CDs as a greener and recyclable catalyst

Molecular Catalysis 436 (2017) 157–163

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Highly regio-selective hydroformylation of biomass derived eugenol using aqueous biphasic Rh/TPPTS/CDs as a greener and recyclable catalyst Samadhan A. Jagtap a , Eric Monflier b , Anne Ponchel b , Bhalchandra M. Bhanage a,∗ a b

Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai, 400 019, Maharashtra, India Univ. Artois, CNRS, Centrale Lille, ENSCL, Univ. Lille, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), Lens, F-62300, France

a r t i c l e

i n f o

Article history: Received 3 February 2017 Received in revised form 17 March 2017 Accepted 18 April 2017 Keywords: Biphasic catalysis rhodium TPPTS Cyclodextrins Hydroformylation Eugenol

a b s t r a c t A Rh/TPPTS catalyzed aqueous biphasic hydroformylation of eugenol was performed in an aqueous medium in the presence of different modified cyclodextrins. The internal olefin such as anethole shows high selectivity towards the branched aldehydes (78%) where as terminal alkene like eugenol shows high selectivity towards the linear aldehydes (87%). The various reaction parameters such as effect of syngas pressure, time, temperature, catalyst precursor and loading have been studied. The high activity and high selectivity towards the linear aldehydes is due to the steric crowding of methyl group present in RAMEˇ-cyclodextrins. The effect of ratio of Rh/TPPTS/RAME-ˇ-CD were also studied for the hydroformylation of eugenol. Moreover, this catalytic system was recycled up to four consecutive cycles without loss in its catalytic activity and selectivity. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Hydroformylation is a very important homogeneous catalytic industrial process by use of rhodium metal for the synthesis of aldehydes from alkenes using syngas (CO/H2 ) [1,2]. The difficulties in controlling the selectivity of products, separation and recovery of the catalysts from the reaction mixture are the biggest challenges [3]. The phosphine or phosphite ligands were used to enhance the regio-selectivity towards the expected linear or branched aldehydes [4,5]. While homogeneous rhodium catalysts affords high conversion and selectivity for desired product in less reaction time, they suffer from the trouble of separating the catalyst from the reaction mixture and catalyst recovery [6]. Aqueous biphasic catalysis provides a straightforward solution to the problem of product separation and catalyst recovery [7]. The general schematic representation of aqueous biphasic organometallic catalysis has been shown in (Fig. 1). Aqueous biphasic organometallic hydroformylation has been growing importance since the synthesis of sodium salt of trisulfonated triphenylphosphine (TPPTS) early in 19th century [8]. Formerly, in 1984 the Rh/TPPTS/H2 O aqueous biphasic catalytic

∗ Corresponding author E-mail addresses: [email protected], [email protected] (B.M. Bhanage). http://dx.doi.org/10.1016/j.mcat.2017.04.019 2468-8231/© 2017 Elsevier B.V. All rights reserved.

system was used by Ruhrchemie and Rhone-Poulenc for the hydroformylation of propene [9]. During this process, the rhodium catalyst was capably anchored in aqueous phase through water soluble TPPTS ligand which leads to negligible amount of metal leaching in ppb. However, the scope of this process is reduced by the low solubility of organic substrate in water and need of synthesis of water soluble ligands. To overcome these drawbacks the addition of co-solvent [10], surfactants [11,12], cyclodextrins [13], surface active ligand [14] and activated carbon [15] was reported. Along with the different approaches proposed, the use of cyclodextrins (CDs) proves to be challenging in aqueous biphasic systems [16]. The cyclodextrins (CDs) are cyclic oligosaccharides consist of (␣-1,4) -linked ␣-d-glucopyranose units which is obtained from the enzymatic conversion of starch [17]. It contains a somewhat lipophilic central cavity and a hydrophilic outer surface. The natural ␣-, ␤- and ␥-cyclodextrin consist of six, seven, and eight glucopyranose units, respectively [18]. Naturally occurring olefins are the green alternative source of renewable feedstocks for the chemical industry. The derivatives of allyl benzenes such as eugenol, anethole and estragole are the biorenewable starting materials obtained from (biomass) cloves, basil and sweet basil, respectively [19]. The hydroformylation of these biorenewable starting materials provides aldehydes of high addedvalue with an interesting properties that are significant in the cosmetic, pharmacological, fragrance and food industries [20,21].

