Phosphonate functionalized carbon spheres as Br?nsted acid catalysts for the valorization of bio-renewable a-pinene oxide totrans-carveol

Article abstract of DOI:10.1039/d0dt00921k

Herein, we report a simple route for the synthesis of phosphonate functionalized Br?nsted solid acid carbon spheres as heterogeneous catalyst for the valorization of bio-derived a-pinene oxide. The Br?nsted acidity was generatedviatwo steps; hydrothermal carbonization of sugar to produce carbon microspheres followed by PCl₃treatment to form phosphonate functionalized carbon. The presence of phosphonate was confirmed by CP-MAS³¹P and¹³C NMR. In addition, the presence of the P-C, O-P-C and HO-P?O bonds of the phosphonate group was confirmed by FT-IR,³¹P NMR, and XPS. SEM-EDAX analysis revealed the presence of a phosphorus content of ~1.71 wt% on the surface of the catalyst while elemental mapping showed a uniform dispersion of phosphorus over the carbon spheres. The as-synthesized Br?nsted solid acid catalyst was used for the isomerization of a-pinene oxide which gave 100% conversion with 67%trans-carveol selectivity in highly polar basic solvent in 1 h reaction time. Also, the catalyst showed good recyclable activity even after five cycles.

Full text of DOI:10.1039/d0dt00921k

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DOI: 10.1039/D0DT00921K
ARTICLE
Phosphonate Functionalized Carbon Spheres as a Brønsted Acid
Catalysts for Valorization of bio-renewable α-Pinene Oxide to
trans-Carveol
Received 00th January 20xx,
Accepted 00th January 20xx
Amravati S. Singh, [a,b] Jacky H. Advani, [a,b] and Ankush V. Biradar[a,b]
*
DOI: 10.1039/x0xx00000x
Herein, we report a simple route for the synthesis of phosphonates functionalized Brønsted solid acid carbon spheres as
heterogeneous catalysts for the valorization of bio-derived α-Pinene oxide. The Brønsted acidity was generated via two
steps; hydrothermal carbonization of sugar to produce carbon microspheres followed by the PCl3 treatment to form
phosphonate functionalized carbon. The presence of phosphonate was confirmed using by solid 31P and 13C NMR.
Additionally, the presence of P–C, O–P–C and HO–P=O bond of phosphonates group were confirmed by FT -IR, 31P NMR, and
XPS. The SEM-EDAX analysis revealed the phosphorus content of ~1.71wt% present on the surface of the catalyst while the
elemental mapping showed the uniform dispersion of Phosphorous over the carbon spheres. The as-synthesized Brønsted
solid acid catalyst was used for isomerization of α-Pinene oxide which gave 100% conversion with 67% trans-Carveol
selectivity in highly polar basic solvents like DMF in 1 h reaction time. Also, the catalyst showed good recyclable activity even
after five cycles.
chemical is extensively used as an orange essence in the perfumery,
food and flavor adducts.6 It also possesses chemopreventive
properties in the mammary and other tumor rodent models.7
Furthermore, the isomerization of α-pinene oxide is spontaneous
Introduction
and takes place easily even in the presence of a small amount of acid
catalyst producing various high-value products. Predominantly, this
reaction results in the formation of more than 200 compounds at or
above 100 °C reaction temperature.8 Therefore, achieving a single
product selectively is a challenging task. The selectivity of these
isomerization products generally depends on the type of acid catalyst
used; the formation of CA is favored by the Lewis acid-catalyzed,
while that of TCV, TPC, TSB, P, TPCV, and PC are favored by the
Brønsted acid-catalyzed reaction.9-10
Valorization of biomass-derived intermediates into value-added
products has become an attractive and interesting topic for research
in recent years.1 The abundant and naturally available biomass-
derived organic compounds (terpene: hemiterpenes (C5),
monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20),
sesterterpenes (C25) and triterpenes (C30), etc. are present as acyclic
or mono to pentacyclic derivatives containing alkoxy, ether,
carbonyl, keto, or ester ketone groups (terpenoids). These molecules
are cost-effective and highly utilized for the synthesis of the variety
of fine chemicals. Among all, terpenes and their oxides are the largest
and cheaper raw material for industrial production of food, flavor,
fragrance, and pharmaceutical chemicals.2-3 Particularly, α-pinene
isolated from the abundantly available turpentine is the key
intermediate for the production of a synthetic substitute for natural
aromas and undergoes epoxidation to produce α-pinene oxide. The
isomerization of this α-pinene oxide produces a variety of products
which include trans-carveol (TCV), campholenic aldehyde (CA), trans-
pinocarveol (TPC), p-cymene (PC), pinol (P), trans-pinocarvone
(TPCV), trans-sobrerol (TSB), etc. (Scheme 2). Among all, the
campholenic aldehyde is used as a key intermediate for the
production of East Indian Sandalwood fragrance such as santanol,
givaudam, Bachane, dragons, and Firmenich.4 Further, it is also used
as a substitute for the ecologically harmful nitro and polycyclic
musks.5 On the other hand trans-carveol, an essential and expensive
Till date, several research groups have focused on the synthesis of CA
while only a limited number of studies on the selective synthesis of
TCV has been carried.6,11-15 For instance, Hölderich et al. synthesized
campholenic aldehyde selectively by the isomerization of APO using
Lewis acid-based catalyst.16 Lewis acids like ZnBr2 and ZnCl2 are found
to be the most effective homogenous catalysts and give about 85%
selectivity towards CA.17 Several Lewis acid heterogeneous catalysts
