fallsem2014 15 cp1454 13 oct 2014 rm01 esterification unit 5

8/10/2019 FALLSEM2014 15 CP1454 13 Oct 2014 RM01 Esterification Unit 5

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Esterifiication

Dr. G. Madhumitha

Organic Chemistry Division,

SAS


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Introduction

Formed when an alcohol reacts with a acid.

Very slow reaction, unless! an acid catalyst used(usually sulphuric acid)

A condensation reaction

The condensation reaction between the hydroxylgroup and the carboxylic acid known asesterification.

Reverse reaction = ester hydrolysis


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Naming

Named after alcohol & acid from which theyare derived.

Names of estersend in oate.

CH3C

CH2 O

O

CH3

ethyl ethanoate

this part from the acidand is named after it

this part comes from thealcohol & is named after it

lets name

some esters!


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Structural formulae

Although the previous structural formula are the clearestway of showing esters, they can draw out in a

shortened form.

ethyl ethanoate

CH3CCH2 O

O

CH3

Either

Or

CH3C CH2O

O

CH3

In this versionthe acid part

has beenwritten first

Identify the group attached to the C=O this is fromthe acid

The group attached to the O- is from the alcohol.


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Esterification by organic acids An ester is defined as a compounds formed by

substituting an orgaic radical for an ionizablehydrogen of an acid

In direct esterification, eg. Acetic acid by alcohol(ethanol), the possibility is there in breaking the C=Obond or alkyl oxygen bond.

The evidence for the breaking of carbonyl oxygen bondwas found by the following rxn.

If the alkyl sulfur bond had broken, hydrogen sulfide would have formed.


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Berthelot and Pean de St Gilles made the first measurement on the acetic acid

ethanol equilibrium and determined the equilibrium point.

The results showed that the reaction was reversible and depends on the amount of

compound present.

The equilibrium constant for the reaction is

[Ester X water] / [Acid X Alcohol] = K

Menschutkin has done extensive work on the equilibrium constant of large numbers

of acids and alcohols. (Tabulation

12-I, Pg 697)

It was observed that methyl showed the greatest initial rate of esterification

The primary alcohols such as ethyl, propyl and butyl same initial values

The secondary alcohol showed lower than primary alcohol

In case of tertiary alcohol, the limit is very less, since they get dehydrated very

easily to unsaturated hydrocarbons.

Formic acid reacts much faster than other branched- chain acids.


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The trimethylacetic acid dimetylethyl acetic acid are relatively slow.

Maleic acid is esterified 14 times as rapidly as fumaric acid

The esterification of unsaturated acids such as cinnamic and sorbic

starts very slowly that corresponding saturated acids but goes in

faster rate.

The purely aromatic acids such as benzoic, p-toluic esterfies very

slowly.


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Esterification of carboxylic acid derivatives Alcoholysis

In the alcoholysis or ester interchange rxn, an alcohol reacts with anester to give new ester

If a mixture of amyl nitrite and ethyl alcohol containing an acid catalyst

is warmed- ethyl nitrite distils out.

Friedal crafts heated ethyl acetate with amyl alcoholand amyl acetate

with ethyl alcohol and observed alcoholysis occurs. They also heated ethyl benzoate and amyl acetate together and

obtained ethyl acetate and amyl benzoate though the reaction was

slow below 300 C.

Completing Alcoholysis:

The removal of one reactant makes the reaction to complete.

When higher alcohols were heated in fractionating column, the volatile

constituents distils off.


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Utilization of Alcoholysis

Preparation of monomeric cyclic polymethylene

carbonates

Higher polymethylene glycol and sodiumare heated

with butyl carbonatesto obtain polymeric polymethylene

carbonate

Corrosion resistant usage of anhydrous esters, alcohols

Batch Process Kettle and Column

Kettle

alcohol + Sodium

Later Ester run then heated

Volatile component distils off

EQUIPMENT & OPERATION FOR ALCOHOLYSIS


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Esterification by addition of unsaturated systems

Addition of an acid to Olefin

Esters from Acetylene

Esterification by ketene Esterification by ethylene oxide

Esters from Carbon Monoxide


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Addition of an acid to Olefin

Addition of organic acid to an unsaturated hydrocarbonin the presence of strong acid

The addition of carboxylic acids to the double bonds of

isobutylene and trimethylethylene gives tertiary esters.

Formic acid to olefins is easily controlled and gives highyields of esters.

Optimum condition for the esterification of olefins by

carboxylic acids require low reaction temperature, high

concentrations of reactants and anhydrous conditions


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Esters from Acetylene

Acetylene and acetic acid vinyl ester or ester of

ethylidene diacetate formed Vinyl acetate used for polymer preparation

Ethylidene diacetate acetic anhydride synthesis

Zinc acetate widely used in vinyl acetate preparation

200 C or above

Strong acids as catalyst


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Ketene + alcohol esters

No by products

Salicylic acid can be acetylated by ketene

BF3 is an excellent catalyst

Esters from ketene


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Carbon monoxide with an alcohol at elevated temperature

and high pressure in the presence of metal alkoxide gives

alkyl formate

Esters from Carbon monoxide

fallsem2014 15 cp1454 13 oct 2014 rm01 esterification unit 5

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