Solvent free one pot synthesis of amidoalkyl naphthols over phosphotungstic acid encapsulated montmorillonite clay catalysts

Accepted Manuscript Solvent free one pot synthesis of amidoalkyl naphthols over phosphotungstic acid encapsulated montmorillonite clay catalysts Divya P. Narayanan, Resmi M. Ramakrishnan, Sankaran Sugunan, Binitha N. Narayanan PII: DOI: Reference:

S1319-6103(15)00135-0 http://dx.doi.org/10.1016/j.jscs.2015.10.007 JSCS 775

To appear in:

Journal of Saudi Chemical Society

Received Date: Accepted Date:

7 September 2015 31 October 2015

Please cite this article as: D.P. Narayanan, R.M. Ramakrishnan, S. Sugunan, B.N. Narayanan, Solvent free one pot synthesis of amidoalkyl naphthols over phosphotungstic acid encapsulated montmorillonite clay catalysts, Journal of Saudi Chemical Society (2015), doi: http://dx.doi.org/10.1016/j.jscs.2015.10.007

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SOLVENT FREE ONE POT SYNTHESIS OF AMIDOALKYL NAPHTHOLS OVER PHOSPHOTUNGSTIC ACID ENCAPSULATED MONTMORILLONITE CLAY CATALYSTS Divya P Narayanana, Resmi M Ramakrishnana, Sankaran Sugunanb, Binitha N Narayanana,* a

Department of Chemistry, Sree Neelakanta Government Sanskrit College (Affiliated to University of Calicut), Pattambi, Palakkad-679306, Kerala, India b

Department of Applied Chemistry, Cochin University of Science and Technology, Cochin 22, Kerala, India Email: Binitha N Narayanan- [email protected] *

Corresponding Author Ph: +91 466-2212223. Fax: +91 466-2212223,

Abstract: Montmorillonite KSF (Mont.KSF) clay was effectively modified by the encapsulation of phosphotungstic acid (PTA) into the clay layers via sonication followed by incipient wet impregnation method. The catalytic activities of the prepared systems were investigated in the solvent free synthesis of amidoalkyl naphthols by the multicomponent one-pot condensation of an aldehyde, β- naphthol and an amide or urea. The prepared catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) techniques. Excellent yield, shorter reaction time, easy work-up, and reusability of the catalyst are the main attractions of this green procedure. Keywords: Encapsulation; Heterogeneous catalysis; Amidoalkyl naphthol; Multicomponent reactions; Solvent free synthesis

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1. Introduction Green chemical transformation is highly preferred since it avoids the formation of environmental pollutants as well as maintains ecological balance. Many organic reactions catalyzed by Brønsted acids and Lewis acids can be effectively done over clay catalysts .Use of clays as an ecofriendly heterogeneous catalyst in synthetic organic reactions eliminates harmful effects of commonly used homogeneous acid catalysts. Specific features such as ease of handling, commercial availability, high versatility, non-corrosiveness, low cost and regeneration made clays as an environmentally benign catalyst [1-3]. Catalytic performance of clay can be improved by suitable modifications such as doping, pillaring, cation exchange etc.. Incorporation of heteropoly acids (HPAs) in to the caly layers enhances acidity of clays . Uses of heteropoly acids (HPAs) as catalysts for organic reactions have several advantages which make them economically and environmentally attractive. [4]. The Brønsted acidity of (HPAs) approaches the super acid region and it can be varied over a wide range by changing the chemical composition. HPA’s ionic structure comprises of the heteropoly anions and counter cations including H+, H3O+, H5O2 +, etc which are mobile in nature. The heteropoly anions thus can stabilize cationic organic intermediates [5] thereby promoting the reaction. Also the immobilization of HPAs over organic and inorganic supports, such as carbons [6], SiO2 [7, 8] etc. is desirable for improving the catalytic performance and for imparting reusable nature to the catalyst. HPAs were widely used as effective catalysts for multicomponent recations (MCRs) [4,8]. Phosphotungstic acid (PTA), both in bulk form and loaded on silica has been used for the synthesis of 1, 3 dihydropyrimidinones by Amini et al [9]. Keggin HPAs such as H3[PW12O40], H4[SiW12O40], H3[PMo12O40], H4[PMo 11VO40] and HNa2[PMo12O40] were used as solid acid catalysts for the synthesis of 1, 2, 4, 5-tetrasubstituted imidazoles [10]. MCRs