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instrument (Rtx-17, 30 m × 25 mm ID, film thickness 0.25 ␮m df) (column flow 2 10 mL min−1 , 80 ◦ C–240 ◦ C at 10◦ /min rise). 2.2. General experimental procedure for aqueous biphasic hydroformylation of eugenol

Fig. 1. The general schematic representation of aqueous biphasic catalysis.

Several groups have studied the hydroformylation of eugenol over the years. In 1980, Siegel and Himmele reported the Rhcatalyzed hydroformylation of eugenol [22]. Santos and coworkers reported the rhodium catalyzed hydroformylation of various allylbenzenes and propenylbenzenes with 97–99% chemoselectivity in the presence of phosphine ligands [23]. Recently, Santos and co-workers utilized cetyltrimethylammonium bromide (CTAB) as a cationic surfactant in rhodium catalyzed biphasic hydroformylation of eugenol in the presence of water soluble phosphines can provide 97–99% chemoselectivity [24]. In 2011, Baricelli and co-workers first time reported the biphasic hydroformylation of substituted allylbenzenes with water-soluble rhodium [Rh(CO)(Pz)(L)]2 or ruthenium [HRu(CO) (CH3 CN)(L)3 ][BF4 ] complexes [25]. Afterwards, Escalante and co-workers reported biphasic hydrogenation and hydroformylation of natural olefins with a binuclear rhodium complex in ionic liquid/toluene as a catalytic system [26]. The hydroformylation of the naturally occurring olefins, such as eugenol, anethole and estragole has been rather extensively investigated in the literature [27]. In the last decade, various homogenous catalytic protocols were developed [28,29]. However, with these homogeneous catalytic processes, the recovery and reutilization of the expensive metal catalysts is a difficult task which affects the overall process economy. Herein, we report the aqueous biphasic hydroformylation of natural olefin such as eugenol using Rh/TPPTS/CDs/H2 O as greener and recyclable catalytic system (Scheme 1). In the present protocol, native and modified cyclodextrins were used in the aqueous biphasic catalysis. The aim of the present work is screening an effect of the various cyclodextrins such as ␣-cyclodextrins (␣-CD), ˇ-cyclodextrin (ˇ-CD), -cyclodextrin (-CD), hydroxyl propyl ˇcyclodextrin (hp-ˇ-CD) and RAndomly MEthylated ˇ-cyclodextrin (RAME-ˇ-CD). 2. Experimental 2.1. Materials and methods All the chemicals were purchased from Sigma Aldrich, Alfa Aesar, Spectrochem Pvt. Ltd., India and used without further purification. Distilled deionized water was used in all experiments. All catalytic reactions were performed under nitrogen atmosphere. A syngas containing mixture of hydrogen (49.9%) and carbon monoxide (49.9%) were purchased from Rakhangi Gas Service, Mumbai. All reactions were performed in a 100 mL autoclave. The reaction process was monitored by gas chromatography on Perkin Elmer Clarus 400 GC equipped with flame ionization detector with a capillary column (Elite-1, 30 m × 0.32 mm × 0.25 ␮m)). GC-MS-QP 2010

