H2SO4/SiO2 as an efficient catalyst for the preparation of phenylhydrazones and 2,4-dinitrophenylhydrazones under solvent-free conditions

Article abstract of DOI:10.1080/10426500490422227

H₂SO₄ mixed with silica gel (1:1) by weight produces a white powder which is an effective catalyst for the conversion of carbonyl compounds to their corresponding phenylhydrazones and 2,4-dintrophenylhydrazones under solvent-free conditions.

Full text of DOI:10.1080/10426500490422227

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Phosphorus, Sulfur, and Silicon and the Related
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H2SO4O2 AS AN EFFICIENT CATALYST FOR THE
PREPARATION OF PHENYLHYDRAZONES AND 2,4-
DINITROPHENYLHYDRAZONES UNDER SOLVENT-FREE
CONDITIONS
Ali Reza Kiasat a , Foad Kazemi a & Kazem Nourbakhsh a
a Shahid Chamran University, Ahvaz, Iran
Published online: 12 Aug 2010.
To cite this article: Ali Reza Kiasat , Foad Kazemi & Kazem Nourbakhsh (2004) H2SO4O2 AS AN EFFICIENT CATALYST FOR THE
PREPARATION OF PHENYLHYDRAZONES AND 2,4-DINITROPHENYLHYDRAZONES UNDER SOLVENT-FREE CONDITIONS, Phosphorus,
Sulfur, and Silicon and the Related Elements, 179:3, 569-573, DOI: 10.1080/10426500490422227
To link to this article: http://dx.doi.org/10.1080/10426500490422227
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Phosphorus, Sulfur, and Silicon, 179:569–573, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490422227
H2SO4/SiO2 AS AN EFFICIENT CATALYST FOR THE
PREPARATION OF PHENYLHYDRAZONES AND
2,4-DINITROPHENYLHYDRAZONES UNDER
SOLVENT-FREE CONDITIONS
Ali Reza Kiasat, Foad Kazemi, and Kazem Nourbakhsh
Shahid Chamran University, Ahvaz, Iran
(Received September 9, 2003)
H2SO4 mixed with silica gel (1:1) by weight produces a white
powder which is an effective catalyst for the conversion of car-
bonyl compounds to their corresponding phenylhydrazones and 2,4-
dintrophenylhydrazones under solvent-free conditions.
Keywords: 2,4-Dinitrophenylhydrazone; carbonyl compound; phenyl-
hydrazone; protection; silica gel; solvent free; sulfuric acid
Protection of carbonyl groups is often a necessary requirement in
reactions involving substrates with multifunctional groups.1 Deriva-
tives of carbonyl compounds such as phenylhydrazone and 2,4-
dintrophenylhydrazones not only are used for the characterization and
purification of carbonyl compounds but also play an important role in
the protection of carbonyl compounds.2 Phenylhydrazones are largely
oils or possess low melting points for many aliphatic aldehydes and ke-
tones, but are generally crystalline for aromatic carbonyl compounds
and also for cycloaliphatic and hetrocyclic aldehydes and ketones.
2,4-Dinitrophenylhydrazones are generally crystalline and are there-
fore eminently more suitable than phenylhydrazones for the detection,
characterization, and protection of carbonyl compounds.3
The formation of these derivatives involves Brønsted as well as Lewis
acid catalysis.4 Although a protecting system consisting of phenyl-
hydrazine or 2,4-diphenylhydrazine and acidic zeolite in methanol
was recently reported1 for the protection of carbonyl compounds,
Partial support of this work by Shahid Chamran Ahvaz University Research Council
is gracefully acknowledged.
Address correspondence to Ali Reza Kiasat, Chemistry Department, College of
Science, Shahid Chamran University, Ahvaz, Iran.
569

