Esterification

Esterification

** By: Jody and Liz **

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What is Esterification?
Esterification is the reaction to form an ester.These reactions are considerably easy, and very commonly used in organic chemistry. To accelerate or decelerate a reaction, a [|catalyst] can be used. One of the most common being sulfuric acid. An ester is a combination of an alcohol and a carboxylic acid. This reaction usually happens when you heat an alcohol and an acid together, while removing all water that is formed, then they react to form an ester. Esters can also be formed with the reaction of an alcohol and an [|acid chloride] or an [|acid anhydride]. Esters are what give many foods their flavoring, as shown in the examples below.


 * Below is the general formula for an esterification: **


 * [|alkanol] || + || [|alkanoic acid] || → || alkyl alkanoate (ester) || + || water ||
 * R'**O** **H** || + || R**CO** **OH** || → || R**CO** ** O ** R' (ester) || + || **H2O** ||

Some exapmles of this reaction are: 1. Banana:


 * pentanol || + || ethanoic acid || → || pentyl ethanoate (ester) || + || water ||

2.Rum Essence:


 * ethanol || + || methanoic acid || → || ethyl methanoate (ester) || + || water ||

3.Pineapple:


 * ethanol || + || butanoic acid || → || ethyl butanoate (ester) || + || water ||

History
The Fischer Esterification reaction was first described in 1895 by Emil Fischer, a German chemist, and Arthur Speier. Sometimes referred to as Fischer-Speier esterification, after the two chemists who founded it.

Reactions
These types of reactions occur with a carboxilic ([|acyl halide]) acid and an alcohol or a phenol. The general formula for an acyl halide is just ** R CO X**, "** R **" being the alkyl group, " ** CO ** " obviously being the carbonly group, and finally the " **X** " which represents the halide.
 * With Acyl Halides: **

//**Ex:**// ** H3C ** - ** CO Cl** **﻿ +** HO-CH2-CH3 → H3C-COO-CH2-CH3 + H-Cl

These reactions occur with a carboxylic [|acid anhydride] and an alcohol. The general formula for an acid anhydride is ** (RC(O))2O **, and it is basically two alkyl groups bound to one oxygen atom. //** Ex: **//**H3C-CO-O-CO-CH3** + HO-CH2-CH3 → H3C-COO-CH2-CH3 + H3C-COOH
 * With Acid Anhydrides: **

Finally, the last reaction...

This is the esterification of an alkali carboxylate and alkylating agent, such as an akyl halide, for example. This, unlike the others,is irreversible, and can be done naturally. Shown below is the reaction between [|Sodium Ethanoate](Cmedia type="custom" key="7482729"Hmedia type="custom" key="7482733"NaOmedia type="custom" key="7482735") and [|Ethyl Bromide](Cmedia type="custom" key="7482737"Hmedia type="custom" key="7482739"Br)
 * Alkylation of Carboxylate Salts: **



Fisher Esterification Mechanism
Ethanoic acid reacts with ethanol with the presence of a [|catalyst], which is a substance that will accelerate or decelerate a chemical reaction. In this specific example, Hmedia type="custom" key="7477257"SOmedia type="custom" key="7477263" will be the desired catalyst. This catalyst will decrease the reaction time, and is also reversible.

//**Step 1:**// Ethanoic acid will acquire one hydrogen ion from the sulfuric acid//**.**// Then, the hydrogen ion will attach to one of the lone pairs on the oxygen that is double bonded to the carbon. (See Figure 1 below).

//**Step 2:**// One of the lone pairs of the oxygen molecule attaches to the positive carbon. (See 2).

//** Step 3: **// Next, a hydrogen ion will be transferred from the bottom oxygen to a different one, at random ( See Figure 3).

A water molecule will break off of the ion. The positive charge is delocalised at the end of the ion, and other structures will also contribute to the charges on the other oxygens. Basically, the "contributions" from other substances are the resonance structures for this reaction. (See Figure 4).
 * // Step 4: //**

Finally, the hydrogen is removed from the oxygen, and placed back onto your catalyst, sulfuric acid. After this happens, you are left with the ester, ethyl ethanoate (See Figure 5). //**NOTE:**// This specific type of esterification is quite complex, so below is a step by step animation tutorial and even a video if you are in need of some extra help!
 * // Step 5: //**

[|Click Here for animation!]

Below is a video on esterification! media type="youtube" key="XtHaRL7IzZw" height="390" width="640"