3,4,5-trimethoxy-benzaldehyde from 3,4,5-trimethoxy-benzoic acid
Turn your attention to Patent US4240984 for procedure details.
A process for preparing aromatic aldehydes starting from the corresponding aromatic acid, comprising two steps, the first one consisting of the reaction of said acid with ethyl or isobutyl chlorocarbonate to obtain the corresponding anhydride, and the second one to hydrogenate the thus-obtained anhydride to yield to aldehyde.
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Step (a): preparation of 3,4,5-Trimethoxy-ethyl carbonate.
10.8 g (0.10 moles) of ethyl chloroformate are dissolved in ml 100 of tetrahydrofuran. This solution is then added under stirring and cooling at 5.degree.-10.degree. C., during 10-30 minutes to a solution of 21.2 g (0.10 moles) of 3,4,5-trimethoxy-benzoic acid and 12.12 g (0.12 moles) of triethylamine in 200 ml of tetrahydrofuran. At the end of the addition the reaction mixture is kept at the room temperature during 2 hours under continuous stirring.
The so-formed precipitate is filtered, throughly washed with tetrahydrofuran, and discarded.
On the joined reaction solution and washing liquids, we may directly proceed to the catalytic reduction for the preparation of the 3,4,5-trimethoxy-benzaldehyde.
The 3,4,5-trimethoxy-benzoyl-ethyl carbonate may be isolated by means of complete evaporation under a vacuum of the mother liquids at the temperature between 50.degree. C. and 70.degree. C. The residue is a white microcristalline solid (26.7 g; yield 94%) with mp 92-94°C.
The substance is remarkably stable and keeps well also at room temperature. It is not affected by moisture.
Step (b): Reduction to 3,4,5-trimethoxy-benzaldehyde.
To a solution of 28.4 g (10.1 moles) of 3,4,5-trimethoxy-benzoylethyl carbonate in ml 300, prepared as described in step (a), 14.2 g of Pd supported on BaSO.sub.4 (10%) and 0.1 ml of a solution of sulfur and quinoline prepared following Rosemund and Zetzsche and diluted 1:3000 are added. The mixture is hydrogenated in a PARR apparatus in an hydrogen atmosphere at ordinary pressure and 25.degree. C. under efficient shaking during 12 hours. The catalyst is removed by filtration and recovered, whereas the organic solution is washed with a 5% NaOH solution and finally evaporated in a vacuum. 17.64 g of 3,4,5-trimethoxybenzaldehyde are obtained, with the same characteristics generally described in the literature.
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