocyanines. 

The second process to finish phthalocyanine, which is more important for P-copper phthalocyanine, involves grinding the dry or aqueous form in a ball mill or a kneader (64). Agents such as sodium chloride, which have to be removed by boiling with water after the grinding, are used. Solvents like aromatic hydrocarbons, xylene, nitrobenzene or chlorobenzene, alcohols, ketones, or esters can be used (1). In the absence of a solvent, the cmde P-phthalocyanine is converted to the a-form (57,65) and has to be treated with a solvent to regain the P-modification. The aggregate stmcture also has an impact on the dispersion behavior of a- and P-copper phthalocyanine pigments (66). 

Some references cover direct preparation of the different crystal modifications of phthalocyanines in pigment form from both the nitrile—urea and phthahc anhydride—urea process (79—85). Metal-free phthalocyanine can be manufactured by reaction of o-phthalodinitrile with sodium amylate and alcoholysis of the resulting disodium phthalocyanine (1). The phthahc anhydride—urea process can also be used (86,87). Other sodium compounds or an electrochemical process have been described (88). Production of the different crystal modifications has also been discussed (88—93). 

Unsubstituted phthalocyanines and also halogenated phthalocyanines show very poor solubility in organic solvents. In the solid state, unsubstituted phthalocyanines exhibit, in most cases, inclined one-dimensional stacking of the planar molecules. Besides other polymorphous modifications PcCu shows an x- and / -arrangement.74-75... 

In the case of PcCu and PcH2, the most stable modification, which is formed during synthesis, is the -modification. For a more detailed discussion on the polymorphism in phthalocyanines, see refs 36 and 76. 

A practical method of modification of polysaccharides by clean oxidation using H2O2 as oxidant and cheap iron phthalocyanine as catalyst has been developed. Since no acids, bases or buffers and no chlorinated compounds were used, a pure product can be recovered without additional treatment. Importantly, this flexible method provides materials with a wide range of DScho and DScooh just by an appropriate choice of the reaction conditions. Oxidized polysaccharides thus obtained possess various, tailormade hydrophihc/hydrophobic properties which have been tested successfully in cosmetic and other apphcations. 

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

In addition to the discussed cyclotetramerizations, direct metallation of the metal-free ligands or metal exchange of a labile metal ion or ions for one held more robustly, the desired complexes may be prepared by the direct substitution, exchange or modification of substituents on preformed phthalocyanine derivatives. However, a review of works carried out on these types of transformations lies out of the scope of this chapter. 

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

Keywords Crystal structure Modification Phthalocyanine Property Synthesis... 

The complex mechanism underlying this dispersion process of the epsilon modification of phthalocyanine blue is conceptually resolved into three steps ... 

The correlation between rheological data and the most frequent particle diameter Dmf has been studied on a dispersion of the gamma modification of Pigment Violet 19 and various types of copper phthalocyanine blue in an offset vehicle on... 

Copper Phthalocyanine Blue exhibits more than one crystal modification. This is also true for the metal-free ligand whose greenish blue crystal phase was used on a large industrial scale for a certain period of time (Sec. 3.1.2.6). Free-base Phthalocyanine Blue was largely displaced by (3-Copper Phthalocyanine Blue as it became possible to produce the latter more economically (Sec. 3.1.2.3). 

Knowledge of the most important types of copper phthalocyanine pigments is useful for the understanding of the processes concepts underlying pigment manufacture. Heading the list are the a- and [i-modil i cations of unsubstituted Copper Phthalocyanine Blue (Sec. 3.1.2.3). The a-modification exhibits an unstabilized and a stabilized form as to change of crystal modification. 

This simple one-step route leads to the starting material for the solvent-stabilized a-modification of Copper Phthalocyanine Blue. 

Reaction between phthalic anhydride and urea always affords chlorine-free Copper Phthalocyanine Blue. Chlorinated derivatives are obtained only in the absence of bases (ammonia) or urea. The phase stabilized a-modification is prepared by essentially the same but slightly modified route it is derived from mixed con-... 

Unsubstituted Copper Phthalocyanine Blue is polymorphous. X-ray diffraction diagrams point to five different crystal modifications (a, (3, y, 8, e) (Fig. 91). The relative thermodynamic stability of the individual cystal phases decreases in the following order (3>e>8>a = y [13-16],... 

Crude Copper Phthalocyanine Blue which is prepared by the phthalonitrile or urea process typically evolves as the -modification with a coarse particle size. 

The synthesis of the crystal modification is controlled primarily by the finishing technique of the crude pigment. There are basically two different methods to produce a finely dispersed pigment treatment with acid to form copper phthalocyanine salts, followed by precipitation in water on the one hand, and mechanical treatment (milling, kneading) on the other hand. The following methods are used ... 

Dissolving or swelling of crude Copper Phthalocyanine Blue in sulfuric acid, followed by precipitation in water (hydrolysis) affords the a-modification with a fine particle size. Emulsifiers may be present if desired. Dry milling of the crude (3-crys-tal phase, for instance in the presence of sodium chloride or sodium sulfate, also yields the a-phase. 

The -modification as a rule evolves as a more coarse-grained material than the a-phase. It is prepared by milling the crude Copper Phthalocyanine Blue with salt in the presence of a crystallization stimulating solvent. Aromatic hydrocarbons, esters, or ketones are normally used. 

The S-form can be obtained by treating Copper Phthalocyanine Blue in benzene or toluene with aqueous sulfuric acid in the presence of a surfactant [21], The e-phase is produced by comminution of the a-, 7-, or 8-modification, for instance in a planetary ball mill. The mill base is then aftertreated in an organic solvent at elevated temperature. It is important to realize that the temperature, depending on the solvent, must be kept below the transition temperature at which the e-phase converts to the (3-modification (30 to 160°C). The e-modification is made best from the 7-phase, and the most preferred solvents are alcohols [22], For the industrially hitherto insignificant tt, X, and R-forms of Copper Phthalocyanine Blue (see [1], Vol. II, 34-35). 

Only a minor amount of chlorinated copper phthalocyanine, for instance, especially in the 4-position of the copper phthalocyanine molecule, prevents a change of modification from a to (3. Approximately 3 to 4% chlorine is commonly used, which corresponds to the formula CuPc-Cl0.5, also referred to as semi-chloro-CuPc . The phthalic anhydride/urea synthesis, for instance, affords a partially chlorinated product if 4-chlorophthalic anhydride is added to the reaction mixture. Copper chlorides in the phthalonitrile process have the same effect. 

Polyhalogenated green copper phthalocyanine pigments are not polymorphous and thus exempt from change of modification. 

The similarly blue and equally polymorphous metal-free phthalocyanine existing in five different crystal modifications (a, (3, y, k, t) is chemically somewhat less stable than its copper complex [26] it decomposes slowly in a sulfuric acid solution. On the other hand, it can be chlorinated to afford metal-free Phthalocyanine Green. 

Three dimensional X-ray diffraction analysis has been employed to elucidate the molecular and crystal structure of Copper Phthalocyanine Blue ((3-modifica-tion). In all modifications, the planar and almost square phthalocyanine molecules are arranged like rolls of coins, i.e., in one dimensional stacks. The modifications vary only in terms of how these stacks are arranged relative to each other. One important aspect is the angle between staple axis and molecular plane. The a-phase features an angle of 24.7°, while the stacks in the -modification deviate by as much as 45.8° [13]. 

Fig. 92 Arrangement of the CuPc molecules of the a- and the p-modification. The data for the ot-modification relate to the structure of 4-mono-chloro copper phthalocyanine, which is isomorphous with ot-CuPc [13].

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