Phthalocyanine electrosynthesis

Lead(II) phthalocyanine can be prepared by heating lead(II) oxide with the respective phthalonitrile without solvent150-159 or in 1-chloronaphthatene.154 Addition of anhydrous lead(II) acetate to a solution of dilithium phthalocyanine in anhydrous alcohol gives a precipitate of lead phthalocyanine.59 Lead phthalocyanine can also be obtained by electrosynthesis.160... 

In this respect, we note that also earlier [318,618] the template electrosynthesis was used to produce phthalocyanine complexes elemental metals or dissolved metal salts were used as a source of metal center (see details in Sec. 5.1). 

The phthalocyanine radical complex of lithium (PcLi ) is a member of the class of intrinsic molecular semiconductors [27]. Its preparation is carried out by electrosynthesis at 70°C under... 

Electrosynthesis of Metal-Free and Metal-Containing Phthalocyanines Starting from Metal Salts [9]... 

Table 5.1 Metal Salts and Alcohols Used as Anolytes During Electrosynthesis of Phthalocyanines...

The reaction yield is calculated on the charge passed through the solution in the case of the electrosynthesis, or on the phthalocyanine formed in the conventional chemical synthesis. 

Table 5.3 Temperature Effect in the Electrosynthesis of Phthalocyanines Using Phthalonitrile as a Precursor...

Table 5.4 Electrosynthesis of Phthalocyanine Starting from 1,3-Di-iminoisoindoline...

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). 

Recommendations on the synthesis of metal phthalocyanines. It is still difficult to evaluate real reaction mechanisms in each synthetic procedure applied. It is clear that the use of such polar protic solvents as alcohols contributes to higher yields of Pc from PN in the electrosynthesis conditions due to the ease of nucleophilic attack of the generated additional RO-. In the further steps of Pc formation from PN or 1,3-D, a solvent s nature has no significant importance. These data about the importance of, first of all, the initial stage correspond to those reported on UV irradiation [40] of PN solutions, where such a treatment is effective only at the beginning of the process. However, in the case of the use of urea and PA, a solvent must be completely inert (or be close to urea s nature) to carry out the one-step synthesis of metal phthalocyanines, in order to exclude any negative influence on the reaction course. The fact that the yields are almost always higher in the case of direct electrosynthesis could serve as an additional confirmation about the usefulness and necessity of this technique. 

It is possible to improve the existing techniques of synthesis of PcCu and other metal phthalocyanines from phthalimide or urea and PA, applying electrosynthesis. These processes have many peculiarities. The solvent nature greatly affects the course of the majority of reactions of coordination compound formation [119,120]. The solvent used for PcCu preparation must be inert in order not to influence the desirable reaction course, and simultaneously must have electroconductivity to carry out electrolysis. It is recommended to use the derivatives of urea as such solvents and promoters at the same time. The use of a standard electrochemical procedure [9-14,20,121-124a] could be useful for the PcCu industry, since a typical industrial... 

Sdnehez-Vergara M, Islas-Bemal I, Rivera M, Ortiz-Rebollo A, Alvarez-Bada J (2007) Formation and characterization of thin films from phthalocyanine complexes an electrosynthesis study using the atomic-force microscope. Thin Solid Films 515 5374—5380... 

Giraudeau A, Lobstein S, Ruhlmann L, Melamed D, Barkigia KM, Fajer J (2001) Electrosynthesis, electrochemistry, and crystal stmcture of the tetracationic Zn-meso-tetrapyridiniumyl-p-octaethylporphyrin. J Porphyrins Phthalocyanines 5 793-797... 

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