including silica-supported H3PW12O40,8 Ti and Fe modified zeolites 16
,
Montmorillonite 18, Silica modified with Al, Zr, Ti oxides19, mixed
oxide B2O3/SiO220, acid-treated MOF21, Ionic liquid 22 Ti-MMM 23 have
been known to selectively produce CA. In the case of synthesis of
TCV, the highest selectivity of 73% was obtained using Sn/SiO2 and
Ce/SiO2 metal oxides.11 A few reports that focused on the selective
synthesis of TCV use various catalysts like molecularly impregnated
acid polymers,6 Ceria supported mesoporous materials MCM-
41/SBA-15,14 H/Fe modified zeolite beta zeolite,13 and finally ZSM-5
based micro-mesoporous materials.15 However, the selectivity of
TCV using these catalysts was in the range of 43-46% only. The
selectivity for the production of trans-carveol is known in the
presence of the Brønsted acid catalysts. These catalysts can be
a. Inorganic Material and Catalysis Division, CSIR-Central Salt and Marine
Chemicals Research Institute, Bhavnagar 364002, Gujarat, India
b. Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, Uttar
Pradesh, India
c. *Ankush Biradar. ankush@csmcri.res.in,Tel.: Fax +91278-2567760 Ext. No.: 7170
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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synthesized via various methods including co-precipitation, post-
synthetic functionalization of homogeneous Brønsted acids,
polymerization, and in-situ functionalization methods.6,24
View Article Online
DOI: 10.1039/D0DT00921K
The carbon-based materials have attracted much attention owing to
the unique chemical, physical and mechanical properties and ease of
synthesis.20,25,26 The low-temperature hydrothermal (LTH) method is
a versatile method for the preparation of a functional carbon micro-
spheres and offers a facile route for the synthesis of different
functionalized carbon framework.25-27 Furthermore which can
accelerate the naturally occurring biomass coalification in a shorter
time, rather than millions of years. Biomass is importantly cheap and
readily available precursors, e.g. bioderived or simple carbohydrates,
can be turned into valuable carbonaceous material by HTC
method.25-29
Scheme 1. Schematic representation and reaction involved in the
hydrothermal synthesis of carbon and functionalization of
phosphonates on carbon derived from biomass.
The modification of these carbon materials using heteroatoms like
nitrogen, phosphorus, boron, and sulfur are known to enhance
hydrophilicity, metal-support interactions, and additional acidic or
basic sites.24,26,30-35 The functionalization of phosphorus onto carbon
materials enhances the electron-donor properties and used in many
energy harvesting applications. One such report utilized phosphoric
acid as a precursor to obtaining phosphorus-functionalized carbon
which was used as supercapacitor material.32 The surface impurities
and defects serve as preferential sites for the successful anchoring of
the functional groups. Herein, we report a two-step synthesis of
phosphonate functionalized carbon spheres and its further use as a
catalyst for the liquid phase isomerization of α-pinene oxide to
selectively give TCV, a high value-added fragrance compound. The
as-synthesized catalyst possesses the phosphonate group which
gives Brønsted acidity which accelerates the rate of reaction to
selectively produce TCV. To the best of our knowledge, this is the first
report of phosphonates functionalized sugar-derived carbon a
Brønsted solid acid catalyst for the isomerization of α-pinene oxide
to yield trans-carveol selectively.
The phase purity of the synthesized catalyst was analyzed by powder
XRD (Fig. 1A). The XRD pattern of the CS(α) showed broad diffraction
peaks at 2θ = 21°, which can be attributed to C (002) diffraction plane
of the amorphous carbon material.35 Post functionalization, the
carbon catalyst (PCS) showed two diffraction peaks at 2θ = 10° and
2θ = 20.4°. The broad peak at 10° indicating the successful
functionalization of phosphorous. No significant change in the PXRD
pattern was observed on increasing the phosphorus content on the
carbon mesosphere. However, there is a slight shift of 2θ value by
increasing moles of phosphonate functionalization on CS(α) (Fig. 1A).
The FTIR spectra (Fig. 1 B(a)) of the CS(α) showed an intense and
broad band centred at 3420-3463 cm-1 due to the stretching mode of
O–H bond and band at 1637 cm-1 attributed to bending mode of O–
H group. The band at 2923 and 2855 cm-1 is attributed to C–H
stretching. After functionalization of the phosphonate group on the
surface of CS(α), several new peaks appeared in the spectra (Fig.
1B(d)) the absorption band at 3430, and 1633 cm-1 are assigned to
stretching and bending mode of O–H bond of phosphate group into
PCS(α1).36-39 The band at 1385 cm-1 is assigned to P=O stretching
vibration, whereas the band at 1020, 1164, 1203 cm-1 displayed the
stretching frequency of P–O, C–O bond in PCS(α1) (Fig. 1B(d)). The
strong band at 795 and 672 cm-1 is attributed to P–O–C, P–OH, and
P–C stretching vibration.39-42
Results and discussion
A series of phosphonate functionalized carbon microspheres were
synthesized by functionalization with phosphorus trichloride. Herein,
we used the easily and cheap disaccharide carbon available source,
i.e., table sugar which is naturally extracted and refined from
sugarcane or sugar beet. The synthesis of carbon spheres via
hydrothermal treatment is highly reported by various groups.25,28
The oxalic acid used in the reaction sufficiently dehydrates the sugar
at the carbonizing temperature (120-210 °C) and produces the
carbon microspheres (Scheme 1).
