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Hydroarylation of arenes with styrenes usingMontmorillonite K-10 as an efficient, selective, andrecyclable catalystSatish R. Lanke a , Ziyauddin S. Qureshi a , Aniruddha B. Patil a , Dinkar S. Patil b &Bhalchandra M. Bhanage aa Department of Chemistry , Institute of Chemical Technology , N. Parekh Marg, Matunga,Mumbai , 400 019 , Indiab Laser and Plasma Technology Division , Bhabha Atomic Research Centre , Mumbai , 400085 , IndiaPublished online: 18 Jun 2012.

To cite this article: Satish R. Lanke , Ziyauddin S. Qureshi , Aniruddha B. Patil , Dinkar S. Patil & Bhalchandra M. Bhanage(2012) Hydroarylation of arenes with styrenes using Montmorillonite K-10 as an efficient, selective, and recyclable catalyst,Green Chemistry Letters and Reviews, 5:4, 621-632, DOI: 10.1080/17518253.2012.688880

To link to this article: http://dx.doi.org/10.1080/17518253.2012.688880

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RESEARCH LETTER

Hydroarylation of arenes with styrenes using Montmorillonite K-10 as an efficient, selective, and

recyclable catalyst

Satish R. Lankea, Ziyauddin S. Qureshia, Aniruddha B. Patila, Dinkar S. Patilb and Bhalchandra M. Bhanagea*

aDepartment of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai, 400 019, India; bLaser andPlasma Technology Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India

(Received 16 September 2011; final version received 18 April 2012)

Hydroarylation of styrene and its derivatives with arenes and heteroarenes was studied using Montmorillonite

K-10 as an efficient, environmentally benign, economical, greener, and recyclable catalyst. The reaction gives1,1-diarylalkanes with a very high selectivity and excellent yields in short time with greater substrate compatibility.

Keywords: Alkene; heterogeneous catalysis; hydroarylation; Markovnikov adduct; styrene

1. Introduction

Catalytic functionalization of arenes and heteroar-

enes has gained considerable interest in recent years

due to its applications in the pharmaceutical, (1)

agrochemical, (2) fine, and bulk chemical industry (3).

It is one of the important methodologies for C�Cbond formation in organic synthesis (4�6). Tradi-

tionally, acylation, alkylation, nitration, and halo-

genations of arenes were carried out by Friedel�Crafts reactions (7�9) for such transformations.

However, these methods have several limitations

like the use of stoichiometric amount of Lewis acids,

drastic reaction conditions (i.e. high temperature,

longer reaction time etc.), lower selectivity, over

alkylation products and large amount of salt forma-

tion. Formation of new C�C bond in the aromatic

ring requires multiple steps like protection, deprotec-

tion or incorporation of activating groups. Therefore,

there is a need to develop an efficient, environmen-

tally benign, and recyclable catalytic protocol for

hydroarylation of arenes. Recently, several organo-

metallic catalysts were found to be useful as an

efficient tool for the environmentally benign C�Hfunctionalization like Freidel�Crafts hydroarylation

of the arenes with electron rich aromatic and hetero-

aromatic compounds (10). The products of these

reactions contain diarylalkanes which has great im-

portance as they are a part of various valuable

biological active compounds and pharmaceutics

such as papaverine, beclobrate, pheneprocoumene,

dimetindene, haplopappin, nafenopin, and avrainvil-

leol trimethoprim (Figure 1). Various catalysts like

FeCl3, CoBr2, Ir(III) complex, bimetallic nanoporous

FeAl-KIT-5 catalyst, Bi(OTf)3, BiBr3, BiCl3, I2,

and Sm(OTf)3 are reported for this transformation

(4, 11�19).Usually, hydroarylation of arenes is catalyzed by

homogeneous non-recyclable catalysts. Hence, the

review of literature suggests that there are still

challenges in developing a greener and metal free

protocol for the hydroarylation of arenes. In contrast,

Bronsted solid acids (20, 21) catalyzed methods have

gained important attention over the decades and now

they are widely preferred for various organic trans-

formations. Among the several solid acid catalysts

Montmorillonite K-10 is a one of the inexpensive,

greener, and commercially available catalyst (22�26).Herein, we introduced new application of Mon-

tmorillonite K-10 as a catalyst for the synthesis of

1,1-diarylakane, via the reaction of styrene with

arene. The catalyst was found to be highly efficient,

selective, environmentally benign, scalable, and re-

cyclable (Scheme 1).

