1999 - The Hofmann Rearrangement Using Household Bleach Synthesis of 3-Nitroaniline.pdf

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In the Laboratory
The Hofmann Rearrangement Using Household Bleach:
Synthesis of 3-Nitroaniline
Keith A. Monk and Ram S. Mohan*
Department of Chemistry, Illinois Wesleyan University, Bloomington, IL 61702; *rmohan@titan.iwu.edu
The Hofmann rearrangement involves the conversion of
an amide to an amine containing one fewer carbon atoms,
by treatment with bromine (or chlorine) and alkali (1). The
mechanism of this reaction is discussed in detail in most
sophomore organic chemistry text books. Yet very few examples
of this rearrangement are found in lab texts (2). With aromatic
amides containing an electron-withdrawing group, hydrolysis
to the corresponding carboxylic acid under the basic reaction
conditions is often a serious competing side reaction. It has been
reported that at elevated temperatures, the rearrangement is
much more rapid than hydrolysis (3). We have successfully
carried out the rearrangement of 3-nitrobenzamide at 80
°C
using household bleach.
1
This procedure avoids the use of
bromine and sodium hydroxide, which is typically used to
effect the Hofmann rearrangement. The preparation of 3-
nitrobenzamide from benzamide has been previously reported
as a laboratory experiment (4 ). These two reactions can be
completed in two-and-a-half hours, making this sequence a
new and useful addition to the list of organic chemistry labo-
ratory experiments.
Experimental Procedure
3-Nitrobenzamide was prepared by nitration of
benzamide or purchased from Aldrich Chemical Co. The
concentration of household bleach solution was determined
to be 5.25% (wt/wt) by iodometric titration.
C
AUTION
:
Nitro compounds are often toxic. Gloves
should be worn throughout this experiment. Contact should
be avoided with bleach solutions.
Finely powdered 3-nitrobenzamide (1.5 g, 9.03 mmol)
was added to a 125-mL Erlenmeyer flask containing a mag-
netic stir bar, 18 mL of 1 M NaOH (18 mmol), and 13.3 mL
(14.1 g) of household bleach (9.93 mmol).
2
The well-stirred
mixture was heated at 80
°C
in a water bath for 30 min. The
mixture was cooled to 50
°C
and then 10% aqueous NaHSO
3
(10 mL) was added, which resulted in the precipitation of a
yellow solid. The flask was cooled in an ice bath and the solid
was collected by suction filtration. Recrystallization from 95%
ethanol gave 1.01 g (80%) of silky yellow crystals. The product
was identical by TLC, mp,
1
H NMR, and
13
C NMR with
an authentic sample of 3-nitroaniline.
1
H NMR (270 MHz)
(DMSO):
δ
5.82 (s, NH
2
), 6.96 (doublet of triplets, 1 H),
7.28 (m, 2 H), 7.39 (t, 1 H).
13
C NMR (DMSO):
δ
107.7,
111.4, 120.5, 130.3, 149.3, 150.6.
3
Notes
1. It has been reported that 2-nitroaniline, the product of
Hofmann rearrangement of 2-nitrobenzamide, reacts with NaOCl and
alkali to give benzofuroxan (5). Under the same conditions 4-nitro-
benzamide gives 50% 4-nitroaniline and 50% 4-nitrobenzoic acid (3).
2. The presence of excess bleach is checked using starch–iodide
paper.
3. 3-Nitroaniline is not sufficiently soluble in CDCl
3
. Hence spectra
were recorded in
d
6
-DMSO.
Literature Cited
1. For a review see
Organic Reactions,
Vol. III; Adams, R.; Bachman,
W. E.; Fieser, L. F.; Johnson, J. R.; Snyder, H. R., Eds.; Wiley:
New York, 1947; p 247.
2. For an example, see Campbell, B. N.; Ali, M. M.
Organic Chem-
istry Experiments. Microscale and Semi-Microscale;
Brooks/Cole: Pa-
cific Grove, CA, 1994. Schreck, J. O.
J. Chem. Educ.
1968,
10,
670.
3. Hauser, C. R.; Renfrow, W. B.
J. Am. Chem. Soc.
1937,
59,
121.
4. McElveen, S. R.; Gavardinas, K.; Stamberger, J. A.; Mohan, R.
S.
J. Chem. Educ.
1999,
76,
535.
5. Green, A. G; Rowe, F. M.
J. Chem. Soc.
1912,
101,
2443.
JChemEd.chem.wisc.edu • Vol. 76 No. 12 December 1999 • Journal of Chemical Education
1717

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