TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The lanthanide metal catalyst used in step (i) is lanthanide(III) halides, preferably lanthanum(III) halides and cerium(III) halides, which are anhydrous lanthanum(III) chloride or cerium(III) chloride. The amount of lanthanide metal catalyst used in step (i) is 0.1-1.5 mole equivalent, preferably 0.4-0.8 equivalent, relative to the amount of (IV). The amount of organometallic reagent used in step (i) is 2-10, preferably 5-8 mole equivalents, based on the amount of (IV).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The process further comprises (ii) removing an impurity comprising (2-(1-(((1R)-3-(2-acetylphenyl)-1-(3-((E)-2-(7-chloro-2-quinolyl)vinyl)phenyl)propyl)sulfanylmethyl)cyclopropyl)acetyl)oxy compounds of formula (VIII) by reacting (VIII) with a compound capable of reacting with the keto function at the position marked with a1 in (VIII), and separating the reaction product thus formed form solution of (2-(1-(((1R)-3-(2-acetylphenyl)-1-(3-((E)-2-(7-chloro-2-quinolyl)vinyl)phenyl)propyl)sulfanylmethyl)cyclopropyl)acetyl)oxy compounds of formula (VI) and (1-((R)-1-(3-((E)-2-(7-chloro-quinolin-2-yl)-vinyl)-phenyl)-3-(2-(1-hydroxy-1-methyl-ethyl)-phenyl)-propylsulfanylmethyl)-cyclopropyl)-acetic acid (VII). The lanthanide metal catalyst used in step (i) is added to a solution of (IV) up to 12 hours, preferably 1 hour before the organometallic agent is added. The process comprises: converting 2-((S)-3-(3-((E)-2-(7-chloro-quinolin-2-yl)-vinyl)-phenyl)-3-hydroxy-propyl)-benzoic acid methyl ester (II) to substituted 2-(3-(3-((E)-2-(7-chloro-quinolin-2-yl)-vinyl)-phenyl)-propyl)-benzoic acid methyl ester compounds of formula (III); converting (III) to (IV); converting (IV) to 2-((R)-3-(3-((E)-2-(7-chloro-quinolin-2-yl)-vinyl)-phenyl)-3-mercapto-propyl)-benzoic acid (V); reacting (V) with ester compounds of formula (XI) to give (VI); converting (Vi) into (VII); and converting (VII) into its sodium salt. The reaction equipment used for step (i) is dried before performing step (i). A crystalline form of (IV) is used in step (i). The step (ii) comprises separating the reaction product, which is formed by a reaction of (VIII) with a compound capable of reacting with the ketone function at the position marked with a1, from a solution of (VI) and (VII) involving the removal of a precipitate of the reaction product from the solution or an aqueous work-up.R2 = H 1-8C-alkyl or optionally substituted 5-10C-aryl;L, L1a = a leaving group comprising Cl, Br or I, 1-8C-alkylsulfonyloxy or substituted 5-10C-arylsulfonyloxy; andR = 1-8C-alkyl or substituted 5-10C-aryl.Preferred Components: The compound capable of reacting with the ketone function at the position marked with a1 used in step (ii) is hydrazine or its derivatives or semicarbazides. ACTIVITY - Antiasthmatic; Antiallergic.    MECHANISM OF ACTION - Leukotriene receptor antagonist.    SPECIFIC COMPOUNDS - 1 Compound (IV) is specifically claimed i.e. (R,E)-methyl-2-(3-(acetylthio)-3-(3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)propyl)benzoate of formula (IVa).    EXAMPLE - (S,E)-methyl 2-(3-(3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)-3-hydroxypropyl) benzoate (0.109 mole) and toluene (1 l) were charged into reactor. Half of the amount of toluene was distilled under reduced pressure to azeotropically dry substance. The solution was cooled to -10 degrees C and 4-dimethylaminopyridine (8.19 mmole) and triethylamine (0.201 mole) were added followed by the addition of methanesulfonyl chloride (0.109 mole) over 1-2 hours while the internal temperature was maintained at -10 degrees C. After the completion of the addition, the solution was stirred for 3 hours then quenched into cold saturated sodium hydrogen carbonate aqueous solution (400 ml). The organic layer was washed twice with cold saturated aqueous sodium hydrogencarbonate solution (400 ml) and than dried with anhydrous sodium carbonate. The solution was filtered off into reactor charged with potassium thioacetate (0.136 mole) in tetrahydrofuran (500 ml). The reaction mixture was stirred at 45-50 degrees C for 24 hours and then at 20-30 degrees C for another 24 hours. The reaction mixture was poured into saturated aqueous solution of sodium chloride (400 ml). Layers were separated and aqueous layer was extracted twice with toluene (300 ml). Combined organic layers were washed with saturated aqueous sodium chloride solution (300 ml). The solvent was evaporated to one fourth of the starting volume, to obtain montelukast acid.