1) Paracetamol extraction
40 500mg Paracetamol tablets were ground up and added to a beaker. An arbitrary amount of methanol was then added (100-150ml), and the flask was swirled for a while. The mixture was then filtered, and the solids on the filter washed with a bit more methanol. The filtrate was then left to evaporate, leaving the product. An unexpected thing happened after a couple of hours, the methanol solution turned red. The red colour is apparently due to oxidation of the product to brightly coloured benzoquinone imines. This could be avoided by evaporation in vacuum, leading to a pure colourless product. I didn't do this however, and was left with 15.72g of white-pink brittle paracetamol crystals. probably still fairly pure, lets hope. If so, this is a 79% recovery yield.
To a two-necked 500ml round bottom flask was added 15.72g of paracetamol and 69ml of 5% hydrochloric acid (10% excess of a 1 to 1 molar ratio). The side neck of the flask was stoppered, and the other neck was set up for reflux with a water circulated liebig condenser. The mixture was then refluxed for 1 hour on medium heat. The paracetamol dissolved into solution as the mixture heated up, giving a clear yellow/brown solution which did not change appearance as the reflux progressed. After reflux, the apparatus was dismantled, and the solution transferred to a 250ml beaker (the flask being washed with did of water to ensure all product was transferred). The beaker was then heated till approximately one 1/4 of the liquid had boiled off. The solution (now diminished in volume) was then placed in a fridge, and allowed to cool to around room temperature. A mass of transulest needle like crystals had formed in the flask once cooled (presumebly 4-aminophenol hydrochloride). The solution was stirred, then the pH tested with litmus and found to be acidic (unsurprisingly). I proceeded to make up about 30ml of 20%ish w/w sodium hydroxide solution in a separate beaker, and added this to the reaction mixture in small portions, checking pH in between additions until the pH was close to neutral. This was done because in acidic conditions, the amino group in 4-aminophenol is protonated, forming a somewhat soluble, undesirable salt form of the product. In basic conditions, 4-aminophenol is deprotonated to give a water soluble 4-aminophenolate. So at neutral pH, just the non-salt form of 4-aminophenol should be present which can be more easily extracted then salt forms, and is the form I wanted. As the sodium hydroxide solution was added, the "4-aminophenol hydrochloride" crystals dissolved and were replaced with a fine off-white precipitate which made the solution thick at a neutral pH. This should be the non-salt, freebase 4-aminophenol. The mixture was chilled in a freezer for ghg hours to allow more product to crystallize out. The product was then filtered off, washed with a bit of ice cold water, and finally dried, giving 3.9g of 4-aminophenol. The product looked pure enough as a tan powder, but never the less, I decided to recrystallize it from water. this turned out not to be such a great idea, as the product is sensitive to atmospheric oxidation when heated. As a result, the final recrystallized product appeared as fine dark drown crystals. if pure, this represents a yield of 34%. Pretty shitty yield and product, but it was fun.
Left = extracted paracetamol / Right = 4-aminophenol
For the hydrolysis: (OH)C6H4NHCOCH3 + H2O ==> (OH)C6H4NH2 + CH3COOH
with the excess HCl: (OH)C6H4NH2 + HCl ==> (OH)C6H4NH3(+)Cl(-)
neutralizing with NaOH: (OH)C6H4NH3(+) Cl(-) + NaOH ==> (OH)C6H4NH2 + NaCl + H2O