Efficient nickel-catalyzed hydrocyanation of alkenes using acetone cyanohydrin as a safer cyano source

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

An active nickel catalyst prepared in situ from a Ni(II) compound, phosphine ligand, and zinc powder was found to be an efficient catalyst system for the hydrocyanation of various alkenes using acetone cyanohydrin as a safer cyano source. The combination of NiCl₂·6H₂O and 1,3-bis(diphenylphosphino)propane was the most efficient catalyst precursor in DMF. Under the optimized conditions, various styrenes, heterocyclic alkenes, and aliphatic alkenes were converted to their corresponding nitriles in excellent yields.

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

Tetrahedron Letters 57 (2016) 3199–3203
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Efficient nickel-catalyzed hydrocyanation of alkenes using acetone
cyanohydrin as a safer cyano source
a
Koji Nemoto a, , Tsuyoshi Nagafuchi , Ken-ichi Tominaga a,b, Kazuhiko Sato a,b
⇑
a Interdisciplinary Research Center for Catalytic Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
b Catalysis Research Center, Hokkaido University, Kita21, Nishi10, Kita-ku, Sapporo, Hokkaido 001-0021, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
An active nickel catalyst prepared in situ from a Ni(II) compound, phosphine ligand, and zinc powder was
found to be an efficient catalyst system for the hydrocyanation of various alkenes using acetone cyanohy-
drin as a safer cyano source. The combination of NiCl2ꢀ6H2O and 1,3-bis(diphenylphosphino)propane was
the most efficient catalyst precursor in DMF. Under the optimized conditions, various styrenes, hetero-
cyclic alkenes, and aliphatic alkenes were converted to their corresponding nitriles in excellent yields.
Ó 2016 Elsevier Ltd. All rights reserved.
Received 1 April 2016
Revised 4 June 2016
Accepted 9 June 2016
Available online 11 June 2016
Keywords:
Nickel catalyst
Hydrocyanation
Cyanohydrin
Alkene
Introduction
Alternative cyano sources to hydrogen cyanide were also
considered, with acetone cyanohydrin being selected as a safer
The nitrile functional group is particularly useful in organic
synthesis as it can be converted into a range of other functional
groups. For example, amine, amide, carboxylic acid, ester,
aldehyde, and ketone moieties can be obtained from nitriles.1 In
addition to being versatile compounds in chemical transforma-
tions, nitriles are also important building blocks in the preparation
of pharmaceuticals, pesticides, and other functional materials
widely used in daily life.2 To date, various methods have been
reported for the preparation of nitriles.3 Pioneering examples of
alkene hydrocyanation using homogeneous Co(0) have been
reported,4 and Pd(0)5 and Ni(0)6 catalyst systems have also been
proposed, with Ni(0)-promoted hydrocyanation being developed
recently.7 In particular, the DuPont adiponitrile synthesis is one
of the most studied processes.8 This hydrocyanation process
requires an expensive Ni(0) catalyst and an excess amount of
hydrogen cyanide as the cyano source. However, the Ni(0) catalyst
is difficult to handle due to its sensitivity to moisture and oxygen,
while hydrogen cyanide is extremely toxic. Therefore, an
alternative, more environmentally benign method is required.
We considered that the preparation of an active catalyst species
and the choice of cyano source were key to developing such a
strategy. Thus, we focused on the in situ preparation of an active
cyano source. This reagent is liquid at room temperature, and so
is considered easier to handle than cyanide compounds. The com-
bination of these approaches yielded an efficient hydrocyanation
system, the details of which are disclosed and discussed below.
