Celite-Polyaniline supported palladium catalyst for chemoselective hydrogenation reactions

Article abstract of DOI:10.1002/aoc.4767

Polyaniline coated on particles of celite is used as support to load palladium catalyst. This heterogenized Celite?PANI?Pd system, is used as an efficient catalyst for chemoselective hydrogenation reactions. The catalyst is characterized by usual spectral, analytical techniques and studied for hydrogenation reactions at ambient conditions. The mild reaction conditions allow the control over the reactions and excellent selectivity is achieved in number of conversions. Hydrogenation of a carbon–carbon double bond was favored over other polar π-bond systems, while labile functional groups such as benzyl ether, benzyl esters, cyano, nitro and halogen remained unaffected. Primary amines were converted to N,N-dimethyl amines with formaldehyde, the double bond of coumarin was selectively hydrogenated without opening of the lactone functionality.

Full text of DOI:10.1002/aoc.4767

Received: 21 September 2018
DOI: 10.1002/aoc.4767
Revised: 20 November 2018
Accepted: 23 November 2018
F U L L P A P E R
Celite‐Polyaniline supported palladium catalyst for
chemoselective hydrogenation reactions
Heta A. Patel | Maitreyee Rawat | Arun L. Patel | Ashutosh V. Bedekar
Department of Chemistry, Faculty of
Polyaniline coated on particles of celite is used as support to load palladium cat-
alyst. This heterogenized Celite•PANI•Pd system, is used as an efficient catalyst
for chemoselective hydrogenation reactions. The catalyst is characterized by
usual spectral, analytical techniques and studied for hydrogenation reactions
at ambient conditions. The mild reaction conditions allow the control over the
reactions and excellent selectivity is achieved in number of conversions. Hydro-
genation of a carbon–carbon double bond was favored over other polar π‐bond
systems, while labile functional groups such as benzyl ether, benzyl esters,
cyano, nitro and halogen remained unaffected. Primary amines were converted
to N,N‐dimethyl amines with formaldehyde, the double bond of coumarin was
selectively hydrogenated without opening of the lactone functionality.
Science, M. S. University of Baroda,
Vadodara 390 002, India
Correspondence
Arun L. Patel and Ashutosh V. Bedekar,
Department of Chemistry, Faculty of
Science, M. S. University of Baroda,
Vadodara 390 002, India.
Email: arunpatel_5376@yahoo.co.in;
avbedekar@yahoo.co.in
Funding information
University Grants Commission, Grant/
Award Number: F No. 42‐240/2013
KEYWORDS
celite•PANI support, chemoselective transformations, heterogeneous catalysis, hydrogenation,
palladium catalysis
1 | INTRODUCTION
adds another dimension to the selective hydrogenation
reactions.
Chemoselective transformations of functional groups in
organic compounds containing more than one reactive
sites, remains a fascinating area of contemporary syn-
thetic chemistry. Of the variety of selective organic trans-
formations carried out by reagents and catalysts,
hydrogenation reaction occupies a pivotal position due
to its versatility, wide applications and its adoptability
for large scale industrial applications. Selectively
achieved catalytic hydrogenation of π‐systems, in pres-
ence of other reducible groups, to access saturated or
reduced compounds, is also an important synthetic tool
in modern organic chemistry.[1] A strategy to selectively
target slightly more reactive functional group, while
keeping the other moieties unaffected during hydrogena-
tion reactions require precise tuning of the catalysts,
reaction conditions and other parameters. The hydroge-
nation reaction also has other interesting role of causing
cleavage of certain specific groups, particularly used in
deprotections in synthetic manipulations. Hence, this
Many heterogeneous catalysts have been designed for
selective catalytic transformations based on different
metals, however the ones with palladium remain most
widely investigated and utilized. Usually palladium on
charcoal (Pd/C) is considered to be very active heteroge-
neous catalyst and not particularly useful for achieving
chemoselective conversions. Heterogeneous palladium
catalysts anchored on various solid supports are
commonly used to hydrogenate several reducible func-
tional entities and knockout protecting groups such as
N‐benzyloxycarbonyl (Cbz), O‐tert‐butyldimethylsilyl
(TBS), O‐benzyl; from amines, acids, and alcohols under
mild and neutral reaction conditions. Due to high cata-
lytic activity, Pd/C and similar catalysts, are used to com-
plete the reactions while reducing most of the reducible
groups. In order to achieve chemoselectivity one needs
to tame the activity of the catalyst so that its efficiency
drops considerably, and this type of tuning can lead it
to react preferentially to more reactive of the possible
Appl Organometal Chem. 2019;e4767.
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© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4767

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PATEL ET AL.
groups, while not targeting the more robust groups. In
case of Pd/C this is often achieved by introducing chemi-
cally polar impurities, or referred as poisons, which bind
with catalyst sites and effectively blocking the active loca-
tions, making it less reactive. These poisons are often
nitrogen containing organic compounds such as quino-
line, ethylenediamine,[2] sulphur derivatives such as
diphenylsulfide,[3] thiophene, butylmercaptan[4] or few
other inorganic materials like boron nitride,[5a] mesopo-
rous silica, MCM‐48,[5b] MS3A etc.[1e]
SCHEME 1 Anchoring of palladium catalyst on heterogenized
PANI on celite
Many new hybrid materials are being considered to
anchor the metal ions to be used as heterogeneous cata-
lysts.[6] One such type of material is polyaniline (PANI)
or similar polymers prepared from derivatives of aniline.
