Phthalocyanine Dye Muhammad Minhas Azeem

MSc Applied Chemistry

Govt. College University Faisalabad, Pakistan

Contents

1. Introduction

2. History

3. Structure

4. General Synthesis

5. Properties

6. Industrial Production

7. Derivatives

8. Application

9. Reference

1. Introduction

The name phthalocyanine originates from the Greek terms naphtha for mineral oil and cyanine

for dark blue. The term phthalocyanine was first used by R. P. Linstead in 1933 to describe a

class of organic dyes, whose colors range from reddish blue to yellowish green.In 1930-1940,

Linstead et al. described the structure of phthalocyanine and its metal complexes.

Phthalocyanine forms complexes with numerous metals of the Periodic Table. A large number of

complexes with various elements are known. Metal phthalocyanine and compounds with

metalloids such as B, Si, Ge, and As or nonmetals such as a wide variety in their coordination

chemistry. The coordination number of the square-planar complexes of Cu, Ni, or Pt is 4. Higher

coordination numbers of 5 or 6 with one or two additional ligands such as water or ammonia

result in square-based pyramidal, tetrahedral, or octahedral structures.

The phthalocyanines are structurally related to the macrocyclic ring system porphyrin. Formally,

phthalocyanine can be regarded as tetrabenzotetraazaporphyrin and as the condensation product

of four isoindole units. The phthalocyanines are structurally similar to naturally occurring

porphyrins such as hemoglobin , chlorophyll a, and vitamin B12.Phthalocyanines themselves do

not occur in nature.

2. History

Braun and Tschernak obtained phthalocyanine for the first time in 1907 as a byproduct of the

preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this

discovery was of no special interest at the time.

In 1927, de Diesbach and von der Weid prepared CuPc in 23% yield by treating o-

dibromobenzene with copper cyanide in pyridine. Instead of the colorless dinitriles, they

obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid,

alkalis, and heat.

The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 . During the

preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel,a greenish

blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the

compound, which was analyzed as an iron complex. It was formed in a chipped region of the

enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was

soon realized that these products could be used as pigments or textile colorants. Linstead et al. at

the University of London discovered the structure of phthalocyanine and developed improved

synthetic methods for several metal phthalocyanines from 1929 to 1934.Properties such as

polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and

reduction, photoconductivity and semiconductivity, solubility, and photochemical and dielectric

properties were investigated from the 1930s to the 1950s.

Copper phthalocyanine was first manufactured by ICI in 1935, where its production from

phthalic anhydride, urea, and metal salts was developed. Use of catalysts such as ammonium

molybdate improved the method substantially. In 1936, I.G. Farbenindustrie began production of

CuPc at Ludwigshafen, and in 1937 Du Pont followed in the United States. The most important

of the phthalocyanines, CuPc, is now produced worldwide. The first phthalocyanine dye was a

phthalocyanine polysulfonate. Other derivatives, such as sulfonyl chlorides, ammonium salts of

pyridyl phthalocyanine derivatives, sulfur and azo dyes, and chrome and triazine dyes, have been

patented since 1930. At that time, the use of phthalocyanines as colorants for printing ink, paint,

plastics, and textiles began. Of the industrial uses, the application of CuPc in printing inks is its

most important use.

3. Structure

4. General Synthesis

Phthalocyanine complexes have been synthesized with nearly all the metals of the periodic table.

Despite the apparently complex structure of the Pc system, it is formed in a single-step reaction

from readily available starting materials. The reaction is strongly exothermic. For example, the

synthesis of CuPc from phthalodinitrile (4 C8H4N2 + Cu <Pr> C32H16N8Cu) has a reaction

enthalpy of .829.9 kJ/mol. The low energy of the final product can be accounted for by

resonance stabilization; this explains at least partially the relatively facile formation of the

complex. The most important metal phthalocyanines are derived from phthalodinitrile, phthalic

anhydride, Pc derivatives, or alkali metal Pc salts.

From o-Phthalonitrile.

Where M is a metal, a metal halide (MX2), or a metal alkoxide [M(OR)2]. The reaction is

carried out in a solvent at ca. 180 °C or by heating a mixture of solid reactants to ca. 300 °C.

From Phthalic Anhydride.

This synthesis is carried out either in a solvent at 200 °C or without solvent at 300 °C.

From phthalimide derivatives, e.g., diimidophthalimide:

This synthesis is carried out in a solvent (e.g., formamide).

Metal-free phthalocyanine is obtained by the following procedures.

