# Aromatic Amines in Organic Synthesis Part III; \(p\)-Aminocinnamic Acids and Their Methyl Esters
## 3 Materials and Methods
### Synthesis
#### 3.1.2 Synthesis of the Methyl \(p\)-(Dimethylamino)cinnamate  
For Method B, thionyl chloride (21 mmol) was added dropwise to a solution of \(p\)-(dimethylamino)cinnamic acid (15 mmol) in anhydrous methanol within 2 h under vigorous stirring. After 5 h, most of the methanol was distilled off, and the residue was poured onto 70 mL of ice water. Saturated NaHCO\({}_{3}\) was added while stirring until the CO\({}_{2}\) bubbles were stopped to volatilize. The precipitate was filtered and recrystallized from methanol. For Method C, concentrated H\({}_{2}\)SO\({}_{4}\) (4 g) was added dropwise to anhydrous methanol (30 mL). Then \(p\)-(dimethylamino)cinnamic acid (15 mmol) was put into the flask. The mixture was heated and held at gentle reflux for 20 h. Most of the methanol was distilled off, and the residue was poured onto 80 mL of ice water. Next, KHCO\({}_{3}\) was added in portions until the CO\({}_{2}\) bubbles were stopped to volatilize. The precipitate was filtered and recrystallized from methanol. For Method D, a total of 40 mL of acetone, 15 mmol of \(p\)-(dimethylamino)cinnamic acid, 20 mmol of dimethyl sulfate, and 21 mmol of potassium carbonate were put into a flask and stirred at r.t. for 24 h. The resulting mixture was filtered, and the filtrate was concentrated by evaporation to 15 mL and poured onto 100 mL of ice water. The precipitate was filtered off and dried. The crude product was crystallized from methanol. _4-Dimethylaminocinnamic acid (2a)_  
The compound was obtained as a brown solid; yield: 71%; mp 221 \({}^{\circ}\)C.  
\({}^{1}\)H NMR (400 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 11.96 (s, 1H, COOH), 7.50-7.46 (m, 3H), 6.70 (d, \(J\) = 8.9 Hz, 2H), 6.22 (d, \(J\) = 15.8 Hz, 1H, -CH =), 2.97 (s, 6H, N(CH\({}_{3}\))\({}_{2}\)). \({}^{13}\)C NMR (100 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 168.3 (COOH), 151.6 (C), 144.7 (CH), 129.8 (CH), 121.6 (C), 113.0 (CH), 111.8 (CH), 39.8 (N(CH\({}_{3}\))\({}_{2}\)). IR (KBr): 1679, 1605, 1529, 1372, 1231, 1203, 1191, 816. Anal. Calcd for C\({}_{11}\)H\({}_{3}\)NO\({}_{2}\): C, 69.09; H, 6.85; N, 7.33. Found: C, 69.01; H, 6.74; N, 7.28. _3-[4-(Diethylamino)phenyl]acrylic acid (2b)_  
The compound was obtained as a yellow solid; yield: 80%; mp 184 \({}^{\circ}\)C.  
\({}^{1}\)H NMR (400 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 11.91 (s, 1H, COOH), 7.47-7.43 (m, 3H), 6.65 (d, \(J\) = 9.0 Hz, 2H), 6.17 (d, \(J\) = 15.8 Hz, 1H, -CH =), 3.38 (q, \(J\) = 6.9 Hz, 4H, NCH\({}_{2}\)), 1.10 (t, \(J\) = 7.0 Hz, 6H, CH\({}_{3}\)). \({}^{13}\)C NMR (100 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 168.8 (COOH), 149.4 (C), 145.2 (CH), 130.5 (CH), 121.1 (C), 112.7 (CH), 111.5 (CH), 44.2 (NCH\({}_{2}\)), 12.9 (CH\({}_{3}\)). IR (KBr): 1670, 1658, 1598, 1356, 1261, 1208, 1184, 818. Anal. Calcd for C\({}_{13}\)H\({}_{17}\)NO\({}_{2}\): C, 71.21; H, 7.82; N, 6.39. Found: C, 71.15; H, 7.70; N, 6.32. _3-[4-(Diethylamino)phenyl]acrylic acid (2c)_The compound was obtained as a pale-yellow solid; yield: 68%; mp 138.5-140.5 \({}^{\circ}\)C.  
\({}^{1}\)H NMR (400 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 11.91 (s, 1H, COOH), 7.47-7.43 (m, 3H), 6.62 (d, \(J\) = 8.9 Hz, 2H), 6.16 (d, \(J\) = 15.8 Hz, 1H, -CH=), 3.31 (q, \(J\) = 7.6 Hz, 4H, NCH\({}_{2}\)), 1.50 (m, 4H), 1.35 (m, 4H), 0.92 (t, \(J\) = 7.3 Hz, 6H, CH\({}_{3}\)). \({}^{13}\)C NMR (100 MHz, DMSO-\(d_{6}\)) \(\sigma\) (ppm): 168.7 (COOH), 149.8 (C), 145.1 (CH), 130.4 (CH), 121.1 (C), 112.7 (CH), 111.6 (CH), 50.3 (NCH\({}_{2}\)), 29.5 (CH\({}_{2}\)), 20.1 (CH\({}_{2}\)), 14.3 (CH\({}_{3}\)). IR (KBr): 1670, 1578, 1525, 1403, 1204, 1185, 819. Anal. Calcd for C\({}_{17}\)H\({}_{25}\)NO\({}_{2}\): C, 74.15; H, 9.15; N, 5.09. Found: C, 74.10; H, 9.06; N, 5.11.