Selective Primary Alcohol Oxidation of Lignin Streams from Butanol-Pretreated Agricultural Waste Biomass

Article abstract of DOI:10.1002/cssc.201801971

Chemically modified lignins are important for the generation of biomass-derived materials and as precursors to renewable aromatic monomers. A butanol-based organosolv pretreatment has been used to convert an abundant agricultural waste product, rice husks, into a cellulose pulp and three additional product streams. One of these streams, a butanol-modified lignin, was oxidized at the γ position to give a carboxylic acid functionalized material. Subsequent coupling of the acid with aniline aided lignin characterization and served as an example of the flexibility of this approach for grafting side chains onto a lignin core structure. The pretreatment was scaled up for use on a multi-kilogram scale, a development that enabled the isolation of an anomeric mixture of butoxylated xylose in high purity. The robust and scalable butanosolv pretreatment has been developed further and demonstrates considerable potential for the processing of rice husks.

Full text of DOI:10.1002/cssc.201801971

Accepted Article
Title: Selective Primary Oxidation of Lignin Streams from Butanol-
Pretreated Agricultural Waste Biomass
Authors: Isabella Panovic, Christopher S Lancefield, Darren Phillips,
Mark Gronnow, and Nicholas James Westwood
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemSusChem 10.1002/cssc.201801971
Link to VoR: http://dx.doi.org/10.1002/cssc.201801971
A Journal of
www.chemsuschem.org

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
Selective Primary Alcohol Oxidation of Lignin Streams from
Butanol-Pretreated Agricultural Waste Biomass
Isabella Panovic,[a] Christopher S. Lancefield, [a] Darren Phillips,[b] Mark J. Gronnow,[b] and Nicholas J.
Westwood*[a]
chemicals and functional materials could be generated from lignin
if suitable processes can be found.
Abstract: Chemically modified lignins are important for the generation
of biomass-derived materials and as precursors to renewable
aromatic monomers. A butanol-based organosolv pretreatment has
been used to convert an abundant agricultural waste product, rice
husks, into a cellulose pulp and three additional product streams. One
of these streams, a butanol-modified lignin, was oxidised at the γ-
position to give a carboxylic acid functionalized material. Subsequent
coupling of the acid with aniline aided lignin characterization and
served as an example of the flexibility of this approach for grafting side
chains onto a lignin core structure. The pretreatment was scaled up
for use on a multi-kilogram scale, a development that enabled the
isolation of an anomeric mixture of butoxylated xylose in high purity.
The robust and scalable butanosolv pretreatment has been developed
further and demonstrates considerable potential for the processing of
rice husks.
Introduction
Lignocellulosic biomass consists of a mixture of cellulose (c.a. 30-
50%), lignin (c.a. 10-30%) and hemicellulose (c.a. 20-35%).[1]
Currently, the Kraft and lignosulfonate processes deliver large
quantities[2,3] of valuable saccharide product streams at the
required high purity levels. These methods also give a lignin
stream which is typically burnt on-site to return energy back into
the process or is used in low value materials as an additive or
binding agent.[4] There is considerable interest in higher value
uses for lignin, due to its aromatic-rich structure, with research
dominated by two main approaches; (i) its use in polymeric
materials for co-polymer blending and grafting applications,[5,6]
and (ii) its depolymerisation to useful aromatic monomers.[7–9] The
structural complexity of lignin offers both a challenge and an
opportunity. In theory a wide range of different feedstock
Figure 1. A Comparison of dioxasolv and butanosolv lignins. A Mechanism of
formation of butoxylated β-O-4 units during the butanosolv process. In an acidic
organosolv pretreatment, benzylic cation 3 is formed from native β-O-4 unit 1.
For butanosolv, 3 is convert to a butoxylated β-O-4 unit 2. In contrast for
dioxasolv, 3 reacts to form condensed C-C bond containing units and lignin-
bound Hibbert’s ketones (LB-HK).[10] B and C 2D HSQC NMR (700 MHz, d6-
DMSO) analysis of B dioxasolv walnut shell lignin and C butanosolv walnut shell
lignin. Full conversion to the butoxylated β-O-4 unit 3 (orange signals) often
occurs in the butanosolv process, as shown by the complete loss of the cross-
peaks (highlighted in dashed red circle) corresponding to the native β-O-4 unit
1 (blue signals).
