Question

We need to make a flow chart, then use extraction and recrystallization to isolate component to purify. What should we use as a solvent to spot on a thin layer chromatography silica plate? ,

Solvents: acetone, ethanol, methanol, ethyl acetate, hexanes, dichloromethane

Aqueous solutions: 1M NaOH, 1M HCl, 3M NaOH, 3M HCl, 1 M NaHCO3, saturated NaCl

Drying Agent: sodium sulfate

During an oxidation of benzyl alcohol to benzoic acid, a student did not have adequate time during the lab period to let the reaction mixture stir long enough. Consequently, the benzoic acid he obtained was still contaminated with benzyl alcohol. Purify the benzoic acid and demonstrate its final purity.

An organic chemistry student reacted salicylic acid with an acid and methanol. The reaction did not have enough time to allow the reaction to got to completion and the student ended up with a mixture of salicylic acid (75%) and methel salicylate (oil of wintergreen). Purify the salicylic acid. Provide data to show your compound is pure

Answer 1

Hi,

A) methanol will be a goo solvent to spot on TLC

B) Well, if you want to do it properly this is what you will need to do:

1) remove any excess benzy alcohol:

a) take the whole mess and suspend it in 10% NaOH solution (benzoic acid is soluble in 10% NaOH the benzyl alcohol is not).

b) extract the solution three time with diethyl ether, and discard the ether extracts.

c) re-liberate the benzoic acid by neutraliziling the NaOH solution with 1M HCl (it will precipitate). Filter the precipitate, and proceed to the recrystallization:

2) Recystallization:

Benzoic acid is soluble is hot water but not is cold, so you will dissolve the Benzoic acid in a minimal amount of boiling water.

If the solution is colored or if there are any undissolved particles at all, add about 1-2 spatuals of activated carbon to the boiling solution (stop the boil 1st - if you don't, adding the activated carbon to the boiling solution could cause the solution to boil over).

Filter the solution. The solution may crystallize an filteration, if this is the case, heat the solution up again - and now you should get a clear solution. Once you have this, set is undisturbed on a cork ring on the benchtop and let it cool slowly - you will get nice crsytals of benzoic acid.

Filter them and dry them in a vacuum oven first before taking a MP which should be around 122.4