Zur Darstellung von Säureamiden und Acylierung der AminogruppeHerman DeckerAnn. Chem. 395, 282 (1915)
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https://www.thevespiary.org/rhodium/Rhodium/pdf/decker.mdpea.pdf)
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Brazilin and Haematoxylin. Part VII.
Synthesis of Derivatives of Hydrindene closely allied to Brazilin and HaematoxylinWilliam Henry Perkin (Jr) and Robert RobinsonJ. Chem. Soc. 91, 1073 (1907)Preparation of VeratraldehydeThe conversion of vanillin into veratraldehyde is not a very easy operation, and a number of comparative experiments were necessary before the best conditions for obtaining a good yield were obtained.
Vanillin (250 grams) dissolved in methyl alcohol (750 mL) is stirred vigorously and mixed with a solution of caustic soda (70 grams) in as little water as possible, when the sodium derivative separates. Methyl sulphate (250 grams) is now poured in, and as soon as the reaction has subsided a further quantity of methyl sulphate (200 grams) is added sufficiently quickly to keep the liquid just boiling, and care is taken by the frequent addition of small quantities of 50 per cent. caustic soda solution that the solution is always distinctly alkaline. After remaining for half an hour the product is diluted with 6-7 volumes of water, and the veratraldehyde, which separates as a voluminous mass of felted needles, is collected by the aid of the pump, washed with water, and dried on porous porcelain. The yield of crystalline aldehyde is 90%, and further quantities may be obtained from the mother liquor by concentration under reduced pressure and extraction with ether.
3,4-Dimethoxyphenylpropionic AcidThis acid has already been prepared by Tiemann and Nagai
(Ber., 1878, 11, 653) from 3,4-dimethoxycinnamic acid by reduction with sodium amalgam, and Perkin and Schiess
(Trans., 1904, 85, 164) have shown that the latter acid is readily obtained when veratraldehyde is condensed with ethyl acetate in the presence of sodium. In preparing the large quantities of 3,4-dimethoxycinnamic acid required for the present investigation, we found the following method to yield excellent results.
Sodium (20 grams), in the finely divided condition obtained by melting it under boiling toluene and then shaking it vigorously, is mixed with veratraldehyde (100 grams) and ethyl acetate (200 grams) in a large flask fitted to a long reflux condenser. In a short time a very energetic reaction sets in which must be just sufficiently controlled by cooling in running water to prevent loss by frothing. In about five. minutes the decomposition is usually complete, and after remaining for an hour the product is mixed with a solution of potash (90 grams) in methyl alcohol, and as soon as the reaction has subsided water (1.5 litres) is added, and the whole evaporated on the water-bath with the addition from time to time of small quantities of water until quite free from alcohol. The solution yields, on acidifying, dimethoxycinnamic acid which, after recrystallisation from acetic acid, is pure and melts at 180°C.
In preparing 3,4-dimethoxyphenylpropionic acid, the alkaline solution of the potassium salt, obtained as just described, is directly treated with sodium amalgam (2000g of 3%) in an apparatus fitted with a mechanical stirrer, and small quantities of hydrochloric acid are frequently added so as to neutralise most of the alkali as it is formed. The product is rendered just acid by the addition of hydrochloric acid, when a small quantity of tar is precipitated together with a little of the dihydro-acid, and if a slight excess of sodium carbonate is now added the latter is dissolved, but the tar remains. The solution is digested with animal charcoal, filtered, cooled, and acidified, and the dimethoxyphenylpropionic acid, which is deposited at first usually as an oil but soon solidifies, is purified by recrystallisation from benzene from which it separates in colourless needles melting at 97°C. The yield is about 85% of that theoretically possible.