Facile Method for the Synthesis of Cyanoacrylates by Knoevenagel Condensation

Full text of DOI:10.1080/00304948.2020.1831894

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
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Facile Method for the Synthesis of Cyanoacrylates
by Knoevenagel Condensation
Thabile Mabaso , Nhlanhla Gracious Shabalala , Nagaraju Kerru &
Sreekantha B. Jonnalagadda
To cite this article: Thabile Mabaso , Nhlanhla Gracious Shabalala , Nagaraju Kerru &
Sreekantha B. Jonnalagadda (2021) Facile Method for the Synthesis of Cyanoacrylates by
Knoevenagel Condensation, Organic Preparations and Procedures International, 53:1, 18-24, DOI:
10.1080/00304948.2020.1831894
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ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
2021, VOL. 53, NO. 1, 18–24
https://doi.org/10.1080/00304948.2020.1831894
EXPERIMENTAL PAPER
Facile Method for the Synthesis of Cyanoacrylates
by Knoevenagel Condensation
Thabile Mabaso, Nhlanhla Gracious Shabalala, Nagaraju Kerru, and Sreekantha B.
Jonnalagadda
School of Chemistry & Physics, University of KwaZulu-Natal, Westville Campus, Chiltern Hills, Durban,
South Africa
ARTICLE HISTORY Received 28 February 2020; Accepted 27 June 2020
The Knoevenagel condensation is a powerful tool to build carbon-carbon bonds.
Knoevenagel synthesis of cyanoacrylates has received considerable attention, mainly
because the compounds possess wide-ranging applications. They are, as examples, useful
in medicine as instant adhesives,1 in forensic science as fingerprint revealers12 and in
the automotive industry as sealants.3 Despite the venerable status of the Knoevenagel
reaction for the preparation of these essential compounds, many of the traditional
methods used in its application rely on long reaction times, high temperatures or the
use of toxic metals as catalysts.4,5 There is a growing need for new approaches that
improve the Knoevenagel condensation for the synthesis of cyanoacrylates.6 Ultrasound
irradiation is a safe, cost-effective and sustainable technique to activate reactions.7–9 In
this communication, we report the catalyst-free synthesis of cyanoacrylates in excellent
yields, via the ultrasound facilitated Knoevenagel condensation of methyl cyanoacetate
and aromatic aldehydes in water (Scheme 1).
We chose 2,3-dimethoxybenzaldehyde (1l, R 5 2,3-OCH3) and methyl cyanoacetate
(2) as model substrates for the condensation reaction. We used an ultrasound bath
(50 kHz, see Experimental section) and examined the advantages of water, ethanol, and
their mixtures, as solvents. Table 1 summarizes the results. The best performance was
with water at room temperature (Entry 4), producing the desired compound 3l in 90%
yield within 5 min. Lower yields resulted at higher temperatures. When water is soni-
cated, the cavitation resulting from irradiation is more efficient at low temperatures.
This produces an effective agitation which maximizes contact between the aqueous and
organic phases and results in a greatly improved yield.
With the best conditions determined, we studied other substituted aromatic aldehydes
as precursors for the synthesis (Table 2). All the compounds studied gave consistently
impressive results, offering excellent yields (88-99%). The substituents on the precursor
did not influence yields much. The products were isolated by simple filtration and fur-
1
ther purified through recrystallization from ethanol. FTIR, H NMR, 13C NMR, HRMS
and single-crystal X-ray analysis were used to characterize the compounds prepared.
CONTACT Sreekantha B. Jonnalagadda
jonnalagaddas@ukzn.ac.za
School of Chemistry & Physics, University of
KwaZulu-Natal, Westville Campus, Chiltern Hills, Durban-4000, South Africa
Supplemental data for this article can be accessed here.
ß 2020 Taylor & Francis Group, LLC

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
19
Scheme 1. Synthesis of methyl 2-cyano-acrylates in water with ultrasound irradiation.
Crystals of compound 3l were grown by slow evaporation from dichloromethane.
Figure 1 illustrates the resulting structure from single-crystal X-ray diffraction. This
crystal is of monoclinic structure and P21 space group. This study unambiguously dem-
onstrates that the molecular formula of the crystal is C13H13NO4.
