Table 2 Commercial applications of selected alpha cyanoacrylic acids
Sr. no. (Table 1)
Compound
Commercial application
3
8
9
4
11
(E)-2-cyano-3-(4-hydroxyphenyl)acrylic acid
High value matrix substance in MALDI MS
High value matrix substance in MALDI MS
Possible entacapone intermediate
Intermediate for animals food-preservative
Intermediate for agrochemicals
(E)-2-cyano-3-(4-hydroxy-3-methoxyphenyl)acrylic acid
(E)-2-cyano-3-(4-hydroxy-3-methoxy-5-nitrophenyl)acrylic acid
(E)-2-cyano-3-(furan-2-yl)acrylic acid
(2E,4E)-2-cyano-5-phenylpenta-2,4-dienoic acid
Scheme 4 Proposed mechanism for IL catalyzed Knoevenagel condensation.
(A similar ratio of reactants and IL gave 80% yield from a
10 g batch of 4-methoxy benzaldehyde.)
Scheme 5 Synthesis of ionic liquid tri-(2-hydroxyethyl) ammonium
acetate.
3.5 Spectroscopic data for ionic liquid and selected compounds
Tri-(2-hydroxyethyl)
ammonium
acetate. IR
(KBr,
n
max/cm-1): 3310, 3154, 2936, 1560, 1482, 1456, 1404,
completion, (E)-2-cyano-3-(4-methoxyphenyl)acrylic acid, was
isolated (1.33 g,79%) by acidification with aqueous hydrochloric
acid (pH~5) at 5 ◦C and subsequent filtration. Traces of aldehyde
if any, were removed by washing the product with hexane.
1326, 1295, 1092, 1077, 1062, 1025, 1000, 911; dH (300 MHz;
DMSO-d6): 1.792 (s, 3H, CH3COO), 2.4 (t, 6H, J = 6 Hz,
CH2N), 3.32 (t, 6H, J = 6 Hz CH2O), 5.4, (br s, 3H, OH); dC
(300 MHz; DMSO-d6): 21.16, 57.15, 59.13, 172.
(Table 1. Entry 7). Yellow crystals, melting point 228 ◦C.
IR (KBr, nmax/cm-1): 2824, 2550, 2230, 1697, 1602, 1587, 1492,
1430, 1290, 1213, 1094, 921, 833.
dH (300 MHz; DMSO-d6): 3.85 (s, 3H, OCH3), 7.11(d, 2H,
J = 9 Hz, ArH), 8.03 (d, 2H, J = 9 Hz, ArH), 8.23 (s, 1H); dC
(300 MHz; DMSO-d6); 53, 104, 119, 121, 128, 137, 158, 167, 168.
3.3 Typical experimental procedure (Table 1, entries 23–28)
Malononitrile (0.4884 g, 0.0074 mol) and 4-methoxy ben-
zaldehyde (1 g, 0.0074 mol) were stirred with 2 g of ionic
liquid in a round bottom flask at room temperature. The
reaction was monitored by TLC and after completion, 2-(4-
methoxybenzylidene)malononitrile (1.177 g, 87%) was isolated
by quenching the reaction mixture with water at 5 ◦C and
subsequent filtration. Traces of aldehyde if any, were removed
by washing the product with hexane.
(Table 1. Entry 13). White crystals, melting point 131 ◦C.
IR (KBr, nmax/cm-1): 3410, 2886, 2219, 1699, 1602, 1411, 1367,
1290, 1255, 1089, 917, 780, 759, 599; dH (300 MHz; CDCl3;
Me4Si): 2.36 (s, 3H, CH3), 2.44 (s, 3H, CH3), 10 (s br, 1H, COOH).
dC (300 MHz; CDCl3; Me4Si); 23.27, 27.95, 104.5, 115.22,
166.7, 177.2.
3.4 Experimental procedure for a larger batch
To 200 g ionic liquid in a three neck round bottom flask
with overhead stirrer, cyanoacetic acid (93.5 g, 1.1 mol) was
added and the temperature was raised to 85 ◦C. To this, 4-
methoxy benzaldehyde (100 g, 0.74 mol) was added portion
wise over a period of 15 min. The reaction was monitored
by TLC. After completion of the reaction (3 hours) (E)-2-
cyano-3-(4-methoxyphenyl) acrylic acid was isolated (122 g,
82%) by quenching the reaction mixture in 2 liters of chilled
water, acidification with aqueous hydrochloric acid (pH ~ 5–6)
and subsequent filtration. Traces of aldehyde were removed by
washing the product with hexane. The ionic liquid was recovered
by evaporating the water under reduced pressure.
(Table 1. Entry 20). Yellow crystals, melting point 80 ◦C.
IR (KBr, nmax/cm-1): 2990, 2916, 2215, 1710, 1584, 1561, 1513,
1431, 1262, 1211, 1184, 1127, 1089, 1017, 837; dH (300 MHz;
CDCl3; Me4Si): 1.39 (t, J = 7.1 Hz, 3H, CH3), 3.89 (s, 3H,
OCH3), 4.38 (q, J = 7.1 Hz, 2H, CH2), 7.01 (d, J = 9 Hz,
2H, ArH), 8.02 (d, J = 9 Hz, 2H, ArH), 8.19 (s, 1H, CH); dC
(300 MHz; CDCl3; Me4Si): 14.2, 55.6, 62, 99.36, 114.7, 116.2,
124.37, 133, 154.4, 163.13, 163.79.
(Table 1. Entry 23). Yellow crystals, melting point 115 ◦C.
IR (KBr, nmax/cm-1): 2921, 2211, 1603, 1571, 1512, 1406, 1369,
1319, 1277, 1183, 1155, 1093, 1021, 833; dH (300 MHz; CDCl3;
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The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 526–530 | 529
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