MXPA01000356A - Concentrated leucoindigo solutions - Google Patents

Abstract

Concentrated leucoindigo solutions, comprising the following essential ingredients:25-55 wt.%leucoindigo in the form of a leucoindigo salt, a mixture of at least two alkali metal hydroxides, whereby the respective proportion of each metal hydroxide does not exceed 70 mol%and the amount thereof corresponds to the stochiometrically required amount for the leucoindigo to be converted into said neutral leucoindigo salt, in addition to water. The invention also relates to the production of said leucoindigo solutions and the use thereof for colouring textile material containing cellulose.

Description

CONCENTRATED LEUCO SOLUTIONS INDEX DESCRIPTION The present invention relates to novel concentrated solutions of indigo leuco consisting essentially of 25 to 55% by weight of indigo leuco in the form of the indigo leuco salt, an amount essentially stoichiometrically sufficient to convert the indigo leuco. in the neutral leuco-indigo salt of a mixture of at least two alkali metal hydroxides wherein none of the alkali metal hydroxides represents more than 70 mol%, and water.

This invention also relates to the preparation of these leuco indigo solutions and their use for dyeing cellulosic textile material. Indigo is a well-known vat dye that is used to dye cellulosic textile material, especially cotton warp threads for blue denim articles. To dye, indigo insoluble in water is first reduced (in vat) to convert it into the water-soluble leuco form having affinity for fiber and which, after passing to the material to be dyed, is oxidized again in the water-insoluble vat dye pigment. WO-A-94/23114 discloses an ecologically beneficial staining process employing indigo in the form of a caustic indigo leuco aqueous solution which is obtained by the catalytic reduction of an indigo suspension and dramatically reduces sulfate levels or organic particles in the wastewater compared to conventional staining processes. However, since to date it has not been possible to prepare stable solutions of indigo leuco stable and which do not tend to crystallize, the leuco indigo solutions employed in WO-A-94/23114 have only an indigo leuco content of 20% by weight, too. It is an object of the present invention to provide highly concentrated leuco indigo solutions that allow a further reduction of the proportioned volumes required for dyeing and therefore are more effective in reducing the risk of dye bath spillage and also contribute to lower costs of transport of the coloring solution from the address of the manufacturer to the address of the dyer. We have found that this object is achieved through the concentrated solutions of indigo leuco defined at the beginning. This invention further provides a process for preparing these solutions of indigo leuco by the catalytic hydrogenation of aqueous alkaline suspensions of indigo, which comprises carrying out stepwise hydrogenation and hydrogenation first of a suspension of indigo at 20 to 30% by weight which comprises from 4 to 10% by weight of a mixture of at least two alkali metal hydroxides wherein none of the alkali metal hydroxides represent more than 70 mol% to form indigo leuco, then adding additional indigo to adjust the content of indigo leuco finally desired and also, if appropriate, a mixture of alkali metal hydroxide, and the continuation of hydrogenation. The present invention also offers a further preparation process comprising first the catalytic hydrogenation of an alkaline aqueous suspension at 20 to 30% by weight of indigo comprising from 4 to 10% by weight of the alkali metal hydroxide mixture described above and adjusting the resulting leuco indigo solution to the desired content of indigo leuco by