1
Consistent with this crystal structure, the H NMR spectrum compound 3l showed
the presence of three signals at 3.90, 3.91 and 3.93 ppm, for three methoxy groups, aro-
matic peaks between 7.10-7.92 ppm and the characteristic C-H singlet at 8.70 ppm.
Our study described the successful synthesis of fourteen substituted methyl 2-cyano-
3-acrylate derivatives via a green method using ultrasound irradiation, mild reaction
conditions, and water as a solvent. This afforded products in excellent yields in short
reaction times, with no by-products. With the ability to prepare different cyanoacrylates
so conveniently, we hope our method will encourage researchers to explore further the
applications of these useful molecules as synthetic building blocks.
Experimental section
Reagent grade chemicals were used with no further purification. 400 MHz and 100 MHz
1
(Bruker Avance) instruments were employed to record H NMR and 13C NMR spectra
with TMS as an internal standard. A Perkin Elmer Precisely 100 FT-IR spectrometer
was used to record the FT-IR spectra of the compounds. A Waters Micromass LCT
premier mass spectrometer with electrospray ionization in positive/negative mode was
employed to record the HRMS. A Scientech ultrasonic cleaner with a frequency of
50 kHz and a nominal power 150 W was used for the ultrasonic irradiation of the reac-
tion mixtures. A hot stage melting point apparatus (Ernst Leitz, Wetzlar, Germany) was
used for recording melting points, and they are reported uncorrected. The purity of the
products was established by thin-layer chromatography (TLC) using aluminum plates
coated with Merck Kieselgel 60 F254 silica gel, and hexane:ethyl acetate (9:1) was the
eluting solvent. We examined the spots in an iodine chamber under UV light.
A Bruker Smart APEX diffractometer with MoKa radiation (1 ¼ 0.71073A) equipped
with an Oxford cryostream low-temperature apparatus operating at 100 K was used for
the evaluation of synthesized products and data collection.20 SAINT (Bruker) facility
was employed for the data processing and absorption corrections. SADABS technique
was explored for the multi-scan absorption corrections, while the SHELXS program
(refined by the ShelXL program) was utilized for solving the structure by the direct
method.21 The refining of the non-hydrogen atoms was achieved anisotropically. The
riding model was used to calculate and refine the hydrogen atom positions. A complete
data set for the x-ray crystallography for 3l is available from the corresponding author

20
T. MABASO ET AL.
Table 1. Effect of solvent on the synthesis of 3l.
Sonication
Entry
Temperature (oC)
Solvent
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
50
45
35
25
25
35
40
50
H2O
H2O
H2O
30
30
15
5
25
25
35
40
55
58
60
90
71
54
52
49
H2O
EtOH/H2O(1:1)
EtOH/H2O(1:1)
EtOH/H2O(1:1)
EtOH/H2O(1:1)
aIsolated yield.
Table 2. Catalyst-free synthesis of methyl 2-cyano-3-(substituted-phenyl) acrylates under ultrasound
irradiation.
Sonication
Entry
R
Products
Time (min)
Yield (%)a
mp (oC)
Lit mp (oC)ref
10
1
2
3
4
5
6
7
8
2-OCH
3-OCH3
3,4-(OCH3)2
4-Br
4-N(CH3)2
4-Cl
2-CF3
2-Cl, 6-F
2-Cl
2,4-Cl2
4-F
2,3-(OCH3)2
2,3,4-(OCH3)3
H
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3
3
3
3
3
3
5
4
4
4
5
5
3
3
98
98
89
96
92
97
95
96
98
98
97
90
88
99
89-91
99-101
123-125
106-108
129-131
119-121
106-108
94-96
99-101
102-104
93-95
123-125
158-160
85-87
-
-
10
12611
104-10512
13113
119-12014
10715
9416
9
102.8-103.917
10316
10
11
12
13
14
91-9212
12518
16319
83.9-85.417
aIsolated yield. Melting points not previously reported for 3a and 3b. See the Experimental section.
Figure 1. Crystal structure of compound 3l.
upon request. In the online version of this article, the information can be found in the
Supporting Information.
