Phthalocyanines, metal free metallic

However, they can also be prepared by metal exchange from alkali-metal phthalocyanines. If proton donors like hydrochloric acid, water or methanol are added to the reaction mixture of a freshly prepared alkali-metal phthalocyanine, metal-free phthalocyanines (PcH2) are formed (see Section 2.1.4.1,). If, on the other hand, the appropriate metal salt is added to a solution of an alkali-metal phthalocyanine, the product is the metalated compound (PcM) (see Section 2.1.6.). 

SWCNTs-porphyrin nanosensors have been fabricated for monitoring toxic substances in the enviromnent [215], Free-base, Ru and Fe octaethyl-and tetraphenyl-substituted porphyrins provided good selectivity and sensitivity to various VOCs tested (acetone, butanone, methanol, ethanol). Nonco-valently functionalized SWCNTs with iron tetraphenylporphyrin were used for benzene detection [216], SWCNTs noncovalently functionalized with copper phthalocyanine and free-base porphyrins were used as sensing layers for the detection of toluene [217]. Also, MWCNTs were used as sensors for benzene, toluene, and xylene, when fnnctionalized with metal tetraphenyl porphyrins [218], SWCNTs-poly(tetraphenylporphyrin) hybrid was prepared and tested as a low-power chemiresistor sensor for acetone vapor [219]. A chemiresistive sensor array was fabricated from SWCNTs noncovalently functionalized with metallo mcxo-tetraphenylporphyrins (Cr(III), Mn(III), Fe(III), Co(III), Co(n), Ni(n), Cu(II), and Zn(II)) [220]. Its responses were treated by statistical analyses and allowed to classify VOCs into five classes alkanes, aromatics, ketones, alcohols, amines. Amines detection as an indicator of meat spoilage was achieved by the same group with the same sensor array [221]. 

Keywords Spectroelectrochemistry Spectroelectrochemistry of phthalocyanines Phthalocyanines Metal-free phthalocyanines Metallophthalocyanines (MPcs-RlAM) bearing redox Inactive metal centers Metallophthalocyanines (MPcs-RAM) bearing redox active metal centers Electrochemistry and spectroelectrochemistry of CoPcs Electrochemistry and spectroelectrochemistry of X-Mn(lll)Pcs Electrochemistry and spectroelectrochemistry of EePcs Electrochemistry and spectroelectrochemistry of TiOPcs Sandwich metallophthalocyanines (MPc2)... 

Phthalocyanine (metal-free) (pure untreated surface)... 

The phthalocyanine molecule is remarkably stable to heat and chemical reagents. The metal-free and heavy metal compounds sublime practically unchanged at 550-580 C. 

Metal phthalocyanines may also be prepared using alkaU metal salts or from metal-free phthalocyanine by boiling the latter in quinoline with metal... 

Very unstable modifications, like the reddish, chlorine-free a-copper phthalocyanine, can be stabilized with amides or salts of copper phthalocyanine sulfonic acids (59—63). Mixture with other metal phthalocyanines, eg, tin, vanadium, aluminum, or magnesium, also inhibits crystallization change and poor performance in binders and prints (flocculation) due to the hydrophobic character of unsubstituted phthalocyanines. 

Some references cover direct preparation of the different crystal modifications of phthalocyanines in pigment form from both the nitrile—urea and phthahc anhydride—urea process (79—85). Metal-free phthalocyanine can be manufactured by reaction of o-phthalodinitrile with sodium amylate and alcoholysis of the resulting disodium phthalocyanine (1). The phthahc anhydride—urea process can also be used (86,87). Other sodium compounds or an electrochemical process have been described (88). Production of the different crystal modifications has also been discussed (88—93). 

Metal-free copper phthalocyanine blue, ie. Pigment Blue 16 [574-93-6] is one of the eadiest forms of phthalocyanine. Environmental concerns about copper in pigments tended to increase the use of metal-free copper phthalocyanine, but certain shortcomings (greenish hue, lack of stabiHty in aromatic solvents) allowed only specialty uses (109). The stabiH2ed a-NC-type is used in certain automotive coatings. 

Metal-free, chloroaluminum phthalocyanine [14154-42-8] vanadyl phthalocyanine [13930-88-6], or magnesium phthalocyanines are sufficiently soluble in organic solvents and show enough bleachable absorption at 694.3 nm to serve as repeated Q-switching elements for mby lasers (qv) (180). Phthalocyanines have been used in other lasers as weU (181). 

Especially in the case of metal-free phthalocyanines, a template effect cannot be involved and the reaction has to pass via intermediates 4, 5 and 6 which have been isolated6,87,88 or like 7 which has only been postulated.89... 