To a 100 mL autoclave, Eugenol (1 mmol), [Rh (acac) (CO) 2 ] (0.0015 mmol), TPPTS (0.0075 mmol), RAME-ˇ-CD (0.015 mmol) and water (10 mL) were added. The autoclave was closed, flushed three times with syngas, pressurized with 25 bar of syngas and heated at 80 ◦ C for 6 h. After the completion of the reaction, the reactor was cooled to room temperature, and the remaining syngas gas was vented carefully, and the reactor was opened. The organic layer containing product from aqueous layer was separated by a simple separation technique using separating funnel. The reactor vessel was thoroughly washed with ethyl acetate (3 × 5 mL) to remove traces of the product. The reaction mixture was collected in separating funnel and separates the organic layer containing product. The separated aqueous layer containing catalytic system was reused as catalyst for further recycle experiment. The organic layer containing product was passed through dry Na2 SO4 to remove traces of water (moisture) if present and it is used as for further GC and GC–MS analysis. 2.3. General experimental procedure for recycling of the catalyst The recovery and recycling of the catalysts have been performed under nitrogen atmosphere. After the completion of the reaction, the catalytic system was recovered by separating the aqueous layer from the organic layer in the separating funnel. The reaction mixture was washed three times with 3 mL of ethyl acetate to remove the product present in the reaction mixture. After the separation of organic layer of reaction mixture, remaining aqueous solution containing metal, ligand and cyclodextrin as a catalyst was collected and used as it is for next recycle experiment. This biphasic Rh/TPPTS/CDs catalytic system was easily recycled up to four consecutive cycles without loosing its catalytic activity and selectivity. 3. Results and discussion 3.1. Aqueous biphasic hydroformylation of eugenol The aqueous biphasic hydroformylation of eugenol (1a) to the synthesis of respective aldehydes i.e. 4-(3-hydroxy-4methoxyphenyl) butanal (4a) was chosen as model reaction. The reaction was carried out in presence of Rhacac(CO)2 as a catalyst precussor, TPPTS as water soluble phosphine and cyclodextrin as mass transfer promoter. 3.2. Effect of various modified cyclodextrins and its concentration on the hydroformylation of eugenol The chemical structure and characteristics of native cyclodextrins (␣-CD, ˇ-CD and -CD) and derivatives (RAME-␣-CD, RAME-ˇ-CD and hp-ˇ-CD) were shown in Table 1. The cyclodextrins are cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. The ␣-CD, ˇ-CD and -CD contain 6, 7 and 8 (␣-1,4) linked ␣-d-glucopyranose units, respectively (Fig. 2). The RAME-␣-CD and RAME-␤-CD were a mixture of CDs partially O-methylated with statistically 11.8 OH and 12.6 groups modified per CD, respectively. The OH groups in C-6 position are fully methylated whereas those in C-2 and C-3 positions are partially methylated (Table 1, entries 4 and 5). The hp-␤-CD is a mixture of ␤-CDs partially O-hydroxypropylated with statistically 5.6 OH groups modified per CD. The OH groups can be in C-2, C-3 or C-6 positions (Table 1, entry 6).

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Scheme 1. Regio-selective hydroformylation of eugenol using Rh/TPPTS/CDs as a greener and reusable catalyst. a Reaction Conditions: Eugenol (1 mmol), Rhacac(CO)2 (0.0015 mmol), TPPTS (0.0075 mmol), CD (0.015 mmol), CO/H2 (25 bar), Water (10 mL), 80 ◦ C, 6 h. b Determined by GC and GC–MS. c Reaction carried out with Rh/TPPTS/H2 O as catalyst. Table 1 Chemical structure and characteristic of the cyclodextrin derivatives.