Optimized procedure for the synthesis of methyl 2-cyano-3-(substituted-
phenyl) acrylates
The appropriate aromatic aldehyde (1a-n, 1.0 mmol) was added to a solution of methyl
cyanoacetate (2, 0.145 g, 1.0 mmol) and H2O (10 mL) in a conical flask (100 mL). This

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
21
flask was transferred into the ultrasonic bath so that the level of the reactants was
slightly below the surface of the water. The mixture was exposed to ultrasonic waves at
a frequency of 50 kHz and power of 150 W, at 25 ꢀC. TLC was used to monitor the
extent of the reaction. After reaction completion, the mixture at room temperature was
filtered dry under vacuum to recover the solid product. The product was further puri-
fied through recrystallization from ethanol (ꢁ 5 to 10 mL). All of the products were
1
known compounds. They were identified by comparison of H and 13C NMR spectra
and melting points, where the latter were available, with the literature values provided
in the references cited in Table 2.
Methyl 2-cyano-3-(2-methoxyphenyl) acrylate (3a)
1
0.255 g, 98%, pale yellow solid, mp 89-91 ꢀC, IR: (cmꢂ1) 2887, 2218, 1729, 1592. H
NMR (400MHz, DMSO-d6): d ¼ 3.85 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 7.12-7.16
(t, J ¼ 7.56 Hz, 1H, ArH), 7.23 (d, J ¼ 8.36 Hz, 1H, ArH), 7.62-7.66 (m, 1H, ArH), 8.10-
8.12 (dd, J ¼ 7.80 Hz, J ¼ 1.44 Hz, 1H, ArH), 8.58 (s, 1H, CH). 13C NMR (100 MHz,
DMSO-d6): d ¼ 53.3, 56.1, 101.9, 112.2, 115.6, 119.7, 120.8, 135.5, 149.0, 158.8, 162.4.
HRMS (M þ Na): Calcd for C12H11NO3, m/z 240.0637. Found, m/z 240.0638.
Methyl 2-cyano-3-(3-methoxyphenyl)acrylate (3b)
1
0.255 g, 98%, yellow solid, mp 99-101 ꢀC, IR: (cmꢂ1) 2843, 2218, 1726, 1603. H NMR
(400MHz, DMSO-d6): d 3.80 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 7.20-7.23 (dd,
J ¼ 8.24 Hz, J ¼ 1.60 Hz, 1H, ArH), 7,48-7.52 (t, J ¼ 8.24 Hz, 1H, ArH), 7.63-7.65 (m,
2H, ArH), 8.38 (s, 1H, CH). 13C NMR (100 MHz, DMSO-d6): d 53.3, 56.1, 101.9, 112.2,
115.6, 119.7, 120.8, 135.5, 149.0, 158.8, 162.4. HRMS (M þ H): Calcd for C12H11NO3,
m/z 217.0739. Found, m/z 217.0748.
Methyl 2-cyano-3-(3,4-dimethoxyphenyl)acrylate (3c)
1
0.263 g, 89%, pale yellow solid, mp 123-125 ꢀC, IR: (cmꢂ1) 2841, 2217, 1725, 1584. H
NMR (400MHz, CDCl3): d 3.92 (s, 3H, OCH3), 3.96 (s, 3H, OCH3), 3.97 (s, 3H, OCH3)
6.96 (d, J ¼ 8.44 Hz, 1H, ArH), 7.46-7.48 (dd, J ¼ 8.40 Hz, 2.08 Hz, 1H, ArH), 7.81
(d, J ¼ 2.04 Hz, 1H, ArH), 8.17 (s, 1H, CH). 13C NMR (100 MHz, DMSO-d6): d 53.3,
56.0, 61.4, 103.3, 115.3, 118.0, 119.4, 124.5, 124.9, 149.0, 149.2, 152.5, 162.3. HRMS
(M þ Na): Calcd for C13H13NO4, m/z 270.0742. Found, m/z 270.0741.
Methyl 3-(4-bromophenyl)-2-cyanoacrylate (3d)
1
0.301 g, 96%, white solid, mp 106-108 ꢀC, IR: (cmꢂ1) 2848, 2221, 1719, 1606. H NMR
(400MHz, DMSO-d6):d 3.86 (s, 3H, OCH3), 7.81 (d, J ¼ 8.56 Hz, 2H, ArH), 7.96
(d, J ¼ 8.56 Hz, 2H, ArH), 8.39 (s, 1H, CH). 13C NMR (100 MHz, DMSO-d6): d 53.3,
62.4, 103.0, 103.3, 115.3, 127.1, 130.5, 153.7, 153.9, 161.6, 162.1. HRMS (M þ Na): Calcd
for C11H8NBrO2, m/z 287.1006. Found, m/z 287.1011.

