Atom-Economical Selective-Ring-Opening Reaction of Glycidol with 1

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Atom-Economical Selective-Ring-Opening Reaction of Glycidol with 1‑Naphthol Catalyzed by Magnesium Silicate of a Biogenic Silica Source Godfree P. Fernandes and Ganapati D. Yadav* Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400 019, India ABSTRACT: Ring-opening reaction is one of the most important processes in organic transformations wherein selectivity of the desired product is dependent on a number of parameters. Selective ring opening of glycidol with 1-naphthol was studied to make propanolol glycol [or 3-(1-naphthyloxy)propane-1,2-diol] over magnesium silicate as a heterogeneous catalyst. Propanolol glycol is used in the treatment of hypertension. Magnesium silicate catalyst was produced by combusting a biogenic silica source material such as rice hulls to give rich hull ash (RHA), and it was characterized by using several techniques such as X-ray diffraction, scanning electron microscopy, temperature-programmed desorption, and Brunauer−Emmett−Teller N2 adsorption. The catalyst was highly active in ring-opening reaction, and 3-(1-naphthyloxy)propane-1,2-diol was the only product. The reaction was 100% atom selective. The effects of different kinetic parameters on the rate of ring opening of glycidol with 1naphthol were studied systematically to establish the kinetics of the reaction. Magnesium silicate derived from RHA exhibited better catalytic behavior in the production of propanolol glycol with conversions of up to 80% in 3 h with 90% selectivity. The catalyst was characterized after the reaction and found to be robust without any loss of activity.

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INTRODUCTION Epoxides are used as starting materials and intermediates in organic synthesis. Epoxides are much more reactive than simple ethers because of the inherent ring strain. The nucleophilic opening of epoxides has been studied to form C−C, C−N, C− O, and C−S bonds with 100% atom economy. There are several references to the opening of epoxides with alcohols, water, acetic anhydride, thiols, and amines.1,2 One of the important reactions is the selective ring opening of glycidol with 1-naphthol to make propanolol glycol, which has important applications. The intermediate has been used in the pharmaceutical industry for the treatment of hypertension.3 These days there is a tremendous emphasis on biobased routes for the synthesis of chemicals. Glycerol has been found to be an attractive feedstock4 for making a variety of valueadded chemicals including bulk chemicals to specialties using novel solid acids, bases, and supported metal catalysts.5−8 Glycidol can also be synthesized from decarboxylation of glycerol carbonate, which, in turn, is obtained from glycerol.9−12 Thus, a green atom-economical-route of the synthesis of propanolol glycol can be theorized by the epoxide ring opening of glycidol with 1-naphthol using heterogeneous catalysts. Magnesium sulfate has the potential to be used as a catalyst for this reaction, and it can be synthesized by different routes. We thought of synthesizing it from rice hull or husk, which is a major byproduct of paddy processing and it consists of ∼20% w/w of paddy produced. The Food and Agriculture Organisation estimates paddy production of 750.9 million tonnes in 2014,13 leading to a huge quantity of hull. The main constituents of rice hull are cellulose, pentosan, lignin, and silica, which can be used as a biosource of chemicals. Rice hull power plants have been built in the Indian subcontinent with the main objective to provide cheap, reliable, and sustainable © XXXX American Chemical Society

energy to rural masses. Rice hull ash (RHA) is generated upon combustion and is made of >80% silica. Particularly amorphous silica so produced is an excellent source for the preparation of pure silicon and other silicon compounds. This biogenic silica is a very good source for making silica gel,14 silica xerogel, silicate films, and sodium silicate.15 The ash is also used in green concrete,16 refractory,17 insulators,18 fire brick insulation,19 and the formation of activated carbon.20 The synthesis of magnesium silicate from silica found in RHA was used as a catalyst in this work, and its performance was compared with the chemically sourced one. The catalyst has been fully characterized and used for the synthesis of propanolol glycol from ring opening of glycidol with 1naphthol. Both the catalyst synthesis and its application to an atom-economical reaction are new results.

