Nitrile synthesis through catalyzed cascades involving acid-nitrile exchange

Article abstract of DOI:10.1055/s-0033-1341227

Irreversible acid-nitrile exchange reactions using both glutaronitrile and (phenylsulfonyl)acetonitrile may be catalyzed by Lewis acids. Whereas a cyclization towards imides displaces the equilibria in the reaction with dinitriles, a decarboxylation step is involved when using the (phenylsulfonyl)acetonitrile. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1341227

1802▌
PAPER
pNapietrrile Synthesis through Catalyzed Cascades Involving Acid–Nitrile
Exchange
Catalyzed Irreversible Acid–Nitrile Exchang
a
e
b
b
c
d
Damien Cartigny, Aurélie Dos Santos, Laurent El Kaïm,* Laurence Grimaud,* Roland Jacquot,*
Philippe Marion*d
a
Eco-Efficient Products and Processes Laboratory (E2P2L), UMI 3464 CNRS – Solvay, 3966 Jin Du Road, Xin Zhuang Ind. Zone,
01108 Shanghai, P. R. of China
2
b
DCSO-UMR 7652: CNRS-ENSTA-Ecole Polytechnique, Laboratoire Chimie et Procédés, Ecole Nationale Supérieure de Techniques
Avancées, 828 Bd des maréchaux, 91128 Palaiseau, France
E-mail: laurent.elkaim@ensta-paristech.fr
c
Ecole Normale Supérieure, Département de chimie, CNRS-UMR 8640-UPMC, 24 rue Lhomond, 75231 Paris Cedex 05, France
E-mail: laurence.grimaud@ens.fr
d
Solvay Recherches & Innovation Centre de Lyon, 85 rue des frères Perret, BP62, 69192 Saint Fons Cedex, France
E-mail: philippe.marion@solvay.com
Received: 25.02.2014; Accepted: 21.03.2014
much lower yields under these conditions. Despite these
drawbacks, the reaction remains attractive as an alterna-
tive to the use of ammonia in the conversion of acids into
nitriles. In an effort to find a better compromise between
the advantages of sulfuric and phosphoric acid as cata-
lysts, we have decided to study the effect of various Lewis
acids as catalyst for the acid–nitrile exchange process.
Herein, we wish to present the results of this study togeth-
er with new lines of approach towards the displacement of
acid–nitrile equilibrium at high temperature.
Abstract: Irreversible acid–nitrile exchange reactions using both
glutaronitrile and (phenylsulfonyl)acetonitrile may be catalyzed by
Lewis acids. Whereas a cyclization towards imides displaces the
equilibria in the reaction with dinitriles, a decarboxylation step is in-
volved when using the (phenylsulfonyl)acetonitrile.
Key words: acylation, carboxylic acids, nitriles, imides, Lewis
acids
Nitriles represent an important class of organic deriva-
tives finding use as solvents, starting materials for poly-
mers as well as synthetic intermediates. Among the
numerous methods available for their preparation, the
most commonly exploited involves the conversion of car-
boxylic acids to primary amides followed by dehydra-
3
50 °C
R1 CO2H + R2 CN
R1 CN
R2 CO H
+
2
H
N
CN
CN
H3PO4 (cat.)
O
O
R1 CO2H +
R1 CN +
1
tion. Though efforts to reach the shortest synthetic route
3
00 °C
2
n
has led to the disclosure of various one-pot procedures,
n
the most straightforward transformation of carboxylic
acids into nitrile is certainly the so-called acid–nitrile ex-
change reaction. Indeed, at high temperature, carboxylic
acids react with nitriles leading to a functional exchange
between the two partners (Scheme 1). To convert this pro-
3
CN
CO2H
R1 CN
+
n
cess into a useful transformation of carboxylic acids into Scheme 1 Acid–nitrile exchange reactions
nitriles the equilibrium that settles must be totally dis-
placed. This has been done by choosing a nitrile of low
Considering the reaction mechanism and the activating ef-
fect observed with Brønsted acids, we postulated that the
reaction probably starts with a proton exchange in order to
activate the electrophilicity of the nitrile group. Due to the
low basicity of the nitrile, this first step should be highly
boiling point in large excess (as solvent)3 or a short-
e,j
3
c,i
chain dinitrile such as succinonitrile or glutaronitrile. In
the latter case, the irreversibility is brought by the forma-
tion of cyclic imides (Scheme 1).
