Clay catalysed rapid valorization of glycerol towards cyclic acetals and ketals

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Clay catalysed rapid valorization of glycerol towards cyclic acetals

and ketals

Radheshyam R. Pawar^a,b, Kalpeshgiri A. Gosai^a, Adarsh S. Bhatt^a, S. Kumaresan^a,

Seung Mok Lee^*band Hari C. Bajaj^*a

Biodiesel production usually results in a huge amount of glycerol, raising a critical need to transform it into high added

value products. The present study highlights that solvent-free, conventional thermal activation, and non-conventional

microwave/ultrasonic activation in the liquid phase are able to selectively transform glycerol into cyclic acetals and ketals

using an optimised acid activated clay catalyst. Several parameters for the acid activation of bentonite clay were optimized

under mild reaction conditions with a high concentration of clay (6%) and varying the acid concentration in the range of 6

to 15N. The alteration features of acid-activated clay were characterized by XRD, FT-IR, BET, and XRF analysis. The active

sites of the catalyst were examined by volumetric titration and confirmed by pyridine adsorbed FT-IR and advanced NH₃-

TPD analyses. The activation performed at relatively mild conditions, i.e.; 6N H₂SO₄and 6% w/v clay, reproducibly resulted

in an improved surface area (180 m²g⁻¹) and surface acidity (23 mg KOH g⁻¹), with superior quantitative Brönsted and

Lewis acidic sites. Moreover, the eco-friendly process involving a catalyst, microwave, or ultra-sonication were successfully

utilized to achieve commercially valuable hyacinth fragrance, in addition to furan-based fuel additive precursors exhibiting

high conversion of glycerol and excellent selectivity within very less activation time (2 minute).

Received 00th January 20xx,

Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

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oxidation stability and flash point.¹³Traditionally, Brönsted

acids such as HCl, H₃PO₄, and p-toluenesulfonic acid (PTSA)

Introduction

The requirement of biofuels is continuously growing due to

diminishing fossil fuel reserves.^{1, 2}Biodiesel is one of the most

promising and feasible alternatives among the unconventional

sources of energy, however, biodiesel production results in a

have been employed for the acetalization of glycerol in

hazardous organic solvents to improve the conversion of

glycerol.⁶However, such protocols poses

a

serious

huge quantity of glycerol ³

. Global biodiesel production is

environmental concerns and thus improved catalytic processes

are highly desirable wherein the use of expensive and toxic

reagents, tedious work-up procedures, and the generation of

estimated to yield _~4 billion gallons of glycerol by 2016.⁴

Therefore, it is essential to develop viable methods to dispense

or utilize the anticipated large quantity of glycerol, in order to

add value to the biodiesel production chain.⁵These motives

have triggered rigorous research in recent years with a view to

finding applications for cheap and off grade glycerol by

catalytic conversion processes including hydrogenolysis,

oxidation, dehydration, polymerization, steam reforming,

etherification, esterification, cyclization and acetalization.^6-10In

fact, glycerol derivatives such as acetal, ketal, ether, and ester

large amounts of waste is avoided.²

A variety of

15

heterogeneous catalysts such as ion exchange resins,^14,

zeolites,¹⁶silica supported heteropoly acids,¹⁷acid

functionalized carbon/silica,¹⁸supported activated carbon, and

19, 20

metal oxides,

acidic ionic liquids,²¹Mg-Al-LDH as base

catalyst²²have been studied as catalyst for the acetalization of

glycerol.

The modified clay minerals and their derivatives are a class of

heterogeneous solid acid catalysts that has received

considerable interest in diverse areas of organic synthesis due

to their environmental compatibility, reusability, high

selectivity, operational ease, non-corrosivenes, in addition

their large availability in nature^{23, 24}. One of the most common

modifications of smectite clays is the treatment with mineral

acid, usually HCl or H₂SO₄, resulting in the delamination of the

clay structure.²⁵A number of metal ions in the octahedral layer

and impurities such as calcite are removed by leaching with an

inorganic acid at elevated temperatures. In addition, the edges

find applications in the cosmetic, plastic, pharmaceutical,

detergent, fuel additive and fine chemical industries ^11,

12

.

Particularly, acetalization of glycerol with furfural and its

derivatives produces 1, 3-dioxalane and 1, 3-dioxane are used

as fuel additives. These products enhance the viscosity and

cold properties of biodiesel, in addition to improving the

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of the platelets are opened, and as a result, the pore

diameters and surface area of the clay is increased.²⁶Acid

activation promotes catalytic activity by increasing the number

of Brönsted and Lewis acid sites.²⁵The effect of acid

concentration, time, and temperature during acid treatment

on the surface acidity and physicochemical properties of the

obtained clays have been well documented.²⁷However, there

has been little information on the systematic efforts to

Catalyst synthesis

Acid activation experiments were performed using a clay

concentration of 6% (w/v), optimized by varying the clay

concentration in the range of 4 to 6 % under optimized

activation conditions. Moreover a clay concentration beyond

6% (w/v) resulted in unsuitable mixing of the acid and clay due

to swelling and the high viscous nature of the clay slurry.

Hence, in order to achieve a homogenous mixture, a clay

develop an optimized acid activation protocol under mild concentration of 6% (w/v) was used. The acid concentration

was varied in the range of 6 to 15N. In detail experiments,

precisely 60 g of purified clay was treated with a calculated

synthetic conditions with a high clay content to prepare clay

catalyst in bulk. Numerous approaches have been employed to

address the application of non-traditional activation methods

such as microwave irradiation, sonochemistry, and solvent-

free transformations for green organic syntheses.²⁸The

combined applications of heterogeneous catalysis with

microwave or ultrasonic activation is a proficient and swift

route to carry out chemical transformations, and becoming a

widely accepted non-conventional protocol for organic

synthesis.²⁹The significant decrease in reaction time and the

direct energy transformation via a solid catalyst is the unique

amount of sulphuric acid, at 65°C for 10 hours. After

completion of the reaction, the solid product was separated by

centrifugation (Kubota 6500 centrifuge) and washed with

deionized water. The washing cycle was repeated until the

solid product was free from sulphate ions (BaCl₂test), and the

sample was subsequently dried at 110°C overnight. The solid

activated product was ground by passing through a 100 Mesh

BSS sieve. The obtained products were designated as

N/BBnU/C, where N is the normality of sulphuric acid used for

each experiment, and

C is the percentage w/v clay

combination

microwave/ultrasonic irradiation that would also be more

energy efficient than its conventionally-heated counterparts ³⁰

of

heterogeneous

catalysis

and

concentration in the reaction mixture.