1) Decomposition of an unstable MPc with alcohol or acid

PcNa 2 + 2H3O+ PcH 2 + 2Na+ + 2H2O

2) Direct synthesis (e.g., from phthalodinitrile).

Syntheses of MPc from phthalodinitrile or phthalic anhydride in the presence of urea are the two

most important laboratory and industrial methods. They were also used originally by Linstead et

al. . This procedure allows the production of many phthalocyanine compounds. Catalysts such as

boric acid, molybdenum oxide, zirconium and titanium tetrachloride, or ammonium molybdate

are used to accelerate the reaction and improve the yield. Ammonium molybdate is especially

effective. Reaction is carried out either in a solvent or by heating the solid components. When

metal chlorides and phthalodinitrile are used as starting materials, the reaction products are

partially chlorinated

Lowering the reaction temperature or adding urea or basic solvents decreases the extent of

chlorination. Solvents such as nitrobenzene, trichlorobenzene, alcohols, glycols, pyridine, and

aliphatic hydrocarbons are employed. By using substituted phthalic acids such as 4-

chlorophthalic acid anhydride, 4-sulfophthalic acid anhydride, or 4-nitrophthalimide,

phthalocyanines with inner substitution can be produced. The products can often be purified by

sublimation in vacuo at 300. 400 °C. Soluble Pc’s can be purified by recrystallization.

5. Properties

Of all the metal complexes evaluated, copper phthalocyanines give the best combination of color

and properties and consequently the majority of phthalocyanine dyes (and pigments) are based

on copper phthalocyanines;C.I. Direct Blue 86 is a typical case. As well as being extremely

stable, copper phthalocyanines are bright and tinctorially strong ( max ca. 100 000); this renders

them cost-effective.

5.1 Absorption Spectra

The spectrum of phthalocyanine in the visible region is composed of at least seven bands, the

main absorption occurring between 6000 and 7000 A0. The spectra of the metallic derivatives of

phthalocyanine differ in some respects from that of phthalocyanine and among themselves but

certain features appear in common: there are one or two intense bands in the region 5600-7000 X

and a relatively strong band near 6000 X. The intensity of the absorption increases in general

with increasing wavelength except that the band at about 6000 X is nearly always more intense

than that next to it of longer wave length. The shift is systematically to the higher frequencies in

the sequence of the phthalocyanines:

v Mg < v Zn < v Cu < v Fe < v Co

5.2 Magnetic Properties

The magnetic properties of compounds give information relating to their structure. In particular,

the magnetic properties of the phthalocyanines refer to the bonding of the central metal atom with the surround46 ing four isoindole nitrogen atoms, which form the corners of a square about the central atom. The advantage of magnetic measurements when used to study chemical

bonding relates to the information they give on one atom and its immediate surroundings with no additional information from the rest of the molecule. The magnetic properties of the

phthalocyanines are of interest also because of the similarity of the central portion of phthalocyanine, chlorophyll, and hemoglobin molecules. Klemm and Klemm (135) made the first measurements of magnetic properties of phthalocyanines in 1935. They determined the

magnetic moments of nickel and copper phthalocyanines to be -0.30 and 1.73 Bohr magnetons per gram at room temperature respectively. Thus, nickel phthalocyanine is diamagnetic in

accordance with Pauling's theory for similar compounds with arrangement of the bonds in a plane around the central metal atom and sixteen electrons in the intermediate layer. The copper compound, on the other hand, is paramagnetic because of an unpaired electron in the

intermediate layer in which eight electrons are supplied by the four nitrogen atoms and nine electrons are supplied by the copper atom. The molar magnetic susceptibility of copper

phthalocyanine was calculated to be x ~ 970 x

5.3 Oxidation

The remarkable stability of phthalocyanines includes resistance to atmospheric oxidation at

temperatures up to 100 or higher depending on the particular metal complex (83). However, in

aqueous acid solution strong oxidizing agents oxidize phthalocyanines to phthalic residues, such

as phthalimides, while in nonaqueous solution an oxidation product which can be reduced readily

to the original pigment is usually formed. In Linstead 's initial work, copper phthalocyanine

heated with concentrated nitric acid formed an intermediate compound with a strong purple color

transitorily Oxidation also takes place readily with potassium permanganate or with eerie sulfate.

A quantitative method using eerie sulfate for the estimation of copper phthalocyanine, developed

by Linstead (51), is described in Appendix II. Linstead found that the oxidation of one molecule

of copper phthalocyanine requires one atom of oxygen, which is donated by one molecule of

eerie sulfate which is thereby reduced to cerous sulfate.