Though the reaction may proceed without any catalyst, demanding in energy and should be favored by strongly
addition of Brønsted acids such as phosphoric acid facili- acidic conditions such as observed in the activation by
4
tates the conversion, but temperatures over 280 °C are sulfuric acid. All optimization trials were done using 2-
3
h
still required for completion. Recently, the use of sulfu- phenylbutanoic acid (1a) as the benzylic proton is well
ric acid in excess (20 equiv) has allowed to lower the tem- differentiated in the carboxylic acid and in the nitrile. Glu-
4
perature around 100 °C. However, nitriles are formed in taronitrile was selected as the second partner due to the ir-
reversible imide formation. Different Brønsted acids were
SYNTHESIS 2014, 46, 1802–1806
Advanced online publication: 30.04.2014
first tested performing the reaction at 200 °C for 2.5 hours
(Table 1, entries 1–5). However, isolated yields were still
limited to 64% (Table 1, entries 3 and 5). Similar effects
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1341227; Art ID: SS-2014-T0131-OP
Georg Thieme Verlag Stuttgart · New York
©

PAPER
Catalyzed Irreversible Acid–Nitrile Exchange
1803
were observed with Lewis acids and the best isolated The effect of the nature of the starting dinitrile was then
yields were obtained when using aluminum chloride. In- investigated and the same reaction was performed using
deed, in this case, 67% of the desired nitrile 2a was isolat- succinonitrile (Scheme 2). In similar conditions, with 2
ed within the same reaction time (Table 1, entry 9) and if mol% of aluminum chloride, the desired product was iso-
it was prolonged to 5 hours, the yield went up to 83% (Ta- lated in 76% yield after 5 hours of reaction time (vs 83%
ble 1, entry 11). Analogous results were observed with for glutaronitrile). Therefore, glutaronitrile was selected
4
mol% of catalyst within 2.5 hours of stirring (Table 1, as the second partner to set out the scope of this reaction.
entry 10). Nevertheless, the reaction time can be notably
shortened under microwave irradiations. Indeed, when
performed at 300 °C for 10 minutes, 75% of the 1-phenyl-
butyronitrile (2a) could be isolated compared to 83% at
Various carboxylic acids were then tested in the presence
of 2 mol% of aluminum trichloride as catalyst using both
thermic conditions and microwave irradiations as present-
ed in Table 2. The results indicate that the reaction is effi-
cient with aromatic and aliphatic nitriles.
200 °C after 5 hours (Table 1, entry 12).
Table 1 Optimization of the Experimental Conditions
Table 2 Scope of the Transformation
O
H
N
NC
O
O
O
NC
CN
cat. (2 mol%)
00 °C, 2.5 h
CN
OH +
+
R
CN
NC
R
OH
2
AlCl3 (2 mol%)
Ph
Ph
2a
1
2
1
a
glutaronitrile
glutarimide
A: 200 °C, 5 h
B: 300 °C, 10 min, MW
conditions
Entry
Catalyst
Conversiona
2a Yield (%)b
Yield (%)
1
2
3
4
5
6
7
8
9
–
30
55
65
71
76
58
53
67
68
84c
92d
85e
29
–
Entry Product
Conditions A Conditions B
H PO4
3
Cl
CN
CF CO H
64
–
3
2
1
2b
72
50
PTSA
Cl
ClSO H
64
57
–
3
MeO
MeO
CN
ZnCl2
2
3
2c
46
48
52
–
FeCl ·6H O
3
2
OMe
CN
Al(OTf)3
–
AlCl3
67
83c
83d
75e
2d
1
1
1
0
1
2
AlCl3
MeO
CN
AlCl3
4
5
2e
2f
35
72
40
80
AlCl3
Ph
a
b
c
d
e
1
Determined by H NMR spectroscopy.