2. Results and discussion

2.1. Optimization of the reaction parameters

Initially, the hydroarylation of anisole with styrene

was chosen as a model reaction. Various reaction

parameters such as catalyst screening, catalyst load-

ing, solvent effect, molar ratio of substrate, reaction

time, and temperature were investigated for this

transformation. The results obtained were summar-

ized in (Table 1). Various Bronsted acid and solid

*Corresponding author. Email: bm.bhanage@ictmumbai.edu.in

Green Chemistry Letters and ReviewsVol. 5, No. 4, December 2012, 621�632

ISSN 1751-8253 print/ISSN 1751-7192 online

# 2012 Satish R. Lanke, Ziyauddin S. Qureshi, Aniruddha B. Patil, Dinkar S. Patil and Bhalchandra M. Bhanage

http://dx.doi.org/10.1080/17518253.2012.688880

http://www.tandfonline.com

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acid catalysts such as p-Toluene sulphonic acid

(p-TSA), Cu(OTf)2, Montmorillonite K-10,

½NMPH�þHSO�4 , ZnCl2, ZrOCl2, and tungstopho-

sphoric acid (TPA) were screened (Table 1 entries 1�7), wherein Montmorillonite K-10 was found to be

the best catalyst providing 75% yield of the desired

para-alkylated product (Table 1, entry 3) under the

screening conditions. It was noted that when the

reaction was carried out in the absence of catalyst,

there was no product formation thus emphasizing

that the Montmorillonite K-10 was solely responsible

to catalyze the reaction with higher yield (Table 1,

entry 8). To obtain the optimum amount of catalyst,

the catalyst amount was varied in the range of 60�100

mg (Table 1, entries 9�11). The optimum results were

obtained with 80 mg of Montmorillonite K-10 as a

catalyst; further increase in catalyst amount had

no significant effect on the yield of desired para-

alkylated product (Table 1, entry 11). We observe

that reaction was more favorable under solvent free

condition rather than conventional organic solvents

because arene itself can act as a very good solvent

(Table 1, entries 12�14). The other reaction para-

meters like reaction temperature, substrate ratio for

styrene:arene and reaction time were also studied (see

Table 1, entries 15�27). On the basis of these, the

optimized reaction conditions for hydroarylation of

arenes with styrenes are: styrene:arene (1:10), catalyst

Montmorillonite K-10 (80 mg), solvent (neat), at

808C, for 0.5 h.

2.2. Characterization of catalyst

2.2.1 TGA analysisThe thermogravimetric analysis of the Montmorillo-

nite K-10 was carried out to provide information on

the degradation pattern when decomposed under

nitrogen. The catalyst was found to be stable up to

101.68C with a weight loss of only 8.9% which

might be due to the water content loss. After that it

undergoes very slow decomposition up to 5508C.

Hence, the decomposition temperature of the catalyst

was determined to be more than 5508C. A total weight

loss of 12.5% was observed at 5508C. Thus, Thermo-

gravimetric analysis (TGA) of the Montmorillonite

K-10 catalyst shows that the catalyst is thermally

stable at the reaction temperature (Figure 2).

2.2.2. TPD analysis of Montmorillonite K-10 catalystThe TPD analysis of the catalyst Montmorillonite

K-10 was carried out on model AutoChem II 2920

V3.03 at a flow rate of 40.05 mL STP/min. The acid-

base properties are regarded as being the main factor

that can influence significantly the clay behavior,

NH3-TPD measurements were performed on

Montmorillonite K-10. The total number of acidic

sites expressed in terms of millimoles of ammonia

desorbed per gram of dry Montmorillonite K-10 on

increasing temperature. The range of desorption

temperature is 74�4508C and NH�3 TPD indicates

higher acidity at 748C, that is 9.23 mL/g (Figure 3).

