FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1.. 1. TITLE OF THE INVENTION:
"AN IMPROVED PROCESS FOR PREPARING C-ACID"
2. APPLICANT:
(a) NAME: AGARWAL, SANDEEP
(b) NATIONALITY: Indian
(c) ADDRESS: Mohan Polyfab Pvt. Ltd., Plot No.6509 & 6510, GIDC,
Near New Water Tank, Ankleshwar - 393 002, Gujarat, India.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be performed.

Technical field of the invention:
The present invention relates to a process for preparing 2-chloro-5-toluidine-4-sulphonic acid (C-acid).
Background and Prior art:
C-acid is chemically known as 2-chloro-5-toluidine-4-sulphonic Acid, represented by formula I. It is an important intermediate for manufacturing printing ink, paint, Lake red C, rubber and plastics scarlet LC etc.

Various processes are known in the prior art for the synthesis of C-acid, such as toluene sulfonation method, intermediate amino toluene method, o-chloro toluene method, intermediate xylene method etc.
US4207254 describes a process for preparing 2-chloro-5-amino-para-toluene sulfonic acid, wherein a process for preparing alkali metal salt of 2-chloro-5-amino-para-toluene sulfonic acid comprises a reaction of toluene with sulfuric acid to produce para-toluene sulfonic acid, followed by its reaction with chlorine to produce 2-chloro-para-toluene sulfonic acid, which is reacted with a mixture of 50% nitric acid and 50% sulfuric acid to obtain the nitrated product. Nitrated product is then neutralized in aqueous lime slurry, which is subsequently filtered. The aqueous nitrated product is further reduced with iron to form amine and the reaction mixture is neutralized with sodium hydroxide to a pH of about 9.5-10.5. The desired toluene sulfonic acid derivatives (that exist in aqueous salt solution), may be precipitated by incrementally mixing the aqueous alkali metal salt solution containing the desired product and the mineral acid at a rate such that the pH of the mixture is maintained from about 0.5 to 1.2.

US4427600 relates to a process of preparation of l-alkyl-2-chloro-5-nitrobenzene-4-sulfonic acid, by sulfonation, chlorination and nitration starting from an alkylbenzene: wherein the alkylbenzene is sulfonated (at 100-130°C) with from about 2.5 to 3 moles of concentrated sulfuric acid per mole of alkylbenzene, the reaction product is then reacted with from about 1.1 to 1.3 moles of chlorine (at 50-100 °C) in the absence of a catalyst, the product is subsequently nitrated with highly concentrated nitric acid (98-100%) at elevated temperatures (35-100°C) to isolate the nitro compound of 65.7% yield and of 95% purity.
CN101219977 describes a process for preparing CLT acid (6-chlorine-3-aminotoluene-4-sulfonic acid) comprising toluene azeotropic dehydration method for preparing toluene sulfonic acid, using excess toluene. In the method of reduction, toluene sulphonic acid is used as standard with water (1000-2500ml) to dissolve the nitration products. l/10th of recovery solution (1) of this nitrated solution is taken to activate iron powder. The pH of the remaining solution is adjusted to 5-7 with sodium carbonate, which is then dropped into activated iron powder mixture to carry out reduction reaction; followed by adjusting pH to 9-10 by using sodium carbonate and filtering. Already neutralized hot recovery solution is used to wash iron mud. Further, combining the filtering and washing solution, followed by adjusting pH to 1.2-1.3 by using dilute sulfuric acid to obtain CLT acid. The characteristics of the invention are preparation of CLT acid without any waste sulfuric acid and to recycle the waste acidic salt solution. The yield of CLT acid obtained with toluene sulfonic acid is 59.8-63.8%.
British patent GB967874 relates to the production of para-toluenesulfonic acid, which uses a substantial excess of toluene to carry out sulfonation and to precipitate sulfonation product in hydrate form. The hydrate is filtered under vacuum and then dried to obtain p-toluene sulfonic acid monohydrate. More particularly, this invention relates to a method of separating p-toluenesulfonic acid in both anhydrous and monohydrate form from a mixture of isomeric toluenesulfonic acids.
JP58096056 (A) describes a process for the preparation of 6-chloro-3-toluidine-4-sulfonic acid from o-chlorotoluene via the stage of 5-amino-2-chlorotoluene and "baking" the latter, which comprises nitrating the o-chlorotoluene with mixed acid, separating the 2-

