Phthalonitrile solvent process

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. 

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. 

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... 

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... 

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). 

In this process, phthalonitrile, 5.9, is heated to around 200 °C with copper metal or a copper salt, with or without a solvent. A mechanism... 

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