FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
"PROCESS FOR PREPARATION OF DIMETHYL FUMARATE"
Glenmark Pharmaceuticals Limited;
Glenmark Generics Limited
an Indian Company, registered under the Indian company's Act 1957 and having its
registered office at
Glenmark House,
HDO- Corporate Bldg, Wing-A,
B. D. Sawant Marg, Chakala, Andheri (East), Mumbai- 400 099
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a process for the preparation of dimethyl fumarate.
BACKGROUND OF THE INVENTION
Dimethyl fumarate is represented by the structure of formula I.

Dimethyl fumarate is indicated for the treatment of patients with relapsing forms of multiple sclerosis. Dimethyl fumarate is marketed under the brand name TECFIDERA® in the United States.
Processes for the preparation of dimethyl fumarate known in the art show presence of impurities such as dimethyl sulfate, monomethyl fumarate, dimethyl maleate in dimethyl fumarate. Use of acid such as sulfuric acid as a catalyst in esterification reaction is also known to pose several problems such as corrosion of reaction vessels, catalyst recovery and waste disposal.
Impurities in dimethyl fumarate or any active pharmaceutical ingredient (API) are undesirable and, in extreme cases, might even be harmful to a patient being treated with a dosage form containing the API.
It is also known in the art that impurities in an API may arise from degradation of the API itself, which is related to the stability of the pure API during storage, and the manufacturing process, including the chemical synthesis. Process impurities include unreacted starting materials, chemical derivatives of impurities contained in starting material, synthetic by-products, and degradation products.
Impurities introduced during commercial manufacturing processes must be limited to very small amounts, and are preferably substantially absent.
Thus there is a need in the art for improved processes for preparing pure dimethyl fumarate, which are more industrially applicable.

The present invention provides commercially viable simple scalable process for the preparation of dimethyl fumarate free of genotoxic impurities.
SUMMARY OF THE INVENTION
The present invention provides a process for the preparation of dimethyl fumarate, a compound of formula I,

in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumaric acid with an acyl halide in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with a base; and
(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate.
In another embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid.
In another embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid and free of dimethyl sulfate.
In another embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15%.
In another embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15% and dimethyl maleate content of less than 5 ppm.

In another embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 5 ppm of dimethyl maleate. BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Fig 1: XRD pattern of dimethyl fumarate according to example 6.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for the preparation of dimethyl fumarate, a compound of formula I,

in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumaric acid with an acyl halide in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with a base; and
(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate.
In the present application, the term "room temperature" means a temperature of about 25°C to about 30°C. The term "anion of a mineral acid" includes group consisting of chloride, bromide, iodide, fluoride, sulphate, nitrate and phosphate. The term "acyl" includes groups such as acetyl, optionally substituted benzoyl, pivaloyl. The term "optionally substituted benzoyl" means benzoyl which is optionally substituted with halo or nitro group wherein halo includes C1, Br, I. The term "halide" includes group consisting of chloride, bromide, iodide.
In (a) of the process for the preparation of dimethyl fumarate, fumaric acid is reacted with an acyl halide in methanol to obtain dimethyl fumarate, the compound of formula I.

