[dancool]

Recently been doing organic labs and had to perform TLC.
 
In 1 exp. Production of aspirin using salicylic acid, acetic anhydride with acetic acid.
performed a TLC of salicylic acid, crude product and recrystalised product.

R_f values:
S. Acid: 0.69
Recryst: 0.48
Crude: 0.39

I know basic concept of R_f values, but i do not really know about comparing them.

What would these values
- tell us about the extent of conversion of S. acid into aspirin? (no idea)
- why would the recryst travel further than crude? (impurities lower solubility, therefore it travels a shorter distance?)

many thanks
Dan

[stewie griffin]

Regarding your first question about extent of conversion. You know that salicylic acid has an R_f of .69. Let's say that when the reaction is running you go ahead and TLC it. You run the TLC plate and view the spots. Is there a spot on the plate with an R_f of .69? If so, that means you've still got some salicylic acid in there. What if there's nothing with an R_f of .69??? What do you think that says about the salicylic acid.... do you think there's any left in there?

[dancool]

I guess as there is no spot at 0.69 on crude section, this means that there is 100% concersion of S.acid? Am i right?