A highly efficient MW assisted synthesis of different nitrogen containing heterocyclic compounds under solvent free conditions was reported. Their aminomethylation was carried out on acidic alumina under microwave irradiation to give the corresponding Mannich bases. The method is clean, fast, facile, efficient, low cost and environmentally benign. The structure of synthesized compounds has been characterized on the basis of their elemental analysis and spectral data. These compounds were evaluated for their antimicrobial activity against bacteria and fungi

Ameta, Rakshit

Punjabi, Pinki

Rawal, Manish

Sharma, V.

Vyas, Madhuri

Revistes Catalanes amb Accés Obert

AfinidAd LXVii, 550, Noviembre - Diciembre 2010 467
RESUMEN
Se presenta una síntesis muy eficiente de distintos com-
puestos heterocíclicos nitrogenados, en condiciones de 
ausencia de disolvente asistida por microondas. Su ami-
nometilación se llevó a cabo sobre alúmina ácida con ra-
diación de microondas para obtener las correspondientes 
bases de Mannich. El método es limpio, rápido, fácil, efi-
ciente, económico y medioambientalmente benigno. La 
estructura de los compuestos sintetizados se caracterizó 
en base a su análisis elemental y datos espectroscópicos. 
La actividad antimicrobiana de estos compuestos se eva-
luó frente a bacterias y hongos. 
Palabras clave: Aminometilación, Alúmina ácida, irradia-
ción con microondas.
SUMMARY
A highly efficient MW assisted synthesis of different ni-
trogen containing heterocyclic compounds under solvent 
free conditions was reported. Their aminomethylation was 
carried out on acidic alumina under microwave irradiation 
to give the corresponding Mannich bases. The method is 
clean, fast, facile, efficient, low cost and environmentally 
benign. The structure of synthesized compounds has been 
characterized on the basis of their elemental analysis and 
spectral data. These compounds were evaluated for their 
antimicrobial activity against bacteria and fungi.
Keywords: Aminomethylation, Acidic alumina, Microwave 
irradiation
RESUM
Es presenta una síntesi molt eficient de diferents compos-
tos nitrogenats heterocíclics, en condicions d’absència 
de dissolvent, i assistida per microones. La seva amino-
metilació es va realitzar sobre alúmina àcida, amb radi-
ació de microones per obtenir les corresponents bases 
de Mannich. El mètode es net, ràpid, eficient, econòmic, i 
mediambientalment benigne. La estructura dels compos-
tos sintetitzats se va caracteritzar en base al seu anàli-
si elemental i les dades espectroscòpiques. La activitat 
antimicrobiana d’aquests compostos es va avaluar amb 
bacteris i fongs.  
Paraules clau: Aminometilació, Alúmina àcida, irradiació 
amb microones.
MW assisted synthesis of some heterocyclic 
compounds and their Mannich bases under 
solvent free conditions and their biological assay
aMadhuri Vyas, aManish K. Rawal, aV. K. Sharma, bRakshit Ameta, a*Pinki B. Punjabi
aMicrowave Chemistry Laboratory, Department of Chemistry, University College of Science, Mohanlal Sukhadia University, 
Udaipur - 313 001 (Raj.), INDIA. bDepartment of Pure and Applied  Chemistry, University of  Kota, Kota (Raj.), India
Síntesis asistida por microondas de algunos compuestos heterocíclicos y sus bases 
de Mannich en condiciones de ausencia de disolvente y ensayos biológicos
Síntesi assistida per microones d’alguns compostos heterocíclics y les seves  bases 
de Mannich en condicions d’absència de dissolvent i assaigs biològics
Recibido: 29 de mayo de 2010; revisado: 22 de diciembre de 2010; aceptado: 28 de enero de 2011
*Corrresponding author: pb_punjabi@yahoo.com
AfinidAd LXVii, 550, Noviembre - Diciembre 2010468
INTRODUCTION
The growth of chemistry has been closely associated with 
the development of new bioactive molecules, which have 
been synthesized using newer and greener routes. Con-
ventional methods of synthesis of chemical compounds 
with desired biological properties are time consuming and 