N

O

OO

O

Cl O

O

O

N

N

O

OH

O

O

O

OO

HO

HO

OOH

O

Papaverine Beclobrate

Dimetindene Nafenopin Pheneprocoumene

Haplopappin

Figure 1. Examples of natural products and biologically active compounds.

R"

R' R'

+80 oC, 6 h

R' = Me, -ter-butylR" = Me, H,

Montmorrolinite K-10

R" R

Para Ortho

R

R=H, -OH,Me, OMe

R"

R R'

+

1 2

Scheme 1. Hydroarylation of arene and heteroarenes with styrenes.

622 S.R. Lanke et al.

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2.2.3 Surface area analysis of Montmorillonite K-10catalystSurface area and pore volume of the Montmorillo-

nite K-10 was measured using surface area analyzer

model SMART SORB 93 (N2 adsorption-BET

Dynamic method). The surface area of Montmor-

illonite K-10 was 215 m2/gm. The total pore volume

of Montmorillonite K-10 was (At N2 P/P0�95%)

0.2797 cc/gm. From this total pore volume, we

calculated the average pore diameter of Montmor-

illonite K-10 is 52.522 A8. For regeneration condi-

tions the catalyst was kept in furnace at 1008C for

1 h and then used further for BET surface area

analysis.

Table 1. Optimization of reaction parameters for hydroarylation of anisole with styrene.

R"

R' R'

+80 oC, 6 h

R' = Me, -ter-butylR" = Me, H,

Montmorrolinite K-10

R" R

Para Ortho

R

R=H, -OH,Me, OMe

R"

R R'

+

1 2

Entry Catalyst SolventTemperature

(8C)Time(h)

Conversion(%)a

Yield (1�2)(%)a

Selectivity (1:2)(%)a

Catalyst screening1 p-TSA Neat 80 6 100 65 85:15

2 ½NMPH�þHSO�4 Neat 80 6 0 0 0

3 Mont K-10 Neat 80 6 100 75 80:204 TPA Neat 80 6 90 65 85:15

5 Cu(OTf)2 Neat 80 6 50 40 80:206 ZnCl2 Neat 80 6 n. r. � �7 ZrOCl2 Neat 80 6 n. r. � �8 Neat Neat 80 6 n. r. � �

Effect of catalyst loading

9b Mont K-10 Neat 80 6 80 78 82:1810c Mont K-10 Neat 80 6 100 98 80:2011d Mont K-10 Neat 80 6 100 98 80:20

Solvent study12 Mont K-10 THF 80 6 n. r. � �13 Mont K-10 CH3CN 80 6 n. r. � �14 Mont K-10 Toluene 80 6 100 90 75:25

Effect of temperature15 Mont K-10 Neat 60 6 90 88 80:2016 Mont K-10 Neat 80 6 100 98 80:2017 Mont K-10 Neat 100 6 100 98 80:20

18 Mont K-10 Neat RT 6 n. r. � �

Effect of mole ratio

19e Mont K-10 Neat 80 6 100 75 80:2020f Mont K-10 Neat 80 6 100 98 80:2021g Mont K-10 Neat 80 6 100 58 80:20

22h Mont K-10 Neat 80 6 100 98 82:1823i Mont K-10 Neat 80 6 100 98 86:14

Time study24 Mont K-10 Neat 80 6 100 98 86:1425 Mont K-10 Neat 80 2 100 98 86:14

26 Mont K-10 Neat 80 0.5 100 98 86:1427 Mont K-10 Neat 80 0.16 100 95 86:14

Reaction conditions: styrene (1 mmol), arene (3 mmol), catalyst conc. (10 mol%), n. r. (No reaction), aConversion (with respect to styrene),

selectivity, yield based on GC analysis, bCatalyst (60 mg), cCatalyst (80 mg), dCatalyst (100) mg, eStyrene: arene (1:1), fStyrene: arene (1:3),gStyrene: arene (3:1), hStyrene: arene (1:6), iStyrene: arene (1:10).

