Copper phthalocyanine (CuPc), also called phthalocyanine blue, phthalo blue and many other names, is a bright, crystalline, synthetic blue

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

from the group of phthalocyanine dyes. Its brilliant blue is frequently used in paints and dyes. It is highly valued for its superior properties such as light fastness, tinting strength, covering power and resistance to the effects of alkalis and acids. It has the appearance of a blue powder, insoluble in most solvents including water.

History

The discovery of metal phthalocyanines can be traced to the observation of intensely colored byproducts from reactions of

phthalic acid Phthalic acid is an aromatic dicarboxylic acid, with formula C6H4(CO2H)2. Although phthalic acid is of modest commercial importance, the closely related derivative phthalic anhydride is a commodity chemical produced on a large scale. Phthalic acid ...

(benzene-1,2-dicarboxylic acid) or its derivatives with sources of nitrogen and metals. CuPc (copper phthalocyanine) was first prepared in 1927 by the reaction of

copper(I) cyanide Copper(I) cyanide is an inorganic compound with the formula CuCN. This off-white solid occurs in two polymorphs; impure samples can be green due to the presence of Cu(II) impurities. The compound is useful as a catalyst, in electroplating copper ...

and ''o''-dibromobenzene, which mainly produces colorless

phthalonitrile Phthalonitrile is an organic compound with the formula C6H4(CN)2, which is an off-white crystal solid at room temperature. It is a derivative of benzene, containing two adjacent nitrile groups. The compound has low solubility in water but is sol ...

as well as an intensely blue by-product. A couple of years later, workers at Scottish Dyes observed the formation of traces phthalocyanine dyes in the synthesis of phthalimide by the reaction of

phthalic anhydride Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form of phthalic acid. It was the first anhydride of a dicarboxylic acid to be used commer ...

and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

in the presence of metallic iron. In 1937, DuPont started producing copper phthalocyanine blue in the USA under the trade name ''Monastral Blue'' after it had been previously launched in Great Britain ( ICI) and Germany ( I.G. Farbenindustrie) in 1935. Difficulty was experienced in forming stable dispersions with the first alpha forms, especially in mixtures with

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

, where the blue pigment tended to

flocculate Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from p ...

. The beta form was more stable, as was the improved stabilized alpha form. Today, there are even more isomeric forms available.

Synonyms and trade names

The substance,

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name (29''H'',31''H''-phthalocyaninato(2−)-''N''29,''N''30,''N''31,''N''32)copper(II), is known by many names such as ''monastral blue'', ''phthalo blue'', ''helio blue'', ''thalo blue'', ''Winsor blue'', ''phthalocyanine blue'', '' C.I. Pigment Blue 15:2'', ''copper phthalocyanine blue'', ''copper tetrabenzoporphyrazine'', ''Cu-phthaloblue'', ''P.B.15.2'', ''C.I. 74160'', and British Rail Blue. Numerous other trade names and synonyms exist. The abbreviation "CuPc" is also used.

Manufacture

Two manufacturing processes have gained commercial importance for the production of copper phthalocyanine: * The

process, mainly used in Germany * The

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

process, developed in Great Britain and in the USA. Both approaches can be carried out either without (baking process) or with a solvent (solvent process). Higher yields may be achieved with the solvent process (> 95%) than with the baking process (70 to 80%), so that the solvent process has initially simulated more interest. However, recents trends show a reverse tendency for the baking process mainly on the grounds of economical and ecological concerns (solvent-free, shorter lead time).

Phthalonitrile process

This approach involves heating

with a copper salt, usually copper(I)chloride at 200°C to 240°C. The gross reaction equation from

may be written as follows: :4 C6H4(CN)2 + Cu^2+ + 2e- -> CuPc

Phthalic anhydride/urea process

The gross reaction equation from

and

may be written as follows: :4 C6H4(CO)2O + 4(NH2)2CO + Cu^2+ + 2e- -> CuPc + 8H2O + 4CO2 + 4NH3

Applications

Catalysis

Metal phthalocyanines have long been examined as catalysts for redox reactions. Areas of interest are the

oxygen reduction reaction In chemistry, the oxygen reduction reaction refers to the reduction half reaction whereby O2 is reduced to water or hydrogen peroxide. In fuel cells, the reduction to water is preferred because the current is higher. The oxygen reduction reaction ...

and the sweetening of gas streams by removal of hydrogen sulfide.

Colorant

Due to its stability, phthalo blue is also used in inks, coatings, and many

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

s. The pigment is insoluble and has no tendency to migrate in the material. It is a standard pigment used in printing ink and the packaging industry. Industrial production was of the order of 10,000 tonnes per annum in the 1980s and 1990s in Japan alone. The pigment is the highest volume pigment produced. All major artists' pigment manufacturers produce variants of copper phthalocyanine, designate
color index PB15 (blue)
an

A common component on the artist's palette, phthalo blue is a cool blue with a bias towards green. It has intense tinting strength and easily overpowers the mix when combined with other colors. It is a transparent staining color and can be applied using glazing techniques. It is present in a wide variety of products, such as color deposition hair conditioner, eye patches, parfum, shampoo, skin-care products, soap, sunscreen, tattoo ink, toothpaste. and even turf colorants

Research

CuPc has often been investigated in the context of

molecular electronics Molecular electronics is the study and application of molecular building blocks for the fabrication of electronic components. It is an interdisciplinary area that spans physics, chemistry, and materials science. The unifying feature is use of mo ...