CS
PCS
1348
1335
(d)
(c)
(D)
1589
1586
2923
672
795
1020
1633
1203
1385
1164
(c)
(b)
(b)
(b)
(a)
1023
(a,)
(a)
1637
3420
B3463
C
500 1200
A
10
The sugar disaccharides undergo hydrolysis by oxalic acid to yield 5-
hydroxy methyl furfural (5-HMF) which gets condensed and
polymerizes to form solid microspheres containing –OH, –C=O and –
COOH groups on the surface of the carbon. Due to the high pressure
generated inside the reactor, the polymerized product attains a
spherical morphology and reduce its surface energy.26,32 The as-
synthesized CS was then functionalized using PCl3. The
functionalization occurs via the widely available surface hydroxyl or
carboxyl groups present on the microspheres.26
5
15
20
25
2
30
35
40
4000 3500 3000 2500 2000 1500 1000
1400
1600
Wavenumber(cm
)
Raman shift (cm-1
)
-1
Figure 1. (A) XRD pattern of (a) CS(α), (b) PCS(α1), (c) PCS(α2), (d)
PCS(α3); (B) FTIR spectra of (a) CS(α), (b) PCS(α1), (c) PCS(α2), (d)
PCS(α3).; (C) FT-Raman spectroscopy of (a) CS(α), (b) PCS(α2).
Variation in the structure of carbon by functionalization with
phosphonate was also investigated by Raman spectroscopy. As
2 | J. Name., 2012, 00, 1-3
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shown in Fig. 1C, two peaks were found in both the samples; carbon (phosphonates) formed in PCS(α2) due to the phosphorylation of
sphere (CS(α)) and phosphonate functionalized carbon sphere phenol-formaldehyde groups on the surface of CS(α)V(ieFwigA.rt3icale)O[4nl3in]e.
DOI: 10.1039/D0DT00921K
(PCS(α2)). The D band at 1335 cm-1 and G band at 1586 cm-1 appear The 31P NMR spectrum shows a strong signal of phosphate like
in CS(α) catalyst. A slight shift of D band at 1348 cm-1 and G band at structure at δ ~0 ppm. The signal at δ ~7.6 and δ 18.6 ppm indicate
1589 cm-1 occurs after phosphonate functionalization. The the presence of phosphate monoester and polyester
integrated intensity ratio ID/IG is generally used to estimate the (phosphonates), respectively in the case of PCS(γ) (See SI, S3) 44
defect in the carbon materials. The higher ID/IG value of 1.061 of PCS
than that of 1.065 of CS, indicates phosphonate functionalization on
CS(α) showed structural defects. The BET surface area of the CS(α)
13C CP-MAS Spectroscopy was used to investigate the backbone
structure of carbon derived from sugar (CS(α)) and phosphonate
functionalized carbon (PCS(α2)). Figure 4B shows the peak at 0-45
ppm attributed to the alkyl carbon. The peak at 70-75 ppm and 80
ppm resulted from the sugar carbon. A weak peak observed at 150
ppm arises from the aromatic carbon. Finally, the peak at 110 ppm
corresponding to the furanic (-C-O) carbon structure of the
and PCS (α2) catalysts were 10.42 and 29.61 m²/g respectively. The
pore volume of CS(α) and PCS (α2) was found to be 0.0271 cm³/g and
0.0103 cm³/g while the pore diameter of CS(α) and PCS (α2) was
found to be ~30 Å and ~27 Å.
Furthermore, the field-emission scanning electron microscopy carbonaceous material. Weak NMR peak at 207 ppm corresponds to
(FESEM) image of CS (α) shows the formation of monodispersed aromatic carboxyl or carbonyl carbon.26 From this analysis, we can
microspheres with 4-5 µm in diameter (See SI, S 2.1) which is well conclude that there is more sp2 carbon present in CS(α) and PCS(α2)
supported by transmission electron microscopy image (Fig. 2G). (Fig.4b).43,44 The comparative 13C CP-MAS NMR of CS(γ) and PCS(γ) is
These carbon spheres after functionalization gave similar shown in SI, S3.
morphology (Fig. 2H). The elemental mapping of this functionalized
carbon showed the uniform distribution of the C, P and O atoms over
The successful functionalization of phosphonate on the carbon
sphere was verified by X-Ray photoelectron spectroscopy (XPS). The
XPS survey spectrum of PCS(α2) showed the characteristic signals of
C, P and O elements (See SI, S4). The high-resolution XPS spectra of
C 1s (Fig. 4a) can be deconvoluted into three peaks; 284.4 eV
corresponding to C–C bonds, 285.3 eV for C=C bond and 286.5 eV for
C–O/C–O–P and C=O bond respectively.42,45 The XPS spectrum of
phosphorus clearly shows the presence of P 2s and P 2p peak at 191
and 133 eV. The deconvoluted peak located at 132.9 and 134 eV of P
2p spectra can be assigned to the P–C and P–O bond (Fig. 4c). These
binding energies are attributed to pentavalent tetra coordinated
the complete material (Fig. 2B-E). Also, the elemental analysis using
SEM-EDAX gave 1.71 wt.% phosphorus (Fig. 2F) in PCS (α2). Similar
results were observed in case of other CS materials and the post-
functionalized PCS samples (See SI, Fig.2.2-2.4)
-
phosphorus (PO4 tetrahedra) surrounded by the different chemical
environment (phosphate-like structure). It should be noted that
compounds with C–P bonding, i.e. phosphonates fall in this region.
42,43,46,48
The O 1s peak was deconvoluted into four individual
chemical states of oxygen for the PCS(α2) material (Fig. 4b). The peak
at 531.6 eV corresponds to the C=O/P=O bond while that at 532.6 eV
for C–O/P–O–C. The peak at 533.3 eV corresponds to C–OH/P–OH
group and the peak at 534.2 arises due to the presence of -
COOH/H2O.43,46,49-50 The acidity of the catalyst PCS (α2) is measured
by potentiometric titration and also confirmed by ICP-OES analysis.
