Transcription
In this video, we are to obtain phenyl acetic acid. Phenyl acetic acid is used in perfumery, in the production of penicillin, and combined with sodium benzoate in the treatment of type 2 hyperaminemia to form phenylacetyl-glutamine, which can be naturally secreted by the patient. If you like this video, please give a like and subscribe.
Phenyl acetic acid can be produced by hydrolyzing benzyl cyanide. Benzyl cyanide is produced by reaction of benzyl chloride and alkali cyanide. Benzyl chloride and cyanide are tear gas and they are very toxic. In this operation, we will obtain phenyl acetic acid by eliminating the hydroxyl group from mandelic acid with phosphorus and hydroiodic acid. Mandelic acid is a hydroxyl acid obtained from almonds; it is easily available and cheap. It is used in cosmetics to exfoliate and remove skin imperfections.
For this synthesis, we will use a 500-milliliters flask with three necks. In one neck, we will put a thermometer, and another we will cover it with a glass plug. Add reagents in the sequence below: 30 grams of mandelic acid, 4 grams of potassium iodide, 8 grams of red phosphorus, 20 milliliters of water. Add 140 milliliters of phosphoric acid and fix the reflux condenser. With moderate stirring, heat to 144 degrees during four hours. When left to cool, a solid white is observed on the surface. Add 50 milliliters of water and break the solid with a glass rod. Add 50 milliliters of cold ether. Filter the contents of the flask by suction to eliminate the non-reacted phosphorus. 4.2 grams of phosphorus were recovered.
The white solid in the flask is dissolved with 50 milliliters of ether and also filtered through the funnel. In this filtrate, we put an ice trap to condense the ether that evaporates by aspiration. In order to dilute the solid, three parts of 50 milliliters of ether were used. The ether solution is mixed with the aqueous solution and cooled with ice. Add 100 milliliters of chilled water to separate the organic layer. We use a separation funnel. Observe the separation of the layers. Decant the organic phase from the aqueous. The organic phase is washed twice with 50 milliliters of sodium hydrogen sulfide solution at 15 percent. In this wash, we observe that the red color of the iodine disappears. Then wash twice with 50 milliliters of water. Decant and dry with enough anhydrous sodium sulfate. Leave in place for 12 hours. Filter and distill the ether until the volume is 20 milliliters.
Transfer to a 100-milliliters flask, washing the 250-milliliters flask twice with 25 milliliters of ethanol. Distill ethanol and continue with vacuum distillation. With vacuum distillation, I observe that the phenyl acetic acid vapor goes directly to the vacuum tube. After several invalid assemblages for that distillation, I opted to pass the vapors through the cold ethanol. The first assembly had a problem that the acid vapors condense into the narrow parts and plugged the system with the danger of overpressure. The solution was not to put very tight tubes to allow the vapors of phenyl acetic acid to pass through. My final setup was a trap flask with ethanol and an effective condenser before the vacuum outlet. We let the trap flask fill with the distilled ether and ethanol, and when we see that the temperature rises more than 80 degrees, we adjust the ethanol level in the trap flask and connect the vacuum. During the distillation of the acid, crystallization was observed at the mouth of the trap balloon. Do not let the crystals build up in the tube before the trap bottle; it can block the system. Once it is observed that the red product is distilling, the distillation is stopped.
The ethanol solution is transferred to a 250-milliliters flask, and the 100-milliliters flask is washed using 20 milliliters of ethanol. Distill all that ethanol. A reddish residue remained in the flask, which we allow to cool. Dilute the product with two parts of 30 milliliters of ether and place in a 250-milliliters separator funnel. Add 40 milliliters of saturated sodium hydrogenocarbonate solution. Shake vigorously to neutralize the acid and obtain the hydro-soluble sodium phenyl acetate solution. In the extraction process, carbon dioxide is produced. Open the separator funnel valve frequently. Repeat this operation twice. The aqueous sodium phenyl acetate solution is cooled with ice and acidified with concentrated hydrochloric acid to pH 2. The white precipitate is pure phenyl acetic acid. Collect the solid by suction. Wash twice with ice water. Dry in a desiccator for 24 hours. When dry, the melting point is determined. The theoretical melting point of phenylacetic acid is 77 degrees. In our test, a melting point between 76 and 80 degrees was obtained. In this synthesis, 20 grams of phenyl acetic acid were obtained for a yield of 74.5 percent.