Stage 1 Synthesis of piperonal
Extraction of piperine from black pepper has been demonstrated previously.
Starting reagents and materials
- 5 g recrystallized piperine
- 100 + 50 ml THF
- 10 g Potassium permanganate + 200-300 ml water
- 800-1000 ml DCM
- 50-100 g anhydrous sodium sulfate
- 25 ml EtOH 95%
- Beakers
- Three-necked flask 1000 ml
- Reflux
- Magnetic stirrer with heating
- Funnels
- Separatory funnel 2000 ml
- Thermometer
- Porous glass filter
- Paper filter
The process of piperine oxidation to piperonal by potassium permanganate proceeds according to Scheme 1
To 10 g of potassium permanganate added 200-250 ml of water Fig 1
Fig 1
Piperine is placed in a three-necked flask equipped with a thermometer, magnetic stirrer and reflux condenser. 100 ml of THF is added to it and heating with stirring Fig 2
Fig 2
The piperine solution in THF should have a temperature of 30-50℃. A solution of potassium permanganate is added to the heated piperine solution in portions over 2.5 hours Fig 3
Fig 3
After adding all solution of potassium permanganate, the RM was kept at heating and stirring for 3 hours. Fig 4
Fig 4
Filtration through a porous filter and through a paper filter without vacuum is shown. Filtration through a porous filter is accompanied by clogging of the filter pores and a decrease in pressure that's why the mother liquor boils. Filtration through a paper filter is more effective. (The filtered MnO2 should be saved for conversion back to permanganate) Fig 5
Fig 5
The flask and manganese dioxide are washed with 50 ml THF Fig 6
Fig 6
The filtrate is transferred to a 2000 ml separatory funnel. Fig 7
Fig 7
Add DCM in 100 ml portions Fig 8
Fig 8
The layers are very bad separated. Therefore, DCM and water are added in turns. Fig 9
Fig 9
When the layers are visible, the DСM is separated. Fig 10
Fig 10
The extraction is repeated several times. The total volume of extract in DСM is 800-1000 ml Fig 11
Fig 11
DCM is dried over anhydrous sodium sulfate and distilled off. Fig 12
Fig 12
Distillation is carried out at a temperature of 100-105℃ Fig 13
Fig 13
When DCM has been distilled off, the pressure is reduced and distillation of THF is continued. Oil after solvent distilled off. Fig 14
Fig 14
From the distillation flask, piperonal (it has a pleasant floral, slightly vanilla smell) is extracted by dissolving in 25 ml of ethanol. Fig 15
Fig 15
A solution of piperonal in ethanol is filtered through a paper filter. Fig 16
Fig 16
Vacuum grease remains in the distillation flask. Fig 17
Fig 17
The filtered solution of piperonal in ethanol is evaporated. Fig 18
Fig 18
The resulting product is a syrup with a sweet, pleasant smell of heliotrope that does not crystallize when cooled. Fig 19
Fig 19
Yield 2.1 g oil (Impurities ~15-20%)
Stage 2 Qualitative Test for Piperonal
To determine the presence of piperonal (and aldehydes), a qualitative reaction with acid fuchsine is used. The color of the reagent changes to red, which indicates the presence of aldehydes in the sample.
Reagents and materials
- ~50 mg Basic fuchsine (CAS 632-99-5)
- 3-5 ml H2SO4 83%
- ~10 mg Piperonal
- 2-3 ml EtOH 88%
- Test tubes
- Beakers
- Stand
- Pipettes
Preparation of acid fuchsin solution:
Dissolve a small amount of fuchsin in concentrated sulfuric acid. The approximate concentration of acid fuchsin should be 1-2%. Fig 20
Fig 20
Sample preparation:
A small amount of piperonal 1-2 drops or about 1-2 mg dissolved in a small amount of alcohol. Fig 21
Fig 21
Carrying out the reaction:
Place 1–2 ml of acid fuchsin solution in a clean test tube.
Then add 1–2 drops of piperonal solution.
In the presence of piperonal, a characteristic violet or red color will form (according to the concentration). This indicates the presence of an aldehyde group in the analyzed substance. Fig 22
Fig 22
Stage 3 MDP2NP
To prove that piperonal is obtained from oxidation of piperine, direct condensation with nitroethane and formation of yellow MDP2NP was chosen.
Starting Reagents and Materials
- 2.1 g Piperonal from black pepper
- 11-15 ml glacial acetic acid (GAA)
- 2.1 ml nitroethane
- 1.4 ml cyclohexylamine CAS 108-91-8
- 5-10 ml water
- Flask 50 ml
- Pipettes
- Funnel
- Reflux condenser
- Heater
- Beakers
Glacial acetic acid is added to piperonal for obtain a solution Fig 23
Fig 23
A solution of piperonal in acetic acid is transferred to a 50 ml flask Fig 24
Fig 24
2.1 ml of nitroethane is added to a solution of piperonal in acetic acid. Fig 25
Fig 25
Next, cyclohexylamine is added. Fig 26
Fig 26
A reflux condenser is connected and the RM is heated at 80-95℃ for 6 hours. Fig 27
Fig 27
Next, RM is transferred to the beaker Fig 28
Fig 28
5-10 ml of water is added to RM Fig 29
Fig 29
The RM is placed in a freezer (at 3-10 °C) for crystallization for several hours. Fig 30
Fig 30
The precipitated crystals are filtered (it is possible to separate an additional portion of crystals from the mother liquor by adding water and cooling) Fig 31
Fig 31
The crystals are dried on a filter and in a vacuum desiccator over alkali. Fig 32
Fig 32
Yield is 0.93 g of 1-(3,4- methylenedioxyphenyl)-2-nitropropene or 39.9% Fig 33
Fig 33
Stage 4 Recrystallization of MDP2NP
To obtain a clearer crystalline form of MDP2NP, it recrystallizes from alcohol or GAA.
Starting Reagents and Materials
- 0.93 g MDP2NP
- 10-15 ml EtOH 95%
- Beakers
- Heater
Add 10-15 ml of ethanol to the MDP2NP Fig 34
Fig 34
Heat the mixture until most of the MDP2NP is dissolved. Fig 35
Fig 35
Evaporate the solution until complete crystallization or filter off the precipitated crystals in case of purification. Fig 36
Fig 36
Conclusions
From experiment it is clear that the syrup (contains up to 80-85% piperonal) can be directly used to obtain MDP2NP.
Yield is 2.1 g of piperonal oil (Impurities ~15-20%)
Yield is 0.93 g of MDP2NP or 39.9%
