Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine intermediate

Article abstract of DOI:10.1016/j.cattod.2016.06.036

Supported metallic and bimetallic systems were used for the selective oxidation of but-3-en-1,2-ol (BDO) to hydroxybut-3-en-2-one (HBO), an intermediate in the hydroxymethionine synthesis. All catalysts were active in this reaction. However, bimetallic systems were found more active and selective to HBO in the liquid aqueous phase at 50 °C using molecular O₂ as a benign oxidant. The best performance (87% BDO conversion and 88% HBO selectivity) was observed over a 2%PdPt/TiO₂ catalyst. No metal leaching was observed under the conditions studied.

Full text of DOI:10.1016/j.cattod.2016.06.036

G Model
CATTOD-10283; No. of Pages4
ARTICLE IN PRESS
Catalysis Today xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine
intermediate
F. Grasseta, P. Reyb, V. Bellière-Bacab, M. Araquea, S. Paula, F. Dumeignila,
R. Wojcieszaka,∗, B. Katrynioka,∗
a Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 – UCCS – Unité de Catalyse et Chimie du Solide, F-59000 Lille, France
b ADISSEO France SAS, Antony Parc 2-10, 92160 Antony, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Supported metallic and bimetallic systems were used for the selective oxidation of but-3-en-1,2-ol (BDO)
to hydroxybut-3-en-2-one (HBO), an intermediate in the hydroxymethionine synthesis. All catalysts were
active in this reaction. However, bimetallic systems were found more active and selective to HBO in the
liquid aqueous phase at 50 ◦C using molecular O2 as a benign oxidant. The best performance (87% BDO
conversion and 88% HBO selectivity) was observed over a 2%PdPt/TiO2 catalyst. No metal leaching was
Received 25 November 2015
Received in revised form 14 May 2016
Accepted 13 June 2016
Available online xxx
observed under the conditions studied.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Heterogeneous catalysis
Green conditions
Oxidation
BDO
Hydroxymethionine
1. Introduction
diol (BDO) to hydroxybut-3-en-2-one (HBO) followed by Mickael
addition of methanethiol on the remaining C C double bond
Methionine is an essential sulfur-containing amino acid that
participates in various metabolic processes such as protein synthe-
sis and lipid metabolism. In cattle breeding, an adapted methionine
feed can increase the quality of milk and the yield in recover-
able proteins. However, methionine is degraded by the rumen of
cows, and only a small part of the ingested methionine reaches
the blood system of the animal [1]. Various strategies to cope
with this drawback have been proposed such as the coating of
methionine (Mepron®, Smartamine® M, Met-Plus®) or the syn-
thesis of its hydroxy analogs 2-hydroxy-4-methylthiobutyric acid
(HMB) and esters derivatives (MetasmartTM) [2]. HMB is often
qualified as liquid methionine because it is mainly produced as a
88% aqueous solution of racemic dl-HMB and is fully converted
to l-methionine by enzymes present in animal digestive system
(alcohol dehydrogenase and transaminase) [3,4]. Even if hydroxy-
4-methylthiobutuan-2-one (HMBO) seems to be a key compound
for the synthesis of HMB or its derivatives, its synthesis reported
so far is not sufficiently efficient (HMBO yield of 52%) [5]. Another
option to prepare HMBO could be the oxidation of but-3-ene-1,2-
(Scheme 1).
Various systems have been developed for the efficient addi-
tion of alkylthiols on carbon–carbon double bond using amines
[1,5,6] or boron catalysts [7]. However, only a few works have
been reported on the oxidation of ␣,ˇ-unsaturated diols cat-
alyzed by heterogeneous catalysts using oxygen [8]. Rey et al.
found that a PtPdBi/C catalyst in the presence of a base was
capable to oxidize both the secondary and primary alcohols of
but-3-ene-1,2-diol into 2-oxobut-3-enoic acid with 85% yield [1].