Isolated yield.
CN
Ph
With 4 mol% of catalyst.
After 5 h of reaction time.
Under microwave irradiation at 300 °C for 10 min.
CN
CN
6
7
2g
2h
78
79
–
–
PhO
O
t-Bu
+
NC
OH
CN
CN
n
CN
Ph
8
2i
2j
Ph
92a
51a
83
76
AlCl3 (2 mol%)
200 °C, 5 h
CN
H
9
Ph
N
O
O
+
a
After heating for 2.5 h.
Ph
n
n = 1 succinonitrile 76%
n = 2 glutaronitrile 83%
83%
88%
The mechanism probably involves activation of the nitro-
gen of the nitrile moiety as the first step. It could be done
by simple protonation (HCl may be released in the medi-
um) or by complexation of the Lewis acid. The nitrilium
Scheme 2 Comparison of succinonitrile/glutaronitrile
©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 1802–1806

1804
D. Cartigny et al.
PAPER
O
+
NA
NH
O
A = H, AlCl3
R
+
OH
O
R
NC
CN
O
CN
CN
CN
R
O
–
Mumm
rearrangement
O
O
O
R
O
O
RCOOH
HN
N
O
N
R
N
R
H
H
+
imide
N
H
acyl transfer
H
R
N
H
H
N
R
N
N
O
N
O
O
O
O
R
CN
+
O
glutarimide
Scheme 3 Possible mechanistic pathway for the formation of imide
ion resulting from this activation is then trapped by the on the equilibrium of the nitrile-acid exchange reaction in-
carboxylate anion to form an O-acyl imidate. The latter dicates that the reaction spontaneously produces the
3
h
can further undergo a Mumm rearrangement to give the weaker carboxylic acid. This property explains as well
corresponding imide. The formation of the latter was first the failure of cyanoacetic acid ethyl ester to act as an effi-
3
a
observed by Gautier and it was further studied by Wiley cient promoter of the nitrile-acid exchange. Seeking for
3
f
and Guerrant. More recently, Kappe fully characterized alternative substituents that could allow the decarboxyl-
3
j
the imide by NMR analyses. When using a dinitrile, the ation, we were delighted to observe a much more efficient
formation of the final cyclic imide could result from a nu- transformation when (phenylsulfonyl)acetonitrile was
cleophilic attack of the nitrogen atom of the imide on the used as the nitrogen donor. Indeed, after heating the latter
second nitrile moiety to form the acyl amidine, which fur- with a stoichiometric amount of 1f for 3 hours at 200 °C,
ther undergoes an acyl transfer followed by an intramolec- the sulfone completely reacted with the formation of the
ular Michael addition (Scheme 3). The latter reaction expected methyl phenyl sulfone isolated in 75% yield
forms an unstable four-membered-ring intermediate, (Scheme 4). However, nitrile 2f was only obtained in a
which spontaneously opens towards the nitrile and glu- modest 56% isolated yield. Adding 2 mol% of aluminum
tarimide. The formation of this cyclic imide ensures the trichloride as catalyst allowed raising this yield to 62%.
efficiency of the exchange by displacement of the equilib- Under these conditions 1c, 1g, and 4-phenylbenzoic acid
ria.
(1k) were converted into 2c, 2g, and 4-phenylbenzonitrile
2k) in 54%, 53%, and 68% isolated yield, respectively.
(
This method allows a convenient and fast functional ex-
change in rather smooth conditions. However, in all the
cases, the desired nitrile is formed along with one equiva-
lent of glutarimide, which is eliminated by flash chro-
matographic purification. In order to avoid such tedious
step, alternative methods to displace equilibria were in-
vestigated. As a carboxylic acid is formed as a by-product,
we surmised that a possible decarboxylation process
could constitute an efficient irreversible step towards the
formation of the desired nitrile. Otherwise, the decarbox-
ylation should provide a low-boiling point by-product,
which can thus be easily removed from the reaction mix-
ture. Malonitrile was first examined as a potential partner.