Mostly PANI is studied from the angle of its electrically
conducting properties.[7] Few studies have indicated that
PANI incorporated in inorganic supports like silica can
affect its conducting properties.[8] Some nanoparticles of
the PANI composites[9] and micrometer‐size hollow parti-
cles[10] have also been prepared and studied for various
properties. The widely accepted quinonoidal‐benzenoid
emeraldine structure of PANI has nitrogen atoms ideally
situated to act as ligands to bind with metal ions. This
ability is exploited to attach metal ions and scan them
as heterogeneous catalysts for a number of organic trans-
formations. Many different metal ions are loaded on
PANI and scanned for effective reactions such as oxida-
tions,[11] Michael reaction,[12] coupling reactions,[13] ace-
tyl transfer reaction,[14] Biginelli reaction[15] along with
few miscellaneous transformations.[16]
The active species of catalyst for the Suzuki‐Miyaura
coupling reaction and its variants could most likely be
Pd(0) species. The same catalyst will also be useful candi-
date for hydrogenation reactions on active π‐systems to
access saturated compounds. Interestingly there are only
a few reports of PANI•Pd catalysts, being explored for
conducting this type of transformation.[19] Since the pal-
ladium is loaded on a support which is weakly basic in
nature, there is all the possibility of its being tamed as
compared to Pd/C and hence the system shows some
degree of chemoselectivity towards certain functional
groups. In this paper we shall extend this concept with
our heterogenized Celite•PANI•Pd catalyst system and
explore possibility to conduct new chemoselective organic
transformations. In a way we shall explore the possibility
of the role of basic polymer backbone of PANI to act as a
deactivator or a catalyst poison in the system and see if
chemoselectivity can be achieved similar to Lindlar cata-
lyst[20] or Rosenmund reduction.[21]
Some of these catalyst systems encounter practical dif-
ficulties of restricted contact of reagents with catalyst or
leaching of active metal ions during the repeated reac-
tions. This affects its performance as a recyclable and
reusable catalyst, also the amount of PANI used for gen-
eration of final product is quite high which is a matter
of concern due to its slight toxicity.[17] In some other
cases the porosity of the PANI‐Metal composite is also
an issue, which indirectly affects the access of reagents.
To overcome some of these difficulties and trying to make
the PANI catalysts truly heterogeneous in nature,
increase its surface area to more efficiently bind with
metal ions, we have attempted to heterogenize it on solid
support (Scheme 1). In our earlier effort we have coated
the particles of celite with PANI, then this heterogenized
Celite•PANI was treated with palladium metal salt to pre-
pare the active catalyst, Celite•PANI•PdCl2 and tested it
for suitable coupling reactions.[18] The catalyst was then
effectively used to carry out Suzuki‐Miyaura coupling
reaction along with one‐pot Suzuki‐aldol reaction. This
is the first report of such approach of heterogenization
of PANI and utilizing it as supports for loading catalysts
for organic transformations.
1.1 | Experimental
Thin layer chromatography was performed on silica gel
plates coated on aluminum sheets. The spots were visual-
ized under UV light or with iodine vapor. All the com-
pounds were purified by column chromatography on
silica gel (60–120 mesh). All the reactions were carried
out under H2 balloon at room temperature. NMR Spectra
were recorded on a Bruker Avance 400 Spectrometer
(400 MHz for 1H NMR, in CDCl3 and TMS as an internal
standard). Melting points were recorded in Thiele tubes
using paraffin oil.
General procedure for hydrogenation using Cat‐A3 as
catalyst:
Starting material (0.1 g), Cat‐A3 (0.1 g, 0.39 mmol of
Pd) and methanol (10 mL) were taken in a round bottom
flask, fitted with a balloon filled with H2 and the reaction
mixture was stirred at room temperature. The air from
the flasks was replaced by altering vacuum and hydrogen
gas. The reactions were stirred at the ambient conditions

PATEL ET AL.
3 of 11
for the duration mentioned in each cases. All the reac-
tions were monitored by tlc, on completion of the reac-
tion, the catalyst was separated by filtration and the
products were purified by short column chromatography
over silica gel. The yields mentioned refer to the isolated
2H), 5.65 (br s, 1H), 7.15–7.17 (m, 2H), 7.21–7.25 (m, 3H),
7.28–7.33 (m, 5H).
N‐Phenyl‐3‐phenylpropionamide (20).
m.p. 97–98 °C (Lit.[30] 96 °C).
1H NMR (400 MHz, CDCl3): δ 2.65–2.68 (t, J = 7.6 Hz,
2H), 3.04–3.08 (t, J = 7.6 Hz, 2H), 7.09–7.13 (m, 1H),
7.23–7.32 (m, 7H), 7.45–7.47 (m, 2H).
2‐Diphenylethane (21).
1
yield and the products have been characterized by H
NMR and by comparing their physical properties.
Methyl 3‐phenylpropanoate (4).
m.p. 144 °C [Lit.[22] 142‐145 °C].
m.p. 54 °C (Lit.[31] 52 °C).
1H NMR (400 MHz, CDCl3): δ 3.69 (s, 3H), 2.64–2.68
(t, J = 8 Hz, 2H), 2.96–3.0 (t, J = 8 Hz, 2H), 7.21–7.25
(m, 3H), 7.30–7.33 (m, 2H).
1H NMR (400 MHz, CDCl3): δ 2.94 (s, 4H), 7.18–7.24
(m, 8H), 7.30–7.35 (m, 4H).
1‐Nitro‐4‐phenethylbenzene (22).
Ethyl 3‐phenylpropanoate (6).
m.p. 55‐57 °C (Lit.[32] 55‐56 °C).
m.p. 122 °C [Lit.[23] 122‐124 °C].
1H NMR (400 MHz, CDCl3): δ 2.95–3.00 (m, 2H),
3.04–3.08 (m, 2H), 7.15–7.17 (m, 2H), 7.21–7.26 (m, 1H),
7.29–7.32 (m, 4H), 8.13–8.16 (m, 2H).