Physical measurements

.

The powder X-ray diffraction analysis was carried out with the

In continuation of our efforts towards the rapid valorisation of

glycerol to value added acetals and ketals³¹herein we report

the microwave- and ultrasonic-assisted catalytic protocol for

the conversion of glycerol to value added acetals and ketals.

Moreover, we have successfully utilized this sustainable and

green protocol to achieve a commercially valuable hyacinth

fragrance, in addition to furan-based fuel additive precursors

in high glycerol conversion and selectivity.

Philips X pert MPD system in a 2θ range of 2–70°using Cu Kα

(l= 1.54178Å) radiation. Nitrogen adsorption/desorption

measurements for the evaluation of textural properties

(surface area, total pore volume, and pore size distribution)

were performed at 77 K using ASAP 2010, a surface area

analyser, (Micrometrics USA). Prior to measurements, the

samples were degassed at 423 K for 4 hours to remove any

residual moisture. The BET specific surface areas were

calculated from adsorption data in the relative pressure (P/P₀).

Pore size and pore volume were calculated using the BJH

method applied to the desorption leg of the isotherms. The

FTIR spectroscopic measurements and diffuse reflectance FTIR

(DRIFT) measurements were carried out using a Perkin Elmer

GX spectrophotometer. Chemical analysis of the samples was

carried out by X-ray fluorescence (XRF), using an S4 pioneer

Bruker AXS XRF analyser. Bulk density measurement

experiments were performed on the electro tab density tester

Experimental

Materials

The clay mineral bentonite was collected from bentonite

mines in the Banskantha district of Gujarat, India.

Approximately 500 g raw bentonite lumps, after hot air drying,

was grind in a mixer and passed through a 100 Mesh BSS sieve.

The obtained sample was designated as BBnR (Banaskantha

Bentonite Raw). The raw bentonite lumps were purified by

sedimentation techniques, dried, grind, and passed through a

100 Mesh BSS sieve. This sample was designated as BBnU,

(Banaskantha Bentonite Upgraded); (S1 and Table S1). K10-

Montmorillonite acid-activated clay, p-toluenesulphonic acid

monohydrate (PTSA), Amberlyst 15 hydrogen form of acidic

cation exchange, and fullers earth were obtained from Sigma

Aldrich.

1

(USP). H and ¹³C NMR spectra were recorded on a Bruker AX

200 MHz spectrometer at ambient temperature using TMS as

an internal standard and CDCl₃as a solvent. The reaction

products were analysed using a gas chromatograph (Varian,

GC–450), equipped with a Factor 4 capillary column (30 m long

and 0.32 mm internal diameter) employed with a flame

ionization detector. The oven temperature varied from 80 to

240°C, programmed at the ramp rate of 10°C min⁻¹. The GC

oven was programmed in the temperature range of 40–200°C

with helium as a carrier gas and the MS was programmed in EI

mode with a 70 eV ion source. The calibration of the GC peak

areas was carried out by taking solutions of known

compositions with n-hexadecane as an internal standard.

Chemicals

All the reagents, viz concentrated H₂SO₄98%, glycerol,

aldehydes, ketones, solvents, and other chemicals used for the

experiments were of analytical reagent (A.R.) grade and were

obtained from Merck, SD Fine, and Spectrochem. All the

chemicals were used without further purification.

Product identiﬁcation was performed using

a

gas

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chromatograph mass spectrometer (Shimadzu GCMS-QP-2010, reaction mixture by centrifugation and then assignment of the

products was confirmed by GC-MS and also by ¹H and ¹³C NMR

recorded in CDCl₃at 200 MHz (S4).

Japan) equipped with a RTX-5 fused silica capillary column.

Acidity measurements

The reaction performances were studied with respect to the

conversion of aldehydes or ketones. The conversion and

selectivity of the desired components were analysed by gas

chromatography analysis (GC) with n-hexadecane used as an

internal standard (IS). The calibration of the GC peak areas was

carried out by taking standard solutions of known

compositions with n-hexadecane as an internal standard. The

conversion and selectivity were calculated as per the formulas

(i) and (ii), respectively. (S3).

pH and Titratable acidity

Acidity of the acid-activated clay was measured with pH

measurement (Toshniwal pH meter at 30°C) by suspending 2.5

g clay in 25 ml distilled water (Table 1). Moreover, the acid

activated clay has an acidity resulting from adsorbed sulphuric

acid and aluminium sulphate. This acidity is determined by the

so-called “boil-out” titration method. The acidity expressed in

milligrams of KOH per gram of sample and is usually termed as

“acidity”. For preparing the effective catalysts, all acid

activation conditions (i.e. effect of clay concentration, acid

concentration, effect of activation temperature and time etc.)

were optimized on the basis of “titratable acidity”(S2.1).

{C_i- C_f}_(substrate)

% Conversion_(substrate)

=

X 100

i

{C_i}_substrate

Ammonia TPD and pyridine FT-IR study

NH₃-temperature programmed desorption experiments

were performed by using Auto-Chem 2910 instrument of

Micromeritics. Exactly 200 mg of the catalyst was placed in a

quartz tube and degassed at 423 K under the flow of helium.

Then the ammonia gas was passed through the catalyst

surface for 30 min and subsequently flushed with helium to

remove the physisorbed gases. Then, the chemisorbed amount

of NH₃was determined in flowing helium gas with a flow rate

of 20 mL min⁻¹from 323 to 873 K at a heating rate of 10 K

min⁻¹.

{C_f}_(product)

% Selectivity_(product)

=

ii

{C_i- C_f}_(substrate)

where C_iand C_fare the initial and final concentrations of the

respective species in the reaction mixture.

Acetalization of glycerol by Non-conventional heating

Pyridine, a weak base is adsorbed on the clay surface through

acid-base interactions. Pyridine is adsorbed on the Bronsted

acid sites generated by the exchange of interlamellar cations

with protons and A1³⁺present in octahedral sheet. For the

FTIR analysis of adsorbed pyridine, samples were oven dried at

The microwave assisted synthetic manipulations were

conducted using SINEO M-II microwave in a 25 ml RB flask

synthesis assembly with variable MW frequency and

temperature provision. The ultrasonic radiation assisted

synthetic manipulations were conducted on Hielscher

ultrasonic processor UP400S (Synthesis assembly with

sonotrode H₃, variable frequency and adjustable pulse). Each

set of reactions is treated under controlled sonication

parameters by keeping 100 % amplitude and continuous

probing. The typical acetalization reactions were carried out

with a neat mixture of glycerol and aldehyde or ketones in

presence of 50 mg catalyst and without solvent for pre-set

time as required to complete the reaction. The conversion and

selectivity were calculated as per the formulas (i) and (ii),

respectively.