Farhadi reported the photocatalytic oxidation of various 1-aryl-2-
hydroxyethanols to the corresponding hydroxymethyl-arylketones
using H3PW12O40/ZrO2 under photocatalytic oxidative conditions
at room temperature in acetonitrile. Yields between 68 and 88%
were obtained in the 3–6 h range [9]. This scarce representation of
unsaturated diols among reported scientific oxidation work may
arise from side reactions occurring either because of the diol func-
tionality or from the presence of unsaturated bond. For example,
Mori et al. have developed a catalyst based on supported palladium
on hydroxyapatite (Pd/HAP). This catalyst proved to be efficient
for the oxidation of primary alcohols to aldehydes and secondary
alcohols to ketone in aromatic solvent and under oxygen [10,11].
They also tried to oxidize the 1-phenylethane-1,2-diol using their
catalyst in trifluorotoluene at 110 ◦C under oxygen (1 atm.). While
∗
Corresponding authors.
E-mail addresses: robert.wojcieszak@univ-lille1.fr, wojcieszakr@gmail.com
(R. Wojcieszak), benjamin.katryniok@ec-lille.fr (B. Katryniok).
http://dx.doi.org/10.1016/j.cattod.2016.06.036
0920-5861/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: F. Grasset, et al., Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine intermediate,
Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.036

G Model
CATTOD-10283; No. of Pages4
ARTICLE IN PRESS
2
F. Grasset et al. / Catalysis Today xxx (2016) xxx–xxx
OH
OH
OH
of TiO2 P25 was added to 4 mL of an aqueous solution of H2PtCl6
Cat.
MeSH
S
and H2PdCl4 containing 10 mg of Pt and 10 mg of Pd at room tem-
perature and under vigorous stirring. The solution was then stirred
at room temperature during 16 h and evaporated to dryness. The
resulting solid was grounded and calcined at 400 ◦C for 3 h.
O2
O
OH
BDO
O
HBO
HMBO
Scheme 1. Alternative pathway for HMBO synthesis from BDO.
2.2. Characterization
2.2.1. X-ray diffraction study
Powder XRD patterns were recorded on a Bruker D8 Advance
diffractometer using a Cu-K␣ radiation (ꢀ = 0.154 nm) as a X-ray
source in the 2ꢁ range of 0.5–80◦ (0.02◦/s, 0.5 s/step).
Scheme 2. Products obtained during the oxidation of BDO in water with O2.
2.2.2. ICP analysis
The chemical composition of catalysts was determined by
inductively coupled plasma atomic emission spectroscopy, using
Thermo Jarrel Ash Iris Advantage equipment. The samples were
first brought into solution by subsequent dissolution with diluted
aqua regia (HCl and HNO3).
they obtained full conversion, the main product (96% yield) was
benzaldehyde, attesting C C cleavage of the vic-diol bond [12].
However, concerning the polyols oxidation, a lot of works on
the oxidation of sugars and glycerol have been published using
notably platinum- and gold-based catalysts [13–15]. It is impor-
tant to note that the use of these supported metal catalysts such
as PtBi/C [16] or AuPd/TiO2 [17] generally requires a basic media
(more than 2 equivalents of NaOH versus substrate) to oxidize pri-
mary alcohols to acids or – more precisely – to the corresponding
acid salts, thus necessitating the re-protonation of the latter. Con-
trary to that, the oxidation of the secondary alcohol from glycerol
does not require the use of base and can even be performed in
acidic media [14,18]. To fulfill the increasing demand for environ-
mentally benign chemical processes, the combination of efficient
and reusable catalytic formulations for oxidation reactions under
mild condition, is one of the most important issues. In this regard,
we report herein exploratory catalytic experiments with the differ-
ent catalytic materials (Pd, Pt and Pd-Pt supported heterogeneous
catalysts) in the selective oxidation of BDO to HBO in water using
oxygen. Typically, this reaction of industrial interest was performed
at 50 ◦C under 1 bar of molecular oxygen as a terminal oxidant.
Different supports (TiO2, MgO, HAP-hydroxyapatite, Al2O3, ZrO2)
modified with Pd, Pt or Pd-Pt bimetallic nanoparticles were tested.
