Process for preparing indigo carmine

Abstract

Process for preparing disodium 5,5′-indigosulfonate, the feedstock being indigo, this process including the following steps: i) the indigo is subjected to a sulfonation treatment resulting in a mixture that contains 5,5′-indigosulfonic acid, this process including: ii) a reduction treatment is applied to the mixture obtained in step i), and optionally a purification step, so as to obtain a composition including leuco-5,5′-indigosulfonic acid, iii) the leuco-5,5′-indigosulfonic acid is isolated from the composition resulting from step ii), iv) the leuco-5,5′-indigosulfonic acid resulting from step iii) is oxidized to give disodium 5,5′-indigosulfonate.

1 . A composition comprising at least 99.5% of disodium 5,5′-indigosulfonate, the percentage being measured by high-pressure liquid chromatography with detection at 290 nm. 
     
     
         2 . The composition as claimed in  claim 1  comprising at least 99.7% of disodium 5,5′-indigosulfonate, the percentage being measured by high-pressure liquid chromatography with detection at 290 nm. 
     
     
         3 . The composition as claimed in  claim 1  in which no impurity is present in an amount of greater than 0.10%, the percentage being measured by high-pressure liquid chromatography with detection at 290 nm. 
     
     
         4 . The composition as claimed in  claim 3  in which no impurity is present in an amount of greater than 0.05%, the percentage being measured by high-pressure liquid chromatography with detection at 290 nm. 
     
     
         5 . A medicament or a diagnostic product comprising the composition as claimed in  claim 1  and a pharmaceutically acceptable support. 
     
     
         6 . The medicament or diagnostic product as claimed in  claim 5 , which is in the form of a tablet or a gel capsule comprising from 1 to 1000 mg of the disodium 5,5′-indigosulfonate. 
     
     
         7 . The medicament or diagnostic product as claimed in  claim 5 , which is in the form of an aqueous solution comprising the disodium 5,5′-indigosulfonate in a concentration ranging from 0.1% to 10% by mass. 
     
     
         8 . A food composition comprising the composition as claimed in  claim 1  and a support that is compatible with a food application. 
     
     
         9 . The food composition as claimed in  claim 8 , which is in powder form. 
     
     
         10 . The food composition as claimed in  claim 8 , which is in aqueous solution form. 
     
     
         11 . The composition as claimed in  claim 1 , wherein the disodium 5,5′-indigosulfonate is obtained by a process comprising the following steps, the starting material being indigo:
 i) indigo is subjected to a sulfonation treatment leading to a mixture which contains 5,5′-indigosulfonic acid, 
 ii) the mixture obtained in step i) is subjected to a reduction treatment, and optionally a purification step, so as to obtain a composition comprising leuco-5,5′-indigosulfonic acid, 
 iii) the leuco-5,5′-indigosulfonic acid is isolated from the composition derived from step ii), and 
 iv) the leuco-5,5′-indigosulfonic acid obtained from step iii) is oxidized to disodium 5,5′-indigosulfonate. 
 
     
     
         12 . The composition as claimed in  claim 11 , in which the reduction treatment of step ii) is performed using sodium dithionite in aqueous medium. 
     
     
         13 . The composition as claimed in  claim 11 , in which the leuco-5,5′-indigosulfonic acid precipitates in the reaction medium on conclusion of step ii). 
     
     
         14 . The composition as claimed in  claim 11 , in which step iii) includes the steps of:
 iiia) filtration of the composition obtained from step ii), and   iiib) recovery of the solid retained on the filter.   
     
     
         15 . The composition as claimed in  claim 14 , in which step iii) also includes, after step iiib), at least one step iiic) consisting of washing the solid with an aqueous medium. 
     
     
         16 . The composition as claimed in  claim 15 , in which step iiic) is applied from one to five times. 
     
     
         17 . The composition as claimed in  claim 11 , in which the composition obtained on conclusion of step iii) includes at least 90 mol % of leuco-5,5′-indigosulfonic acid relative to the total number of moles of the composition. 
     
     
         18 . The composition as claimed in  claim 11 , in which step iv) includes at least one step iva) consisting of a treatment with a base in alcoholic medium in the presence of an oxidizing agent. 
     
     
         19 . The composition as claimed in  claim 18 , in which step iva) consists of a treatment with sodium ethoxide in ethanol, in the presence of an oxidizing agent. 
     
     
         20 . The composition as claimed in  claim 18 , in which the oxidizing agent is gaseous oxygen. 
     
     
         21 . The composition as claimed in  claim 18 , which also includes, after step iva), at least one step ivb) consisting of one or more washes with one or more alcoholic and/or aqueous-alcoholic solvents.