2007-03-25 03:38:31 · 2 answers · asked by shigure 1 in Science & Mathematics ➔ Chemistry
Acids protonate the carbonyl oxygen of the carboxylic acid, which ends up via resonance putting the positive charge on the carbonyl carbon. The oxygen of the alcohol then goes after the positive charge, forming an intermediate where the carbonyl carbon is bonded to three oxygens (the original carbonyl oxygen, the acid oxygen, and the alcohol oxygen) as well as the alkyl group. The alcohol hydrogen is lost, after which the acid oxygen is protonated by additional acid, the entire group leaves as H2O, and then the carbonyl oxygen deprotonates, reforming the C=O bond. In the end, the ester oxygen comes from the alcohol, not the acid.
Sulfuric acid is preferable because the anion is innocent. HCl has the possibility of forming side reactions, as chloride is a decent nucleophile, and HNO3 is an oxidizing acid, having the potential of oxidizing the alcohol to an aldehyde or another carboxylic acid.
2007-03-25 03:54:36 · answer #1 · answered by TheOnlyBeldin 7 · 1⤊ 0⤋
The H+ ions gives the preparation mixture the acidity required for the condensation reaction, while the sulphates have a water driving effect. The protonation of the carboxyl acid is enabling the nucleophilic attack that allows the alcohoc and the acid to form the intermediate.
Other acids could be used as well (anhydrous HCl or acidic resins).
2007-03-25 10:57:16 · answer #2 · answered by Ivan 5 · 0⤊ 0⤋