Title of Invention	A METHOD FOR THE PREPARATION OF 5-CARBOXYPHTHALIDE
Abstract	The present invention relates to a method for the preparation of 5-carboxyphthalide comprising reaction of terephthalic acid with paraformaldehyde HO(CH2)nH in 20-25% oleum.

Full Text

The present invention relates to a method for the preparation of 5-carboxyphthalide, a starting material for the manufacture of the well-known antidepressant drug citalopram, l-[3-(dimethylamino)propyl]-l-(4-fluorophenyl)-l,3-dihydro-5-isobenzofurancarbonitrile. Citalopram is a selective serotonin reuptake inhibitor which has successfully been marketed as an antidepressant drug for some years, it has the following structure: and it may be prepared by the process described in US Patent No 4,650,884 according to which 5-cyanophthalide is subjected to two successive Grignard reactions, i.e. with 4-fluoro-phenyl magnesium halogenide and N,N-dimethylaminopropyl magnesium halogenide, respectively, and the resulting dicarbinol compound is subjected to a ring closure reaction by dehydration. The 5-cyanophthalide may in its turn be obtained by reaction of 5-carboxyphthalide with a dehydrating agent and a sulfonamide of the formula H2N-SO2-R wherein R is NH2, alkyloxy, optionally substituted phenyloxy, or substituted phenyl in order to obtain 5-cyanophthalide, cf our co-pending Indian patent application No.IN/PCT/2001/00854/CHE. 5-Carboxyphthalide has been described as a useful intermediate in the polymer and paint industry. However, no reliable commercial source is available at present. A known process comprises catalytic hydrogenation of trimellithic acid (DE-Al 2630927). This process provides a mixture of the 5- and 6-carboxyphthalides and, accordingly, it requires elaborate and costly purification. According to J. Org. Chem. 1970, 35, p. 1695-1696, 5-carboxyphthalide is synthesised by reaction of terephthalic acid with trioxane in liquid SO3. During this process, trioxane sublimates and precipitates thereby obstructing the equipment. Though a number of other methods failed, it has now been found that 5-carboxyphthalide may be prepared from terephthalic acid in high yields by a convenient, cost-effective procedure. Description of the invention Accordingly, the present invention provides a process for the manufacture of 5-carboxyphthalide By the process of the invention, 5-carboxyphthalide is obtained with very high purity and in high yields (> about 75%). Furthermore, as compared with the prior art process (J. Org. Chem. 1970, 35, p. 1695-1696), the process of the invention takes place without precipitation of sublimated trioxane which obstructs the equipment e.g. by precipitating in condensers. The oleum used is commercially available oleum. So the following are available from Aldrich/Fluka: 12-17% SO3 (Fuming sulfuric acid) - 15% oleum 18-24% SO3 (Fuming sulfuric acid) = 20% oleum 27-33% SO3 (Fuming sulfuric acid) = 30% oleum From other sources 20% oleum contains 20-25% SO3 In the method of the invention, the terephthalic acid is condensed with paraformaldehyde liberating water, which reacts with the SO3. When the reaction is complete, 5-carboxy¬phthalide may be isolated as follows: The reaction mixture is hydrolysed with water. The condensed product, 5-carboxyphthalide inclusive possible diphthalide impurities may then be filtered off, and the 5-carboxyphthalide may be dissolved in aqueous medium by adjusting pH to about 6.7 to 7.3, leaving possible diphthalide impurities in the solid phase. The diphthalide present may be filtered off whereupon 5-carboxyphthalide may be precipitated by acidification, filtered off, washed with water and dried. Preferably 1.0-1.33 equivalents CH.O and 1.0-2.5, preferably 1.0-2.0 are used. More preferably 1.25-1.5 