Why is that absolute ethanol be used in preparing an ester with ethanol as one of the reactants?
My Guess:
It will cause hydrolysis of the ester as it is formed in the reaction vessel.
Is this reasoning right? Pls. I need help about this...
The preparation of an ester using a carboxylic acid and an alcohol is an equilibrium reaction involving
RCOOH + HOR' ==> RCOOR' + H2O.
For acetic acid and ethanol, the products are approximately 2/3 mole each of ester and water and the reactants are about 1/3 mole each of the starting materials. The equilibrium mixture is favored to the right (about 67% yield) but not all that much. Adding water (by not using absolute ethanol BOTH drives the reaction to the left (less yield) (LeChatelier's Principle) and provides an easier path for hydrolysis (the reverse direction of esterification).
Your reasoning is almost correct, but not entirely accurate. The use of absolute ethanol in preparing an ester with ethanol as one of the reactants is to ensure that water, which can interfere with the reaction, is minimized.
When preparing an ester, it is important to have dry conditions because water can react with the reagents and hydrolyze the ester as it forms. Hydrolysis occurs when water breaks the ester bond, resulting in the ester being converted back into the original carboxylic acid and alcohol.
Using absolute ethanol, also known as anhydrous ethanol, helps to minimize the presence of water in the reaction mixture. Absolute ethanol is a form of ethanol that contains very low levels of water, typically less than 1%. This significantly reduces the likelihood of hydrolysis occurring during the reaction.
To obtain absolute ethanol, you can follow these steps:
1. Start with regular ethanol, commonly available as a solvent or for drinking purposes.
2. Add a drying agent, such as calcium oxide (CaO), magnesium sulfate (MgSO4), or molecular sieves, to the ethanol.
3. Allow the drying agent to absorb the water present in the ethanol.
4. Filter the mixture to remove the drying agent, leaving behind the dried ethanol.
By using absolute ethanol, you can ensure a successful esterification reaction with minimal interference from water, thus preventing hydrolysis of the ester.