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EXPERIMENTAL SECTION Chemicals. Glycidol was obtained from Sigma-Aldrich Co. LLC. Methanol, magnesium nitrate hexahydrate [Mg(NO3)2· 6H2O], 1,4-dioxane, silica mesh, and 1-naphthol were obtained from M/s S.D. Fine Chemicals Pvt. Ltd., Mumbai, India. A sample of rice hull was obtained from Karnataka, India. All chemicals were of analytical reagent grade. Catalyst Preparation. A sufficient quantity of rice hull was burned in a muffle furnace at 600 °C for 4 h to obtain the ash (RHA), which contained 92.8% silica. A total of 100 cm3 of a 1 M aqueous NaOH solution was added to 5 g of ash in a 500 Special Issue: Doraiswami Ramkrishna Festschrift Received: January 26, 2015 Revised: March 6, 2015 Accepted: March 9, 2015

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DOI: 10.1021/acs.iecr.5b00364 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

NMR (400 MHz, DMSO): δ 8.24 (dd, J = 3.2 and 7.2 Hz, 1H), 7.86 (dd, J = 4.0 and 6.8 Hz, 1H), 7.54−7.38 (m, 4H), 6.95 (d, J = 7.2 Hz, 1H), 5.10 (d, J = 5.2 Hz, 1H), 4.74 (t, J = 5.6 Hz, 1H), 4.19−3.93 (m, 3H), 3.62−3.53 (m, 2H). 13C NMR (400 MHz, DMSO): δ 154.33, 134.11, 127.465, 126.51, 126.34, 125.20, 125.13, 121.94, 119.89, 105.13, 7.16, 69.82, 62.90.

cm3 round-bottomed flask and boiled under reflux condition for 2 h with constant stirring using an overhead stirrer. The resulting sodium silicate solution was filtered using ashless filter paper to make it free of carbonaceous matter, and the unwanted residue was washed with 10 cm3 of warm water. The filtrate was collected, cooled to room temperature, and added to the earlier-collected aqueous sodium silicate. A magnesium nitrate solution containing 16.0 g of Mg(NO3)2·6H2O in 50 cm3 of water was added to the above solution to precipitate white magnesium silicate at room temperature, which was filtered under vacuum and subsequently washed with distilled water followed by acetone. The white precipitate of magnesium silicate was dried at 110 °C for 3 h, then calcined in a muffle furnace at 600 °C for 4 h, and designated as MS-RHA. Magnesium silicate was also prepared from commercial silica mesh in a similar fashion and designated as MS-SM. Catalyst Characterization. Both MS-RHA and MS-SM were characterized by using a variety of techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS; JEOL model JSM 6380LA; 10 kV, counting rate 519 cps, energy range 0−20 keV), Brunauer− Emmett−Teller (BET) N2 adsorption (Micromeritics ASAP 2020), CO2 and NH3 temperature-programmed desorption (TPD) for surface basicity and acidity (Micromeritics model 2920), powder X-ray diffraction (XRD; Bruker AXS diffractometer model D8; Cu Kα1 radiation; λ = 1.540562), and NMR spectrometer (Mercury Plus 300 MHz, Varian, USA). Catalytic Reaction. Selective-ring-opening reaction of glycidol with 1-naphthol was conducted by using a pressure reactor (100 cm3 size; Hastelloy C from Amar Equipments Pvt. Ltd., Mumbai, India). The autoclave was provided with a 45° four-blade-pitched turbine impeller, a pressure indicator, a speed regulator, and PID-controlled electrical heating and cooling arrangements. Calculated quantities of glycidol (0.014 mol), 1-naphthol (0.007 mol), and 1,4- dioxane as the solvent (to make the total volume of the organic phase 25 cm3) and the catalyst (0.02 g/cm3 of liquid volume) were charged into the autoclave. The temperature was increased to 120 °C, an initial sample was taken out, and agitation was started thereafter at 1000 rpm. The conversion was calculated based on the limiting reactant 1-naphthol. Synthetic mixtures were prepared to make a calibration plot. Analytical Method. Clear liquid samples were collected at regular time intervals by reducing the speed of agitation to zero. Sample preparation was done manually in which 20 μL of the sample was diluted in a 2 mL standard volumetric flask followed by a makeup volume with the mobile phase of 1:1 (v/ v) acetonitrile/water. Analysis was performed by a highperformance liquid chromatograph provided with ChemStation software and an autosampler (Agilent Technology 1260 Infinity), a XDB C-18 column (Agilent Zorbax Eclipse; 250 × 4.6 mm, poetical size 5 μm) at room temperature, a column oven, and a UV−vis detector at 260 nm. A mobile phase of 1:1 (v/v) acetonitrile/water at a flow rate of 1 cm3/min was used with 15 μL injector volume adjusted by the autosampler. The products were confirmed through the retention time of the authentic samples and by 1H and 13C NMR spectroscopy. The conversions were based on the disappearance of 1-naphthol, the limiting reactant. Purification and isolation were achieved by column separation, and 3-(1-naphthyloxy)propane-1,2-diol was confirmed by 1H NMR (Mercury Plus 300 MHz, Varian, USA) in deuterated dimethyl sulfoxide (DMSO). 1H and 13C NMR spectra of 3-(1-naphthyloxy)propane-1,2-diol are as follows. 1H