chloro-5-nitro-toluene from its isomers and reducing it, and baking the obtained 5-amino-2-chloro-toluene with the equimolar amount of sulfuric acid or sodium-hydrogensulfate with or without subsequent isolation of the intermediary formed aminohydrogensulfate or amine sodiumsulfate respectively, by heating to temperatures above 180°C to 6-chloro-3-toluidine-4-suIfonic acid or to its sodium salt respectively.
China's Ministry of Chemical Industry listed improvement in the techniques for synthesizing CLT acid (6-chlorine-3-aminotoluene-4-sulfonic acid) using ortho-chlorotoluene as a key item in its seventh Five Year Plan for dyeing and finishing auxiliary technology and carried out further study.
Japanese patent (Patent Publication No. 54-151945(1979)) provides a method of synthesis of CLT acid with ortho-chlorotoluene as starting material. o-Chlorotoluene is brominated by dropping Br2 in the presence of a nuclear substituted bromination catalyst, e.g. a cocatalyst of anhydrous FeCl3 and h to give 3-brom0-6-chlorotoluene, which is then reacted with an animation catalyst, e.g. Cu^O or CuCl, at 80W180°C, preferably 100W150°C, to form 6-chloro-3-toluidine. Thetoluidine is then baked with an equivalent amount of conc.sulfuric acid to afford 6-chloro-3-toluidine-4-sulfonic acid.
CN 1099027A describes a technique for synthesizing CLT acid using ortho-chlorotoluene comprising the bromination reaction to obtain 3-bromo-6-chlorotoIuene. The resultant of the bromination reaction directly takes part in the amination reaction wherein 3-bromo-6-chlorotolueneis treated with ammonia to form 3-amino-6-chlorotoluene, leached with dil. HC1, purified, followed by sulfonation reaction to finally yield 95% of CLT-acid. The object of this invention is to provide a technique for the synthesis of CLT-acid using ortho-chlorotoluene, which is simple, produce less waste and has low production cost.
Disadvantages of the processes using ortho-chlorotoluene as a starting reagent are: (1) Steam distillation which is used while purifying resultants of amination reaction has a very low efficiency (2) Solvent reflux method or vacuum baking method used in sulfonation method, require the reaction to be carried out at 180°C for 8 hours, which has severe product carbonization that affects outer appearance and quality of the product,

which further requires use of active carbon for decoloration that directly affects the yield and increases production cost.
Thus, there is still a need in the art for an improved, cost effective and commercially viable process for preparing pure 2-Chloro-5-Toluidine-4-Sulphonic Acid (C-Acid), which will be suitable for large-scale preparation of C- acid, in terms of chemical yield and purity. Accordingly, in order to improve the yield and purity of the desired product C- acid, present inventors have come up with an improved process for preparing C- acid.
Object of the Invention:
The main object of the present invention is to provide an improved process for preparing 2-chloro-5-toluidine-4-sulphonic Acid (C-Acid) with high yield and purity.
Summary of the invention:
The present invention discloses an improved process for preparing 2-chloro-5-toluidine-4-Sulphonic Acid (C-Acid) which involves sulphonation of toluene with 98% sulphuric acid to obtain sulphur mass, followed by chlorination using chlorine gas to obtain chloro mass and nitration with 70% nitric acid to obtain liquid nitro mass. Nitro mass thus obtained was chilled and neutralized by liquid ammonia (25%) or ammonia gas of 99% purity to get neutral nitro mass before reduction. The nitro mass was then further reduced with iron powder in the presence of acetic acid (32%) to obtain amino compound (C-acid). The amino compound thus obtained was filtered and isolated using hydrochloric acid with sodium hydrosulphide (NaHS) for better yield and purity.
Detailed description of the invention:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated. It is not intended to limit the invention to these particular embodiments.
As described herein the term "sulfur mass" is "p-toluene sulfonic acid"; "chloro mass" is "2-chloro-p-toluene sulfonic acid"; "nitro mass" is "2-chloro-5-nitro-p-toluene sulfonic

acid"; "amino mass" is "2-chloro-5-toluidine-4-sulphonic acid" or "C-acid" and are used in the following text interchangeably.
Accordingly, in one embodiment, the present invention provides an improved process for preparing 2-Chloro-5-Toluidine-4-Sulphonic Acid (C-Acid) with high yield and purity, wherein toluene is first reacted with concentrated sulphuric acid to yield para-toluene sulfonic acid, which is further converted into 2-chloro-p-toluene sulfonic acid and then after reaction with 70% nitric acid to 2-chloro-5-nitn-p-toluene sulfonic acid, which is further neutralized by liquid ammonia or ammonia gas and reduced with iron powder in presence of acetic acid of 32% strength to finally give 2-chloro-5-toluidine-4-sulphonic acid or C-acid of formula I
In a preferred embodiment, the present invention provides a one pot process for the preparation of nitro mass (2-chloro-5-nitro-p-toIuene sulfonic acid) comprising the steps of:
(i) sulfonating toluene with 98% sulphuric acid to obtain sulphur mass (p-toluene sulfonic acid);
(ii) chlorinating sulphur mass using chlorine gas to obtain chloro mass (2-chloro-p-toluene sulfonic acid) and
(iii) nitrating chloro mass with 70% nitric acid to obtain liquid nitro mass (2-chloro-5-nitro-p-toluene sulfonic acid).
Thus, the process according to the invention is advantageously carried out by adding 98% strength sulfuric acid to toluene in a manner such that the temperature remains in the range from 55°C to 65°C, preferably 60°C to obtain sulfur mass.
Further, chlorine is introduced at from about 50°C-60°C, preferably at 55°C to obtain chloro mass.
Concentrated nitric acid of preferably 70% strength is employed for nitrating chloro mass at a temperature range of 20-40°C, preferably at 30°C.