Results and discussion
The hydrocyanation of 2-norbornene was attempted using
various Ni(II) precatalysts in N-methyl-2-pyrrolidone (NMP), which
is known to be a suitable solvent for catalytic C–C bond forming
reactions.9 The results of the various experiments are summarized
in Table 1. Initially, Ni(acac)2ꢀ4H2O was selected, as it is a good pre-
cursor to Ni(0) species.10 Hydrocyanation proceeded to give 2-nor-
bornanecarbonitrile as the major product, as determined by GC-FID
(gas chromatography–flame ionization detection). However, a poor
yield of only 4% was obtained. Nickel halide hydrates were also
screened (entries 2–4), with NiCl2ꢀ6H2O giving relatively good pro-
duct yields and selectivities. No improvement in yield was obtained
even upon employing anhydrous precatalysts. Poor results were
also obtained for Ni(OAc)2ꢀ4H2O (entry 5). In an attempt to improve
conversion, a range of solvents were screened for use with
NiCl2ꢀ6H2O. Slightly polar solvents such as THF, MeOH, and acetoni-
trile were not effective in this reaction (entries 6–8) due to the poor
solubility of NiCl2ꢀ6H2O, indicating that precatalyst solubility is
important in this reaction. Strongly polar solvents such as DMSO
and DMF gave similar results to NMP, but as with DMAc, selectivity
species from
a metal precatalyst and a phosphine ligand.
⇑
Corresponding author. Tel.: +81 29 861 3553; fax: +81 29 861 4872.
E-mail address: k-nemoto@aist.go.jp (K. Nemoto).
http://dx.doi.org/10.1016/j.tetlet.2016.06.036
0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.

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K. Nemoto et al. / Tetrahedron Letters 57 (2016) 3199–3203
Table 1
Hydrocyanation of 2-norbornene using various Ni(II) precatalysts, solvents, and reductantsa
Entry
Precatalyst
Solvent
Reductant
Ligand
Product yieldb (%)
Substrate remainingb (%)
Selectivityb (%)
1
2
3
4
5
Ni(acac)2ꢀ2H2O
NiCl2ꢀ6H2O
NMP
NMP
NMP
NMP
NMP
Zn
Zn
Zn
Zn
Zn
PPh3
PPh3
PPh3
PPh3
PPh3
4
91
61
56
36
73
44
79
55
52
26
31
24
33
7
NiBr2ꢀ3H2O
NiI2ꢀ6H2O
Ni(OAc)2ꢀ4H2O
6
7
8
9
10
11
12
13
14
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
THF
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
3
3
2
48
16
44
1
1
3
87
63
89
34
59
40
96
94
78
23
8
MeOH
Acetonitrile
DMF
18
73
39
73
25
17
14
DMAc
DMSO
CH2Cl2
Toluene
Hexane
15
16
17
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
DMF
DMF
DMF
Mg
Al
Mn
PPh3
PPh3
PPh3
Trace
Trace
21
92
94
60
—
—
53
a
Reaction conditions: 2-norbornene, 16.0 mmol; acetone cyanohydrin; 16.0 mmol, catalyst, 3 mol %; ligand, 6 mol %; reductant, 30 mol %; solvent, 5 mL, under N2
(0.5 MPa), 90 °C, 15 h.
b
Determined by GC-FID analysis.
was poor (entries 9–11). Weakly polar solvents such as CH2Cl2,
toluene, and hexane were not suitable, yields of 1–3% being
obtained (entries 12–14). Subsequently, Mg, Al, and Mn were also
screened as reductants combined with NiCl2ꢀ6H2O, but no improve-
ment in yield was observed (entries 15–17), thus indicating that the
choice of reductant was also important. Adequate generation of the
Ni(0) species is therefore expected to be key in this reaction.
Initially, NiCl2ꢀ6H2O reacts with triphenylphosphine to give
NiCl2(PPh3)2 complexes, which are readily reduced to the Ni(0)
species by Zn via transmetalation. The active species in this reaction
system appears to be the Ni(0)-phosphine complex, as reported by
Miyaura et al.11 As this Ni(0) complex is unstable and short-lived
at room temperature,11b spectroscopic confirmation is
problematic, even at low temperatures. Identification of the Ni(0)
species by NMR spectroscopy was unfortunately not successful.
We hypothesized that the Ni(0) species was stabilized by the
coordination of a 2-norbornene-like Ni(cod)2 complex, and that
hydrocyanation was triggered by this stabilization. We therefore
attempted to synthesize the nickel bis(triphenylphosphine)-bis(2-
norbornene) complex, but all attempts were unsuccessful. Instead
of the desired Ni(0) complex, a norbornene dimer was observed
by mass spectrometry.12 Examination of the literature revealed that
such dimerizations were likely induced by an Ni(0) species
coordinated to two norbornene molecules.13 Indeed, this
dimerization itself confirms our hypothesis, and so we expect that
our hydrocyanation proceeded in a similar manner.
