Problem with refs on phenylacetic acid from nitrile
Wed Feb 09, 2005 6:10 am
Swib would like to point out that following Vogel or Org. Synth Col. Vol 1 word for word (chem for chem), one will often (always?) encounter a dilema that your PAA will not form solid, and you're left with a liquid PAA layer under water.
It is this poster's belief that the use of sulfuric acid is the cause of this. The refs instruct one to basify with sodium carbonate, and if there is cloudiness (phenylacetamide), filter it out. After following the refs to this point, it is best to abandon and substitute HCl acid for the stated sulfuric acid to precipitate your solid PAA.
I would also like to give credit to Mastermind for guidance(?) to the above solution, and his suggestion of distilling the benzyl cyanide without vacuum. The high temp doesn't hurt it a bit, and vacuum causes so much bumping that the column packing gets loaded with undistilled material.
If you're trying to hydrolyze phenylacetonitrile with dilute sulfuric acid and you find that it isn't solidifying when its cooled (PAA is solid at room temperature) add some hydrochloric acid, heat it again for a while (with stirring) and then cool to see if it solidifies. One German reference I've seen mentions purifying PAA by converting it to the sodium salt dissolved in water and then precipitating it with acid. PAA reacts easily with baking soda. You can treat the aqueous sodium PAA solution with activated charcoal and/or probably extract impurities (ie. wash) with an organic solvent before precipitating with acid (ie. HCl). PAA can be purified by recrystalization from water, but difference in solubility of PAA in cold vs. hot water doesn't seem to be too great. Repeatedly heating, melting and stirring the PAA in water and then cooling will produce crystals in the water layer under a solid block (after cooling) of PAA on top of the water. The crystals suspended in the water layer can be filtered out after the block of PAA is removed. Put the block of PAA back in with the water, heat, melt, and repeat the process....
Doing this a lot will make you and your room smell like cat piss for months. Don't be surprised if people start calling you stinky.
Good point, Lief. Swib still opens an occasional box and finds equipment that wasn't necessarily used, but just being stored in the room that swib worked with this shit, and gets remenders of this synthesis a year later.
I was thinking of posting a few ideas on keeping the smell to a min. Gotta go-later.
Forums
Rhodium
The Hive
Shop
Profile
Log in
Register
Log in to check your private messages
86