373 K for 3 h. The oven dried sample (∼0.2 g), in a sample cup,

was exposed to pyridine vapours in vacuum desiccators with

25 ml of dry pyridine. The sample cup was then kept in vacuum

for 4 h, subsequently; the samples were evacuated for 30 min

at room temperature to desorb physisorbed pyridine and FTIR

spectrum was recorded in the spectral range of 1200–1900

cm⁻¹using a KBr disc.

Acetalization of glycerol

The catalytic performance of the synthesized catalyst was

investigated for the acetalization of glycerol with aldehydes

and ketones. In order to optimize the reaction conditions, the

reaction of glycerol with cyclohexanone, which yields two

isomeric products namely, 1, 3-dioxalane and 1, 3-dioxane,

Results and Discussion

In the variation study of acid activation experimental

conditions, It was observed that under mild acid activation

conditions i.e., 6 to 8N, surface acidity was found to be in the

range of 23 to 25 mg KOH g^-1whereas, in case of higher

concentration (12 N and 15 N) a sudden decrease in surface

acidity occurred 14 and 12 mg KOH g^-1respectively. Moreover,

the % weight loss was found to be higher at harsh acid

activation conditions (12 N and 15 N). Further alteration

features of acid-activated clay were characterized by various

physiochemical techniques (Table 1).

was studied as

a model reaction. Typically, 1.0 g

cyclohexanone and 0.93-2.79 g glycerol (varied reactant ratio)

were fed to the reaction vessel along with 50 mg pre-activated

catalyst (5% w/w to cyclohexanone) for each catalytic run. The

reaction mixture was heated to the desired reaction

temperature (27–60°C) for 0.5–19 hours. All experiments were

carried out under vigorous stirring (700 rpm) to achieve a

homogeneous mixture of glycerol and cyclohexanone. On

completion of the reaction, catalyst was separated from the

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Table 1. Effect of acid activation conditions on the properties of bentonite clay, with

an activation temperature 65^oC, a reaction time of 10 hours, and a batch size of 60 g for

each experiment.

in the clay material due to acid treatment were also studied

using X-ray diffraction (Fig. 1.). Generally, after acid activation,

the ‘001’ reflection appeared broad and weak due to the

partial destruction of the layered structure of the smectite.

The reduction in intensity and increase in width of the ‘001’

peak indicates that the crystallinity of the ‘BBnU’ was

considerably affected by acid activation. If the activation is

conducted under harsh acidic conditions, the ‘001’ reflection

would completely disappear, with the process favouring the

production of the amorphous phase by decomposing of the

clay structure. The acid treatment used for the synthesis of

6/BBnU/6 and its activation process did not damage the

inherent layered structure of bentonite. Here this can assume

that the structure has been partially destroyed. The balance

between acid treatment and structural preservation hold the

key for the establishment of optimal catalytic parameters (Fig.

1.). An increase in acid concentration to 8N (H₂SO₄) showed

slight reduction in the peak intensity of the ‘001’ plane,

indicating the stacking disorder of the layers. Further

increments in acid concentration of 12-15 N H₂SO₄resulted in

even broader ‘001’ reflection peaks than that of activated

samples synthesized under mild conditions. However the ‘020’

and ‘060’peaks of ‘BBnU’ remained unchanged by 12-15 N

H₂SO₄acid activation.

Samples

Properties

BBnR BBnU 6/BBnU/6 8/BBnU/6 12/BBnU/6 15/BBnU/6

Acid conc (N) ---

---

6

8

12

15

Acid:clay¹

SA²(m²/g)

APD³(nm)

Vt⁴(cc/g)

pH⁵

---

1

1.33

209

5.5

0.29

2.56

25

2

2.50

308

6.2

87

5.1

74

5.2

180

5.2

302

6.5

0.5

2.81

14

0.11 0.11 0.23

7.53 7.16 2.70

0.48

3.06

12

Acidity⁶

---

23

20

% Wt. Loss

24

38

50

¹Normality of acid/% concentration of clay in suspension (w/v); ²BET surface area

(m²/g); ³Average pore diameter (nm); ⁴Total pore volume (cc/g); ⁵pH of the clay

suspension (2.5 g of clay in 25 ml distilled water) measured via a toshniwal pH

meter with 1% w/v clay at 30ºC. ⁶Surface acidity mg KOH g⁻¹of the clay

XRF analysis for chemical composition

The XRF analysis was carried out to determine the chemical

compositions of the clay and the subsequent chemical changes

that occurred due to acid treatment. Table 2 shows the results

of the chemical analysis of the purified and acid-activated

bentonite samples. The BBnU clay contained SiO₂, Al₂O₃, and

Fe₂O₃in major quantities, whereas other oxides such as MgO,

CaO, Na₂O, K₂O, and TiO₂were present in trace amounts.

During the acid treatment, it was observed that the

composition of the parent clay changed considerably. As the

strength of the acid increased, the amount of Fe₂O₃, Al₂O₃,

MgO, CaO, K₂O and Na₂O in the acid-treated material

decreased progressively.³²

Table 2. Effect of acid activation conditions on chemical composition of activated

bentonite clay.

% wt. oxide

Na₂O

MgO

Al₂O₃

SiO₂

BBnU

0.75

1.63

17.2

49.5

0.84

0.60

3.07

9.78

16.6

6/BBnU/6

0.07

8/BBnU/6

0.04

12/BBnU/6

----

15/BBnU/6

----

1.02

0.87

0.38

0.52

16.98

50.46

0.69

16.01

55.32

0.53

11.15

63.03

0.26

11.54

71.01

0.15

K₂O

CaO

0.07

0.06

0.03

0.06

TiO₂

3.10

3.22

3.58

1.28

Fe₂O₃

LOI

10.0

6.82

3.47

1.07

Fig. 1. Powder X-ray diffraction patterns of [A]: BBnR, [B]: BBnU, [C]: 6/BBnU/6, [D]:

8/BBnU/6, [E]: 12/BBnU/6, [F]: 15/BBnU/6. Where, M: Montmorillonite, Q: Quartz, A:

Anatase.