We then carried out ligand screening to improve product yields
and selectivities. According to previous reports, phosphite ligands
tend to be effective in hydrocyanation reactions. Indeed, the
product yield was improved to 86% when triphenylphosphite
was used (Table 2, entry 1). However, as some decomposition to
phenol was observed, the phosphite ligands were unsuitable for
reuse. Similarly, alkyl phosphines such as trimethylphosphine,
tributylphosphine, and tri-tert-butylphosphine were easily decom-
posed, and spontaneously caught fire upon contact with air. These
ligands were therefore excluded as ligand candidates. Other mon-
odentate ligands such as tri(mesityl)phosphine, tri(1-naphthyl)
phosphine, and tri(o-tolyl)phosphine were investigated, with no
reaction being observed (entries 2–4), suggesting that steric
bulkiness affected the Ni(0) species activity. Bidentate ligands with
a wide bite angle were therefore expected to influence the activity
of the Ni(0) species, and so various bisphosphine ligands
were tested in the presence of NiCl2ꢀ6H2O and Zn in DMF
(entries 5–10). The use of bisphosphine ligands drastically
increased both the product yield and selectivity. In particular, the
reaction proceeded smoothly and almost quantitatively when
1,3-bis(diphenylphosphino)propane
(dppp)
was
employed
(entry 7). The reaction solution became a bright red-orange color
when dppp was used, indicating that the NiCl2(dppp) complex
was generated in situ, which supported the above-mentioned
reaction mechanism. Indeed, a stoichiometric quantity of acetone
cyanohydrin was sufficient to achieve almost complete conversion.
Other bidentate ligands, such as N,N,N0,N0-tetramethylethylenedi-
amine and ethylene glycol dimethyl ether, were not beneficial to
the reaction. However, the reaction proceeded moderately when
2,20-bipyridine was used, the product yield was 49%.
Further optimization allowed reduction in the catalyst amount
to 1 mol %, ligand loading to 2 mol % and reductant amount to
10 mol % without any significant decrease in yield for the
hydrocyanation of 2-norbornene (Table 3, entry 1).14 Our catalyst
system was then compared to typical homogeneous catalysts for
the hydrocyanation reaction, but the reaction was not successful
(entries 2–8). The reaction gave only trace amounts of product in
the presence of Ni(CO)2(PPh3)2, Ni(PPh3)4, Ni[P(OPh)3]4, and Pd
(PPh3)4. With the exception of entry 4 (Ni(PPh3)4), adequate
amounts of 2-norbornene remained intact. In these reactions, the
inactivated species were presumably formed through catalyst
poisoning. Indeed, it has been reported that some Ni(0), Pd(0),
and Co(0) catalysts were deactivated through the formation of
cyanide complexes.15 However, our reaction proceeded smoothly,
demonstrating that a distinguished and convenient system had
been developed.
With the optimized conditions in hand, we attempted the
hydrocyanation of a range of aromatic and heterocyclic alkenes
(Table 4). Styrene was converted to their corresponding mononi-
trile mixtures in good yields (entry 1). Moreover, halogenated
styrenes were also converted to their corresponding mononitrile
mixtures in good yields (entries 2–4). It was interesting that
aromatic carbon–bromine bond was not cleaved. Strong
electron-donating group such as –OMe group accelerated the
reaction, to give their corresponding mononitrile mixtures in good
yields (entry 5). Indeed, our catalyst system was not affected by the
coordination effect of the methoxy group. However, the reaction
was disturbed by a strong electron-withdrawing group such as
the -CO2Me group. The conversion was notably decreased to give
corresponding mononitrile mixture only in 19% (entry 6). We also

K. Nemoto et al. / Tetrahedron Letters 57 (2016) 3199–3203
3201
Table 2
Ligand screening in the hydrocyanation of 2-norbornene using NiCl2ꢀ6H2O and Zna
Entry
Precatalyst
Solvent
Reductant
Ligand
Product yieldb (%)
Substrate remainingb (%)
Selectivityb (%)
1
2
3
4
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
DMF
DMF
DMF
DMF
Zn
Zn
Zn
Zn
P(OPh)3
86
N.D.