Liquid nitro mass obtained according to the invention is highly acidic (pH=2), which is chilled and neutralized by liquid ammonia (25%) or ammonia gas of 99% purity to get neutral nitro mass. Further, after neutralization of nitro mass by ammonia, the mass was caked by pressing.
Further in an embodiment, the nitro mass prepared according to the invention is reduced to amino compounds using iron powder in the presence of acetic acid of 32% to obtain C-acid.
Reduction is then done with iron at a temperature in the range of 90°C-95°C preferably at 90°C, for not less than 6 hours to get maximum yield of the amino compound.
According to the invention, amino compound thus obtained is filtered, isolated and purified using hydrochloric acid and sodium hydrosulphide (NaHS) to give pure C-acid cake of better yield and purity.
After total recovery of amino compound from the iron mass, iron mass obtained was washed with caustic lye till neutral pH is obtained, to easily dispose off the iron sludge without creating any pollution.
Printing ink, paint, Lake red C and other pigments, which are made with 2-chloro-5-toluidine-4-sulphonic acid or C-acid are prepared from the above said cake, employing the standard procedures for preparing such paints and pigments.
The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.
Examples:
Example 1
Preparation of 2-chloro-5-nitro-p-toluenesulfonic acid (nitro mass)

Toluene (86gm) was charged in a reactor, followed by addition of 98% sulphuric acid (340gm)at 60°C to obtain p- toluene sulfonic acid (sulphur mass). Sulphur mass obtained was maintained at 150°C.Chlorine -gas(96gm) was then passed at 55°C to obtain 2-chloro-p-toluene sulfonic acid (chloro mass); followed by nitration of chloro mass using 70% of nitric acid (82gm) at 30°C to form 2-chloro-5-nitro-p-toluenesuIfonic acid nitro mass). The liquid acidic nitro mass so obtained was chilled, further neutralized with 25% liquid ammonia (480gm) or ammonia gas of 99% purity to neutral nitro mass.The neutral nitro mass was then pressed to form a cake of nitro compound. Yield: 160gm Purity: 60%
Example 2
Preparation of 2-chloro-5-toluidine-4-sulphonic acid" or "C-acid" (amino mass)
32% acetic acid (I30gm) was added to the nitro mass (160gm) formed in Example 1 to maintain acidic pH, followed by addition of activated iron (100gm) at 90°C, for about less than 6 hours to form 2-chloro-5-toluidine-4-sulphonic acid" (amino mass).The amino mass of 32% purity was filtered and washed using HC1 (240gm) and sodium hydrosulphide (NaHS) (l.5gm).This was followed by first washing with 3000 lit water, followed by second washing (1000L water) to get total recovery of amino compound from the iron mass. Iron mass obtained was washed with caustic lye to neutral pH, to easily dispose off the iron sludge without creating any pollution. Yield: 110gm (11%) amino compound of the total volume.
Example 3
Purification of 2-chloro-5-toluidine-4-sulphonic acid" or "C-acid"(amino mass).
2-chloro-5-toluidine-4-sulphonic acid" or "C-acid" (1 l0gm) of Example 2 was taken in a brick lined vessel and 32% HC1 (240gm) was added to get cake out of liquid amino compound in the form of C-acid cake (of 50% purity) with 50% moisture, which was further filtered in nutch and washed with sodium hydrosulphide(NaHS) for removing impurities. Further, both the washings having amino compound were taken to another vessel and recycled, to yield 2-chloro-5-toluidine-4-sulphonic acid" or "C-acid" cake. Yield: 110 gm (1.3% of toluene) Purity: 65%

We Claim,
1. A process for preparing 2-chloro-5-toluidine-4-sulphonic Acid (C-Acid)
comprising the steps of:
i) sulfonating toluene with 98% sulphuric acid in the temperature range from
55 C to 65 C to obtain p-toluene sulfonic acid;
ii) chlorinating p-toiuene sulfonic acid using chlorine gas in the temperature
range from 50 C-60 C to obtain 2-chloro-p-toluene sulfonic acid;
iii) nitrating 2-chloro-p-toluene sulfonic acid with 70% nitric acid at 20-40°C
to obtain 2-chloro-5-nitro-p-toluene sulfonic acid;
iv) neutralizing reaction mass obtained in step (iii) by liquid ammonia (25%)
or ammonia gas of 99% purity; and
v) reducing neutral reaction mass obtained in step
vi) using iron powder in
the presence of 32% acetic acid in the temperature range of 90°C-95°C to
obtain C-acid.
2. The process for preparing 2-chloro-5-toluidine-4-sulphonic Acid (C-Acid)
according to claim 1, further comprising purification using hydrochloric acid and
sodium hydrosulphide (NaHS).