The acyl halide that may be utilized for this step includes, but is not limited to acetyl chloride, acetyl bromide, acetyl fluoride.
The reaction may be carried out at a temperature in the range of about 25°C to about the reflux temperature of the solvent. Preferably the reaction is carried out at a temperature of about 40°C to about 65°C.
The reaction is carried out for a period of about 1 hour to about 15 hours. Preferably the reaction is carried out for a period of about 2 hours to about 6 hours.
The molar equivalent of acyl halide employed is from about 0.5 times the molar amount to about 3 times the molar amount with respect to fumaric acid. Preferably acyl halide used is in the range from about an equimolar amount to about 2 times the molar amount of fumaric acid.
In one embodiment, the molar equivalent of acyl halide employed is >0.5% times the molar amount with respect to fumaric acid.
In one embodiment, fumaric acid is reacted with acetyl chloride in methanol to obtain dimethyl fumarate.
In (b) of the above process, dimethyl fumarate, the compound of formula I is subjected to treatment with a base.
Treatment of dimethyl fumarate with a base includes either dissolving dimethyl fumarate in a suitable solvent followed by washing with a base, or slurrying dimethyl fumarate with a base, or directly treating the reaction mixture containing dimethyl fumarate with a base.
The base that may be utilized for this step includes, but is not limited to alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide; alkaline earth metal hydroxides; alkali metal carbonates such as sodium carbonate, potassium carbonate, caesium carbonate; alkaline earth metal carbonates; alkali metal bicarbonates such as sodium bicarbonate. Preferably the base selected is sodium bicarbonate.
In one embodiment, the reaction mixture containing dimethyl fumarate is treated with a base.
In one embodiment, dimethyl fumarate is isolated from the reaction mixture and then treated with a base.

In one embodiment, dimethyl fumarate, the compound of formula I is isolated from the reaction mixture and then slurred in aqueous base solution.
In one embodiment, dimethyl fumarate, the compound of formula I is isolated from the reaction mixture and then slurred in aqueous sodium bicarbonate solution.
Advantageously the treatment of compound of formula 'I with base leads to dimethyl fumarate free of genotoxic impurity methyl chloride and having less than 400 ppm of an anion of a mineral acid.
The content of impurities in dimethyl fumarate such as an anion of a mineral acid, fumade acid, dimethyl sulfate, monomethyl fumarate, dimethyl maleate is monitored by analytical techniques described herein.
In (c) of the above process, dimethyl fumarate, the compound of formula I is
isolated with a purity of at least 99.0% as determined by HPLC, containing less than 400
ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate.
In one embodiment, the isolation of the compound of formula I includes
crystallization in a solvent.
The solvent that may be utilized for this step includes, but is not limited to alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 1-octanol and the like; esters such as methyl acetate, ethyl acetate, n-propyl acetate, and tert-butyl acetate and the like; ketones such as acetone, ethyl methyl ketone and methyl isobutyl ketone and the like; ethers such as dimethyl ether, diethyl ether, diisopropyl ether, tert-butyl methyl ether, tetrahydrofuran, dibxane and the like; haloalkanes such as dichloromethane, chloroform and the like; acetonitrile; dimethyl sulfoxide; dimethyl formamide; dimethyl acetamide; water or mixtures thereof. Preferably the solvent selected is methanol.
In one embodiment, the isolation of the compound of formula I includes crystallization in methanol.
Removal of solvent may be accomplished by substantially complete evaporation of the solvent or concentrating the solution, cooling the solution if required and filtering the obtained solid.
The solid material obtained above may be further dried. Drying may be suitably carried out by any method, known in the art, including but not limited to, using a tray

drier, vacuum oven, air oven, fluidized bed drier, spin flash drier, flash drier, and the like. The drying may be carried out under reduced pressures and at elevated temperatures. The temperature may range from about ambient temperature to about 100°C, for a time period that produces the desired result.
In one embodiment, the drying may be carried out at temperature range of 25-30°C, for a period of about 6 hours followed by drying at temperature range of 45-50°C.
In one embodiment, the isolation of the compound of formula I is carried out without use of column chromatography purification.
In one embodiment, the isolation of the compound of formula I in a purity of at least 99% is carried out directly from the reaction mixture without use of column chromatography purification.
In one embodiment, the present invention provides a process for the preparation of dimethyl fumarate, a compound of formula I, in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumaric acid with an acyl halide in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with a base; and
(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate without use of column chromatography purification.
In one embodiment, the present invention provides a process for the preparation of dimethyl fumarate, a compound of formula I, in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of chloride ion and less than 5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumaric acid with an acyl halide in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with a base; and