4‐Phenethylbenzonitrile (23).
1H NMR (400 MHz, CDCl3): δ 1.23–1.27 (t, J = 7.2 Hz,
3H), 2.62–2.66 (t, J = 7.6 Hz, 2H), 2.95–2.97 (t, J = 7.6 Hz,
2H), 4.12–4.17 (q, J = 7.2 Hz, 2H), 7.20–7.23 (m, 3H),
7.21–7.33 (m, 2H).
Low melting solid (Lit.[33] 41‐42 °C).
1H NMR (400 MHz, CDCl3): δ 2.93–2.96 (m, 2H),
2.99–3.01 (m, 2H), 7.14–7.16 (m, 2H), 7.23–7.32 (m, 6H),
7.56–5.59 (m, 2H).
Benzyl 3‐phenylpropanoate (8).
Thick liquid at room temperature.[24]
1H NMR (400 MHz, CDCl3): 2.70–2.74 (t, J = 7.6 Hz,
2H), 2.98–3.02 (t, J = 7.6 Hz, 2H), 5.14 (s, 2H), 7.21–
7.25 (m, 3H), 7.29–7.39(m, 7H).
1‐Fluoro‐4‐(4‐methylphenethyl)benzene (24).
m.p. 65 °C.
3‐Phenyl‐N‐propylpropanamide (10).
1H NMR (400 MHz, CDCl3): δ 2.35 (s, 3H), 2.89 (t,
J = 5.6 Hz, 4H), 6.96–7.00 (m, 2H), 7.07–7.09 (m, 2H),
7.11–7.16 (m, 4H).
m.p. 50 °C (Lit.[25] 46‐49 °C).
1H NMR (400 MHz, CDCl3): 0.84–0.88 (t, J = 7.6 Hz,
3H), 1.43–1.48 (m, 2H), 2.46–2.50 (t, J = 7.6 Hz, 2H),
2.96–3.00 (t, J = 7.6 Hz, 2H), 3.16–3.21 (m, 2H), 5.44 (br
s, 1H), 7.20–7.23 (m, 3H), 7.30–7.32 (m, 2H).
N‐Butyl‐3‐phenylpropanamide (12).
1‐Chloro‐4‐phenethylbenzene (25).
m.p. 51‐52 °C (Lit.[34] 49 °C).
1H NMR (400 MHz, CDCl3): δ 2.92 (s, 4H), 7.11–7.13
(d, J = 8.4 Hz, 2H), 7.18–7.20 (d, J = 8.4 Hz, 2H), 7.21–
7.28 (m, 3H), 7.30–7.33 (m, 2H).
Thick liquid at room temperature.[26]
1H NMR (400 MHz, CDCl3): δ 0.88–0.92 (t, J = 7.6 Hz,
3H), 1.24–1.29 (m, 2H), 1.37–1.39 (m, 2H), 2.45–2.49 (t,
J = 7.6 Hz, 2H), 2.95–2.99 (t, J = 7.6 Hz, 2H), 3.18–3.23
(m, 2H), 5.46 (br s, 1H), 7.19–7.22 (m, 3H), 7.27–7.32
(m, 2H).
1‐Methoxy‐4‐phenethylbenzene (26).
m.p. 61‐62 °C (Lit.[35] 58‐60 °C).
1H NMR (400 MHz, CDCl3): δ 2.91 (s, 4H), 3.82 (s,
3H), 6.85–6.87 (d, J = 8.4 Hz, 2H), 7.12–7.14 (d,
J = 8.4 Hz, 2H), 7.20–7.25 (m, 3H), 7.32–7.33 (m, 2H).
3‐Phenylpropanenitrile (27).
N‐(2‐Hydroxyethyl)‐3‐phenylpropanamide (14).
m.p. 73 °C (Lit.[27] 72.5–73.5 °C).
Liquid at room temperature.[36]
1H NMR (400 MHz, CDCl3): δ 2.50–2.53 (t, J = 7.6 Hz,
2H), 2.95–3.03 (t, J = 7.6 Hz, 2H), 3.35–3.39 (q, J = 5.2 Hz,
2H), 3.62–3.65 (t, J = 5.2 Hz, 2H), 5.94 (br s, 1H), 7.21–
7.24 (m, 3H), 7.28–7.33 (m, 2H).
1H NMR (400 MHz, CDCl3): δ 2.63–2.76 (t, J = 7.6 Hz,
2H), 2.97–3.00 (t, J = 7.6 Hz, 2H), 7.25–7.32 (m, 3H),
7.35–7.39 (m, 2H).
(2‐Nitroethyl)benzene (28)
N‐(1‐Hydroxy‐2‐methylpropan‐2‐yl)‐3‐
Liquid at room temperature.[37]
phenylpropanamide (16).
1H NMR (400 MHz, CDCl3): δ 3.33–3.36 (t, J = 7.6 Hz,
2H), 4.62–4.66 (t, J = 7.6 Hz, 2H), 7.22–7.25 (m, 2H),
7.29–7.32 (m, 1H), 7.33–7.38 (m, 2H).
1,3‐Diphenylpropan‐1‐one (29).
m.p. 93‐95 °C (Lit.[28] 95‐97 °C).
1H NMR (400 MHz, CDCl3): δ 1.12 (s, 6H), 2.44–2.45
(t, J = 7.6 Hz, 2H), 2.94–2.98 (t, J = 7.6 Hz, 2H), 3.51 (s,
2H), 4.87(br s, 1H), 5.45 (br s, 1H), 7.20–7.25 (m, 3H),
7.28–7.33 (m, 2H).
m.p. 72‐73 °C (Lit.[38] 74‐75 °C).
