Microwave-induced conversion of acid hydrazides to N,N′- diacylhydrazines in solvent-free conditions

Article abstract of DOI:10.1080/00397910600602677

A new and efficient method of converting acid hydrazides 1 to the corresponding N,N′-diacylhydrazines 2 under microwave irradiation and in solvent-free conditions has been described. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600602677

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Microwave‐Induced Conversion of Acid
Hydrazides to N,N′‐Diacylhydrazines in
Solvent‐Free Conditions
B. Sailu a , A. Komaraiah a & P. S. N. Reddy a
a Department of Chemistry, Osmania University, Hyderabad, India
Published online: 18 Aug 2006.
To cite this article: B. Sailu , A. Komaraiah & P. S. N. Reddy (2006) Microwave‐Induced Conversion of Acid
Hydrazides to N,N′‐Diacylhydrazines in Solvent‐Free Conditions, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 36:13, 1907-1910
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Synthetic Communicationsw, 36: 1907–1910, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600602677
Microwave-Induced Conversion of Acid
Hydrazides to N,N0-Diacylhydrazines
in Solvent-Free Conditions
B. Sailu, A. Komaraiah, and P. S. N. Reddy
Department of Chemistry, Osmania University, Hyderabad, India
Abstract: A new and efficient method of converting acid hydrazides 1 to the corre-
sponding N,N0-diacylhydrazines 2 under microwave irradiation and in solvent-free
conditions has been described.
Keywords: Acid hydrazides, ammonium acetate, microwave, N,N0-diacylhydrazines
Earlier, the oxidation of acid hydrazides to N,N0-diacylhydrazines was
mediated by oxidizers such lead tetraacetate,[1] trifluorotoluonyl sulfonyl
peroxide,[2] diacetoxy iodobenzene,[3] and oxone,[4] copper(II) acetate[5] and
by acids such as Sulfuric acid,[6] phenylselenic acid,[7] NaBO3-AcOH,[8]
and Amberlyst A-26.[9] This reaction has also proceeded under neutral con-
ditions. The conditions used in these reactions varied from aqueous media
to dry pyrolysis. Recently, copper(II) acetate–mediated conversion of acid
hydrazides 1 to diacylhydrazines 2 was reported under microwave
conditions,[5] but the proposed mechanism appeared highly speculative.
This prompted us to explore this reaction further, and we discovered that
the microwave reaction of 1 to 2 does not require any catalyst.
We report here the direct conversion of 1 to 2 in solvent-free conditions
under microwave irradiation and without the use of any oxidant. The general-
ity of this reaction has been established by irradiating the acid hydrazides 1a–i
for 4–6 min and isolating the corresponding N,N0-diacylhydrazine 2a–i in
good yields (70–80%). The reaction was clean and free of by-products.
Received December 20, 2005
Address correspondence to P. S. N. Reddy, Department of Chemistry, Osmania
University, Hyderabad 500 007, India. Tel.: þ91-40-27682337; E-mail: psnreddyou@
yahoo.com
1907

1908
B. Sailu, A. Komaraiah, and P. S. N. Reddy
Table 1.
Irradiation time
(min.)
Yield (%)
No No
AcONH4 reagent AcONH4 reagent
Product
Ar
M (8C) (Lit.)
2a
2b
C6H5
4-CH3C6H4
82
86
80
83
3
3.5
4
4.5
235(238–240)[5]
252–253
(253–254)[5]
225(228–228.5)[5]
220(219–221)[5]
290–292(292)[5]
195
2c
2d
2e
2f
4-CH3OC6H4
2-Cl-C6H4
4-Cl-C6H4
2-CH3C6H4
2-Br-C6H4
2-OH-C6H4
4-OH-C6H4
2-I-C6H4
78
84
85
60
75
76
80
55
80
82
84
56
73
72
78
54
2.5
2
3
3.5
4.5
5.5
3.5
2.5
3.5
3.2
3
4
2g
2h
2i
2.5
1.3
2.3
2
220–222(245)[10]
295–298(298)[5]
235–242
2j
252(267)[11]
The results are summarized in Table 1. A plausible mechanism for the reaction
is given in the scheme and is vindicated by cross-condensation experiments
(vide TLC).
The addition of ammonium acetate to acylhydrazine in stoichiometric
quantities and microwave irradiation of the mixture accelerated the reaction
as evidenced by shorter reaction times (1–4 min) and improved product
yields. Perhaps ammonium acetate decomposes under microwave irradiation,
providing acid medium for the reaction. The conversion of 1 to 2 has also been
independently achieved by refluxing in acetic acid far 18–24 h. Thus,
microwave irradiation of acid hydrazides in solvent-free conditions is a
superior method for preparing N,N0-diacylhydrazines in terms of shorter
reaction times, higher yields, and easy workup.

Conversion of Acid Hydrazides to N,N0-diacylhydrazines
EXPERIMENTAL
1909
Melting points were determined on a Polomon melting-point apparatus (model
no. M.P.-96) and are uncorrected, given is degrees Centigrade. The IR spectra
were recorded on a Shimadzu-435 as KBr pellets, and H1 NMR spectra were
taken in d6-DMSO on a Varian Gemini 200-MHz spectrometer using TMS as
an internal standard. Microwave irradiations were carried out on BPL-Sanyo,
BMO, and 700 T domestic microwave ovens at an output of 600 W.
General Procedure for the Conversion of Acid Hydrazide (1) to
N,N0-diacylhydrazines (2)
In Dry Medium without Catalyst
The acid hydrazide 1 (1 g) was taken in a Pyrexw test tube and covered with a
cotton plug. The test tube was kept in a microwave oven and irradiated at
700 W for 4–6 min (Table 1); the reaction was monitored by TLC (silica
gel) for its completion. The reaction mixture was cooled and triturated with
dil. HCl (1 mL in 25 mL of water). The corresponding N,N0-diacylhydrazines
2 that separated out as solids were filtered and recrystallized from ethanol to
afford 2a–j (Table 1).
In Dry Medium using Ammonium Acetate
A mixture of the acid hydrazide 1 (0.01 M) and ammonium acetate (0.01 M)
was taken in a boiling tube covered with a cotton plug and irradiated with
microwaves at 700 W for the appropriate time (Table 1). After complete
conversion as indicated by TLC (silica gel), the reaction mass was cooled
to room temperature and triturated with dil. HCl (2 mL in 50 mL of water).
The corresponding N,N0-diacylhydrazines 2 that separated out as solids
were filtered and recrystallized from ethanol to afford 2a–j (Table 1).
In Glacial Acetic Acid
The acid hydrazide 1 (5 g) and glacial acetic acid (20 mL) were heated under
reflux for 18–24 h (TLC). Excess of acetic acid was removed by vacuum dis-
tillation. The reaction mixture was cooled to room temperature and poured on
crushed ice. The corresponding N,N0-diacylhydrazide 2 was filtered, dried,
and recrystallized from ethanol.
ACKNOWLEDGMENTS
Our sincere thanks to the director, IICT, Hyderabad, India, for providing
NMR spectra.

1910
B. Sailu, A. Komaraiah, and P. S. N. Reddy
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