equivalents SO, per equivalent terephthalic acid are used. Most preferably, about 1.37 equivalents (corresponding to about 3.3 kg 20-25% oleum/kg terephthalic acid) are used per equivalent terephthalic acid. The reaction of terephthalic acid with paraformaldehyde is carried out at elevated tempera¬ture, conveniently at about 50-148 °C, preferably 115-125°C or 138-148°C. The reaction time is not critical and may easily be determined by a person skilled in the art, a reaction time of 17-21 hours is preferably used for a 210 kg batch at 115-125°C. The time is decreased with increasing temperature. The adjustment of pH to 6.3 to 7.3 in order to dissolve the 5-carboxyphthalide formed may be effected by NaOH, e.g. about 10% aqueous NaOH. Acidification in order to precipitate the 5-carboxyphthalide may be carried out by adding sulphuric acid until pH = 2. The terephthalic acid used as a starting material is commercially available. Examples The invention is further illustrated by the following example. Example 1 5-Carboxyphthalid Terephthalic acid (10 kg) is charged into a reactor. Oleum (20% (18-24% SO3); 6 kg/kg terephthalic acid ) is added and then paraformaldehyde (1.33 equivalents, 0.24 kg/kg terephthalic acid) is added. The mixture is agitated at 125 °C for 17 hours. Water (13 kg/kg terephthalic acid and filter aid is added, the temperature is adjusted to about 70 °C. The precipitate is filtered of, washed with water and suspended in water. The pH of the suspension is adjusted to about 7 with NaOH, activated carbon, 0.07 kg/kg terephthalic acid is added, and then the mixture is filtered, the precipitate is rinsed with water. The temperature of the filtrate is adjusted to about 65°C and the pH is adjusted to about 2 with 50% sulfuric acid. The 5-carboxyphthalide precipitated is separated by filtration washed and dried. Yield 83%. Example 2 5-Carboxyphthalid Oleum (20-25% SO, 43 kg) is charged into a reactor. Terephthalic acid (13 Kg ) and then paraformaldehyde (3.8 Kg) is added. The mixture is agitated at 138-148 °C for 4"/2 hours. Water (87 L) is added and the temperature is adjusted to about 100 °C. The precipitate is filtered of, washed with water and suspended in water. The pH of the suspension is adjusted to about 7 with NaOH (about 10%), activated carbon, 0.5 Kg is added, and then the mixture is filtered, the precipitate is rinsed with water. The temperature of the filtrate is adjusted to about 85°C and the pH is adjusted to about 2 with 96% sulfuric acid. The 5-carboxyphthalide precipitated is separated by filtration washed and dried. Yield 82%. WE CLAIM; 1. A method for the preparation of 5-carboxyphthalide 2. The method any as claimed in claim 1 wherein 1.0-1.33 equivalents CH2O and 1.0- 2.5 equivalents SO3 per equivalent terephthalic acid are used. 3. The method as claimed in claim 2 wherein 1.0-2.0, in particular 1.25-1.5 equivalents SO3 per equivalent terephthalic acid are used. 4. The method as claimed in claim 3 wherein 1.37 equivalents SO3 per equivalent terephthalic acid are used. 5. The method as claimed in claim 3 wherein 3.3 kg 20-25% oleum is used per kg terephthalic acid.

Documents:

in-pct-2002-0774-che abstract duplicate.pdf

in-pct-2002-0774-che abstract.pdf

in-pct-2002-0774-che claims duplicate.pdf

in-pct-2002-0774-che claims.pdf

in-pct-2002-0774-che cprrespondence-others.pdf

in-pct-2002-0774-che cprrespondence-po.pdf

in-pct-2002-0774-che description (complete) duplicate.pdf

in-pct-2002-0774-che description (complete).pdf

in-pct-2002-0774-che form-1.pdf

in-pct-2002-0774-che form-19.pdf

in-pct-2002-0774-che form-26.pdf

in-pct-2002-0774-che form-3.pdf

in-pct-2002-0774-che form-5.pdf

in-pct-2002-0774-che others.pdf

in-pct-2002-0774-che pct.pdf

in-pct-2002-0774-che petition.pdf