Patent ID: 8871936

Claim:
A method for preparing a compound of formula (I) wherein, R1 is ethyl, R2 is ethyl and R3 is H; or R1 is chloro, R2 is ethyl and R3 is H; or R1 is methoxy, R2 is methyl and R3 is trifluoromethyl; the method comprising: (i) reacting a compound of formula (II) wherein, R1 is ethyl, chloro or methoxy; and R4 is C1-C4 alkyl; with a compound of formula (III) wherein, R2 is ethyl and R3 is H; or R2 is methyl and R3 is trifluoromethyl; in a refluxing mixture containing an aliphatic solvent or a mixture of aliphatic solvents, said aliphatic solvent(s) having a boiling point in the range of 68-191° C.; (ii) condensing vapors of the refluxing mixture; (iii) treating the condensed vapors with an alcohol scavenging agent selected from molecular sieves or with an alcohol scavenging agent which is a mixture of molecular sieves, to remove an alcohol byproduct (R4OH) from the condensed vapors; and (iv) returning the treated condensed vapors free of the removed R4OH back to the reaction mixture.