Copper phthalocyanine Monastral Blue

COPPER PHTHALOCYANINE (MONASTRAL BLUE) The pure pigment may be obtained by heating phthalonitrile (4 mols) and copper bronze (1 atom) at 209-220  

Phthalamide. Mix 200 g. of phthalimide (Section IV,169) with 600 ml. of concentrated ammonia solution in a 1 litre beaker and stir mechanically for 24 hours. Filter oflF the micro-crystalline cake of phthalamide and dry at 100°. The yield is 200 g., m.p. 220° (decomp.). 

Phthalonitrile. In a 1 litre round-bottomed flask, provided with a reflux condenser, place 100 g. of phthalamide and 350 ml. of acetic anhydride. Reflux for 5-6 hours. Add the reaction product whilst still hot cautiously to 700 ml. of boiling water this decomposes the excess of acetic anhydride. Cool in ice, and then render the reaction mixture alkaline with sodium hydroxide solution. Filter off the precipitated crystals at the pump, wash with water, and dry at 100°. The yield of the crude nitrile is 70 g. After one or two recrystallisations from tenzene, the m.p. should be 141°—that of pure phthalonitrile. It is usually best to distil the crude nitrile under reduced pressure (Figs. II, 19, 3-4) the distillate has m.p. 137-138°, and the m.p. is raised to 141° after one recrystallisation from benzene. 

The reaction between phthalonitrUe and copper also takes place readily in boiling quinoline or a methylnaphthalene 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. 

Phenol condenses with phthalic anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkali is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a hypothetical unstable intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows  

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In the synthetic pigment field the discovery and introduction (1935) by ICI of copper phthalocyanine (Monastral Blue) set new standards in all-round fastness properties. 

Depending upon the metallic compound used, different metallic phthalocyanine derivatives are obtained, e.g. when copper chloride is used copper phthalocyanine (Monastral Fast Blue B) is obtained. 

Phthalocyanine pigments. Discovered in 1928, the copper phthalo-cyanine pigment Monastral Blue was introduced in 1935 by ICI. The pigment... 

In Britain during 1932-1933, a major discovery took place at what would soon be an ICI acquisition, Scottish Dyes. By chance, a blue colorant was obtained during preparation of phthalimide from phthalic anhydride and ammonia. Though not an aromatic amino compound, the stable product is important in the history of dye discovery. It was a phthalocyanine compound, of the type first prepared in 1907. ICI manufactured the copper analogue, known as Monastral fast blue. Introduced in 1934, it represented the first member of the only new structural class of synthetic dye in the 20th century83. 

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