Phthalonitriles

Prepared by stirring phthalimide with cold concentrated ammonia solution. Hydrolysed to phlhalic acid with dilute acids. Dehydration with ethanoic anhydride gives first n-cyano-benzamide and then phthalonitrile. 

Structurally, the molecule is formed by the union of one atom of the metal with four molecules of phthalonitrile. Copper phthalo-cyanine is typical, and has the formula... 

The pure pigment may be obtained by heating phthalonitrile (4 mols) and copper bronze (1 atom) at 200-220° ... 

Phthalonitrile may be prepared by the following series of reactions from phthalimide —... 

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 ofiF 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 benzene, 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. 

Almost all of the OX that is recovered is used to produce phthaUc anhydride. PhthaUc anhydride is a basic building block for plasticizers used in flexible PVC resins, for polyester resins used in glass-reinforced plastics, and for alkyd resins used for surface coatings. OX is also used to manufacture phthalonitrile, which is converted to copper phthalocyanine, a pigment. 

Hydroxyphthalazin-l(2//)-one is obtained in a smooth reaction between phthalic anhydride and hydrazine hydrate and this is again the starting compound for many 1-substituted and/or 1,4-disubstituted phthalazines. The transformations of 1,4-dichloro-phthalazine, which is prepared in the usual manner, follow a similar pattern as shown for pyridazines in Scheme 110. On the other hand, phthalonitrile is the preferential starting compound for amino- and hydrazino-phthalazines. The most satisfactory synthesis of phthalazine is the reaction between a,a,a, a -tetrachloro-o-xylene and hydrazine sulfate in sulfuric acid (67FRP1438827), alt iough catalytic dehalogenation of 1-chloro- or 1,4-dichloro-phthalazine or oxidation of 1-hydrazinophthalazine also provides the parent compound in moderate yield. 

Phthalonitrile [91-15-6] M 128.1, m 141°. Crystd from EtOH, toluene or benzene. Can also be distd under high vacuum. 

Halide complexes are also well known but complexes with nitrogen-containing ligands are rare. An exception is the blue phthalocyanine complex formed by reaction of Be metal with phthalonitrile, 1,2-C6H4(CN)2, and this affords an unusual example of planar 4-coordinate Be (Fig. 5.5). The complex readily picks up two molecules of H2O to form an extremely stable dihydrate, perhaps by dislodging 2 adjacent Be-N bonds and forming 2 Be-O bonds at the preferred tetrahedral angle above and below the plane of the macrocycle. 

Phthalic anhydride is also used to make polyester and alkyd resins. It is a precursor for phthalonitrile by an ammoxidation route used to produce phthalamide and phathilimide. The reaction scheme for producing phthalonitrile, phthalamide, and phathilimide is shown in Figure 10-17. ... 

Figure 10-17. The reaction scheme for o-xylene to phthalonitrile. " CH3 COOH...

Phthalocyanines have been synthesized with nearly all metals of the periodic table.77 Normally they are formed in a single-step reaction from available derivatives of phthalic acid, in particular phthalic acid (see Section 2.1.1.1.), phthalic anhydride (see Section 2.1.1.2.), phthalimide (see Section 2.1.1.3.), 2-cyanobenzamide (see Section 2.1.1.4.), phthalonitrile (see Section 2.1.1.5.), isoindolinediimine (see Section 2.1.1.6.), or 1,2-dibromobenzene (see Section 2.1.1.7.), usually in a high-boiling solvent or by heating the neat components.1 4... 

Not only steric hindrance, but also electronic effects seem to be important in the cyclocondensation of the phthalonitrile (see refs 90 and 94. 

They can be prepared from the respective 4-, 4,5- and 3-, 3,6-substituted phthalonitriles. Besides these most common tetra- and octasubstituted phthalocyanines, 1,3,8,10,15,17,22,24-octasub-stituted and 1,2,3,4,8,9,10.11,15,16.17,18,22,23,24,25-hexadecasubstituted phthalocyanines have been prepared.102... 

Besides the technical method starting from naphthalene, phthalic acid and its substituted derivatives can be prepared by oxidation of o-xylene to phthalic acid with potassium permanganate. This compound can be subsequently transformed via an anhydride, imide, and amide to a derivative of phthalonitrile, which is the more convenient starting material for several coordination compounds. The synthesis of the ferf-butyl-substituted dicarbonitrile, which is a very common starting material for highly soluble phthalocyanines, is shown below.97,105... 

A second reaction which is very often used for the preparation of phthalonitriles, although the yields are usually not reproducible, is the Rosenmund-von Braun reaction (see Houben-Weyl, Vol. E5, p 1460).106 107 Herein, a benzene derivative with a 1,2-dibromidc or 1,2-dich-loride unit is treated with copper(I) cyanide in dimethylformamidc or pyridine. During this reaction the formation of the respective copper phthalocyanine often occurs. This can be used as an easy procedure for the exclusive synthesis of copper phthalocyanines (see Section 2.1.1.7.),1 os-109 but can also lead to problems if the phthalonitrile is required as the product. For example, if l,2-dibromo-4-trifluoromethyl-benzene is subjected to a Rosenmund-von Braun reaction no 4-trifluoromethylphthalonitrile but only copper tetra(tri-fluoromethyljphthalocyanine is isolated.110... 

