Evaluating Gold and Selenium Chemistry for Selective Transformations of Lignin Model Compounds

Article abstract of DOI:10.1002/adsc.201701207

Applications of gold and selenium chemistry are reported as novel approaches to promote lignin depolymerization into more valuable chemicals via selective oxidation reactions (alcohol oxidations and Baeyer-Villiger reactions). In this study, we proposed two different oxidative methodologies using Au/SiO₂ and phenylseleninic acid resin (PAR) as stable and reusable catalysts to promote selective transformations of the β-O-4 linkage of lignin model compounds. After evaluating the catalytic systems under batch conditions, they were both applied in a packed-bed reactor for continuous flow operations. By using Au/SiO₂ as a catalyst under flow conditions, ketones were efficiently obtained (up to 86% conversion) from the oxidation of alcohols with a residence time (t_R) of 30 min. In the case of Baeyer-Villiger oxidations catalyzed by phenylseleninic acid resin, the corresponding esters were obtained in up to 91% conversion (t_R=30 min). Both systems efficiently catalyzed the conversion of the lignin model compounds. (Figure presented.).

Full text of DOI:10.1002/adsc.201701207

Title: Evaluating Gold and Selenium Chemistry for Selective
Transformations of Lignin Model Compounds
Authors: Leandro Andrade, Wagner Santos, Kevin Dias, Leidaiany
Santos, Camila Kisukuri, Thenner Rodrigues, Rafael
Geonmonond, and Pedro Camargo
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201701207
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Evaluating Gold and Selenium Chemistry for Selective
Transformations of Lignin Model Compounds
a
a
a
a
Wagner C. C. Santos, Kevin A. Dias, Leidaiany P. Santos, Camila M. Kisukuri,
a
a
a
Thenner S. Rodrigues, Rafael S. Geonmonond, Pedro H. C. Camargo, Leandro H.
a
Andrade *
a
Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo, SP, Brazil.
Tel.Fax: +55(11)30912287; e-mail: leandroh@iq.usp.br
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
and C
1
-C
(α-1) linkages in lignin.[7] Some of theses
α
Abstract. Applications of gold and selenium chemistry
are reported as novel approaches to promote lignin
depolymerization into more valuable chemicals via
selective oxidation reactions (alcohol oxidations and
Baeyer-Villiger reactions). In this study, we proposed
methods involve environmentally friendly approaches,
including mild conditions, photocatalysis, metal-free
[8-12]
catalysis, and biocatalysis.
Among the chemical transformations employed for
lignin depolymerization, oxidation reactions have
two different oxidative methodologies using Au/SiO
2
and phenylseleninic acid resin (PAR) as stable and
reusable catalysts to promote selective transformations
of the β-O-4 linkage of lignin model compounds. After
evaluating the catalytic systems under batch conditions,
they were both applied in a packed-bed reactor for
become common methods for producing a wide range
[13]
of aromatic compounds.
Lignin transformations
can lead to phenols, carboxylic acids, aldehydes,
[14]
ethers, esters and ketones. Esters can be produced
by esterification reactions or oxidation of C
β-1 linkages.
β
-C and
γ
continuous flow operations. By using Au/SiO
2
as a
[15]
catalyst under flow conditions, ketones were efficiently
obtained (up to 86% conversion) from the oxidation of
alcohols with a residence time (t ) of 30 min. In the
R
case of Baeyer-Villiger oxidations catalyzed by
phenylseleninic acid resin, the corresponding esters
R
were obtained in up to 91% conversion (t = 30 min).
Considering the chemical structure of lignin, we
decided to focus on the reactivity of the β-O-4
linkage, specifically the benzylic alcohol moiety. A
3
-step approach to break the lignin up into shorter
fragments was proposed (Scheme 1).
Both systems efficiently catalyzed the conversion of the
lignin model compounds.
Keywords: Lignin; Selectivity; Gold; Selenium.
In recent years, scientists as well as governmental and
non-governmental organizations noted the urgency
for the development of new strategies to reduce the
[1]
impact of using nonrenewable carbon resources.
From this perspective, biomass, which is mainly from
lignocellulosic softwood, gained attention as a
feedstock for biofuels and fine chemicals based on
lignin valorization.[ Lignin is a biopolymer present
in the cell walls of plant that is composed of
2]
[
3]
interconnected aromatic monomers.