>99
>99
>99
86
—
—
P(mesityl)3
P(1-naphthyl)3
P(o-tolyl)3
N.D.
N.D.
N.D.
—
5
6
7
8
9
10
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
NiCl2ꢀ6H2O
DMF
DMF
DMF
DMF
DMF
DMF
Zn
Zn
Zn
Zn
Zn
Zn
dppmc
dpped
dpppe
dppbf
88
95
97
83
95
95
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
88
95
97
83
95
95
dppfg
dpephosh
a
Reaction conditions: 2-norbornene, 16.0 mmol, acetone cyanohydrin; 16.0 mmol, catalyst, 3 mol %; ligand, 6 mol %; reductant, 30 mol %; solvent, 5 mL; under N2
(0.5 MPa), 90 °C, 15 h.
b
Determined by GC-FID analysis.
Abbreviation of 1,1-bis(diphenylphosphino)methane.
Abbreviation of 1,2-bis(diphenylphosphino)ethane.
Abbreviation of 1,3-bis(diphenylphosphino)propane.
Abbreviation of 1,4-bis(diphenylphosphino)butane.
Abbreviation of 1,1-bis(diphenylphosphino)ferrocene.
Abbreviation of bis[2-(diphenylphosphino)phenyl] ether.
c
d
e
f
g
h
them were converted to their corresponding nitrile compounds
in moderate to excellent yields. All reactions proceeded cleanly
and with almost complete conversion, as observed within the ana-
lytical limits of GC-FID.In addition, substrates such as vinyl acetate,
vinyl trimethylsilane, ethyl acrylate, and 2-propenal did not react,
as they appeared to either decompose or polymerize under the
reaction conditions. If protected, 1,1-diethoxy-2-propene was
converted to their corresponding mononitrile mixtures, but in poor
yields. In terms of regioselectivity for the styrenes reaction, the
linear product was generated in preference to the branched
product. In also, for both 1-hexane and 4-cyano-1-butene, the
linear product was generated preferentially (entries 1 and 4). Ster-
ically bulky butenes gave only linear product (entries 2 and 3).
They were less reactive compounds because of their steric
hindrance of the reactive site. In the reaction of 1,3-butadiene, both
1,6-adiponitrile and 2-methylglutaronitrile were detected
(entry 5). Regioselectivity is likely due to the coordination styles
toward the Ni(0) complex. These results will therefore help us to
understand the reaction mechanism.
Table 3
Comparison with typical homogeneous catalystsa
Entry Catalyst
Product yield
(%)
Substrate remainingb
(%)
1c
NiCl2ꢀ6H2O + dppp
94
N.D.
+ Zn
2d
3
4
5
6
Ni(cod)2 + dppp
Ni(CO)2(PPh3)2
Ni(PPh3)4
Ni[P(OPh)3]4
Pd(PPh3)4
Pd2(dba)3
N.D.
>99
>99
82
>99
>99
>99
>99
Trace
Trace
Trace
Trace
N.D.
7
8
Co2(CO)8
N.D.
a
Reaction conditions: substrate, 16.0 mmol; acetone cyanohydrin, 16.0 mmol;
catalyst, 1 mol %; solvent, 5 mL; under N2 (0.5 MPa), 90 °C, 15 h.
b
Determined by GC-FID analysis.
2 mol % dppp and 10 mol % Zn were employed additionally.