(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of chloride ion and less than 5 ppm of dimethyl maleate
In one preferred embodiment, the present invention provides a process for the preparation of dimethyl fumarate, a compound of formula I, in a purity of at least 99.0% as determined by HPLC, containing less than 100 ppm of chloride ion and less than 3.5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumaric acid with acetyl chloride in about equimolar amounts in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with alkali metal bicarbonate; and
(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 100 ppm of chloride ion and less than 3.5 ppm of dimethyl maleate
The compound of formula I prepared by the process of the present invention has a purity of at least about 99.0%. Preferably the total purity is at least about 99.5%, more preferably the total purity is at least about 99.9%, as measured by high performance liquid chromatography.
The compound of formula I prepared by the process of the present invention has fumaric acid content of less than 0.2%, preferably less than 0.1%, more preferably less than 0.05%, as measured by high performance liquid chromatography.
Fumaric acid is a known compound and can be prepared by processes known in the art. Fumaric acid can be prepared by isomerization of maleic acid, by heating malic acid, by oxidation of furfural, by reduction of tartaric acid with phosphorus and iodine.
In one embodiment, maleic anhydride was heated in water to give maleic acid which was converted to fumaric acid in presence of inversion agent such as thiourea.
In one embodiment, fumaric acid obtained is slurried in water and the slurry obtained is heated at 85-90°C for about 30 minutes, followed by cooling the slurry at 25-30°C and maintaining at 25-30°C and isolating the fiimaric acid.
In one embodiment, fumaric acid obtained has maleic acid content less than 0.15%w/w as determined by HPLC.

In one embodiment, the present invention provides fumaric acid wherein maleic acid is absent.
The present invention provides dimethyl fumarate, obtained by the above process, having chemical purity, as described, analyzed by using high performance liquid chromatography (HPLC) with the conditions described below: Reagents, Solvents and Standards: Water (Milli Q or equivalent) Perchloric acid 70% (AR Grade) Acetonitrile (HPLC Grade) Chromatographic Conditions:
Apparatus: A High Performance Liquid Chromatograph equipped with quaternary gradient pumps, variable wavelength UV detector attached with data recorder and integrator software.
Column: GL Science, Inertsil ODS 3V, 250 X 4.6mm, 5μ Column temperature: 30°C Sample cooler temperature: 15°C Mobile Phase: Mobile phase A = Buffer
Buffer: 0.5mL of Perchloric acid dissolve in l000mL of water. (0.05% Perchloric acid in water) Mobile phase B = Acetonitrile

Time (min.) % Mobile Phase A % Mobile Phase B
0.01 90 10
03 90 10
30 50 50
40 50 50
43 90 10
50 90 10
Diluent: Acetonitrile: Water (20:80, v/v) Flow Rate: 1 .OmL/minute Detection: UV 210nm Injection Volume: 20μL

The retention time of dimethyl fumarate is about 20.0 minutes under these conditions. Relative retention time for fumaric acid is about 0.23 and for monomethyl fumarate is about 0.57 with respect to dimethyl fumarate under these conditions.
The present invention provides dimethyl fumarate, obtained by the above process, wherein the amount of an anion of a mineral acid is determined by analytical techniques, for example, chloride ion content can be monitored by ion chromatography, potentiometric titration with silver nitrate, turbidimetric method; sulphate ion content can monitored by ion chromatography, turbidimetric method.
The present invention provides dimethyl fumarate, obtained by the above process, wherein the chloride ion content was determined by USP method as described below: Preparation of Standard Solution:
Take 0.2mL of 0.02N hydrochloride acid solution in 30-40mL of water and mix. Filter this solution through 0.45fi Nylon filter. Add lmL each of nitric acid and 0.1N silver nitrate TS and sufficient water to make 50mL. Mix and allow stand for 5 minutes protected from direct sunlight. Preparation of Test Solution:
Take 0.35g sample in suitable test tube. Add 30-40mL of water and sonicate for 3-4 minutes and filter through 0.45μ Nylon filter. Add lmL each nitric acid and 0.1N silver nitrate TS and sufficient water to make 50mL. Mix and allow stand for 5 minutes protected from direct sunlight. Then compare the turbidity of test and standard solution.
The present invention provides dimethyl fumarate, obtained by the above process, having dimethyl maleate content, as described, analyzed by using high performance liquid chromatography (HPLC) with the conditions described below: Reagents, Solvents and Standards: Water (Milli Q or equivalent) Potassium dihydrogen phosphate (AR Grade) Acetonitrile (HPLC Grade) o-phosphoric acid (AR Grade) Chromatographic Conditions:

Apparatus: A High Performance Liquid Chromatograph equipped with quaternary
gradient pumps, variable wavelength UV detector attached with data recorder and
integrator software.
Column: GL-Science, Inertsil ODS 3V, 250 x 4.6mm, 5μ
Column temperature: 30°C
Sample cooler temperature: 15°C
Mobile Phase:
Mobile Phase A = Buffer
Buffer: 0.01M Potassium dihydrogen phosphate. Adjust pH 4.0 with o-phosphoric acid.
Mobile Phase B = Acetonitrile

Time (min.) % Mobile Phase A % Mobile Phase B
0.01 80 20
03 80 20
30 50 50
32 80 20
40 80 20
Diluent: Acetonitrile:Water (40:60, v/v)
Flow Rate: 1.0 mL/minute
Detection: UV210nm
Injection Volume: 50μL
The retention time of dimethyl maleate is about 10.0 minutes under these conditions.
The present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of chloride ion.
In one preferred embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 100 ppm of chloride ion.
The present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid and free of dimethyl sulfate.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of chloride ion and free of dimethyl sulfate.

In one preferred embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 100 ppm of chloride ion and free of dimethyl sulfate.
The present invention provides dimethyl fumarate, obtained by the above process, having dimethyl sulphate content, as described, determined by residual solvent analysis using gas chromatography (GC) with the conditions described below: Chromatographic Parameters:
Instrument: Gas chromatograph equipped with FID detector and autosampler. Column: DB-1, 30m x 0.32mm, l.Oμm
Column Temperature: 40°C (hold for 2 minutes) to 240°C @ 20°C/minute, hold at 240°C for 20 minutes Injector/detector: 150°C/270°C Carrier gas: Nitrogen Linear velocity: 30cm/sec Split Ratio: (2:1) Injection Volume: 5.0μL Diluent: Dichloromethane (Merck, HPLC grade)
The present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15%.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, having monomethyl fumarate content of less than 0.15% preferably less than 0.1%, more preferably less than 0.05%.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of chloride ion, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15%.
In one preferred embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 100 ppm of chloride ion, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.05%.

The present invention provides dimethyl fumarate, obtained by the above process, having monomethyl fumarate content, as described, analyzed by HPLC with the conditions as described supra.
The present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15% and dimethyl maleate content of less than 5 ppm.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, having dimethyl maleate content of less than 5 ppm, preferably less than 3.5 ppm.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 400 ppm of chloride ion, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15% and dimethyl maleate content of less than 5 ppm.
In one preferred embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 100 ppm of chloride ion, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.05% and dimethyl maleate content of less than 3.5 ppm.
The present invention provides dimethyl fumarate, a compound of formula I, containing less than 5 ppm of dimethyl maleate.
In one embodiment, the present invention provides dimethyl fumarate, a compound of formula I, containing less than 3.5 ppm of dimethyl maleate.
The X-Ray powder diffraction of dimethyl fumarate can be measured by an X-ray powder diffractometer equipped with a Cu-anode (1=1.54 Angstrom), X-ray source operated at 45 kV, 40 mA and a Ni filter is used to strip K-beta radiation. Two-theta calibration is performed using an NIST SRM 640c Si standard. The sample was analyzed using the following instrument parameters: measuring range=2-50o 2θ; step width=0.017°; and measuring time per step=5 sec.
The D10, D50, and D90 values are useful ways for indicating a particle size distribution. D90 is a size value where at least 90 percent of the particles have a size smaller than the stated value. Likewise D10 refers to 10 percent of the particles having a