17.85

17.13

18.11

14.77

Total

100

Infrared spectroscopic studies

X-ray diffraction studies

The spectra of original, purified bentonite and the samples

treated with 6-15 N H₂SO₄acid concentrations are shown in

Fig. S1. The spectrum of the original clay exhibits absorption

bands at 3441 and 1636 cm^-1assigned to the stretching and

bending vibrations of the OH groups of the water adsorbed on

the clay surface, and a band at 3617 cm^-1representing the

stretching vibration of the OH groups coordinated to

octahedral Al³⁺cations. The Si–O bands are strongly evident in

the silicate structure of the original clay, and can be easily

recognized in the infrared spectrum as very strong absorption

bands in the 1100–1000 cm^-1region. The most intensive band

Powder X-ray diffraction (XRD) is one of the primary

techniques used for tracking changes in the layer spacing of

clay minerals. The strong basal reflection around 2θ = 5.97° is a

common characteristic of calcium bentonite.³³Powder X-ray

diffraction patterns of bentonite samples from Banaskantha,

before and after up gradation (BBnR and BBnU), were

compared (Fig. 1 A and Fig 1 B). In beneficiated samples, the

removal of the non-clay matter is reflected in the XRD patterns

by the decrease in the intensities of the characteristic peaks of

quartz after up gradation. The structural changes that occurred

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at 1039 cm^-1is attributed to Si–O in plane stretching and the

band at 1127 cm^-1is due to Si–O out of plane stretching

vibration. The bands at 537 and 474 cm^-1correspond to Si–O–

Al (octahedral) and Si–O–Si bending vibrations, respectively.

The FTIR spectrum of raw clay depicts a band at 794 cm^-1

attributed to cristobalite phase. The treatment of bentonite

with 12 and 15 N H₂SO₄acid resulted in the formation of

amorphous silica, which complements the data obtained from

PXRD. The intensity of the absorption bands at 907 cm^-1

decrease due to leaching and partial depletion of Al, Mg, and

Fe from the clay structure, in accordance with the changes in

chemical composition. The intensity of the bands at 3441 and

1636 cm^-1for water of hydration and the hydroxyl stretching

band at 3617 cm^-1also show a significant decrease after acid

activation. However, the persistence of a weak band at 1039

cm^-1indicates that the layered structure of the original clay is

not fully destroyed, which is in agreement with the XRD

results. The progressive widening of the 1039 cm⁻¹bands,

together with the increase in intensity of the 795 cm⁻¹band

(tridymite), indicates the formation of amorphous silica.³⁴In

conclusion, an IR spectrum of activated clays indicates that

acid leaching affects both the octahedral and the tetrahedral

sheets.^{35, 36}

of interlayer water molecules coordinated to the exchangeable

cations.²⁷The total acidity of various clays samples by pH

measurements on aqueous clay suspensions (Table 1) shows

that acidity increases from ‘BBnU’ (pH 7.16) to 6BBnU6 (pH 2.70)

after which it shows a decreasing trend for the acid treated samples

under harsh conditions

The NH₃TPD patterns for acid activated samples and

desorption peak areas are shown in Fig. 2 and Table S2. The

relative position of the peak maxima (Fig 2) is an evidence of

the magnitude of the ammonia desorption activation energy,

which indicates the relative strength of the acidic sites.²It can

be noted from NH₃-TPD study that the harshness in acid

activation conditions decreases the acidic strength as well as

its concentration. The total peak area due to ammonia in

ammonia TPD plot (concentration for amount of acidic sites)

was found to be ~3.15, 2.57, 1.44 and 1.33% for the 6/BBnU/6,

8/BBnU/6, 12/BBnU/6 and 15/BBnU/6 respectively (Fig.2 and

Table S2).

0.55

0.50

0.45

6/BBnU/6

0.40

Textural properties

0.35

0.30

0.25

0.20

0.15

8/BBnU/6

12/BBnU/6

15/BBnU/6

The N₂adsorption and desorption isotherms of the raw,

purified and acid-activated clay samples are presented in Fig.

S2. The isotherms of these samples are of type IV according to

the IUPAC classification.³⁷The hysteresis loop indicated the

presence of the slit pores with the capillary condensation of

39

The most important

liquid nitrogen on its mesopores.^38,

100

200

300

400

500

600

textural change in acid-activated clays was an increase in the

specific surface area (SA) and the pore volume (PV) due to

splitting of particles within the leached octahedral sheets. The

extent of these changes depended on the activation conditions

such as acid strength, temperature, and length of the

treatment. The textural properties of the samples before and

after acid treatment are given along with upgraded bentonite

in Table 1. An approximate 2.4 times increase in SA and a 2

time increase in PV was observed after treatment with 6 N

H₂SO₄acid. When the acid concentration was increased to 15

N, SA and PV of the treated sample increased by 3.5 and 4.5

times, respectively, indicating the formation of amorphous

silica with high SA and PV. The BJH pore diameter and average

pore diameter of all the acid-activated samples were almost

similar, indicating the narrow pore size distribution. Similar

trends in the textural change results have been observed in

previous reports.^{27, 32}

Temperature (°C)

Fig.2. NH₃TPD profiles of the acid-activated bentonite samples

The activated sample, 6/BBnU/6 shows the highest acidity

among all other samples considered for this study which

indicates presence of maximum number of acidic sites on it.

The result corroborates well with those obtained from

volumetric titration experiments. Moreover, the observed

difference between acidic properties of 6/BBnU/6 and

8/BBnU/6 indicated by KOH titration and TPD experiments is

worth mentioning. Since the KOH treatment of clay samples

involve ‘boil-out’ titration which employs rather drastic

conditions than the TPD experiment. It is inferred that during

KOH titration 8/BBnU/6 sample exfoliate and leach metal ions

from octahedral sites are responsible for observed acidity.

However, TPD being more sophisticated technique render

acidic properties more precisely. This observation and

inference also helped us to screen and chose the superior

catalyst among all, i.e., 6/BBnU/6.