. It is potentially suited for

organic solar cell An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport t ...

s because of its high

chemical stability In chemistry, chemical stability is the thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibri ...

and uniform growth. CuPc usually plays the role of the

electron donor In chemistry, an electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. Typical reducing agents undergo permanent chemi ...

in donor/ acceptor based solar cells. One of the most common donor/acceptor architectures is CuPc/C₆₀ (

buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a soccer ball. Each of its 60 carbon atoms is bonded ...

) which rapidly became a model system for the study of small organic molecules. Photon to electron conversion efficiency in such system reaches approximately 5%. CuPc has also been investigated as a component of

organic field-effect transistor An organic field-effect transistor (OFET) is a field-effect transistor using an organic semiconductor in its channel. OFETs can be prepared either by vacuum evaporation of small molecules, by solution-casting of polymers or small molecules, or ...

s. Copper Phthalocyanine (CuPc) has been suggested for data storage in quantum computing, due to the length of time its electrons can remain in superposition. CuPc can be easily processed into a thin film for use in device fabrication, which makes it an attractive

qubit In quantum computing, a qubit () or quantum bit is a basic unit of quantum information—the quantum version of the classic binary bit physically realized with a two-state device. A qubit is a two-state (or two-level) quantum-mechanical system, ...

candidate.

Derivatives

Approximately 25% of all artificial organic pigments are phthalocyanine derivatives.Gerd Löbbert "Phthalocyanines" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. . Copper phthalocyanine dyes are produced by introducing solubilizing groups, such as one or more sulfonic acid functions. These dyes find extensive use in various areas of textile dyeing (Direct dyes for

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...

), for spin dyeing and in the

paper industry The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products. Manufacturing process The pulp is fed to a paper machine where it is formed as a paper web a ...

. Direct blue 86 is the

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

salt of CuPc- sulfonic acid, whereas direct blue 199 is the

quaternary ammonium salt In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cation ...

of the CuPc-sulfonic acid. The

s of these sulfonic acids are used as solvent dyes because of their solubility in

organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

s, such as Solvent Blue 38 and Solvent Blue 48. The dye derived from cobalt phthalocyanine and an

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...

is Phthalogen Dye IBN. 1,3-Diiminoisoindolene, the intermediate formed during phthalocyanine manufacture, used in combination with a copper salt affords the dye GK 161. Copper phthalocyanine is also used as a source material for manufacture of Phthalocyanine Green G.

Structure, reactivity and properties

Copper phthalocyanine is a complex of

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

(II) with the conjugate base of

phthalocyanine Phthalocyanine () is a large, aromatic, macrocyclic, organic compound with the formula and is of theoretical or specialized interest in chemical dyes and photoelectricity. It is composed of four isoindole units linked by a ring of nitrogen ato ...

, i.e. Cu²⁺Pc²⁻. The description is analogous to that for copper porphyrins, which are also formally derived by double deprotonation of porphyrins. CuPc belongs to the ''D''_4h point group. It is paramagnetic with one unpaired electron per molecule. The substance is practically insoluble in water (< 0.1 g/100 ml at ),Copper phthalocyanine
''chemblink.com'' but soluble in concentrated sulfuric acid. Density of the solid is ~1.6 g/cm³.COPPER PHTHALOCYANINE, CAS No.: 147-14-8
''inchem.org'' The color is due to a π–π* electronic transition, with λ_max ≈ 610 nm.

Crystalline phases

CuPc crystallizes in various forms (polymorphs). Five different polymorphs have been identified: phases α, β, η, γ and χ. The two most common structures in CuPc are the β phase and the metastable α phase. Those phases can be distinguished by the overlap of their neighboring molecules. The α phase has a larger overlap and thus, a smaller Cu-Cu spacing (~3.8 Å) compared to the β phase (~4.8 Å).

Toxicity and hazards

The compound is non-biodegradable, but not toxic to fish or plants. No specific dangers have been associated with this compound. Oral LD₅₀ in mammals is estimated to be greater than 5 g per kg, with no ill effects found at that level of ingestion, for chronic ingestion estimated dose of low concern was 0.2 mg/kg per day in rats. No evidence indicates carcinogenic effects. Sulfonated phthalocyanine has been found to cause neuroanatomical defects in developing chicken embryos when injected directly into incubating eggs.

References

External links

* ''colorantshistory.org''
Patrick Linstead talking about phthalocyanine
''Imperial College London, Chemistry department'' {{Shades of blue Pigments Organic pigments Phthalocyanines Shades of blue Copper(II) compounds Copper complexes