22
T. MABASO ET AL.
Methyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate (3e)
1
0.254 g, 92%, off white solid, mp 129-131 ꢀC, IR: (cmꢂ1) 2908, 2211, 1708, 1610. H
NMR (400MHz, CDCl3): d 3.07 (s, 6H, 2 ꢃ CH3), 3.79 (s, 3H, OCH3), 6.82
(d, J ¼ 8.96 Hz, 2H, ArH), 7.93 (d, J ¼ 8.92 Hz, 2H, ArH), 8.08 (s, 1H, CH). 13C NMR
(100 MHz, CDCl3): d 14.1, 52.6, 61.4, 91.7, 117.5, 118.2, 133.8, 153.7, 154.2, 163.9.
HRMS (M þ Na): Calcd for C13H14N2O2, m/z 253.0953. Found, m/z 253.0956.
Methyl 3-(4-chlorophenyl)-2-cyanoacrylate (3f)
1
0.257 g, 97%, white solid, mp 119-121 ꢀC, IR: (cmꢂ1) 2960, 2224, 1722, 1606. H NMR
(400MHz, DMSO-d6): d 3.86 (s, 3H, OCH3), 7.68(d, J ¼ 8.56 Hz, 2H, ArH), 8.06 (d,
J ¼ 8.60 Hz, 2H, ArH), 8.42 (s, 1H, CH). 13C NMR (100 MHz, DMSO-d6): d 53.3, 103.0,
115.3, 129.4, 130.2, 132.4, 138.0, 153.7, 162.1. HRMS (M þ Na): Calcd for C11H8NClO2,
m/z 244.0542. Found, m/z 244.0541.
Methyl 2-cyano-3-(2-(trifluoromethyl)phenyl)acrylate (3g)
1
0.290 g, 95%, cream white solid, mp 106-108 ꢀC, IR: (cmꢂ1) 2958, 2233, 1728, 1624. H
NMR (400MHz, DMSO-d6): d 3.89 (s, 3H, OCH3), 7.78-7.82 (t, J ¼ 7.68 Hz, 1H, ArH),
7.88-7.92 (d, J ¼ 7.56 Hz, 1H, ArH), 7.94 (d, J ¼ 7.88 Hz, 1H, ArH), 8.54 (s, 1H, CH).
13C NMR (100 MHz, CDCl3): d 48.3, 102.9, 109.0, 117.3, 119.1, 121.2, 121.3, 124.4,
124.6, 124.8, 126.5, 127.2, 146.5, 156.5.
Methyl 3-(2-chloro-6-fluorophenyl)-2-cyanoacrylate (3h)
1
0.275 g, 96%, white solid, mp 94-96 ꢀC, IR: (cmꢂ1) 2960, 2232, 1729, 1619. H NMR
(400MHz, CDCl3): d 3.96 (s, 3H, OCH3), 7.14-7.18 (t, J ¼ 8.80 Hz, 1H, ArH), 7.32
(d, J ¼ 8.04 Hz, 1H, ArH), 7.40-7.46 (m, 1H, ArH), 8.29 (s, 1H, CH). 13C NMR
(100 MHz, DMSO-d6): d 53.6, 112.2, 113.5, 115.1, 115.3, 119.9, 120.1, 125.7, 133.0,
133.1, 135.2, 135.3, 147.2, 147.2, 158.7, 161.3, 161.5.
Methyl 3-(2-chlorophenyl)-2-cyanoacrylate (3i)
1
0.259 g, 98%, white solid, mp 99-101 ꢀC, IR: (cmꢂ1) 2962, 2233, 1723, 1621. H NMR
(400MHz, CDCl3): d 3.96 (s, 3H, OCH3), 7.39-7.43 (td, J ¼ 7.32 Hz, J ¼ 1.48 Hz, 1H,
ArH), 7.45-7.53 (m, J ¼ 8.04 Hz, 1H, ArH), 7.40-7.46 (m, 2H, ArH), 8.23-8.25 (dd,
J ¼ 8.04 Hz, 1.48 Hz, 1H, ArH), 8.70 (s, 1H, CH). 13C NMR (100 MHz, CDCl3): d 53.5,
105.7, 114.7, 127.4, 129.8, 130, 3, 136.5, 151.4, 162.3.