(C,H4N2 )4Cu + 3H2S04 + 7H2 + O * 4C 8H5 2N + CuSO4 + 2 (NH4 )2S04

Copper phthalocyanine is oxidized by aqueous sodium hypochlorite. However, the rate of

oxidation of copper phthalocyanine by aqueous sodium hypochlorite is slow because of the

negligible solubility of copper phthalocyanine in water

5.4 Reduction

In terms of the definition of reduction as the addition of electrons to an atom or to a group of

atoms, reduction in the phthalocyanine molecule can take place at the central metal atom or at

the 16 peripheral carbon atoms of the four phenylene rings.

Complete reduction of the central metal atom to a valency of zero has been attained by Watt and

Dawes in the case of copper phthalocyanine. "The reduction of copper (II) phthalocyanine with

potassium in liquid ammonia has been shown to yield an anionic phthalocyanine complex of

copper in the zero oxidation state. Evidence is presented for the possible intermediation of

copper (I) phthalocyanine and its disproportionation."

Certain metal phthalocyanines or their sulfonated derivatives form highly colored reduction

products when subjected to a treatment with hydrosulfite in dilute alkali These include the

complexes of iron, titanium, chromium, tin and molybdenum.

5.6 Flourescence

Evstigneev and Krasnovskif found that magnesium phthalocyanine does fluoresce with

absorption in the red band, in alcoholic soljution, and with emission as a narrow red band in the

region 670-675 m^t,

5.7 Absorption

Unsubstituted phthalocyanines strongly absorb light between 600 and 700 nm, thus these

materials are blue or green. Substitution can shift the absorption towards longer wavelengths,

changing the color from pure blue to green to colorless (when the absorption is in the near

infrared).

5.8 Structurally Similarity

Phthalocyanines are structurally related to other macrocyclic pigments, especially the porphyrins.

Both feature four pyrrole-like subunits linked to form a 16-membered ring. The pyrrole-like

rings within H2Pc are closely related to isoindole. Both porphyrins and phthalocyanines function

as planar tetradentate dianionic ligands that bind metals through four inwardly projecting

nitrogen centers. Such complexes are formally derivatives of Pc2−, the conjugate base of H2Pc.

Many derivatives of the parent phthalocyanine are known, where either carbon atoms of the

macrocycle are exchanged for nitrogen atoms or where the hydrogen atoms of the ring are

substituted by functional groups like halogens, hydroxy, amino, alkyl, aryl, thiol, alkoxy, nitro,

etc. groups.

5.9 Color Ranges

The color of most Pc’s ranges from blue-black to metallic bronze, depending on the

manufacturing process. Ground powders exhibit colors from green to blue. Most compounds do

not melt but sublime above 200 °C, which can be used for purification.

5.10 Solubility

The color of phthalocyanine solutions in sulfuric acid depends on the degree of protonation (the

N atoms of the ring systems are protonated by H2SO4; metals such as Cu influence this

protonation): H2Pc gives a brownish yellow color; CuPc, greenish yellow to olive. The

phthalocyanines can be precipitated from these solutions by addition of water. Solubility can be

improved in some cases by reversible oxidation with organic peroxides or hypochlorites; the Pc’s

are oxidized to substances soluble in organic solvents, from which they can be regenerated by

reduction. Both H2Pc and its derivatives exhibit high thermal stability. For example, CuPc can

be sublimed without decomposition at 500.580 °C under inert gas and normal pressure. In

vacuum, stability up to 900 °C has been reported. Polychloro CuPc is thermally stable up to 600

°C in vacuum. At higher temperature it decomposes without sublimation. H2Pc, CuPc, and

halogenated phthalocyanines have very poor solubility in organic solvents. Only in some high-

boiling solvents such as quinoline, trichlorobenzene and benzophenone is recrystallization

possible at higher temperature.

However, the solubilities have a maximum of several milligrams per liter. In common solvents

such as alcohols, ethers, or ketones the solubility is considerable lower. Phthalocyanine and its

unsubstituted metal derivatives dissolve in highly acidic media such as concentrated sulfuric

acid, chlorosulfuric acid, or anhydrous hydrofluoric acid, presumably due to protonation of the

bridging nitrogen atoms. In the presence of strong bases, reversible deprotonation of the central

imino groups occurs . The solubility in sulfuric acid depends on temperature and concentration.

