Process for preparing highly pure temozolomide

A processor the preparation of Temozolomide of formula (VI):

• wherein the process comprises the following steps:
• a) reacting a compound of formula (I):
• with a compound of formula (II):
• at a temperature in the range of 100° C. to 120° C., over a duration of time in the range of 4 hours to 10 hours, to provide a compound of formula (III):
• b) reacting the compound of formula (III) above with a compound of formula (IV):
• in the presence of (i) a non-alcoholic solvent selected from the group consisting of acetonitrile, dichloromethane, dichloroethane, and toluene, or a mixture thereof, and (ii) an inorganic acid selected from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid, or a combination thereof, to provide a compound of formula (V):
• c) reacting the compound of formula (V) above with (i) (C1-C3) organic acid selected from the group consisting of formic acid, acetic acid, and propanoic acid, or a mixture thereof, and (ii) sodium nitrite, in the presence of aqueous medium, eta temperature in the range of −5° C. to 10° C., followed by the addition of (iii) a desiccant selected from the group consisting of sodium dithionate, sodium sulfate, barium chloride, and calcium chloride, in an amount in the ran of 20% w/w to 40% w/w with respect to the total amount of aqueous medium, to provide Temozolomide of the following formula:
• and
• d) purifying the Temozolomide provided in step c) above in-situ with a 4% w/w to 10% w/w dimethyl sulfoxide solution in a halohydrocarbon solvent selected from the group consisting of dichloromethane, chloroform, and carbon tetrachloride, or a mixture thereof, to provide Temozolomide of formula (VI):