The elemental analysis has been performed by assuming all
phosphorus atoms present in the HO–P=O group and total
phosphorus present in this catalyst is 0.42 mmol/g. (See SI S5)
Figure 2. (A) SEM of PCS(α2); elemental mapping of PCS(α2) (B)Overall
map of C, O, P, (C) Phosphorous, (D) Oxygen (E) carbon; (F) SEM-EDX
of PCS(α2), TEM images of (G) CS(α) and (H) PCS(α2).
The PCS was analyzed by solid-state 31P NMR which showed a strong
signal of phosphate monoester at δ 6.0 ppm. Additionally, a signal at
δ 24.9 ppm indicates the presence of phosphate polyester Figure-3.
(a)
(c)
(b)
C-P
C-O/P-O-C
O-P
C-C
C=C
C-OH/P-OH
COOH/H
PCS(α2)
O
2
C=O/P=O
C-O/C-O-P
C=O
CS(α
PCS(α2
282
285
288
291
294
528
531
534
537
540
543 128
130
132
134
136
138
140
Binding Energy (eV)
Binding Energy (eV)
Binding Energy (eV)
Figure 4. XPS spectra of phosphonates functionalized carbon (a) C 1s
spectra of carbon (b) O 1s spectrum (c) P 2p spectrum.
230
200
170
140
110
f1 (ppm)
80
60
40
20
0
-20
-40
40
120
100
80
60
40
20
f1 (ppm)
0
-10
-30
-50
-70
-90
-110
Figure-3. A) Solid-state 31P NMR of PCS (α2); B) 13C CP-MAS Spectrum
of CS (α) and PCS (α2).
Catalytic activity
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The isomerization of α-pinene oxide by Brønsted acid-catalyzed Table 1. Result of α-pinene oxide isomerization using different
View Article Online
catalysts.a
reaction gives a variety of different products such as TCV, CA, CY, TPC,
P, TPCV, TSB, etc. depending on the catalyst used (Scheme 2). The
DOI: 10.1039/D0DT00921K
synthesized Brønsted solid acid (PCS(α2)) catalyst was used for value
Entry
Catalyst
%
Selectivity %
addition through the isomerization of naturally occurring α-pinene
oxide to TCV. The isomerization reaction in the absence of any
catalyst converted 5% of α-pinene oxide after 8 h at 140 °C (Table1,
entry 1). Then pristine carbon spheres (CS(α)) synthesized by the HTC
method at 120, 150, 180, and 210 °C were used for the same
reaction. It was found that isomerization of α-pinene oxide took
place at a reasonable rate with high selectivity for TCV; 61% (Table 1,
entry 2), 65% (Table1, entry 4), 70% (Table 1, entry 6), 70% (Table 1,
entry 8), respectively.
Conv.
TCV
-
CPA
-
TPC
-
6
9
4
4
5
9
5
3
5
8
10
-
-
9
13
Others
-
8
2
13
15
2
3
5
5
20
9
12
-
1.
2.
3.
4.
5.
6.
7.
8.
-
5
CS (α)
PCS (α2)
CS (β)
PCS(β2)
CS (γ)
PCS (γ2)
CS (δ)
PCS (δ2)
CS1st (α)
AC
97
100
93
87
65
66
75
73
22
7
39
6
8
30
55
41
7
61
67
65
62
70
66
70
69
52
59
50
-
25
22
18
19
23
22
20
23
23
24
28
-
OH
OH
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
PAC
CNT
PCNT
GO
2-methyl-5-(propan-2-
ylidene) cyclohex-2-
enol
Trance-carveol
(TCV)
H+
-
-
-
O
-H2O
O
51
60
54
-
20
12
26
-
20
15
11
-
Lewis acid
sites
PGO
PGO 1st
Graphite
9
-
-H2O
Campolenic
aldehyde (CA)
alpha-pinene
oxide (APO)
H
2 O/H
+
aReaction conditions: 0.5 g (3.28 mmol) α-pinene oxide,
Catalyst 50 mg, DMF 2 mL, 140 °C, 1 h, PAC (p-doped activated
carbon), AC (activated carbon). PCNT (p-doped carbon
nanotube), CNT (carbon nanotube), PGO (p-doped graphene
oxide), GO (graphene oxide).
OH
-H2O
H+
p-cymene
(CY)
O
OH
OH
O
Trans-sobreol
(TSB)
Trans-pinacarveone
(TPCV)
Pinol (P)
Trans-pinacarveol
(TPC)
The effect of temperature was studied in the range of 80-160 °C. The
isomerization of APO at 80 °C gave only 20% conversion of α-pinene
oxide with 48% (TCV) and 30% (CA) selectivity (Table 2, entry 1). A
marginal increase in conversion and selectivity was observed by
increasing temperature to 100 °C (Table 2, entry 2). Further
increment in the reaction temperature dramatically increased the
conversion to 83% with 63% selectivity towards TCV (Table 2, entry
3). The complete conversion was obtained at 140 °C with a marginal
increase in TCV selectivity (Table 2, entries 4 and 5). The rate of
reaction, as well as the selectivity of TCV, increased at a higher
temperature. The increment in temperature favors the
deprotonation of both solvent as well as a substrate, thus resulting
in the formation of TCV in high yield at higher temperatures.
Scheme 2. Possible products from isomerization of α-pinene oxide.
On the other hand, different phosphonate functionalized carbon
PCS(α) catalyst 120 °C PCS(α), 150 °C PCS(β), 180 °C PCS(γ) and 210
°C PCS (δ) show the excellent rate of reaction with highest selectivity
towards TCV; 67% (Table 1, entry 3), 62% (Table 1, entry 5), 66%
(Table 1, entry 7), and 69% (Table 1, entry 9). Although the selectivity
of the TCV using PCS (α2) was 67% and that of CS(δ) was found to be
70%, there was an issue with the recyclability of the CS (δ) catalyst.
