Phthalocyanine Dyes

(or phthalocyanine pigments), a group of dyes, derivatives of tetrabenzotetraazoporphyrin (phthalocyanine) and its complex compounds with metals. The most widely used phthalocyanine dye is copper phthalocyanine (I), a blue pigment.

The polymorphism of phthalocyanine dyes is important for their use: for example, (I) has α-, β-, and γ-modifications, which differ substantially in color and stability in organic solvents.

Copper phthalocyanine (I) is obtained by heating phthalic anhydride with urea, cuprous chloride (CuCl), and a catalyst, such as As₂O₅, at 160°–200°C in a medium of trichlorobenzene or nitrobenzene. It is also obtained by heating phthalonitrile, C₆H₄(CN)₂, with CuCl, in which case a partially chlorinated light-blue pigment is formed. To obtain the α- and γ-forms, (I) is dissolved and reprecipitated from 98-percent and 60-percent sulfuric acid, respectively; preparation of the β-form involves the mechanical grinding of (I) in the presence of organic solvents and sodium chloride or sodium sulfate.

Phthalocyanine dyes containing 14–16 chlorine atoms in the benzene residue (bright-green pigment) are prepared by the chlorination of (I). Water-soluble direct phthalocyanine dyes are obtained by the sulfonation of (I).

Turquoise-colored reactive dyes are synthesized by the action of chlorosulfonic acid and thionyl chloride on (I), followed by the conversion of the tetrasulfochloride obtained to sulfamide by interaction with aromatic amines containing active groups. Water-soluble phthalocyanine dyes, called Alcians, are isothiouronic salts of (I) and contain one to three of the following group:

They are prepared by first subjecting (I) to the action of paraformaldehyde and hydrochloric acid and then to the action of tetramethyl thiourea; when applied to fabric these phthalocyanine dyes, after steam treatment, form a pigment in the pores of the fiber. Another method of obtaining phthalocyanine dyes during the dyeing process is by the interaction of l-amino-3-iminoisoindoline [phthalocyanogen, or phthalogen (II)] with copper salts in the presence of organic solvents; a fast pigment is formed on heating the fabric impregnated with this mixture to 120°–150°C.

Phthalocyanine dyes that are not water-soluble are widely used as pigments in the manufacture of printing colors, plastics, resins. and other products. Water-soluble phthalocyanine dyes (direct, active, sulfur, or other types) are used for dyeing fabrics.

The central fragments of phthalocyanine dyes and biological pigments—hemoglobin and chlorophyll—have similar structures.