esterification

First of all - a refulx system is usually CLOSED otherwise the solvent will evaporate over time! Reflux systems can be closed because there's a water condenser attached, which will condense the vapour of the solvent back into the reaction and hence, preventing the loss of products (if your product is volitale)
The reflux method will give you better yield of the final prodcut because of the above reason AND also, because of temp. of the reaction. To product ester from alcohol and carboxylic acid needs enough temp. to heat up otherwise the nucleophilic attack at the carboxyl carbon cannot be completed (not enough energy).
The test tube method is not hot enough and the alcohol starting material will be evapourated, meaning that the equilibrium cannot be pushed all the way to the product side. And not enough alcohol to react with the acid won't give you a good yield.
Hope that helps.

2006-10-31 04:43:14 補充：
volatile...

2006-11-01 00:55:31 補充：
reflux...spelling mistake againClosed systems are usually used in organic reactions, we close it up with a constant N2(g) flow to keep the water out of the reaction.

2006-11-01 00:55:53 補充：
Likewise, the reaction of forming ester would probably done in a closed system in the lab - the water condenser will cool the vapour down back into the reaction.

2006-11-01 00:56:53 補充：
You can't reflux something WITHOUT a condenser, then that's dangerous because under heat, the volitale solvent and products with heat up ripidly and blow up!

2006-11-01 00:58:37 補充：
The reaction CAN be done in an open-top reflux system BUT your reactants will be more likely to evapourate over time due to air...unless if you have the heat on low to do the reaction, which in that case the reaction will be slow and incomplete.

2006-11-01 00:59:33 補充：
When I say water, it's in fact the moisture from air Iøm talking about

HEATING UNDER REFLUX 可以防止化合物流失
而方法2就可能會有揮發