2 mol % dppp was employed additionally.
c
d
investigated the hydrocyanation of the internal alkene trans-stil-
bene. The desired hydrocyanated product was obtained in 25%,
although a significant amount of substrate remained intact (entry
7). Even with a catalyst loading of 10 mol %, ligand loading of
20 mol %, and reductant charge of 100 mol % could not improve
the product yield. In addition, much more sterically hindered sub-
Finally, we examined the reaction mechanism, as shown in
Scheme 1. The hydrocyanation was catalyzed by the Ni(0) species,
which was prepared in situ as described above. In the initial step,
Ni(0) is stabilized by coordination to the C@C moiety of the
substrate molecule. The resulting complex reacts with hydrogen
cyanide derived from the acetone cyanohydrin to give a five-coor-
dinate complex. Insertion of another substrate molecule and
proton migration regenerates a four-coordinated complex. This
complex then reacts with hydrogen cyanide once again to afford
the nitrile compound, and regenerates the active species through
reductive elimination. Subtle differences in stability between the
mono and bidentate ligands induce undesired polymerization,
while the regioselectivity depends on the coordination geometry
of the Ni(0) intermediate. For styrenes, a benzylic complex is less
stable because of side chain steric hindrance, and so proton
migration to give the linear species is favored (Scheme 1, right).
strate
a-methylstyrene was tested, only a trace amount of corre-
sponding mononitrile was obtained (entry 8). This confirmed that
our catalytic system was strongly affected by the steric hindrance
of the reactive site. We also investigated the hydrocyanation of the
heterocyclic alkenes. In the case of 4-vinylpyridine, hydrocyana-
tion reaction did not proceed at all, even if in the presence of a
large amount of acetone cyanohydrin (entry 9). Instead of that, a
large amount of white solid which seemed to be poly(4-vinylpyri-
dine) was obtained. Ni(0) species may have induced unexpected
polymerization. Then, control experiment for styrene polymeriza-
tion in the absence of acetone cyanohydrin. Indeed, polystyrene
was obtained with high catalyst loadings. Thus, our catalyst system
essentially has a polymerization activity. Contrarily, 9-vinylcar-
bazole was converted to their corresponding mononitrile mixtures
in excellent yields (entry 10), but a small amount of devinylated
product was simultaneously obtained.
This is also possible for the p-allylic species because of side chain
steric hindrance. Thus, 1-hexene yielded the corresponding linear
hydrocyanation (Scheme 1, left). In the case of 1,3-butadiene, the
formation of a
p-allylic species initially yielded 2-methyl-3-but-
nenitrile (1,2-product) and 3-pentenitrile (1,4-product), which
were mainly converted into 2-methylglutaronitrile in the second
hydrocyanation. Similar reaction mechanisms have indeed been
described in the literature.16
We attempted the hydrocyanation of a range of aliphatic alke-
nes based on the optimized conditions in hand (Table 5). Each of

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K. Nemoto et al. / Tetrahedron Letters 57 (2016) 3199–3203
Table 4
Hydrocyanation of various aromatic and heterocyclic alkenesa
Entry
1
Substrate
Products
Yieldb and Distributionb
CN
CN
89%c (1a:1b = 1:2.3)c
75% (1a:1b = 1:2.2)
1b
1a
CN
CN
2
3
4
5
F
68% (2a:2b = 1:1.4)
61% (3a:3b = 1:1.0)
53% (4a:4b = 1:1.2)
81% (5a:5b = 1: 3.0)
F
2b
CN
F
2a
CN
Cl
Cl
3b
Cl
3a
4a
CN
CN
Br
Br
4b
Br
CN
CN
MeO
MeO2C
MeO
5b
CN
MeO
MeO2C
5a
CN
6
7
19% (6a:6b = 1:1.2)
MeO2C
6b
6a
CN
25%
CN
8
9
Trace
—
Hydrocyanated product was not detected.
N
N
N
10
87% (10a:10b = 1: 3.4)
N
NC
10a
CN
a
Reaction conditions: substrate, 16.0 mmol; acetone cyanohydrin, 16.0 mmol; catalyst, NiCl2ꢀ6H2O, 3 mol %; ligand, dppp, 6 mol %; reductant, Zn, 30 mol %; solvent, DMF,
5 mL, under N2 (0.5 MPa), 90 °C, 15 h.
b
Yield was determined based on the quantity of isolated regioisomer mixture and distribution was determined by 1H NMR analysis.
