Über die Einwirkung von Diazo-methan auf PiperonalErich MosettigChem. Ber., 1928, 61, 1391-1395
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https://www.thevespiary.org/rhodium/Rhodium/pdf/piperonal.diazomethane-1.pdf)
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As the experiments show (see below) the addition of methanol and the way the aldehyde is added to reaction are very important. By varying both parameters the relative and absolute amounts of the reaction products can be influenced, e.g. if piperonal is dissolved in ether and mixed with diazomethan in ether acetopiperon is obtained as a main product and the non-ketone product is a trace product.
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Description of the experiments10 g Piperonal were melted in a 500 ml Erlenmeyer flask, the flask was put in a ice-salt-mixture and on the piperonal which solidified to a disc a cooled solution of 350 ml diazomethan in ether
9 and 60 ml methanol was poured over a period of 10 min. After standing for 2 days at room temperature the solution completely lost its colour. 10 more grams of piperonal were treated in the same way and solutions were combined. After removal of the solvent 23 g of a weakly coloured oil with an intense and pleasent smell were isolated. It distilled with a decomposition at 140-145 °C at 9-10 mm pressure. The distillation residue is viscous, light yellow oil which decomposes on further distillation and was not investigated any further. The distillate were 20 g of a completely colourless oil with low viscosity. It was dissolved in 300 ml ether and shaken mechanically for 3 h in 150 ml of a saturated sodium bisulfite solution in a seperating funnel.
The precipitated bisulfite product was collected by filtration, washed with ether, the keton was liberated with concentrated sodium carbonate solution and extracted with ether. After drying with sodiums sulfate and evaporation of the solvent 4.4 g oil were obtained which was colourless and almost odourless after vacuum distillation (boiling point: 140-145 °C). The semicarbazone was prepared in the same manner, recrystallized twice from methanol and had a melting of 163-165 °C. The melting point of piperonylacetone (
MD-P2P) which was prepared according to Höring
10 by isomerisation of isosafroloxide had a melting point of 163-164 °C. The mixed melting point of both semicarbazones was 163-164 °C.
After isolating the ketone from the ether solution the ether was washed several times with water and very diluted KOH solution, dried and after evaporated gave 12 g oil. In order to further purify it was digested about ten times with each 30 ml cold petroleum ether (boiling point: 20-30 °C). 2.2 g of a colourless, but very viscous oil could not be dissolved. Only a few amount of acetopiperon could be detected as the semicarbazone. The pooled petroleum ether gave 9.5 g of a colourless oil (boiling point: 145-147 °C) which was treated with seed crystals of acetopiperon and immediately formed a crystalline precipitate, which was filtrated and recrystallized from water. Yield: 0.7 g, melting point: 87-88.5 °C.
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In order to understand the the influence of methanol in the reaction of piperonal and diazomethane two experiments without methanol were performed:
Experiment I: To a solution of 5 g piperonal in ether a solution of diazomethane in ether was added while the whole mixture was cooled. The nitrogen development ceased within a short time and after two weeks the solution was discoloured. The overall yield is bad. The main product was acetopiperon (2.5 g). The non-ketone product was only present in traces and could not be isolated.
Experiment II: On 10 g solid piperonal a solution of diazomethane in ether (prepared of 20 ml nitrosomethylurea) was poured at -15 °C. The devolopment of nitrogen is vigorous at the beginning but ceases after a short time. After two weeks the solution is discoloured. The yield is not good, too (2 g piperonylacetone, 1.5 g acetopiperon und about 2 g of non-keton product). The yield of acetonpiperon might be increased if the vacuum distillation is avoided while isolating the last two products.
9 The diazomethane solution was prepared in the usual manner from 20 ml nitrosomethylurea and 25% KOH in methanol.
10 P. Höring, B. 38, 3481 (1905)
Acetopiperon = 3,4-Methylendioxyacetophenone
The rest of the articles will bee translated after some hours of sleep......