evaporation. The present invention finally offers the use of leuco indigo solutions for dyeing cellulosic textile material. The leuco indigo solutions of the present invention comprise from 25 to 55% by weight, preferably from 30 to 55% by weight, particularly preferably from 35 to 50% by weight, especially from 40 to 45% by weight of leuco indigo in the form of alkali metal salt of leuco indigo. The second essential constituent of the leuco indigo solutions of the present invention is the mixture of alkali metal hydroxides with which the leuco indigo vat acid is converted to the indigo leuco vat salt. The mixture of alkali metal hydroxides of the present invention comprises at least two different alkali metal hydroxides provided that none of the alkali metal hydroxides represents more than 70 mol% of the mixture. Suitable alkali metal hydroxides include, for example, lithium hydroxide, sodium hydroxide and potassium hydroxide, which may be present in the form of a triple mixture or in the form of the respective double combinations, in which case mixtures of sodium hydroxide and potassium hydroxide are preferred. . In mixtures of two alkali metal hydroxides, the proportion of one of the hydroxides is preferably within a range of 70 to 30 mol% and the proportion of the other correspondingly lies within a range of 30 to 70 mol%. Levels of 60 to 40 mol% on the one hand and 40 to 60 mol% on the other hand are especially preferred. Particularly preferably, the two hydroxides (sodium hydroxide and potassium hydroxide) are present in approximately equal weight amounts, ie their weight ratio is within a range of 0.8: 1 to 1.2: 1, especially approximately 1: 1 The leuco indigo solutions of the present invention include the mixture of alkali metal hydroxides in an amount essentially stoichiometrically sufficient for the complete formation of the neutral tub salt, i.e., generally from 1.5 to 2.5 moles of mixture of alkali metal hydroxides. per mole of leuco indigo. Surprisingly, the leuco indigo solutions of the present invention are very stable and, unlike the known solutions of leuco indigo in which the indigo leuco is present in the form of a pure sodium salt, they do not have a tendency to crystallize. For example, the leuco indigo solutions of the present invention of up to about 40% by weight have an unlimited storage path in nitrogen at low temperatures up to about 10 ° C (30-35% by weight solutions can be transported and handled when it is frosty); 50 to 55% by weight solutions are best stored at a temperature of about 40 to 60 ° C to avoid crystallization. The leuco indigo solutions of the present invention can be profitably prepared through the two processes also disclosed in the present invention. In one of the processes, the preparation is carried out by catalytic hydrogenation in stages. The procedure employed is advantageously the following: First, an aqueous alkaline suspension of low concentration of indigo, comprising from about 20 to 30% by weight of indigo and from 4 to 10% by weight of the mixture of alkali metal hydroxide of the present invention, is hydrogenated in a conventional manner using a nickel catalyst (Raney nickel) at a hydrogen pressure typically of 2-6 bar and at a temperature generally within a range of 60 to 90 ° C. This is followed by addition of the amount of missing indigo to adjust the desired final content of leuco indigo, either as a solid or aqueous suspension, and also, if an insufficient amount of alkali metal hydroxide was used in the first stage, of a complementary amount of mixture of alkali metal hydroxide, and the continuation of hydrogenation. After removal of the catalyst by filtration, the leuco indigo solution is stored under a protective gas, for example nitrogen.