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RESULTS AND DISCUSSION Catalyst Characterization. Powder XRD. The XRD patterns of both magnesium silicate samples MS-RHA and MS-RHA (reused), MS-SM, and silica were recorded (Figure 1). They are more or less identical and also amorphous in

Figure 1. Powder XRD patterns of (a) MS-RHA catalyst (virgin), (b) MS-SM, (c) MS-RHA catalyst (reused), and (d) SiO2: (○) cristobalite SiO2; (◇) cristobalite MgSiO3.

nature. The XRD patterns also confirmed that both samples have the structure of cristobalite SiO2 (JCPDS card 27-605) and MgSiO3 (JCPDS card 19-768). BET Surface Area and Pore Size Analysis. The BET N2 adsorption isotherm for MS-RHA is shown in Figure 2. The surface area and average pore size for MS-RHA (virgin), MSSM, and MS-RHA (reused) are presented in Table 1. MS-RHA has the largest surface area of 103 m2/g, in which the foremost part is contributed by pores with a diameter of 7.9 nm characteristic of the mesoporous region, whereas the MS-SM surface area is much lower at 52 m2/g with an average pore diameter of 16.6 nm. MS-RHA (virgin) and MS-RHA (reused) have almost the same pore-size distribution, which proved its fidelity during reaction. All three samples of synthetic magnesium silicate contained type IV or V with a small plateau at high relative pressure of the adsorption isotherms, which are characteristic of mesoporous materials. SEM and EDXS. Parts a and b of Figure 3 show images of MS-RHA (virgin) and MS-RHA (reused) catalysts, confirming that the fidelity of the catalyst was maintained during the reaction. Figure 3c of MS-SM shows that the samples are made of strongly agglomerated fine particles. Parts a−c of Figure 3 for MS-RHA (virgin), MS-RHA (reused), and MS-SM show average size particles of 5−20 μm of irregular morphology. EDXS confirmed the successful incorporation of the silica and magnesium ratio, which was kept constant during the preparation (Table 2). TPD. TPD with CO2 and NH3 respectively was used to measure the total basic and acidic nature of sites generated on the surface of a catalyst. Well-defined peaks were obtained at 150 and 450 °C, indicating the presence of intermediate and strong basic sites (Figure 4a,b). Single broad peaks were obtained at 150 °C, indicating the presence of intermediate and strong acidic sites (Figure 4c,d). TPD thermograms with CO2 B


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Figure 2. BET N2 isotherm plots for (a) MS-RHA (fresh), (b) MS-RHA (reused), and (c) MS-SM.

and NH3 for MS-RHA (virgin), MS-RHA (reused), and MSSM are presented in Table 3. Catalyst Activity. The catalytic activity of RHA-MS was compared with that of MS-SM under identical conditions at 100 °C (Figure 5) to observe that RHA-MS is a better catalyst because of the its high basic characteristics and surface area. The reusability of RHS-MS was also good. It gave 85% conversion of 1-naphthol with 91 ± 0.5% selectivity toward propanolol glycol. Hence, the effect of different parameters was studied using MS-RHS.

Table 1. Textural Characterization of Catalyst Samples catalyst

surface area (m2/g)

pore volume (cm3/g)

pore diameter (Å)

MS-RHA (virgin) MS-SM MS-RHA (reused)

103.48 52.01 106.56

0.206 0.217 0.210

79.58 166.0 84.85

C


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Figure 3. SEM images (magnification 1000×): (a) MS-RHA (virgin); (b) MS-RHA (reused); (c) average size 5−20 μm for MS-SM.