expensive, too. Thus, traditional medicinal chemistry re-
mains the bottlenecks in the drug discovery processes. 
Consequently, there is an increased interest in technolo-
gies and concepts that facilitates more rapid synthesis and 
screening of chemical substances to identify compounds 
with appropriate qualities. One such high-speed technol-
ogy is Microwave Assisted Organic Synthesis (MAOS). In 
recent years, the acceleration of a wide range of chemical 
reactions using microwave dielectric heating has been re-
ported1. The solvent free conditions under microwave irra-
diation offer several advantages; solvents are often expen-
sive, toxic and difficult to remove and are polluting agents.
A considerable amount of work has been reported on the 
synthesis and pharmacological activity of various Man-
nich bases for analgesic, antispasmodic, anesthetic and 
antimicrobial activity as well as intermediate in drug syn-
thesis2-14. In this context, literature survey has revealed a 
number of reports on antimicrobial activity of N-Mannich 
bases derived from different heterocycles such as pyrrole, 
pyrazole, benzimidazole, benzotriazole etc14-20.  
Microwave induced aminomethylation using solid support 
fulfils the need of ‘Green chemistry’ to a greater extent be-
cause it minimizes the use of solvents. Moreover, these 
supports are reusable. In the present paper, a simple, 
highly efficient and eco-friendly process for synthesis of 
some heterocyclic compounds and corresponding Man-
nich bases has been reported.
RESULTS AND DISCUSSION
All heterocyclic compounds have been synthesized under 
microwave exposure. The structures of these compounds 
have been confirmed by their physical, analytical and 
spectral data. The synthesized compounds on reaction 
with formaldehyde and secondary amines (morpholine / 
N-methyl piperazine) yielded the corresponding Mannich 
bases on alumina under MW irradiation. When compound 
(1) was treated with formaldehyde and secondary amines, 
1-[(morpholin-4-yl/4-methyl piperazin-1-yl)methyl]-1H-
benzotriazole were obtained (2a & 2b). Disappearance of 
N-H stretching band at 3500-3400 cm-1 and appearance 
of IR bands at 1226/1215, 2832/2850 & 1097 cm-1 due 
to C-N, CH2 and C-O groups indicate presence of mor-
pholine / N-methyl piperazine moiety in the desired com-
pound. 1H NMR and mass spectrum were also confirmed 
the structure of product.
Compound (3) on reaction with formaldehyde and second-
ary amines afforded (4a & 4b). The structure of compounds 
(4a & 4b) has been confirmed by disappearance of N-H 
stretching at 3480 cm-1 and bands appearing at 1203 and 
1072 cm-1, respectively due to C-N and C-O stretching, 
which shows that morpholine / N-methyl piperazine moi-
ety has been entered. 1H NMR and molecular ion peaks 
appearing in mass spectra further supported the structure 
of Mannich bases.
Compound (5) on aminomethylation yielded (6a & 6b). 
In the IR spectrum, disappearance of N-H stretching at 
3420cm-1 and appearance of bands at 1213 and 1081 cm-1 
due CN & C-O groups indicate the formation of Mannich 
bases. In 1H NMR spectrum, single singlet appeared at δ 
9.12 due to the presence of one N-H group indicating that 
one N-H group underwent aninomethylation reaction
Similarly, reaction of compound (7) afforded (8a & 8b). Disap-
pearance of broad band due to N-H group between 3300-3100 
and appearance of peaks at 1225 and 1122 cm-1 due to C-N and 
C-O groups favour the structure of compounds (8a & 8b). Fur-
ther, 1H NMR and mass spectra also supported the structure of 
aminomethylated compounds. The physical and analytical data 
are presented in Table (1) and spectral data are given in Table (2).
Table 1 :  Characterization data of synthesized compounds
Com-
pound R’
Molecular 
formula 
Mole-
cular 
weight
Mel-
ting 
point
Yield 
(%)
Analysis 
of N (%) 
Calcd. 
(Found)
2a
C11H14N4O
218 135 78
25.67 
(25.64)
2b C12H17N5
231 163 75
30.28 
(30.25)
4a
 
