Dimethylformamide → 2,4-Bis(trifluoromethyl)benzaldehyde

Beteiligte Stoffe

Reaktionsschritte

A solution of 68 ml (0.4 mol) of 2,2,6,6-tetramethyl- piperidine in 1 l of tetrahydrofuran is cooled under argon to -10° and at this temperature there are added dropwise thereto while stirring 250 ml of a 1.6M solution of n-butyllithium in hexane. Subsequently, 62 ml (0.4 mol) of 1,3-bis(trifluoromethyl)-benzene are added dropwise thereto at -10° within 5 minutes. The resulting wine-red solution is stirred at -10° for a further 5 minutes and then 62 ml (0.8 mol) of N,N-dimethylformamide are allowed to flow in rapidly. The internal temperature rises by 15° as a consequence of the exothermic reaction. The dark brown solution obtained is then added slowly and under a slight argon pressure to 1.2 l of stirred, ice-cold 1M hydrochloric acid. The internal temperature rises to 10° as a consequence of the stongly exothermic reaction in spite of constant cooling. The resulting emulsion is diluted with 750 ml of hexane, the aqueous phase (1.5 l) is separated and stored for the recovery of 2,2,6,6-tetra- methylpiperidine. The organic phase (1.9 l) is extracted twice with 1 l of water each time, dried over sodium sulphate, filtered and the organic solvent is distilled off at 40° under a vacuum (20 kPa). The residue (about 100 ml) is distilled over a column having a length of 20 cm, firstly at 50° bath temperature under a vacuum of 20 kPa in order to remove the residual solvent, then the bath temperature is increased to 80° and the vacuum is increased to 1.4 kPa. A forerun is removed until the constant internal temperature of 57° has been reached and then the residue distils over as a fraction at 57°/1.4 kPa. There are obtained 68 g (70%) of 2,4-bis(trifluoromethyl)benzaldehyde with a purity (GC) of 96-98%.

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