Phthalonitrile Process

Only two techniques have gained commercial importance. The phthalonitrile process, developed in England and Germany, is particularly important in Germany, while the phthalic anhydride/urea process has stimulated more interest in 

The technical importance of the phthalonitrile process is only second to the phthalic anhydride/urea technique, of which two varieties are commercially used (Sec. 3.1.2.2). BASF is the primary European user of the phthalonitrile method. 

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. 

Likewise, halogenated copper phthalocyanine green pigments also have a major impact on the market (Sec. 3.1.2.5). 

The first technical process involved heating phthalonitrile with copper bronze or copper(I)chloride at 200 to 240°C in copper pans. Several variations of this technique were developed in Germany prior to the Second World War. The reaction was performed either without or in the presence of a solvent. A basic distinction is commonly made between the baking process and the solvent process both may be carried out either by continuous or by batch technique. 

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The phthalonitrile process has the particular advantage over the phthalic anhydride process of forming ring-substituted chloro-copper phthalocyanines. Using copper(I)chloride produces so-called semi-chloro Copper Phalocyanine Blue, a pigment which possesses a statistical average of 0.5 chlorine atoms per copper phthalocyanine molecule. Copper(II)chloride, on the other hand, affords a product which comprises an average of one chlorine atom per copper phthalocyanine molecule. A prerequisite for the formation of the chloro substituted compound, however, is the absence of ammonia or urea in the reaction mixture. 

The synthesis of the chlorine-free crude pigment by either the continuous or the batch version of the phthalonitrile process involves adding up to 20% urea or ammonia to the reaction mixture. The latter will provide an effective chlorine trap. 

Moreover, the phthalonitrile process has the added advantage of being the more elegant of the two syntheses. This technique makes it possible to produce comparatively pure copper phthalocyanine without obtaining substantial amounts of side products, a phenomenon which is understandable in view of the fact that the phthalonitrile molecule provides the parent structure of the phthalocyanine ring. Formally, rearrangement of the bonds necessitates donation of two electrons to the system ... 

The advantages of the phthalonitrile process are compromised by the fact that phthalonitrile is not only much more costly than phthalic anhydride but also less easily available. In view of the intermediates which have been found so far, and in conjunction with a study of the thermal course of the reaction using differential scanning calorimetry a reaction mechanism has been proposed for the phthalonitrile route which may be visualized as follows [11] ... 

Phthalic anhydride initially reacts with ammonia, which in turn is liberated, for instance, by decomposition of urea. Diiminophthalimide is then produced via phthalimide and monoiminophthalimide. Subsequent self-condensation (as in the phthalonitrile process) under cleavage of ammonia affords polyisoindolenines, which form complexes with copper ions. Ring closure is achieved through further release of ammonia, and copper phthalocyanine is finally obtained by reduction. 

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. 

The synthetic pigment CuPc was obtained by serendipity in 1927 but not identified as such by the authors probably due to analytical limitations and/or because attention was focused on other compounds (de Diesbach von der Weid, 1927). Upon reaction of o-C6H4Br2 with cuprous cyanide and C5H5N a blue insoluble compound was obtained, which undoubtedly was CuPc. Basically there are two commercially important processes to produce CuPc. One is based on phthaloni-trile and the other one uses phthalic anhydride. The phthalonitrile process often yields a product with fewer impurities and using metallic copper gives CuPc by cyclotetramerization. 

The template methods have also been used for the synthesis of a number of substituted Ln di(naphthalocyanine) complexes, LnNc2 [82-88]. Apart from thermal fusion by conventional heating processes, complexation has been initiated by microwave radiation, although only a few publications are devoted to the template synthesis of lanthanide bis(phthalocyanine) complexes by this method [89, 90]. The use of microwave radiation (MW) reduces the reaction time from several hours to several minutes. Unsubstituted complexes LnPc2 (Ln = Tb, Dy, Lu) were prepared [90] by irradiation (650-700 W) of a mixture of phthalonitrile with an appropriate lanthanide salt for 6-10 min (yields >70%). 

Yet another method of avoiding PCB formation in the solvent process is to dispense with the need for urea as a reactant by using the more expensive phthalonitrile instead of phthalic anhydride. 

In another process [20] phthalonitrile, dissolved in an alcohol is reacted with a base and, without isolating, condensed with barbituric acid in a mixture of formic acid and water. 

Baking is currently performed by continuous operation. Modern variations involve using heated crushing or milling equipment, such as kneader dispersers or oscillating mills at approximately 200°C [9]. This technique significantly improves the reaction control over a batch process. If baking is performed by continuous process, phthalonitrile only remains within the reaction vessel for a very short period of time (between 3 and 20 minutes). It is important to remember that the temperature may not exceed 250°C. The product which evolves from this process is usually purified by acid treatment. 