The most
common interconnections are the β-O-4 (β-aryl
ethers) bonds between benzylic and aliphatic alcohols,
and C -C
α β
or C
1
-C bonds, present in p-coumaryl,
α
[4]
coniferyl and sinapyl alcohols. Various processes
have been developed to extract lignin from the
biomass feedstock, including kraft and organosolv
processes.[ Several strategies have been reported
Scheme 1. β-O-4-type lignin structure[4] and strategies
proposed herein.
According to our approach, an alcohol oxidation
catalyzed by gold can produce ketones, which go on
5,6]
for the cracking of the β-O-4 (β-aryl ethers), C
α
-C
β
1
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
to serve as substrates for Baeyer-Villiger oxidations
catalyzed by selenium compounds. Finally, after
hydrolysis of the corresponding esters, we would be
able to produce lignin fragments containing alcohols
and carboxylic acids.
the ketone in >99% conversion (Table 1, Entry 5).
According to the proposed reaction mechanism, the
oxidant participates in the regeneration of the
catalytic gold surface once the gold-hydride species
(Au-H) is formed (Scheme 2).
Despite the known applications of gold
nanoparticles in the synthesis of carbonyl compounds
via alcohol oxidations,[ different molecular targets,
including lignin, could be challenging for gold
chemistry.
Table 1. Oxidation of 1-(4-methoxyphenyl)ethanol (1a)
using Au/SiO as catalyst under batch conditions.
2
16]
After the seminal study by Prati and Rossi[16i]
involving gold nanoparticles supported on carbon for
the oxidation of alcohols, several advances have been
described in the literature. In recent years, gold
nanoparticles have also been used for C−C cross-
coupling reactions, cycloadditions, hydrosilyation,
etc.[
Entrya) Solvent Oxidant t (h)
Conv (%)b)
1
2
3
4
5
6
7
8
THF
THF
THF
THF
O
O
O
O
H
H
H
H
H O
H O
H O
-
2
2
2
2
2
2
2
2
2
4
8
24
2
2
2
2
2
2
2
2
2
2
26
42
87
92
>99
97
63
35
35
10
36
10
n.r.
n.r.
16j]
Our approach to lignin transformations also
requires a Baeyer-Villiger oxidation, and a literature
THF
O
O
O
O
2
2
2
2
2
2
2
[17]
survey revealed that Grieco et al. described the use
of benzeneperoxyseleninic acid as oxidizing agent for
this reaction. Hydrogen peroxide can be used to
regenerate the active selenium species for the Baeyer-
Villiger reaction.
MTBE
Dioxane
Acetone
DMF
DMSO
MeOH
THF
9
2
10
11
12
13
14
2
Inspired by the very interesting results with gold
and selenium chemistry, we developed a study
focused on the transformations of lignin in which
both methodologies could be applied either under
batch or continuous flow conditions.[18]
2
c)
d)
e)
THF
THF
-
H O
2
2
a)
Reaction conditions: 1a (1 mmol), solvent (2 mL),
oxidant [O (atmospheric pressure) or H
0 mmol)], KOH (1 mmol), Au/SiO (80 mg/ 4 mol %)
Initially, we synthesized Au nanoparticles from the
2
2
O2 (aq.) (aq. 30%,
-
[19]
reduction of AuCl
4
(aq) with ascorbic acid.
SEM
4
2
images (Figure S1) of the Au nanoparticles revealed
that they were monodisperse, 20 nm in diameter, and
spherical in shape. Since our approach involves the
use of gold nanoparticles in a packed-bed reactor for
a continuous flow application, we decided to
immobilize these nanoparticles in an inert and
b)
and room temperature. Conversions were calculated
based on GC-MS analysis (none byproduct was
c)
d)
observed). Without H
2
O
2
.
2 2 2
Without H O and Au/SiO .
e)
2
Without Au/SiO . n.r. = no reaction was observed.
inexpensive material, SiO
2
. Au/SiO particles were
2
A solvent screen was also performed, and MTBE,
dioxane, acetone, DMF, DMSO and MeOH were
tested (Table 1, Entries 6-11). Despite the good
results with all these solvents, the best results were
achieved with MTBE and THF (97-99% conv, Table
prepared via the immobilization of Au nanoparticles
2
-1
onto SiO
Au on Au/SiO
found to be 0.252% (%w/w). The Au/SiO
2
(pore size 22 ꢀ, 800 m g ). The loading of
was determined by ICP-OES and was
particles
2
2
were also characterized by SEM (Figure S2) and
XRD (Figure S3) analyses. The SEM results showed
1
, Entries 5 and 6). Additional reactions were carried
out in the absence of catalyst and H O2 (aq.) (Table 1,
2
a uniform dispersion of Au NPs over SiO
2
support.
