A process for the preparation of the compounds of general formula (I)whereinR is selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec.-butyl and allyl;R5 is selected from methyl, ethyl, n-propyl, iso-propyl, methoxy, ethoxy, methylthio, ethylthio, n-propylthio, methylsulphinyl, ethylsulphinyl, fluoro, chloro, bromo, trifluoromethyl, and OCHxFy; wherein x=0-2, y=1-3 with the proviso that x+y=3; R6 is hydrogen; or R5 and R6 taken together are methylenedioxy; R′ is selected from hydrogen, methyl, methoxy, fluoro, chloro, bromo, trifluoromethyl, and OCHxFy, wherein x=0-2, y=1−3 with the proviso that x+y=3; R″ is selected from hydrogen, fluoro and chloro, with the proviso that R″ is selected from fluoro and chloro only when R′ is selected from fluoro and chloro; by reacting a quinoline-3-carboxylic acid ester derivative of formula A, where Z is methyl, with an aniline derivative of formula B according to the following reaction diagram, to give the compound of general formula (I), designated “C”, and an alcohol, designated “D”.in a solvent selected from straight or branched alkanes and cycloalkanes or mixtures thereof with a boiling point between 80 and 200° C.