The former was found to be recyclable while the latter lost its activity
after single use owing to the leaching of the active functional groups
from the surface of the carbon spheres (Table 1, entry 10). A similar
observation was made in the case of all the CS catalysts. For
comparison purposes, we also studied the effect of other carbon
materials like Activated carbon (AC), CNT, graphite, and graphitic
oxide (GO) and their phosphonated derivatives. CNT and its
phosphonated derivative and graphite catalysts were found to be
inactive for this reaction giving no conversion of APO. Further, the
activated carbon converted only 7% APO while its phosphonated
derivative converted 39% of APO with 50% TCV selectivity. When GO
was used as the catalyst, a 30% conversion of APO was observed with
51% selectivity towards TCV. However, no considerable effect of the
phosphonation of this GO was observed for the isomerization of
APO. Although the selectivity towards trans-carveol increased by 9%,
the activity of this catalyst started decreasing just after a single cycle.
Table 2. The product distribution of the isomerization of α-pinene
oxide at different temperature by using PCS (α2)a
Entry
Temp. Conv.
Selectivity %
°C
%
TCV
48
CA
30
25
TPC
10
Others
12
1.
2.
80
20
26
100
53
12
10
3.
4.
5.
120
140
160
83
100
100
63
67
73
21
22
22
8
9
3
7
3
2
aReaction condition: 0.5 g (3.28 mmol) α-pinene oxide, PCS (α2) 50
mg, DMF (2 mL), 1 h.
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The difference in the activity of each catalyst used for the with 64-67% selectivity towards TCV (Table 4, entries 4 and 5). Thus,
View Article Online
these results strongly support the observations that
DOI: 10.1039/D0DT009t2h1Ke
isomerization of α-pinene oxide may be explained in terms of catalyst
loading and the type of support used for this study. As we assume,
the loading of the catalyst has a remarkable impact on the reaction
rate. The catalyst PCS(α1) gave 76% conversion with 60% selectivity
towards desired product TCV in 30 min at 140 °C (Table 3, entry 1).
On the other hand, the higher amount of phosphonate loaded
catalyst, PCS(α2), gave 98% conversion with 62% selectivity towards
desired product TCV (Table 3, entry 2). On further increase in
phosphorus loading on carbon, PCS(α3), there is no significant effect
on the conversion and selectivity (Table 3, entry 3). These results
indicate that the functionalization of phosphonate on carbon
support has a major role in the selective formation of TCV. For
instance, with catalyst PCS (α1), the lower rate of reaction may be
due to low loading of phosphonate on a carbon support while a fast
rate of reaction with catalyst PCS (α2) and PCS (α3) result owing to
the higher phosphonate loading (Table 3, entries 2 and 3).
isomerization of α-pinene oxide is indeed influenced by the nature
of the solvent, which strongly affects the reaction pathways and
composition of products.52
Table 4. Product distribution on the isomerization of α- pinene oxide
by using different solvent PCS(α2).a
Selectivity %
Conv.
%
Entry Solvent
Temp. °C
TCV CA TPC Others
1. Acetone
50
48
15
20 40
13 50 24 15
5
35
2. Dichloroethane 70
Isopropyl
3.
4.
5.
70
50
40
7
3
5
5
50
11
5
alcohol
Dimethyl
acetamide
N,N Dimethyl
formamide
140 100
64 20
140 100
67 22
aReaction condition: 0.5 g (3.28 mmol) α-pinene oxide, Catalyst PCS
(α2) 50 mg, DMF 2 mL, 140 °C, 1h.
Table 3. Product distribution on the isomerization of α-pinene oxide
by using different loading of phosphonate in PCS (α).a
Reaction mechanism:
Entry
Catalyst
Conv.
%
Selectivity %
TCV
CA TPC Other
Based on the above observations and the earlier literature reports,
the plausible mechanism for the formation of various products
catalyzed by the Brønsted acid catalyst is proposed (Scheme 3).
1.
2.
3.
PCS (α1)
PCS (α2)
PCS (α3)
93
61
24
22
22
6
9
8
9
3
4
100
100
67
66
aReaction condition: 0.5 g (3.28 mmol) α-pinene oxide, Catalyst 50
mg, DMF 2 mL, 140 °C, 1 h.
H
N
HO
O
P
O
O
O
H
O
O
O
1
Me
Me
Me
Me
Me
N
H
N
H
N
Me
H
For further optimization, the amount of catalyst was varied (SI, S6
Table S1). For instance, 71% conversion of APO was observed with
high selectivity 66% towards desired product TCV in 1 h at 140 °C (SI,
Table S1, entry 1) using 10 mg of PCS(α2) catalyst. The increase in the
amount of the catalyst results in the increase in the conversion of
APO and selectivity towards TCV. A maximum of 94% conversion of
APO with 67% selectivity was obtained using the PCS(α2) catalyst (See
SI, Table S1, entries 3 and 4). Thus, we conclude that the lower
amount of the catalyst does not influence the selectivity of the
catalyst, however, it does have a positive effect on the conversion of
APO.
O
H
O
H
O
O
Me
Me
APO
H
H
-H
+H
F
TPCR
6
H
H
O
b
O
H
O H
O
H
a
c
-H
E
Intermediate
5
TPC
H
A
a
O
b
1,2 shift
H
O
H
O
H
1,2 shift
-2H
c
H
1,2 shift
B
7
CY
O
TCV
2
8
O
H
-H
O
O
O
H
The role of solvent has a profound influence for this reaction which
is well reported in the earlier literature.50 The isomerization of APO
in the presence of partially polar solvent like acetone gave moderate
conversion (48%) with higher selectivity towards CA (Table 4, entry
1). A similar activity was observed in the case of DCM. The use of
polar protic solvent like IPA gave around 50% conversion of APO with
40% selectivity towards TCV. Thus, it was observed that an increase
in the polarity brought an increase in the selectivity of the desired
product, TCV.
