12 research outputs found
Selective crystallization of indigo B by a modified sublimation method and its redetermined structure
Good-quality single crystals of the title compound, indigo B [systematic name: 2-(3-oxoindolin-2-ylÂidene)indolin-3-one], C16H10N2O2, have been prepared with high selectivity by a sublimation process. The previous structure of indigo B [SĂŒsse & Wolf (1980 â¶). Naturwissenschaften, 67, 453], which showed that the complete molÂecule is generated by crystallographic inversion symmetry has been confirmed, but the present study reports more realistic geometrical parameters and modern standards of precision (e.g. Ï for CâC bonds = 0.002â0.003â
Ă
). Each molÂecule features two intraÂmolecular NâHâŻO hydrogen bonds. In the crystal, molÂecules are linked by strong face-to-face ÏâÏ stacking interÂactions involving both the six- and five-membered rings [centroidâcentroid separations = 3.6290â
(14) and 3.6506â
(14)â
Ă
] and interÂmolecular NâHâŻO hydrogen bonds
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The development of indigo reduction methods and pre-reduced indigo products
The continuing importance of blue denim maintains indigo as an important vat dye industrially. In this review, we examine the various methods that have been used in the past and are currently used to reduce and dissolve indigo for dyeing. We discuss recent insights into the bacterial fermentation technology, the advantages and disadvantages of the direct chemical methods that have predominated for the last century and potentially cleaner technologies of catalytic hydrogenation and electrochemistry, which are becoming increasingly important. With considerations of environmental impact high on the dyeing industry's agenda, we also discuss the developments that have led to the production of pre-reduced indigo