[a]
[b]
Miss I. Panovic, Dr. C. S Lancefield, Dr N. J. Westwood*
School of Chemistry & Biomedical Sciences Research Complex,
University of St Andrews and EaStCHEM,
North Haugh, St Andrews, Fife (UK) KY16 9ST
E-mail: njw3@st-andrews.ac.uk
Mr D. Phillips, Dr M. J. Gronnow
Biorenewables Development Centre,
1 Hassacarr Close, Chessingham Park, Dunnington, York (UK)
YO19 5SN
Most biorefineries focus on the carbohydrate product
streams, meaning severe conditions are used to remove the
“contaminating” lignin. Typically the lignin’s β-O-4 unit (structure
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
1 in Figure 1A), which is the most abundant unit in native lignins,
is heavily degraded. Destruction of the β-O-4 unit and extensive
formation of additional C-C bonds (condensation) yields lignins
that are less chemically tractable than the native biopolymer.[11,12]
In contrast, some organosolv pretreatments treat lignocellulosic
biomass[13,14] more gently with the drawback that less pure
carbohydrate streams are formed. In addition, due to the frequent
use of acidic conditions, some organosolv lignins are still
condensed. We[15] and others[16–20] have previously reported the
use of biorenewable butanol as a pretreatment solvent for woody-
biomass sources, using both hardwoods and softwoods.[15] Under
the acidic butanosolv conditions, the hydroxyl at the α-position of
the β-O-4 unit is replaced by butanol leading to stabilisation of the
β-O-4 unit in a “protected”[21] form (structure 2, Figures 1 and S1).
Failure to trap benzylic cations such as 3 results in condensation
or the formation of (lignin-bound) Hibbert’s ketones (LB-HK,
Figure 1).[10] Another example of a “protected lignin” was reported
recently by Luterbacher et al. who created a aldehyde-stabilised
lignin in which the β-O-4 α- and γ-hydroxyls were tethered
together (double protection).[22,23]
coupling reactions. Butoxylated xylose (mixture of anomers) is
also isolated in high purity from a hemicellulose-derived stream.
Results and Discussion
Previously we have described the application of butanosolv
pretreatment of beech (hardwood), walnut shells (hardwood
endocarp) and Douglas fir (softwood) (Table S1, entries 1-3,
Figure S4).[15] In each case the cellulose was retained in a pulp
and
a soluble fraction containing modified hemicellulose
monosaccharides and lignin was removed by filtration (Figure S2).
Here, the initial goal was to optimise the butanosolv pretreatment
for use with a herbaceous monocot agricultural waste product
(Figure S3).[34] The aim was to determine mild conditions capable
of delivering rice husk butanosolv lignin (RHBL) in optimal yields
with high retention of β-O-4 content (β-O-4 per 100 C9 unit
calculation, Figure S5 and Table S2).
In agriculture the majority of crops produced come from
herbaceous monocots, such as rice, wheat, sugarcane and maize,
and therefore large volumes of agricultural waste from these
sources are generated annually. Among these, rice is one of the
most cultivated crops in the world with around 680 million tonnes
produced per annum.[24] Rice husks make up around 20 wt% of
the rice grain and are composed of approximately 22% lignin,
38% cellulose, 18% hemicelluloses, 2% extractives and 20%
ashes with variations depending on geographical origin.[25,26] As a
result of high lignin and ash content, the husks are not a viable
animal feed,[27] but they can be burnt to yield large quantities of
silica that can be used in a number of material applications.[25,27–
33]
However, compared to the relatively well valorised
polysaccharide fractions and processing of rice husk-derived
silica, little attention has been paid to the abundant lignin fraction.
Here, we report that
a
butanol-based organosolv
pretreatment of rice husks allows for efficient processing of the
biomass. We show that this process is scalable up to a multi-
kilogram scale and that the resulting rice husk butanosolv lignin
(RHBL) has high β-O-4 content with the expected incorporation of
butanol at the α-position of the β-O-4 unit. RHBL is shown to be a
suitable substrate in an organocatalytic oxidation to give a γ-
carboxylic acid-containing lignin that can be used in amide
Figure 2. Graphs showing lignin weight % yields (bar charts) and total β-O-4
per 100 C9 data (line chart); A Effect of changing biomass loading (conditions
identical except for quantity of solvent system used per gram of rice husks); B
Pretreatment time (time pretreatment was maintained at reflux);
C Final
hydrochloric acid molarity in 95:5 butanol/water solvent system; D Ratio of
butanol to water using a fixed final concentration of 0.2 M HCl. The optimal
conditions based on both lignin wt% yields (green bars) and β-O-4 per 100 C9
values are shown. All pretreatments were performed on a 4 g scale. Error bars
are based on three repeats of each pretreatment.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
A range of biomass loadings were initially assessed varying
were hampered by very long filtration times after lignin
precipitation (Figure S7D). The requirement to use large
quantities of water for the lignin precipitation also meant that
from 5-12 mL of solvent per gram of rice husks. Whilst all the
loadings led to the isolation of RHBL with a high total β-O-4
content, the lignin yield was optimal at 10 mL/g (Figure 2A). Using
this loading level, it was then shown that the reflux time also
affected the lignin yield. The optimal outcome was obtained after
6 hours at reflux with yields dropping at extended times,
presumably due to lignin condensation resulting in a significant
proportion of the lignin being in the insoluble pulp (Figure 2B).