Also, previous reports have shown that the basicity of the solvent
also has an impact on the selectivity of the final product for this
reaction.11-14,51 Thus, based on this literature and the observations
made, DMA and DMF were chosen as the solvent for this reaction.
To our surprise, we found that the reaction proceeds spontaneously
in these solvents resulting in the complete conversion of the APO
Me
Me
O
P
-H
-H
C
N
CA 3
O
O
b
O
H
H
HO
O
O
P
O
O
Me
-H
N
FA
D
4
Me
H
Scheme 3: Detail reaction mechanism of Brønsted solid acid-
catalyzed the isomerization of α-pinene oxide.
The Brønsted acid catalyst transfers the proton to the DMF giving a
DMF-H+ intermediate. This intermediate transfers its proton to the
epoxide moiety inducing the ring-opening and production of a
carbenium ion (A). This carbenium ion undergoes a direct hydrogen
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shift resulting in the formation of TPC or TPCV. The carbenium ion A Catalytic activity
rearrange through 1,2 hydrogen shift giving other carbenium ions,
namely B, C and D. The formation of TCV results from the shifting of
View Article Online
DOI: 10.1039/D0DT00921K
The isomerization of α-pinene oxide was carried out as follows. In a
typical catalytic experiment, 0.5g α-pinene oxide (3.28 mmol), 50 mg
catalyst and 2 mL DMF were charged to a round bottom flask. This
reaction mixture was then heated to the desired reaction
temperature under stirring. The sample aliquots were withdrawn
after a regular interval of time to assess the progress of the reaction
and analyzed using Agilent 7890B GC equipped with HP-5 capillary
column of 30 m x 0.250 mm x 0.25 µm dimension and FID detector
and GC-MS (Shimadzu, GC-MS QP 2010, Japan). The major product
was purified by column chromatography using silica (100-200 mesh)
as stationary phase and hexane: ethyl acetate as eluent (70:30). Light
yellow color, viscous liquid was obtained. The purified product was
characterized by 1H and 13C NMR, GC-MS and FT-IR spectroscopy. The
catalyst was filtered from the reaction mixture by centrifugation at
10,000 rpm, washed with isopropyl alcohol, dried at 70 °C and reused
for next recycle.
two hydrogen atoms from B while the formation of CA results from
the 1,2 carbon shift followed by loss of hydrogen atom from C. The
abstraction of a proton from the catalyst mainly occurs via DMF
owing to its high basicity (pKa ~0.5 for DMF-H+).12 of CA results from
the 1,2 carbon shift followed by loss of hydrogen atom from C. The
abstraction of a proton from the catalyst mainly occurs via DMF
owing to its high basicity (pKa ~0.5 for DMF-H+) [12]. The nature of
the solvent as observed has a direct influence on the reaction
pathway and product composition. The high basicity of the solvent
facilitates the abstraction of a proton from the Brønsted acid carbon
catalyst which in turn results in the high conversion of the APO. The
reusability of the synthesized catalyst was performed by filtering the
catalyst after each reaction cycle, washed with isopropyl alcohol,
dried in a hot air oven at 60 °C and the recovered catalyst was used
for the next cycle. The result showed that the catalyst activity was
retained even after five cycles (See SI, S7). Also, to check the leaching
of Brønsted acidic sites, a hot filtration experiment was carried out
by filtering the catalyst after 15 min and the filtrate was further
allowed to react. No significant change in the conversion of α-pinene
oxide was found (See SI, S8). The SEM-EDAX analysis of recycled PCS
(α2) catalyst shows 0.32 wt.% of Phosphorus (See SI, S9). The
decrease in the content of phosphorus from 1.71 wt% (fresh catalyst)
to 0.32 wt% (fifth cycle) arises from the leaching of the phosphorous
at each successive washing step of the catalyst during the recycling
studies which affects the conversion of APO. However, selectivity to
trans-carveol remained almost constant.
1
Product analysis: Trans-Carveol was analyzed by H and 13C NMR
(See SI, S10), FT-IR (See SI, S11) and GC-MS (See SI, S12)
NMR of trans-carveol (TCV): 1H NMR CDCl3 (600 MHz) δ 5.59 (s, 1H),
4.75 (s, 2H), 4.02 (s, 1H), 2.34 (s, 1H), 2.13 (s, 1H), 1.93 (s, 1H), 1.85
(s, 1H), 1.80 (s, 3H), 1.75 (s, 3H), 1.61 (s, 2H). 13C NMR (600 MHz) δ
148.17 (s), 133.29 (s), 124.35 (s), 108.01 (s), 67.52 (s), 35.71 (s), 34.20
(s), 29.98 (s), 28.69 (s), 19.85 (s).
Experimental Section
Conclusions
Synthesis of carbon sphere (CS): The carbon spheres were
synthesized by following a reported procedure.26 Typically, 10 g of
table sugar and 2.5 g oxalic acid were dissolved in 110 mL distilled
water and was transferred to 170 mL stainless-steel hydrothermal
autoclave. The autoclave was heated to the desired temperature for
12 h. After cooling, the obtained black precipitates were collected by
vacuum filtration using Gooch crucible grade IV and washed with
This work reports a novel strategy for the synthesis of solid
Brønsted acid carbon catalyst synthesized using hydrothermal
carbonization of the bio-derived sugar as the carbon source
followed by functionalization. This environmentally benign
metal-free phosphonate functionalized carbon was found to be
efficient for the isomerization of α-pinene oxide. A maximum
plenty of deionized water, cyclohexane and isopropyl alcohol (10 mL selectivity of 67% was observed using the phosphonate
x three times), and dried in a hot air oven at 60 °C. The obtained black
solid synthesized at different temperatures was termed as CS(x)
where x indicates the carbonization temperature; (α) 120 °C, (β) 150
°C, (γ) 180 °C (δ) 210 °C. The yield of the CS(α), CS(β), CS(γ) and CS(δ)
was 13, 15, 33 and 30%, respectively.
functionalized carbon under the optimized conditions. It was
observed that the chemoselectivity towards the desired
product TCV can be achieved through the appropriate choice of
the solvent. The catalyst was successfully recycled without any
significant loss of activity and selectivity.