The catalysts studied in this work were prepared according
to procedures described in the literature and compared to the
commercial materials available on the market. In all cases, the
oxidation occurred on the secondary alcohol of BDO. The main by-
products observed (Scheme 2) were hydroxybutan-2-one (HBaO)
obtained by hydrogenation of the HBO and 1,4-dihydroxybutan-2-
one (DHBO) obtained by hydration of HBO. No triols corresponding
to the hydration of BDO were observed.
2.2.3. X-ray photoelectron spectroscopy
XPS analysis was performed on a Kratos Axis Ultra spectrome-
ter (Kratos Analytical, U.K.). The spectrometer was equipped with a
monochromatized aluminum X-ray source (powered at 10 mA and
15 kV). The pressure in the analysis chamber was about 10–6 Pa. The
angle between the normal to the sample surface and the direction
of photoelectrons collection was about 0◦. Analyses were per-
formed in the hybrid lens mode corresponding to a combination
of magnetic and electrostatic lenses. The analyzed area was about
700 ␮m × 300 ␮m. The pass energy of the hemispherical analyzer
was set at 160 eV for the wide scan and 40 eV for narrow scans. In
the latter conditions, the full width at half- maximum (fwhm) of the
Ag 3d5/2 peak of a standard silver sample was about 0.9 eV. Charge
stabilization was achieved by using the Kratos Axis device. Peak
decomposition was performed using curves with a 70% Gaussian
type and a 30% Lorentzian type and a Shirley nonlinear sigmoid-
type baseline. The following peaks were used for the quantitative
analysis: O 1s, C 1s, Ti 2p, Pd 3d, Pt 3d, Mg 2p, Al 2p and Au 4f.
Moreover, the Cl 2p, S 2p and N 1s peaks were also monitored and
C 1s again to check for charge stability as a function of time. Molar
fractions were calculated using peak areas normalized on the basis
of acquisition parameters after a Shirley background subtraction
and corrected with experimental sensitivity factors and transmis-
sion factors provided by the manufacturer. Au foil was used as the
reference material for study of prepared catalysts. Au foil was ana-
lyzed before and after Ar+ etching during 50 min with the Kratos
Minibeam I ion gun (4 kV, 15 mA) to remove oxidized species from
the foil surface. The surface atomic concentrations were calculated
by correcting the intensities with theoretical sensitivity factors
based on Scofield cross sections and the mean free path varying
according to 0.7 power of the photoelectron kinetic energy. The C-
(C,H) component of the C 1s peak of adventitious carbon was fixed
to 284.8 eV to set the binding energy scale, and the data treatment
was performed using CasaXPS software (Casa Software Ltd., U.K.).
2. Experimental
2.1. Materials
H3PO4 (85%), 2-butanol, toluene, cyclopentylmethylether
(CpOMe), 4-methyltetrahydrofuran (MeTHF), TiO2 P25, basic
alumina, neutral alumina and but-3-en-1,2-diol (BDO) were
obtained from Aldrich. D2O, chloroform-d, acetonitrile, ethylac-
etate (EtOAc), pentane, ammonium hydrogen phosphate, hydrogen
tetrachloro aurate hydrate, sodium borohydride, palladium chlo-
ride, palladium nitrate, ammonium hydroxide, tetradecyl and
hexadecyl-trimethylammonium bromide were purchased from
Alfa Aesar (99% analytical grade). Methylisobutylketone (MIBK),
ethanol, methanol were purchased from Laboratoires Verbièse.
Puralox was obtained from Evonik-Degussa (99% analytical grade).
All the chemicals were used without any further purification.
2%AuPd/TiO2 catalyst was prepared according to the literature pro-
cedure [19]. All the other catalysts were prepared by impregnation
methods. For example, 2%PdPt/TiO2 was prepared as follows: 0.98 g
2.2.4. NMR analysis
NMR analyses were performed on a Bruker AC 300. All the
chemical shifts are reported in ppm relative to the residual sol-
vent peak of deuterated solvent [1]. H NMR and [13] C NMR studies
are described in details in Supplementary information.
