Synthesis And Analysis Of Nitobenzoic Acid[1]

Organic Synthesis starting with the aromatic ester methyl benzoate

O

C

OCH3 ester

H

H

H

H

and finishing with the nitro aromatic acid 3-nitro benzoic acid:

O

C

OH acid

NO2

H in three separate stages

nitro Original slide prepared for the

Stage 1 O

C

Nitration of the aromatic ring to form methyl 3-nitrobenzoate

OCH3

O

C

OCH3

+ HNO3

+ H2O NO2

Cool with concentrated H2SO4

Original slide prepared for the

Identification of methyl 3-nitrobenzoate

O

C

OCH3

White crystalline solid at room temperature Melting point 77.5 oC

NO2

Impurities reduce melting point and discolour the solid

Compare with 3-nitrobenzoic acid Original slide prepared for the

mass spectrum of methyl 3-nitrobenzoate O OCH3 m/z relative intensity C 75 14 76 24 104 27 NO2 150 100 181 23 C6H4(NO2)CO+ Mass of molecular ion:181

C6H4

+

C6H4CO+

+

C6H4(NO2)COOCH3+

Compare with 3-nitrobenzoic acid Original slide prepared for the

Infra red spectrum of methyl 3-nitrobenzoate Compare with 3-nitrobenzoic acid

The “finger print” region < 1500 cm-1 unique pattern for each molecule C=O 1750 cm-1

Original slide prepared for the

nmr spectrum of methyl 3-nitrobenzoate 1H NMR

399.65 MHz

C8 H A7NO4

E

Assign. A

0.038 gmagnetic in 0.5 ml CDCl 3 nuclear resonance B C

B

D

Shift(ppm) 8.86 8.43

C

8.38

D

7.68

E

4.00

Compare with 3-nitrobenzoic acid Original slide prepared for the

Stage 2 O

C

Hydrolysis of the ester group to form the 3-nitrobenzoate ion

O

OCH3 + OH

C

-

NO2

O + CH3OH NO2

Reflux with concentrated NaOH alkaline hydrolysis Original slide prepared for the

Stage 3 O

C

Displacement of weak acid to form 3-nitrobenzoic acid

O

O

C

OH

+ H+ NO2

NO2

Warm with HCl acid displacement Original slide prepared for the

Identification of 3-nitrobenzoic acid OH

O

White crystalline solid at room temperature

C

Melting point 141.0 oC

NO2

Impurities reduce melting point and discolour the solid

Compare with methyl 3-nitrobenzoate Original slide prepared for the

mass spectrum of 3-nitrobenzoic acid m/z relative intensity 65 100 121 44 167 53 Mass of molecular ion:167.0

O

C

OH

+

NO2

C6H4(NO2)CO2H+ C6H4(NO2)+

Compare with methyl 3-nitrobenzoate Original slide prepared for the

Infra red spectrum of 3-nitrobenzoic acid Compare with methyl 3-nitrobenzoate

The “finger print” region < 1500 cm-1 acid O-H unique pattern 2600 cm-1 for each molecule C=O 1700 cm-1

Original slide prepared for the

nmr spectrum of 3-nitrobenzoic acid 1H NMR

89.56A MHz B

D NO C7 H 4 4

0.025 g in 0.5 ml CDCl3 E C Assign.

Compare with methyl 3-nitrobenzoate

Shift(ppm)

A

11.67

B

8.96

C

8.49

D

8.47

E

7.74 Original slide prepared for the

References Steve Lewis for the Royal Society of Chemistry Source of the spectral information http://www.aist.go.jp/RIODB/SDBS/menu-e.html

Original slide prepared for the