G: H or R Entry

Abbreviation

n

1 2 3 4 5 6

␣-CD ␤-CD ␥-CD RAME-␣-CD RAME-␤-CD HP-␤-CD

6 7 8 6 7 7

Substituent R

CH2

(–) (–) (–) CH3 CH3 CHOH CH3

Carbons bearing the OR group

Number of R groups per CD

Molecular weight (g mol−1 )

(–) (–) (–) 2, 3 and 6 2, 3 and 6 2, 3 and 6

0 0 0 10.8 12.6 5.6

972 1134 1297 1127 1314 1460

Initially, we screened the effect of various modified cyclodextrins and its concentration on the hydroformylation of eugenol (1a) as shown in Table 2. The reaction with the Rh/TPPTS/H2 O catalytic system provides good conversion (68%) with moderate yield of aldehydes (60%) and the selectivity (52%) was less (Table 2, entry 1). It was observed that the better yield (72%) of aldehydes and selectivity (78%) of 4a was obtained when 0.0052 mmol concentration of ˇ-CD used in the reaction (Table 2, entry 6). The better results were obtained using ˇ-CD (Table 2, entries 5–7) as compared to ␣-CD and -CD. The less yield and selectivity was observed using ␣-CD (Table 2, entries 2–4) and -CD (Table 2, entries 8–10) at the same

rection conditions. From these results, it is concluded that the size of CDs cavity was appeared to be key limit to manage the catalytic activity. Moreover, we studied some modified CDs are RAME-␣-CD, RAME-ˇ-CD and hp-ˇ-CD for the hydroformylation reaction of eugenol under the optimum reaction conditions. The reaction with RAME-␣-CD provides better conversion, but selectivity was observed less as compared to the RAME-ˇ-CD and hp-ˇ-CD (Table 2, entries 11–13). The addition of 0.053 mmol of RAME-␣-CD in the reaction provides 84% conversion and 69% yield of aldehydes with 60% selectivity of 4a (Table 2, entry 12). The modified RAME-ˇ-

Fig. 2. The structures of native cyclodextrins (␣-CD, ˇ-CD and -CD).

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Table 2 Effect of various cyclodextrins and its concentration on the aqueous biphasic hydroformylation of eugenol (1a).a Entry c

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 a b c

CDs

Conc. in mmol

Conversion (%)b

Aldehyedes (%)b

Selectivity (%)b 2a:3a:4a

– ␣-CD ␣-CD ␣-CD ␤-CD ␤-CD ␤-CD ␥-CD ␥-CD ␥-CD RAME-␣-CD RAME-␣-CD RAME-␣-CD RAME-␤-CD RAME-␤-CD RAME-␤-CD hp-␤-CD hp-␤-CD hp-␤-CD

– 0.030 0.061 0.102 0.026 0.052 0.088 0.025 0.050 0.083 0.026 0.053 0.088 0.015 0.025 0.050 0.020 0.041 0.070

68 82 84 83 88 92 91 69 79 77 79 84 82 92 97 99 78 86 89

60 65 72 69 69 72 69 59 64 64 67 69 65 86 89 81 84 85 83

14:34:52 15:25:60 15:20:65 10:28:62 12:16:72 06:16:78 10:20:70 12:20:68 14:16:70 16:12:62 20:16:64 19:21:60 16:22:62 08:12:80 03:10:87 10:15:75 16:22:62 12:20:68 19:21:60

Reaction Conditions: Eugenol (1 mmol), Rhacac(CO)2 (0.0015 mmol), TPPTS (0.0075 mmol), CO/H2 (25 bar), Water (10 mL), 80 ◦ C, 6 h. Determined by GC and GC–MS. Reaction carried out with Rh/TPPTS/H2 O as catalyst. RAME- RAndomly MEthylated, hp- hydroxy propyl.