Upon varying the acid molarity whilst retaining a butanol:water
ratio of 95:5 (using 10 mL/g loading and 6 hours at reflux), the
highest yield of high quality RHBL was obtained when a final
concentration of acid of 0.2 M was used. A significant decrease in
the β-O-4 content was observed when higher concentrations of
acid were used (Figure 2C) as expected.[13] Finally, when the final
acid concentration was fixed at 0.2 M, varying the butanol:water
ratio showed that with increasing amounts of water relative to
butanol, there was a decrease in yield (Figure 2D). Optimal
conditions for the butanosolv pretreatment of rice husks were
determined to be: biomass loading of 10 mL/g, 6 h pretreatment
time, 0.2 M final concentration of hydrochloric acid in a 95:5
butanol:water ratio.
Gel permeation chromatography (GPC) analysis of RHBL
was conducted during the optimisation study (Table S2). A
general decrease in Mw was observed with an increase in final
acid molarity (Mw 3939 for 0.05 M c.f. Mw 2842 for 0.8 M)
consistent with more acidic conditions leading to increased lignin
cleavage and a reduction in chain length.
The scalability of the process was studied next. The quality
of the RHBL was very similar over a pretreatment scale that
ranged from 4 g to 400 g to 4000 g. This was assessed using 2D
HSQC NMR analysis and semi-quantitative integration of the
spectra obtained for the different batches of RHBL (Figure 3,
Table S3 and Figure S6). Yields of the different product streams
were also reproducible across all the scales tested (Table S3).
The separation of the RHB lignin and the hemicellulose-
derived (RHBH) streams using our published work-up protocol[15]
proved challenging on larger scale (Figures S1 and S7A-E). The
use of the contrasting solubility of the lignin (insoluble) and the
hemicellulose-derived streams (soluble) in aqueous solution was
effective for small-scale pretreatments (Figure S7B) and small
portions (28 g) of the crude hemicellulose-derived/lignin mixture
retained from larger pretreatments (Figure S7C). However,
attempts to process all the material from a 400 g pretreatment
Figure 3. Sidechain and aromatic regions of 2D HSQC NMR spectra (700 MHz,
d6-Acetone) of extracted RHBL at different scales; A Small scale pretreatment
(4 g rice husks); B Medium scale (400 g rice husks); C Large scale (4 kg rice
husks). Colour palette used for different linkages, with the rest of the colour
palette shown with Scheme 1. Magnification shown is x2 intensity.
obtaining the RHBH was tiresome (Figure S7D & S7E). A
modified work-up protocol was developed for large scale work
(Figure S7A) in which the aqueous solution of the RHBH was first
extracted with EtOAc giving separate water- and EtOAc-soluble
RHBH streams. In one run, this led to 34% of the RHBH being in
the EtOAc layer with the remainder being in the water.
Furthermore, extended filtration times were avoided by
centrifugation.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
In previous work with hardwood butanosolv lignins[15] it was
system), from 2 g of the crude lignin/hemicellulose mixture, 0.4 g
of 4 and 0.2 g of 5 were obtained in excellent purity (Figure S9).
Unfortunately, other native monosaccharides proved too polar to
be eluted. Based on quantitative HSQC NMR analysis of the
crude hemicellulose stream we estimate that the yields of
butoxylated xylose 4 and glucose 5 are approximately 16 and 5
wt% respectively, and non-butoxylated xylose 6 <2 wt%, with
respect to the starting biomass (Tables S4-S7 and Figures S13-
S15). Furthermore, the yield of butoxylated xylose 4 in the EtOAc
extract was found to be approximately 4 wt%, again with respect
to the starting biomass (Table S7).
demonstrated that hemicellulose was depolymerised and
chemically modified by butoxylation at the anomeric position of
the monomeric sugars. In this work, the presence of specific sugar
monomers was determined using 2D HSQC NMR analysis with
spectra of authentic butoxylated xylose 4, butoxylated glucose 5
and xylose 6 being used for comparison (Figure 4 and Figure
S8A-G). The ethyl acetate-soluble stream was shown to be
almost entirely comprised of butoxylated xylose 4 with some
minor unknown contaminants (Figure 4). Whereas, the water-
soluble stream was comprised of a mixture of native and
butoxylated monosaccharides 4-7 (Figure S8) and some minor
unidentified components. In an attempt to purify the mixture by
flash column chromatography (using a 0-15% MeOH/DCM
TEMPO-mediated formation of β-O-4 γ-carboxylic acid-
substituted butanosolv lignins
In contrast to other RH product streams,[35–37] the lignin has been
understudied
with
the
exception
of
its
structural
characterisation.[26,38,39] It was therefore decided to assess if
RHBL could be converted into a precursor for novel materials.