C13H14N2O3 246 230 80
11.38 
(11.35)
4b
C14H17N3O2
259 200 75
16.20 
(16.18)
6a
C13H17N3O2 247 187 82
16.99 
(16.95)
6b
C14H20N4O
260 233 70
21.52 
(21.50)
8a
C9H15N3O2 197 287 80
21.30 
(21.28)
8b
C10H18N4O 210 215 75
26.64 
(26.62)
AfinidAd LXVii, 550, Noviembre - Diciembre 2010 469
Table 2 :  Spectral data of synthesized compounds
Compd. Spectral Data
2a IR (cm-1):  3064 (C-H str., Ar-H),  2832 (C-H str.,CH2),
1600 (N=N str.), 1411 (CH2 bend.), 1226 (C-N str.),
1097 (C-O str.), 795 (Ar-H bend.).
1H NMR (δ): 7.50-7.32 (m, 4H, ArH), 4.32 (s, 2H, N-CH2-N),
3.86 (t, 4H, CH2-O-CH2), 2.50 (t, 4H, CH2 – N-CH2
MS (m/z) 218 [M]+, 190 [M-N2]
 +, 146 [M-C4H8O]
+,
132 [M - C4H8NO]
+, 119 [C2H5N3]
 +, 118 
[M -  C2H10NO]
+, 104 [C6H4N2]
+, 100 [C5H10NO]
+
86 [C4H8NO]
+.
2b IR (cm-1):  3075 (C-H str., Ar-H), 2850 (C-H str., CH2), 
1580 (N=N str.), 1251 (C-N str.), 790 (Ar-H bend).
1H NMR (δ): 8.0- 7.52 (m, 4H, ArH), 4.23 (s, 2H, N-CH2 -N),
3.55 (t, 4H, CH2-N-CH2 ), 2.85 (s, 3H, N-CH3), 
2.58 (t, 4H, CH2-N(Me)CH2).
MS (m/z) 231[M] +, 203 [M-N2]
+, 202 [M-NCH3]
+,
174 [M-C3H7N]
+, 146 [M-C5H11N]
+, 132 [M-C5H11N]
+,
119 [C6H5N3]
+, 113 [C6H13N2]
+, 104 [C6H4N2]
+.
4a IR (cm-1):  3150 (C-H str., Ar-H), 2855 (C-H str.,CH2),
1750, 1705 (C=O str.), 1072 (C-O str.), 790 (Ar-H bend).
1H NMR (δ): 7.89-7.54 (m, 4H, ArH), 4.46 (s, 2H, N-CH2-N), 
3.90 (t, 4H, CH2-O-CH2), 2.65 (t, 4H, CH2-N-CH2)
MS (m/z) 246 [M]+, 218 [M-C2H4]
 +, 174 [M-C4H8O]
+ ,
160 [M-C4H8NO]
+, 147 [C8H5NO2]
 +, 146 [M-C2H10NO]
+,
132 [C8H4O2]
+, 100 [C5H10NO]
+, 104 [C7H4O]
+, 86 [C4H8NO]
+
4b IR (cm-1): 3214 (C-H str., Ar-H), 2903 (C-H str., CH2),
1716, 1790 (C=O str.), 1203 (C-N str.), 749 (Ar-H) 
1HNMR (δ): 8.03- 7.56 (m, 4H, ArH), 4.31 (s, 2H, N-CH2 -N),
3.68 (t, 4H, CH2-N-CH2), 2.80 (s, 3H, NCH3), 
2.31 (t, 4H, CH2-N(Me)CH2).
MS (m/z) 259 [M] +, 231 [M- C2H4]
+, 230 [M-NCH3]
+,
202 [M-C3H7N]
+, 174 [M-C5H11N]
+, 160 [M-C5H11N2]
+, 
147 [C8H5NO2]
+, 132 [C8H4O]
+, 113 [C6H13N2]
+, 140 [C7H4O]
+.
6a IR (cm-1): 3300 (N-H str.), 3086 (C-H str., Ar-H), 
2850 (C-H str., CH2), 1725 (C=Ostr.), 1081 (C-O str.), 
760 (Ar-H bend.).
1H NMR (δ): 7.84 - 7.68 (m, 4H, ArH), 9.12 (s, 1H, NH),
4.30 (CH2 – N-CH2), 3.75 (t, 4H, CH2-O-CH2),
2.95 (t, 4H, CH2-N-CH2). 
MS (m/z) 247  [M]+, 246 [M-H] +, 219 [M-C2H4]
 +,
175 [M-C4H8O]
+, 161 [M-C4H8NO]
+, 147 [M-C5H10NO]
 ,
146 [M-C2H10NO]
+, 119 [C7H5NO]
+ , 100 [C5H10NO]
+, 
86 [C4H8NO]
+.
6b IR (cm-1): 3321 (N-H str), 3021 (C-H str., Ar-H), 