Synthesis of the Phosphonate Functionalized Carbon
Spheres (PCS): In a two-necked round bottom flask, 1 gm of carbon
spheres (CS) was dispersed in 2 mL isopropyl alcohol (IPA), followed
by slow addition of 0.5 mL phosphorous trichloride. The reaction
mixture was stirred for 6 h and the obtained black precipitates were
filtered using Gooch crucible grade IV, washed with IPA (10 mL each
x 3 times). The obtained material was dried at 60 °C giving the final
yield of 0.98 gm (98%). The amount of PCl3 was varied from 0.5 mL,
1 mL and 1.5 mL in the above procedure and the obtained catalysts
were named as PCS(α1), PCS(α2) and PCS(α3), respectively. Similarly,
the PCS(β), PCS(γ) and PCS(δ) were also synthesized. The synthesized
catalysts were characterized by several physicochemical techniques
(For details see SI, S1).
Conflicts of interest
There are no conflict to declare.
Acknowledgements
CSMCRI communication No. 66/2019. ASS acknowledges to
UGC govt. India for the senior research fellowship. AVB
acknowledges to Science & Engineering Research Board
(SERB/F/2139/2017-2018), India for financial support. The
Analytical Division and Central Instrumentation Facility of CSIR-
6 | J. Name., 2012, 00, 1-3
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Central Salt and Marine Chemicals and Research Institute,
Bhavnagar, for providing all requisite instrumental analysis.
[21] F. Vermoortele, R. Ameloot, L. Alaerts, R. MatthesVsieewn,ABrt.icCleaOrlnileinre,
DOI: 10.1039/D0DT00921K
E. V. Ramos Fernandez, J. Gascon, F. Kapteijn, D. D. Vos, J. Mater.
Chem., 2012, 22, 10321-10313.
[22] E. Salminen, P. Mäki-Arvela, P. Virtanen, T. Salmi, J. Wärnå, J. P.
Notes and references
[1] D. P. Serrano, J. A. Melero, G. Morales, J. Iglesias, P. Pizarro, Catal.
Mikkola, Ind. Eng. Chem. Res., 2014, 53, 20107-20115.
[23] M. P. Štekrová, P. Eliášová, T. Weissenberger, M. Shamzhy, Z.
Rev., 2018, 60, 1-70.
Musilová, J. Čejka. Catal. Sci. & Tech.,2018, 18, 4690-4701.
[2] W. Schwab, C. Fuchs, F. C. Huang, Eur. J. Lipid Sci. Technol, 2013,
[24] J. H. Advani, A. S. Singh, N. H. Khan, H. C. Bajaj, A. V. Biradar,
Appl. Cat. B: Environ. 2019, 118456
115, 3-8.
[3] W. F. Erman, M. Dekker, An Encyclopedic Handbook, New York,
1985.
[25] R. Demir-Cakan, N. Baccile, M. Antonietti, M. M. Titirici, Chem.
Mater., 2009, 21, 484-490.
[4] G. Orloff, B. Winter, C. Fehr, (Eds.: P. M. Muller, D. Lamparsky),
Elsevier, New York, 1991, 287.
[26] D. S. Doke, J. H. Advani, D. R. Naikwadi, M. B. Gawande, P. Walke,
S. B. Umbarkar, A. V Biradar, ACS Sustainable Chem. Eng. 2019,
7,3018-3026.
[5] N. Ravasio, F. Zaccheria, A. Gervasini, C. Messi, Catal. Commun.,
2008, 9, 1125-1127.
[27] Wang Q, Li H, Chen L, Huang X. Carbon. 2001, 39, 2211-2214
[6] W. B. Motherwell, M. J. Bingham, J. Pothier, Y. A Six, Tetrahedron,
[28] M. M. Titirici and M. Antonietti, Chem. Soc. Rev., 2010, 39, 103–
2004, 60, 3231-3241.
116.
[7] P. L. Crowell, W. S. Kennan, J. D. Haag, S. Ahmad, E. Vedejs, M. N.
[29] B. Hu, K. Wang, L. H. Wu, S. H. Yu, M. Antonietti and M. M. Titirici,
Gould, Carcinogenesis, 1992, 13, 1261-1264.
Adv. Mater., 2010, 22, 813–828.
[8] K. A. D. S. Rocha, I. V. Kozhevnikov and E. V. Gusevskaya, Appl.
[30] J. P. Paraknowitsch, A. Thomas, Energy Environ. Sci., 2013, 6,
Catal. A, Gen., 2005, 294, 106-110.
2839-3855.
[9] J. Kaminska, M. A. Schwegler, A. J. Hoefnagel, H. V. Bekkum, Recl.
[31] Z. Qiang, Y. Xia, X. Xia, B. D Vogt, Chem. Mater., 2017, 29, 10178-
Trav. Chim. Pays-Bas, 1992, 111, 432-437.
10186.
[10] J. E. Sánchez-Velandia, A. L. Villa, Appl. Catal. A, Gen., 2019, 580,
[32] D. Hulicova-Jurcakova, A. M. Puziy, O. I. Poddubnaya, F. Suarez-
Garcia, J. M. D. Tascon and G. Q. Lu, J. Am. Chem. Soc., 2009,
131, 5026-5027.