The rate of decomposition of CuPc increases with increasing H2SO4 concentration, reaching a

maximum at about 80% H2SO4 . The stability of metal phthalocyanines increases in the order:

ZnPc<CuPc<CoPc<NiPc<CuPcCl .

CuPc decomposes vigorously at 405-420 °C in air. In nitrogen, sublimation and decomposition

occur simultaneously at 460-630 °C [45, 46]. Generally all metal Pc’s are more stable thermally

in N2 than in O2. CuPc changes from the - to the -form at 250.430 °C.

6. Industrial Production

Copper Phthalocyanine

Two processes are commonly used for the production of copper phthalocyanine:

phthalic anhydride–urea process patented by ICI I.G. Farben dinitrile process

Both can be carried out continuously or batchwise in a solvent or by melting the starting

materials together ( bake process ). The type and amount of catalyst used are crucial for the

yield. Especially effective as catalysts are molybdenum(iv) oxide and ammonium molybdate.

Copper salts or copper powder is used as the copper source use of copper(I) chloride results in a

very smooth synthesis. Use of copper(I) chloride as starting material leads to the formation of

small amounts of chloro CuPc. In the absence of base, especially in the bake process, up to 0.5

mol of chlorine can be introduced per mole of CuPc with CuCl, and up to 1 mol with CuCl2. The

patent literature gives details of modifications and refinements of the original processes. A

review of older processes is given in examples of more modern production methods.

As apparatus for the batch process, an enamel or steel reactor with an agitator and pressure steam

or oil heating suffices. The choice of process depends on the availability and cost of the

starting materials phthalodinitrile or phthalic anhydride. Although the phthalodinitrile

process has certain advantages over the phthalic anhydride process, the latter is preferred

worldwide because of the ready accessibility of phthalic anhydride. In this process the molar

ratio of phthalic anhydride, urea, and copper(I) chloride is 4:16:1, with ammonium molybdate as

catalyst. The mixture is heated in a high-boiling solvent such as trichlorobenzene, nitrobenzene,

or kerosene. The solvent is removed after the formation of copper phthalocyanine. Frequently a

purification step follows. Carrying out the reaction under pressure gives a high-purity CuPc

pigment. Several dry processes have also been described. The solvent can be replaced by

ammonium chloride a fourfold excess of phthalic anhydride, sodium chloride or a 1:1

NaCl.MgCl2 mixture. In the dry reaction, the ammonium molybdate catalyst can be replaced by

a molybdenum or molybdenum alloy agitator Another dry process is run continuously. The dry

powdered reaction mixture is fed into a rotary furnace kept at 180 °C, and the dry product is

discharged into a drum at a yield of 96% .A vacuum method for the preparation of relatively pure

CuPc is described in. One improvement of the process consists of grinding phthalodinitrile,

anhydrous CuCl, and urea; mixing the powder thoroughly (or grinding in a ball mill); and

heating it to 150 °C. The temperature increases to 310 °C due to the heat of reaction, thus

completing the reaction within a few minutes. After purification the yield is 97 %, and the

product contains 0.3% Cl. Carrying out the reaction in the presence of a salt that decomposes at

30-200 °C to form ammonia improves the yield .The reaction has also been carried out in

solvents such as trichlorobenzene in the presence of pyridine . Pyridine converts the insoluble

copper(I) chloride into a soluble complex, which reacts more quickly.The reaction can be

accelerated by the use of sodium hydroxide or sulfonic or carboxylic acids instead of pyridine.

Other high-boiling solvents such as nitrobenzene, benzophenone, or naphthalene can be used

instead of trichlorobenzene

Diimino isoindolenine Process. An alternative route is the formation of the isoindolenines,

which are then treated with copper(II) salts. 1,3-Diiminoisoindolenine is prepared by reaction of

phthalonitrile with ammonia. The isoindolenine is then treated with copper acetate in ethylene

glycol and 2-chlorobenzonitrile at 60.70 °C for 1 h. Copper phthalocyanine can also be made by

milling diiminoisoindolenine, copper(I) chloride, anhydrous sodium sulfate, and ethylene glycol

at 100-110 °C.

7. Phthalocyanine Derivatives

The copper phthalocyanine derivatives are of major industrial importance as green dyes and

organic pigments (halogenated products). The first phthalocyanine dye was polysulfonated CuPc.

Since then, many patents describing various phthalocyanine compounds have been registered .

