Tobacco contains a variety of alkaloids. In addition to the main component nicotine (containing 2%~8%), it also contains demethylnicotine (i.e., nornicotine), anabasine (i.e., anabasine) and at least seven trace alkaloids. Nicotine is a nitrogen-containing base composed of two heterocyclic compounds, pyridine and pyrrole. The pure product is a colorless oily liquid with a boiling point of 246℃, optically active (levorotatory), and soluble in water and many organic solvents.
Nicotine often exists in the form of salts with organic acids such as citric acid and malic acid in plants. When extracting, tobacco can often be heated with an inorganic strong acid solution, and then neutralized with alkali to free nicotine. Then extract with an organic solvent, and evaporate the solvent to obtain nicotine. Because it is volatile, it can be extracted by steam distillation.
In addition, since nicotine is a liquid, it is difficult to separate and purify. Therefore, nicotine is often reacted with picric acid to form nicotine dipicrate crystals for easy processing.
I. Experimental steps
(I) Steam distillation method
1. Instruments, drugs and experimental materials
(1) Instruments 250mL round-bottom flask, 250mL beaker, 50mL conical flask, steam distillation apparatus, 200℃ thermometer and test tube.
(2) Drugs and experimental materials 5g dry cigarette dust (or 5 cigarettes without paper), 10% tannic acid solution, 0.05% potassium permanganate solution, 10% sulfuric acid solution, iodine potassium iodide reagent, 30% sodium hydroxide solution, phenolphthalein, potassium mercuric iodide reagent, 20% acetic acid solution and saturated picric acid solution.
2. Extraction
Weigh 5g dry cigarette dust (or 5 cigarettes without paper) in a 250mL beaker, add 50mL 10% sulfuric acid solution, stir continuously, and heat to boil for 20 min (Note: add appropriate amount of water during boiling to compensate for volatilization). After cooling slightly, slowly add 30% sodium hydroxide solution (about 40 mL) to neutralize, and use litmus paper to test until it is obviously alkaline. Transfer the mixture into a 250mL round-bottom flask and add 2~3 zeolites. Perform steam distillation. Stop distillation when about 12 mL of distillate is collected. Perform property experiments on the distillate.
3. Properties of Nicotine
Take six clean test tubes, add 2 mL of nicotine solution to each, and then perform the following operations:
(1) Add 1 drop of phenolphthalein to the first test tube. What color changes occur?
(2) Add 1-2 drops of 0.05% potassium permanganate solution and 10 drops of 10% sulfuric acid solution to the second test tube, shake the test tube, and observe what color changes occur?
(3) Add 2 drops of iodine potassium iodide reagent to the third test tube. What phenomena occur?
(4) Add 5 drops of saturated picric acid solution to the fourth test tube. What phenomena occur?
(5) Add 2-3 drops of 10% tannic acid solution to the fifth test tube. What phenomena occur?
(6) Add 3 drops of 20% acetic acid solution and 5 drops of potassium mercuric iodide reagent to the sixth test tube. What phenomena occur?
(II) Picrate Method
1. Instruments, drugs and experimental materials
(1) Instruments Filtration device, 150 mL separatory funnel, 100 mL, 150 mL, 250 mL beakers, small porous funnel, 50 mL conical flask, glass wool, filter paper, cotton wool, water bath.
(2) Drugs and experimental materials 8.5 g dry tobacco dust, 78 mL chloroform, methanol, saturated picric acid methanol solution, 5% sodium hydroxide solution.
2. Extraction
Accurately weigh 8.5 g dry tobacco dust and place it in a 250 mL beaker, add 100 mL 5% sodium hydroxide solution, and stir for 20 min. Pour the mixture into a Buchner funnel (without filter paper, but with a layer of glass wool on the bottom) for filtration, and squeeze the tobacco dust to squeeze out more alkali solution. Place the tobacco leaves back in the original beaker, add 2 mL distilled water (stirring) to wash, and then filter again, and combine the two filtrates.
Transfer the filtrate to a separatory funnel and add 25 mL chloroform for extraction. Gently shake the contents of the separatory funnel, let it stand and separate the layers. Put the lower layer (organic phase) into a 150mL beaker, and extract the upper layer (aqueous phase) twice with 50mL chloroform. Combine the three extracts and carefully pour all the extracts into a 150mL round-bottom flask. Heat and distill in a water bath to recover the chloroform. When 8~10mL of solution is left, immediately cool the flask and transfer all the extracts to a 50mL round-bottom flask. Wash the original flask with 3mL chloroform and combine them into the 50mL flask. Heat and distill in a water bath to concentrate to dryness. A small amount of oil or solid residue is left. Add 1mL of distilled water and shake gently to dissolve the residue. Add 4mL of methanol (yellow precipitate is immediately produced). Pass this methanol solution through a funnel padded with glass wool and filter it into a 100mL beaker, and wash it once with 5mL of methanol (the filtrate should be clear without any suspended matter at this time, otherwise it must be filtered again). Add 10 mL of saturated picric acid methanol solution, and immediately precipitate a fluffy yellowish nicotine dipicrate. Filter under reduced pressure using a small porous funnel or glass nail funnel padded with filter paper.
Yield: about 50 mg.
3. Recrystallization
Put the obtained nicotine dipicrate in a 50 mL conical flask, and gradually add hot 50% (volume ratio) ethanol-water solution under heating until the solid is just dissolved. Let stand and cool, and long, bright yellow prismatic crystals will appear (because the crystallization process is slow, it is best to plug the conical flask with a stopper and let it stand until the next experiment). Filter under reduced pressure using a small porous funnel or glass nail funnel padded with filter paper, and dry overnight. Collect the product and determine the melting point.