1H NMR (400 MHz, CDCl3): δ 3.08–3.12 (t, J = 8 Hz,
2H), 3.20–3.35 (t, J = 8 Hz, 2H), 7.22–7.35 (m, 4H),
7.46–7.50 (m, 2H), 7.57–7.60 (m, 2H), 7.98–8.00 (m, 2H).
1,3‐Diphenylpropan‐1‐ol (30).
N‐Benzyl‐3‐phenylpropanamide (18).
m.p. 85 °C (Lit.[29] 84.5–86.5 °C).
1H NMR (400 MHz, CDCl3): δ 2.51–2.55 (t, J = 7.6 Hz,
2H), 3.02–3.04 (t, J = 7.6 Hz, 2H), 4.41–4.42 (d, J = 6 Hz,
Colourless oil.[39]

4 of 11
PATEL ET AL.
1H NMR (400 MHz, CDCl3): δ 1.94 (br s, 1H), 2.04–
N‐Benzyl‐4‐methylaniline (54).
m.p. 57‐58 °C (Lit.[44] 59‐60 °C).
2.17 (m, 2H), 2.67–2.78 (m, 2H), 4.70–4.73 (m, 1H),
7.19–7.29 (m, 2H), 7.30–7.32 (m, 4H), 7.33–7.38 (m, 4H).
3‐(4‐Methoxyphenyl)‐1‐phenylpropan‐1‐one (31).
m.p. 66 °C (Lit.[38] 64‐65 °C).
1H NMR (400 MHz, CDCl3): δ 2.38 (s, 3H), 4.02 (br s,
1H), 4.31 (s, 2H), 6.66–6.68 (d, J = 7.6 Hz, 2H), 6.73–6.76
(t, J = 7.6 Hz, 1H), 7.15–7.23 (m, 4H), 7.28–7.31 (m, 2H).
N‐(4‐Methoxybenzyl)aniline (55).
1H NMR (400 MHz, CDCl3): δ 3.02–3.05 (t, J = 8 Hz,
2H), 3.28–3.31 (t, J = 8 Hz, 2H), 6.85–6.88 (dd,
J1 = 6.8 Hz, J2 = 2 Hz, 2H), 7.19–7.21 (d, J = 8.8 Hz, 2H),
7.46–7.49 (m, 2H), 7.56–7.60 (m, 1H), 7.97–7.99 (m, 2H).
3‐(4‐Methoxyphenyl)‐1‐phenylpropan‐1‐ol (32).
m.p. 62‐63 °C (Lit.[39] 65 °C).
m.p. 47‐48 °C (Lit.[43] 45‐46 °C).
1H NMR (400 MHz, CDCl3): δ 3.92 (s, 3H), 4.01 (br s),
4.49 (s, 2H), 6.66–6.68 (m, 2H), 6.74–6.76 (m, 1H), 6.90–
6.92 (m, 2H), 7.19–7.23 (m, 2H), 7.31–7.33 (m, 2H).
N‐(4‐Fluorobenzyl)aniline (56).
1H NMR (400 MHz, CDCl3): δ 1.90 (br s, 1H), 1.91–
2.14 (m, 2H), 2.60–2.72 (m, 2H), 4.68–4.72 (m, 1H),
6.83–6.87 (m, 2H), 7.12–7.38 (m, 7H).
m.p. 100–101 °C (Lit.[45] 102 °C).
1H NMR (400 MHz, CDCl3): δ 4.05 (br s, 1H), 4.32 (s,
2H), 6.63–6.66 (m, 2H), 6.73–6.77 (m, 1H), 7.03–7.08 (m,
2H), 7.17–7.23 (m, 2H), 7.34–7.37 (m, 2H).
N‐Benzyl‐4‐chloroaniline (57).
1‐Phenyl‐3‐(p‐tolyl)propan‐1‐one (33).
Low melting solid (Lit.[40] 37–38 °C).
1H NMR (400 MHz, CDCl3): δ 2.35 (s, 3H), 3.04–3.07
(t, J = 8 Hz, 2H), 3.29–3.33 (t, J = 8 Hz, 2H), 7.13–7.19
(m, 4H), 7.46–7.49 (m, 2H), 7.56–7.58 (m, 1H), 7.97–7.99
(m, 2H).
Thick oil (Lit.[44]).
1H NMR (400 MHz, CDCl3): δ 4.12 (br s, 1H), 4.33 (s,
2H), 6.55–6.59 (m, 2H), 7.11–7.15 (m, 2H), 7.28–7.38 (m,
5H).
1‐Phenyl‐3‐(p‐tolyl)propan‐1‐ol (34).
Chroman‐2‐one (59).
m.p. 55‐56 °C (Lit.[39] 54‐56 °C).
Low melting solid (Lit.[46] 23–26 °C).
1H NMR (400 MHz, CDCl3): δ 2.02–2.16 (m, 2H), 2.38
(s, 3H), 2.65–2.74 (m, 2H), 4.69–4.73 (q, 1H), 7.12–7.28
(m, 4H), 7.31–7.33 (m, 1H), 7.38–7.39 (m, 4H).
3‐(Benzo[d][1,3]dioxol‐5‐yl)‐1‐phenylpropan‐1‐one
(35).
1H NMR (400 MHz, CDCl3): δ 2.79–2.83 (m, 2H),
3.01–3.04 (m, 2H), 7.06–7.14 (m, 2H), 7.21–7.29 (m, 2H).
Methyl 3‐(2‐hydroxyphenyl)propanoate (60).
Low melting solid (Lit.[47] 41.5 °C).
