Experimental steps and phenomena of preparation of adipic acid

Preparation experimental steps and phenomena of adipic acid
Preparation of instruments: three necked flask, thermometer, filtration device, measuring cylinder, condenser tube, heating jacket, magnetic stirrer. Nitric acid and cyclohexanol are the main raw materials, and ammonium vanadate, acid-base test strips, and weighing tools for catalysis are also required. Place acid and alkali resistant pads on the control panel in advance, and ensure that there are multiple types of corrosive drugs. Wear gloves and glasses for protection within 30 minutes.
Construction device: The main flask is installed in the middle, and the condenser tube is vertically connected to ensure reflux stability. Insert the thermometer into the left port to ensure that the mercury ball is completely immersed in the liquid. The drip funnel is connected to the right bottle mouth, and the side port must be in an open state for smooth ventilation. Perform air tightness test after assembly: plug the inlet and outlet tightly, add water and observe no leakage before starting the mixing function and running it for ten minutes to stabilize the speed.
Synthesis reaction stage: First, add 18 milliliters of 50% concentrated nitric acid into the bottle. Be careful not to pour it out, as it may cause strong, corrosive, and irritating odors to come out of the nose. At this time, the laboratory needs to fully open the fume hood. Slowly add 0.08 grams of ammonium vanadate catalyst. After the temperature of the water bath is adjusted to 65 ℃ and stabilized, the actual uniformity of heating is measured using a micro sampling method. Slowly drip 4 grams of cyclohexanol through a funnel at a flow rate controlled at 22-28 seconds per drop. At this point, observe the solution gradually turning from colorless to light yellow, and after ten seconds, continue to emit orange red smoke, which is a characteristic sign of the generation of nitrogen dioxide gas products. The gas forms a columnar upward trajectory from the top of the condenser tube and is partially recovered as a deep brownish red liquid. The presence of weak acidity in the smoke near the neck of the flask using pH test strips meets the reaction conditions.
Termination time: After the dropwise addition is completed, maintain a constant temperature of 80 degrees and stir. Over a period of three quarters of an hour, the reddish brown color gradually became lighter, and the smoke gradually faded into light powder before almost disappearing, indicating the formation of the product. At the critical checkpoint, a blue halo appears when starch potassium iodide test paper is suspended at the gas overflow end, indicating that the oxidation process has been completed. At this moment, immediately remove the heat source and start the ice bath wrapping.
Treatment of residues: the reaction mixture is transferred to the cooling sedimentation tank for preliminary precipitation of coarse white crystals on the surface. Attention shall be paid to the commissioning of the suction filtration system in advance when the crystallization is not completed and preheating until the vacuum value reaches the standard. Slowly pour out the mixed liquid, pay attention to the easy adsorption of crystal blocks on the dish wall, and use a slight shaker to accelerate the feeding process. The first filter residue contains a large amount of by-product adhesive substances, which should be filtered in two steps: the initial filter paper should be taken from thick chromatography, and the clear and light powder residue should be collected and re heated and concentrated to produce a large amount of flocculent substances before the second filtration. The filter cake obtained in the second batch was combined with the main product for cleaning, and the crystal gaps were moistened with anhydrous ethanol on ice. After low-temperature drying, the finished product was measured to be around 22 grams.
Abnormal situation response: Some students encountered incomplete dissolution of residual particles during the acidification stage. The solution is to reflux the filtrate for ten minutes to allow concentrated sulfuric acid to corrode the remaining permanganate. Another common malfunction is the ejection of material during vacuum distillation. Applying silicone seal through the device interface and using a four step lifting during heating can prevent sudden gasification and blockage of the pipeline.