FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)
.1. TITLE OF THE INVENTION
An improved process for preparing isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoqunolin-7-one and Benzimidazo [2,1 -a]thioxanthino[2,1,9-def]isoquinolin -8-one.
2. APPLICANT
(a) NAME : SUDARSHAN CHEMICAL INDUSTRIES LTD
(b)NATIONALITY. : Indian Company registered under
the provisions of the Companies Act, 1956.

(c) ADDRESS

: 162,Wellesley Road„Pune 411001, Maharashtra state, India.

3. PREAMBLE TO THE DESCRIPTION

COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

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Title :
An improved process for preparing isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,1,9-def]isoquinolin-7-one and Benzimidazo[2,1 -a]thioxanthino[2,l ,9-def]isoquinolin-8-one.
Technical Field:
The present invention relates to a preparation of isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) by the reaction of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride with ortho-phenelenediamine in presence of organic polar solvent.
Background and Prior Art:
Benzothioxanthene compounds of present invention have excellent properties as dyestuff for synthetic fibres.
In prior art processes, the preparation of isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) have been prepared by known methods reported in the literature.
One such method is described by Peters et al. in Tetrahedron vol. 30, 1974, page 2245, wherein, benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride is reacted with excess ortho-phenelenediamine in glacial acetic acid at elevated temperatures to obtain products. In this process, glacial acetic acid is used as reaction medium in large excess. Even though, it does not appear to provide complete conversion.
Another method is disclosed in Bayer patent no.FR2232578 (1974), in which various derivatives have been prepared by using methyl carbitol as reaction medium in presence potassium acetate at about 200°C. This process claims complete conversion at high reaction temperature condition which is undesired for this mixture of products and
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use of potassium acetate as accelerator could be a draw back to obtain product in desired shade.
It has been found that the method for producing valuable dyestuff constitutes mixture of isomeric compounds of formula I & II in prior art processes. These processes can be further improved by using appropriate condensing medium which overcomes various disadvantages to provide safer process for commercial success with good yield and high purity.
Description:
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention as described bellow in the preferred embodiment.
The present invention relates to a process for producing an isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) that comprises mixing of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride with ortho-phenelenediamine and heating the mixture in presence of organic polar solvent to provide an essentially quantitative yield products with an improved color specification.
(Ill) (IV)
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The isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) prepared by the process of the present invention by reacting benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride of formula III with ortho-phenelenediamine of formula IV in presence of polar organic solvent at temperature ranging from about 100°C to 170°C as shown below.


According to the present invention, an isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) is produced by reacting the reactants described above at 100°C-170°C in polar organic solvent medium.
The suitable organic polar solvent used in present invention is substantially unreactive toward reactants and products that is N,N'- Dimethyl acetamide. The N,N'-Dimethyl acetamide is preferred organic solvent in present invention.
The process typically is carried out over a temperature range of about 100°-170°C, preferably 130°- 155°C. Pressure normally is not an important process condition and the process therefore normally is performed at ambient pressure or moderately elevated pressure generated in a sealed reactor if used, i.e., autogenously pressures
The reaction is conducted in a substantially oxygen-free atmosphere. For example, an inert gas such as nitrogen or argon can be continuously passed through the reaction zone during the condensation.
The isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) in the present invention obtained are reddish orange powder having strong orange fluorescence in UV light.
Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or matter.
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Present invention is illustrated with the help of following example. Example
Into a four neck round bottom flask equipped with a nitrogen inlet and outlet, mechanical stirrer and a condenser were charged 15-25 part N,N'- Dimethyl acetamide(DMAC) per gm of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride of formula III, and 0.16 moles of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride of formula III, 2-3 mole equivalent of ortho-phenelenediamine with nitrogen protection. The mixture was stirred at room temperature under nitrogen purging for 15-45 minutes. The mixture was heated slowly to 130 ° C and maintained at 130-160 °C for period of 10-20 hours. The progress of reaction was monitored by Thin Layer Chromatography(TLC). After completion of reaction, the resultant reddish suspension was cooled to 30 °C, -10°C filtered through suction and washed with DMAC(2 x. 50ml) followed with water (2x.l00 ml) and methanol( 2x 50ml) to get pure product. The product thus obtained was dried under reduced pressure at 70-90°C till constant weight Yield 79-82 %( 48gm-50gm). It was analyzed by High performance liquid chromatography (HPLC) for its purity. The product thus obtained having combined purity 98%-99% of both isomers of formula I &II by qualitative HPLC analysis was characterized by elementary analysis, IR and UV.
Advantages of the Present Invention:
1. The present invention does not require high reaction temperature conditions(above 200°C) and is performed at lower temperature than conventional methods reported elsewhere.
2. The present invention provides improved color with high yield and purity.
3. Solvent used in present invention is low cost and easily available. This can be easily recycled where as in prior art processes has used solvents which either difficult to recycle or can not be recycled.
The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention; which is defined by the scope of the following claims.
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We Claim:
1. An improved process for preparing an isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) that comprises mixing of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride with ortho-phenelenediamine and heating the mixture at temperature 100°C-170°C, in presence of organic polar solvent as shown below.

2. A process as claimed in claim 1 wherein, polar organic solvent used is N,N'-Dimethyl acetamide
3. A process as claimed in claim 1 wherein, reaction medium and condensing agent used is N,N'-Dimethyl acetamide
4. A process as claimed in claim 1 wherein ortho phenelenediamine is used in 2-3 mole equivalent.
5. A process as claimed in claim 1 substantially as herein described with reference to
the example and specification.

Abstract
An improved process for preparing an isomeric mixture of Benzimidazo[l,2-b]thioxanthino[2,l,9-def]isoquinolin-7-one of formula (I) and Benzimidazo[2,l-a]thioxanthino[2,l,9-def]isoquinolin-8-one of formula (II) that comprises mixing of benzo[k,l]thioxanthene-3,4-dicarboxylic anhydride of formula (Ill)with ortho-phenelenediamine of formula of formula (IV) and heating the mixture in presence of organic polar solvent in oxygene free atmosphere as shown below.