Entries 12-14), and the results indicated that both
components are essential to the oxidation of the
alcohol.
The mechanism of this reaction likely involves
three main steps (Scheme 2). Initially, alkoxide is
generated from the base, and then it is adsorbed on
the gold surface to afford species B. In the second
step, -hydride elimination affords the corresponding
ketone and gold-hydride species (Au-H, species C).
Finally, Au-H is oxidized by the presence of an
After the preparation of Au/SiO materials, the
2
next step was the evaluation of their catalytic activity
towards the oxidation of 1-(4-methoxyphenyl)
ethanol (1a) to the corresponding ketone (2a). For the
optimization study, alcohol 1a was subjected to
different oxidants and organic solvents (THF, MTBE,
dioxane, acetone, DMF and MeOH) for appropriate
times (2, 4, 8 and 24 h) (Table 1).
The reaction using THF as the solvent and O as
2
the oxidant (Table 1, Entry 1) afforded 1-(4-
methoxyphenyl)ethanone (2a) in 26% after 2 h. By
extending the reaction time to 4, 8 and 24 h, increases
in the conversion were observed (to 42, 87 and 92%
conversion, respectively; Table 1, Entries 2-4).
oxidant (by H
2
O
2
or O
2
)20]to regenerate the catalytic
[
gold surface (species A).
However, instead of using a gaseous oxidant (O
decided to evaluate an aqueous solution of H
Fortunately, the alcohol oxidation with peroxide gave
2
) we
2
O .
2
2
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
(
PBR) (1/4 in. × 4.6 mm × 5 cm; reactor volume with
particles: 0.5 mL). The oxidation of 1-(4-
methoxyphenyl)ethanol (1a) was chosen as model
reaction for the optimization of the continuous flow
conditions (Table 2).
As shown in Table 2, Entry 1-4, various attempts
to run the reaction using different conditions were not
successful, since the injection pump shut off due to
clogging. We used silica (SiO ) as the support
2
material, and a high pressure was generated due to
the large amount of water in the reaction mixture.
Fortunately, the fluidic system worked very well
when methanol was employed as the solvent. In
addition, the amount of H
with the concomitant decrease in the amount of water
Table 2, Entry 5). The reaction was carried out at
0 °C with 30 min of residence time, and the ketone
2
O2 (aq) was decreased along
(
4
was prepared in 57% conversion. When the residence
time was increased to 60 min, higher product
formation was observed (75% conv; Table 2, Entry 6).
When a back pressure regulator (100 psi) was
attached to the system, higher ketone formation was
obtained (77% conv) in a shorter residence time
(Table 2, Entry 7). When the continuous production
of 2a was maintained for 8 h, no decrease in catalytic
activity was observed. Finally, another attempt to
Scheme 2. Proposed mechanism for alcohol oxidation
[
20]
2
catalyzed by Au/SiO .
Table 2. Oxidation of 1-(4-methoxyphenyl)ethanol (1a)
using Au/SiO as the catalyst and H (aq.) under
continuous flow conditions.
2
2 2
O
further decrease the amount of H O2 (aq) (4 equiv) was
not effective (Table 2, Entry 10 and 11).
2
From this set of experiments, we were able to
identify suitable reaction conditions for other
substrates, namely, benzylic alcohols 1b-d (Table 3).
Table 3. Substrates for alcohol oxidation catalyzed by
Au/SiO particles under continuous flow conditions.
2
Entrya) Solvent T ( C)
o
H
(equiv) Conv (%)b)
2
O
2
1
2
3
4
5
6
7
8
9
1
THF
THF
rt
40
rt
40
40
40
40
60
60
rt
400
400
400
400
40
60
40
40
40
4
n.p.
n.p.
n.p.
n.p.