2831 (C-H str., CH2), 1710 (C=O str.), 1213 (C-N str.),
757 (Ar-H bend).
1H NMR (δ): 7.72- 7.23 (m, 4H, ArH), 9.15 (s, 1H, NH), 
4.38 (s, 2H, N-CH2 -N), 3.71 (t, 4H, CH2-N-CH2 ),
2.72 (s, 3H, NCH3), 2.37 (t, 4H, CH2-N(Me)-CH2).
MS (m/z) : 260 [M] +, 259 [M-H]+, 232 [M-C2H4]
+,
231 [M-NCH3]
+, 203 [M-C3H7N]
+,
175 [M-C5H11N2]
+, 161 [M-C5H11N2]
+,
147 [C8H5NO2]
+, 132 [C8H4O]
+, 119 [C7H5NO]
+,
113 [C6H13N2]
+.
8a IR (cm-1): 3056 (C-H str. Ar-H), 1777 (C=O str.), 1595 (C=N str.), 
1122 (C-O str.), 738 (Ar-H bend.).
1H NMR (δ): 4.55 (s, 2H, CH2), 4.25 (s, 2H, N- CH2 – N), 375 
(t, 4H, CH2- O-CH2), 2.43 (t, 4H, CH2 – N-CH2),
1.88 (s, 3H, CH3).
MS (m/z) 197  [M]+,182 [M-CH3]
 +, 169 [M-CO] +, 156 [M-C2H3N]
+,
125  [M-C4H8O]
+, 111 [M-C4H8NO]
 +, 100 [C5H10NO]
+, 97 
[M-C5H10NO]
+, 86 [C4H8NO]
+.
 8b IR (cm-1):  3070 (C-H str., Ar-H), 1750 (C=O str.), 1610 (C=N str.), 
1225 (C-N str.), 745 (Ar-H bend.).
1H NMR (δ): 4.55 (s, 2H, CH2), 4.31 (s, 2H, N-CH2 -N),
3.80 (t, 4H, CH2-N-CH2 ), 2.67 (s, 3H, CH3), 
2.30 (t, 4H, CH2-N(Me)CH2).
MS (m/z). 210 [M]+, 195 [M-CH3]
 +, 182 [M-CO] +, 181 [M-NCH3]
 +,
169 [M-C2H3N]
+, 153 [M-C3H7N]
 +, 113 [C6H13N2]
+, 
111 [M-C5H11N2]
+.
AfinidAd LXVii, 550, Noviembre - Diciembre 2010470
EXPERIMENTAL SECTION
General Procedure
All the reactions were carried out in a domestic microwave 
oven (Kenstar, Model No. OM-26 EGO, Power-1200W). 
Melting points were determined in open capillaries. Reac-
tions were monitored by thin layer chromatography using 
silica gel-G as adsorbent. IR spectra (KBr pellets) were re-
corded on Perkin-Elmer 1800 (FTIR) spectrometer. 1H NMR 
spectra (CDCl3) were taken on a Bruker DRX spectrometer 
(300 MHz FTNMR) using TMS as internal standard and 
chemical shift are expressed in d (ppm). Mass spectra 
were taken on JEOL SX-102/PA-6000 (EI) spectrometer.
1H- benzotriazole (1):
o-pheneylenediamine (0.01 mol) was dissolved in a mix-
ture of glacial acetic acid (0.2 mol) and water (30.0 mL). 
The solution was cooled to 150C and then a solution of 
sodium nitrite (0.11 mol) in water (15.0 mL) was added in 
lot to the stirred solution of o-phenylenediamine. The reac-
tion mixture was irradiated in microwave oven for 20-30 
sec. It attains temperature of 80-85 0C. It was cooled at 
room temperature and chilled in ice water for 30 min. The 
resulting solid was separated, filtered and washed with ice 
water, dried and recrystallized from benzene (m.p.100 0C).
 
