Copper compounds metallic pigments

Metal-dye complexes play a very important role in dyestuff technology and find applications in many other fields, e.g. in analytical chemistry.119-123 Except for copper phthalocyanine, metal-azo compound complexes are the most important and the most widely used as dyes and pigments. Typical precursors are shown in Scheme 1. 

Other copper compounds are found in battery fluid fabric dye fire retardants food additives for farm animals fireworks (bright emerald color) manufacture of ceramics and enamels photographic film pigments (coloring agents) in paints, metal preservatives, and marine paints water purification and wood preservatives. 

Many other metal compounds exist including the following often toxic examples barium compounds, eg., barium bromide beryllium compounds, eg., beryllium hydroxide cadmium compounds, e.g., cadmium iodide copper compounds like copper hydroxide, used as a pigment, in paper manufacturing, and as a pesticide lead compounds, like the soluble lead fluorosilicate thallium compounds, e.g., thallium sulphide and vanadium compounds, e.g., vanadium dichloride. 

Scott Schilling (1991) Scott, D.A. Schilling, M. The pigments of the Canosa vases a technical note Journal of the American Institute for Conservation 30 (1991) 35-40 Scott (1997) Scott, D.A. Copper compounds in metals and colorants oxides and hydroxides Studies in Conservation 42 2 (1997) 93-100... 

The phthalocyanines constitute an important class of synthetic pigments and dyes. The parent compound is Pigment Blue 16 (phthalocyanine). One method of preparation involves the fusion of phthalonitrile with cyclohexylamine in an inert solvent. The two central hydrogen atoms can be replaced by metals such as copper, nickel, iron, and cobalt. 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

The reaction between phthalonitrUe and copper also takes place readily in feoihng quinoline or a-methyhiaphthalene the pigment is precipitated as fast as it is formed as a crystalline product. It is separated from the excess of copper by shaking with alcohol, when the metal sinks and the pigment, which remains in suspension, can be poured off the process may be repeated to give the pure compound. 

The stable form of arsenic is the gray or metallic form, although other forms are known. Cooling the vapor rapidly produces yellow arsenic, and an orthorhombic form is obtained if the vapor is condensed in the presence of mercury. Arsenic compounds are used in insecticides, herbicides, medicines, and pigments, and arsenic is used in alloys with copper and lead. A small amount of arsenic increases the surface tension of lead, which allows droplets of molten lead to assume a spherical shape, and this fact is utilized in the production of lead shot. 

Special consideration should be paid to metal complexes such as azomethine pigments (Sec. 2.10). At high temperatures, the yellow copper complex with the chemical constitution 10, incorporated in PVC, will exchange its chelated copper atoms with the metal atoms present in the application medium. Stabilizers containing barium/cadmium or lead produce yellow shades, while dibutyl tin thiogly-colate or other tin compounds produce a brilliant medium red. Color change is slow at low temperatures, but at 160°C the effect is rapid [108],... 

The commercially most interesting metal complex pigments within the azo series are those obtained from aromatic o,o -dihydroxyazo compounds, while important products within the azomethine series are nickel or copper complexes of aromatic o,o -dihydroxyazomethine compounds. 

The synthetic pigment CuPc was obtained by serendipity in 1927 but not identified as such by the authors probably due to analytical limitations and/or because attention was focused on other compounds (de Diesbach von der Weid, 1927). Upon reaction of o-C6H4Br2 with cuprous cyanide and C5H5N a blue insoluble compound was obtained, which undoubtedly was CuPc. Basically there are two commercially important processes to produce CuPc. One is based on phthaloni-trile and the other one uses phthalic anhydride. The phthalonitrile process often yields a product with fewer impurities and using metallic copper gives CuPc by cyclotetramerization. 

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