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involve the synthesis of complex molecules in a single one-pot reaction without the isolation of intermediates. This green organic synthesis reduces time and save energy as well as raw materials required for the reaction [11-18]. The development and discovery of more feasible methods for MCRs is of current importance. The one pot multicomponent condensation of aryl aldehydes, β -naphthol, and amides in the presence of various Lewis or Brønsted acid catalysts, resulted in the formation of amidoalkyl naphthols (AANs). These 1, 3-amino oxygenated functional groups containing compounds are present in variety of biologically important natural products, nucleoside antibiotics, HIV protease inhibitors etc. [19-21]. 1-amidoalkyl-2-naphthols can be converted to useful and important biological building blocks and to 1-aminomethyl-2-naphthols, which exhibit depressor effects and bradycardia [22], by an amide hydrolysis reaction. Montmorillonite K10 clay [23], K5CoW12O40.3H2O [24], iodine [25], H4SiW12O40[26], Ce(SO4)2 [27], dodecylphosphonic acid [28], Fe(HSO4)3 [29], HClO4-SiO2[30] etc. are some of the catalysts reported for the synthesis of amidoalkyl naphthols.

However these

procedures involve demerits such as long reaction time, low yield, use of hazardous materials, use of solvents, tedious work-up etc. The demand of environmentally benign, efficient procedure made us to develop a new green synthetic route for the preparation of amidoalkyl naphthols (AAN). In the present study Montmorillonite KSF (Mont.KSF) clay was effectively modified by encapsulation of tungstophosphoric acid (PTA) via sonication followed by incipient wet impregnation method. The catalytic performance of the developed catalyst was examined under solvent free condition. 2. Experimental section Mont. KSF clay and PTA were purchased from Sigma Aldrich Chemicals Pvt. India Ltd. and the rest of the chemicals used for the study were from Nice Chemicals Pvt. Ltd. The 3

products were characterized by comparing their spectral (IR and NMR) and physical data with authentic samples. 2.1. Preparation of PTA encapsulated Mont.KSF clay catalysts In a typical procedure, the 10% PTA/Mont.KSF catalyst was synthesized as follows. 1g of H3PW12O40 was dissolved in 100 ml distilled water and 9 g of Montmorillonite KSF clay was added slowly to the resultant solution with stirring which was continued for overnight. The above mixture was sonicated for 45 minutes then the water was removed by distillation under vacuum followed by drying at 150 °C for 2 h. Same procedure were used for the preparation of 5, 25 and 40 wt% of PTA encapsulated Mont. KSF samples. The prepared systems were designated as n%PTA/Mont. KSF where n% indicates the weight percentage of PTA loading over Mont. KSF clay. 2.2. Synthesis of Amidoalkyl naphthols In a representative procedure for the preparation of Amidoalkyl naphthols, 1mmol of benzaldehyde, 1mmol of β - naphthol and 1.1mmol of amide/urea were added to 0.1g of 10%PTA/Mont. KSF caly catalyst and the reaction mixture was stirred for appropriate time at 120 ºC in an oil bath. After completion of the reaction as indicated by TLC, the resultant solid mass was extracted to hot methanol and the catalyst was separated by filtration. Solvent on evaporation yields crude product and pure crystals were obtained after recrystallization from ethanol-water (1:3) mixture. All products were identified by comparing their spectral and physical data with those for authentic samples. For investigating the reusability of 10%PTA/Mont. KSF catalyst the reaction between benzaldehyde, β - naphthol, and benzamide was selected as the model reaction. The catalyst after each run was washed several times with hot methanol and dried at 120 ºC for 2 h before

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the subsequent reactions. The catalyst was reused up to 4 times. 2.3.Characterization techniques Fourier Transform Infrared (FTIR) spectra of all prepared catalytic systems were recorded using Jasco FT/IR (4100) spectrometer. The X-ray diffraction patterns of catalysts were recorded on Rigaku Miniflex 600 diffractometer. The morphology studies of prepared catalytic systems were done on Scanning Electron microscope (ESEM Quanta 200, FEI). The 1

