Organic compounds -- part of the class 532-570 series – Organic compounds – Azo
Patent
1992-02-21
1993-09-07
Ramsuer, Robert W.
Organic compounds -- part of the class 532-570 series
Organic compounds
Azo
534745, 534801, 534863, C09B 4100, C09B 2932
Patent
active
052430324
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the preparation of azo pigments based on chlorinated benzene-diazonium salts or biphenyl-bis-diazonium salts and acidic CH coupling components.
Industrially produced organic pigments may contain polychlorinated biphenyls (PCBs) as an impurity if certain structural conditions exist in the starting components and because of side reactions, depending on the type of synthesis process chosen [compare R. Anliker, Swiss Chem 3 (1981), No. 1-2, pages 17-23 (German) or pages 25-29 (English); and W. Herbst and K. Hunger in "Industrielle Organische Pigmente (Industrial Organic Pigments)", VCH-Verlag, Weinheim 1987, pages 577-578].
The persistence and bioaccumulative properties of relatively highly chlorinated biphenyls (containing three or more chlorine atoms) above all have meant that production of this class of compounds, which was previously widely used industrially, has been stopped and marketing of compounds and formulations which contain PCBs as impurities has even been subjected to restrictions and controls. The corresponding legal regulations have become increasingly stricter in recent years and the threshold values of amounts of polychlorinated biphenyls permitted in commercial products have been drastically reduced (in the USA, for example, to not more than 25 .mu.g of PCB per gram of the substance marketed).
It has been found, however, that amongst the azo pigments, chiefly monoazo compounds based on di- and trichloroanilines, and also disazo pigments of the chlorinated biphenyl series may be obtained having an undesirable contamination with polychlorinated biphenyls if the pigments are prepared by conventional large-scale industrial coupling processes. The PCB contents in these azo pigments in these cases often exceed the tolerance specified in the USA.
It was thus initially obvious for the PCBs to be removed by solvent extraction from the coloring agents contaminated with them. European Patent EP-B-0,063,321 thus explains, for example, that crude organic pigments of varying chemical category can be converted into products of high purity by treatment with a mixture of a hydrophilic and a hydrophobic organic solvent at 50.degree.-180.degree. C., these solvents being of only limited miscibility with one another. In this technique, the impurities then collect in one of the organic phases and can be removed by the route mentioned. However, the amounts of PCBs present are often only incompletely affected by these and similar purification methods, since pigments of high specific surface area, that is to say with a high content of extremely fine particles, usually primarily bond impurities securely to their active surface by adsorption and moreover also securely hold them occlusively in agglomerates. Solvent treatment of a pigment is furthermore almost always associated with a change in the coloristic properties, so that there are narrow tolerances on the duration and intensity of an intended purification procedure. In the case of pigments of low solvent stability, purification analogously to the processes described above therefore cannot be used at all.
Another factor which makes things difficult is the fact that in all purification operations using organic solvents the impurities enriched therein, i.e., for example the polychlorinated biphenyls, must be eliminated again and subsequently destroyed, which raises considerable technical problems, particularly in the case of PCBs: Because of the exceptional resistance of the class of compounds to be removed, degradation thereof by chemical methods, thermal methods, photolysis and the like is extremely difficult [Review Article by D. Martinetz in
Chem. Techn. 39 (1987)/Volume 11, pages 466-470]. The severity of these degradation methods as a rule also does not allow PCB impurities in pigments to be destroyed, if appropriate, without at the same time damaging the coloring agent.
For the reasons mentioned, it was in all cases desirable to develop synthesis processes for pigments which exclude or at least largely suppress the formation of trace
REFERENCES:
patent: 4459233 (1984-07-01), Fabian et al.
patent: 5086168 (1992-02-01), Rieper
patent: 5194597 (1993-03-01), Rieper
R. Anliker, Swiss Chem. 3 (English Edition), 25-29 (1981).
Hoechst Aktiengesellschaft
Powers Fiona T.
Ramsuer Robert W.
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