size smaller than the stated value. D50 refers to at least 50 percent of the particles having a size smaller than the stated value and D[4,3] value refers to a mean particle size. Methods for determining D10, D50, D90 and D [4,3] include those using laser light diffraction with equipment sold by Malvern Instruments ltd.
The particle size distribution of dimethyl fumarate was determined by laser diffraction on Malvern Mastersizer 2000..
In one embodiment, the present invention provides coarser particles of dimethyl fumarate having D90 of at least 400 urn.
In one embodiment, the present invention provides dimethyl fumarate wherein D90 is between 400-600 urn.
The examples that follow are provided to enable one skilled in the art to practice the invention and are merely illustrative of the invention. The examples should not be read as limiting the scope of the invention as defined in the features and advantages.

EXAMPLES
EXAMPLE 1 Preparation of fumaric acid
A suspension of maleic anhydride (250g) in water (375mL) was stirred at about room temperature for about 15min. The reaction mixture was heated to about 45°C to about 50°C and was maintained at about the same temperature for about 2h. Thiourea (7.75g) was then added to the clear solution at about 45°C to about 50°C. The reaction mixture was stirred at about the same temperature for about lh. The reaction mixture was then cooled to about 10°C to about 15°C and maintained at about the same temperature for about lh. The solid obtained was filtered and washed with water, dried at about 55°C to about 60°C under vacuum for about 12h. The quality of the product complies as per USP specification. Yield: 290g
EXAMPLE 2 Preparation of dimethyl fumarate
To a suspension of fumaric acid (500g) in methanol (2500mL) was added acetyl chloride (337g) at controlled temperature (at about below 45°C) over a period of about 30min. The reaction mixture was maintained at about 50°C to about 60°C for about 5h. The reaction mixture was then cooled to about 15°C to about 20°C and was maintained at about the same temperature for about lh. The solid obtained was filtered and washed with methanol. The wet solid was slurred in 2% aqueous sodium bicarbonate solution, filtered and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for about 12h. Yield: 550g
The above crude dimethyl fumarate was dissolved in methanol (11L) at about 60°C and the hot solution was filtered through 2 micron cartridge. The particle-free filtrate was concentrated and the obtained slurry mass was cooled to about room temperature and further to about 10°C to about 15°C and maintained at about the same temperature for about lh. The solid obtained was filtered, washed with methanol and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for about 12h. Yield: 510g
Purity (HPLC): 99.85% Chloride ion content: < 100 ppm

Dimethyl sulfate content: below detection limit
Monomethyl fumarate content: < 0.05%
Dimethyl maleate content: <3.1 ppm
PSD: Before milling- D90: 672μm, D50: 242μm, D10: 72μm
After milling- D90: 45μm, D50: 21μm, D10: 9μm XRPD peaks of dimethyl fumarate before milling:

Pos.
[°2Th.] d-spacing
[A] Rel. Int. [%] Pos. [°2Th] d-spacing
[A] Rel. Int.
[%]
6.81 12.97 0.03 31.08 2.87 0.03
9.91 8.92 0.30 32.15 2.78 0.28
10.98 8.05 83.33 32.67 2.73 0.23
16.73 5.29 0.20 32.78 2.72 0.25
17.54 5.05 0.54 33.29 2.68 1.76
19.88 4.46 0.37 33.96 2.63 0.62
21.30 4.17 0.38 36.67 2.44 0.08
22.03 4.03 100.00 40.53 2.22 0.12
23.81 3.73 0.95 41.36 2.18 2.03
24.03 3.70 3.58 42.80 2.11 0.40
24.63 3.61 0.15 43.62 2.07 0.05
26.24 3.39 .0.34 44.90 2.01 1.24
27.32 3.26 17.37 46.33 1.95 0.19
28.90 3.08 0.09 47.93 1.89 0.07
XRPD peaks of dimethyl fumarate after milling:

Pos.
[°2Th.] d-spacing
[A] Rel. Int. [%] Pos. [°2Th.] d-spacing
[A] Rel. Int.
[%]
10.95 8.07 59.02 35.37 2.53 0.29
16.75 5.29 10.22 36.64 2.45 0.98
17.52 5.06 25.19 37.23 2.41 0.25
19.75 4.49 0.16 38.93 2.31 1.08
22.00 4.03 66.62 39.53 2.27 0.42
22.31 3.98 3.30 40.14 2.24 1.12
24.04 3.70 100.00 40.49 2.22 1.23
26.24 3.39 15.20 41.33 2.18 8.91
27.35 3.25 95.19 42.98 2.10 5.58
28.88 3.09 2.80 44.86 2.01 0.72
31.08 2.87 0.21 45.56 1.98 0.46
32.15 2.78 0.98 46.48 1.95 2.82
32.83 2.72 4.91 46.96 1.93 0.95
33.24 2.69 1.69 47.94 1.89 1.49
33.90 2.64 8.56 48.65 1.87 1.29
34.70 2.58 2.76

EXAMPLE 3 Preparation of dimethyl fumarate
To a suspension of fumade acid (l0g) in toluene (80mL) was added trimethyl orthoacetate (16.9g) drop wise. The reaction mixture was refluxed for about 6h. The reaction mixture was then cooled to about room temperature. Water (50mL) added to the reaction mixture. The reaction mixture was stirred for about 30min and the two layers were separated. The organic layer was washed with 5% aqueous sodium bicarbonate solution and then with water and concentrated under reduced pressure at about below 40°C. The obtained residue was slurred with methanol (30mL) for about 30min. The slurry mass was filtered, washed with methanol and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for about 12h. Yield: 6.66g
EXAMPLE 4 Preparation of dimethyl fumarate
To a suspension of fumaric acid (lOg) in tert-butyl methyl ether (50mL) was added perchloric acid (1.67g) and the reaction mixture was refluxed for 18h. The reaction mixture was then cooled to about room temperature and 20% sodium carbonate solution (lOOmL) was added to it. The reaction mixture was stirred for about 30min and methylene chloride (50mL) was added to it. The reaction mixture was stirred for about 30min and the two layers were separated. The aqueous layer was again extracted with methylene chloride (50mL) and the combined organic layer was concentrated under reduced pressure at about below 35°C. The obtained residue was slurred with methanol (30mL) for about 30min. The slurry mass was filtered, washed with methanol and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for about 12h. Yield: 9.3g
EXAMPLE 5 Preparation of dimethyl fumarate
To a suspension of fumaric acid (lOg) in methanol (65.22mL) was added p-toluene sulfonic acid (14.83g) in one lot at about 25°C. The reaction mixture was heated to about 67°C to about 70°C and was maintained at about the same temperature for about 5h. The reaction mixture was then cooled to about 15°C to about 20°C and was maintained at about the same temperature for about 2h. The solid obtained was filtered and washed with methanol and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for about 12h. Yield: 10.3g