HNMR spectra of the samples were run on a Bruker (500MHz) spectrometer. The melting

points of the products were recorded on a melting point apparatus in open capillary tubes and are uncorrected 3. Results and discussion Mont.KSF clay was efficiently modified by encapsulating tungstophosphoric acid (PTA) via sonication followed by incipient wet impregnation method. Different catalysts were prepared by varying the amount of PTA over Mont.KSF so as to find out the best percentage loading of PTA over the clay catalyst that resulting maximum yield of Amidoalkyl naphthols. In order to examine the active phase responsible for catalytic activity and to know the effect of PTA loading on Mont. KSF, the prepared catalysts were characterized using Fouriertransform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) techniques. The surface interaction between PTA and support was analyzed using FTIR technique. FTIR spectrum (Figure 1(a)) of PTA shows characteristic vibration bands for the Keggin type HPA at 1081, 985, 894, and 801 cm· 1 [31,32]. Bands at 894 cm−1 and 801 cm−1 were associated with the asymmetric vibrations (W–O–W) of the Keggin polyanion [9, 10, 31,32]. In the clay based systems, the intensity of the Keggin bands at 894 cm−1 and 801 cm−1 were low which increased with increase in PTA loading whereas

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the other two bands were found to be merged up with the broad asymmetric stretching vibration bands of SiO2 tetrahedra of the clay layers [33]. FTIR spectral analyses indicate the retention of basic clay framework even after high percentage loading of PTA. The diffraction corresponding to the (100) plane with interplanar distance 9.8 Å at 2θ value of 8.9º present in XRD patterns (Figure 1(b)) of different catalysts is in agreement with reports [33] . The peak shift towards left in the PTA loaded samples indicates an increase in the basal spacing upon incorporation of PTA. The d spacing (~12 Å) of prepared catalytic systems suggests the encapsulation of heteropoly acid in its keggin structure into the clay layers. The SEM images (Fig. 3) revealed the presence of aggregated stacked layers in parent Mont.KSF where as the heteropoly encapsulated Mont. KSF clays contains small stacks of layers with the retention of the basic clay layer structure. The separation of layer stacks may be a result of the high power sonication during the material preparation. In the present study PTA encapsulated Mont.KSF clay catalysts were effectively used for the preparation of various 1-amidoalkyl-2-naphthols. General representation of the reaction inside the PTA encapsulated clay catalysts is given in Fig. 4. The synthesis of N[Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide

by

the

multicomponent

condensation reaction between benzaldehyde, β-naphthol, and benzamide was conducted under solvent-free conditions over various percentage of PTA encapsulated mont.KSF clay catalysts at125 ºC (Table 1). It can be seen that the catalyst prepared by 10% PTA loading over Mont.KSF resulted in maximum yield of 95%. With further increase in the percentage of PTA, the reaction became faster (but with reduced yield) and the total time required for the reaction decreased. 10%PTA/Mont.KSF was selected for further catalytic reactions since it offered the highest yield. Parent Mont.KSF clay without any PTA loading has given a lowest

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yield of 75%, in a comparatively long duration of 45 minutes. Reactions were also conducted at different temperatures. From the Figure 4 (a), it can be seen that the activity increased with temperature till 120 °C, which remained constant thereafter. The time required for the reaction decreased with temperature up to 120 °C and then remained constant from 120 °C onwards. Thus 120 °C is the best suited lower temperature for the effective reaction. The molar ratio of benzaldehyde: β-naphthol: benzamide was varied and it found that the best suitable ratio of reactants was 1:1:1.1 respectively. The catalyst weight was varied (Figure 4(b)) and it can be seen that the activity first increased and reached maximum and decreased thereafter. The decrease in conversion with a higher amount of catalyst under the similar reaction conditions can be depict as ‘‘catalyst inhibitor conversion’’, which is previously reported in some heterogeneous catalyzed reactions [34, 35]. Time required for the reaction decreased drastically with increase in the catalyst weight and attained the least at a catalyst weight of 0.075 g and remained constant thereafter. After investigating the influence of different reaction parameters in the MCR between benzaldehyde, benzamide and 2-naphthol as model reactants, the reactions were further extended to other derivatives of benzaldehyde and different amides such as benzamide, acetamide or urea. The yield of various AANs obtained and the duration of each reaction is given in Table 2. The reusability of the catalyst was performed in AAN synthesis and it can be seen that the catalyst is effectively reusable till four repeated cycles (Figure 4(c)). There was a slight reduction in the yield, and also the time required for the reaction was found to increase with repeated use. The decrease in activity may be due to the leaching of PTA from the clay 7

support during the sequential washing with methanol after each reaction. The nature of the reused catalyst (10%PTA/Mont.KSF) is investigated using XRD analysis. From Figure 5 it is observed that the parent clay peak at 8.9 ° is shifted to left in the reused catalyst also, which indicates the existence of heteropoly acid between the clay layers even after washing of catalyst subsequent to

each reaction. The catalyst structure remained

unaffected after the catalytic reaction. In the present work, we have got superior results within short interval, compared to the other catalysts reported in the literature. The comparison of results with the literature is given in the Table 3. The spectral data of the products are given below N-[Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide

(C24H19NO2),

Table

2.

