Phthalimide blue

Phthalocyanines. Phthalocyanine is the only novel chromogen of commercial importance discovered siace the nineteenth century. It was discovered accidendy ia 1928, when duriag the routine manufacture of phthalimide from phthaUc anhydride and ammonia it was found that the product contained a blue contaminant. Chemists of Scottish Dyes Ltd, now part of Zeneca, carried out an iadependent synthesis of the blue material by passiag ammonia gas iato molten phthaUc anhydride containing iron filings. The importance of the colorant was realized (it was iatensely colored and very stable), and a patent appHcation was filed ia the same year. 

Electrostatic potential map for phthalimide anion shows most negatively-charged regions (in red) and less negatively-chaiged regions (in blue). 

As early as 1907, A.V. Braun and J. Tscherniak first obtained phthalocyanine from phthalimide and acetic anhydride [5]. The prepared blue substance, however, was not investigated further. In 1927, de Diesbach and von der Weid, in an attempt to synthesize phthalonitrile from o-dibromobenzene and copper cyanide in pyridine at 200°C, obtained a blue copper complex. The substance was found to be exceptionally fast to acid, alkali, and high temperature [6], Approximately one year later, in trying to manufacture phthalimide from phthalic anhydride and ammo-... 

In 1929, Linsted obtained samples of this complex from ICI chemists (Scottish Dyes Ltd was now owned by ICI). ICI had developed two routes leading to the phthalocyanine iron complex. One method started from phthalic anhydride, iron, and ammonia, while the second pathway proceeded from phthalimide, iron sulfide, and ammonia. In 1933/34, elucidation of the phthalocyanine structure was credited to Linstead. The corresponding copper and nickel phthalocyanines had been prepared in the meantime. ICI introduced the first Copper Phthalocyanine Blue to the market as early as 1935, and the Ludwigshafen subsidiary of the IG Farben-industrie followed suit with a corresponding product. 

Phthalocyanines were discovered by accident. During the manufacture of phthalimide from phthalic anhydride and ammonia in a reactor vessel, a blue impurity was observed,... 

History. Braun and Tschemak [23] 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 [24], 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 [25], 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 phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

A 2-1. three-necked round-bottomed flask, fitted with a sealed stirrer and a reflux condenser carrying a drying tube, is charged with 100 g. (0.75 mole) of phthalide (Note 1), 150 g. (0.81 mole) of potassium phthalimide (Note 2), and 500 ml. of dimethyl-formamidc (Note 3). The stirred suspension is heated under reflux by means of an electric mantle for 5 hours the deep blue solution is then cooled to room temperature (Note 4). A solu-... 

Remarks. The copper phthalocyanine was first obtained by de Diesbach jn the course of an attempt to prepare phthalonitrile from o-dibromobenzene by heating with cuprous cyanide. Independently, and a short time later, it was observed by Scottish Dyes that a blue dye was formed in the preparation of phthalimide in an iron container. Extensive research, especially by Linstead and collaborators, showed that this blue dye was an iron derivative of the same compound obtained earlier. Linstead named the parent substance phthalocyanine and pro-... 

In Britain during 1932-1933, a major discovery took place at what would soon be an ICI acquisition, Scottish Dyes. By chance, a blue colorant was obtained during preparation of phthalimide from phthalic anhydride and ammonia. Though not an aromatic amino compound, the stable product is important in the history of dye discovery. It was a phthalocyanine compound, of the type first prepared in 1907. ICI manufactured the copper analogue, known as Monastral fast blue. Introduced in 1934, it represented the first member of the only new structural class of synthetic dye in the 20th century83. 

In 1928, at Grangemouth, Scotland, at the works of Messrs. Scottish Dyes Ltd., traces of a dark blue insoluble complex were noticed in the iron vessels used to prepare phthalimide from phthalic anhydride and ammonia (65, 221). This product was subsequently shown to be ferrous phthalo-cyanine. Since then literally thousands of patents and publications concerning the phthalocyanines have appeared. It is probable that the phthalocyanines have been the subject of more physical studies than any other single class of compound, partly as a result of their unique structure and partly because of their high thermal and chemical stability. 

Bright blue mtcrocrystals with purple lustre sol in 98% H2SQ4 from which it can be almost quantitatively pptd by dilution with water- Practically insoi in water alcohol, and hydrocarbons. Stable toward heat (crystalline and analyti -cally pure sublimate obtained at about 580" in low pressure atmosphere of nitrogen or carbon dioxide), alkalies dilute acids. Dec by hot nitric acid or dilute acid permanganate to yield phthalimide. 

In 1932, a dark blue by-product was isolated during the industrial production of phthalimide from phthalic anhydride and ammonia in an iron vessel. This unexpected by-product was eventually identified as iron(II)phthalocyanine Now we know that the iron had templated the formation of this macrocycle [8]. Curtis investigated the condensation of acetone 4 and 1,2-diaminoethane 3 in the presence of metal cations and showed that the macrocycles 5 and 6 could be prepared both by templated and untemplated processes (Scheme 1-2) [9, 10],... 

Template reactions are those in which formation of a complex places the ligands in the correct geometry for reaction. One of the earliest was for the formation of phthalocyanines (Figure 12.17). The study of this chanistry began in 1928, after discovery of a blue impurity in phthalimide prepared by reaction of phthalic anhydride with ammonia in an enameled vessel. This impurity was later discovered to be an iron phthalocyanine complex, created from iron released into the mixture via a scratch in the enamel surface. A similar reaction takes place with copper intermediates isolated from this reaction are shown in Hgure 12.17. Phthalic acid and ammonia first form phthalimide, then l-keto-3-iminoisoindoline, and then l-amino-3-iminoisoindolenine. The cyclization reaction then occurs, probably with the assistance of the metal ion, which holds the chelated reactants in position. This is confirmed by the lack of cyclization in the absence of the metals. The essential feature of these reactions is the formation of the cyclic compound by coordination to a metal ion. 

Braun and Tcherniac obtained Pc for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride [40,51], which did not draw the attention of scientific peers at that time. Later, a similar synthesis was reported by de Diesbach and von der Weid, in 1927, who prepared copper-phtalocyanine (CuPc) by reacting o-dibromobenzene with copper cyanide in pyridine [52]. The deep-blue CuPc exhibited exceptional stability to sulfuric acid, alkahes, and heat. An extensive study of the Pcs was conducted by Linstead during the 1930s and elucidated their structure. He also developed and improved methods to synthesize several metal Pcs. 

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