Esterification

**Esterification**
**What is esterification?**
 * Esterification is a reaction of an alcohol with an acid that produce an ester and water. For example:

CH 3 OH+C 6 H 5 COOH⇌CH 3 OOCC 6 H 5 +H 2 O


 * Consists of reacting a carboxylic acid with an alcohol in presence of a dehydrating agent
 * The dehydrating agent is usually sulfuric acid, which acts as a catalyst
 * The reaction is an equilibrium and is slow under normal conditions
 * The reverse reaction is called Ester Hydrolysis

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=**What are esters used for? ** =


 * Methyl Salicylate is used in perfumery and for flavoring sweets, as well as a therapeutic use as a counter-irritan.
 * Ethyl Acetate is used in pharmaceutical aid, artificial fruit essences, solvent for nitrocellulose, varnishes, airplane dopes and cleaning textiles.

=What are the variables? = > >  **Catalyst:**
 * For primary alcohols to achieve a maximum yield of an ester through simple reactants the catalyst used must be graphite bisulfate, as it would allow for there to be a 94% ester yield.
 * For secondary and tertiary alcohols, the catalyst to be used is [[image:file://localhost/Users/ehmgee/Library/Caches/TemporaryItems/msoclip/0/clip_image002.png height="16"]] since it mediates the reaction between the alcohols and acetic and propanoic acid. The ester yield would be 85-96%.
 * The temperature for the reaction should be 150+% as it would allow for more reactions to take place between the acids and the alcohol.


 * When a carboxylic acid reacts with an alcohol to produce an ester, the presence of concentrated sulphuric acid is used as a catalyst.




 * For the reaction to take place, the carboxylic acid first takes a proton (hydrogen ion) from the concentrated sulphuric acid. The proton then attaches to one of the lone pairs on the oxygen which is double-bonded to the carbon.




 * This transfer gives the oxygen a positive charge, and the positive charge is delocalized. The ion therefore looks like this:




 * The double headed arrows mean that the individual structures make a contribution to the real structure of the ion.
 * Next, one of the lone pairs on the oxygen of the alcohol molecule attacks the positive charge on the carbon atom.


 * A proton (hydrogen ion) gets transferred from the bottom oxygen atom to one of the others. It then gets picked off by one of the other substances in the mixture (by attaching to a lone pair on an unreacted alcohol molecule) and then dumped back onto one of the oxygens more or less at random.




 * Now a molecule of water is lost from the ion.
 * When hydrogen sulphate ion reacts, hydrogen is removed from the oxygen.




 * Finally, the ester is formed and the sulphuric acid catalyst has been regenerated.

= = =**Advantages and Disadvantages: ** =
 * =<span style="font-family: Geneva,helvetica,sans-serif; font-size: 13px; font-weight: normal; line-height: 14px;">It is relatively simple compared to other reactions. =
 * =<span style="font-family: Geneva,helvetica,sans-serif; font-size: 13px; font-weight: normal; line-height: 14px;">Finally, the ester is formed and the sulphuric acid catalyst has been regenerated. Straightforward acidic conditions can be used if acid-sensitive functional groups are not an issue. =
 * Low environmental impact in terms of waste products and harmful reagents.
 * Esterification is a slow process, but tends to be a major product
 * =<span style="font-family: Tahoma,Geneva,sans-serif; font-size: large; line-height: 27px;">**<span style="font-family: arial,helvetica,sans-serif; font-size: 13px; font-weight: normal; line-height: 19px;">be If the product has a lower boiling point than water or the reagents, the product may be distilled rather than water. ** =