Strategies for lignin modification often focus on the use of
phenolic end groups and/or the unselective conversion of β-O-4
units by reaction at both the α- and γ-hydroxyls. In the case of
butanosolv lignins, only the β-O-4 α-hydroxyl is substituted,[8]
providing an opportunity to carry out site selective oxidation of the
γ-hydroxyl to the corresponding γ-carboxylic acid (to give ligninγ-
oxCA). It should be noted that a proportion of the β-O-4 units in
RHBL are natively γ-acylated with sidechain esters such as p-
coumarates (Figure S10) and that these γ-Ac-β-O-4 units would
be inert to the planned oxidation reactions.[26,38,39]
Previous reports on β-O-4 γ-oxidation have focussed on the
generation of aldehydes (ligninγ-oxALD) in model systems and en
route to lignin depolymerisation.[40,41] To the best of our knowledge,
only three reports describe the preparation of model β-O-4 γ-
carboxylic acids and organosolv ligninγ-oxCA. All of these use
TEMPO as the catalytic oxidant under electrochemical catalyst
regeneration conditions.[42–44] The initial report focussed on non-
phenolic native β-O-4 models[42] and showed that the use of
alkaline conditions was advantageous. Later, Stahl reported
additional studies on the γ-oxidation of phenolic native β-O-4
models and concluded that, whilst cleavage reactions dominated,
quinone methide structures were formed under basic conditions
with TEMPO.[43,44] It seems clear that the presence of phenolic
end-groups in lignin may well be problematic for the γ-oxidation of
β-O-4 unit. Indeed, Stahl indicated that using lignins with lower
native phenolic content resulted in more efficient γ-oxidation.
Figure 4. A Multiplicity edited 2D HSQC NMR analysis (700 MHz, D2O) of
EtOAc-soluble hemicellulose stream (blue and pick signals) overlaid with the
spectra obtained on analysis of an authentic sample of α/β-butoxylated xylose
4
(black). Multiplicity-edited cross-peaks corresponding to CH2 proton
environments (blue) and multiplicity-edited cross-peaks corresponding to CH
proton environments (red) shown. The anomeric region (inset box) highlights
the absence of native monosaccharides (dashed regions). The absence of the
distinctive G5α/β cross-peak observed in butoxylated glucose 5 is highlighted
(dashed regions).
B Reaction scheme showing preparation of authentic
butoxylated monosaccharide standards 4 and 5.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
Quantitative 31P NMR analysis was also supportive of a
significant increase in carboxylic acid environments in the RHBLγ-
oxCA compared to unoxidised RHBL (Figure S12). However, there
was a significant loss of signals corresponding to phenols,
potentially consistent with the previously reported quinone
methide formation.[43,44] The analogous γ-oxidation of other
butanosolv lignins was conducted and demonstrated that this
approach was generally applicable. Walnut shell butanosolv lignin
(WSBL, from a hardwood source, Figure 1 and Figure S4C),
buckwheat butanosolv lignin (BWBL, hardwood, Figure S4K) and
Douglas fir butanosolv lignin (DFBL, softwood, Figure S4I) were
all successfully converted to the corresponding γ-carboxylic acid-
containing materials (Figure S11).
Figure 5. HSQC NMR analysis (700 MHz, d6-DMSO) of RHBLs; Signals
corresponding to a selected region of the analysis of: A unmodified RHBL; B
model 9; C overlay of model 8 and unmodified RHBL; D RHBLγ-oxCA (prepared
using general procedure C); E overlay of RHBLγ-oxCA and model 8; F overlay of
model 8 (black) and model 9 (red); G overlay of RHBLγ-oxCA and model 9; H
δ1H/δ13C 9-10 ppm/190-210 ppm region in RHBLγ-oxCA highlighting the absence
of an aldehyde signals (dashed red region). For a full labelled RHBLγ-oxCA
spectrum, refer to Figure S11A.
Despite the fact that lignin from grasses is known to have a
high native phenolic content due to coumarates and ferulates, it
was decided to attempt to convert our RHBL to RHBLγ-oxCA using
a TEMPO/NCS system that had previously been reported to
oxidise relatively simple primary alcohols.[45]
With RHBLγ-oxCA in hand, it was decided to couple the newly
introduced carboxylic acids with aniline 10, as it was felt this
represented a flexible approach to grafting onto the lignin
backbone that complemented other recent reports by us and
others.[5,46–52] Initially, model 11 was synthesised from 9 and 10 to
aid characterisation of the final lignin (Scheme 1). RHBLγ-oxCA was
then coupled with 10 using EDC, Et3N and HOBt at rt for 24 hours
(Lignin general procedure D).[53] The resulting lignin was
characterised using HSQC NMR analysis (Figure 6) and
compared with model 11 (Figure 6A). Aniline 10 was selected for
these studies as on formation of the lignin-aniline amide bond a
distinctive change in the chemical shift of the aniline aromatic
protons was expected. Comparison of the signals observed for
the γ-coupled lignin with those of aniline 10 and acetylated aniline
12 (and model 11) supported the formation of the desired amide
bond in the lignin (Figures 6A and 6B). As expected, the cross-
peaks corresponding to the aromatic protons in aniline 10
(δ1H/δ13C 7.0 ppm/129 ppm, 6.5 ppm/116 ppm and 6.6 ppm/114
ppm) were very distinct from the cross-peaks in acetylated aniline
Encouragingly, butoxylated β-O-4 model 8 was oxidised
allowing isolation of γ-acid model 9 (Schemes 1 and S2).