CD of 0.0252 mmol concentration shows the best results for better conversion (97%) of 1a and 87% selectivity of 4a (Table 2, entry 15). The high activity can probably be attributed to the surface-active properties of RAME-ˇ-CD and selectivity towards the linear aldehydes could be due to the steric crowding of randomly presence of methyl groups in the RAME-ˇ-CD. As we increase the concentration of RAME-ˇ-CD from 0.015 mmol to 0.050 mmol resulting into the conversion increases from 92% to 99%. However, the yield of aldehyde and selectivity of linear aldehydes initially increases and then decreases at the end (Table 2, entries 14–16). The hp-ˇ-CD was also shows better results in the conversion of eugenol and the better selectivities of 4a (Table 2, entries 17–19). At the 0.041 mmol concentration of hp-ˇ-CD it can provide the 86% conversion and 85% yield of aldehydes with 68% selectivity of 4a (Table 2, entry 18). From this first set of expriments, it clearly appears that the presence of CD allows in all case to increase the eugenol selectivity. This result can be likely attributed to the inclusion of eugenol inside the CD cavity. Indeed, CD can transitorily accommodate the substrate into its cavity restricting its conformational flexibility and masking a part of the allyl group while exposing distal position of the allyl group to Rh catalytic species. This result is remarkable as it is well-known that CD can interact with TPPTS to form phosphane low-coordinated species which are expected to be less regioselective in the hydroformylation reaction (Scheme 2) [30–32].

3.3. Optimization of reaction conditions for the eugenol hydroformylation Aqueous biphasic hydroformylation of eugenol (1a) for the synthesis of respective aldehydes i.e. 4-(3-hydroxy-4-methoxyphenyl) butanal (4a) was chosen as a model reaction for an optimization study. The various reaction parameters such as the effect of syngas (CO/H2 ) pressure, time, temperature, catalyst screening and loading were studied for the regio-selective hydroformylation of eugenol (1a) and the results are summarized in Tables 3 and 4. Similarly the effect of metal to ligand to CDs ratio were screened and results are shown in Table 5. Initially, we studied the effect of syngas pressure in the hydroformylation reaction of eugenol using Rh/TPPTS/CDs as a recyclable catalytic system. When the use of 45 bar and 35 bar of syngas pressure, then conversion was almost complete but selectivity of the

product (4a) was very less about 60% and 64% respectively (Table 3, entries 1 and 2). The best results were observed at 25 bar of syngas pressure provides 97% conversion of 1a and 76% selectivity of 4a (Table 3, entry 3). Then we reduced the pressure up to 15 bar both conversion reduces to 92% and selectivity decreases to 58% (Table 3, entry 4). Thus the 25 bar was fine pressure for a successful conversion and better selectivity of 4a. Furthermore, we have studied the effect of time in the range of 12 h–4 h (Table 3, entries 5–8). Initially, we increase the time from 10 h to 12 h, the conversion has no significant change, but selectivity of 4a decreases to 74% (Table 3, entry 5). Then, we reduce the raction time to 8 h we get the slightly decrease in conversion (97%) but selectivityof 4a increases up to 86% (Table 3, entry 6). Between all the reaction time the 6 h time was the favourable reaction time to get the best results as 97% conversion of 1a with 87% selectivity of 4a (Table 3, entry 7). As we reduced time reaction at 4 h the conversion decreases to 89% and selectivity of 4a decreases to 79% (Table 3, entry 8). Afterwards, we examine the range of temperature of (120 ◦ C–40 ◦ C) to optimize the suitable temperature for the biphasic hydroformylation of eugenol (Table 3, entries 9–12). If we increase the reaction temperature up to 120 ◦ C then the conversion was almost complete, but the selectivity of 4a decreased to 58% (Table 3, entry 9). At the 100 ◦ C of reaction temperature, conversion does not affected but slightly increase in selectivity up to 65% (Table 3, entry 10). The best results were observed at the reaction temperature of 80 ◦ C which can afford 97% conversion of 1a and 87% selectivity of 4a (Table 3, entry 7). Moreover, at lower temperatures of 60 ◦ C, the conversion and selectivity both decreases (Table 3, entry 11). Finally, the 78% conversion and 52% selectivity was observed at a low reaction temperature of 40 ◦ C (Table 3, entry 12).

