[littlepuppy]

Hi guys..i'm new to this forum and i am glad to find out about this forum. I think it helps me to discuss and share my chemistry knowledge with others and also get a chance to know you guys.  To start with, i have a question about the Ester synthesis lab (Ester synthesis via condensation reactions: The effect of molecular structure on smell). So the quesiton is : The reverse of this reaction may occur (going from an ester to an alcohol and a carboxylic acid). what is done in this reaciton to ensure that the reverse of the desired reaction does not complete?
I was thinking it would the distillation process that helps to removes the ester and maximizes its yield but not sure if i am right. So if you guys know about it please help me out by sharing your thoughts and opinion. Thank you!

[azmanam]

Write out the complete balanced equation to start.  think of a principle from gen chem to control equilibrium.  also, if you can give us a brief description of the lab procedure, that will help, too.

[Mitsunobo]

Water is on of the products in this reaction so removing water will promote the formation of ester.

[littlepuppy]

thanks guys for your opinion...i appreciate it...here is the prodecure of the experiment:

To a 50mL round bottom flak containing 3-5 boiling chips, add 6.0 g of actetic acid and 6.0 g of an unknown alcohol and be sure to record your choice. To this solution, add 0.5 mL of concentrated sulfuric acid.  After addtion of reagents is complete, attach a reflux condenser to the round bottom flask and gently reflux the mixture for 60 mins. then allow the mixture to cool and transfer the liquid to a separatory funnel and wash it with 2X 20 mL of water followed by a washing with 1X 20mL of a saturated NaHCO3 solution. Dry the organic layer over anhydrous Na2SO4. Decant the mixture into a 25mL round bottom flask and purify the product by distillation. obtain a mass of the final oil recovered after distillation.record odor of oil.

by the way, also, based on the starting amounts of carboxylic acid and alcohol given, is the carboxylic acid the limiting reagent? i was thinking it is but again not sure. are they equal amount in all cases?   Thanks alot guys

[carboneel]

i remember doing an ester synthesis but i knew the balanced equation (needed to find your limiting reagent). like one of the previous responses, controlling the equilibrium (forcing the forward reaction to occur) is a simple way of preventing the reverse from occurring. (i guess its simple to say rather than implement in most cases )  in mine, i remember using acetic anhydride and with isoamyl (isopentyl alcohol) to make the yummy smelling isopentyl acetate (banana laffy taffy)

you mentioned something about distillation in your original question. sounds great to me it seems like you haven' been given a whole lot about the reactants themselves (being that your alcohol was unknown) but i think it would be safe to say that your ester would boil off before the water, so yeah it would shift your equilibrium right.

sorry if that was too much babble (i like chem)

[macman104]

It's unlikely the ester will boil off first.  For example, isopentyl acetate boils at 143. You drive the reaction to the right by removing water.  Another way to accomplish this is through a Dean-Stark Trap (or Apparatus), or through use of Molecular Sieves.  Although, I'm not sure how large of a scale molecular sieves is feasible on, but Dean-Stark is useful through large-scale productions!

[carboneel]

well with a BP of 143 yeah its unlikely the ester in this case would boil off first  BUT at any rate, i guess its still boiling off a product to push equilibrium to the right. thank you macman

[kuchiku]

ei.. am i too late for a reply? u wer askin wat must be done to prevent hydrolysis to happen? simply maintain anhydrous condition of the system (that is to not allow droplets of water from d sides of teh container to get inside d rxn mxture). hydrolysis, reverse of esterification, is a possible side product which will lower the yield. In esterification, the reaction is reversible. take note of le chatelier's principle. an x's of either of the reactants will shift the reaction to d ryt. in d same way, water as product, in x's amount, wil shift the rxn backward resulting to d formation of d starting materials.

[Borek]

u wer askin wat

Oficjalnym jezykiem forum jest angielski.

(transl: English is an official forum language).

[cundi]

Hi!!
At first, my english is quite bad. I'm sorry.
The hydrolsys of an ester is usually carried out under basic conditions, not in acid media.
Generally, in order to obtain an ester, it is usually to employ an excess of the alcohol and catalityc amounts of an acid.
In these cases is not necesary to keep anhydrous conditions in the reaction media.
Obviously, it depens on each situation.

Alternatively it us posible to "activate" the acid by generation of an acid chloride or similar.