Entry 1 : 1H NMR (500 MHz, DMSO) δ= 10.36 (s, 1 H), 9.04-9.02 (d, JH-H = 8 Hz, 1 H), 8.11-8.09 (d, J=8 Hz, 1 H), 7.80-7.88 (m, 4 H), 7.57-7.47 (m, 4 H), 7.35-7.18 (m, 8 H) ppm; IR (KBr, cm-1) λ-1 = 3414, 3058, 3019, 2722, 1628, 1568, 1533, 1433, 1346, 1267, 1074, 1024, 934, 856, 820, 750, 701. N-[4-Nitro Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide (C24H18N2O4), Table 2. Entry 2: 1H NMR (500 MHz, DMSO) δ = 10.41 (s, 1 H), 9.07-9.06 (d, 1 H), 8.17-8.16 (d, 2 H), 8.08-8.06 (d, 1 H), 7.91-7.83 (t, 4 H), 7.57-7.50 (m, 6 H), 7.40-7.33 (m, 2 H), 7.267.24 (d, J=8Hz, 1 H). IR (KBr, cm-1) λ-1 = 3423, 3177, 2930, 2372, 1644, 1528, 1345, 1059, 812, 824, 747. N-[4-Methyl

Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide

(C25H21NO2),

Table 2. Entry 3: 1H NMR (500 MHz, DMSO) δ = 10.32 (s, 1 H), 9.00-8.98 (d, J=8Hz, 1 H), 8.09-8.07 (d, J=8.4Hz, 1 H), 7.86-7.78(m, 4 H), 7.57-7.45 (m, 4 H), 7.33-7.24 (m, 3 H), 8

7.19-7.17 (d, 2 H), 7.09-7.07 (d, 2 H), 2.24 (s, 3 H). IR (KBr, cm-1) λ-1 = 3416, 2920, 2843, 2356, 1630, 1429, 1324, 1019, 818, 717. N-[4-Methoxy

Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide

(C25H21NO3),

Table 2. Entry 4: 1H NMR (500 MHz, DMSO) δ = 10.33 (s, 1 H), 9.03-9.01 (d, J=8.4Hz, 1 H), 8.09-8.07 (d, J=8.8Hz,1 H),7.86-7.83 (m, 3 H), 7.81-7.79 (d, J=8Hz, 1 H), 7.57-7.53 (m, 1 H), 7.50-7.45 (m, 3 H), 7.33-7.30 (t, 1 H), 7.26-7.21 (m, 4 H), 6.85-6.83 (d, 2 H), 3.69(s, 3 H). IR (KBr, cm-1) λ-1 = 3423, 3073, 2942, 2358, 1630, 1513, 1345, 1254, 1163, 1020, 824, 708 N-[2-Nitro Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-benzamide (C24H18N2O4), Table 2. Entry 5: 1H NMR (500 MHz, DMSO) δ = 9.93 (s, 1 H), 9.07-9.09 (d, J=8Hz, 1 H), 7.977.99 (d, J=8Hz, 1 H), 7.87-7.89 (d, 2 H), 7.81-7.84 (t, 2 H), 7.73-7.78 (m, 2 H), 7.60-7.63 (t, 1 H), 7.49-7.54 (m, 3 H), 7.41-7.45 (m, 3 H), 7.28-7.31 (t, 1 H), 7.11-7.13 (d, J=8Hz, 1 H). IR (KBr, cm-1) λ-1 = 3406, 3132, 2919, 1633, 1513, 1430, 1323, 1251, 1049, 823, 704.

N-[Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-cetamide (C19H17NO2), Table 2. Entry 6: 1H NMR (500 MHz, DMSO) δ = 9.98 (s, 1 H), 8.44-8.42 (d, J=8Hz, 1 H), 7.87-7.76 (m, 3 H), 7.38-7.35 (t, 1 H), 7.28-7.22 (m, 4 H), 7.18-7.14 (m, 4 H), 1.99 (s, 3 H). IR (KBr, cm-1) λ-1 = 3398, 3241, 3059, 1644, 1579, 1513, 1345, 1059, 812, 747, 695.