570
A. R. Kiasat et al.
a literature survey reveals that no attention has been focused on
the protection of carbonyl compound as phenylhydrazones or 2,4-
dintrophenylhydrazones using inorganic solid supports under solvent-
free conditions.
Recently considerable attention has been paid to solvent-free
reactions.5,6 These reactions are not only of interest from an environ-
mental point of view, but in many cases also offer considerable synthetic
advantages in terms of yield, selectivity, and simplicity of the reaction
procedure.
Sulfuric acid on silica gel (2.5:1) by weight has been used as a catalyst
for the nitration of aromatic compounds.7 Now, we report that a mixture
of H2SO4 and SiO2 in the ratio 1:1 (w/w) gives a white powder that can
be used as efficient catalyst for conversion of carbonyl compounds to
the corresponding phenylhydrazones and 2,4-dintrophenylhydrazones
in the absence of solvent.
TABLE I SiO2/H2SO4 Catalyzed Conversion of Carbonyl Compounds
to Phenylhydrazone
Time Yield
Entry
1
Substrate
Product
(min)
(%)
10
85
2
3
4
8
10
7
87
88
83
5
6
8
8
67
91
7
5
90
aYields refer to pure isolated products.
bProducts were characterized by comparsion of their physical data, IR, NMR
spectra with known samples.

Phenylhydrazones
571
H2SO4/SiO2 was prepared by simply cogrinding silica gel with sul-
furic acid in the ratio 1:1 (w/w) in an agate mortar. In this simple and
efficient method the starting aldehydes and ketones were converted to
TABLE II SiO2/H2SO4 Catalyzed Conversion of Carbonyl Compounds
to 2.4-Dinitrophenyl Hydrazonea,b
Time
(min)
Yield
(%)
Entry
1
Substrate
Product
10
65
85
90
2
3
8
9
4
10
87
5
6
7
10
8
79
71
68
8
8
10
83
aYields refer to pure isolated products.
bProducts were characterized by comparsion of their physical data, IR, NMR
spectra with known samples.

572
A. R. Kiasat et al.
the corresponding arylhydrazones in a mortar with grinding by a pestle
in the presence of H2SO4/SiO2 and arylhydrazine.
As shown in Tables I and II, various types of aldehydes and ke-
tones were cleanly and rapidly condensed with phenylhydrazine and
2,4-dinitrophenylhydrazine under solvent free conditions, giving the
corresponding phenylhydrazones and 2,4-dinitrophenylhydrazones in
good to excellent isolated yields in the presence of H2SO4/SiO2. The
scope and generality of this process is illustrated with several exam-
ples and the results are summarized in Table I and II. The structure
of all the products were settled from their analytical and spectral (IR,
1H NMR) data and by direct comparison with authentic samples.
CONCLUSION
In summary, we have demonstrated an efficient, mild, and novel protec-
tion methodology of the carbonyl group using phenylhydrazine and 2,4-
dinitrophenylhydrazine in the presence of silica gel and sulfuric acid
under solvent-free conditions. We believe that the present procedure
provides an easy, mild, efficient, versatile, and general methodology for
the protection of different classes of carbonyl compounds, and we feel
that it may be a suitable addition to methodologies already present in
the literature.
EXPERIMENTAL
General
All products are known compounds and are identified by comparison
of their physical and spectral data with those of authentic samples.
The purity determination of the products and reaction monitoring were
accomplished by TLC on silica gel polygram SILG/UV 254 plates.
General Procedure for the Preparation of
Phenylhydrazones and 2,4-Dinitrophenylhydrazones
H2SO4 (98%, 2 g) and SiO2 (2 g) were thoroughly mixed together in
a mortar to form an intimate mixture. A neat carbonyl compound
(1 mmol) and phenylhydrazine or 2,4-dinitrophenylhydrazine (5 mmol)
were added to this mixture. The reaction mixture was ground for the
time specified in Table I and II. The progress of reaction was monitored
by TLC using ether-CCl4. On completion of the reaction, the reaction
mixture was poured into ether (30 ml). The silica gel was filtered off

Phenylhydrazones
573
and the filtrate washed with water (30 ml). The organic layer was dried
over anhydrous sodium sulfate and solvent evaporated under reduced
pressure to give the product which was recrystallized from a suitable
solvent to afford the TLC and 1HNMR pure products in 65–91% isolated
yields. (Caution: Phenylhydrazine and 2,4-dinitrophenylhydrazine are
toxic and cancers suspect agent.
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