Subsequent formation of the β-O-4 γ-carboxylic acid in RHBL was
observed when the reaction was run with catalytic quantities of
TEMPO at pH 9-10 for extended reaction times (Scheme S1,
general procedure C) with a significant excess of NCS being used
as a co-oxidant. Noticeable changes in the chemical shift of the
cross-peaks corresponding to the butoxylated β-O-4 unit were
seen upon γ-oxidation (from δ1H/δ13C 4.5 ppm/82 ppm for the α-
proton and 4.4 ppm/83 ppm of the unreacted unit to 4.7 ppm/82
ppm for the α-proton and 4.6 ppm/81 ppm for the β-proton of the
γ-oxidised unit, Figure 5). Evidence for the successful formation
of RHBLγ-oxCA also came from good overlay with signals from the
relevant model 9 (Figure 5G) and not the unoxidised model 8
(Figure 5E and 5G). The formation of RHBLγ-oxCA occurred
selectively under these conditions with no detectable formation of
RHBLγ-oxALD (absence of signals corresponding to aldehyde
environments in RHBLγ-oxCA, Figure 5H inset).
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
MeO
MeO
for the controlled preparation of a range of complex lignins via this
overall approach is considerable.
TEMPO (0.1 eq.), NCS
(10 eq.), TBAB,
O

O



BuO
OH
BuO
OH


(1:1) DCM/
aq. NaHCO3 (pH 9.5)
rt, 24 h
O
9
8
53%
MeO
MeO
OMe
OMe
MeO
O
H
EDC, HOBt, Et3N
DCM, rt, 16 h
BuO
N
O
NH2
11
30%
MeO
10
OMe
Scheme 1.
Preparation of butoxylated γ-acid β-O-4 model 9 and
EDC/HOBt/Et3N amide coupling with aniline 10 to give γ-coupled model 11.
12 (δ1H/13C 7.6 ppm/119 ppm, 7.3 ppm/129 ppm and 7.0 ppm/123
ppm), model 11 and in the coupled RHBLγ-amide. There was a clear
appearance of new aniline-related aromatic cross peaks that were
not present in the starting RHBLγ-oxCA (Figure 6C).
Conclusions
The butanosolv pretreatment process was applied to rice husks
with variations in a number of the reaction parameters being
carried out. Optimal conditions were determined to be a 10 mL/g
solvent to biomass loading, in a 95:5 ratio of butanol to water at a
final acid molarity of 0.2 M for a pretreatment time of 6 h at reflux.
This process was shown to be efficient on a variety of scales, with
repeatably good conversion of biomass into high quality product
streams on scales of up to 4 kg of biomass. Pure butoxylated
xylose (anomeric mixture) was isolated directly from the
pretreatment in high yield based on the amount of xylose present
in the starting biomass. In addition, selective γ-oxidation of the
butoxylated β-O-4 units in the butanosolv rice husk lignin gave γ-
carboxylic acids despite the presence of phenolic end groups in
the lignin. Evidence for the success of this selective lignin
oxidation protocol came from detailed HSQC and 31P NMR
analysis including comparison with relevant model compounds.
However, preparation of RHBLγ-oxCA required a significant amount
of the co-oxidant NCS and the system is relatively complex.
Future work will strive to reduce the complexity of the oxidation
system.
Figure 6: HSQC NMR analysis (700 MHz, d6-DMSO) of RHBLγ-amide. A spectrum
of γ-coupled RHBL overlaid with spectrum of model 11 (black). Environments
corresponding to γ-coupled β-O-4 protons are coloured in orange. B aromatic
region from analysis of γ-coupled RHBL overlaid with spectra of aniline 10 (red)
and acetylated aniline 12 (green). C aromatic region from analysis of starting
RHBLγ-oxCA highlighting absence of signals corresponding to aniline aromatic
environments are clearly absent (highlighted in blue dashed circles).
Experimental Section
All chemicals used in this report were obtained from commercial sources.
