Nano-γ-Al2O3/SbCl5: an efficient catalyst for the synthesis of 2,3-dihydroperimidines.

Nano-γ-Al2O3/SbCl5 as a new Lewis acid nano catalyst was synthesized and characterized by FTIR, XRD, FESEM, TEM, EDS, BET and TGA techniques. Nano-γ-Al2O3/SbCl5 has been employed for synthesis of 2-substituted perimidines via reaction of naphthalene-1,8-diamine with various aldehydes at room temperature under solvent-free conditions. This protocol proffers several benefits including high yields, easy workup, short reaction times and simple reaction conditions. This journal is © The Royal Society of Chemistry.

Introduction

Perimidines exhibit a diverse range of biological activities; such as antibacterial, antifungal, anti-inflammatory and antitumor.[1-6] It was of interest to explore the suitability of some perimidines derivatives as potential DNA-intercalating ligands.[7] A synthetic method for the preparation of perimidines is the condensation reaction of 1,8-diaminonaphthalene with various carbonyl groups.[8-10] However, most of these methods suffers of significant side reaction, low yield and have cumbersome work-up procedures.

Some catalysts are reported for perimidine synthesis such as zeolite,[11] CMK-5-SO3H,[12] BiCl3,[13] BF3·H2O,[14] Yb(OTf)3,[15] Cu(NO3)2·6H2O,[16] FePO4,[17] Fe3O4/SiO2/(CH2)3N+Me3Br3−,[18] [BTBA]Cl–FeCl3,[19] nano-silica sulfuric acid,[20] amberlyst 15 (ref. 21) and molecular iodine.[22]

Antimony pentachloride (SbCl5), a thin and fuming liquid, is applied in industry and organic synthesis. Where of, antimony pentachloride is a liquid with a great specific gravity that fumigates in air and reacts with the humidity to form HCl, the tactility and the usability of SbCl5 as a liquid form is arduous and the supported form is really preferable. It has been acclaimed that the supported SbCl5 is a solid superacid. SbCl5 is used immensely in organic synthesis as a Lewis acid for elevating a variety of organic reactions.[23] Solid-acid catalysts are commonly classified by their Brønsted and/or Lewis acidity, the intensity and number of these positions, and the morphology of the support. The synthesis of net Brønsted and net Lewis acid catalysts attracts a major degree of academic concern.[24] Alumina (Al2O3) is applied both as a catalyst for divers types of reaction and as a support for metals. Al2O3 is very repeatedly applied as a support of industrial divers' types of reaction and as a support for metals. Al2O3 is very repeatedly applied as a support of catalysts for its mechanical intensity also its potent interaction with metals and metal oxides that provides high propagation of the supported compounds. As for the surface properties,  alumina is commonly considered as acidic rather than basic,  but basic positions coexist.[25] Alumina is a main material for usages in ultrafiltration of salts, as an automobile exhaust catalyst, and in petroleum purification. Porous γ-alumina with equal channels, high surface area, and slender pore-size repartition possesses conjunction better physicochemical properties. However, the manufacturing of ordered and thermally constant porous alumina is demonstrated due to its susceptibility for hydrolysis and phase transition-induced demolition of ordered pore structure.[26]

Here in, we wish to report a simple method for the synthesis of nano-γ-Al2O3/SbCl5 and its usage in the synthesis of 2,3-dihydroperimidines under solvent-free grinding condition at room temperature.

Experimental

Material and methods

All compounds were purchased from Fluka and Merck chemical company and used without any additional purification. Fourier transform infrared (FT-IR) spectra were run on a Nicolet Magna 550 spectrometer. A Bruker (DRX-400 Avance) NMR was used to record the 1H-NMR and 13C-NMR spectra. XRD pattern using Philips Xpert MP diffractometer (Cu Kα, radiation, k = 0.154056 nm) was achieved. FE-SEM was obtained on a Mira Tescan. Transmission electron microscope (TEM) was recorded on a Philips-CM 120-with LaB6 cathode instrument on an accelerating voltage of 120 kV. The thermal gravimetric analysis (TGA) was done with “STA 504” instrument. Energy-dispersive X-ray spectroscopy (EDS) of SbCl5/nano-γ-Al2O3 was measured by EDS instrument, Phenom pro X. BET surface area analysis of catalyst was done with Micrometrics, Tristar II 3020 analyser.

Preparation of nano-γ-Al2O3

NaOH (600 ml, 1 M), was added drop-wise to a slurry containing Al2(SO4)3·18H2O (66 g). The mixture was stirred at room temperature. The resulted suspension was filtered to obtain the white solid Al(OH)3. Then solid were washed with distilled water until no more sulfate ions were detected in the washings. Following the aging step, NaOH (100 ml, 1 M) was added to a beaker containing Al(OH)3 (20 g) to produce NaAl(OH)4. Then PEG 4000 (0.3%) was added to solution and it was neutralized with HCl (0.1 M), to pH 8 until Al(OH)3 produced again.