1-[(Morpholin-4-yl/ 4-methylpiperazin-1-yl) methyl]-1H-
benzotriazole (2a & 2b): 
Compound (1) (0.001 mol) was dissolved in ethanol and 
acidic alumina (5.0 g) was added to it. The slurry formed 
was kept in an oven at 600C for 1 hour. After cooling, form-
aldehyde (0.003 mol) and morpholine (0.001 mol) were 
added to the reaction mixture. It was exposed to micro-
wave for 9 min. Single spot in TLC indicated completion 
of reaction and product was separated from alumina us-
ing methanol. It was recrystallized from methanol to give 
compound (2a). Compound (2b) was synthesized using 
N- methylpiperazine under similar reaction conditions.
1 H – Isoindol- 1,3- (2H)- dione (3):
The mixture of phthalic anhydride (0.01 mol) and urea (0.01 
mol) was grinded thoroughly in mortar. The mixture was 
transferred to beaker and few drops of DMF were added to 
it. The reaction mixture was irradiated in microwave oven 
for 15 seconds. After cooling of reaction mixture, 50 mL 
Reaction Scheme
AfinidAd LXVii, 550, Noviembre - Diciembre 2010 471
cold water was added to it. A white crystalline solid was 
formed. It was filtered, washed with water, dried and re-
crystallized from ethanol (m.p. 235 0C). 
 2-[(Morpholin-4-yl/4- methylpiperazin-1-yl) methyl]-1 
H- isoindol-1,3 (2H) - dione (4a & 4b):
Compound (3) (0.001 mol) was dissolved in absolute alco-
hol and acidic alumina (5.0 g) was added to it. It was kept 
in oven at 600C. After cooling, formaldehyde (0.003 mol) 
and morpholine (0.001 mol) were added to it. The reac-
tion mixture was exposed under microwave irradiation for 
2 minutes. The target product was separated from acidic 
alumina using mixture of methanol and conc. HCl. It was 
recrystallized from methanol to give compound (4a). Com-
pound (4b) was synthesized by similar method using N- 
methylpiperazine in place of morpholine.
3,4-Dihydroquinoxalin-2- (1H)- one (5):
Chloroacetic acid (0.001 mol) neutralized with 1N NaOH 
solution was added to o-phenylenediamine (0.001 mol) so-
lution and the reaction mixture was irradiated for 2.30 min. 
in microwave oven. The reaction mixture was cooled for 
4-5 hrs at room temp., brown colored solid was separated 
which was recrystallized from ethanol (m. p. 75 0C)
 