Table 2. Elemental Composition (EDAX) wt % catalysts element

MS-RHA (virgin)

MS-SM

MS-RHA (reuse)

Mg K Si K Ca K* Fe K*

48.76 49.10 1.47 0.67

15.75 84.25

49.81 48.90 1.29

Figure 4. TPD thermograms with NH3 for (a) MS-RHA (virgin) and (b) MS-RHA (reused) and with CO2 for (c) MS-RHA (virgin) and (d) MS-RHA (reused).

Table 3. TPD of the Catalysts Effect of the Speed of Agitation. The effect of the speed of agitation was studied at 100 °C for a catalyst loading of 0.02 g/ cm3 (Figure 6). There was no significant effect of the speed of agitation at 1000 and 1200 rpm on the conversion and rate, confirming the absence of external mass-transfer resistance beyond 1000 rpm. The reaction was highly selective. The main product was 3-(1-naphthyloxy)propane-1,2-diol (propanolol glycol; Scheme 1). Only after prolonged times was a second product, 2-(1-naphthyloxy)propane-1,3-diol, formed. For this reason, further studies were carried out at 1000 rpm. Effect of the Catalyst Loading. The catalyst loading was studied from 0.01 to 0.03 g/cm3 (Figure 7a). The conversion of 1-naphthol proportionately increased with increasing catalyst loading. The initial rate of reaction was directly proportional to the catalyst loading (Figure 7b). An increase in the catalyst loading results in a proportional increase in the active sites, which helps to increase the rate of reaction and the conversion of 1-naphthol. Effect of the Mole Ratio. The mole ratio of 1-naphthol to glycidol was studied at 1:1, 1:2, and 1:3 with 1,4-dioxane as the solvent. The amount of 1-naphthol was kept constant, and changes in the amount of glycidol were made according to the mole ratio, with the final liquid phase volume of 25 mL made up by 1,4-dioxane as the solvent. The overall reaction rate of 1naphthol increased with an increase in the moles of glycidol

catalyst

TPD with CO2 (mmol/g)

TPD with NH3 (mmol/g)

MS-RHA (virgin) MS-SM MS-RHA (reused)

0.507 0.486 0.519

0.29 0.35 0.31

due to an increase in the concentration of 1-naphthol (Figure 8). Effect of the Temperature. The effect of temperature was studied at 100, 120, and 140 °C (Figure 9) to determine that the temperature had a pronounced effect on the conversion and rate, indicating a kinetically controlled mechanism, which will be discussed later. Reusability of the Catalyst. After each experiment, the catalyst was filtered and washed with 15 cm3 of 1,4-dioxane and then dried at 120 °C. It was also calcined at 600 °C for 3 h. On average, there was attrition of particles during intense agitation and some loss of catalyst during filtration. The lost catalyst was made up of fresh catalyst, and the activity was tested to demonstrate that the catalyst was stable and retained its activity for four uses and there was no change in selectivity (Table 4). Reaction Mechanism and Kinetic Model. Because the catalyst had acidic (S1) and basic (S2) sites, a mechanism was proposed. Glycidol (B) and 1-naphthol (A) are adsorbed on sites S1 and S2, respectively. The ring opens on site S1, leading to the a carbocation that is attacked by 1-naphthol on adjacent D


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Figure 5. Catalytic activity on conversion of 1-naphthol [catalyst loading, 0.02 g/cm3; temperature, 100 °C; 1-naphthol 0/007 mol; glycidol, 0.014 mol; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm]: MS-MS (green ▲); RHA-MS (blue ◆); reused RHA-MS (red ■).

Figure 7. (a) Effect of the catalysis loading on the conversion of 1naphthol [catalyst, MS-RHA; temperature, 100 °C; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm]: 0.01 g/cm3 (blue ◆); 0.02 g/cm3 (red ■); 0.03 g/cm3 (green ▲). (b) Plot of the initial rate versus catalyst loading [catalyst, MS-RHA; temperature, 100 °C; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm].

