Experiment 17:
NITRATION OF
p-methylacetanilide
H
N
O
C
H
CH 3
+ HNO3
p-methylacetanilide
H2SO4
Acetic acid
N
O
C
CH 3
NO 2
Nitromethylacetanilide
Objectives:




To synthesize methylnitroacetanilide isomers
using an electrophilic aromatic substitution.
To purify product by recrystallization.
To identify and determine purity of product by
melting point, TLC and HPLC analysis.
To characterize product by analysis of 1H-NMR
and 13C-NMR spectra.
Before coming to lab…

Review these techniques:

TLC analysis

Recrystallization

Suction filtration

HPLC analysis

Melting Point Analysis
CHEMICAL EQUATION
H
N
O
C
H
CH 3
+ HNO3
H2SO4
Acetic acid
N
O
C
CH 3
NO 2
H
N
O
C
CH 3
or
NO 2
4-methylacetanilide
C9H11NO
4-methyl-2-nitroacetanilide
C9H10N2O3
MW: 149.19
MW: 194.19
o
mp: 92-95oC
mp:148-151 C
INHALATION HAZARD,
INGESTION HAZARD
4-methyl-3-nitroacetanilide
C9H10N2O3
MW: 194.19
ELECTROPHILIC AROMATIC
SUBSTITUTION
E
+
E
H
+E
+
+
H
E
E
H
+
This reaction takes place in two steps:
1. Initial reaction of an electrophile, E+ with the
aromatic ring.
2. Loss of H+ from the resonance stabilized
carbocation intermediate to regenerate the
aromatic ring.
+ H+
MECHANISM
(Preliminary steps…)
• Reaction
of the aromatic compound with nitric acid
alone is slow and potentially hazardous.
• It is safer and faster to use a catalytic amount of
sulfuric acid.
•Sulfuric acid reacts with nitric acid to form the
nitronium ion, a powerful electrophile.
Sulfuric acid
Nitric acid
O
H O N O
+
O
H O S O H
O
• Sulfuric
nitronium ion
(STRONG electrophile)
H O
H O N O
+ HSO4-
O N O
+ H2O
acid protonates the hydroxyl group of
nitric acid, allowing it to leave as water and form
a nitronium ion.
MECHANISM
(Nitration of Aromatic Ring…)
• Electrophilic aromatic substitution by the nitronium
ion gives the nitro product.
O
O
H
H
N
CH 3
+
+ O N O
O
N
CH 3
O+ N O
H
• Attack on the electrophile
forms the sigma complex…
N
H
O
N + O
+ H3O
..
+
..
H3C
O H
H
• …loss of proton to water…
• …gives the aromatic
nitro product.
REACTIVITY OF AROMATIC
RINGS




The substituents ALREADY ON the aromatic
ring affect the reactivity of the aromatic ring,
or how FAST the substitution will occur.
The substituent ALREADY ON the aromatic
ring determines orientation of the substitution,
or the position of the second (INCOMING)
substituent.
Both the methyl group (-CH3) and the
acetamide group (-NHCOCH3) are o, p
activators.
The acetamide group is a STRONGER o, p
director than the methyl group.
Week 1:
Synthesis






Mix p-methylacetanilide and acetic
acid in 50 mL Erlenmeyer flask.
Prepare nitrating mixture in small
test tube (CAUTION!).
*IMPORTANT!* Cool this tube in
ice water!
Add nitrating mixture drop wise
while swirling.
Allow to react at room temp for 15
minutes.
Add cold deionized water.
Week 1:
Crude Product Isolation

Prepare suction filtration apparatus, seating
filter with cold deionized water.

Pour crude product slowly into center of
funnel. Rinse with cold deionized water.

Prepare CRUDE PRODUCT TLC and HPLC
samples in small sample vials.

Set crude solid aside to purify by
recrystallization.
Week 1:
Preparation of Filtrate Samples





Transfer 2 mL filtrate to a small test tube.
Add 10% NaOH drop wise until neutral
(check every 5 drops with pH Hydrion paper).
Add 3 mL ethyl acetate. Cork tube and
shake to mix.
Allow layers to separate.
Filtrate
Prepare HPLC and TLC samples of FILTRATE
using 5 drops of this solution for each.
Remember to add appropriate sample solvent
for each!
Week 1:
Purification

Transfer CRUDE PRODUCT to 50 mL
flask.

Dissolve in hot 90:10 ethanol/water.

