NOVELTY - Improved process for the preparation of bosentan (I) comprises preparation of (2-methoxyphenoxy)-2,2'-bipyrimidine (II) by reacting 2-cyanopyrimidine with dimethyl 2-(2-methoxy phenoxy)malonate in the presence of e.g. methanol; reacting (II) with phosphorus oxychloride; refluxing the obtained compound with 4-tert-butylbenzene sulfonamide in presence of base and solvent; reacting the obtained compound with alkali metal amides or alkali metal hydrides and ethylene glycol; and isolating and purifying the crude (I).    USE - (I) is useful for treating pulmonary arterial hypertension (WHO group I) in patients with WHO Class III or IV symptoms, to improve exercise ability and decrease the rate of clinical worsening. No biological data given.    ADVANTAGE - (I) is free of dimeric impurity 4-tert-butyl-N-(6-(2-(6-((4-tert-butylphenyl)sulfonylamino)-5-(2-methoxyphenoxy)-2-pyrimidin-2-yl-pyrimidin-4-yl)oxyethoxy)-5-(2-methoxyphenoxy)-2-pyrimidin-2-yl-pyrimidin-4-yl)benzenesulfonamide. (I) has a purity of greater than 99% as measured by HPLC. (I) produced by the method comprises less than about 0.1% of dimeric impurity. The process: is more direct; gives quantitative yield; is environmental friendly; and is applicable of industrial scale production.    DETAILED DESCRIPTION - Improved process for the preparation of bosentan (I) comprises: (a) preparation of (2-methoxyphenoxy)-2,2'-bipyrimidine (II) by reacting 2-cyanopyrimidine with dimethyl 2-(2-methoxy phenoxy)malonate in the presence of methanol, sodium methoxide and ammonium chloride at 25-30 degrees C without isolation of the intermediate, pyrimidine-2-carboxamidine hydrochloride; (b) reacting (II) with phosphorus oxychloride to yield 4,6-dichloro-5-(2-methoxyphenoxy)-2,2'-bipyrimidine (III); (c) refluxing (III) with 4-tert-butylbenzene sulfonamide in the presence of base and solvent to give 4-tert-butyl-N-(6-chloro-5-(2-methoxyphenoxy)-4-pyrimidinyl) benzenesulfonamide (IV); (d) reacting (IV) with alkali metal amides or alkali metal hydrides and ethylene glycol to give crude (I); (e) isolating the crude (I); and (f) purifying crude (I) to obtain pure (I). INDEPENDENT CLAIMS are included for:    (1) an improved process for the preparation of (I) comprising: steps (a)-(c); reacting (IV) with glycolaldehyde diethylacetal in presence of a base to form 4-tert-butyl-N-(6-(2,2-diethoxy-ethoxy)-5-(2-methoxyphenoxy)-(2,2') bipyrimidin-4-yl)-benzene sulfonamide in situ (IVA); reacting (IVA) with aqueous acid to give 4-tert-butyl-N-(5-(2-methoxyphenoxy)-6-(2-oxoethoxy)-(2,2')bipyrimidin-4-yl)-benzene sulfonamide (V); reacting (V) with a reducing agent in a solvent to give crude (I); and steps (e) and (f); and    (2) a composition comprising (I) and a carrier.