1H NMR (400 MHz, CDCl3): δ 2.73–2.76 (t, J = 6.8 Hz,
2H), 2.91–2.95 (t, J = 6.8 Hz, 2H), 6.87–6.91 (m, 2H),
7.10–7.16 (m, 2H), 7.19 (br s, 1H).
General procedure for Reductive N‐methylation of
aromatic primary amines using Cat‐A3 as catalyst
(Table 6):
A mixture of aromatic amine (0.1 g, 1.07 mmol), form-
aldehyde (0.34 ml, 3.22 mmol), Cat‐A3 (0.1 g, 0.39 mmol
of Pd) and methanol (10 ml) was taken in a round bottom
flask. It was attached a balloon of H2 gas, the air was
replaced by altering vacuum and hydrogen gas and the
contents were stirred at room temperature (20 hr, tlc).
The catalyst was separated by filtration and the products
were purified by short column chromatography over sil-
ica gel. The yields mentioned refer to the isolated yield
m.p. 88‐89 °C (Lit.[41] 87‐88 °C).
1H NMR (400 MHz, CDCl3): δ 2.99–3.03 (m, 2H),
3.26–3.30 (m, 2H), 5.94 (s, 2H), 6.71–6.77 (m, 3H), 7.46–
7.50 (m, 2H), 7.56–7.60 (m, 1H), 7.96–7.99 (m, 2H).
3‐(Benzo[d][1,3]dioxol‐5‐yl)‐1‐phenylpropan‐1‐ol (36).
m.p. 90‐93 °C (Lit.[42] 93‐94 °C).
1H NMR (400 MHz, CDCl3): δ 1.61 (br s, 1H), 1.61–
2.15 (m, 2H), 2.58–2.73 (m, 2H), 4.68–4.71 (dd,
J1 = 7.6 Hz, J2 = 5.6 Hz, 1H), 5.94 (s, 2H), 6.65–6.76 (m,
3H), 7.29–7.40 (m, 5H).
1‐(4‐Chlorophenyl)‐3‐phenylpropan‐1‐one (37).
m.p. 80 °C (Lit.[38] 78‐80 °C).
1H NMR (400 MHz, CDCl3): δ 3.06–3.10 (t, J = 8 Hz,
2H), 3.28–3.32 (m, 2H), 7.22–7.28 (m, 3H), 7.31–7.34 (m,
2H), 7.44–7.46 (m, 2H), 7.90–7.93 (dd, J1 = 6.4 Hz,
J2 = 2 Hz, 2H).
1
and the products have been characterized by H NMR
and m.p.
1‐(4‐Chlorophenyl)‐3‐phenylpropan‐1‐ol (38).
N,N‐Dimethylaniline (40).
Low melting solid (Lit.[39] 42 °C).
b.p. 193 °C (Lit.[48] 193 °C).
1H NMR (400 MHz, CDCl3): δ 1.95–2.15 (m, 3H),
2.74–2.74 (m, 2H), 4.67–4.70 (dd, J1 = 8 Hz, J2 = 5.2 Hz,
1H), 7.13–7.41 (m, 9H).
1H NMR (400 MHz, CDCl3): δ 2.98 (s, 6H), 6.74–6.80
(m, 3H), 7.27–7.31 (m, 2H).
4‐Chloro‐N,N‐dimethylaniline (42).
Low melting solid (Lit.[49] 35–37 °C).
1H NMR (400 MHz, CDCl3): δ 2.92 (s, 6H), 6.74–6.80
(m, 2H), 7.17–7.20 (m, 2H).
N‐benzylaniline (53).
Low melting solid (Lit.[43] 36‐37 °C).
1H NMR (400 MHz, CDCl3): δ 4.36 (s, 2H), 6.65–6.69
(m, 2H), 6.73–6.77 (m, 1H), 7.19–7.23 (m, 2H), 7.29–7.36
(m, 1H), 7.37–7.42 (m, 4H).
4‐Bromo‐N,N‐dimethylaniline (44).
m.p. 56 °C (Lit.[50] 53‐55 °C).

PATEL ET AL.
5 of 11
1H NMR (400 MHz, CDCl3): δ 2.93 (s, 6H), 6.74–6.80
TABLE 1 Preparation of different samples of Celite•PANI
(dd, J1 = 6.8 Hz, J2 = 2 Hz, 2H), 7.07–7.08 (dd,
J1 = 6.8 Hz, J2 = 2 Hz, 2H).
Amount of aniline
used during
polymerization
Amount of
Code of
Celite•PANI
4‐Methoxy‐N,N‐dimethylaniline (46).
No
Celite•PANIa
obtainedb
m.p. 46 °C (Lit.[51] 46‐48 °C).
1
2
3
Celite•PANI (1)
Celite•PANI (2)
Celite•PANI (3)
1.0 g
2.5 g
5.0 g
5.35 g
5.62 g
6.05 g
1H NMR (400 MHz, CDCl3): δ 2.89 (s, 6H), 3.79 (s,
3H), 6.77–6.81 (m, 2H), 6.85–6.89 (m, 2H).
N,N‐4‐Trimethylaniline (48).
b.p. 200 °C (Lit.[52] 204‐206 °C).
aFor 5.0 g of celite.
bAfter proper drying.
1H NMR (400 MHz, CDCl3): δ 2.28 (s, 3H), 2.84 (s,
6H), 6.71–6.73 (d, J = 8.4 Hz, 2H), 7.07–7.10 (d,
J = 8.4 Hz, 2H).