Examples of the synthesis of 4,5-dialkoxy-, 4,5-di(alkoxymethyl)- and 4,5-dialkyl-substituted phthalonitriles are shown below. 

Both 4,5- and 3,6-disubstituted phthalonitriles are commonly used to prepare phthalocyanines with liquid crystalline properties. An example of the Rosenmund-von Braun reaction is shown below.107... 

Further examples of the Roscnmund-von Braun reaction107 in the synthesis of 4,5-disubstituted phthalonitriles from 1,2-dibromobenzenes98-112-121 are given below. 

For the synthesis of phlhaloeyanines with some special central metals (c.g., silicon), phthalonitriles are not sufficiently reactive. Using the respective isoindolinediimine which shows a higher reactivity may be of advantage. The isoindolinediimine derivative can be prepared by treating the phthalonitrile with gaseous ammonia and a catalytic amount of a base (sodium methoxide) in methanol. 

Usually metal-free phthalocyanine (PcH2) can be prepared from phthalonitrile with or without a solvent. Hydrogen-donor solvents such as pentan-l-ol and 2-(dimethylamino)ethanol are most often used for the preparation.113,127 128 To increase the yield of the product, some basic catalyst can be added (e.g., DBU, anhyd NH3). When lithium or sodium alkoxides are used as a base the reaction leads to the respective alkali-metal phthalocyanine, which can easily be converted into the free base by treatment with acid and water.129 The solvent-free preparation is carried out in a melt of the phthalonitrile and the reductive agent hydroquinone at ca. 200 C.130 Besides these and various other conventional chemical synthetic methods, PcH2 can also be prepared electrochemically.79... 

Dilithium phthctlocyanine (PcLi2) can be prepared by the method of Linstead.59 Lithium metal is added to pentan-l-ol and heated to dissolve the metal. Then, the phthalonitrile is added and the mixture is refluxed for some hours. Due to its lability toward water and acid, both have to be excluded during the reaction and purification.79131132... 

Disodium phthalocyanine (PcNa2) can be prepared in the same way as the dilithium compound by reacting sodium pentoxide in pentan-l-ol with phthalonitrile. It is more sensitive towards moisture and even alcohol than the dilithium phthalocyanine and is readily demeta-lated.58... 

Dipotassium phthalocyanine (PcK2) can be prepared analogously to the dilithium compound by refluxing phthalonitrile and potassium pentoxide in pentan-l-ol.58 With additional oxygen-donor ligands (e.g., crown ethers) it forms crystals with the potassium bulging outside of the phthalocyanine ring.133134... 

Beryllium phthalocyanine (PcBe) can be obtained by heating a mixture of phthalonitrile and beryllium metal, which has to be activated beforehand by etching with dilute acid.58... 

Magnesium phthalocyanine (PcMg) can be prepared in a melt of the phthalonitrile and elemental magnesium. Often some ammonium molybdatc(VI) is added. Remaining phthalo-nitrilc and magnesium are removed by extraction with a suitable solvent and by washings with hydrochloric acid, respectively.55-83-97 136 137... 

Barium phthalocyanine (PcBa) can be prepared by the reaction of phthalonitrile and barium oxide.58... 

Aluminum phthalocyanine (PcAlX) can be prepared from the phthalonitrile and aluminum trichloride either in refluxing quinoline138 13g or without a solvent under addition of ammonium molybdate(VI).137 The chloro compound can be transformed to a hydroxy derivative by treatment with sulfuric acid.58-140 Also, the insertion of aluminum in a metal-free phthalocyanine is possible, for example trialkylaluminum can be used.141,142... 

Indium phthalocyanine (PcInCl) can be prepared by treating indium(III) chloride with phthalonitrile in a high-boiling solvent like quinoline139 or 1-chloronaphthalene.143 Dimeric indium(III) phthalocyanine complexes of the type Pc2In,144 Pc3In2145 as well as a bicyclic phthalocyanine (Pc3/2ln)146 are also known. 

Thallium phthalocyanine (PcT12) can be obtained by heating phthalonitrile with an inter-metallic alloy of indium and thallium in an evacuated glass ampule.145 The structure of this compound is unique among metal phthalocyanines as the two thallium cations occupy two opposite corners of an octahedron, which is formed by the thallium cations and the four iso-indolinc nitrogen atoms facing the center of the macrocycle.147 Another unusual type of phthalocyanine can be prepared by heating phthalonitrile with thallium metal.148 It was identified as a bicyclic thallium(III) phthalocyanine (Pc3/2T1).14S... 

Lead(II) phthalocyanine can be prepared by heating lead(II) oxide with the respective phthalonitrile without solvent150-159 or in 1-chloronaphthatene.154 Addition of anhydrous lead(II) acetate to a solution of dilithium phthalocyanine in anhydrous alcohol gives a precipitate of lead phthalocyanine.59 Lead phthalocyanine can also be obtained by electrosynthesis.160... 

Antimony phthalocyanine can be prepared in a melt of antimony(III) chloride and phthalonitrile. The obtained product is of the formula [PcSb(Cl)2] SbClfi.164 PcSbX is formed by the reaction of metal-free phthalocyanine with antimony(III) chloride in l-chloronaphthalene59 or by the reaction of metal-free phthalocyanine with antimony(III) fluoride.165... 

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