57
75
77
74
82
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
c)
d)
d)
c)
0
1
-
-
1
40
4
a)
-1
Reaction conditions: 1a (12 mmol L ); H
2
O
2 (aq.) (30%
-
1
aq., 4-400 equiv); KOH (12 mmol L ); t
particles (460 mg) were packed into stainless-steel tube
PBR: 1/4 in. × 4.6 mm × 5 cm; reactor volume with
Au/SiO : 0.5 mL); Continuous flow operation for 1.5 h, 3 h
Entries 6 and 9) or 8 h (Entry 7). Conversions were
determined by GC-MS at the end of each t (no byproduct
60 min. A Celite pad (380 mg) and a
R 2
30 min; Au/SiO
(
2
b)
(
R
c)
d)
was observed).
t
R
a)
Reaction conditions: Substrates 1b-d (12 mmol L-1 in
BPR (back pressure regulator: 100 psi) were attached to
the system. n.p. = Not performed (The injection pump shut
off due to clogging).
-
2
MeOH); H O2 (aq.) (30% aq., 40 equiv); KOH (12 mmol L
1
)
; t
R
= 30 min; 40 °C; Continuous flow operation for 8 h;
(460 mg) was packed into stainless-steel tube (1/4
Au/SiO
2
in. × 4.6 mm × 5 cm; reactor volume with beads: 0.5 mL);
b)
Celite pad (380 mg); and BPR (100 psi). Conversions
were determined by GC-MS and H NMR analysis, and at
the end of the t no byproduct was observed.
R
Aiming to enhance the Au catalyst recycling, we
designed a packed-bed reactor that can be used in
1
continuous flow mode (Table 2). The Au/SiO
particles were confined into a packed-bed reactor
2
3
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
By running the reactions with a t
°C, the mono-alcohols
benzyloxy)phenyl)ethanol (1b) and
benzyloxy)phenyl)-2-phenylethanol (1c)
R
= 30 min at
diphenyl diselenide, which is a commercially available
selenium compound.
4
(
(
0
1-(4-
1-(4-
were
oxidized to the corresponding ketone in 80 and 51%
conv, respectively (Entries 1 and 2, Table 3). In
addition, when substrate 1-(4-(benzyloxy)phenyl)-2-
phenyl-propane-1,3-diol (1d) was submitted to
continuous flow oxidation, ketone 2d was prepared in
Table
4.
Baeyer-Villiger
oxidation
of
4-
a)
b)
methoxyacetophenone employing (PhSe)
catalysts.
2
and PAR as
68% conv. Notably, only the benzylic alcohol moiety
was oxidized, which indicates the oxidation is highly
selective.
Due to concerns about gold leaching during
continuous flow operation, we analyzed the reaction
effluent by ICP-OES. The results are illustrated in
Table S1, and showed that there is no significant loss
Entry
Solvent Oxidant
Se
Catalyst
Conv (%)e)
3
a
6a
1
2
3
4
5
6
7
8
CH
CH
CH
2
2
2
Cl
2
Cl
2
Cl
2
TBHP
UHP
(PhSe)
(PhSe)
(PhSe)
(PhSe)
(PhSe)
(PhSe)
(PhSe)
(PhSe)
(PhSe)
PAR
2
2
2
2
2
2
2
2
2
-
-
of Au from the Au/SiO
operation.
2
during the continuous flow
2
4
-
-
-
-
H
2
O
2 (aq.)
After preparing the ketones by the Au-catalyzed
alcohol oxidations, we turned our attention to the
Baeyer-Villiger oxidation using selenium species as
oxidizing agents.[ We also envisioned a packed-bed
reactor loaded with solid catalyst for the oxidation
reaction, i.e., phenylseleninic acid resin (PAR)
THF
THF
THF
TBHP
UHP
5
-
H
2
O
2 (aq.)
89
-
-
-
17]
MeOH TBHP
MeOH UHP
-
-
9
1
MeOH
MeOH
MeOH
H
H
H
2
2
2
O
O
O
2 (aq.)
2 (aq.)
2 (aq.)
94
35
38
-
23
24
(
Scheme 3).
c)
0
1
c),d)
1
PAR
a)
Reaction conditions: 2a (0.5 mmol); oxidant (2 mmol);
b)
(
PhSe)
2
(0.025 mmol); solvent (3 mL).
(30% aq., 5 mmol); PAR
50 mg); MeOH (3 mL). PAR was recycled three times.
Reaction
conditions: 2a (0.5 mmol); H
2
O
2
c)
(
d)
o
e)
3
0 C. Conversions were determined based on GC-MS
analysis (no byproduct was observed).
