Phthalocyanine formation

Phthalic anhydride derivatives are also not typical precursors in phthalocyanine formation. Their use is of interest in cases where the substituents prohibit conversion of the anhydride to nitrogen-containing derivatives like phthalimides or phthalonitriles. 

Naphthalocyanines can be regarded as benzo-annulated phthalocyanines. The number of substituted naphthalocyaninc precursors leading to structural isomers is even higher than in the case of phthalocyanine formation. 1,2-Naphthalocyanine, e.g. 26,71 73 exists as at least four different isomers, even in the unsubstituted form (see p 736). 

This overall reaction equation points to the fact that copper phthalocyanine formation formally requires two reduction equivalents. 

As expected, addition of IV tended to increase the sol fraction in the cured specimens. The statistical theory of gelation (9) can be used to calculate the expected gel fraction as a function of crosslink functionality, extent of reaction, and proportion of difunctional units in the mixture. For these mixtures, an adequate fit to the extraction data was obtained by assuming that the primary reaction is isoindoline formation (Figure 5). Triazine or phthalocyanine formation alone cannot account for the data. 

This scheme in principle is also conserved at present [318,319,328,332-334]. Thus, the structural isomers of octa-tert-butylphthalocyanines 712 (R — /-Hu) were obtained in 1997 according to a similar scheme (3.154) MX =Ni(OAc)2 f O, Solv — C dIK OII, / — 139 C] [334]. A more detailed description of phthalocyanine formation from various precursors is presented in Sec. 5.1. 

Di-iminoisoindoline was used as a precursor for Pc in different protic and aprotic systems, without catalysts or promoters, to study the solvent effect on the possibility of phthalocyanine formation [32], As can be observed (Example 13), it is possible to carry out the chemical and electrochemical synthesis of metal-free Pc in aprotic solvents, such as DMF or DMSO, in contrast to the results with PN. It is surprising that the yields of Pc in ROH are comparatively small. The N,N-dimethyletanolamine is characterized by the best yields, as in the case when PN was used as precursor. 

The authors of Ref. 32 have chosen four metals for interaction with the Pc precursors in nitrobenzene and trichlorobenzene, according to their capacity to form stable (Cu, Fe) and unstable (Mg, Sb) compounds with Pc [1-4]. As a result, the use of Cu and Fe leads to their phthalocyanines formation the yields are considerably higher in pure chemical experiments (69-77%). Applying the electrosynthesis, only a small amount of CuPc (7%) is observed. Mg and Sb do not produce phthalocyanines in the above conditions. 

Therefore, the solvent used for successful electrosynthesis of PcCu should be inert in relation to PA and, on the other hand, should have electroconductivity. The compounds used as promoters [41] could theoretically serve as such solvents. Tetramethylurea (TMU) and l-methyl-2-pyrolidinone were chosen by the authors of Ref. 32 among other promoters used in the work [41]. The first one has a nature close to that of the principal precursor (urea), and thus should not influence the reaction course negatively. The TMU has sufficient conductivity to permit electrolysis in its medium, and reasonable viscosity. The boiling point of 174-178 C is ideal for such research, since conventional syntheses of Pc from urea and PA are carried out at similar temperatures. The results of TMU use as a solvent are presented in Table 5.7. The results seem promising, and this solvent is recommended to study Pc formation in its medium in further research work. In the case of l-methyl-2-pyro-lidinone, no phthalocyanine formation was observed. No phthalocyanine was observed also in the following systems (1) urea, PA, TBA, TMU (without copper) (2) urea, PA, TBA, TMU, Sb, or Mg (anodes (3) TMU, urea (or without urea), phthalimide, TBA (in all cases with or without electrolysis). 

Cation-induced or solvent-induced supermolecular phthalocyanine formation - crown-ether substituted phthalocyanines, N. Kobayashi and A. B. P. Lever, J. Am. Chem. Soc., 1987, 109, 7433. 

Polymerization of Bisphthalonitriles Metal Free Phthalocyanine Formation... 

Table 1 summarizes the analytical results obtained for the thermal reaction of I and of VI. With the exception of the experiment in which methanol was added to VI, the extent of phthalocyanine formation was very small. Moreover, the infrared spectra of these reacted samples exhibited absorptions characteristic of amide or imide carbonyl as well as those for tria-zine. Under these conditions, phthalocyanine formation is not favored. For example, the yield of phthalocyanine ring formation, based on the consumption of starting material, was less than 5% for the model phthalonitrile VI, and less than 10% for the bis-phthalonitrile I. In a separate experiment a thin film of I deposited on a salt plate was allowed to cure while exposed to the atmosphere. Periodic infrared examination of the curing film showed that as the cyano absorbance diminished the absorbance in the carbonyl region increased until the latter was the predominant infrared band. These results demonstrate that... 

Table 2 summarizes some of our initial efforts with regard to catalysis and to the promotion of phthalocyanine formation. 

The tabulated reaction times are those required to cause a 90% or more decrease in CsN infrared absorbance at a reaction temperature of 165°C and demonstrate the marked catalytic effect of each additive. The powerful base, benzyl trimethylammonium hydroxide was employed as the solvent free solid and is by far the most powerful catalyst, however, it gave no detectable quantity (less than one part per million) of phthalocyanine. This is consistent with the proposed mechanistic criteria and dramatically demonstrates that in the absence of a viable redox pathway, reactions other than phthalocyanine formation can occur very rapidly. All other entries gave substantial amounts of phthalocyanine hydroquinone being superior in this regard. 

Whalley M (1961) Conjugated macrocycles. Part XXXn. Absorption spectra of tetrazaporphins and phthalocyanines. Formation of pyridine salts. J Chem Soc 866-869... 

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