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2.3. Substrate compatibility

We explored the scope of the Montmorillonite K-10

catalyzed hydroarylation of various arene with sty-rene and its derivatives under optimized reaction

conditions (Table 2). In general, 1,1-diarylalkaneswere prepared from the reaction of arene with good

yield in short reaction time (0.5�6 h). In all the cases

para-substituted products was obtained as the majorproduct but for the phenol and its derivatives gave

ortho-substituted products as a major product. For

generalization of Montmorillonite K-10 catalyzed

hydroarylation under optimized condition, we

decided to explore protocol for differently substituted

arenes with styrene (Table 2, entries 1�11) which gives

moderate to high yield. We have also studied electron

rich arenes like anisole for hydroarylation which gave

98% yield of para-arylated 1,1 diarylalkane (Table 2,

entry 1), whereas phenol and its derivatives gave

ortho-arylated product with very good yield as well

as selectivity (Table 2, entries 2�7). Less reactive

Figure 2. Thermogravimetric analysis of Montmorillonite K-10 catalyst.

Figure 3. TPD analysis of Montmorillonite K-10 catalyst.

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Table 2. Hydroarylation of styrene and its derivatives with arenas.

R"

R' R'

+80 oC, 6 h

R' = Me, -ter-butylR" = Me, H,

Montmorrolinite K-10

R" R

Para Ortho

R

R=H, -OH,Me, OMe

R"

R R'

+

1 2

No Arenes Product Time (h) Conversion (%)a Yield (%)a Selectivity (%)a

Reaction of styrene with different arenas

1 O

O

0.5 100 98 86:14

2 OH

OH

6 97 80 70:30

3

OH OH

6 100 98 100

4OH

O

OH

O 6 99 95 69:31

5OH

OH

6 95 95 79:21

6

OH

Cl OH

Cl

6 98 35 100

7OH

Cl OHCl 6 90 30 100

8 6 100 40 70:30

9 6 92 70 99:1

10 6 100 95 90:10

11 6 95 85 100

Reaction of a-methyl styrene with different arenes

12 OO

6 100 95 87:13

13 OH

OH

6 100 92 b65: 5:30

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substrates like toluene, ortho-, meta-, and para-xylenes were also reacted very smoothly and cleanlygiving moderate to high yield of the desired productsusing Montmorillonite K-10 catalyst (Table 2, entries8�11). a-Methyl styrene under acidic condition re-acted with activated arene and gives the selectivelypara-arylated product in 90�95% yield (Table 2,entry 12�16). The reaction of sterically hindered4-tert-butyl styrene with anisole provided a mixtureof para- and ortho-alkylated anisole in 90% and 10%,respectively (Table 2, entry 17). Moreover, it wasobserved that the sterically hindered 4-tert-butylstyrene smoothly undergoes arylation with differentarene derivatives providing 80�100% yield of ex-pected products. The proposed method of hydroar-ylation of styrene was proved to be efficient,

affording good yields of 1,1-diarylalkane with arenes.Synthesized 1,1-diarylalkanes were characterized by1H NMR, 13C NMR, IR, and mass spectroscopy (seeSupporting information).

2.4. Recyclability of the catalyst

Montmorillonite K-10 based protocol is consideredto be greener, as the catalyst can be separated easilyfrom the reaction mixture by simple filtration andrecycled further. Hence, recycling experiments wereconducted. It was observed that the catalyst can berecycled for four consecutive cycles with same activityand selectivity. No significant decrease in yield duringthe four recycles was observed. The yield declined upto 88% for the fifth cycle (Table 3).

