CLIAMS:1. A process for the preparation of Dantron crude comprising the step of treating dimethylformamide dissolved 1, 8-dinitroanthraquinone-9, 10-dione with a metal salt at 105 – 110 0C allowing the completion of reaction.
2. The process of claim 1 wherein the reaction is completed in 5 hours.
3. The process of claim 1 wherein the metal salt is sodium formate.
4. The process of claim 1 wherein the Dantron crude is of 97.43% purity.
5. A process for the purification of Dantron crude; the purification comprises
(i) dissolving Dantron crude 1, 8-dihydroxyanthraquinone in an organic solvent ;
(ii) removed the organic solvent and treating of the residue with acetone at 40-600C and
(iii) isolate the pure Dantron by cooling.
6. The process of claim 5, wherein the organic solvent is toluene in step (i).
7. The process of claim 5, wherein Dantron is isolated after cooling at 5-200C.
8. The process of claim 5, wherein the purity of 1, 8-dihydroxyanthraquinone is greater than 98.5%.
9. The process of claim 5, wherein the particle size is not more than 50 µm.
,TagSPECI:Description

The present invention relates to process for preparation of dantron (1, 8-dihydroxyanthraquinone) from 1,8-dinitroanthraquinone instead of a mixture of nitroanthraquinone of very high yield and high purity dantron of particle size not more than 50 µm.

Dantron also known as chrysazin or 1,8-dihydroxyanthraquinone, is an organic substance, formally derived from anthraquinone by the replacement of two hydrogen atoms by hydroxyl groups (–OH). It is used in some countries as a stimulant laxative.

Formula I

US patent No. 4,292,248 relates to the preparation of hydroxyanthraquinones and, more particularly, to the preparation of 1-hydroxyanthraquinone and dihydroxyanthraquinones from the corresponding nitroanthraquinone

The prior art process for the preparation of 1, 8-dihydroxyanthraquinone involve dinitroanthraquinone and other isomers.

The present inventors while developing a process for the preparation of dantron i.e. 1, 8-dihydroxyanthraquinone have surprisingly observed a very high yield and a high purity crude product formation at a much reduced reaction time when the starting material is 1,8-dinitroanthraquinone instead of mixture of nitroanthraquinone. The inventors have also observed that high purity crude dantron may further be purified by sequentially washing with different organic solvents namely toluene and acetone yielding pure dantron of particle size not more than 50 µm.

In one of the embodiment of the inventions 1, 8-dintroanthraquinone-9,10-dione may be dissolved in dimethylformamide and treated with a metal salt by maintaining a temperature of around 105 -1100C allowing the reaction to go to completion in about 5 hours by checking the absence of 1,8-dinitroanthraquinone and 1-hydroxy-8-nitroanthraquinone. The metal salt may be sodium formate.

Crude dantron may be cooled to 35-450C. The reaction contents may be stirred after adding acetone, water and acidified hydrochloric acid (30-35%). High purity crude dantron (HPLC purity 97.43%) may be isolated after washing with acetone and water.

In another embodiment of the invention crude dantron may be purified by dissolving in two different organic solvents sequentially resulting in high yield (0.5-0.65 w/w) pure dantron (HPLC purity 98.57%) of particle size not more than 50 µm.

The organic solvents may be toluene and acetone respectively. Crude dantron may be dissolved in toluene and the reaction contents stirred at a temperature of 40 - 500C. After achieving temperature charcoalised and filtered, toluene removed under reduced pressure and solid obtained may further be dissolved in acetone and refluxed for 1 hr under stirring. The cooled and filtered reaction contents may be washed with acetone to yield high purity and high yield dantron (HPLC purity 98.57%) of particle size not more than 50 µm. The crystalline dantron x-ray diffraction 2? values produced by the process of this invention are tabulated in Table below. Figure 1 gives the x-ray diffraction spectrum.
Table
2? Relative Intensity (%)
11.206460 100
15.573890 5.05
17.509450 4.38
19.032650 32.14
20.857970 0.16
21.941190 0.89
22.584260 3.13
23.398650 3.21
24.553260 15.59
25.978250 11.89
27.695350 14.75
29.504450 2.25
31.572350 2.89
32.187490 0.33
34.153550 2.19
34.940560 7.13
35.934580 1.19
37.608810 1.36
38.589480 2.25

The metal salt may be selected from one or more of metal salts such as sodium formate, potassium formate, sodium carbonate and potassium carbonate.

The present invention is further illustrated by the following examples which are provided merely to be exemplary of the invention and do not limit the scope of the invention. Certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

Example 1

Preparation of Dantron crude (1, 8-dihydroxyanthraquinone)
1,8-Dinitroanthraquinone (100 g, 0.335 mol) was dissolved in DMF (700 mL) and treated with sodium formate (68.4 g, 1.00 mol). The reaction mixture stirred at 105 – 110 0C with air purging for 5 hours. Sample analyzed in HPLC to ensure absence of 1, 8-Dinitroanthraquinone and 1-hydroxy-8-nitroanthraquinone. The reaction mixture cooled to 35-45 °C and acetone (400 mL), water (100 mL) added and further acidified with (30-35 %) hydrochloric acid (200 mL). The resulting suspension stirred for 30 min, filtered and washed with acetone (100 mL) and water (1.0 L) to get 62.0 g Dantron Crude (HPLC purity 97.43 %).

Example 2

Preparation of pure Dantron (1, 8-dihydroxyanthraquinone)

Dantron Crude (62.0 g) dissolved in toluene (2000 mL) and charcoalised and stirred at 45 – 50 oC for 30 min. Filtered to remove charcoal and recovered toluene under vacuum. To the resultant semi solid acetone (500 mL) added and refluxed for 1 h under stirred, cooled to 5 – 10 oC, filtered and washed with acetone to get 51.1 g Dantron (HPLC purity 98.57 %).