Though moderate in yields, these preliminary trials sup-
port the concept of a decarboxylative acid–nitrile ex-
change reaction, avoiding a tedious purification step.
Ph
O
PhO2S
CN
+
Ph
OH
1f
2
00 °C
3 h
Ph
CN
f (56%)
+
PhSO2Me
75%
Ph
2
5
The decarboxylation of the resulting cyanoacetic acid
Scheme 4 Decarboxylative acid–nitrile exchange process
would afford a convenient way to shift the equilibrium
with formation of acetonitrile, easily removed from the re-
action medium. However, attempts to convert 3,3-diphen-
ylpropionic acid (1f) into the corresponding nitrile by this
method only afforded traces of the expected 2f under heat-
ing for three hours at 200 °C. Analysis of previous studies
In conclusion, we have described new Lewis acid cata-
lyzed conditions for the acid–nitrile exchange reaction of
glutaronitrile and succinonitrile. The reaction may be
done under thermal or microwave conditions. In both
cases, formation of cyclic imides displaces all equilibria.
6
Synthesis 2014, 46, 1802–1806
© Georg Thieme Verlag Stuttgart · New York

PAPER
Catalyzed Irreversible Acid–Nitrile Exchange
1805
We have explored the use of decarboxylative processes as 3,4,5-Trimethoxybenzonitrile (2c)8
Yield (GP1): 266 mg (46%); yield (GP2): 313 mg (54%); colorless
solid; mp 91–93 °C.
an alternative to irreversible imide formation and have
shown the potential of (phenylsulfonyl)acetonitrile in pro-
moting the first decarboxylative acid–nitrile exchange.
Though yields of the latter are moderate, it affords mild
conditions for the direct conversion of carboxylic acids
into nitriles. Further modifications of the sulfone are un-
der investigation to improve the yields.
1
H NMR (400 MHz, CDCl ): δ = 6.86 (s, 2 H), 3.90 (s, 3 H), 3.88
3
(s, 6 H).
13
C NMR (100 MHz, CDCl ): δ = 153.5, 142.2, 119.0, 109.4, 106.7,
3
61.0, 56.3.
Benzonitrile (2d)9
Yield (GP1): 148 mg (48%); colorless oil.
1
H NMR (400 MHz, CDCl ): δ = 7.65 (d, J = 7.6 Hz, 2 H), 7.61 (t,
NMR spectra were recorded on a Bruker Avance 400 spectrometer,
3
J = 7.6 Hz, 1 H), 7.46 (t, J = 7.70 Hz, 1 H).
13
using CDCl solvent as reference and/or internal deuterium lock.
3
1
1
1
Two-dimensional NMR spectroscopy [ H- H COSY spectra, H-
C COSY spectra (HSQC) and long-range H- C COSY spectra
HMBC)], were carried out to determine the correlation between H
and C. The chemical shifts for all NMR spectra are expressed in
parts per million to high frequency of TMS reference. Coupling
constants (J) are quoted in Hz and are recorded to the nearest 0.1
Hz. The IR spectra were obtained using ATR accessories. High-
resolution mass spectra were performed on a GC/MS system spec-
trometer. TLC was carried out using precoated plates of silica gel
C NMR (100 MHz, CDCl ): δ = 132.7, 132.1, 129.1, 118.8, 112.4.
3
1
3
1
13
1
(
(E)-3-(3-Methoxyphenyl)acrylonitrile (2e)
Yield (GP1): 167 mg (35%); yellow oil.
1
3
IR (thin film, ATR): 2215, 1619, 1597, 1577, 1488, 1455, 1431,
1
–1
275, 1244, 1157, 1036 cm .
1
H NMR (400 MHz, CDCl ): δ = 7.38–7.30 (m, 2 H), 7.05–6.95 (m,
3
3
H), 5.87 (d, J = 16.8 Hz, 1 H), 3.83 (s, 3 H).
13
60F254.
C NMR (100 MHz, CDCl ): δ = 159.9, 150.5, 134.7, 130.1, 119.9,
3
1
18.0, 116.8, 112.4, 96.6, 55.3.