Table 2 (Continued )

No Arenes Product Time (h) Conversion (%)a Yield (%)a Selectivity (%)a

14

OH OH

6 100 90 100

15 6 100 94 90:10

16 6 100 90 100

Reaction of 4-ter-butyl styrene with different arene

17 OO

6 100 95 90:10

18

OH OH

6 100 95 100

19 OH

OH

6 100 80 100

20

O

OH OH

O

6 100 85 100

21 6 20 10 100

Reaction and conditions: styrene (1 mmol), arene (10 mmol), Montmorillonite K-10 (80 mg), reacted at 808C, aGC yield, and bselectivity

(ortho:meta:para).

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3. Conclusion

In summary, we have developed MontmorilloniteK-10 as an efficient, environmentally benign,economical, and commercially available catalyst forthe hydroarylation of styrene and its derivatives witharenes and heteroarenes, which afforded 1,1-diary-lalkane with high selectivity and excellent yield inshort time. Solid acid Montmorillonite K-10 catalystwas thoroughly characterized with different techni-ques. Notable advantages offered by this metal-freereaction system are the use of Montmorillonite K-10as a heterogeneous recyclable catalyst, simple workupprocedures; higher yields of the desired products andgreater substrate compatibility making this approachan important supplement to the existing methods.

4. Experimental

4.1. General

All chemicals, reactants, and reagents including cata-lyst Montmorillonite K-10 were purchased fromcommercial suppliers and used without further pur-ification. The products were characterized using 1HNMR, 13C NMR spectra (Varian mercury 300 NMRspectrometer) and IR (Perkin-Elmer FT-IR) spectro-scopic techniques. Surface morphology and elementalcontent in Montmorillonite K-10 was studied by SEM-EDAX analysis; TPA-TPD for Bronsted acidity study;BET dynamic method for surface area, total porevolume and average pore diameter analysis. Theprogress of reaction was monitored using GC analysis(Perkin-Elmer clarus 400) (BP-10 GC column,30 m�0.32 mm ID, film thickness 0.25 mm). Productswere confirmed by GC-MS (Shimadzu GC-MS QP2010). All products are known in the literature.

4.2. Typical experimental procedure for thehydroarylation of alkenes with arenes

In a 10 mL of sealed tube with a spin bar, alkene(1 mmol), arene (10 mmol), and MontmorilloniteK-10 catalyst (80 mg) were taken and sealed properly.

The reaction mixture was heated at 808C with stirringfor desired time and was cooled to room temperatureon completion of reaction. Alkene conversion as wellas product formation was monitored by gas chroma-tography. After completion of reaction mixture wasdiluted with ethyl acetate (5 mL), filtered off andwashed with ethyl acetate (3�5 mL). The organicsolution was analyzed with GC. The residue obtainedwas purified with column chromatography (silica gel,60�20 mesh; PE-EtOAc, 95:05) to afford the desiredhydroarylated products. The structure of obtainedproduct confirmed by GC-MS, 1H NMR, 13C NMR,and IR spectroscopic techniques (see Supportinginformation). The purity of compounds was deter-mined by GC-MS analysis.

4.3. Typical procedure of recycling Montmorillonite K-10catalyst for hydroarylation of anisole with styrene

After completion of reaction, the reaction mixturewas cooled to room temperature reaction mixture wasdiluted with ethyl acetate (5 mL). The catalyst wasfiltered off and washed with ethyl acetate (3�5 mL).Then, separated catalyst was dried at 80�858C inoven for 1 h and used further for the catalystrecyclability experiment. It was observed that therecovered catalyst could be reused for the fiveconsecutive cycles for the hydroarylation of anisolewith styrene through slight decrease in yield ofdesired product.