In general, the two steps of hydrogenation together require approximately 10 to 12 hours. In the other process, a solution of indigo leuco at 20-30% by weight is initially prepared by catalytic hydrogenation, in a manner similar to the process described above and is then concentrated by evaporation until the desired content of leuco indigo is obtained. The removal by distillation of the water is preferably carried out in the absence of oxygen and at a pressure of about 60 to 1000 mbar and at a temperature of 45 to 100 ° C.

Any process of the invention offers a simple reproducible way to prepare the novel solutions of leuco indigo. They are used profitably to dye cellulosic textile material, for which the method described in WO-A-94/23114 can be used. EXAMPLES Preparation of leuco indigo solutions according to the invention. Example 1 In a 1 1 glass autoclave equipped with a disk agitator, 262 g of an aqueous 23 wt.% Indigo suspension containing 48 g (1.2 moles) of sodium hydroxide and 45 g (0.8 moles) of Potassium hydroxide had 6 g of Raney nickel in the form of a 50% by weight aqueous suspension and were purged with nitrogen, heated to 100 ° C and hydrogenated under a hydrogen pressure of 3 bar for 8 hours. After decompression, purging with nitrogen and cooling to 30 ° C, an additional 262 g of indigo granule, 48 g of sodium hydroxide and 45 g of hydroxide and also an additional 2 g of Raney nickel were added to the 23% by weight indigo leuco solution obtained in the first stage of hydrogenation. After purging with nitrogen, the indigo leuco solution was hydrogenated at a temperature of 70 ° C under a hydrogen pressure of 3 bar for an additional 3 hours. After decompression, purging with nitrogen and cooling to room temperature, the catalyst was removed by filtration. The resulting solution of 46% by weight leuco indigo showed no tendency to crystallize when stored in nitrogen at room temperature. EXAMPLE 2 500 ml of the indigo leuco solution obtained in the first step of example 1 were purged with nitrogen and then subjected to pressure initially of 120 mbar and then 80 mbar and a bath temperature of 180 ° C to remove by distillation 213 ml of water for 2 hours. The remaining solution was cooled to room temperature under nitrogen. The resulting solution of 40% by weight indigo leuco showed no tendency to crystallize after 4 weeks of storage under nitrogen at room temperature. EXAMPLE 3 In a 1 1 hydrogenation flask equipped with an intensive stirrer, a mixture of 474 g of 23 wt.% Aqueous leuco indigo salt solution (potassium salt / sodium salt, 1: 1 weight ratio) ), 90 g of a 45% by weight aqueous alkali metal hydroxide solution (KOH / NaOH, 1: 1 weight ratio) and 220 g of light indigo were added with 10 g of Raney nickel as a solution 50% by weight and purged with nitrogen, heated to 70 ° C and hydrogenated with hydrogen under atmospheric pressure for about 4 hours. After purging with nitrogen, cooling to 40-50 ° C, the catalyst was removed by filtration and the concentration of indigo leuco salt was adjusted to 40% by weight by the addition of water. Example 4 333 g of water were removed by distillation from 750 g of a 25% by weight aqueous solution of an indigo leuco salt (potassium salt / sodium salt, weight ratio 1: 1) at a bath temperature of 140 ° C at atmospheric pressure passing a low nitrogen current there. A solution of 45% by weight indigo leuco was obtained. Example 5 A mixture of 500 g of water, 132 g of dry indigo, 12.8 g of sodium sodium hydroxide, 17.9 g of solid potassium hydroxide and 7.7 g of solid lithium hydroxide had 5 g of Raney nickel in the form of a 50% aqueous suspension by weight added there; said mixture was purged with nitrogen, heated to 70 ° C and hydrogenated under atmospheric pressure for about 3.5 hours. The resultant indigo leuco solution of approximately 20% by weight was adjusted to the 45% by weight indigo leuco content, similar to Example 4 by distilling off 226 g of water.

Claims (5)

1. CLAIMS 1. A concentrated solution of indigo leuco consisting essentially of 25 to 50% by weight of indigo leuco in the form of the indigo leuco salt, an amount that is essentially stoichiometrically sufficient to convert the indigo leuco into the neutral salt of leuco indigo of a mixture of at least two alkali metal hydroxides wherein none of the alkali metal hydroxides represents more than 70 mol%, and water.
2. 2. Indigo leuco solutions according to claim 1, wherein the alkali metal hydroxides are selected from the group consisting of lithium hydroxide, sodium hydroxide and potassium hydroxide.
3. 3. Indigo leuco solutions according to claim 1 or according to claim 2, comprising sodium hydroxide and potassium hydroxide. .
4. Indigo leuco solutions according to any of claims 1 to 3, comprising sodium hydroxide and potassium hydroxide in a molar ratio of 3: 2 to 2: 3.
5. 5. Indigo leuco solutions according to any of claims 1 to 4, comprising 35 to 45% by weight of indigo leuco. A process for preparing indigo leuco solutions according to any of claims 1 to 5 by the catalytic hydrogenation of aqueous alkaline indigo suspensions, comprising carrying out stepwise hydrogenation and first hydrogenating an indigo suspension of 20 to 30% by weight comprising from 4 to 10% by weight of the mixture and at least two alkali metal hydroxides, wherein none of the alkali metal hydroxides represent more than 70 mol% to form the indigo leuco, the addition after additional indigo to adjust the desired final content of leuco indigo and also, if appropriate, of a mixture of alkali metal hydroxides, and the continuation of hydrogenation. A process for preparing indigo leuco solutions according to any of claims 1 to 5, which first comprises the catalytic hydrogenation of an aqueous alkaline indigo suspension at 20 to 30% by weight comprising from 4 to 10% by weight of a mixing of at least two alkali metal hydroxides wherein none of the alkali metal hydroxides represent more than 70 mol% and the adjustment by evaporation of the resulting solution of leuco indigo to the desired content of leuco indigo.