Phthalocyanine Complexes of the Non-Transition Elements

The parent ligand may be prepared by acid demetallation of the so-called labile metal phthalocyanines. These include the phthalocyanines of 

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). 

Phthalocyanine is slowly decolorized in concentrated sulfuric acid at room temperature 20) (see Section VI,B). Boiling in 20% nitric acid also results in decomposition, phthalimide being precipitated 40). The two central hydrogen atoms may be replaced by deuterium 118, 213, 323) (see Section VI,A). Metal-free phthalocyanine is readily purified by rapid recrystallization from concentrated sulfuric acid (a modification) or by sublimation in vacuum at 400°C (/J modification). 

The alkali metal phthalocyanines are, with the exception of the dilithium derivative, fairly insoluble in most organic solvents. The dilithium complex is unique in being soluble in a wide range of organic solvents including alcohol and acetone 11). All the complexes are readily demetallated by dilute aqueous acid. Dilithium phthalocyanine is rapidly demetallated by cold water 11), while disodium phthalocyanine is more resistant to hydrolysis, reacting slowly with hot water. The dipotassium derivative is said to be more readily demetallated than the sodium complex, perhaps because of its larger size 10). 

Dilithium phthalocyanine was originally prepared from lithium amyl-oxide and phthalonitrile in boiling amyl alcohol 11), but may also be prepared from lithium hydride 53) or lithium metal 214) and phthalonitrile. It is readily purified by recrystallization from acetone. A monolithium derivative, presumably lithium hydrogen phthalocyanine, is formed when a deficiency of lithium or lithium salt is used in these reactions. It is a black insoluble compound of unknown structure 11). The high solubility of the dilithium complex makes it a very useful intermediate in double decomposition reactions. Many comparatively unstable metal phthalocyanines can be formed by the reaction of dilithium phthalocyanine and the appropriate metal salt in a solvent such as acetone, dimethylformamide, or quinoline 11, 119, 120). 

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