Synthesis of Esters

[mclaran10]

In your book, there is a lab concerning the synthesis of methyl salicylate from aspirin. Last year in AP Chemistry we did a lab where we synthesized several esters on a small scale, including making methyl salicylate from methanol and salicylic acid. We placed a large test tube containing the organic acid, alcohol, and a few drops of catalytic sulfuric acid in a hot water bath over a hot plate and nestled a small test tube containing ice water inside the larger test tube, suspended over the reaction. The esters condensed onto the bottom of the smaller test tube, and we simply noted their odor and disposed of them. This also served to remove the esters from the reaction to prevent it from reaching equilibrium (which is not very favorable to the formation of the ester products). In my own lab I would like to purify the products and save them for future use.

I am wondering if it would be appropriate to use a similar protocol to the one mentioned in the book for synthesizing some of the other esters. I am also concerned that some of the esters will be difficult to purify because of their high boiling points (octyl acetate boils at 211 degrees Celsius). I also do not have a formal condenser (I use the two flasks connected by rubber tubing setup), so I am worried that my yields from distillation will be reduced even further. Does anybody have any suggestions in the way of methodology or for esters that are particularly worth making?

Finally I am wondering about the feasibility of using butyric acid in the formation of esters. I know that the acid has a notoriously bad odor, and Elemental Scientific even charges extra shipping for a "stench pack." Is it worth using butyric acid? Will I even be able to smell the esters?

Thanks,
McLaran

[mclaran10]

Ok I've done some more research and I've run across a different protocol. Esters with a boiling point lower than the boiling points of their components can be distilled directly off the reaction mixture as the reaction proceeds. Again this prevents the reaction from reaching equilibrium. However esters with boiling points higher than their components (which would be esters with high molecular weights) are best reacted under reflux and separated afterward. I expect the same extraction protocol as detailed in your book would work fine. Unfortunately I still don't have a proper condenser, but I've looked at the distillation apparatus sold by Maker Shed, and it looks like an amazing deal. The only thing is it doesn't look like the condenser would be able to mate with a reaction flask for reflux reactions without some sort of adapter. Any thoughts? Perhaps there is an alternative to using a traditional condenser in reflux applications?

-McLaran

[thompson]

Alas, we're out of stock on those and I'm not sure we'll be getting any more. I ordered a case of eight initially. Of those, five were broken in shipment to Maker Shed. Of the remaining three, two were broken in shipment from Maker Shed to customers. Our supplier replaces breakage for items that arrive at Maker Shed broken, but we eat the (not insignificant) cost for items that break in shipment to customers, not to mention shipping charges. So we ended up losing a fair amount of money on those items, and I suspect my boss won't want to continue carrying them.

[mclaran10]

That's a shame. It was definitely the best offer I could find. The page is still up though at http://www.makershed.com/ProductDetails.asp?ProductCode=YLBCA16, although it does show that it is out of stock. The HMS Beagle (http://www.hms-beagle.com) sells a student distilling apparatus for $120. It comes with a ring stand, clamp, tripod stand, wire mesh, boiling and Erlenmeyer flasks, what appears to be a Liebig condenser, and several connecting bits that I'm not familiar with save the drip tube. The setup uses rubber stoppers instead of ground glass joints which I suppose simplifies things and makes them compatible with ordinary glassware for other applications like reacting under reflux. The image of the setup is available at http://www.hms-beagle.com/xampp/htdocs/shop/index.php?main_page=popup_image&pID=6590. Does anybody have an idea what functions the two pieces connecting the boiling flask to the condenser serve? One ought to be what the site calls a "splash preventer," but I don't understand the purpose of it. I suppose it just prevents solution from running through the condenser if you get a bit overenthusiastic with the boiling. Anyhow, I live within driving distance of the store so can save on shipping and any hazmat fees if I order chemicals with them--definitely a plus!