N-[4-NitroPhenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-acetamide (C19H16N2O4), Table 2. Entry 7: 1H NMR (500 MHz, DMSO) δ = 10.15 (s, 1 H), 8.59-8.57 (d, J=8Hz, 1 H), 8.15-8.13 (d, 2 H), 7.84-7.81 (t, 3 H), 7.41-7.39 (d, 3 H), 7.31-7.17 (m, 3 H), 2.02 (s, 3 H). IR (KBr, cm-1) λ-1 = 3423, 3177, 2930, 2372, 1658, 1513, 1436, 1345, 1266, 1066, 824, 747.

N-[4-MethylPhenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-acetamide (C20H19NO2), Table 9

2. Entry 8: 1H NMR (500 MHz, DMSO) δ = 9.98 (s, 1 H), 8.41-8.39 (d, J=8Hz, 1 H), 7.867.85 (brs, 1 H), 7.81-7.75 (m, 2 H), 7.36-7.34 (d, J=7.2Hz , 1 H), 7.28-7.21 (m, 2 H), 7.117.06 (m, 5 H), 2.23 (s, 3 H), 1.98 (s, 3 H). IR (KBr, cm-1) λ-1 = 3398, 3063, 2930, 1621, 1515, 1439, 1334, 1058, 809, 742. N-[4-ChloroPhenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-acetamide

(C20H16NO2Cl),

Table 2. Entry 9: 1H NMR (500 MHz, DMSO) δ = 10.03 (s, 1 H), 8.45 (brs, 1 H), 7.81 (brs, 3 H), 7.39-7.11 (m, 8 H), 1.99 (s, 3 H). IR (KBr, cm-1) λ-1 = 3390, 2918, 2693, 2603, 2349, 1642, 1583, 1513, 1434, 1365, 1247, 1146, 815, 747. N-[4-HydroxyPhenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-acetamide

(C20H19NO3),

Table 2. Entry 10: 1H NMR (500 MHz, DMSO) δ = 9.99 (s, 1 H), 9.24 (s, 1 H), 8.42-8.40 (d, J=8Hz, 1 H), 7.88(s, 1 H), 7.81-7.75 (m, 2 H), 7.37 (s, 1 H), 7.28-7.22 (m, 2 H), 7.05 (s, 1 H), 7.04-6.98 (m, 2 H), 6.65-6.65 (d, 2H ), 1.98 (s, 3 H). IR (KBr, cm-1) λ-1 = 3406, 3204, 1620, 1513, 1441, 1335, 1263, 1156, 1049, 811,739. N-[Phenyl-(2-hydroxy-naphthalen-1-yl)-methyl]-Urea (C18H18N2O2), Table 2. Entry 11: 1

H NMR (500 MHz, DMSO) δ = 9.92 (s, 1 H), 7.88-7.75 (m, 3 H), 7.41 (s, 1 H), 7.3-6.94

(m, 7 H), 6.92 (s, 2 H), 5.81 (s, 2 H). IR (KBr, cm-1) λ-1 = 3410, 3216, 3054, 2920, 2833, 2365, 1639, 1505, 1487, 1439, 1344, 1268, 1009, 809, 685, 579. 4. Conclusions Highly efficient heterogeneous catalysts were developed by encapsulating Phosphotungstic acid (PTA, H3PW12O40.xH2O) over Montmorillonite KSF clay. The catalyst characterization studies revealed the successful encapsulation of PTA into Mont. KSF and its existence in the interlayer spacing of clay layers. Prepared catalysts were effectively used for multicomponent

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1-amidoalkyl-2-naphthol synthesis. The best percentage loading of PTA over Mont. KSF was found to be 10% and the catalyst gave excellent yield in a variety of amidoalkyl naphthols within short duration. The reaction was vastly effective under solvent free conditions which eliminate the use of harmful solvents. The catalyst was found to be reusable even after four repeated cycles.

