Scottish Dyes

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. 

The appearance of synthetic fibers in the 1920s accelerated the further development of anthraquinone dyes. Soon after British Celanese succeeded in commerciali2ing cellulose acetate fiber in 1921, anthraquinone disperse dyes for this fiber were invented by Stepherdson (British Dyestuffs Corp.) and Celatenes (Scottish Dyes) independendy. Anthraquinone disperse dyes for polyester fiber were developed after the introduction of this fiber by ICI and Du Pont in 1952. These dyes were improved products of the disperse dyes that had been developed for cellulose acetate fiber 30 years before. 

That spring, Perkin mailed a precious sample of his purple to a Scottish dye firm. After exposing the sample to sunlight, the company s owner, Robert Pullar, wrote back that Perkin s mauve had kept its color better than any other lilac on the market. If your discovery does not make the goods too expensive, it is decidedly one of the most valuable that has come out for a very long time. This colour is one which has been very much wanted in all classes of goods, and could not be obtained fast on silks, and only at great expense on cotton yarns. ... 

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. 

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-... 

Dandridge AG, Drescher HAE, Scottish Dyes Ltd (1928) Improvements in and relating to the manufacture and use of colouring materials. GB patent 322169... 

Figure 8.9. First described in 1928 by chemists working for the Scottish Dye Works (now part of ICI Americas, Inc.) this pigment has steadily increased in importance to become a product with worldwide significance. The only metal derivative of commercial significance is that of copper, derivatives of other metals having been shown...

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. 

---