As shown in Entries 1-3 of Table 4, the use of
diphenyl diselenide as a pre-catalyst for the Baeyer-
Scheme 3. Proposed mechanism/system for the Baeyer-
Villiger oxidation of lignin model ketones with PAR.
Villiger oxidation in CH
2
Cl was not efficient even
2
when using different oxidants, including t-butyl
hydroperoxide (TBHP), urea-hydrogen peroxide
(
UHP) or H
2
O
2 (aq.). However, the reactions in THF
Phenylseleninic acid resin (PAR) was prepared
from poly(styrene-co-divinylbenzene) (4) and n-
dibutyl diselenide (Scheme 4). Commercially
available resin 4 was treated with n-BuLi, and n-
and MeOH with H
2
O
2 (aq.) as the oxidant showed good
conversions (89 and 94%, respectively) (Entries 6
and 9, Table 4). In fact, the water solubility of these
solvents (THF and MeOH) had a positive effect on
the oxidation reaction since that facilitates the
interactions of all chemicals, which was not observed
in the reaction with dichloromethane, a highly
hydrophobic solvent.
dibutyl diselenide [(n-Bu)Se
2
] was added, resulting in
the n-butylselenide resin (5). Then, 5 was oxidized to
[20]
phenylseleninic acid by H
2
O
2 (aq.)
.
The loading of
selenium was evaluated by acid-base titration with
-
NaOH, and was found to be 1.42 ± 0.05 mmol g
1
[21,22]
Based on these results, we evaluated the activity of
.
the phenylseleninic acid resin in the oxidation of 2a
using H O2 (aq.) with methanol as the solvent. The
2
Baeyer-Villiger oxidation was efficient (58% conv,
Table 4, entry 10); however, 4-methoxy-phenol (6a)
was also produced from the hydrolysis of ester 3a.
Considering our lignin transformation approach
Scheme 4. Preparation of the PAR catalyst.
(
Scheme 1), the ester hydrolysis under the Baeyer-
Villiger oxidation conditions is not an issue since the
alcohol is our desired fragment. In addition, by
treating this crude mixture (Table 4, entry 10) with a
With the phenylseleninic acid resin in hand, we then
used it as a catalyst for the Baeyer-Villiger oxidation under
batch conditions (Table 4). Considering the presence of
phenylselenyl moieties on the PAR, we also decided to test
K
2
CO
completely hydrolyzed into the corresponding phenol
6a).
3
/methanolic solution for 30 min, the ester was
(
4
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
Furthermore, a slight increase in the temperature
products were decreased (Entries 1 and 2, Table 5).
did not provide a significant increase in the
conversion (Entry 11, Table 4). A recycling study
was performed with the phenylseleninic acid resin,
which revealed the PAR maintained excellent activity
even after reuse (Entries 10 and 11, Table 4).
The oxidation of 2a with H
2
O2 (aq.) (1:10) with a t =
R
15 min showed good product formation with low
over-oxidation (Entry 2, Table 5, conv = 77%).
These reaction conditions were applied in the
Baeyer-Villiger oxidation of the ketonic lignin
analogues (2b-d) (Table 6).
The apparatus for the Baeyer-Villiger oxidation
under continuous flow operation was very similar to
what was used in the oxidation study (previous
section). A packed-bed reactor (stainless steel tubing:
Table 6. Baeyer-Villiger oxidation of lignin model ketones
employing phenylseleninic acid resin in a flow system.
1
0
/4 in × 4.6 mm × 5 cm; reactor volume with PAR:
.5 mL) was loaded with PAR (570 mg).
The
Baeyer-Villiger
oxidation
of
4-
methoxyacetophenone (2a) was chosen for evaluating
some parameters under continuous flow operation
(
Table 5).
Different ratios between 2a and H
2
O (aq.) were
2
studied, including 1:2 (Entry 3, Table 5), 1:5 (Entry 4,
Table 5) and 1:10 (Entries 1 and 2, Table 5). The
residence time (t
R
) was also evaluated (15 min
(
Entries 2-4, Table 5) and 30 min (Entry 1, Table 5)).
Table
5.
Baeyer-Villiger
oxidation
of
4-
methoxyacetophenone (2a) using PAR under continuous
flow conditions.
Entrya)
t
R
H
Conv (%)e)
2
O
2
:2a
(
min)
b)
b)
f)
f)
1
2
3
30
15
15
15
0.2:0.02
0.2:0.02
34% 3a, 30% 6a, 27%
24% 3a, 43% 6a, 10%
4% 3a, 22% 6a
a)
-1
Reaction conditions: 2b-d (20 mmol L ) and H
2
O
2
(aq.