Acidity measurements

The total acidity of activated clays is higher than that of the

pristine bentonite sample because of the replacement of

exchangeable cations with protons. The acidic properties of

bentonite also originated from the presence of (1) terminal

hydroxyl groups, (2) bridging oxygen, and (3) the dissociation

Fig. S3 shows the IR spectra recorded after pyridine adsorption

on acid-activated clay samples and unmodified BBnU. The IR

spectra of 6/BBnU/6 exhibit prominent vibration bands at

1638, 1543, 1491, and 1443 cm^-1. The bands at 1545-48 cm^-1

were assigned to Brönsted pyridine sites; however, those at

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1445-47 and 1600 cm^-1are due to hydrogen bonding between and low intesity peak with retention time 9.01 min for (1,5-

the pyridine nitrogen and -OH groups of the clay minerals. A dioxaspiro[5.5]undecan-3-ol) (six membered 1,3-dioxalane)

strong band at 1492 cm^-1indicates the combined presence of confirmed by and gas chromatograph with mass spectrometry

all acid sites (Lewis py + Brönsted py + Hydrogen bonding)⁴⁰. It (GC-MS) (Fig. S5), ¹H and ¹³C NMR (S3). With regards to the

is noticeable from the figure S3 that activated 6/BBnU/6 selectivity of the catalytic reactions, the cyclohexanone was

exhibits a high intensity Brønsted and Lewis acid sites peaks found more reactive cyclic substrate for glycerol acetalization.

compared to other acid activated samples and pristine BBnU. The sectivity of five membered 1,3-dioxalane (i.e. 1, 4-

These data also support earlier conclusion that harshness in dioxaspiro [4, 5] decane-2-methanol) was found in the range

acid activation conditions decreases the acidic strength.

of 94-100% ^{6, 43}. Moreover, the acetalization reaction between

glycerol and cyclohexanone can be kinetically or

thermodynamically controlled.⁴⁴During the kinetically-

controlled reaction, the formation of five-membered cyclic

Catalyst screening

Fig.3. presents the effect of different activation conditions on ketals proceeds at a higher rate than that of the six-membered

the performance of materials in terms of surface acidity, cyclic ketals.⁴⁴

surface area, and the final yield of product. Among all the

synthesized materials, 6/BBnU/6 and 8/BBnU/6 were found to

be superior, and specifically considering the mild synthetic

42

protocol, and yield of product. Pushpaletha and co-workers

reported that the iron and aluminium content in acid-activated

clay plays a crucial role in the catalytic activity. The Al₂O₃and

Fe₂O₃content were highest in 6/BBnU/6 after acid activation

(Table 2), which corroborates with the observed highest

acidity. The higher Al₂O₃and Fe₂O₃content results in the

expulsion and relocation of the octahedral cations, Al³⁺and

Fe³⁺, between the interlayer space under optimum acid

activation conditions. Considering the above merits, the

6/BBnU/6 sample was selected for further catalytic

applications.

Scheme 1: Glycerol acetalization with cyclohexanone.

Reaction at room temperature (26-28 C)

°

Initially the catalytic experiments were carried out at room

temperature under solvent-free conditions with 1:1, 1:2, and

1:3 molar ratios of cyclohexanone to glycerol for a reaction

time of 1-19 hours. The results obtained in terms of

cyclohexanone conversion and the selectivity of five-

membered cyclic 1,3-dioxalane and six-membered cyclic 1,3-

dioxane are summarised in Table 3.

Table 3: Acetalization of glycerol with cyclohexanone at RT (26-28°C) and mild

temperature conditions.

Cyclohexanone: Glycerol moles

Time (hr)

1:1

^bII

99

90

92

--

1:2

^bII

87

89

92

98

1:3

^bII

89

90

92

--

^aI

45

67

80

--

^cIII

01

10

08

--

^aI

^cIII

13

11

08

02

^aI

^cIII

11

10

08

--

3

8

65

81

87

86

92

78

83

90

--

19

0.5^#

1^*

70

96

04

93

98

02

c

^aConversion of cyclohexanone,^b% Selectivity of 5-membered cyclic ketal,

%

Selectivity of 6-membered cyclic ketal. ^*Reaction conditions: catalyst amount =

Fig. 3. Relative effects of sample preparation protocols on the product yield, acidity,

and surface area.

5% wt (w.r.t. cyclohexanone), reaction temperature: 60ºC and reaction time = 1

#

hr. Reaction conditions: catalyst amount = 5% wt (w.r.t. cyclohexanone),

reaction temperature: 60ºC and reaction time = 30 min.

Acetalization of glycerol with cyclohexanone

In order to evaluate the catalytic activity of optimized

activated clay (6/BBnU/6), the reaction of glycerol with

cyclohexanone yielding isomeric products 1,3-dioxalane (1,4-

dioxaspiro [4.5]decan-2-ylmethanol) and 1,3-dioxane (1,5-

dioxaspiro[5.5]undecan-3-ol) was studied as a model reaction

When the acetalization reaction of glycerol and

cyclohexanone was carried out with an equimolar ratio for a

period of 3, 8, and 19 hours, the conversion of cyclohexanone

was 45, 67, and 80%, respectively. These conversion values

improved to 65, 81, and 87%, respectively, when the molar

ratio of cyclohexanone to glycerol was increased to 1:2, the

use of excess glycerol than equimolar results in high

conversion. The reason for these high conversions is not

generic and may be specific to certain reactions. However, one

reason that may contribute to higher conversion is the

hydrogen bonding present in the glycerol molecule. It is

(Scheme 1). The reaction outcomes were studied with respect

to temperatures, time, and molar ratios of the reactant. The

analysis of the raw reaction products were performed by gas

chromatography (GC). Typically chromatograph exhibited two

product peaks, first broad and high intesity peak with

retention time 8.67 min for 1,4-dioxaspiro [4.5]decan-2-

ylmethanol (Five membered 1,3-dioxalane) and second small

6 | J. Name., 2012, 00, 1-3

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worthy to mention here that the glycerol is increasingly being The effect of the cyclohexanone to glycerol molar ratio on the

used as a greener solvent for organic transformations for cyclohexanone conversion was studied at room temperature

various reasons such as its polarity, structure and solvent and 60°C. The obtained results suggest that a 1:2 mole ratio of

solubility properties resulting in higher yields^{12, 45}. A further reactants yields the maximum cyclohexanone conversion.

increase in the molar ratio to 1:3 showed 78, 83, and 90% These results also indicate that the experiment performed at

conversion, respectively, at identical reaction times. Since the 60°C for 1 hour yields better results than the reaction carried

higher molar ratio of cyclohexanone to glycerol (1:3) did not out at room temperature for 19 hours (Table 3; entry 1*). The

show significant improvement in the conversion or selectivity dependence of cyclohexanone conversion on the reaction

of products after 8 and 19 hours, hense 1:2 molar ratio was time, with the optimum molar ratio and temperature

chosen as the optimum stoichiometry for the acetalization conditions, was studied (Fig. 4[C]). At the optimized

reactions with 5% catalyst loading at room temperature for 8 temperature (60°C), the acetalization reaction progressed

hours. The reaction time was further optimized by studying the faster than at room temperature.