The obtained precipitate filtered and washed with distilled water. The as-dried solid was calcined in the furnace at 800 °C for 3 hours through atmospheric air to produce nano-γ-Al2O3 powder.

Preparation of nano-γ-Al2O3/SbCl5

To a mixture of nano-γ-Al2O3 (1 g) and CH2Cl2 (10 ml), SbCl5 (0.5 ml) was added drop wise in the well ventilated hood. The resulting suspension was stirred for 1 hour at room temperature, filtered, washed with CH2Cl2, and dried at room temperature.

General procedure for the preparation of 2,3-dihydroperimidines

Naphthalene-1,8-diamine (1 mmol), aromatic aldehydes (1 mmol) and nano-γ-Al2O3/SbCl5 (0.1 g) were grounded in a mortar with a pestle for a few minutes to obtain a homogeneous mixture. After completed conversion as indicated by TLC, 10 ml of ethanol was added then the heterogeneous catalyst was filtered. By adding crushed ice to filtrate, the pure products were obtained as white solids.

Results and discussion

In continuation of our investigation on the utilization of solid acids in organic synthesis, we have synthesized nano-γ-Al2O3/SbCl5 as a new nano catalyst and studied its efficiency in the synthesis of 2,3-dihydroperimidines at room temperature under grinding conditions.

For exploration of the structure of nano-γ-Al2O3/SbCl5, we have studied FT-IR spectra of nano-γ-Al2O3 and nano-γ-Al2O3/SbCl5 (Fig. 1). In nano-γ-Al2O3 FT-IR spectrum, the band in the region of 500–1000 cm−1 is attributed to the stretching vibrations of the (Al–O) bond in γ-Al2O3 (Fig. 1). In nano-γ-Al2O3/SbCl5 spectrum, in addition to γ-Al2O3 signal, two additional band at 701 show binding of SbCl5 to γ-Al2O3.

Fig. 1

FT-IR spectra of (a) nano-γ-Al2O3 and (b) nano-γ-Al2O3/SbCl5.

The FESEM and TEM images of the nano-γ-Al2O3/SbCl5 are demonstrated in Fig. 2. They exhibit disordered spherical shape for nano particles below 50 nm.

Fig. 2

TEM (a) and FESEM (b) images of nano-γ-Al2O3/SbCl5.

The X-ray diffraction (XRD) pattern of nano-γ-Al2O3/SbCl5 is exhibited in (Fig. 3). The signals at 2θ equal to 37 (c), 45 (d) and 67 (e) are displayed nano-γ-Al2O3 structure. According to XRD pattern, the two additional signals at 2θ equal to 28 (a) and 32 (b) respectively, are shown the presentment of bonded Sb to nano-γ-Al2O3 (Fig. 3).

Fig. 3

XRD patterns of nano-γ-Al2O3/SbCl5.

The energy-dispersive X-ray spectroscopy (EDS) of the synthesized catalyst is displayed in Fig. 4. EDX pattern obviously approbates the presence of the anticipated elements in the construction of this catalyst and corroborated supporting of SbCl5 on nano-γ-Al2O3. The elemental compositions of nano-γ-Al2O3/SbCl5 were found to be 58.7, 30.8 and 8.1% for O, Al and Sb, respectively.

Fig. 4

EDS analysis diagram of SbCl5/nano-γ-Al2O3.

Thermal gravimetric analysis (TG-DTA) template of SbCl5/nano-γ-Al2O3 was discovered by heating from 20 °C to 780 °C and then cooling until 165 °C (Fig. 5). The catalyst is stable until 390 °C and only 10.5% of its weight was reduce due to the removal of catalyst humidity. The char yield of the catalyst in 390 °C is 89.5%. According to the TG-DTA pattern of nano-γ-Al2O3/SbCl5 and our discussion, it was disclosed that this catalyst is appropriate for the advancement of organic reactions until 400 °C.

Fig. 5

Thermal gravimetric analysis (TG-DTA) pattern of nano-γ-Al2O3/SbCl5.

The BET N2 adsorption method is applied to measure the surface area. The BET surface areas is assigned as 92.503 m2 g−1. The N2 adsorption isotherm of catalyst is described in Fig. 6. Inductive coupled plasma (ICP) analysis have determined the existence 200 mg of Sb in 1 g of catalyst.

Fig. 6

Nitrogen adsorption isotherm at 77 K of nano-γ-Al2O3/SbCl5.

