80
N. TAVAKOLI-HOSEINI AND A. DAVOODNIA
by organic cations. Additional peaks are probably due to the
triethylammonium cation portion.
Further proof for the formation of the catalyst
[Et3NH]3PW12O40 came from the comparison of the 1H NMR
spectrum of [Et3NH]3PW12O40 with Et3N in d6-DMSO as sol-
vent. While the signals of ethyl group in Et3N appear at δ 0.93
(J = 7.1 Hz, 3H, CH3) and 2.42 (J = 7.1 Hz, 2H, CH2) ppm
1
as triplet and quartet, respectively, the H NMR spectrum of
[Et3NH]3PW12O40 showed a triplet at δ 1.20 (3H, J = 7.2 Hz,
CH3) and a quartet at δ 3.12 (2H, J = 7.2 Hz, CH2) ppm for
ethyl protons as well as a 1H broad band at δ 8.90 ppm for NH
proton, indicating the formation of triethylammonium cation.
The structure of the studied catalyst was finally proven by 13C
NMR spectrum. In d6-DMSO as solvent, 13C NMR spectrum
of [Et3NH]3PW12O40 showed 2 signals of ethyl group at δ 9.55
and 46.74 ppm, while these signals in Et3N appear at δ 12.61
and 46.61 ppm.
FIG. 2. Reusability of the catalyst for the synthesis of compound 3a (color
figure available onlne).
in experimental section and reused for a similar reaction. As
shown in Figure 2, the catalyst could be used at least three times
without appreciable reduction in the catalytic activity.
Evaluation of Catalytic Activity of [Et3NH]3PW12O40 in
the Synthesis of 4(3H)-Quinazolinones
CONCLUSION
To study the catalytic activity of [Et3NH]3PW12O40 in the
synthesis of 4(3H)-quinazolinones, the synthesis of compound
3a was chosen as reaction model. The reaction was carried
out by heating a mixture of 2-aminobenzamide 1 (3 mmol)
and benzoyl chloride 2a (3 mmol) under various amount of
the catalyst and at different temperatures under solvent-free
conditions (Table 1). Only a little amount of the product was
obtained in the absence of the catalyst (entry 1) indicating that
the catalyst is necessary for the reaction. The efficiency of the
reaction is also affected by the reaction temperature (Table 1).
The yield of the product 3a was poor when the reaction was
carried out at room temperature (entry 2). When the amount of
the catalyst or reaction temperature was increased, a ramp in the
yield of the product 3a was observed. The optimal amount of the
catalyst and temperature were 0.30 g and 100◦C, respectively
(entry 8); increasing the amount of the catalyst and temperature
beyond these values did not increase the yield noticeably.
Also, the reaction was carried out in various solvents (Ta-
ble 2). As shown in this table, in comparison to conventional
methods the yield of the reaction under solvent-free conditions
is higher and the reaction time is shorter.
To show the generality of this model reaction, we ex-
tended the reaction of 2-aminobenzamide with a range of other
aroyl chlorides under the optimized reaction conditions. In all
cases the expected products were obtained in high yields in
short reaction times. The results are summarized in Table 3.
As shown, aroyl chlorides with substituents carrying either
electron-donating or electron-withdrawing groups reacted suc-
cessfully and gave the products in high yields.
Reusability of [Et3NH]3PW12O40 was also investigated. For
this purpose, the same model reaction was again studied under
optimized conditions. After the completion of the reaction, the
catalyst was recovered according to the procedure mentioned
In summary, a new Brønsted acidic ionic salt based on Keg-
gin phosphotungstate anion, [Et3NH]3PW12O40, has been syn-
thesized using the reaction of H3PW12O40 and triethylamine,
and characterized by FT-IR, H NMR, 13C NMR spectral, and
1
microanalytical data. The catalyst showed high catalytic activity
in the synthesis of 4(3H)-quinazolinones by cyclocondensation
of 2-aminobenzamide with aroyl chlorides under solvent-free
conditions. High yields, short reaction times, recyclability and
reusability of the catalyst, easy work-up, and absence of any
volatile and hazardous organic solvents are just a few of the
advantages of this procedure.
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