Figure 6. Effect of the speed of agitation on the conversion of 1naphthol [catalyst loading, 0.02 g/cm3; catalyst, MS-RHA; temperature, 100 °C; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; mole ratio, 1:2; solvent, dioxane (makeup volume 25 mL)]: 800 rpm (blue ◆); 1000 rpm (red ■); 1200 rpm (green ▲).

to fit the data well. The Langmuir−Hinshelwood−Hougen− Watson model was found to be appropriate. The adsorption of 1-naphthol (A) on the vacant site S2 is given by KA

site S2, followed by intermolecular rearrangement, leading to formation of the product (Scheme 2). The mechanism is selfexplanatory. When both external mass-transfer and intraparticle diffusion resistances are absent, it is possible to develop a kinetic model. Several models were explored, and the following was observed

A + S2 ↔ AS2

(a)

Similarly, the adsorption of glycidol (B) on the vacant site is presented by KB

B + S1 ↔ BS1

(b)

Scheme 1. Reaction of 1-Naphthol with Glycidol

E


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Industrial & Engineering Chemistry Research K2

AS2 + BS1 ↔ DS1 + S2

(c)

The desorption of DS1 is given by 1/ KD

DS1 ←→ ⎯ D + S1

(d)

The total concentration of the sites, Ct, is expressed as C t = C t1 + C t 2 = CS1 + C BS1 + C DS1 + CS2 + CAS2

(1)

The concentration of the vacant sites is CS2 = C t 2 /(1 + KACA )

(2)

CS1 = C t1/(1 + KBC B + KDC D)

(3)

If the surface reaction controls the rate of reaction, then the rate of reaction of A is given by Figure 8. Effect of the mole ratio on the conversion of 1-naphthol [catalyst, MS-RHA; catalyst loading, 0.02 g/cm3; temperature, 100 °C; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm]: mole ratio 1:1 (green ▲); mole ratio 1:2 (blue ◆); mole ratio 1:3 (red ■).

−dCA = k 2CAS2C BS1 − k 2′C DS1CS2 dt

(4)

dCA = k 2KAKBCAC BCS1CS2 − k 2′KDC DCS1CS2 dt

(5)

−rA =

−

From eq 3: −

dCA = C t1C t 2(k 2KAKBCAC B − k 2′KDC D) dt /[(1 + KACA )(1 + KBC B + KDC D)]

(6)

With surface reaction as the rate-determining step and very weak adsorption: −

dCA = C t1C t 2(k 2KAKBCAC B) dt

(7)

−

dCA = k′wCAC B dt

(8)

where k′w = C t1C t 2k 2KAKB

(9) 3

w is the catalyst loading in g/cm . Let CB0/CA0 = M. The molar ratio of 1-naphthol to glycidol is at t = 0. Then, eq 8 can be written in terms of fractional conversion as dXA = k′wCA0(1 − XA )(M − XA ) dt

Figure 9. Effect of the temperature on the conversion of 1-naphthol [catalyst, MS-RHA; catalyst loading, 0.02 g/cm3; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; mole ratio, 1:2; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm]: 100 °C (blue ◆); 120 °C (red ■); 140 °C (green ▲).

This upon integration leads to

Table 4. Reusability of the MS-RHA Catalysta catalyst use

conversion (%)

selectivity (%)

virgin first use second use third use

85.2 83.65 82.9 80.63

91.26 90.26 92.23 89.9

(10)

ln[(M − XA )/M(1 − XA )] = k′wCA0t

(11)

ln[(M − XA )/M(1 − XA )] = k1t

(12)

where k′wCA0 = k1 is a pseudo constant. The mole ratio was 1:2 and the conversions of the limiting reactant 1-naphthol were 62, 80, and 88% at 100, 120, and 140 °C after 3 h, which showed that there was no thermodynamic equilibrium. The experiments were repeated three times, and the mean values were used. Analysis was done using Polymath to find that the adsorption was weak and thus the terms in the denominator were closer to unity without loss of accuracy. As the temperature was increased, adsorption constants were reduced. Thus, a power law model was used. There was no deactivation because the catalyst was found to be reusable. To validate the above mechanism, plots were made in consonance with eq 12 at different temperatures to fit the data very well

a Conditions: catalyst loading, 0.02 g/cm3; catalyst, MS-RHA; temperature, 100 °C; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; mole ratio, 1:2; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm.

The surface reaction of AS2 with BS1, in the vicinity of the site, leads to the formation of 3-(1-naphthyloxy)propane-1,2diol (DS1) on the site. F


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(Figure 10). These are straight lines passing through the origin, which confirms the second-order behavior of the reaction. The

Figure 11. Arrhenius plot for the reaction of glycidol with 1-naphthol.

