Impurity atomoxetine isolation procedure for the preparation of atomoxetine impurities and their use as reference standards.

Hydrochloride N-methyl-3- (3-methylphenoxy) -3-phenylpropylamine (3-ATM HCl) isolated. Process for the preparation of N-methyl-3- (3-methylphenoxy) -3-phenylpropylamine (3-ATM HCl) comprising: (a) combining N-methyl-3-hydroxy-3-phenylpropylamine with DMSO in presence of a strong base selected from NaOH, KOH, Ca (OH) 2 and Ba (OH) 2 at a temperature of at least 90 to form a mixture; (B) adding 3-fluorotoluene to the mixture formed in (a), to form a reaction mixture, and maintaining the reaction mixture for at least 5 hours; (C) adding a first organic solvent and water to the reaction mixture; (D) recovering the base (n) 3-methyl Tomoxetine crude; (E) combining the base (n) 3-methyl Tomoxetine crude with (S) - (+) - mandelic acid in the presence of a C1 alcohol - 4 and an aromatic solvent, and heating to a temperature of 65 to 70; (F) recovering the salt (S) - (+) - mandelate 3-methyl Atomoxetine; (G) combining the salt (S) - (+) - mandelate 3-methyl Atomoxetine with a second organic solvent, water and a base; (H) recovering the basis of 3-methyl Atomoxetine; and (i) converting the 3-base metilatomoxetina recovered to its hydrochloride salt.