Thermal-Catalyzed Reaction of Acids 1 with Glutaronitrile;
General Procedure 1 (GP1)
HRMS (EI): m/z calcd for C H NO: 159.0684; found: 159.0686.
10
9
In a glass tube, the glutaronitrile (282 mg, 3.0 mmol, 1.0 equiv) was
Diphenylpropanenitrile (2f)10
Yield (GP1): 448 mg (72%); yield (GP2): 385 mg (62%); colorless
solid; mp 86–87 °C.
1H NMR (400 MHz, CDCl
7.6 Hz, 1 H), 3.02 (d, J = 7.6 Hz, 2 H).
added to a mixture of the respective acid 1 (3.0 mmol) and AlCl (8
3
mg, 0.06 mmol, 0.02 equiv). The tube was then sealed (with a screw
cap) and the mixture was allowed to stir at 200 °C for 5 h. After
completion of the reaction, the crude mixture was diluted with
EtOH (10 mL), silica gel (3 g) was then added to this crude material
to make a solid deposit after evaporation of the EtOH. A silica gel
column chromatography (eluent: PE–EtOAc, 95:5) finally afforded
the pure nitrile together with the cyclic imide. Conversion into the
): δ = 7.34–7.21 (m, 10 H), 4.36 (t, J =
3
13
C NMR (100 MHz, CDCl ): δ = 141.2, 128.9, 127.5, 127.4, 118.4,
3
47.1, 24.2.
1
4-Phenoxybenzonitrile (2g)11
Yield (GP1): 450 mg (78%); yield (GP2): 310 mg (53%); colorless
solid; mp 41–43 °C.
desired nitrile was determined by H NMR analysis of the crude
mixture. Given yields were reported for isolated products (Table 2).
Thermal-Catalyzed Reaction of Acids 1 with (Phenylsulfo-
nyl)acetonitrile; General Procedure 2 (GP2)
In a 10 mL round-bottomed flask, (phenylsulfonyl)acetonitrile (544
mg, 3.0 mmol, 1.0 equiv) was added to a mixture of acid 1 (3.0
1
H NMR (400 MHz, CDCl ): δ = 7.61–7.59 (m, 2 H), 7.44–7.40 (m,
3
2
H), 7.25–7.21 (m, 1 H), 7.07 (d, J = 8.4 Hz, 2 H), 7.00 (d, J = 8.4
Hz, 2 H).
13
mmol) and AlCl (8 mg, 0.06 mmol, 0.02 equiv). The mixture was
3
C NMR (100 MHz, CDCl ): δ = 161.6, 154.8, 134.1, 130.2, 125.1,
3
then stirred under argon at 200 °C for 3 h. After completion of the
reaction, the crude mixture was diluted with CH Cl (5 mL + 5 mL),
1
20.3, 118.8, 117.9, 105.8.
2
2
silica gel (3 g) was then added to make a solid deposit after evapo-
ration of the solvent. A silica gel column chromatography (eluent:
PE–EtOAc, 95:5) finally afforded the pure nitrile together with
methyl phenyl sulfone.
4-(tert-Butyl)benzonitrile (2h)12
Yield (GP1): 377 mg (79%); pale yellow oil.
1
H NMR (400 MHz, CDCl ): δ = 7.59 (d, J = 8.4 Hz, 2 H), 7.48 (d,
3
J = 8.4 Hz, 2 H), 1.33 (s, 9 H).
-Phenylbutanenitrile (2a)7
13C NMR (100 MHz, CDCl
35.2, 30.9.
): δ = 156.6, 131.9, 126.1, 119.2, 109.2,
3
2
Yield (GP1): 370 mg (83%); colorless oil.
1
H NMR (400 MHz, CDCl ): δ = 7.40–7.32 (m, 5 H), 3.74 (t, J = 7.2
-Cyclohexyl-2-phenylacetonitrile (2i)13
3
2
Hz, 1 H), 1.90 (quint, J = 7.2 Hz, 2 H), 1.08 (t, J = 7.2 Hz, 3 H).
