Title of Invention

''AN IMPROVED PROCESS FOR THE PREPARATION OF 4-AMINO-1-NAPTHALENESULFONIC ACID SODIUM SALT''.

Abstract

This invention relates to an improved process for the preparation of 4-amino-l-napthalenesulfonic acid sodium salt characterized by the steps of:- reaction of 1-aminonapthalene with sulfuric acid at 90°C ± 5°C, and subjecting the reaction product to the step of washing wherein the reaction product is washed with sodium hydroxide (40%) and 4-amino-l-napthalenesulfonic acid sodium salt is precipitated by the addition of sodium chloride.

Full Text

FIELD OF INVENTION: The present invention relates to an improved process For the preparation oF4-amino-l-napthalenesulfonic acid sodium salt, which by way of example be advantageously employed as an useful intermediate in dye industry, electronics industry and also has haemostatic property. PRIOR ART Methods for preparation of 4-aminoapthalene-l-sulfonic acid and its sodium salt are know in the art. One of the methods reported (CA, vol.31, 1794, 1937) is to heat the 1-napthylamine together with concentrated sulfuric acid under vacuum. This method provides an yield of 88-90% of 4-aminonapthalene-1-sulfonic acid The problems with the method are (i) to conduct the reaction under vacuum, (ii) 12 h of reaction duration (iii) unspecified temperature, (iv) isolation procedure is not clear and (v) undefined quantities of starting materials employed Another procedure (CA, vol.42, 4995, 1948) involves reduction of 4-mitronapthalene-l-sulfonic acid to get 4-aminonapthalene-l-sulfonic acid. The reducing agent used was sodiumbisulfite. This method has the following disadvantages: (i) the reaction temperature is undefined, (ii) reaction time is not mentioned, (iii) yields are not accounted, (iv) incomplete data and (v) this reaction gives further side products. The procedure reported in Practical Organic Chemistry, ELBS-ongman, 1978, p678 also has some disadvantages like (i) uses over 7 equivalent excess of sulfuric acid, (ii) temperature of the reaction is not mentioned and (iii) yield obtained is given in a range 47 to 81%. OBJECTS OF THE INVENTION An object of this invention is to propose an improved method for preparation of 4-aminonapthalene-1-sulfonic acid sodium salt. Another object of this invention is to propose an improved method for preparation of 4-aminonapthalene-1-sulfonic acid sodium salt, which obviates the disadvantages, associated with the prior art. Yet another object of this invention is to propose an improved method for preparation of 4-aminonapthalene-1-sulfonic acid sodium salt which has excellent yield. Still another object of this invention is to propose an improved method for preparation of 4-aminonapthalene-1-sulfonic acid sodium salt wherein the use of sulfuric acid (of 4equivalents) was less compared to the known art. STATEMENT OF INVENTION According to this invention there is provided an improved process for the preparation of 4-amino-l-napthalenesulfonic acid sodium salt characterized by the steps of :- reaction of 1-aminonapthalene with sulfuric acid at 90°C ± 5°C, and subjecting the reaction product to the step of washing wherein the reaction product is washed with sodium hydroxide (40%) and 4-amino-l-napthalenesulfonic acid sodium salt is precipitated by the addition of sodium chloride. DESCRIPTION OF INVENTION According to this invention there is provided an improved process for the preparation of 4-amino-l-napthalenesulfonicacid sodium salt by reacting 1-aminonapthalene with sulfuric acid at 90°C ± 5°, and subjecting the reaction product to the step of washing. The amount of sulfuric acid used was 4 moles to one moles of 1-aminonapthalene. The present invention pertains to the method of preparation of 4-aminonapthalene-l-sulfonic acid sodium salt having formula 1 as shown in the drawing using 1-napthylamine and concentrated sulfuric acid, without any solvent or medium. The prepared 4-aminonapthalene-l-sulfonic acid was converted to its sodium salt using sodiumhydroxide and sodiumchloride and isolated. The present invention describes an altogether modified procedure for the preparation of 