Rice husks biomass was obtained from The Home Brew Shop, walnut shell
biomass was a kind donation from Sharpham Park farm, and all other
biomasses were received from Hot Smoked. Full characterisation data
consisting of 1H NMR, 13C NMR, 2D HSQC NMR, IR and HRMS are
provided for all novel compounds (refer to ESI).
Lignin General Procedure A: Butanosolv Pretreatment
Finally, the oxidised lignin was used in an exemplar amide
coupling reaction leading to an amide-grafted lignin. The potential
Following a literature procedure,[15] to unextracted biomass was added n-
butanol: 0.2 M HCl (95:5, 10 mL/g). The mixture was heated at a gentle
reflux (ca. 100 oC) for 6 h and vacuum filtered when cooled. The residual
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
donation of walnut shells and Dr Daniel Miles-Barrett for helpful
discussions.
pulp was washed with a solution of acetone:H2O (9:1), and the resultant
filtrate was concentrated in vacuo to yield a gum-like residue (azeotrope
with additional portions of water to remove all butanol). The residual pulp
(cellulose-enriched pulp) was dried in a vacuum oven overnight at 50 oC.
The gum-like residue was dissolved in the minimum amount of
acetone:H2O (9:1, 5 mL/g) and added dropwise to rapidly stirring H2O (50
mL/g, 10 v/v minimum). A small portion of sat. sodium sulfate solution
added (1 mL/100 mL water). The resulting crude precipitate was collected
by vacuum filtration, or centrifugation at 8 000 rpm, and dried in a vacuum
oven at 50 oC for 16 h.
Keywords: Sustainable Chemistry • Biomass • Oxidation •
Green Chemistry • Lignin
[1]
[2]
[3]
P. J. Deuss, K. Barta, Coord. Chem. Rev. 2015, 510–532.
A. Berlin, M. Balakshin, Industrial Lignins, Elsevier, 2014.
H. Vappula, Pulp Market Review - Energy and Pulp Business Group.,
2011.
Lignin General Procedure B: Phosphitylation and 31P NMR analysis
of Lignin
[4]
[5]
[6]
[7]
[8]
[9]
[10]
J. Zakzeski, P. C. a Bruijnincx, A. L. Jongerius, B. M. Weckhuysen,
Chem. Rev. 2010, 110, 3552–99.
All lignins were dried for 16 h at 50 oC in a vacuum oven before
measurements. 30 mg of lignin was weighed into a vial and dissolved in
0.5 mL of CDCl3/pyridine (1:1.6, anhydrous, dried over 4 Å MS). Following
a literature procedure,[54] to this solution was added 10 µL cyclohexanol
I. Panovic, J. R. D. Montgomery, C. S. Lancefield, D. Puri, T. Lebl, N.
J. Westwood, ACS Sustain. Chem. Eng. 2017, 5, 10640–10648.
N. J. Westwood, I. Panovic, C. S. Lancefield, Springer Singapore,
2016, pp. 183–216.
(dried over
4 Å MS) and 50 µL 2-chloro-4,4,5,5-tetramethyl-1,3,2-
dioxaphospholane. The solution was transferred to a clean, dry NMR tube,
purged with N2 and sealed, then analysed using quantitative 31P NMR
analysis within 6 h of sample prep.
C. S. Lancefield, O. S. Ojo, F. Tran, N. J. Westwood, Angew. Chemie
Int. Ed. 2015, 54, 258–262.
P. J. Deuss, M. Scott, F. Tran, N. J. Westwood, J. G. de Vries, K.
Barta, J. Am. Chem. Soc. 2015, 137, 150522131446003.
A. Rahimi, A. Ulbrich, J. J. Coon, S. S. Stahl, Nature 2014, 515, 249–
252.
Lignin General Procedure C: TEMPO/NCS γ-Oxidation to Butanosolv
Ligninγ-oxCA
To a solution of butanosolv lignin (0.4 g) and TBAB (0.03 g) in a DCM/aq.
buffered system (1:1, 2 mL, aq. sat. NaHCO3, pH 9-10) was added NCS
(1 g) and TEMPO (0.12 g). The biphasic reaction mixture was stirred
rapidly (ensuring layer mixing) at rt for 24 h. The reaction mixture was
concentrated in vacuo until only the aqueous layer remained. The aqueous
layer was decanted into rapidly stirring water (200 mL/g), and the lignin
precipitate remaining in the flask was dissolved in acetone (10 mL/g) and
also added dropwise into the rapidly stirring water. To the stirring mixture
was added conc. HCl (approximately 20 drops/g), until the lignin was
observable as a precipitate. The lignin precipitate was filtered off and dried
in a vacuum oven for 16 h at 50 oC to give a brown powder.
