Leuco-indigo

Many leuco-compounds are reconverted into the dye even by the oxygen of the atmosphere leuco-indigo (p. 373) and leuco-eosin are examples of this. 

Scheme 112 Cathodic reduction of indigo to leuco-indigo with iron complexes.

The reduction of indigo (293), which is insoluble in water and alkaline solutions, to the disodium salt of leuco-indigo (294), which is soluble in alkaline solutions, is crucial to the application of... 

The aim of an indigo sensor is to keep the leuco-indigo concentration in the solution at a constant value. In the past, different methods were developed for detection of the indigo and sodium dithionite concentration, but up to now with limited success. The sodium dithionite concentration can be determined by volumetric titration with iodine2 22 or with K3[Fe(CN)6]23. The endpoint detection of these titrations can be done visually22,24"25 or... 

Indigo is readily reduced by various reducing agents such as zinc dust, sodium dithionite, hydroxyacetone, and hydrogen, or by electrochemical means. In an alkaline medium, a salt (for example the sodium salt) of leuco indigo is produced (3), which can be converted by acids to so-called indigo white (2). 

Indigo is insoluble in aqueous alkaline media and to be useful in dyeing it must be converted into soluble leuco indigo (3). In dyehouses this is done mostly by reducing it with sodium dithionite in the presence of alkali. 

Amino-4-methyl-n-amyl Alcohol, q.v. Leuco-indigo. 

Aabs range 520-680 mn 2abs niax — 610 nm. Insoluble in water, alcohol, or ether soluble in DMSO and chloroform. The dyeing jHOcess uses the reduced finm of indigo, leuco-indigo, ch is then oxidised to indigo on exposure to air. 

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