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... 

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... 

Tin phthalocyanines can be prepared using tin(II)110 or -(IV)154 chlorides. The reaction can be performed in 1-chloro-1 10,1 37,1 55 or 1-bromonaphthalene,154 starting from phthalonitrile110137154,155 or phthalic anhydride. In the second case, urea and ammonium molyb-date(VI) arc added.137 The central tin atom can also be introduced into metal-free phthalocyanine by the reaction with tin(IV) chloride in dimethylformamide.141 Treatment of PcSnCl2 with disodium phthalocyanine in refluxing 1-chloronaphthalenc forms a sandwich-like bis-(phthalocyanine) Pc2Sn.154... 

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... 

Palladiumphthalocyanine (PcPd) can be synthesized from phthalimide, ammonium molyb-date(VI), urea and palladium(II) chloride in nitrobenzene.285 Peripherally substituted palladium phthalocyanine is prepared by the reaction of phthalonitrile286 or isoindolinediimine114,117 and palladium(II) acetate in 2-(dimethylamino)ethanol. Also a metal insertion into metal-free phthalocyanine in dimethylfonnamide starting from bis(triphenylphos-phane)palladium(II) chloride has been performed.141,287... 

Due to its commercial importance, the synthesis of copper phthalocyanine (PcCu) is the best investigated of all the phthalocyanines. Copper phthalocyanine is prepared from phthalonitrile and copper(I) chloride without solvent137 and also in a melt of urea.229,277 Additionally, the insertion of copper into metal-free phthalocyanine in butan-l-ol and pentan-l-ol is possible. The copper salts used in this case are copper(I) chloride112 and copper(II) acetate.290 Starting from copper(II) acetate, copper phthalocyanine can also be prepared in ethylene glycol.127 As mentioned above, copper phthalocyanine often occurs as a byproduct of the Rosenmund-von Braun reaction. To increase the yield of the phthalocyanine the solvent dimethylformamide can be substituted by quinoline. Due to the higher boiling point of quinoline, the copper phthalocyanine is the main product of the reaction of copper(I) cyanide and 1,2-dibromoben-zene.130... 

The preparation of silver phthalocyanine (PcAg) is carried out by metal insertion into metal-free phthalocyanine from silver(I) nitrate. The reaction is performed in dimethylformamide291 or in a mixture of 1,2-dichloroethane, sodium acetate and acetic acid.231... 

Zinc phthalocyanine (PcZn) is prepared from phthalonitrile in solvents with a boiling point higher than 200 C, e.g. quinoline277,278 or 1-bromonaphthalene,137 or without solvent in a melt of phthalonitrile.83,116 The zinc compound normally used is zinc(ll) acetate or zinc powder. The reaction of zinc(II) acetate with phthalic acid anhydride, urea and ammonium mo-lybdate(VI) is also successful.262 The metal insertion into a metal-free phthalocyanine is carried out in an alcohol (e.g.. butan-l-ol).127,141,290 This reaction can be catalyzed by an alkali metal alkoxide.112,129... 

Almost every metal atom can be inserted into the center of the phthalocyanine ring. Although the chemistry of the central metal atom is sometimes influenced in an extended way by the phthalocyanine macrocycle (for example the preferred oxidation state of ruthenium is changed from + III to + II going from metal-free to ruthenium phthalocyanine) it is obvious that the chemistry of the coordinated metal of metal phthalocyanines cannot be generalized. The reactions of the central metal atom depend very much on the properties of the metal. 

Yields not reported. h The central metal-free phthalocyanine was formed. 

The products are known as 2,3-octasubstituted or 2,3,9,10,16.17,23,24-octasubstituted phthalocyanines. As is the case for 1,4-octasubstituted phthalocyanines, only one structural isomer exists. Metal-free phthalocyanines 18 can be obtained by heating 4,5-disubstituted phthalonitriles 17 in a solvent containing a strong base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Ammonia can also be used as a base. 

Similarly, the metal-free equivalent of phthalocyanine 21 was obtained in a yield of 30% by heating phthalonitrile 20 in the presence of magnesium sulfate, sodium sulfate, urea, and ammonium molybdatc(IV) as catalyst at 260-280 C for 2 hours.4 4... 

Ring enlargement from subphthalocyanines has been used to synthesize unsymmetrically substituted metal-free phthalocyanines of the AAAB type (see p 738). 

In presence of acids or other metal ions the five-unit macrocyclc of superphthalocyanines can be contracted to produce metal-free phlhalocyanine or metal phthalocyanines, respectively. This reaction might be more of scientific interest than of synthetic value. Nevertheless, one example is shown below. 

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