Substituted phthalocyanines are either accessible through synthesis from phthalocyanine

derivatives (with the advantage of defined products) or by substitution of phthalocyanines. The

latter method is favored in industry for economic reasons.

Synthesis .

Usually a substituted phthalodinitrile or a substituted phthalic acid is used as starting material. A

mixture of an unsubstituted and substituted starting material in approximate ratios, respectively,

of 1:3, 2:2, or 3:1 can also be used. When reactivities of the two starting materials are

approximately equal, Pc derivatives whose degree of substitution closely corresponds to the ratio

of the starting materials are obtained. More often, however, a mixture of products results.With

the exception of tetrachlorophthalic acid, substituted phthalic acids, phthalimides, or

phthalonitriles are industrially not readily accessible in pure form.

Substitution.

Copper phthalocyanine is preferred as starting material. Very little is known about the position of

substitution. With the exception of hexadecachloro CuPc, all commercial Pc substitution

products, as well as the tetrasubstituted derivatives synthesized from monosubstituted phthalic

acids, are mixtures of isomers. Despite the 16 hydrogen atoms that can be substituted, only two

different monosubstituted Pc’s are possible. The number of disubstituted isomers is higher.

Mono- to heptasubstituted Pc derivatives have not yet been isolated in isomerically pure form. In

addition, only a limited number of isomers are accessible pure form by synthesis. Only

symmetrically substituted phthalic acids, phthalimides, or phthalodinitriles (3,6-di-, 4,5-di-, or

3,4,5,6-tetrasubstituted derivatives) yield pure isomers of octa- or hexadecasubstituted

phthalocyanine derivatives. All other substituted phthalic acids give mixtures of isomers.

Pthalocyanine Sulfonic Acids and Sulfonyl Chlorides

The sulfonic acids and sulfonyl chlorides, especially those of CuPc, are readily accessible. The

sulfonic acids CuPc(SO 3H)n with n=2, 3, or 4 were significant direct cotton dyes ( C.I. Direct

Blue 86, 74186 and 87, 74200). The sulfonyl chlorides are intermediates in the production of

various copper phthalocyanine colorants. The water-soluble sulfonic acids are produced by

heating copper phthalocyanines in oleum. By varying concentration, reaction temperature, and

time, one to four sulfo groups can be introduced in the 4-position . The products synthesized

from 4-sulfophthalic acid exhibit slightly different properties. This is due to the different isomer

distribution with respect to the 4- and 5-positions. Only one sulfo group is introduced in each

benzene ring, as shown by the fact that only 4-sulfophthalimide is obtained on oxidative

degradation. The most important dyes have two sulfonic acid groups per molecule.

8. Applications

Phthalocyanines are the second most important class of colorant, and copper phthalocyanine

is the single largest-volume colorant sold.

Traditional uses of phthalocyanine colorants are as blue and green pigments for automotive

paints and printing inks and as blue/cyan dyes for textiles and paper.

Phthalocyanines have also found extensive use in many of the modern high technologies, e.g.

as cyan dyes for ink jet printing, in electrophotography as charge generation materials for

laser printers and as colorants for cyan toners.

In the visible region, phthalocyanines are limited to blue, cyan and green colours. However,

their absorption may be extended into the near infrared and by suitable chemical engineering

it is possible to fingerprint the 700-1000 nm region.

The properties and effects of these infrared-absorbing phthalocyanines are diverse and cover

many important hi-tech applications, including photodynamic therapy, optical data storage,

reverse saturable absorbers and solar screens

Copper phthalocyanine (CuPc) 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), for spin dyeing and in the paper industry

All major artists' pigment manufacturers produce variants of copper phthalocyanine,

designated color index PB15 (blue) and color indexes (green).

Phthalocyanine is also commonly used as a dye in the manufacture of high-speed CD-

R media. Most brands of CD-R use this dye.

There is evidence that exposure to phthalocyanine can cause serious birth defects in

developing embryos

The greenish blue CuPc shade is suitable for color printing. Other favorable properties such

as light, heat, and solvent resistance led to the use of this blue pigment for paints and plastics.

The chloro and bromo derivatives are important green organic pigments. Other derivatives

are used in textile dyeing and printing or for the manufacture of high-quality inks (pastes for

ballpoint pens, ink jets, etc.).

9: References

“Industrial Dyes Chemistry” by Klaus Hunger

“Dye Chemistry” by Hans Eduard Fierz –David and Louis Blangey

“Phthalocyanine Compounds” by Frank .H Moser

http://en.wikipedia.org/wiki/Phthalocyanine