In the present study we shall be investigating the
effect of different ratio of palladium with respect to PANI
or indirectly with the basic nature of the support. Accord-
ingly, the dry sample of Celite•PANI of the above mate-
rial was stirred with different quantities of PdCl2 in dry
acetonitrile (24 hr), material was filtered, washed and
dried till constant weight (Table 2). Depending upon the
combination of the quantity of PANI and palladium, four
samples of the final Celite•PANI•Pd were prepared (Cat‐
A1 to Cat‐A4).
N,N‐Dimethyl‐4‐nitroaniline (50).
M.p. 165‐167 °C (Lit.[53] 164‐166 °C).
1H NMR (400 MHz, CDCl3): δ 3.14 (s, 6H), 6.60–6.64
(dd, J1 = 9.6 Hz, J2 = 3.6 Hz, 2H), 8.13–8.16 (dd,
J1 = 9.6 Hz, J2 = 3.6 Hz, 2H).
N,N‐2,4‐Tetramethylaniline (52).
Pale yellow liquid (Lit.[51]).
1H NMR (400 MHz, CDCl3): δ 2.29 (s, 3H), 2.32 (s,
3H), 2.69 (s, 6H), 6.98–7.01 (m, 3H).
The above catalysts were characterized by usual tech-
niques such as IR, XRD, SEM, EDS, BET, TGA, XPS and
ICP‐AES (Supporting information Figure S1 to S7).[18]
The efficacy of the prepared catalysts for hydrogenation
reaction was then checked for a standard reaction with
methyl cinnamate 1 (Table 3). The catalyst with low load-
ing of PANI and palladium (Cat‐A1) showed no conver-
2 | RESULT AND DISCUSSION
One of the common ways to obtain PANI is by oxidative
polymerization of aniline with ammonium persulfate in
aqueous acidic medium.[54] In the present work we
intend to coat the particles of celite with PANI, separate
the heterogenized Celite•PANI, characterize it and then
load palladium on it to make the final catalyst
Celite•PANI•Pd. Hence, the polymerization of freshly
distilled aniline was performed in its aqueous solution
of hydrochloric acid with ammonium persulfate in pres-
ence of suspended particles of celite. The celite particles
coated with PANI were separated by simple filtration
and washed appropriately, and then the free emeraldine
form was generated by treatment with aqueous ammonia.
On drying we obtained a free flowing sample of
Celite•PANI, which was stirred with PdCl2 in dry aceto-
nitrile (room temperature, 24 hr), which was filtered,
washed adequately and dried.[18] For the present study
we have chosen to prepare three samples of Celite•PANI
by varying the amount of aniline used for the polymeriza-
tion reaction. Three samples were prepared when celite
(5.0 g) was taken with different quantities of aniline
(1.0, 2.5 and 5.0 g, see Table 1). The amount of the final,
dried Celite•PANI in each case was different, which was
labelled as Celite•PANI (1), Celite•PANI (2) and
Celite•PANI (3), and used for further modification of
introducing the palladium ion to produce the active cata-
lyst for screening in heterogeneous hydrogenation
reactions.
1
sion under the conditions, detected by H‐NMR analysis
of the crude sample. As expected catalysts with slightly
higher loading of PANI and palladium (Cat‐A2) showed
moderate conversion in a short reaction time. While the
other two catalysts under the similar conditions gave
good to excellent conversion.
Optimum conversion with respect to the PANI and
palladium loading was seen in the case of Cat‐A3 and
hence we selected it for further investigations. The ability
to easily separate and recycle the catalyst is critical for
heterogeneous systems. In order to establish this aspect,
we set up a series of experiments where this catalyst
was recovered and reused for up to five cycles with very
little loss in its activity (Figure 1). The consistent results
TABLE 2 Preparation of different samples of Celite•PANI
Code of
Amount of PdCl2 for Catalyst
No Celite•PANI useda Celite•PANI
Code
1
2
3
4
Celite•PANI (1)
Celite•PANI (2)
Celite•PANI (3)
Celite•PANI (3)
0.05 g
0.10 g
0.15 g
0.20 g
Cat‐A1
Cat‐A2
Cat‐A3
Cat‐A4
aFor 1.0 g of corresponding Celite•PANI.

6 of 11
PATEL ET AL.
TABLE 3 Hydrogenation of methyl cinnamate 1
TABLE 4 Hydrogenation of methyl cinnamate 1
Binding energy (eV)
No
Catalyst
N 1 s
Pd 3d3/2
Pd 3d 5/2
1
2
3
4
PANI
398a
No
Catalyst (W in g)a
Yield (%)b
Celite•PANI
Cat‐A3 (fresh)
Cat‐A3 (After 2 h)
398.5
399.2
1
2
3
4
5
6
7
8
Cat‐A1 (0.05)
Cat‐A1 (0.10)
Cat‐A2 (0.05)
Cat‐A2 (0.10)
Cat‐A3 (0.05)
Cat‐A3 (0.10)
Cat‐A4 (0.05)
Cat‐A4 (0.10)
NRc
NRc
55.1
71.6
89.1
99.4
94.1
99.1
337.8
342.9
335.2
337.6
340.5
342.7
5
Cat‐A3 (After 24 h)
336.1
341.4
aData from ref.13a
3d3/2 and Pd 3d5/2 with binding energy 337.8 eV and
342.9 eV respectively (Figure 2), the values are in agree-
ment with the binding energy for Pd2+ species.[55] To
aFor 0.10 g of 1, methanol (10 mL), r.t., H2 (balloon), 5 hr;
bIsolated;
cNo reaction.
FIGURE 1 Recycle study for hydrogenation of 1 with Cat‐A3
of the five cycles indicate towards negligible leaching of
active metal catalyst during hydrogenation.
