(electrolytic reduction by an amalgam of sodium at presence H3BO3)
Aromatic aldehydes smoothly turn out at electrolytic reduction corresponding aromatic acid on the mercury cathode at the presence of boric acid.
If to subject electrolysis water solution Na salts an aromatic acid, allocated sodium are dissolved in mercury and the formed amalgam reduction acid up to aldehyde. The solution all time should contain small surplus boric acid, and formed aldehyde should be deleted from electrolyte immediately. Therefore reduction conduct without a diaphragm at vigorous stirring at the presence of benzene which emulsion in a liquid and deletes aldehyde from sphere of reaction as soon as last will be formed.
Reception benzaldegyde from benzoic acid
Electrolysis made in a glass with diameter 100 mm. As the cathode mercury which pour on a bottom a layer in 10 mm serves. A current bring to the cathode by means of the copper wire protected by a glass tube which bottom end is shipped in mercury. In the center of a vessel establish powerful Hershberg mixer, and electro conductor a tube strengthen at a wall of a glass. During restoration a reactionary mix cool cold water.
For reception of a good yield it is necessary, that concentration of sodium in mercury was not lower than some minimum i.e. that at the moment of restoration mercury already contained the some amount of amalgams. For this purpose all over again subject electrolysis solution Na2SO4 and the mercury received thus containing sodium, use as the cathode. At recurrence of synthesis of such preparation it is not required, if use the mercury just serving by the cathode at the previous restoration.
For electrolyte prepare from 15 g benzoic acid which will precisely neutralize soda, then lead up volume solution up to 250 ml, add 15 g boric acid, 15 ã Na2SO4 and 100 ml of benzene. Reduction made an electricity 1,5-2 A, at time of reduction stirring should be so vigorous that ÐÌ represented milky-white emulsion.
After through a liquid will pass 8-9 Àh, mercury separate, benzene layer wash out bicarbonate of sodium, dry and solvent drive away. Benzaldegyde for clearing overtake with steam. Yield 12 g (91% from theor.).
Resorcylic aldehyde (2,4-dioxybenzaldehyde)
For electrolyte prepare from 19 g (0,123 mol) resorcylic acid which will neutralize bicarbonate of sodium, 15 g (0,24 ìîëü) H3BO3, 15 g (0,11 mol) Na2SO4, 250 ml of water and 250 ml of benzene. Reduction made since described above, receiving 14,8 g aldehyde (86% from òåîð.).
2,4-dimethoxybenzaldehyde
For electrolyte prepare from 22,4 g (0,123 mol) 2,4-dimethoxybenzoic acid which will neutralize bicarbonate of sodium, 15 g (0,24 mol) H3BO3, 15 g (0,11 mol) Na2SO4, 250 ml of water and 100 ml of benzene. Reduction made since described above, receiving 19 g aldehyde (93% from theor.).
The smaller yield of resorcylic aldehyde in comparison with 2,4- dimethoxybenzaldehyde
is connected, probably, with its smaller solubility in benzene and the greater solubility in water and, as consequence, courses of reaction of its further reduction.
3,4,5- thrimethoxybenzaldehyde
For electrolyte prepare from 26 g (0,123 mol) 3,4,5-trimethoxybenzoic acid which will neutralize NaHCO3, 15 g (0,24 mol) H3BO3, 15 ã (0,11 mol) Na2SO4, 250 ml of water and 100 ml of benzene. Reduction made since described above, receiving 22 g aldehyde
(91% from theor.).