3.4. Effect of metallic precursor on hydroformylation of eugenol In absence of catalyst, the reaction does not occur, confirming that the catalyst is solely responsible for the reaction (Table 4, entry 1). Moreover, we have studied the various metallic precursors of Palladium, Ruthenium, Rhodium and Cobalt metals for the hydroformylation of eugenol in the presence of TPPTS ligand along with RAME-ˇ-CD. Among them the rhodium metal precursors were the active catalysts for the hydroformylation of 1a. The catalyst Pd(OAc)2 provides less conversion of 26%, but the desired product

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Scheme 2. Plausible mechanism for the regioselective hydroformylation of eugenol using Rh/TPPTS with RAME-ˇ-CD as greener and reusable catalytic system. Table 3 Optimization of reaction conditions for an aqueous biphasic hydroformylation of eugenol (1a).a Pressure in bar (CO/H2 )

Time (h)

Temp. (◦ C)

Conv. (%)b

Selectivity (%)b (2a:3a:4a)

Effect of pressure 1 2 3 4

45 35 25 15

10 10 10 10

80 80 80 80

99 99 97 92

16:24:60 12:22:64 12:12:76 14:28:58

Effect of time 5 6 7 8

25 25 25 25

12 8 6 4

80 80 80 80

99 97 97 89

10:16:74 04:10:86 03:10:87 05:16:79

Effect of temperature 9 10 11 12

25 25 25 25

6 6 6 6

120 100 60 40

99 98 86 78

19:23:58 15:20:65 10:22:68 20:28:52

Entry

a b

Reaction Conditions: Eugenol (1 mmol), Rhacac(CO)2 (0.0015 mmol), TPPTS (0.0075 mmol), RAME-␤-CD (0.025 mmol), Water (10 mL), 700 rpm. Confirmed by GC and GC–MS analysis.

(4a) was not observed (Table 4, entry 2). The Ruthenium (III) Chloride can furnish moderate conversion and selectivity towards 4a (Table 4, entry 3). The various rhodium precursors can afford good conversion and better selectivity towards 4a (Table 4, entries 4–9). Among all the rhodium precursors the Rhacac(CO)2 catalyst was active for hydroformylation of 1a, which shows the best results as conversion of 97% and selectivity of 87% towards 4a (Table 4, entry 6). We have also used the Cobalt precursors such as Co2 (CO)8 and CoCl2 ·6H2 O, these precursors was not active so much for hydro-

formylation of 1a, which requires high pressure (50 bar) and high temperature (100 ◦ C) (Table 4, entries 10 and 11). 3.5. Effect of Rh/TPPTS/CDs ratio on eugenol hydroformylation We screened the effect of ratio of metal/TPPTS/CDs for the hydroformylation of 1a for the better conversion and selectivity of 4a. The reaction carried out with Rh/TPPTS as catalyst with 1:2 ratio, which can provide the conversion (68%) and 65% yield of aldehy-

Table 4 Effect of metallic precursors on aqueous biphasic hydroformylation of eugenol (1a).a Entry

Metallic precursors

Conc. (mmol)

Conv. (%)b

Aldehydes (%)b

Selectivity (%)b 2a:3a:4a

1 2 3 4 5 6 7 8 9 10c 11d

– Pd(OAc)2 RuCl3 RhCl3 Rh(acac)(CO)2 Rh(acac)(CO)2 [Rh(COD)Cl]2 Rh(COD)2 BF4 Rh2 (OAc)4 Co2 (CO)8 CoCl2 ·6H2 O

– 0.044 0.048 0.015 0.001 0.0015 0.0025 0.0025 0.0025 0.025 0.05

– 26 59 68 92 97 92 87 89 49 45

– – 62 63 85 89 87 84 89 65 59

– – 10:22:68 16:20:64 08:12:80 03:10:87 10:11:79 12:19:69 04:20:76 15:25:60 11:30:59

a b c d

Reaction Conditions: Eugenol (1 mmol), TPPTS (0.0075 mmol), RAME-␤-CD (0.025 mmol), CO/H2 (25 bar), Water (10 mL), 700 rpm, 80 ◦ C, 6 h. Confirmed by GC and GC–MS analysis. 50 bar, 100 ◦ C, 8 h. 50 bar, 100 ◦ C, 8 h.