4-[Morpholin-4-yl/4-methylpiperazin-1-yl)methyl]-3,4-
dihydroquinoxalin-2- (1H)- one (6a & 6b):
 Compound (5) (0.001 mole) was dissolved in ethanol and 
acidic alumina (5.0 g) was added to it. It was kept in oven 
for 1 hour. Then, formaldehyde (0.003 mol) and morpholine 
(0.001 mol) were added to it and exposed to microwave 
irradiation for 4 minutes. When single spot appeared on 
TLC plate, the product was separated from alumina us-
ing boiling water. It was recrystallized from hot water to 
give compound (6a). Compound (6b) was synthesized by 
similar method using N- methylpiperazine in place of mor-
pholine.
5- Methyl-2, 4-dihydro-3H-pyrazol-5-one (7):
A mixture of ethyl acetoacetate (0.04 mol) and hydrazine 
hydrate (0.04 mol) was irradiated in microwave oven for 2 
seconds. The reaction mixture was cooled and ether (10 
mL) was added to it. The mixture was stirred to give a solid 
product, which was filtered, washed with ether and crys-
tallized from ethanol (m.p. 216 ˚C).
5-Methyl-2-(morphoin-4-yl/4-methylpiperazin-1-yl) 
methyl-2, 4- dihydro-3H-pyrazole-3-one (8a & 8b):
Compound (7) (0.01 mol) was dissolved in ethanol and 
acidic alumina (5.0 g) was added to it. The slurry was kept 
in oven at 60˚ C for 1 hour and cooled. Then, formaldehyde 
(0.03 mol) and morpholine (0.01 mol) were added to it and 
the reaction mixture was exposed to microwaves. Com-
pletion of the reaction was observed by TLC technique, 
the product formed was separated using mixture of meth-
anol and conc. HCl to give compound (8a). Compound 
(8b) was synthesized similarly using N-methylpiperazine in 
place of morpholine.
BIOLOGICAL SCREENING
All synthesized Mannich bases were screened in vitro for 
their antimicrobial activities against two strains of bacteria 
(Bacillus cereus and Escherichia coli) and two strains of 
fungi (Candida albicans and Aspergillus fumigatus) by the 
Cup or Well21 using DMF as a solvent at various dilutions 
of synthesized compounds. Commercial antibacterial drug 
Ciprofloxacin and antifungal drug Amphotericin - B were 
also screened under similar conditions for comparison. 
The diameter of inhibition zones (mm) were measured and 
recorded. The results have been tabulated in the form of 
minimum inhibitions concentration of drug in Table (3).  
From the data reported in Table (3) it could be concluded 
that the synthesized compounds exhibit excellent activ-
ity against both bacterial strains. Evaluation of MIC val-
ues lead us to conclude that among synthesized Mannich 
bases 2a, 4b, 6b, and 8a exhibit excellent activity against 
both B. cereus and E. Coli, while others exhibit moderate 
to good activity. Among the all synthesized Mannich bases 
2a, 4a, 4b, 6b and 8a exhibits good activity against both 
C. albicans and  A.  fumigatus, while others exhibit moder-
ate to good activity.
Table 3: MIC (u g / m L) of synthesized compounds
Compound
Antibacterial activity Antifungal activity 
B. cereus E. coli C. albicans A. fumigatus
2a 0.08 0.017 0.53 1.29
2b 0.10 0.019 0.96 1.09
4a 0.18 0.026 0.69 1.28
4b 0.06 0.015 0.60 1.09
6a 0.08 0.037 1.36 1.28
6b 0.05 0.021 0.58 1.48
8a 0.07 0.012 0.57 1.44
8b 0.08 0.060 0.67 1.67
Ciprofloxacin 0.06 0.010
Amphotericin-B - - 0.50 1.00
ACKNOWLEDGEMENTS
The authors are thankful to Prof. S. C. Ameta for critical 
valuable suggestions and Head, Department of Chemistry, 
Mohanlal Sukhadia University, Udaipur (Raj.) for providing 
laboratory facilities. Authors also pay their thanks to the 
Director, RSIC, CDRI, Lucknow for analytical and spectral 
studies. 
AfinidAd LXVii, 550, Noviembre - Diciembre 2010472
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MW assisted synthesis of some heterocyclic compounds and their Mannich bases under solvent free conditions and their biological assay

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