Cool to room temp, then to 0oC.


Suction filter. Seat filter paper w/90:10
ethanol/water.
Prepare RECRYSTALLIZED PRODUCT
TLC and HPLC samples.
Week 1:
Sample Submission


Transfer small filter paper and product to a
preweighed large filter paper and submit to
instructor to dry until next lab period! Also,
submit all TLC samples to instructor.
At the end of lab, you should have submitted:

To instructor…



3 TLC sample vials
1 packet of pure solid product
For HPLC analysis…

3 auto sampler vials
Table 17.1
Theoretical yield (g)
Actual yield (g)
Percent yield
Experimental melting
range (oC)
Product appearance
Week 1: Calculate this value based on how
much reactant you ACTUALLY used, not just
what the MANUAL SAYS to use.
Week 2: Calculate this value after you have
retrieved your dry product next lab!
Week 2: Calculate this value after you have
retrieved your dry product next lab!
Week 2: Record this value as a Ti-Tf range
Week 1: Record COLOR and PHYSICAL
STATE of product.
Table 17.2
Atom Economy (%)
Week 1: Review Exp. 13 or Appendix I to
review calculation!
Experimental Atom
Economy (%)
Week 1: Be sure to calculate this value using
actual weights/volumes that YOU used, not
just what the MANUAL SAYS to use!
Week 2: You need the PERCENT YIELD for
this calculation!
“Eproduct”
Cost per Synthesis ($)
Cost per Gram ($/g)
Week 1: Be sure to calculate this value using
actual weights/volumes that YOU used, not
just what the MANUAL SAYS to use! Costs of
stock bottles are given on p. 150.
Week 2: You need the final ACTUAL YIELD
value to calculate this!
Week 2:
Product Analysis

TLC Analysis






HPLC Analysis


Prepare TLC plate with 6 lanes.
Apply 3 provided standards along with samples of crude
product, filtrate, and recrystallized product.
Develop in 2:1 ethyl acetate/hexane.
Visualize with UV lamp.
Identify compounds and calculate Rf value.
Compare sample chromatograms to provided standard to
identify compounds in each sample submitted.
Melting Point Analysis


Obtain the experimental melting point of your purified
product.
Compare to the literature value to determine degree of
purity.
Table 17.3
TLC Rf values
Compound
Standards
All Rf values
are unitless!
 All Rf values
are 2 decimal
places ONLY!

p-methylacetanilide
Crude
sample
Filtrate
sample
If reactant
present in this lane,
it explains product
loss!

If major product
present in this lane,
it explains product
loss!

4-methyl-2nitroacetanilide
4-methyl-3nitroacetanilide
Recrystallized
sample
Table 17.4
Standards
Compound
Retention
times
(min)
Crude
Sample
Retention
times
(min)
Filtrate
Sample
Area
%
Retention
times
(min)
Recrystallized
Sample
Area
%
Retention
times
(min)
p-methylacetanilide
4-methyl2-nitroacetanilide
4-methyl3-nitroacetanilide
• All samples are submitted for analysis during 1st lab period. Samples
will be run, and chromatograms returned during 2nd lab period!
Area
%
Product Analysis
(NMR Spectroscopy)
O
H
C
N
8
CH3
9
1
H
NO2
6
H
2
3
5
4
CH3
7
H
Table 17.5
O
H
N
C
8
N
CH3
8
1
6
2
5
3
CH3
7
C
9
1
4
O
H
6
CH3
9
NO 2
2
3
5
4
CH3
7
• Enter chemical shifts ONLY based on the spectra on pages 139 and 146.
• Notice that the reactant is the product from Experiment 16. You should
have already analyzed the NMR spectra!
SAFETY CONCERNS


Nitric acid and sulfuric acid are very
corrosive! Use EXTREME caution when in
use!
Ethanol is flammable! Be careful when
heating!
WASTE MANAGEMENT



Place all liquid waste from experiment into the bottle
labeled “LIQUID WASTE”.
Place solid waste in bottle labeled “SOLID ORGANIC
WASTE”.
Place all used TLC spotters and melting point
capillaries in broken glass container, NOT trashcan!
CLEANING




Clean all glassware with soap, water, and brush
if necessary.
Rinse all glassware with wash acetone before
returning to lab drawer.
DO NOT return any glassware dirty or wet to
lab drawer!
All hotplates and MelTemps must be unplugged
from outlets, with cords wrapped neatly.