CHEM 120L: Acetaminophen

organic synthesis

production of complex, organic molecules from simpler molecules

isolation

removing or separating the desired product from the mixture/solvent it’s in, done in the initial crystaliaxation and filtration

purification

removal of impurities from the desired product, done in the recrystallization step

amide

NH-C(=O)-CH3

amine

NH2

formation of acetaminophen

amine from p-aminophenol is acetylated by acetic anhydride to form an amide functional group of acetaminophen and acetic acid (by product)

how does recrystallization purify the crude solid

• crude solid dissolves by heating in a little solvent (supersaturated solution) → cooled to room temp → ice bath → crystals form

• most impurities remain dissolved in the cold solution when done slowly without disruption

precipitation

forming a solid (crystals)

rxn 1: synthesis of acetaminophen

• p-aminophenol + DI heated for increased solubility

• acetic anhydride added

• heat reaction, mix

• remove from heat, mix

• ice bath, don’t mix

step 2: isolation

• isolate crude via vacuum filtration

• use some DI to transfer solid to funnel

step 3: recrystallization

• mix crude with DI

• heat and mix, fully dissolve crude

• cool to room temp, undisturbed

• ice bath, undisturbed

• filter

saturation

solvent dissolved it’s maximum capacity of solute. this is when the heated solution cools to room temperature because no crystals form yet

supersaturation

solution contains more dissolved solute than usually possible at a given temp, causes crystallization.

solubility

how much solute can dissolve in a given solvent at a specific temperature

how to induce crystals to form if none do

scratch the glass rod to the bottom of the flask, introduced some glass particles and induces precipitation

what does fast recrystallization cause

traps impurities in the lattice. crystallization should be done at room temp, or initiated in ice and then continued at room temp.

compared to the pure solid, the crude solid will have.. (melting point)

lower melting point and a broader melting point range

why must DI used in product transfer be cold or room temperature

won’t dissolve the acetaminophen