acetalization of cyclohexanone with glycerol with a molar ratio

of 1:2 for different time intervals. The conversion reaction Effect of reaction time (60°C)

gradually increased with time and 87% with 92% selectivity of

The experiment performed at the optimum temperature

the five-membered cyclic ketal after 19 hours was found (Fig. 4

[A]).

conditions for 30 minutes gave 86% conversion of

cyclohexanone. These results are better than those obtained

at room temperature for the reaction carried out for 19 hours

(Table 3; entry 0.5#). The reaction under the optimized

Effect of conventional heating

The influence of temperature on the 6/BBnU/6 catalyzed conditions was monitored for 5 hours, and the conversion and

reaction was studied by increasing the reaction temperature selectivity was maximum within 2 hours (Fig. 4.[D]). However,

from 27 to 100°C, while the reactant ratio was kept at 1:2 for the optimum time was considered to be 1 hour, as the results

each set of reactions. As expected, an increase in temperature achieved in a 1 hour reaction time were comparable with the

increased the conversion and selectivity of the products (Fig. longer reaction times.

4[B])

reaction was allowed to progress for

conversion and 99% selectivity for five-membered ketals was

observed. Above 60 no significant improvement in

conversion or selectivity was noted, thus, 60 C was chosen as

the optimum temperature for further studies.

.

When the temperature was kept at 60

°C, and the

1

hour, 90-94% Effect of catalyst loading (60°C)

The catalytic experiments were conducted by varying the

amount of catalyst from 1 to 7 wt % and keeping the other

experimental conditions identical to those optimized.

Interestingly, the optimised catalyst exhibited better

cyclohexanone conversion at 4 to 7wt% cataltst. With the

increase in the catalyst amount, the glycerol conversion

increased being attributed to the availability of a higher

number of acidic sites. At 5% wt of the catalyst, the glycerol

°C

°

conversion was 90% and the selectivity between 1,3‐dioxane

and 1,3 dioxolane was 98:2. However, with a further increase

‐

in the amount of catalyst, there was no considerable change in

the cyclohexanone conversion or selectivity of the products.

The typical acetalization reaction ran under optimized

conditions showed 90-92% conversion and 98 and 2%

selectivity for five-membered 1,3-dioxalane and six-membered

1,3-dioxane, respectively.

Considering the commercial importance of the acetalization

reactions, the model reaction was scaled up to 100 ml,

resulting in 88% conversion and consistent selectivity. For the

sake of comparison, the model reaction was performed under

identical optimized conditions in the absence of the catalyst,

which showed only 10-15% conversion of cyclohexanone. This

result indicates the role of the catalyst in accelerating the rate

of the reaction (Table 4; entry 1).

Fig.4. Influence of reaction parameters on glycerol cyclohexanone acetalization over

the 6/BBnU/6catalyst, [A] Reaction time, [B] Reaction temperature, [C] Reactant molar

ratio, [D] Reaction time at a temperature of 60ºC.

Confirmation of catalyst screening

The clay samples were activated by 6 N to 15 N sulphuric acids

at a 6% clay concentration. The acid-activated clay samples

were screened as a catalyst for acetalization of cyclohexanone

with glycerol under optimum conditions. Among the various

Effect of molar ratio (60°C)

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catalysts, the highest cyclohexanone conversion (90-92%) acetalization reaction is promoted due to the available acidic

along with 98% selectivity for the five-membered 1, 3- sites on acid-modified bentonite (Table 4; entry 2).

dioxalane was obtained from the clay samples activated with 8

N and 6 N acid concentration, which possess higher surface Comparison with commercial catalysts

acidity (25 and 23 mg KOH g⁻¹of clay). The conversion

For the sake of comparison, the catalytic activity of some

decreased with increasing acid concentrations (12 N and 15 N)

commercially available solid acid catalysts was also evaluated

used for activation (Table S3). These results clearly

under the optimised reaction parameters. Thus, the

demonstrate that catalytic activity increased with an increase

commercially available clay catalyst K10 Montmorillonite

in the surface acidity of the acid-activated samples. As clay

showed 88% conversion and 96% selectivity for the cyclic five-

catalysts consist of several metal oxides which contribute

membered ketal. Fuller’s earth clay catalyst showed 86%

towards the acidity of material. It is very hard to ascertain

cyclohexanone conversion with 94% selectivity for the five-

exact details about the active sites of these catalysts. Hence

membered cyclic ketals. Similar experiments in the presence of

the TON and TOF were not calculated. However, the

Amberlyst-15 showed 63% conversion and 87% selectivity for

comparison with respect to surface area in incorporated (Table

the five-membered cyclic acetals. The homogeneous PTSA

S3) for comprehension.

catalyst showed 94% cyclohexanone conversion and 99%

The unmodified sample ‘BBnU’ was also screened for

selectivity for the five-membered cyclic acetals (Table 4; entry

acetalization of cyclohexanone under optimum conditions,

3-6). The catalytic activity of the optimised 6/BBnU/6 catalyst

was compared with some earlier reports (Table 4; entry 7-8)⁶.

which gave no acetalization products, suggesting that the

Table 4: Glycerol acetalization with selective aldehydes and ketones under various experimental conditions, relative data from previous reports

Entry

Catalyst

Temp (ºC)

Time (h)

Mole

Conversion (%)

Selectivity (%)

5-M (%)^a6-M(%)^b

Ref.

Cyc:Gly

Cyclohexanone glycerol acetalization data for finest catalyst screening

1

2

Catalyst free

BBnU

60

01

1:2

15

84

16

--

Trace

Cyclohexanone glycerol acetalization data comparison with commercial catalyst

3

4

5

6

K10 MMT

Fullers Earth

Amb-15

60

01

1:2

84

86

63

94

96

94

87

99

04

06

13

01

--

PTSA

Cyclohexanone glycerol acetalization from literature reports

7

8

[Cp*IrCl₂]₂

40

01

02

1:3

59

76

94

97

06

03

6

Benzaldehyde glycerol acetalization data experimental

9

Catalyst free

6/BBnU/6

60

RT

60

01

15

01

1:2

37

81

64

56

36

44

--

10

11

12

6/BBnU/6

84

64

60

40

60

01

1:1

--

Benzaldehyde glycerol acetalization from literature reports

MOO₃/SiO₂

100

16

1:1.1

20

13

70

30

70

14

15

16

[Cp*IrCl₂]₂

RHASO₃H

40

01

02

08

1:3

1:2

55

67

78

79

78

67

21

22

33

6

120

46

Phenyl acetaldehyde glycerol acetalization data experimental

17

18

19

20

Catalyst free

6/BBnU/6

60

RT

60

01

15

01

1:2

1:1

--

62

68

58

08

09

10

92

91

90

Phenyl acetaldehyde glycerol acetalization from literature reports

21

22

MoO₃/SiO₂

Zeo-USY-2

100

150

08

02

1:1.1

1:2

56

95

09

64

91

31

20

47

Furan-2-carbaldehyde glycerol acetalization data experimental

23

24

Catalyst free

6/BBnU/6

60

RT

60

01

15

01

1:2

--

43

--

1:2

72

69

57

--

25

a

6/BBnU/6

1:2

54

46

b

and

represent

five-

and

six-membered

cyclic

acetal/ketal

products,

respectively

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1

Catalyst stability tests

reaction products were re-confirmed by H and ¹³C NMR (S4).