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Table 5 Effect of Rh/TPPTS/CDs ratio on biphasic hydroformylation of eugenol (1a).a Entry c

1 2 3 4 5d 6 a b c d

Rh/TPPTS/CDs ratio

Conv. (%)b

Aldehyde (%)b

Selectivity (%)b 2a:3a:4a

1:2:0 1:2:4 1:3:6 1:5:10 1:0:4 1:4:4

68 90 94 97 58 95

65 84 86 89 76 86

14:30:56 10:12:78 10:15:75 03:10:87 18:18:64 06:12:82

Reaction Conditions: Eugenol (1 mmol), Rhacac(CO)2 (0.0015 mmol), CO/H2 (25 bar), Water (10 mL), 80 ◦ C, 6 h. Confirmed by GC and GC–MS analysis. Reaction carried out with Rh/TPPTS as catalyst. Reaction carried out with Rh/CDs as a catalyst.

Table 6 Substrate study of biphasic hydroformylation of various derivatives of allyl benzene.

a

Entry

Substrates

Conv. (%)b

Aldehyde (%)b

1 2c 3 4 5 6 7

Eugenol (1a) Anethole (1b) Estragole (1c) Allyl benzene (1d) 4-allyl toluene (1e) 4-allyl-1,2-dimethoxybenzene (1f) 1-allyl-4-(trifluromethyl)benzene (1g)

97 94 98 92 96 96 89

89 84 89 89 88 82 78

Selectivity (%)b 2a-2h:3a-3h:4a-4h 03:10:87 30:55:15 13:12:75 10:22:68 14:14:72 10:12:78 15:20:65

Reaction Conditions: Olefin (1 mmol), Rhacac(CO)2 (0.0015 mmol), TPPTS (0.0075 mmol), RAME-␤-CD (0.015 mmol), CO/H2 (25 bar), Water (10 mL), 80 ◦ C, 6 h. b Confirmed by GC and GC–MS analysis. c 90 ◦ C, 10 h, 40 bar.

Fig. 3. Recyclability study of aqueous biphasic hydroformylation of eugenol (1a) using Rh/TPPTS/RAME-ˇ-CD as a reusable catalyst. a Reaction conditions: 1a (1 mmol), Rh acac(CO)2 (0.0015 mmol), TPPTS (0.0075 mmol), RAME-ˇ-CD (0.015 mmol), CO/H2 (25 bar), H2 O (10 mL), 80 ◦ C, 6 h. b GC Yield.

des with 56% selectivity of 4a (Table 5, entry 1). After the addition of RAME-ˇ-CD to the Rh/TPPTS catalyst the remarkable increase in the 90% conversion and 84% yield with 78% selectivity of 4a (Table 5, entry 2). The Rh/TPPTS/RAME-ˇ-CD ratio of 1:3:6 also provides good conversion (94%) and good yield (86%) with selectivity (75%) of 4a (Table 5, entry 3). The best results were observed at the ratio of 1:5:10 which shows the conversion of 97% and 89% yield with the selectivity of 4a up to 87% (Table 5, entry 4). The reaction carried out using 1:4 ratio of Rh/RAME-ˇ-CD as a catalytic system with water as solvent, it observed that the decrease in conversion to 58% and 76% aldehydes with 64% selectivity of 4a (Table 5, entry 5). In this case, the catalytic system mainly present in organic phase due to absence of water soluble TPPTS ligand which can acquire catalytic system into aqueous phase. Consequently, the TPPTS ligand plays crucial role for the separation of catalytic system in aqueous biphasic organometallic catalysis. The ratio 1:4:4 also supply good conversion of 95%