The characterization of this type of catalysts has been
discussed in our earlier work,[18] however, some addi-
tional analysis of the present set indicated interesting fea-
tures. The IR analysis of this set of catalysts was in
accordance with expected data. The powder XRD data
of fresh sample of Cat‐A3 indicated characteristic signals
corresponding to two theta values at 40 and 46, which are
typical peaks for palladium (Figure S2).[13c] The percent-
age of palladium loading per 1 g of catalyst for Cat‐A3
and Cat‐A4 was found to be 0.42 and 0.50 by ICP‐AES
analysis.[18] In the present study we have extend the char-
acterization of the catalyst and performed XPS analysis of
Celite•PANI and Cat‐A3 (Table 4). The observed binding
energy peaks of N 1 s for PANI was observed at 398 eV,
for Celite•PANI and Cat‐A3, it shifted to 398.5 eV and
399.2 eV. This electron modification indicates coordina-
tion of palladium chloride with nitrogen of polyaniline.
The Pd 3d region of XPS spectra showed presence of Pd
FIGURE 2 XPS analysis of Cat‐A3 before the reaction (a); after
2 hr (b) and after 24 hr (c)

PATEL ET AL.
7 of 11
understand the changes in the catalyst during the hydro-
genation process, we isolated it after suitable duration
(2 hr and 24 hr) and analyzed by XPS. It was observed
that the fresh Pd (II) catalyst was reduced to Pd(0) as
established by the comparison of binding energy of Pd
3d3/2 and Pd 3d5/2. After 24 hr the only signals of Pd
3d3/2 and Pd 3d5/2 were seen at 336.1 eV and 341.4 eV
respectively. These values point towards the presence of
Pd(0), which must be the active catalyst in the hydroge-
nation reaction (see Figure S7 for XPS).[56]
The Cat‐A3 system was initially scanned to establish
effective catalytic activity for the hydrogenation of olefin
in presence ester and amides groups (Table 5). All the
reactions were run at ambient conditions, where the flask
is attached with hydrogen filled balloon (methanol, 5 hr).
The carbon–carbon double bond undergoes reduction
preferentially and high selectivity was observed when
the reaction was run for a limited time. The reduction
of benzyl cinnamate 7 (entry 3) was also successfully
achieved to afford the sole product 8, where the carbon–
carbon double bond underwent selective hydrogenation
reaction. The same was also performed for longer dura-
tion (24 hr) to confirm formation of 8, with the same
selectivity. The products were isolated by column chro-
matography (silica gel), characterized by H NMR analy-
sis and physical properties were compared. These
results, including selectivity and conversions were com-
parable with similar examples,[57] while in some cases
with reduced reaction time.
1
One of the main objectives of the present investiga-
tion is to explore feasibility of applications of
Celite•PANI•Pd for selective hydrogenation of alkene in
presence of other reducible functional groups. We
extended our scanning of the Cat‐A3 for hydrogenation
of molecules containing both groups, including nitro,
cyano or aromatic halides and the results are summarized
in Scheme 2. Aromatic cyano and nitro groups undergo
facile reduction in the presence of H2‐Pd/C to afford
corresponding amino compounds.[58] We tested our sys-
tem of H2/Cat‐A3 for hydrogenation of cyano and nitro
containing alkenes, such as stilbenes and styrenes
(Scheme 2). The catalyst showed distinct preference for
hydrogenation of carbon–carbon double bond over more
polar π‐bonds of ‐CN and –NO2 groups. Similarly fluorine
and chlorine containing stilbenes underwent selective
reduction of alkene group under our conditions.
Another interesting class of compounds is that of
chalcones, which contains ketone which can easily be
reduced along with alkene, were further investigated.
These are challenging substrates as aromatic carbonyl
groups are easily reduced to corresponding methylenes,
via benzyl alcohol intermediates. Selective hydrogenation
of alkene of chalcones without reducing the aromatic
ketones is known to be difficult.[59] We were interested
to explore our catalyst system for selective reduction of
chalcones. In our initial experiments we observed
TABLE 5 Hydrogenation of derivatives of cinnamic acid
No
Olefin
Product
Yielda (%)
1
99
2
3
4
98
95
98
5
6
7
97
96
99
8
9
98
99
SCHEME
2
Hydrogenation of stilbenes and styrenes.
Conditions: Stilbenes or styrenes (0.1 g), Cat‐A3 (0.1 g), H2
balloon, r.t., 5 hr
aIsolated yield.

8 of 11
PATEL ET AL.
preferential hydrogenation of alkene under ambient
conditions, while with prolong reaction time, the ketone
was also reduced to alcohol. Careful examination of
several experiments indicated that in shorter reaction
time (5 hr) the alkene was completely hydrogenated with-
out reducing the ketone, while after a much longer reac-
tion (24 hr), we could isolate the corresponding saturated
r.t., 20 hr, Table 6). Anilines containing reducible groups
like chloro, bromo and nitro gave the corresponding N,N‐
dimethyl anilines. The chemoselectivity of Cat‐A3 was
demonstrated in such examples, where more reactive
imine intermediates underwent catalytic hydrogenation
under the present mild conditions. Significant electronic
effects were observed according to the nature of the
substituents on the anilines. Electron donating groups
on aniline led to an increase in yield while electron
withdrawing group increases the selectivity in N‐
monomethylated anilines which led to decrease in N,N‐
dimethylated product. Hindrance at ortho position did
impair the reactivity (Table 6, entry 7) as compared to
4‐methylaniline (Table 6, entry 5).[63c]
The reduction of imines to the corresponding second-
ary amines is a useful transformation in organic synthe-
sis. Amines constitute important constituents of several
biologically important compounds and hence their prepa-
ration is of considerable commercial value. One of the
more widely followed methods of their synthesis involve
reduction of imines by hydride transfer reagents or by
catalytic hydrogenation.[62] We extended the scope of
applications of our catalyst system for effective conver-
sion of imines to the corresponding secondary amines
(Scheme 4).
