Phthalocyanine Green G

Phthalocyanine green G, which has many commercial names, is a synthetic green pigment from the group of phthalocyanine dyes, a complex of copper with chlorinated phthalocyanine. It is a soft green powder, which is insoluble in water. It is a bright, high intensity colour used in oil and acrylic based artist's paints, and in other applications.

Synthesis, properties, and structure

Phthalocyanine green is derived from phthalocyanine blue by chlorination in the presence of aluminium trichloride. The stoichiometry for the complete chlorination is shown:
In practice, this pigment is a mixture of isomers and degrees of chlorination. The 15th and 16th chlorides are difficult to install. The chemical formula usually ranges from C₃₂H₃Cl₁₃CuN₈ to C₃₂HCl₁₅CuN₈.
Due to the presence of strongly electronegative chlorine substituents, the absorption spectrum is shifted from that of the parent copper phthalocyanine. Phthalo green is highly stable and resistant to alkali, acids, solvents, heat, and ultraviolet radiation.
The structure of the compound has been confirmed by X-ray crystallography. These experiments, which confirmed the expected square planar molecular geometry, were challenging because insolublity of the complex inhibited the growth of crystals.

Uses

Due to its stability, phthalo green is used in inks, oil paint, coatings, and many plastics. In application it is transparent. Being insoluble, it has no tendency to migrate in the material. It is a standard pigment used in printing ink and packaging industry. It is also legal in all cosmetics except those used around the eyes. It is used in some tattoos.

Related compounds

Copper phthalocyanine green 36 is a variant where some of the chlorine atoms are replaced with bromine. Bromination is less efficient than chlorination. Consequently, the degree of bromination is lower.