Methyl 2-cyano-3-(2,4-dichlorophenyl)acrylate (3j)
1
0.299 g, 98%, white solid, mp 102-104 ꢀC, IR: (cmꢂ1) 2968, 2219, 1730, 1603. H NMR
(400MHz, CDCl3): d 3.96 (s, 3H, OCH3), 7.39-7.41 (dd, J ¼ 8.56 Hz, J ¼ 2.00 Hz, 1H,
ArH), 7.54 (d, J ¼ 2.12 Hz, 1H, ArH), 8.19 (d, J ¼ 8.56, 1H, ArH), 8.62 (s, 1H, CH). 13C

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
23
NMR (100 MHz, CDCl3): d 53.6, 105.9, 128.0, 128.2, 130.3, 130.5, 137.3, 139.5,
149.9, 162.1.
Methyl 2-cyano-3-(4-fluorophenyl)acrylate (3k)
1
0.238 g, 97%, white solid, mp 93-95 ꢀC, IR: (cmꢂ1) 2965, 2222, 1720, 1598. H NMR
(400MHz, CDCl3): d 3.94 (s, 3H, OCH3), 7.18-7.22 (t, J ¼ 8.56 Hz, 2H, ArH), 8.01-8.05
(m, 2H, ArH), 8.22 (s, 1H, CH). 13C NMR (100 MHz, CDCl3): d 53.4, 102.1, 115.4,
116.6, 116.8, 127.7, 127.8, 133.6, 133.6, 133.7, 153.7, 162.9, 164.2, 166.7.
Methyl 2-cyano-3-(2,3-dimethoxyphenyl)acrylate (3l)
1
0.266 g, 90%, yellow solid, mp 123-125 ꢀC, IR: (cmꢂ1) 2953, 2219, 1726, 1589. H NMR
(400MHz, CDCl3): d 3.90 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 3.93 (s, 3H, OCH3), 7.10-
7.12 (dd, J ¼ 8.32 Hz, 1.48 Hz, 1H, ArH), 7.15-7.19 (t, J ¼ 7.96 Hz, 1H, ArH), 7.90-7.92 (dd,
J ¼ 7.88 Hz, 1.40 Hz, 1H, ArH), 8.70 (s, 1H, CH). 13C NMR (100 MHz, CDCl3): d 53.3,
55.9, 62.0, 103.3, 115.5, 115.8, 117.2, 120.4, 122.2, 123.6, 124.4, 125.6, 149.9, 150.1, 151.6,
152.7, 163.0. HRMS (M þ Na): Calcd for C13H13NO4, m/z 270.0742. Found, m/z 270.0749.
Methyl 2-cyano-3-(2,3,4-trimethoxyphenyl)acrylate (3m)
1
0.292 g, 88%, white solid, mp 158-160 ꢀC, IR: (cmꢂ1) 2949, 2222, 1709, 1601. H NMR
(400MHz, CDCl3): d 3.86 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 3.95 (s, 3H, OCH3), 3.98
(s, 3H, OCH3), 6.97 (d, J ¼ 9.04 Hz, 1H, ArH), 8.19 (d, J ¼ 9.04 Hz, 1H, ArH), 8.61 (s,
1H, CH). 13C NMR (100 MHz, CDCl3): d 53.1, 56.2, 60.9, 62.1, 99.6, 107.6, 116.3, 118.6,
125.0, 141.2, 149.2, 154.9, 158.5, 163.6. HRMS (M þ Na): Calcd for C14H15NO5, m/z
300.0848. Found, m/z 300.0855.
Methyl 2-cyano-3-phenylacrylate (3n)
1
0.222 g, 99%, white solid, mp 85-87 ꢀC, IR: (cmꢂ1) 2955, 2225, 1724, 1606. H NMR
(400MHz, CDCl3): d 3.94 (s, 3H, OCH3), 7.49-7.53 (m, 2H, ArH), 7.55-7.59 (m, 1H,
ArH), 7.98 (d, J ¼ 7.24 Hz, 2H, ArH), 8.27 (s, 1H, CH). 13C NMR (100 MHz, CDCl3): d
53.4, 102.5, 115.4, 129.3, 131.1, 131.4, 133.4, 155.3, 163.0.
Acknowledgment
The authors thank the University of KwaZulu-Natal for research facilities.
ORCID
Sreekantha B. Jonnalagadda
http://orcid.org/0000-0001-6501-8875
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