After characterization of catalyst, we have investigated catalytic activity of nano-γ-Al2O3/SbCl5 for the synthesis of 2,3-dihydroperimidines derivatives. For optimization of the reaction reservations, 1,8-diaminonaphthalene (1 mmol), and 4-chlorobenzaldehyde (1 mmol) were used as model reactants under solvent-free conditions (Table 1). The best resultant based on yield and time of the reaction was afforded with 0.16 g of nano-γ-Al2O3/SbCl5. At first, in order to show the unrivalled catalytic behaviour of nano-γ-Al2O3/SbCl5 and to contrast its activity with other catalysts. Also, Table 1, shows the performance of our nano-catalyst in the preparation of 2,3-dihydroperimidines contrast to that of other reported methods.

Condensation of 4-chlorobenzaldehyde and 1,8-diaminonaphthalene under various conditionsa

Entry	Catalyst	Solvent	Temp (°C)	Time (min)	Yield%
1	Zeolite	Ethanol	r. t.	2700	40 (ref. 11)
2	Fe3O4/SiO2/(CH2)3N+Me3Br3−	—	80	15	95 (ref. 18)
3	FePO4	Ethanol	r. t.	420	90 (ref. 17)
4	Nano-γ-Al2O3/SbCl5 (0.005 g)	—	r. t.	60	20
5	Nano-γ-Al2O3/SbCl5 (0.008 g)	—	r. t.	60	30
6	Nano-γ-Al2O3/SbCl5 (0.01 g)	—	r. t.	60	35
7	Nano-γ-Al2O3/SbCl5 (0.08 g)	—	r. t.	30	50
8	Nano-γ-Al2O3/SbCl5 (0.1 g)	—	r. t.	15	70
9	Nano-γ-Al2O3/SbCl5 (0.14 g)	—	r. t.	15	80
10	Nano-γ-Al 2 O 3 /SbCl 5 (0.16 g)	—	r. t.	15	95
11	Nano-γ-Al2O3/SbCl5 (0.20 g)	—	r. t.	15	95
12	Nano-γ-Al2O3/SbCl5 (0.25 g)	—	r. t.	15	95

1,8-Diaminonaphthalene (1 mmol), and 4-chlorobenzaldehyde (1 mmol) were used.

Using the optimized reaction provisions, the reactions of various substituted benzaldehydes with naphthalene-1,8-diamine were studied (Scheme 1, Table 2).

Scheme 1

Synthesis of 2,3-dihydroperimidines.

Synthesis of 2-substituted perimidines catalyst by nano-γ-Al2O3/SbCl5a

Entry	R	Product	Time (min)	Yieldb (%)
1	4-Cl	3a	14	95
2	2-NO2	3b	15	90
3	3-NO2	3c	13	95
4	4-NO2	3d	15	93
5	4-COOH	3e	20	80
6	4-NMe2	3f	20	90
7	4-OMe	3g	15	85
8	2,4-OMe2	3h	16	80
9	2,3-Cl2	3i	14	85
10	2,3-OMe2	3j	15	80
11	3,4-OMe2	3k	13	85

1,8-Diaminonaphthalene (1 mmol), aldehyde (1 mmol) and nano-γ-Al2O3/SbCl5 (0.16 g) were used.

Isolated yield.

As displayed in Table 2, a number of aromatic aldehydes bearing electron withdrawing groups and electron-donating groups were further subjected to reaction employing a catalytic amount of nano-γ-Al2O3/SbCl5. In general, with electron-drawing substituents in the aromatic benzaldehydes, increased yields of products were generated, whereas the affect is reversed with electron donating substituents. However, the variations in the yields were little.

A plausible pathway for the preparation of 2,3-dihydroperimidines in the presence of nano-γ-Al2O3/SbCl5 is revealed in Scheme 2. Nucleophilic attack of 1,8-diamino naphthalene 2 to SbCl5-activated aldehyde 1 generated intermediate 3. In situ dehydration of compound 4 and nucleophilic attack of the second amino group to SbCl5-activated imine intermediate 5 afforded intermediate 6 to produce the compound 7.

Scheme 2

Proposed mechanism of the SbCl5/nano-γ-Al2O3-catalysed synthesis of 2,3-dihydroperimidines.

Conclusions

In conclusion, nano-γ-Al2O3/SbCl5 was successfully synthesized, characterized and applied for the synthesis of 2,3-dihydroperimidine derivatives. Short reaction times, high conversions, clean reaction profiles, simple work-up, availability and high activity of catalyst, make this method suitable for many acid catalysed organic reactions.

Conflicts of interest

There are no conflicts to declare.