2.3. Catalytic tests
Oxidation of BDO reactions were performed in 30 mL glass tubes
equipped with a reflux condenser using a general procedure. Typ-
ically, catalysts (30 mg) were introduced in the tubes and then 3
Please cite this article in press as: F. Grasset, et al., Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine intermediate,
Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.036

G Model
CATTOD-10283; No. of Pages4
ARTICLE IN PRESS
F. Grasset et al. / Catalysis Today xxx (2016) xxx–xxx
3
Table 1
Solvent effect on the catalytic activity in BDO oxidation on a 2%AuPd/TiO2 catalyst.
Solvent
Conversion (%)
Selectivity (%)
HBO
HBaO
H2Oa
13
93
53
77
33
18
<5
<5
<5
46
25
99
55
9
70
50
55
–
–
–
12
40
–
H2O
31
71
2
38
31
–
–
–
54
40
H2Ob
H2Oc
iPrOH
EtOH
Acetone
Acetonitrile
MIBK
EtOAc
Toluene
Experimental parameters: 2%AuPd/TiO2 (30 mg) and BDO (0.1 M, 3 mL), 50 ◦C, 5 h.
a
25 ◦C.
b
Reaction performed under N2.
Reaction performed with an O2 pressure of 10 bar.
c
vacuum/oxygen cycles were performed. A solution of BDO (0.1 M,
3 mL) was added and the mixture was put at the desired temper-
ature under oxygen atmosphere and stirring (800 rounds min−1).
At the end of the experiment, the tubes were cooled to room
temperature and clear solutions were recovered by syringe filtra-
tion or centrifugation. Experiments of high-pressure BDO oxidation
were performed in a Hastelloy C 35 mL reactor equipped with a
mechanical stirring. Typically, the catalyst (100 mg) and a solution
of BDO (0.1 M, 10 mL) were introduced to the reactor and 3 consecu-
tive pressurization cycles with oxygen/evacuation were performed.
Then, the oxygen pressure was adjusted to 10 bar and the mixture
was heated to the desired temperature under stirring (1300 rpm).
At the end of the experiment, the reactor was cooled to room tem-
perature, depressurized, and the clear solution was recovered by
syringe filtration. Analyses of the solutions were performed by
HPLC using a Bio-Rad Aminex 87H column (5 mM H2SO4 eluent,
0.5 mL/min, 30 ◦C) equipped with RI and UV (ꢀ = 210 nm) detec-
tors and a GC-FID equipped with a Alltech EC-1000 column (30 m;
0.53 mm; 1.2 ␮m) using external calibration curves. GC–MS analy-
sis were performed on a Varian CP3800-MS Saturn 2000 equipped
with a CP wax 58 (FFAP)CB column (25 m; 0.25 mm; 0.2 ␮m).
Fig. 1. Recycling experiments using (a) 2%PdPt/TiO2 and (b) 2%PdPt/HAP. Reaction
conditions: catalysts (30 mg), BDO in water (0.1 M, 3 mL), 50 ◦C, O2 (1 atm), 5 h.
Table 2
ICP and XPS molar concentrations.
Catalyst
XPS (%)
Pd0
Metal content (ICP)
Pd2+
Pdtotal
Pd
Au
Pt
2%Pd/HAP
2% AuPd/TiO2
2% PdPt/TiO2
2% AuPd/HAP
2% AuPd/MgO
2% AuPd/ZrO2
2%PdPt/Al2O3 basic
2%PdPt/Al2O3 neutral
2%PdPt/Al2O3 acidic
2% PtPd/HAP
1.62
0.83
0.72
0.81
0.82
0.69
0.67
0.73
0.68
0.80
0.22
0.12
0.12
0.02
0.16
0.04
0.09
0.12
0.15
0.30
1.82
0.93
0.81
0.80
0.98
0.72
0.76
0.85
0.87
0.83
1.9
0.9
0.8
0.8
1.0
0.9
1.0
0.9
1.0
0.9
1
1.0
–
1.1
0.9
0.9
–
–
–
–
0.9
–
–
–
3. Results and discussion
0.8
0.9
0.9
1.0
In the first step, the impact of the solvent was studied over
the titania-supported AuPd catalyst, whereby the best results were
obtained in water (Table 1). Correspondingly, all the following tests
were performed in aqueous media. A moderate conversion was
observed for the reaction carried out under N2 atmosphere, but
HBaO was the main product (b in Table 1). In this case, BDO acts
as a hydrogen donor (CH OH) and hydrogen acceptor (C C double
bond) at the same time. Contrary to that, an increase in oxygen pres-
sure strongly decreases the HBaO selectivity and increases the HBO
selectivity (c in Table 1). Besides high catalytic activity, the reusabil-
ity and stability are very important issues for practical applications
of the catalysts in the industry. We thus tested the catalytic perfor-
mance of the used selected Pd catalysts in BDO oxidation (Fig. 1).