1
benzyl alcohol as a single product (Scheme 3). The H
NMR analysis of the product confirmed the absence of
corresponding methylene product (ArCH2CH2CH2Ar)
under this condition. This kind of complete hydrogena-
tion of chalcone was observed with much active catalyst
such as H2/Pd‐C system.[3] This observation further con-
firms that our present catalyst, is much milder as com-
pared to H2/Pd‐C. This selectivity of the present catalyst
system was confirmed by number of examples
(Scheme 3).
Alkylated amines are important class of compounds,
as they are used as intermediates in the synthesis of var-
ious dyes, surfactants, preservatives, pesticides etc.[60]
More common approach of their synthesis involve
dimethylation of primary amines with aqueous formalde-
hyde,[61] followed by hydrogenation of the intermediate
formed. We further extend our catalyst system for this
application. Reductive N‐methylation of primary aro-
matic amines using Cat‐A3, formaldehyde as carbon
source, was carried out at mild conditions (H2 balloon,
TABLE 6 Reductive alkylation of aromatic amines
No
Substrate
Product
Yielda (%)
1
74
2
3
4
5
6
71
73
86
73
43
7
56
SCHEME 3 Hydrogenation of chalcones
aIsolated Yield.

PATEL ET AL.
9 of 11
TABLE 7 Hydrogenation of coumarin 58
Catalyst
(% W/W)
Ratio
(58:59:60)a
No
Solvent
Time (h)
1
2
3
4
5
6
7
8
9
MeOH
MeOH
MeOH
MeOH
EtOAc
THF
7
24
42
7
100
100
100
200
100
100
100
100
150
65:4:31
35:7:58
0:0:100
71:6:23
90:10:0
84:16:0
62:38:0
7:93:0
SCHEME 4 Hydrogenation of imines. Conditions: Imine (0.1 g),
Cat‐A3 (0.1 g), H2 balloon, r.t., 7 hr
12
20
40
80
80
THF
In the next application we have investigated the
reduction of the carbon–carbon π‐bond of coumarin.
Coumarins are an important class of compounds, in
which reduced coumarins i.e. 3,4‐dihydrocoumarins are
widely distributed in nature and exhibit some interesting
biological activities, such as anti‐herpetic, anti‐ inflam-
matory, anti‐oxidative, anti‐aging, and anti‐cancer activi-
ties.[63] Therefore, development of efficient methods for
the synthesis of dihydrocoumarins have attracted consid-
erable interest in recent years.[64] The most conventional
method for hydrogenation of coumarin is by using transi-
tion metals based catalyst systems.[65] Initially we exam-
ined our standard reaction conditions for catalytic
hydrogenation of coumarin 58 with Cat‐A3 in methanol
at ambient conditions (Table 7). The crude product after
THF
THF
0:100:0
aDetermined by 1H NMR.
1
filtration of the catalyst was analyzed by H NMR.
In the shorter reaction time considerable amount of
unreacted coumarin 58 was detected, along with small
amount of dihydrocoumarin 59. However, the other prod-
uct formed was identified as methyl ester of 3‐(2‐
hydroxyphenyl)propanoic acid 60. This product 60 is
probably formed by the ring opening of coumarin moiety
during the hydrogenation reaction in methanol. When
the reaction was conducted in THF, expectedly, the
desired dihydrocoumarin 59 was the only product
formed. The optimization of the reaction indicates the
need for longer reaction time, but at mild condition.
To test the ability of the catalyst to selectively hydro-
genate structurally less hindered alkene in the presence
of more demanding olefinic group, we designed another
experiment (Scheme 5). Two similar alkenes, β‐cyano sty-
rene 61 and β‐phenyl‐β‐cyano styrene 62 were exposed to
the hydrogenation conditions with Cat‐A3. The mixture
SCHEME 5 Selective hydrogenation of structurally accessible
alkene
found to undergo hydrogenation, probably due to the
ease of its adsorption on catalyst surface. On the other
hand trisubstituted and bulkier substrate 62 remained
unaffected, no reduced product 64 was detected. In all
the products the cyano group remained unaffected, estab-
lishing the chemoselective nature of the catalyst.
Thus in this experiment we could establish the typical
behavior of heterogeneous catalyst in preferentially
hydrogenating the structurally less bulky alkene as well
as its chemoselectivity.
In this paper we present our studies on the applica-
tions of a heterogeneous catalyst, where the palladium
was loaded on celite particles coated with PANI as an
anchoring support. The basic nature of PANI behaves
as a poison and suppresses the activity of the catalyst,
1
of the products was analyzed by H NMR to determine
the composition. Due to the heterogeneous nature of
the catalyst system, structurally less demanding 61 was

10 of 11
PATEL ET AL.
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S. Zafari, A. R. Miandashti, Polym. Adv. Technol. 2015, 26, 645.
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transformations.
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ACKNOWLEDGEMENT
We thank University Grants Commission (UGC), New
Delhi for the financial support (F No. 42‐240/2013) and
Council of Scientific and Industrial Research (CSIR),
New Delhi for Senior Research Fellowship to HAP. We
also thank DST‐FIST for the NMR facility in the
department.
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ORCID
Ashutosh V. Bedekar
https://orcid.org/0000-0001-7537-
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How to cite this article: Patel HA, Rawat M,
Patel AL, Bedekar AV. Celite‐Polyaniline supported
palladium catalyst for chemoselective
hydrogenation reactions. Appl Organometal Chem.
2019;e4767. https://doi.org/10.1002/aoc.4767
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