D. M. Miles-Barrett, A. R. Neal, C. Hand, J. R. D. Montgomery, I.
Panovic, O. S. Ojo, C. S. Lancefield, D. B. Cordes, A. M. Z. Slawin,
T. Lebl, et al., Org. Biomol. Chem. 2016, 14, 10023–10030.
C. S. Lancefield, G. M. M. Rashid, F. Bouxin, A. Wasak, W.-C. Tu, J.
P. Hallett, S. Zein, J. Rodriguez, S. D. Jackson, N. J. Westwood, et
al., ACS Sustain. Chem. Eng. 2016, 4, 6921–6930.
S. Constant, H. L. J. Wienk, A. E. Frissen, P. de Peinder, R. Boelens,
D. S. van Es, R. J. H. Grisel, B. M. Weckhuysen, W. J. J. Huijgen, R.
J. A. Gosselink, et al., Green Chem. 2016, 18, 2651–2665.
S. Bauer, H. Sorek, V. D. Mitchell, A. B. Ibáñez, D. E. Wemmer, J.
Agric. Food Chem. 2012, 60, 8203–8212.
[11]
[12]
[13]
[14]
[15]
[16]
Lignin General Procedure D: γ-Coupling of Butanosolv Ligninγ-oxCA
To a solution of butanosolv ligninγ-oxC.A (0.4 g), HOBt (0.14 g) and EDC
(0.14 mL) in DCM (15 mL) was added the amine coupling partner (2 mmol)
and stirred at rt for 1 h. To the reaction mixture was added Et3N (0.32 mL)
and stirred at rt for 16 h. The reaction mixture was concentrated in vacuo,
then dissolved in the minimum amount of acetone (approximately 20 mL/g
of starting lignin) and added dropwise into rapidly stirring water (200 mL/g.
The precipitated lignin was filtered off and washed extensively with
additional water, then dried in a vacuum oven for 16 h at 50 oC to give a
brown powder.
G. Hu, C. Cateto, Y. Pu, R. Samuel, A. J. Ragauskas, Energy and
Fuels 2012, 26, 740–745.
C. S. Lancefield, I. Panovic, P. J. Deuss, K. Barta, N. J. Westwood,
Green Chem. 2016, 19, 1203–1210.
a. a. Pereira, G. F. Martins, P. a. Antunes, R. Conrrado, D. Pasquini,
a. E. Job, a. A. S. Curvelo, M. Ferreira, a. Riul, C. J. L. Constantino,
Langmuir 2007, 23, 6652–6659.
[17]
H. Teramura, K. Sasaki, T. Oshima, F. Matsuda, M. Okamoto, T.
Shirai, H. Kawaguchi, C. Ogino, K. Hirano, T. Sazuka, et al.,
Biotechnol. Biofuels 2016, 9, 1–11.
Acknowledgements
[18]
[19]
[20]
[21]
[22]
L. F. Del Rio, R. P. Chandra, J. N. Saddler, Appl. Biochem. Biotechnol.
2009, 161, 1–21.
We would like to thank the CRITICAT Centre for Doctoral Training
for financial support [Ph.D. studentship to IP; Grant code:
EP/L016419/1] and BBSRC Global Challenges Research Fund
Impact Acceleration Account at St Andrews BB/GCRFIAA/20.
CSL thanks the Leverhulme Trust for funding an Early Career
Fellowship. We acknowledge the EPSRC UK National Mass
Spectrometry Facility at Swansea University for mass
spectrometry analysis, Sharpham Park farms for their kind
K. Wang, H. Yang, S. Guo, X. Yao, R.-C. Sun, J. Appl. Polym. Sci.
2014, 131, n/a--n/a.
K. Wang, H. Yang, S. Guo, Y. Tang, J. Jiang, F. Xu, R.-C. Sun,
Process Biochem. 2012, 47, 1503–1509.
T. Renders, S. Van den Bosch, S.-F. Koelewijn, W. Schutyser, B. F.
Sels, Energy Environ. Sci. 2017, 10, 1551–1557.
L. Shuai, M. T. Amiri, Y. M. Questell-Santiago, F. Héroguel, L.
Yanding, H. Kim, R. Meilan, C. Chapple, J. Ralph, J. S. Luterbacher,
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
et al., Science (80-. ). 2016, 354, 329–334.
[40]
[41]
[42]
S. Dabral, Ø. G. Hern, P. C. J. Kamer, C. Bolm, ChemSusChem 2017,
7, 2707–2713.
[23]
W. Lan, M. Talebi Amiri, C. M. Hunston, J. Luterbacher, Angew.
Chemie Int. Ed. 2017, 5, 1356–1360.
C. S. Lancefield, L. W. Teunissen, B. M. Weckhuysen, P. C.,
Bruijnincx, Green Chem. 2018, 19, DOI 10.1039/c7gc00195a.
Y. Sannami, H. Kamitakahara, T. Takano, Holzforschung 2017, 71,
109–117.
