Old MDPEA synthesis

[Rhodium]

3,4-Methylenedioxycinnamic Acid, and its Conversion into 3,4-Methylenedioxyphenylethylamine 

When piperonal (5 parts), fused sodium acetate (3 parts), and acetic anhydride (6 parts) were heated at 180°C for 6 hours in a reflux apparatus, a 30% yield of the cinnamic acid was obtained, but for the preparation of large quantities of material the following method was found to be much more advantageous. Piperonal (100 g) and malonic acid (150 g) dissolved in pyridine (300 ml) and piperidine (5 ml), were heated for an hour on the steam-bath, when a rapid elimination of carbon dioxide took place and the reaction was completed by boiling the solution for 5 minutes. The product was cooled. poured into water. and the almost quantitative yield of pure 3,4-methylenedioxycinnamic acid (mp 233°C) collected. 3,4-Methylenedioxyphenylpropionic acid was prepared in a yield of 85% from this cinnamic acid by reduction with sodium amalgam as described by Perkin and Robinson (JCS, 1907. 91, 1079).

3,4-Methylenedioxyphenylpropionamide 

This derivative proved to be difficult to prepare. but ultimately the following method was found to give excellent results. The acid (100g), dissolved in chloroform (340 ml), is allowed to react for 12 hours with thionyl chloride (74 ml) at room temperature and the product is then poured into a solution containing sodium hydroxide (50g) and concentrated ammonia (1200 mL). The chloroform is removed by distillation and, after filtering from traces of tar, the filtrate is cooled, and the amide (100g)  separates in a state sufficiently pure for the next operation. The conversion into 3,4-methylenedioxyphenylethylamine was brought about by treatment with sodium hypochlorite essentially as recommended by Decker (Annalen. 1915. 395. 291) in the case of the preparation of homopiperonylamine and the yield was about 50% of the theoretical.

Reference: R.D. Haworth, W.H. Perkin, J. Rankin, -Berberine, J. Chem. Soc. 1686-1698 (1924)

[Rhodium]

Zur Darstellung von Säureamiden und Acylierung der Aminogruppe
Herman Decker

Ann. Chem. 395, 282 (1915)

(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 Haematoxylin
William Henry Perkin (Jr) and Robert Robinson
J. Chem. Soc. 91, 1073 (1907)

Preparation of Veratraldehyde

The 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 Acid

This 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.