-1
3
0%; 200 mmol L ) in MeOH; Continuous flow operation
c)
0.04:0.02
R
for 8 h with a t = 15 min; PAR (570 mg) was packed into
d)
4
0.1:0.02
11% 3a, 26% 6a
stainless-steel tube (1/4 in. × 4.6 mm × 5 cm; reactor
a)
-1
b)
Reaction conditions: 2a (20 mmol L ) and H
aq.; 200 mmol L ; 40 mmol L ; 100 mmol L ) in
MeOH; Continuous flow operation for 1.5 h or 12 h (Entry
2
O
2 aq. (30%
volume with PAR: 0.5 mL); and BPR (100 psi).
b)
-1 c)
-1 d)
-1
1
Conversions were determined by GC-MS and H NMR
c)
analysis at the end of t
R
(no byproduct was observed). 1-
2
); PAR (570 mg) was packed into stainless-steel tube (1/4
(
4-(Benzyloxy)phenyl)-2-phenoxyprop-2-en-1-one (9) was
d)
in. × 4.6 mm × 5 cm; reactor volume with PAR: 0.5 mL);
BPR (100 psi). Conversions were determined based on
GC-MS analysis at the end of each t
identified as quinones.
obtained as the sole product.
performed under batch condition. n.d.: Not detected.
This reaction was
e)
f)
R
.
Byproducts were
The oxidation reaction of 4-benzyloxy-
acetophenone (2b) at rt with a t
the corresponding ester (3b) and 4-benzyloxyphenol
6b), which is from the hydrolysis of the ester (71%
R
= 15 min afforded
As shown in Table 5, a reaction with a t = 30 min
R
afforded the desired products (3a and 6a) in high
conversion (91%, Entry 1, Table 5). However, we
also observed the formation of quinones, which are
(
conv, Table 6, entry 1). Notably, no undesired over-
oxidation products were observed.
[23]
from the over-oxidation of the phenolic products.
A similar reaction profile was also observed for the
Fortunately, the formation of these by-products was
suppressed by using a lower concentration of the
oxidant and a shorter residence time. By decreasing
Baeyer-Villiger
oxidation
of
1-(4-
(
benzyloxy)phenyl)-2-phenoxyethanone (2c), which
gave the ester 4-(benzyloxy)phenyl-2-phenoxyacetate
(3c) and 4-benzyloxyphenol (6b) (86% conv, Entry 2,
Table 6).
the t
R
(15 min), the conversions to 3a and 6a were
not affected, but the conversions to the undesired
5
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
On the other hand, when 1-(4-(benzyloxy)phenyl)- Acknowledgements
3
-hydroxy-2-phenoxy-propan-1-one (2d) was used as
The authors are grateful to the National Council for Scientific
and Technological Development (CNPq: 140956/2014-0,
the substrate, the desired product was not observed
(
(
Entry 3, Table 6); the dehydration product, 1-(4-
1
40828/2016-8) and the São Paulo Research Foundation
benzyloxy)phenyl)-2-phenoxyprop-2-en-1-one (9)
(
FAPESP) for financial support (FAPESP: 2014/22457-5;
was identified as the sole product. We proposed that
the substrate (2d), which is a β-hydroxy ketone,
undergoes an elimination reaction to afford
corresponding unsaturated ketone 9.
15/26308-7, and 15/21366-9).
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Despite the unexpected formation of α,β-
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Entry 10, Table 4), and the corresponding esters
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Advanced Synthesis & Catalysis
10.1002/adsc.201701207
COMMUNICATION
Evaluating Gold and Selenium Chemistry for
Selective Transformations of Lignin Model
Compounds
Batch and
Continuous Flow
Conditions
O
b-O-4 Linkage
OH
O
OH
Au
OH HO
R
Adv. Synth. Catal. Year, Volume, Page – Page
O
OH
R
R
O
HO
OH
R
O
O
Lignin Models
Se
Lignin fragments
Wagner C. C. Santos, Kevin A. Dias, Leidaiany P.
Santos, Camila M. Kisukuri, Thenner S. Rodrigues,
Rafael S. Geonmonond, Pedro H. C. Camargo,
Leandro H. Andrade *
O
b-O-4 Type Lignin
8
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