Determined by GC-FID analysis.
c
Table 5
Hydrocyanation of various aliphatic alkenes
Entry
Substrate
Products
Yielda and Distributiona
CN
CN
1b
94% (11a:11b = 1:3.5)
11b
11a
2b,c
3b
49%
CN
CN
52%d
NC
CN
NC
CN
CN
4b
93% (14a:14b = 1:2.9)
88% (15a:15b = 1: 4.3)
CN
CN
14b
14a
CN
NC
5e,f
15b
15a
a
Determined by GC-FID analysis.
b
Reaction conditions: substrate, 16.0 mmol; acetone cyanohydrin, 16.0 mmol; catalyst, NiCl2ꢀ6H2O, 3 mol %; ligand, dppp, 6 mol %; reductant, Zn, 30 mol %; solvent, DMF,
5 mL, under N2 (0.5 MPa), 90 °C, 15 h.
c
3-Methyl-1-butene in DMF (ꢁ2.0 mol/L) was employed.
d
Yield was determined based on the quantity of isolated regioisomer mixture and distribution was determined by 1H NMR analysis.
e
1,3-Butadiene in THF (ꢁ2.0 mol/L) was employed, and so THF was present in the reaction mixture.
f
Reaction conditions: substrate, 16.0 mmol; acetone cyanohydrin, 16.0 mmol; catalyst, NiCl2ꢀ6H2O, 1 mol %; ligand, dppp, 2 mol %; reductant, Zn, 10 mol %; solvent, DMF,
5 mL; under N2 (0.5 MPa), 120 °C, 15 h.

K. Nemoto et al. / Tetrahedron Letters 57 (2016) 3199–3203
3203
HCN
HCN
R P
2
PR2 + Zn
R P
2
PR2 + Zn
NiCl2 E6H2O +
NiCl2 E6H2O +
P
P
Ni
Ni
P
P
R
Ar
Ar
R
P
P
P
P
H
H
Ar
R
Ni
Ni
CN
CN
P
P
Ni
Ni
CN
Ar
HCN
R
CN
P
P
R
HO CN
HCN
P
P
HO CN
R
P
P
HCN
HCN
branched:
Ni
branched:
Ni
H
Ni
R
P
disfavored
disfavored
H
Ni
CN
CN
R
Ar
CN
P
P
P
CN
Ar
NC
R
P
P
Ar
NC
Ni
Ni
HCN
linear:favored
HCN
linear:favored
CN
CN
P
P
Scheme 1. Reaction mechanisms based on the stability of the Ni(0) intermediate.
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2010, 2, 674–682; (l) de Greef, M.; Breit, B. Angew. Chem., Int. Ed. 2009, 48,
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(n) Bini, L.; Müller, C.; Vogt, D. ChemCatChem 2010, 2, 590–608; (o) Falk, A.;
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Conclusion
We herein established a convenient hydrocyanation of various
alkenes using inexpensive and air-stable catalytic precursors
combined with cyanohydrin as a safer cyano source. Our catalyst
system, prepared in situ from a Ni(II) compound, a phosphine
ligand, and zinc powder, was superior to existing homogeneous
Ni(0), Pd(0), and Co(0) hydrocyanation catalysts.
References and notes
1. Larock, R. C. Comprehensive Organic Transformations: A Guide to Functional Group
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14. Typical hydrocyanation procedure (Table 3, entry 1): In a 50 mL autoclave
equipped with a glass inner tube and a magnetic stirring bar were charged 2-
norbornene (1.51 g, 16.0 mmol), DMF (5.0 mL), NiCl2ꢀ6H2O (1 mol %,
0.16 mmol, 38 mg), dppp (2 mol %, 0.32 mmol, 132 mg), Zn powder (10 mol
%, 1.6 mmol, 105 mg) and acetone cyanohydrin (16 mmol, 1812 lL) and the
apparatus was purged with N2 by repeated pressurization and subsequent
expansion. The final pressure was adjusted to 0.5 MPa. After stirring the
resulting mixture at 90 °C for 15 h, the reactor was depressurized and the
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standard.
a 1-methylnaphthalene internal
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