The solvent process involves treating phthalonitrile with any one of a number of copper salts in the presence of a solvent at 120 to 220°C [10]. Copper(I)chloride is most important. The list of suitable solvents is headed by those with a boiling point above 180°C, such as trichlorobenzene, nitrobenzene, naphthalene, and kerosene. A metallic catalyst such as molybdenum oxide or ammonium molybdate may be added to enhance the yield, to shorten the reaction time, and to reduce the necessary temperature. Other suitable catalysts are carbonyl compounds of molybdenum, titanium, or iron. The process may be accelerated by adding ammonia, urea, or tertiary organic bases such as pyridine or quinoline. As a result of improved temperature maintenance and better reaction control, the solvent method affords yields of 95% and more, even on a commercial scale. There is a certain disadvantage to the fact that the solvent reaction requires considerably more time than dry methods. 

The solvent method may also be performed either by continuous (in cascades) or by batch operation. Continuous techniques in particular have gained considerable technical importance. A phthalonitrile/copper chloride solution is typically treated at 120 to 140°C in a flow tube furnace and the temperature subsequently increased to 180 to 250°C. The entire process requires approximately 1.5 to 2 hours and affords the pigment in practically quantitative yield. The excellent purity of the product eliminates the need for additional purification with dilute acid or base prior to finishing, a procedure which plays a major role in the baking process. These... 

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

A primarily platelet-shaped -modification may also be obtained by the phtha-lonitrile process if particularly pure phthalonitrile is employed [18]. 

The reaction between phthalonitrile and copper also takes place readily in boiling quinoline or a-methylnaphthalene the pigment is precipitated as fast as it is formed as a crystalline product. It is separated from the excess of copper by shaking with alcohol, when the metal sinks and the pigment, which remains in suspension, can be poured off the process may be repeated to give the pure compound. 

Phthalocyanines or tetrabenzoporphyrazines are prepared by the Wyler-Riley process (37BRP464126, 37BRP476243) via condensation of phthalic anhydride and urea in the presence of copper(I) chloride or by reaction of phthalonitrile with copper salts. Metal-free phthalocyanine, no longer of commercial importance, is prepared by reaction of phthalonitrile with sodium amylate, followed by demetallization in methanol. 

In the second manufacturing process for copper phthalocyanine, phthalonitrile, copper(II) acetate and ammonium acetate are heated in the presence of a base, with or without a solvent such as pyridine. The mechanism of this has been less studied than that of the phthalic anhydride/urea reaction. It is, however, significant that metal-free phthalocyanine is manufactured by heating phthalonitrile with the sodium derivative of a high-boiling alcohol in an excess of the alcohol. This reaction is believed148 to occur by the route outlined in Scheme 7, which is supported by the isolation of compounds of types (223) and (224). If this or a related mechanism operates in the... 

The second approach stemmed from the observation that a 1-substituted 3-iminoisoindolenine (223) was a probable intermediate in the synthesis of copper phthalocyanine from phthalonitrile. This led to the development of processes for the manufacture of 1,3-diiminoisoindolenine and its... 

Diiminoisoindolenine Process. An alternative route is the formation of the isoin-dolenines, which are then treated with copper(n) salts [67-69], 1,3-Diiminoisoin-dolenine is prepared by reaction of phthalonitrile with ammonia. The isoindole-nine is then treated with copper acetate in ethylene glycol and 2-chlorobenzoni-trile at 60-70 °C for 1 h. 

Macrocycle 9.105, in the form of its pentaligated uranyl complex, was first characterized by Marks and Day. While earlier reports had claimed the successful preparation of normal U02-phthalocyanine from the reaction of U02 and phthalonitrile, the results of Marks and Day revealed that it is the pentameric uranyl superphthalocyanine, contaminated with only small quantities of metal-free phthalocyanine, that is the dominant product obtained as the result of such a process. The findings of Marks and Day were thus consistent with one other earlier report (see reference 57 and references therein) wherein mass spectrometric evidence... 

Mg, Be, Ag, Fe(II), Sb(III), Mn(II), Sn(II), alkali metals, alkaline earth metals, rare earths, Cd, Hg, and Pb 19, 21, 54, 119, 226). The rate of demetallation varies considerably 19) (see Section VI,B). The phthalo-cyanines of Cu, Zn, Co(II), Ni, Pt, Pd, VO, Al, Ga, and In resist demetallation in concentrated sulfuric acid at room temperature 10, 21, 56, 57). Phthalocyanine may also be prepared by the condensation of phthalonitrile or 1,3-diiminoisoindoline in hydrogen-donor solvents 10, 81, 86, 346), and by the catalytic condensation of phthalonitrile in the dry with platinum metal 10). Processes involving intermediates such as phthalic acid and urea have also been developed 380). 

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