The selectivity to HBO was stable through the 3 recycling tests
(>80%), but the BDO conversion decreased (from 80 to 30%). A drop
in BDO conversion is particularly observed between the first and
the second run using 2%PdPt/TiO2. A less important decrease is
observed using 2%PdPt/HAP (from 53 to 52%). In order to determine
if the reaction is mediated by species in solution, a filtration exper-
iment was performed using 2%PdPt/TiO2 catalyst, as described in
the following.
was introduced back into the reaction vessel under O2 (1 atm) at
50 ◦C. No evolution of the BDO or HBO concentrations in the reac-
tion media was observed after removal of the catalyst. This suggests
that no potential species from catalyst leaching in solution are
involved in the oxidation process. The leaching was also definitely
excluded in the current catalytic system by inductively coupled
plasma atomic emission spectrometry (ICP-AES) analysis with the
concentrations of Pd, Au or Pt in the filtrate below the detection
level of the equipment (0.5 ppm).
Hence, the decrease in the overall conversion should be due to
the strong adsorption of the reaction products on the catalysts sur-
face. The XPS results (Table 2) confirmed the presence of palladium
in metallic state (Pd0). Oxidized palladium (Pd+) was also detected.
This is probably due to air exposition during washing and drying
steps. However, the Pd0/Pd+ ratios confirmed the fact that palla-
dium is mostly in metallic state in all catalysts. No alloy phases
were detected in the XRD patterns (now shown here). However,
the low concentration of the metals and small metal particle size
could be responsible for the absence of the diffraction peaks.
The oxidation of BDO in water under O2 (1 atm) at 50 ◦C was
carried out for 2 h. Then the catalyst was filtrated off. The filtrate
Please cite this article in press as: F. Grasset, et al., Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine intermediate,
Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.036

G Model
CATTOD-10283; No. of Pages4
ARTICLE IN PRESS
F. Grasset et al. / Catalysis Today xxx (2016) xxx–xxx
Acknowledgements
4
Table 3
Catalytic results: conditions: catalyst (30 mg), BDO in water (0.1 M, 3 mL), 50 ◦C, O2
(1 atm.), 5 h.
The REALCAT platform is benefiting from a Governmental sub-
vention administrated by the French National Research Agency
(ANR) within the frame of the ‘Future Investments’ program (PIA),
with the contractual reference ‘ANR-11-EQPX-0037’. Chevreul
Institute (FR 2638), Ministère de l’Enseignement Supérieur et de
la Recherche, Région Nord – Pas de Calais and FEDER are acknowl-
edged for supporting and funding partially this work.
Catalyst
Conversion(%)
Selectivity (%)
HBO
HBaO
Blank test
2%Pd/HAP
<1
73
93
87
48
71
98
90
9
–
–
1
31
3
3
31
–
–
<1
<1
–
87
55
88
82
64
–
11
44
73
90
2% AuPd/TiO2
2% PdPt/TiO2
2% AuPd/HAP
2% AuPd/ZrO2
2% AuPd/MgO
2% Au/HT
1%Pt/Al2O3
2%PdPt/Al2O3
2% PtPd/HAP
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cattod.2016.06.
036.
