Question

Fisher Esterification of m-Nitrobenzoic Acid to produce methyl m-nitrobenzoate Lab Report

Purpose Statement:

Discussion                                                                                                                                                           (15 points)

a. Carbonyl compounds can be divided in two groups. One group will consist of acyl halides, anhydrides, carboxylic acids, esters, amides; the second group consists of aldehydes and ketones. Even though all the compounds are carbonyl compounds, they react by different mechanisms. Differentiate the mechanism of reaction of the two carbonyl groups;

b. What is the order of reactivity of carbonyl compounds (most reactive to least reactive)? Include both carbonyl groups in the sequence and provide an explanation for the order of reactivity

c. Fisher Esterification is a nucleophilic acyl substitution. In this reaction, identify the electrophile and the nucleophile compounds.

The electrophile in this reaction is the carbocation formed, whereas the nucleophile is the

d. Elaborate on the reactivity of carboxylic acids. Explain the need for the acid.
e. How IR changes allow you to predict the success of this reaction (Fisher Esterification)?
f. How 1H NMR can help you to predict the success of this reaction (Fisher Esterification)?

Answer 1

a ) The first group of carbonyl compound contains a leaving group eg. In acyl halide the halide is leaving group, in anhydrides the -OCOCH3 is leaving group like that. But in second goup of compounds ie aldehydes & ketons does not contains any leaving group.The first group react with nucleophile with loss of leaving group while in second group the nucleophile reacts with different mechanism.

b) Order of reactivity of carbonyl compounds-

Acyl halide > acid anhydrides > aldehydes > ketones > Esters = Carboxylic acids > Amides.

This reactivity is depends on substituents present on carbonyl carbon.

1) if the substituents are electron donating the compound is less reactive.

2) if the substituents are electron withdrawing the compound is more reactive.

eg . in acel chlorides the -Cl is electron strong withdrawing group & it has -ve charge & carbon carries +ve charge.

While in amides the -NH2 group is very e- donating group & therefore carbonyl carbon carries less +ve charge & therefore less reactive.

Also in acyl halide contains good leaving group while in amides has poor leavinf group that affects reactivity.

In short the e- donating effect increases from left to right in above series & ability og leaving group leaves decreases from left to right.

c ) In Fischer esterification the Carboxylic acid reacts with alcohol to gives ester. In this reaction the loan pair of oxygen of alcohol attacks on protonated carbolyl group & thereforer alcohol is the Nucleophile While Carboxylic acid is Electrophile.

d ) Carboxylic acids undergo reactions to produce derivatives of the acid. The most common derivatives formed are esters, acid halides, acid anhydrides, and amides.The acid undergoes reaction like salt formation , sustitution, reduction with reducing agents & oxidation.

The ractivity of Carboxylic acid is mailnly due to large pKa value and more acidity. Both the carboxyl group and the carboxylate anion are stabilized by resonance.Due to this resonance the acidity is more .

e ) The IR spectrum for acid is given below.

O–H stretch from 3300-2500 cm^-1

C=O stretch from 1760-1690 cm^-1

C–O stretch from 1320-1210 cm^-1

O–H bend from 1440-1395 and 950-910 cm^-1

After reaction complition this peaks are disappear & a strong peak for alcohol are given.

O–H stretch, hydrogen bonded 3500-3200 cm^-1

C–O stretch 1260-1050 cm^-1