[24]
[25]
F. Stat, “FAO Stat,” 2013.
S. Chandrasekhar, K. G. Satyanarayana, P. N. Pramada, P.
Raghavan, T. N. Gupta, J. Mater. Sci. 2003, 38, 3159–3168.
A. Salanti, L. Zoia, M. Orlandi, F. Zanini, G. Elegir, J. Agric. Food
Chem. 2010, 58, 10049–10055.
[26]
[43]
[44]
[45]
S. S. Stahl, US20170342574A1, 2017.
S. S. Stahl, US20170342219A1, 2017.
[27]
[28]
[29]
R. Pode, Renew. Sustain. Energy Rev. 2016, 53, 1468–1485.
R. Saad, J. Hawari, J. Porous Mater. 2012, 20, 227–233.
F. Adam, T. S. Chew, J. Andas, J. Sol-Gel Sci. Technol. 2011, 59,
580–583.
J. Einhorn, C. Einhorn, F. Ratajczak, J.-L. Pierre, J. Org. Chem. 1996,
61, 7452–7454.
[46]
C. Jin, X. Zhang, J. Xin, G. Liu, G. Wu, Z. Kong, J. Zhang, ACS
Sustain. Chem. Eng. 2017, 5, 4086–4093.
[30]
Z. Wang, J. Yu, X. Zhang, N. Li, B. Liu, Y. Li, Y. Wang, W. Wang, Y.
Li, L. Zhang, et al., ACS Appl. Mater. Interfaces 2016, 8, 1434–1439.
J. Umeda, K. Kondoh, Ind. Crops Prod. 2010, 32, 539–544.
H. Chen, W. Wang, J. C. Martin, A. J. Oliphant, P. A. Doerr, J. F. Xu,
K. M. DeBorn, C. Chen, L. Sun, ACS Sustain. Chem. Eng. 2013, 1,
254–259.
[47]
[48]
H. Liu, H. Chung, Macromolecules 2016, 49, 7246–7256.
K. Xiong, C. Jin, G. Wu, G. Liu, Z. Kong, Chem. Ind. For. Prod. 2016,
36, 115–120.
[31]
[32]
[49]
[50]
[51]
[52]
Y. Han, L. Yuan, G. Li, L. Huang, T. Qin, F. Chu, Polymer (Guildf).
2016, 83, 92–100.
C. Wang, R. A. Venditti, ACS Sustain. Chem. Eng. 2015, 3, 1839–
1845.
[33]
[34]
[35]
W. Wang, J. C. Martin, X. Fan, A. Han, Z. Luo, L. Sun, ACS Appl.
Mater. Interfaces 2012, 4, 977–981.
Pietro Buono, L. Averous, A. Duval, Y. Habibi, ChemSusChem 2018,
11, 2472–2491.
H. Zhang, Y. Luo, L. Wu, Y. Huang, P. Christie, Environ. Sci. Pollut.
Res. 2015, 22, 5908–5918.
K. Isozaki, T. Shimoaka, S. Oshiro, A. Yamaguchi, F. Pincella, R.
Ueno, T. Hasegawa, T. Watanabe, H. Takaya, M. Nakamura, ACS
Omega 2018, 3, 7483–7493.
B. C. Saha, L. B. Iten, M. a Cotta, Y. V Wu, Biotechnol Prog 2005, 21,
816–822.
[36]
[37]
N. Johar, I. Ahmad, A. Dufresne, Ind. Crops Prod. 2012, 37, 93–99.
D. Nabarlatz, A. Ebringerová, D. Montané, Carbohydr. Polym. 2007,
69, 20–28.
[53]
[54]
M. Tsakos, E. S. Scha, L. L. Clement, N. L. Villadsen, T. B. Poulsen,
Nat. Prod. Rep. 2015, 32, 605–632.
A. Granata, D. S. Argyropoulos, J. Agric. Food Chem. 1995, 43,
1538–1544.
[38]
[39]
S. K. Singh, P. L. Dhepe, Bioresour. Technol. 2016, 221, 310–317.
M. Wu, J. Pang, F. Lu, X. Zhang, L. Che, F. Xu, R. Sun, Ind. Crops
Prod. 2013, 50, 887–895.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201801971
ChemSusChem
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Rice husks were extracted efficiently
using butanol as a pretreatment
solvent on a variety of scales (4 g to 4
kg) giving a cellulose-derived pulp,
butanol-modified hemicellulose
monosaccharides and a butanol-
modified lignin. This butanosolv lignin
was selectively oxidised at the γ-
position to give a carboxylic acid and
tested in a coupling reaction with
aniline, demonstrating a new
I. Panovic, D. Phillips, M. J. Gronnow, N.
J. Westwood*
P age No. 1 – P age No. 8
Selective Primary Oxidation of Lignin
Streams from Butanol-Pretreated
Agricultural Waste Biomass
approach for the preparation of lignin
grafted materials.
This article is protected by copyright. All rights reserved.