and 86% yield of aldehydes along with 82% selectivity to the linear aldehyde 4a (Table 5, entry 6). It is concluded that, from the studies of entry no. 1 and 5, it is concluded that the whole catalytic system (Rh/TPPTS/RAME-ˇ-CD) is solely responsible for the aqueous biphasic hydroformylation of 1a. 3.6. Substrate study of hydroformylation of various derivatives of allyl benzene The optimized reaction parameters were further applied to examine the substrate applicability of this protocol. The derivatives of allyl benzenes bearing electron-donating groups ( Me, OMe) and electron withdrawing groups ( OH, CF3 ) were smoothly converted into the desired products. The terminal alkene eugenol (1a) provides conversion (97%) and a yield (89%) of aldehydes with selectivity (87%) of linear aldehyde (4a) (Table 6, entry 1). The internal alkene anethole (1b) can provide 94% conversion and 84%

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yield of aldehyde, but branched aldehyde (3b) selectivity (55%) was observed as a major product (Table 6, entry 2). The estragole (1c) is the derivative of allyl benzene containing group at para position, which affords the conversion (98%) and selectivity (75%) towards the linear aldehyde (4c) (Table 6, entry 3). The simple allyl benzene (1d) was easily converted to the 4d with conversion (92%) and selectivity (68%) of 4d (Table 6, entry 4). The allyl benzenes containing electron donating groups such as −Me (1e) and OMe (1f) also provides better conversion and good selectivities 72% towards 4e, 78% towards 4f (Table 6, entries 5 and 6). Finally, the electron withdrawing group also provides good conversion (89%), but slightly decrease in selectivity (65%) of 4g (Table 6, entry 7). 4. Catalyst reusability Reusability of Rh/TPPTS/CDs catalyst was an important aspect to ensure efficiency of the catalytic protocol. So, we have tested the reusability of Rh/TPPTS/CDs catalyst for the biphasic hydroformylation of naturally occurring olefins such as Eugenol (1a). All the experiments of recovery of catalytic system was performed under the nitrogen atmospheric condition. The catalytic system was found to be reused for four consecutive cycles with an excellent catalytic activity and selectivity towards the formation of desired product 4a (Fig. 3). The leaching of rhodium metal was investigated after the 1st and 4th recycle run by ICP-AES analysis and observed below has detected level (≈0.1 ppm) of rhodium in solution which revealed that negligible leaching of rhodium metal into the solution. 5. Conclusion In conclusions, we have described the effect of various modified cyclodextrins for the aqueous biphasic hydroformylation of biomass derived olefins using Rh/TPPTS/CDs as an efficient, recyclable and greener protocol. The various cyclodextrins such as ␣-CD, ˇ-CD, -CD, RAME-␣-CD, RAME-ˇ-CD and hp-ˇ-CD have been successfully screened for aqueous biphasic hydroformylation of eugenol. Among them RAME-ˇ-CD can provide the best conversion and excellent selectivity towards the linear aldehydes. Because, the internal cavity RAME-ˇ-CD of is hydrophobic in nature which can be resulted into fixation of eugenol benzene ring into the cavity. The allyl group of eugenol remains at outside of cavity which can be resulted into the linear aldehydes as major product instead of isomerisation and branched aldehydes. The natural olefins such as eugenol, anethole, estragole were smoothly converted to the aldehydes with good to excellent yields. The olefins containing various functional groups such as electron withdrawing and donating groups can also be efficiently utilized in hydroformylation reaction giving higher selectivity towards aldehydes as major products. The present protocol gives simple and easy access towards aldehydes which is widely used as raw material in the pharmaceutical industry. Furthermore, the catalyst was found to be reused up to four consecutive cycles with an excellent catalytic activity and selectivity towards the formation of aldehydes as a product. Acknowledgement The author S.A. Jagtap is thankful to the Council of Scientific and Industrial Research (CSIR) India, for providing a Senior Research Fellowship (SRF). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.mcat.2017.04. 019.

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