[Elnino]

Hello all I'm new to the forums!

I'm a undergraduate researcher who's interested in converting a carboxylic group into an ester using silica chloride as a catalyst.

Here's a link to the reaction I am interested in preforming: http://www.organic-chemistry.org/abstracts/literature/269.shtm

Anyway my question is what does 150 mg/mmol substrate mean?

Reaction scheme:

Carboxylic acid +Alcohlol ----(Silica Chloride 150 mg/mmol substrate ---> Ester

 
PS. I don't have access to the paper.

[discodermolide]

Silica chloride, what sort of reagent is that?
150mg/mmol substrate means that you use 150mg silica chloride per mmol of the acid assuming the alcohol is in excess.
You should look up Fischer esterifiication.

[Dan]

Never heard of "silica chloride" either. It's probably a name they coined themselves for silica-supported HCl. I bet it's essentially the same as using any solid supported acid (haven't read the paper).

[Elnino]

Sorry, yes it's silica-supported chloride (HCL and SO2 released as gas when made thionyl chloride)

[discodermolide]

Why not use conc. sulphuric acid like everyone else? It's easier to use and the work-up is simple.
Silica chloride is probably an undefined mixture and it means using thionyl chloride which is not pleasant to handle and dispose of.

[Elnino]

The alcohol I'm using is propargyl alcohol. Wouldn't the triple be hydrolyzed with the H2SO4? I believe my lab mates tried conc. H2SO4 before however I'm not sure.

[discodermolide]

What is your esterI meant acid?
If it's methanol or ethanol you could do an extractive esterification using the alcohol, acid, heptane, conc. sulphuric acid, the ester is extracted into the heptane layer. This should be ok.

[Elnino]

3-hydroxy-4-methoxybenzoic acid + propargyl alcohol

[discodermolide]

That should work.
Suspend everything in heptane/propargyl alcohol (slight excess) stir well and heat to reflux add conc. H₂SO₄. If heptane is too high use hexane. Work-up, separate layers, wash hexane/heptane with bicarbonate (gas evolution) evaporate hexane/heptane.
Crystallise ester.

[Elnino]

Thanks. I'll try this Monday! I thought about doing a fischer esterification, but never attempted it because I assumed my lab mates already tried it.

[discodermolide]

Maybe they did, did you ask them?

[Elnino]

Nope -.- but I'll try both procedures because I'm interested

[discodermolide]

OK, let us know what happens.