EXAMPLE 6 Preparation of dimethyl fumarate
To a suspension of fumaric acid (1 kg) in methanol (6 L) was added acetyl chloride
(0.68kg) at temperature in the range of 25-45°C over a period of about 30min. The
reaction mixture was maintained at about 60°C-70°C for about 2.5h. If required the above
process was repeated and the reaction mass was heated at about 60°C -70°C for about
2.5h. The reaction mixture was then cooled to about 15 -20°C and was maintained for
about In. The slurry obtained was centrifuged to obtain a wet solid. The wet solid
obtained above was slurried with sodium bicarbonate and stirred at 25-30°C for about 1
hour filtered and dried at about 25°C for about 6h and further dried at about 40°C to
about 45°C for about 12h.
Yield: 550g
The above crude dimethyl fumarate was dissolved in methanol and the hot solution was
filtered through 2 micron cartridge. The particle-free filtrate was concentrated and the
obtained slurry mass was cooled to about room temperature first and further to 10°C to
15°C and maintained for about lh. The solid obtained was filtered, washed with methanol
and dried at about 25°C for about 6h and further dried at about 40°C to about 45°C for
about 6 h.
Purity (HPLC): 99.9%
Chloride ion content: < 100 ppm
Dimethyl sulfate content: below detection limit
Monomethyl fumarate content: < 0.02%
Fumaric acid: Not detected (below 0.01%)
Dimethyl maleate content: <3.1 ppm
Monomethyl maleate: <3.1 ppm
XRPD peaks of dimethyl fumarate

Pos. [°2Th.] d-spacing [A] Rel. Int. [%] Pos. [°2Th] d-spacing [A] Rel. Int. [%]
2.063 42.80 0.13 33.97 2.63 0.13
6.85 12.89 0.05 36.44 2.46 0.03
9.88 8.94 0.36 41.28 2.18 2.96
10.95 8.07 87.44 42.82 2.11 0.17
16.76 5.28 0.06 43.62 2.07 0.07
17.41 5.09 0.21 44.87 2.01 1.12

19.85
4.47 0.41 46.22 1.96 0.05
21.23 4.18 0.45 47.96 1.89 0.04
22.00 4.03 100.00 33.26 2.69 1.63
24.04 3.70 3.50 33.97 2.63 0.13
26.20 3.40 0.59 36.44 2.46 0.03
27.36 3.25 1.70 41.28 2.18 2.96
28.86 3.09 0.02 42.82 2.11 0.17
31.07 2.87 0.02 43.62 2.07 0.07
32.14 2.78 0.04 44.87 2.01 1.12
33.26 2.69 1.63 46.22 1.96 0.05
Ex 6a, 6b, 6c, 6d, 6e were carried out by the procedure disclosed in Example 6 to obtain dimethyl fumarate and the particle size distribution obtained was as below.

Ex.No. D(10) μm D(50) μm D(90) D(4,3) μm
6 47.3 181.9 427.2 . 213.8
6a 39.7 168.8 412.6 201.9
6b 55.1 204.6 466,5 236.9
6c 53.6 199.1 465.2 234.0
6d 74.2 234.8 503.0 265.4
6e 97.5 270.9 546.0 299.6

WE CLAIM
1. A process for the preparation of dimethyl fumarate, a compound of formula I,

in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate, the process comprising:
(a) reacting fumade acid with an acyl halide in methanol to obtain dimethyl fumarate, a compound of formula I;
(b) subjecting dimethyl fumarate, the compound of formula I to treatment with a base; and
(c) isolating dimethyl fumarate, the compound of formula I in a purity of at least 99.0% as determined by HPLC, containing less than 400 ppm of an anion of a mineral acid and less than 5 ppm of dimethyl maleate.

2. The process as claimed in claim 1, wherein the anion of a mineral acid may be selected from the group consisting of chloride, bromide, iodide, fluoride, sulphate, nitrate and phosphate.
3. The process as claimed in claim 1, wherein the molar equivalent of acyl halide used in (a) is in the range of 0.5 times the molar amount to 2 times the molar amount with respect to fumaric acid.
4. The process as claimed in claim 1, wherein the isolation of the compound of formula I is carried out without use of column chromatography purification.
5. Dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid.
6. Dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid and free of dimethyl sulfate.

7. Dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15%.
8. Dimethyl fumarate, a compound of formula I, containing less than 400 ppm of an anion of a mineral acid, free of dimethyl sulfate and having monomethyl fumarate content of less than 0.15% and dimethyl maleate content of less than 5 ppm.
9. Dimethyl fumarate, a compound of formula I, containing less than 5 ppm of dimethyl maleate.