Acknowledgements The research has been sponsored by the University Grant Commission (UGC), Delhi, India under the Research Award Scheme. Binitha N. Narayanan and Sankaran Sugunan thank University Grants Commission, New Delhi, India, for UGC Research Award and UGC BSR Faculty Fellowship, respectively. Divya P Narayanan thanks Sree Neelakanta Govt. Sanskrit College Pattambi and University of Calicut for providing the facilities for carrying out the research work. References [1] G. Nagendrappa, Organic synthesis using Clay Catalysts, Clays for 'Green Chemistry, Resonance. 2 (2002) 64-77. [2] R.S. Varma, Silica-Supported Perchloric Acid (HClO4-SiO2): An Efficient Catalyst for the Preparation of β-Amido Carbonyl Compounds Using Multicomponent Reactions, Green Chem. 1 (1999) 43-55. [3] R.S. Varma, Clay and clay-supported reagents in organic synthesis, Tetrahedron. 58 (2002) 1235-1255. [4] M. Misono, Heterogeneous Catalysis by Heteropoly Compounds of Molybdenum and 11

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15

Figure captions Figure 1 (a) FTIR patterns of Mont.KSF, n% PTA/Mont.KSF and PTA, (b) XRD of n% PTA/Mont.KSF and Mont.KSF Figure 2 SEM images of Mont.KSF and PTA encapsulated Mont.KSF catalytic systems Figure 3 Pictorial representation for the synthesis of amidoalkyl naphthols over 10% PTA/ Mont.KSF clay catalysts Figure 4 (a) Effect of temperature on the reaction, (b) Effect of catalyst weight, (c) Reusability data of reaction over 10%PTA/Mont.KSF Figure 5 XRD of fresh 10%PTA/Mont.KSF and reused 10%PTA/Mont.KSF

16

Table 1 n%PTA/Mont.KSF catalyzed synthesis of N-[Phenyl-(2-hydroxy-naphthalen-1-yl)methyl]-benzamidea Catalyst

Time (min)

Yield (%)b

5%PTA/Mont.KSF

15

85

10%PTA/Mont.KSF

6

95

25%PTA/Mont.KSF

5

93

40%PTA/Mont.KSF

4

94

45

75

Mont.KSF

a

Reaction conditions: benzaldehyde:βnaphthol: benzamide – 1 mmol : 1 mmol : 1.1 mmol, over 0.1 g n%PTA/Mont.KSF at 125 °C, b Isolated Yield

17

Table 2 Synthesis of amidoalkyl naphthols catalysed by 10%PTA/Mont.KSFa

R

R1

Time

Yield (%)b

M.p. (°C)

(min)

a

H

Ph

6

96

234-235

4-NO2

Ph

5

98

238-240

4-Me

Ph

8

90

200-202

4-OMe

Ph

20

90

206-208

2-NO2

Ph

5

96

180-182

H

Me

8

91

240-242

4-NO2

Me

5

93

247-249

4-Me

Me

15

92

220-222

4-Cl

Me

10

93

225-228

4-OH

Me

15

90

207-209

H

NH2

10

89

169-170

Reaction conditions: aldehyde (1 mmol), β-naphthol (1mmol), amide/urea (1.1 mmol), 10%PTA/Mont.KSF (0.075 g) at 120 °C, b Isolated yield

18

Table 3 Comparison of 10%PTA/Mont.KSF with reported catalysts in the synthesis of 1amidoalkyl-2-naphthols Catalyst

Time

Yield (%)

Ref

Montmorillonite K10

Benzaldehyde:2-naphthol: benzamide(catalystmol%), reaction conditions 1:1:1.1(0.1g), 125 °C

1.5 h

78

23

K5CoW12O40.3H2O

1:1:1.3(1 mol%),125 °C

2h

80

24

Iodine

1:1:1.3( 5 mol% ),125 °C

5.5 h

85

25

H4SiW12O40

1:1;1.2 ( 5 mol%),110 °C

20 min 88

26

Ce(SO4)2

1:1:1(1mmol), CH3CN,Reflux

36 h

72

27

Dodecylphosphonic acid 1:1:1.2( 10mmol ), 90 °C

20 min 90

28

10% PTA/Mont.KSF *

6 min

-

1:1:1.1 (0.075g), 120 °C

*Catalyst from present work

19

96

Figure 1

20

Figure 2.

21

Figure 3.

22

Figure 4

23

Intensity (a.u)

Reused 10%PTA/Mont.KSF

10%PTA/Mont.KSF

0

10

20

30

40

50

2 Theta (degrees)

Figure 5.

24

60

70

80

90