The performance of the reaction was monitored with respect

to temperature, time, and glycerol molar ratio. The obtained

results of Benzaldehyde conversion and selectivity of the

products are summarized in Table 4; entry 9-12. The

experiment was performed at room temperature with reaction

time of 15 hours, and the other parameters were kept

identical, resulting in 81% conversion of benzaldehyde with

56% selectivity of five-membered cyclic acetals. While

experiment performed at 60 °C and 1h reaction time resulting

in 84 % conversion of Benzaldehyde with 60% selectivity of

five-membered cyclic acetals. Interestingly shows that by

increasing reaction temperature the reaction time diminishes

considerably. The reaction of Benzaldehyde with glycerol in

the absence of catalyst, under optimised reaction conditions

resulted 37% conversion, which clearly specifies the role of the

catalyst in accelerating the reaction. The catalytic activity of

the optimised 6/BBnU/6 for benzaldehyde acetalization

20, 46

(Table 4;

Fig.5. Catalyst recycling test under the optimized reaction conditions.

reaction was compared with earlier reports.^6,

entry 9-12).

In order to study the stability and reusability of the catalyst

6/BBnU/6, the catalyst was successfully reused four times. A

slight decrease in conversion after 4^thrun was observed. Each

Hyacinth fragrance and fuel additives

The phenyl acetaldehyde glycerol acetals are flavouring

materials with a hyacinth fragrance, and are synthesised by

reacting the phenyl acetaldehyde with glycerol, yielding five-

membered cyclic acetal [(2-benzyl-4-hydroxymethyl-1, 3-

dioxolane)] and six-membered cyclic acetal [2-benzyl-5-

hydroxy-1, 3-dioxane], along with the two geometrical isomers

⁴⁷(Scheme 3). (Fig. S7)

operating cycle was carried out at a temperature of 60 °C and

a cyclohexanone to glycerol molar ratio of 1:2 for one h

reaction time. The catalyst used was recovered by

centrifugation, washed with water and methanol, and ﬁnally

dried at 110°C for 2 hours. Fig.5. shows the results of

cyclohexanone conversion and the selectivity of the five- and

six-membered cyclic ketals for each reaction cycle. It is

observed that there was no significant deactivation of the

catalyst under the optimized conditions after fourth cycle

.

Glycerol Acetalization with Benzaldehyde

The catalytic activity of 6/BBnU/6 was tested in the

acetalization reaction between Benz aldehyde and glycerol,

which yielded two isomeric products, a ﬁve-membered cyclic

1, 3-dioxalane acetal [(2-phenyl-1, 3-dioxolan-4-yl) methanol]

and a six- membered cyclic 1, 3-dioxane [2-phenyl-1, 3-dioxan-

5-ol] as depicted in Scheme 2.

Scheme 3: Glycerol valorised as commercially important furan-based fuel additive

precursors.

The acetalization of phenyl acetaldehyde with glycerol was

carried out in the presence of the 6/BBnU/6 catalyst. The

performance of the reaction was monitored with respect to

temperature, time and glycerol molar ratio. The obtained

results for phenyl acetaldehyde conversion and selectivity of

the products are summarized in Table 4; entry 17-20. In the

absence of a catalyst, the reaction of phenyl acetaldehyde with

glycerol under optimised reaction conditions results in no

conversion of phenyl acetaldehyde. The catalytic activity of the

optimised 6/BBnU/6 catalyst for the hyacinth fragrance was

Scheme 2: Glycerol acetalization with benzaldehyde.

The ﬁve- and six-membered products were characterized by

GC chromatograph (Fig. S6) with GC-MS and the crude

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substantial as compared to earlier reports⁴⁷(Table 4; entry 21- The use of the optimised protocol was further extended for

22). In another attempt to utilize our synthetic methodology to acetalization of several aldehydes and ketones. The high

achieve commercially valuable products, we successfully selectivity for five-membered ketals was achieved for

synthesized the fuel additive precursors from furfural and cyclopentanone (93% selectivity; 67% conversion) and

glycerol, which yielded the five-membered cyclic acetal [(2- cycloheptanone (99% selectivity; 40% conversion), where the

(furan-2-yl)-1, 3-dioxolan-4-yl) methanol] and the six- decrease in conversion may be attributed to the geometrical

membered cyclic acetal [2-(furan-2-yl)-1, 3-dioxan 5-ol] hindrance posed by five- and seven-membered ring

(Scheme 4), (Fig. S8) under optimum conditions over the conformations. A noticeable effect of steric factors in the

6/BBnU/6 catalyst.

conversion and selectivity was also observed for methyl

cyclohexanones. Specifically, 2-methyl, 3-methyl, and 4-methyl

cyclohexanone showed 30, 59, and 85% conversion with 20,

43, and 59% selectivity for five-membered ketals, respectively.

The reversal of selectivity in the case of 2-

methylcyclohexanone may be attributed to the steric repulsion

between the methyl and hydroxyl groups residing in proximity

to each other. The detailed results of conversion and

selectivity of various aldehydes and ketones are summarised in

Table 5. Different aldehydes showed a moderate selectivity,

while ketones showed excellent selectivity. The electron

donating or electron withdrawing substituent on the phenyl

ring of benzaldehyde affects the conversion as well as the

selectivity. An increase in selectivity (75%) of five-membered

products was observed in the case of methoxy substituted

benzaldehyde, with a slight decrease in the conversion (69%).

In case of chloro, bromo, and other electron withdrawing

substituents, the conversion of aldehydes and the selectivity of

respective products remained unaffected.

Scheme 4: Glycerol valorised as commercially important furan-based fuel additive

precursors.