Yield (GP1): 550 mg (92%); colorless oil.
13
C NMR (100 MHz, CDCl ): δ = 135.7, 128.9, 127.9, 127.2, 120.7,
1
3
H NMR (400 MHz, CDCl ): δ = 7.39–7.28 (m, 5 H), 3.63 (d, J =
3
3
8.8, 29.2, 11.4.
6
.8 Hz, 1 H), 1.85–1.65 (m, 6 H), 1.25–1.13 (m, 5 H).
13C NMR (100 MHz, CDCl
42.7, 31.1, 29.5, 25.8, 25.7.
): δ = 134.6, 128.7, 127.9, 120.1, 44.2,
3
3
-(3,5-Dichlorophenyl)propanenitrile (2b)
Yield (GP1): 432 mg (72%); white solid; mp 44 °C.
–
1
IR (thin film, ATR): 2247, 2217, 1590, 1566, 1431, 1101 cm .
-Phenylpropanenitrile (2j)14
3
1
H NMR (400 MHz, CDCl ): δ = 7.29 (s, 1 H), 7.13 (s, 2 H), 2.91
Yield (GP1): 201 mg (51%); colorless oil.
3
(
t, J = 7.2 Hz, 2 H), 2.63 (t, J = 7.2 Hz, 2 H).
1
H NMR (400 MHz, CDCl ): δ = 7.52–7.10 (m, 5 H), 2.97 (t, J = 7.6
3
13
C NMR (100 MHz, CDCl ): δ = 141.0, 134.9, 127.2, 126.7, 118.3,
Hz, 2 H), 2.63 (t, J = 7.6 Hz, 2 H).
3
30.5, 18.5.
13
C NMR (100 MHz, CDCl ): δ = 138.2, 128.9, 128.3, 127.2, 119.2,
3
HRMS (EI): m/z calcd for C H Cl N: 198.9956; found: 198.9958.
31.6, 19.3.
9
7
2
4
-Phenylbenzonitrile (2k)15
Yield (GP2): 365 mg (68%); colorless oil.
©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 1802–1806

1806
D. Cartigny et al.
PAPER
1
H NMR (400 MHz, CDCl ): δ = 7.74–7.68 (m, 4 H), 7.60–7.59 (m,
H), 7.51–7.43 (m, 3 H).
1350. (h) Becke, F.; Burger, T. F. Liebigs Ann. Chem. 1968,
716, 78. (i) Klein, D. A. J. Org. Chem. 1971, 36, 3050.
(j) Cantillo, D.; Kappe, C. O. J. Org. Chem. 2013, 78, 10567.
4) Mlinarić-Majerski, K.; Margeta, R.; Veljković, J. Synlett
3
2
13
C NMR (100 MHz, CDCl ): δ = 145.6, 139.1, 132.6, 129.1, 128.6,
3
(
(
1
27.7, 127.2, 118.9, 110.8.
2
005, 2089.
5) Cyanoacetic acid derivatives are known to spontaneously
decarboxylate under 200 °C: (a) Gardette, D.; Gramain, J.-
C.; Seguin, H.; Mademont, J.-C.; Moreau, M.-F. Synth.
Commun. 1998, 28, 4257. (b) Belski, A. J.; Maiella, P. G.;
Brill, T. B. J. Phys. Chem. A 1999, 103, 4253.
Acknowledgment
We thank the ENSTA, CNRS, and Solvay for financial support.
(
6) (a) Marion, P.; Jacquot, R.; Grimaud, L.; Cartigny, D.; El
Kaïm, L. Patent WO2013072466, 2013; Chem. Abstr. 2013,
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis. SnuIoipgfmr tooatrin guSIopi
n
nfo itrmart
1
59, 9015. (b) Jacquot, R.; Marion, P. Patent
WO2011144619, 2011; Chem. Abstr. 2011, 155, 686476.
7) Gaspar, B.; Carreira, E. M. Angew. Chem. Int. Ed. 2007, 46,
(
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Synthesis 2014, 46, 1802–1806
© Georg Thieme Verlag Stuttgart · New York