4.4. Characterization of selected compound 2-[1-(4-tert-Butyl-phenyl)-ethyl]-4-methoxy-phenol (Table 2,entry 20)

4.4.1. Colorless liquid1H NMR (300 MHz, CDCl3): d�1.25 (s, 3H), 1.57(d, J�7.33 Hz, 3H), 3.74 (s, 3H), 4.27 (q, J�7.08 Hz,1H), 4.35 (s, 1H), 6.65 (d, J�2.57 Hz, 1H), 6.67(s, 1H), 6.81 (d, J�2.57 Hz, 1H), 7.15 (d, J�8.43 Hz,2H), 7.27 ( d, J�8.43 Hz, 2H); 13C NMR (75.43MHz, CDCl3): d�21 (CH3), 29.1 (CH), 31.3 (3CH3),38.2 (C), 55.6 (OCH3), 111.4 (CH), 114.3 (CH), 116.5(CH), 125.5 (2CH), 127.1 (2CH), 133.7 (C), 141.9 (C),147.4 (C), 149.1 (C), 153.6 (C); IR (KBr) n�3411,2963, 1506, 1462, 1429, 1363, 1269, 1203, 1034, 836,801, 713, 578 cm�1; MS (EI, 70 ev): m/z (%)�284(57), 269 (48), 228 (16), 213 (15), 198 (4), 165 (4), 150(100), 135 (21), 120 (23), 91 (12), 77 (7), 57 (21).

Acknowledgements

The authors are thankful to Department of Atomic Energy

(DAE-ICT center), Mumbai, India for financial support.

Table 3. Recyclability of Montmorillonite K-10 catalyst.

Entry Run

Conversion

(%)aYield

(%)aSelectivity

(%)a

1 1 100 98 86:14

2 2 100 98 86:143 3 100 98 86:144 4 98 96 86:14

5 5 90 88 86:14

Reaction conditions: catalyst (400 mg), styrene (5 mmol), arene (50

mmol), solvent- neat, reacted at 808C for 0.5 h, aGC yield.

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Supporting information

Typical NMR of the various products:

2-(1-phenylethyl)phenol

Table 2- entry no 3- 1H NMR (CDCl3, 400MHz): d 1.6 (d, 3H, J�7.2 Hz); 3.72 (s, 1H); 4.09 (q, 1H, J �7.2 Hz); 6.73-6.75

(m, 2H, J �2 Hz); 7.05-7.07 (m, 2H); 7.19-7.29 (m, 5H). 13C NMR (CDCl3, 100.6MHz): d 21.98, 29.64, 115.26, 125.82,

127.43, 128.24, 128.57, 138.17, 146.74 and 153.91.

4-methyl-2-(1-phenylethyl)phenol

Table 2- entry no 3- 1H NMR (CDCl3, 400MHz): d 1.6 (d, 3H, J�7 Hz); 2.26 (s, 3H); 4.25 (s, 1H); 4.34 (q, 1H, J �7 Hz);

6.58 (d, 1H, J �8 Hz); 6.88 (d, 1H, J �8 Hz); 7.01 (s, 1H); 7.16-7.28 (m, 5H). 13C NMR (CDCl3, 100.6MHz): d 20.72, 20.94,

38.47, 115.75, 126.22, 127.48, 127.72, 128.44, 128.53, 129.78, 131.81, 145.51 and 150.99.

1-methoxy-4-(2-phenylpropan-2-yl)benzene

Table 2- entry no 12- 1H NMR (CDCl3, 400MHz): d 1.66 (s, 6H); 3.78 (s, 3H); 6.81 (d, 2H, J �3 Hz); 7.14-7.16 (m, 3H, J �6

Hz); 7.24-7.26 (m 4H, J �3 Hz, 6 Hz). 13C NMR (CDCl3, 100.6MHz): d 30.82, 42.18, 55.02, 113.18, 125.46, 126.63, 127.68,

127.88, 142.75, 150.81 and 157.32.

4-methyl-2-(2-phenylpropan-2-yl)phenol

Table 2- entry no 14- 1H NMR (CDCl3, 400MHz): d 1.67 (s, 6H); 2.35 (s, 3H); 3.58 (s, 1H); 7.32-7.33 (m, 4H), 7.33-7.34 (m,

4H). 13C NMR (CDCl3, 100.6MHz): d 20.91, 30.16, 41.56, 117.55, 125.94, 126.84, 126.95, 128.41, 129.09, 129.54, 135.03,

148.46 and 151.52.

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