The present invention provides a one pot process for preparing a compound (R)-(+)-2-[4-(5-halo-3-fluoropyridin-2-yloxy)-phenoxy propionic acid propargyl ester having formula I. wherein X1 represent halides, preferably Cl or Br.The process involves following steps, with an alkali salt M2CO3 to form an alkali salt of formula III a) reacting in a solvent system containing a mixture of polar solvents and hydrocarbon solvents, a compound (R)-2-(p-hydroxyphenoxy)-propionic acid having formula IIb) reacting the alkali salt of formula III in situ with 5-halo-2,3-difluoropyridine of formula IV wherein X represents Cl or Br,to form an alkali salt of (R)-(+)-2-[4-(5-halo-3-fluoropyridin-2-yloxy)-Phenoxypropionic acid of formula V andc) reacting the compound of formula V in situ with propargyl halide of formula (VI) (VI) wherein X represents Cl, or Br , to form the compound of formula (I).