The performance of the reaction was monitored with respect

to temperature, time, and glycerol molar ratio. The obtained

results for furfural conversion and selectivity of the products

are summarized in Table 4; entry 23-25. In the absence of a

catalyst, the reaction of furan aldehyde with glycerol under

optimised reaction conditions does not result in the formation

of fuel additives.

Acetalization with other aldehydes/ketones

Table 5: Glycerol acetalization with other aldehydes/ketones, with an

aldehyde/ketone glycerol molar ratio of 1:2, an IS of 200 µl, a reaction temperature of:

60ºC, a reaction time of 1 hour, and a catalyst of 5% wt aldehydes/ketone.

Non-traditional pathways for glycerol Acetalization

Table 6: Alternative (non-traditional) pathways for glycerol acetalization

with significant aldehydes and ketones.

Aldehydes/Ketone

Alternative energy inputs

Conventional

(60 °C)

^bII ^cIII

60

Microwave

Ultrasonic

(60 °C)

^aI

^bII

2

^cIII

^aI

^bII

2

^cIII

Time (minute)

Cyclohexanone

Benzaldehyde

Ph-acetaldehyde

92 98 02 92 98 02 89 97 03

81 60 40 83 57 43 81 56 44

68

9

91 92 15 85 83 10 90

Furan aldehyde

69 54 46 78 48 52 77 58 42

a

Conversion of aldehyde or ketone,^b% Selectivity of 5-membered cyclic acetal

and ketal, ^c% Selectivity of 6-membered cyclic acetal and ketal.

Furthermore, the optimized catalyst was tested in non-

traditional microwave and ultra-sonication synthesis

pathways, distinctly under solvent- free conditions. The

influence of ultra-sonication time on cyclohexanone

conversion and selectivity is depicted in Fig. S4. The obtained

results suggest that a rapid two minute ultrasonic cavitation

effect was enough for 89% conversion of cyclohexanone with

97%

selectivity

of

five-membered

cyclic

ketals.

Correspondingly, a 2-minute core heating under microwaves is

sufficient for 92% conversion of cyclohexanone with 98%

selectivity of five-membered cyclic ketals. The expected similar

rapid conversion results were observed for hyacinth and furan-

based fuel additives with the use of microwave and ultra-

sonication synthesis pathways. The conventional reflux setup

is relatively slow and inefficient to transfer the energy into a

^aand ^brepresent five- and six-membered cyclic acetals/ketals products respectively.

10 | J. Name., 2012, 00, 1-3

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8.

S. I. a. A. V. Avelino Corma, Chem.Rev., 2007, 107, 2411-

2502.

P. Gallezot, Chemical Society reviews, 2012, 41, 1538-

1558.

reaction mixture, as it relies on convection currents and the

thermal conductivity of the media (reaction vessel, reactants,

and solvent phase, etc.), therefore the results obtained by

conventional heating, owing to the longer reaction time, are

slightly inferior when compared to the ultrasonic and

microwave irradiation pathways (Table 6).

9.

10.

11.

M. J. Climent, A. Corma and S. Iborra, Green Chemistry

,

2014, 16, 516.

L. Moity, A. Benazzouz, V. Molinier, V. Nardello-Rataj, M.

K. Elmkaddem, P. de Caro, S. Thiébaud-Roux, V. Gerbaud,

P. Marion and J.-M. Aubry, Green Chem., 2015, 17, 1779-

1792.

Conclusion

12.

13.

14.

J. I. García, H. García-Marín and E. Pires, Green Chemistry

2014, 16, 1007.

,

In summary, we developed a green heterogeneous process to

synthesize industrially useful chemicals from the acetalization

of glycerol. A solid acid catalysts from naturally abundant

bentonite were prepared by simple acid activation under mild

synthetic conditions. During the acid treatment, the parent clay

composition was considerably changed. The specific surface area

and pore volume of 6 N H₂SO₄-treated clay was found to

increase by _~2.4 and _~2 times respectively. The synthesized

catalyst has been efficiently employed for the valorisation of

B. L. Wegenhart, S. Liu, M. Thom, D. Stanley and M. M.

Abu-Omar, ACS Catalysis, 2012, , 2524-2530.

2

M. B. Güemez, J. Requies, I. Agirre, P. L. Arias, V. L. Barrio

and J. F. Cambra, Chemical Engineering Journal, 2013,

228, 300-307.

X. Hong, O. McGiveron, A. K. Kolah, A. Orjuela, L.

Peereboom, C. T. Lira and D. J. Miller, Chemical

Engineering Journal, 2013, 222, 374-381.

15.

glycerol by means of an optimized mild and eco-friendly 16.

M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and C. Della

Pina, Angewandte Chemie, 2007, 46, 4434-4440.

A. Patel and N. Narkhede, Energy & Fuels, 2012, 26, 6025-

6032.

D. Nandan, P. Sreenivasulu, L. N. Sivakumar Konathala, M.

Kumar and N. Viswanadham, Microporous and

Mesoporous Materials, 2013, 179, 182-190.

process. The catalytic chemical up gradation of glycerol was

further shown to be more efficient and cost effective by using

17.

the non-conventional energy sources such as microwave

irradiation and ultra-sonication. The development process

could be efficiently applied to the solvent-free acetalization of

18.

several aldehydes and ketones with glycerol to produce

19.

S. Zhang, Z. Zhao and Y. Ao, Applied Catalysis A: General

2015, 496, 32-39.

,

corresponding acetals or ketals in high yields. Moreover, we

successfully utilized this sustainable and green protocol to

20.

achieve commercially valuable hyacinth fragrance as well as

S. B. Umbarkar, T. V. Kotbagi, A. V. Biradar, R. Pasricha, J.

Chanale, M. K. Dongare, A.-S. Mamede, C. Lancelot and E.

Payen, Journal of Molecular Catalysis A: Chemical, 2009,

310, 150-158.

furan based fuel additive precursors in good conversion and

selectivity of the products.

21.

B. Wang, Y. Shen, J. Sun, F. Xu and R. Sun, RSC Advances

2014, , 18917.

H. R. Prakruthi, B. M. Chandrashekara, B. S. Jai Prakash

and Y. S. Bhat, Catal. Sci. Technol., 2015, , 3667-3674.

,

4

22.

Acknowledgements

5

The authors are grateful to the Council of Scientific and

23.

R. W. McCabe and J. M. Adams, in Developments in Clay

Science, eds. B. Faïza and L. Gerhard, Elsevier, 2013, vol.

Volume 5, pp. 491-538.

Industrial Research (CSIR) India for financial support under the

Network project. RRP acknowledges CSIR, New Delhi for the

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