Process for reducing sulfur and vat dyes

Details Process for reducing sulfur and vat dyes Process for reducing sulfur and vat dyes

1999-07-22

2000-07-25

Einnsmann, Margaret

Bleaching and dyeing; fluid treatment and chemical modification

Organic additive for dye composition, dye composition...

Oxygen-containing hetero ring

8650, 8651, 8652, 8653, 8607, 8611, D06P 130, D06P 122, C09B 700, C09B 6728

Patent

active

06093221&

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for reducing dyestuffs of the group consisting of sulfur dyestuffs and vat dyestuffs.
Processes for dyeing cellulose-containing textile materials with sulfur dyes and vat dyes have been known. Both vat dyestuffs and sulfur dyestuffs must be converted by reduction before, or during, the dyeing process from their water-insoluble form into a water-soluble form having affinity to the fiber, the so-called leuco form. It has been known to use sodium dithionite or sodium sulfide as reducing agent for this purpose. However, they have the disadvantage that a so-called overreduction occurs particularly with delicate dyestuffs, and this implies that, after reduction and application to the textile material, the dyestuffs no longer can be re-oxidised into the desired pigment. Furthermore, the sulfide ions released affect the environment detrimentally by noxious odours and their toxicity. It has been known from DE 41 15 452 A1 to reduce vat dyestuffs by means of fructose, mannose or glucose. It has been known from EP 0 699 797 A2 to reduce sulfur dyestuffs by means of fructose, galactose, glucose, mannose, maltose or lactose. The reduction of the dyestuffs described in these publications by means of reducing sugars has the advantage that the detrimental environmental effects, which result from the release of sulfide ions, are avoided. In view of the low redox potential, for example, of glucose, the same is capable of reducing most of the dyestuffs employed while the risk of overreduction is avoided at the same time. However, it turns out to be a disadvantage that the equilibrium of the redox potential is reached comparatively slowly. Because of the disadvantageous kinetics of the reduction described, the dyeing processes carried out with the aid of the aforementioned sugars require a comparatively long time for reducing the dyestuffs employed.
The industrial problem underlying the present invention aims at making available a process for reducing vat dyestuffs and sulfur dyestuffs, in which the above-mentioned disadvantages are overcome, which is, in particular, ecologically unobjectionable, is capable of reducing a wide gamut of conventional dyestuffs, avoids the risk of overreduction, and has an improved reduction kinetics.
The industrial problem underlying the present invention is solved with the process according to the main claim. Accordingly, the invention involves a process for reducing dyestuffs of the group composed o sulfur dyestuffs and vat dyestuffs, wherein the reduction is carried out in an aqueous alkaline medium with a reducing agent containing isomaltulose or its mixture with other reducing sugars, particularly trehalulose. The use of isomaltulose, particularly of an isomaltulose mixture containing also trehalulose, as the reducing agent in the reduction of sulfur dyestuffs and vat dyestuffs from the water-insoluble form to the water-soluble leuco form has the advantage that the redox potential equilibrium of isomaltulose, particularly of mixtures containing this sugar, is reached considerably more rapidly than with the conventionally used sugars. The fact that the redox potential equilibrium is reached earlier allows an advantageous shortening of the time of the reduction phase when textile materials are dyed, and this, in turn, results in savings. The reducing agent used in accordance with the invention is ecologically unobjectionable, has a lower redox potential so that practically all commercial dyestuffs can be reduced, and does not cause their overreduction.
In the context of the present invention, sulfur dyestuffse are defined as dyestuffs which can be obtained by boiling chemical compounds in polysulfides or in sulfur. In the content of the present invention, vat dyestuffs are defined as dyestuffs which can be considered derivatives of anthraquinone.
The invention teaches to use isomaltulose, and particularly a mixture containing this sugar, as reducing agent. In a particularly preferred manner, the reducing agent contains, in addition to isomaltulose, trehalulo

REFERENCES:
patent: 5030248 (1991-07-01), Meszaros
patent: 5470356 (1995-11-01), Meszaros
patent: 5632782 (1997-05-01), Carlough
K. Poulakis, et al., "Einfluss von Ultraschall auf die Verkupungsgeschwindigkeit von Indigofarbstoffen mit .alpha.-Hydroxy-aceton als Reduktionsmittel", Textilveredlung, vol. 31, No. 5/6, 1996, pp. 110-113.

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