4-amino-l-napthalenesulfonic acid sodium salt by reacting 1-napthylamine with sulfuric acid and without any solvent or medium. Temperature, reaction time and proper mixing conditions are optimized to obtain over 94% yield of 4-amino-l-napthalenesulfonic acid. The 4-aminonapthalene-l-sulfonic acid was filtered and directly dissolved using sodiumhydroxide solution. The 4-amino-l-napthalenesulfonic acid sodium salt was precipitated by the addition of sodiumchloride. The yield of sodium salt obtained is 92%, Accordingly the present invention relates to a modified process of preparation of 4-aminonapthalene-1-sulfonic acid sodium salt, which comprises of heating the mixture of 1 -aminonapthalene and sulfuric acid, to 90°C ± 5°C without any solvent or medium with proper mixing of the reactants. The temperature of the reaction is very important, that at lower temperatures there was unreacted 1-napthylamine and at higher temperatures there were other side products. Well-powdered 1-napthylamine is preferred and it will give good mixing with sulfuricacid The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example 1. Powdered 1-napthylamine (25 g, 0.175 mol) was added to sulfuric acid (98%; 125g, 68 mL, 1.275 mol) with good stirring. Addition of 1-napthylamine raises the reaction mass temperature to 50°C. Addition of 1-napthylamine was completed in 20 min. The reaction, mass was heated to 90°C and was held there for 4 h. The reaction mixture became a very thick slurry type mass after 4 h of heating. Then the reaction mass was poured into a beaker containing crushed ice (300 g) with stirring. 4-aminonapthalene-1-sulfonic acid was precipitated out and it was filtered, washed with cold water (4x125 mL) and transferred to a beaker. The acid filtered was treated with sodium hydroxide (40% solution; 7 g in 15 mL water) and the pH was alkaline Then added solid sodiumchloride (20 g) to the beaker containing the above alkaline solution. The precipitated 4-aminonapthalene-l-sulfonic acid sodium salt was filtered and dried in an oven at ~120°C. Recrystallised from hot water. The yield is ~92%. Example 2: Powdered 1-napthylamine (143 g, 1.0 mol) was added to sulfuric acid (98%; 392g; 4 mol) with good stirring. Addition of 1-napthylamine raises the reaction mass temperature to 50°C. Addition of 1-napthylamine was completed in 30 mints. The reaction mass was heated to 90°C and was held there for 4 h. The reaction mixture became a very thick slurry type mass after 4 h of heating. Then the reaction mass was poured into a beaker containing crushed ice (1800 g) with stirring. 4-Amino-l-napthalenesulfonic acid was precipitated out and it was filtered, washed with cold water (3x1000 mL) and transferred to a beaker. The acid filtered was treated with sodiumhydroxide (40% solution; 45 g in 30 mL water) and the pH was alkaline. Then added solid sodiumchloride (120 g) to the beaker containing the above alkaline solution The precipitated 4-aminonapthalene-l-sulfonic acid sodium salt was filtered and dried in an oven at ~120°C. Recrystallised from hot water. The yield is ~92°C. WE CLAIM: 1. -An improved process for the preparation of 4-amino-l-napthalenesulfonic acid sodium salt characterized by the steps of :- reaction of 1-aminonapthalene with sulfuric acid at 90°C ± 5°C, and subjecting the reaction product to the step of washing wherein the reaction product is washed with sodium hydroxide (40%) and 4-amino-l-napthalenesulfonic acid sodium salt is precipitated by the addition of sodium chloride. 2. An improved process as claimed in claim 1, wherein the amount of sulfuric acid used is 4moles to one mole of 1-aminonapthalene. 3. An improved process for the preparation of 4-amino-l-napthalenesulfonic acid sodium salt substantially as herein described with reference to the examples.

Documents:

1037-del-2001-abstract.pdf

1037-del-2001-claims.pdf

1037-del-2001-correspondence-others.pdf

1037-del-2001-correspondence-po.pdf

1037-del-2001-description (complete).pdf

1037-del-2001-form-1.pdf

1037-del-2001-form-18.pdf

1037-del-2001-form-2.pdf

1037-del-2001-form-26.pdf

1037-del-2001-form-3.pdf

1037-del-2001-petition-138.pdf