Phthalocyanines demetallation

In general, for a particular metal state, metallophthalocyanines are more difficult to demetallate than are metalloporphyrins (the central hole is marginally smaller in the phthalocyanine ligand). Thus, copper(II) phthalocyanine, dissolved in concentrated sulfuric acid, is precipitated unchanged when the solution is poured into ice/water. However, metallochlorins are demetallated more readily than the corresponding metalloporphyrins (basicity chlorin < porphyrin). 

The first route to preparing metal-free Phthalocyanine Blue involves treating phthalonitrile with the sodium salt of a higher-boiling alcohol, for instance with sodium amylate. The resulting phthalocyanine disodium salt is demetallized by stirring in cold methanol ... 

Although porphyrins and especially phthalocyanines are stable compounds, both will undergo photooxidative degradation or photoexcited ET reactions . An additional problem with magnesium complexes is their low stability in aqueous solution, as they demetallate quite easily. This is one of the main reasons that many photochemical studies targeted at modeling the natural situation use the more stable zinc(II) complexes. In addition, past years have seen increasing evidence that both Mg(II) and Zn(II) chlorophylls do exist in nature. 

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. 

Metal-free superphthalocyanine has not yet been obtained. The attempted demetallation in acidic media resulted in ring contraction to phthalocyanine or complete hydrolysis to phthalic acid (Scheme 110).201... 

Phthalimide, JV-thio-metal complexes, 800 Phthalocyanines, 863-870 chelate complexes, 374 demetallation, 863 IR spectra, 861 mass spectra, 861 metallation, 863 NMR, 861 photochemistry, 869 reactions, 863 at metal, 869 redox chemistry, 870 spectra, 860 synthesis, 861 two-metal complexes, 868 Phytic acid zinc complexes, 985 2-Picoline... 

A black-and-white system based on the silver dye-bleach process contains the single azoxy copper-complexed dye (36).10P During bleaching, low pH solutions are used and the dye is partially demetallized. This necessitates an after-bath treatment with a copper-containing solution. Dyes other than those containing the azo group can also be bleached, and derivatives of sulfonated copper phthalocyanine have been used to form cyan images.101... 

Vanadyl salen is readily converted at 100°C with H2S in the absence of a catalyst to a vanadium sulfide and a free organic ligand (or decomposition products). Vanadyl phthalocyanine is more stable with respect to ring attack and demetallation. Rates relative to catalytic reactions have not been measured. If VO-salen is an appropriate model of vanadium binding in asphaltenes, asphaltenic metals are more readily converted to sulfides under hydrotreating conditions than the porphyrinic metals. This suggests... 

Many of the other properties of the uranyl superphthalocyanine complex 160 may also be explained in terms of the severe strain within the macrocycle. The reaction of 160 with acids, for instance, under conditions which readily demetalates many phthalocyanine and porphyrin complexes [130, 131], results in an unprecedented ring contraction giving ftee-base phthalocyanine as the product (Scheme 23)... 

Capar C, Thomas KE, Ghosh A (2008) Reductive demetalation of copper corroles first simple route to free-base P-octabromocorroles. J Porphyr Phthalocyanines 12 964-967... 

Capar C, Hansen LK, Conradie J, Ghosh A (2010) P-octabromo-me.s0-tris(pentafluoro-phenyl)corrole reductive demetalation-based synthesis of a heretofore inaccessible, perhalo-genated free-base corrole. J Porphyr Phthalocyanines 14 509-512... 

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

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). 

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). 

Disodium phthalocyanine may be prepared by the reaction of phthalo-nitrile with sodium amyloxide in amyl alcohol (10), or from sodium hydride and phthalonitrile (52). It does not sublime, and is readily demetallated by methanol and less readily by the higher alcohols (75). The complex reacts with methyl iodide in ethyl alcohol to give only the unmetallated derivative (10). 

Prepared from baryta and phthalonitrile, barium phthalocyanine does not sublime, and is more readily demetallated by cold hydrochloric acid than is calcium phthalocyanine (10). Heavier group IIA phthalocyanines have not been reported. 

Prepared from phthalonitrile and cadmium filings, little is known about cadmium phthalocyanine. It does not sublime, and is reported to be insoluble in all solvents. It is demetallated by concentrated sulfuric acid (10). 

Mercury(II) phthalocyanine is prepared by the interaction of mercuric chloride with dilithium phthalocyanine in absolute alcohol (11). It is readily demetallated in concentrated sulfuric acid and in boiling chloronaphthalene, and will not sublime (111, 226). 

Lead phthalocyanine, obtained from the exothermic reaction between litharge and phthalonitrile (10, 195), is readily demetallated by concentrated acids and is not very stable in organic solvents. It forms pure green... 

Uranyl phthalocyanine 31) has a linear 0—U—O bond system whose asymmetric stretching frequency occurs at 920 cm-1. A band observed at 278 cm-1 in the far infrared is assigned to the 0—U—O bending vibration. The electronic spectrum of uranyl phthalocyanine in 1-chloronaphthalene is unique in having no absorption in the 500-800 mju region. All other phthalocyanines exhibit bands in this region (see Section V,B). The complex may be purified by sublimation, but is demetallated in sulfuric acid. 

By far the most detailed thermodynamic studies have been made by Berezin, who has looked at the equilibria existing in concentrated sulfuric acid. Linstead s group were the first to observe that some of the metal phthalocyanines were demetallated in concentrated sulfuric acid, whereas others appeared indefinitely stable (10). It was shown that all phthalocyanines which resisted attack were of metals whose radii were of the right size to fit nicely into the space available at the center of the ligand. Berezin has since put these observations on a more quantitative basis (19, 21, 26). Labile complexes (i.e., those which are demetallated instantly or fairly rapidly in concentrated sulfuric acid) include those of the alkali metals, alkaline earth metals, Be, Mg, Cd, Hg, Sb(III), Pb, Sn(II), Mn(II), and Fe(III). Stable complexes (demetallated very slowly in acid) include those of Zn, Al, Cl2Sn(IV), OV(IV), Co(II), Rh(II), Os(IV), Ni(II), Pd(II), Pt(II), and Cu(II). The actual rates of decomposition vary widely thus, while calcium and magnesium phthalocyanines are demetallated very rapidly, silver and lead phthalocyanines react fairly slowly (19). The rates of decomposition in 1 M sulfuric acid increase in the sequence (19) Fe(III)... 

Most of the labile metal phthalocyanines react at a similar rate, indicating that demetallation occurs rapidly by reaction (LXXX) which is followed more slowly by reactions (LXXXII)-(LXXXIV). There is some evidence that silver and chloroferric phthalocyanines may undergo some ring cleav-... 

Phthalocyanines are tetrabenzotetraazaporphyrins. Copper(II) phthalocyanine 37 (Linstead 1934) is prepared from phthalonitrile and copper powder/copper(I) chloride. Magnesium phthalocyanine 38 is obtained from Mg and 2-cyanobenzamide by thermal reaction in nitrobenzene [29], the free ligand system is produced by demetalation with acid of the magnesium complex. 

Klofta, T., P. Rieke, C. Linkous, W.J. Buttner, A. Nanthakumar, T.D. Mewborn, and N.R. Armstrong (1985). Tri- and tetravalent phthalocyanine thin film electrodes Comparison with other metal and demetallated phthalocyanine systems. J. Electrochem. Soc. 132, 2134-2143. 

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