17-27.
[11] V. V. Costa, K. A. D. S. Rocha, L. F. D. Sousa, P. A. R. Dutenhefner,
E. V. Gusevskaya, J. Mol. Catal. A Chem., 2011, 345, 69-74.
[33] N. Kannari, S. Okamura, S. I. Fujita, J. I.Ozaki, M. Arai, Adv. Syn.
[12] K. A. D. S. Rocha, J. L. Hoehne, E. V. Gusevskaya, Chem. Eur. J.,
Catal., 2010, 352, 1476-1484.
2008, 14, 6166-6172.
[34] Li P, Liu H, Ding Y, Wang Y, Chen Y, Zhou Y, Tang Y, Wei H, Cai C,
[13] M. Stekrova, N. Kumar, S.F. Díaz, P. Mäki-Arvela, D. Y. Murzin,
Lu T. J. Mater. Chem. 2012, 30, 15370-15378.
Catal. Today, 2015, 241, 237-245.
[35] J. H. Advani, N. H. Khan, H. C. Bajaj, A. V. Biradar. Appl. Surf. Sci.
[14] M. Stekrova, N. Kumar, P. Mäki-Arvela, O. V. Ardashov, K. P.
Volcho, N. F. Salakhutdinov and D. Y. Murzin, Materials, 2013, 6,
2103-2118.
2019, 487, 1307-1315.
[36]
C. Falco, N. Baccile, M. M Titirici, Green Chem., 2011, 13,
3273-3281.
[15] D. R. Shcherban, Y. Barakov, P. Mäki-Arvela, S. A. Sergiienko, I.
Bezverkhyy, K. Eränen, D. Y. Murzin, Appl. Catal. A, Gen. 2018,
560, 236-247.
[37] W. Du, S. L. Hu, K. Y. Niu, J. Sun, J. Yang, N. Q. Zhao, J. Mater.
Chem., 2009, 19, 484-488.
[38] H. Zhu, X. L. Wang, Y. L. Li, Z. J. Wang, F. Yang, X. R Yang, Chem.
Commun., 2009, 5118-5120.
[16] W. F. Hölderich, J. Rösele, G. Heitmann, A. T. Liebens, Catal.
Today, 1997, 37, 353-366.
[39] F. Hu, M. Patel, F. Luo, C. Flach, R. Mendelsohn, E. Garfunkel, H.
[17] J. B. Lewis and G. W. Hedrick, J. Org. Chem., 1965, 30, 4271-4275.
He, M. Szostak, J. Am. Chem. Soc., 2015, 137, 14473-14480.
[18] A. Yu. Sidorenkoa, A. V. Kravtsova, A. Aho, I. Heinma, T. F.
Kuznetsovad D. Yu. Murzin, V. E. Agabekova, Mol. Catal., 2018,
448, 18-29.
[40] D. C. Marcano, D. V. Kosynkin, J. M. Berlin, A. Sinitskii, , Z. Sun;
A. Slesarev, L. B. Alemany, W. Lu, J. M. Tour, ACS Nano., 2010, 4,
4806-4814.
[19] N. Ravasio, F. Zaccheria, M. Guidotti, R, PsaroTop. Top. Catal.
[41] A. M. Puziy, O. I. Poddubnaya, A. Martinez-Alonso, F. Suarez-
2004, 27, 157-168.
Garcia, J. M. D. Tascon, Carbon, 2005, 43, 2857-2868.
[20] D. B. Ravindra, Y. T. Nie, S. Jaenicke and G. K. Chuah, Catalysis
[42] A. M. Puziy, O. I. Poddubnaya, A. M. Ziatdinov, Appl. Surf. Sci.,
Today, 2004, 96, 147-153.
2006, 252, 8036-8038.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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Please do not adjust margins
Dalton Transactions
Page 8 of 9
ARTICLE
Journal Name
[43] C. Dayanand, G. Bhikshamaiah, V. J. Tyagaraju, M. Salagram, A.
View Article Online
DOI: 10.1039/D0DT00921K
S. R. K. Murthy, J. Mater. Sci., 1996, 8, 1945-1967.
[44] A. M. Puziy, O. I. Poddubnaya, R. P. Socha, J. Gurgul, M.
Wisniewski, Carbon, 2008, 46, 2113-2123.
[45] R. Li, Z. D. Wei, L. X. Gou and W. Xu, RSC Adv., 2013, 3, 9978-
9984.
[46] K. Xiao, L. X. Ding, H. Chen, S. Wang, X. L and, H. Wang, J. Mater.
Chem. A., 2016, 4, 372-378.
[47] J. F. Moulder, W. F. Stickle, P. E. Sobol, K. Bomben,J. Chastain.
2nd ed. Eden Prairie, MN: Perkin-Elmer Corporation, Physical
Electronics Division; 1992, 216-232.
[48] E. Desimoni, G. I. Casella and A. M. Salvi, Carbon, 1992, 30, 521-
526.
[49] R. Li, Z. Wei, X. Gou, ACS Catal., 2015, 5, 4133-4142.
[50] C. Wei, H. Wang, K. Eid, J. Kim, J. H. Kim, Z. A. Alothman, Y.
Yamauchi, L. A. Wang, Chem. Eur. J., 2016, 22, 1-8.
[51] Z. Jin, Z. Sun, L. J. Simpson, K. J. O. Neill, A. P. Philip, Y. Li. Nicholas,
P. Stadie, C. C. Ahn, C. Kittrell, J. M. Tour, J. Am. Chem. Soc., 2010,
132, 15246-15251.
[52] P. M. Arvela, N. Shcherban, C. Lozachmeur, V. Russo, J. Wärnå,
D. Y. Murzin, Catalysis Letters, 2019, 149, 203-214.
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