Preparation of terpyridines

A process for preparing a terpyridine compound of the formula I

• in which
• R are hydrogens or identical C1-C12-alkyl or C1-C12-alkoxy radicals and
• n is 0, 1, 2, 3 or 4 and is the same for both sets of radicals R,
• by successive reaction steps comprising
• A) condensation of a C1-C4-alkyl pyridine-2-carboxylate derivative of the formula a
• with acetone in an aprotic solvent in the presence of a base,
• B) reaction of the 1,5-bis(2-pyridyl)pentane-1,3,5-trione derivative of the formula b
• obtained in reaction step A with ammonia or ammonium salts (NH4)qY with removal of the water of reaction formed, where the variable Y in (NH4)qY is the anion of the parent q-basic acid HqY of the ammonium salt, and
• C) chlorination of the 2,6-bis(2-pyridyl)-4(1H)pyridinone derivative of the formula c obtained in reaction step B,
• where Z is NH in the case of a reaction with ammonia in reaction step B and is NH2⊕[Y1/q]⊖ in the case of a reaction with ammonium salt (NH4)qY in reaction step B,
• wherein
• the reaction step A is preceded by a reaction step A′ in which the C1-C4-alkyl pyridine-2-carboxylate derivative of the formula a is obtained by
• A′) acid hydrolysis of a 2-cyanopyridine derivative of the formula a′
• by means of an anhydrous inorganic acid or its anhydride in the presence of water and a C1-C4-alkanol, with an equimolar amount of water being added to the 2-cyanopyridine derivative of the formula a′ prior to addition of the anhydrous inorganic acid or its anhydride,
• the base used in reaction step A is an alkali metal C1-C4-alkoxide or alkaline earth metal C1-C4-alkoxide,
• the removal of the water of reaction in reaction step B is carried out using a C1-C4-alkanol as entrainer
• and
• the chlorination of the 2,6-bis(2-pyridyl)-4(1H)pyridinone derivative of the formula c in reaction step C is carried out using phosphorus oxide chloride (POCl3) or using a mixture comprising phosphorus oxide chloride and at least one organic solvent selected from the group consisting of toluene, o-xylene, m-xylene and p-xylene.