49
38
References
Among the supports tested with a 2%AuPd bimetallic systems
(HAP, TiO2, ZrO2, MgO), the hydroxyapatite gave the best HBO
selectivity reaching 82%, but with a relatively low conversion of
BDO (48%, Table 3). An increase in palladium content on both
PdPt/TiO2 and AuPd/TiO2 systems increases the BDO conversion,
but decreases the selectivity (Table 3). Using HAP instead of TiO2
with 2%PdPt almost totally suppressed the formation of HBaO (90%
HBO selectivity), but also severely impacted the BDO conversion
(38%). In the case of MgO and ZrO2, the overall conversion remained
high, but the selectivity to HBO was rather low (ZrO2) or null (MgO).
[1] P. Rey, G. Blanchard, Adisseo Ireland Limited, FR2880345A1 (2006).
[2] C. Kobler, M. Hateley, P. Roth, B. Jaeger, R. Peter, C. Weckbecker, K.
Huthmacher, Evonik Degussa GMBH, WO2008061871A1 (2008).
[3] G. Chaintron, Tech. de l’ingénieur j6410 (1996) 1–9.
[4] H. Hasegawa, Y. Shinohara, K. Akahane, T. Hashimoto, K. Ichida, Amino Acids
40 (2011) 1205.
[5] T. Hirose, Sumitomo Chemical Company, WO2012091159A1 (2012).
[6] T. Hirose, Sumitomo Chemical Company, WO2012091158A1 (2012).
[7] G. Gros, M. Garrait, P. Rey, J. Taillades, Aventis Animal Nutrition S.A.,
EP1260500 A1 (2002).
[8] T. Mallat, A. Baiker, Chem. Rev. 104 (2004) 3037–3058.
[9] S. Farhadi, M. Zaidi, Appl. Catal. A: Gen. 354 (2009) 119–126.
[10] M. Norouzi, F. Ashrafi, M. Taharimehr, F. Bagheri, Int. J. ChemTech Res. 2
(2010) 1666–1672.
4. Conclusions
[11] K. Kaneda, H. Ogawa, JP2002275116A (2002).
[12] K. Mori, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 126
(2004) 10657–10666.
Pd-based bimetallic heterogeneous catalysts (Pd-Au and Pd-Pt)
were screened in the oxidation of BDO in water using oxygen as a
terminal oxidant. The screening highlighted the good performance
of supported bimetallic catalysts and revealed that gold could be
advantageously substituted by platinum. Therefore, 2%PdAu/TiO2
gave 93% BDO conversion and 55% HBO selectivity under only 1
atmosphere of oxygen at 50 ◦C in water. 87% BDO conversion and
88% HBO selectivity have been reached with 2%PdPt/TiO2 catalyst
in the same reaction conditions. The support study revealed that
supporting palladium (monometallic or as bimetallic system with
platinum or gold) on HAP is an efficient way to decrease the HBaO
formation in favor of the HBO selectivity. However, in this case, a
decrease in conversion was observed.
[13] M. Besson, P. Gallezot, C. Pinel, Chem. Rev. 114 (2013) 1827–1870.
[14] B. Katryniok, H. Kimura, E. Skrzynska, J.S. Girardon, P. Fongarland, M. Capron,
R. Ducoulombier, N. Mimura, S. Paul, F. Dumeignil, Green Chem. 13 (2011)
1960–1979.
[15] A. Corma, S. Iborra, A. Velty, Chem. Rev. 107 (2007) 2411–2502.
[16] M. Besson, P. Gallezot, Catal. Today 57 (2000) 127–141.
[17] N. Dimitratos, J.A. Lopez-Sanchez, J.M. Anthonykutty, G. Brett, A.F. Carley, R.C.
Tiruvalam, A.A. Herzing, C.J. Kiely, D.W. Knight, G.J. Hutchings, Phys. Chem.
Chem. Phys. 11 (2009) 4952–4961.
[18] H. Kimura, J. Polym. Sci. A Polym. Chem. 34 (1996) 3615–3620.
[19] J. Xu, H. Zhang, Y. Zhao, B. Yu, S. Chen, Y. Li, L. Hao, Z. Liu, Green Chem. 15
(2013) 1520–1615.
Please cite this article in press as: F. Grasset, et al., Oxidation of but-3-en-1,2-diol: Green access to hydroxymethionine intermediate,
Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.06.036