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CONCLUSION An atom-economical process was developed for the synthesis of propanolol glycol from glycidol and 1-naphthol using magnesium silicate as the catalyst. The catalyst was successfully produced by combusting a biogenic silica source material such as rice hull to give RHA. It was characterized to find that both acidic and basic sites were generated. The effect of various parameters on the rate of reaction was studied systematically to establish the kinetics of reaction. The reaction follows secondorder kinetics at a fixed catalyst loading with an apparent activation energy of 30.66 kcal/mol. The maximum conversion obtained at optimum reaction parameters was 85% of 1naphthol in 3 h with 90% selectivity toward 3-(1-naphthyloxy)propane-1,2-diol.

Figure 10. Second-order reaction kinetic plots at different temperatures [catalyst, MS-RHA; catalyst loading, 0.02 g/cm3; 1-naphthol, 0.007 mol; glycidol, 0.014 mol; solvent, dioxane (makeup volume 25 mL); speed of agitation, 1000 rpm]: 100 °C (blue ◆); 120 °C (red ■); 140 °C (green ▲).

slopes of these lines at different temperatures were used to make the Arrhenius plot (Figure 11). The apparent activation energy was found to be 30.66 kJ/ mol. There was no mass-transfer resistance, as revealed by the speed of agitation study, and the Wiesz−Prater modulus was also calculated, as discussed elsewhere,21−23 to find that it was 0.034, which is far less than unity, confirming that the reaction rate is controlled by intrinsic kinetics. G


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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +91-22-3361-1001/ 1111/2222. Fax:+91-22-3361-1020/1002. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS G.D.Y. acknowledges support from the R. T. Mody Distinguished Professor Endowment and J. C. Bose National Fellowship from DST-GOI. G.P.F. acknowledges the University Grants Commission for awarding the Senior Research Fellowship under its Green Technology Basic Sciences Research meritorious fellowship program.

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DEDICATION This paper is dedicated to Professor D. Ramkrishna of Purdue University, who has been a great friend of G.D.Y. and a wellwisher of his Alma Mater, the Institute of Chemical Technology in Mumbai. His accomplishments over the years in both India and the U.S. are phenomenal.

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ABBREVIATIONS A = reactant species A, 1-naphthol B = reactant species B, glycidol CA = concentration of A, 1-naphthol (mol/cm3) CA0 = initial concentration of A in the bulk liquid phase (mol/cm3) CAS2 = concentration of adsorbed A on active sites of type S2 (mol/g-cat) CB = concentration of B (mol/cm3) CBo = initial concentration of B in the bulk liquid phase (mol/cm3) CBS1 = concentration of adsorbed B on active sites of type S1 (mol/g-cat) CD = concentration of D, propanolol glycol (mol/cm3) CDS1 = concentration of adsorbed D on active sites of type S1 (mol/g-cat) CS1 = concentration of vacant sites of type S1 (mol/g-cat) CS2 = concentration of vacant sites of type S2 (mol/g-cat) Ct1 = total concentration of vacant sites of type S1 (mol/gcat) Ct2 = total concentration of vacant sites of type S2 (mol/gcat) D = product species D, propanolol glycol (mol/cm3) KA = adsorption equilibrium constant for A (cm3/mol) KB = adsorption equilibrium constant for B (cm3/mol) KD = adsorption equilibrium constant for D (cm3/mol) M = molar ratio of CB0/CA0 rA = rate of reaction (mol/cm3·s) w = catalyst loading (g/cm3) XA = fractional conversion of A t = time (s)

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REFERENCES

(1) Singhal, S.; Jain, S. Mild organic ammonium tribromide-mediated regioselective ring opening of epoxides with alcohols, water, acetic anhydride, and amines under solvent-free reaction conditions. Synth. Commun. 2012, 41 (12), 1829−1837. (2) Habib, F.; Nasser, I.; Ali, J.; Somayeh, M. Aluminum dodecatungstophosphate (AlPW12O40) as a reusable Lewis acid catalyst. Facile regioselective ring opening of epoxides with alcohols, H


Atom-Economical Selective-Ring-Opening Reaction of Glycidol with 1

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