Indigotins

FD C Blue No. 2 " (2) Indigotine Indigo Carmine Cl Food [860-22-0] 73015 nylon sutures for use in general... 

Because of the long overland route used to bring indigotin from India to Europe, and because of the small amount of indigotin that was present in the leaves, about 2—4%, indigotin ranked among the most expensive of the ancient dyes (105). 

Many investigators attempted to unravel the stmcture of indigotin, including von Baeyer who developed a number of syntheses for the dye. Some of... 

Baeyer assigned a cis-form to indigotin, but x-ray crystallographic studies indicated that the dye molecule has a center of symmetry that is only possible if the molecule has a trans-configutation (119). Many derivatives of indigotin have been prepared that would not have been possible if indigotin had a cis-structure, eg, (36) (120). 

Although there is complete agreement that indigotin has a trans-configutation, many questions remain regarding some of its physical properties (121). 

Baeyer s investigation of indigotin spanned a period of almost 20 years. In 1905, he received the Nobel Prize in recognition of his accomphshments. In 1890, it was observed that treatment of CO-bromoacetanilide with alkali produced oxindole [S9-48-3] (122) (37) ... 

Based on this observation, K. Heumann treated N-phenylglycine [103-01 -5] with alkali and obtained indoxyl (38) (keto form), which on aerial oxidation converted to indigotin ... 

This was the process used by BASF and Floechst for about 30 years. Later, a variation of the original Fleumann process was made aniline, formaldehyde, and hydrogen cyanide react to form phenylglycinonitrile (40) which is hydrolyzed to phenylglycine. This is the most widely used process for manufacturing indigotin. 

The greatest improvement in the manufacture of indigotin came when sodamide was used with alkali in the conversion of phenylglycine to indoxyl (125). Not only was the fusion temperature lowered from about 300°C to 200°C, but also the reaction was made practically anhydrous by the sodamide... 

After the second World War, German firms manufacturing indigotin faced serious competition from Knglish and American dyestuff companies. To counteract this, the Germans developed continuous operations for manufacturing the dye. However, because of the complexity of the equipment and the operations (126), the batch process is still the preferred manufacturing method. 

Although there is still demand for indigotin for dyeing blue jeans, it has lost a good part of the market to other blue dyes with better dyeing properties. At present, practically all the indigotin consumed in the United States comes from abroad. 

Indigotin is available as a 100% pure powder and as a 20% solution. As of Febmary, 1992, the powder form sold for about 20/kg in 80-kg lots. Most of indigotin is sold in solution form. 

Common additives in food are sulfur S(IV) oxospecies. Quinoline Yellow and Tartrazine show excellent stability toward S(IV) oxospecies while erythrosine. Red 2G, and Green S show good stability. - All other colorants show fair stability, except indigotine, which fades. In the presence of metabisulflte. Sunset Yellow FCF is degraded to a lemon yellow compound identified as l-(4 -sulfo-l-phenylhydrazo)-keto-3,3,4-trihydronaphtalene-4,6-disulfonic acid by NMR and FAB-MS techniques. ... 

Indigotin Indirubin Monobromoindigotin Dibromoindigotin Dibromoindirubin Other compounds... 

Indigo is considered as one of the most important dyes. Its preparations are usually analysed by HPLC with UV-Vis [46,60] or APCI MS detection. [61,62] Separation of the colouring components of indigo extracted with DMSO is usually performed with the use of a Cl 8 column. Spectrophotometric detection of blue indigotin is performed at 617 nm, red indirubin at 540 nm, and brown isoindigo at 365 and 490 nm. As mobile phases, mixtures of methanol or acetonitrile and water with the addition of TFA or formic acid are used to ensure compatibility with the requirements of the APCI source. 

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