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Esterification of trans-Cinnamic Acid; Ethyl Cinnamate

SyntheticPage 504
DOI: 10.1039/SP504
Submitted Aug 27, 2011, published Sep 05, 2011
Christopher Kelly (christopher.b.kelly@uconn.edu)
A contribution from Leadbeater Group


			Reaction Scheme: <IMG src="/images/empty.gif">Esterification of <SPAN id=csm1317157547868 class=csm-chemical-name title="trans-Cinnamic Acid" grpid="2">trans-Cinnamic Acid</SPAN><IMG src="/images/empty.gif">

Chemicals Used

Benzene (anhydrous, 99.8%, Purchased from Sigma-Aldrich)
Absolute Ethanol (ACS reagent, ≥99.5% (200 proof), absolute, Purchased from Sigma-Aldrich)
H2SO4 ( ACS reagent, 95.0-98.0%, Purchased from Sigma-Aldrich)
trans-Cinnamic Acid (≥99%, Purchased from Sigma-Aldrich) 
MgSO4 (anhydrous, ReagentPlus®, ≥99.5%, Purchased from Sigma-Aldrich)

Procedure

To a 250 mL round bottom flask was added the trans-cinnamic acid, (37,04 g, 0.25 mol, 1 equiv.),  absolute ethanol1 (51.75 g, 1.125 mol, 4.5 equiv.) and benzene (50 mL, 5 M in trans-cinnamic acid ). The flask was equipped with a stirbar, a soxhlet with cellulose membrane insert (containing 25 g of MgSO4), and a reflux condenser. The flask was heated to ≈ 40 oC in oil bath and concentrated H2SO4 (2.56 mL, 0.0475mol, 0.19 equiv.) was added all at once via a syringe. The solution was heated to reflux (oil bath at 120 oC and allowed to stir overnight. The solution was then diluted with ether (≈100 mL). The mixture was transferred to a separatory funnel and washed with 3 X 100 mL of a 10% w.t. sodium bicarbonate solution (CAUTION: CO2 gas is evolved). The organic layer was then washed with deionized water (≈100 mL), brine (≈100 mL), and dried with Na2SO4. The solvent was removed in vacuo by rotary evaporation to afford ethyl cinnamate as a clear yellow oil (38.49 g, 87%)2.

Author's Comments

1. This procedure has been found to be quite general. Many other types of alcohols (methyl, propyl, isopropyl) all seem to be compatible. Likewise, the acid can varied without compromising yields.
2.  In most cases, the product was found to by completely pure by NMR. In situations when this was not the case (particularly with other acids), the product was purified by vacuum distillation.

Data

1H NMR (400 MHz, CDCl3d ppm 1.37 (t, 3 H)  4.29 (q, 2 H)  6.46 (d, J=16.04 Hz, 1 H), 7.34 - 7.50 (m, 4 H), 7.50 - 7.61 (m, 2 H), 7.71 (d, J=16.04 Hz, 1 H)


Lead Reference

This procedure is a modification of the procedure outlined by Pines et al.
Shabtai, J.; Ney-Igner, E.; Pines, H. J. Org. Chem., 1981, 46, 3795.

Supplementary Information

1H NMR (Ethyl Cinnamate H1 NMR.pdf)

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Get structure file (.cdx, .sk2, .mol)

Keywords: Acid Catalyzed, carboxylic acids, Esterification, esters

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  • Guest BenMay 9 2012 4:58PM

    If you make the methyl ester you can use 10vols MeOH and there is no need for benzene, soxhlet or mag sulfate. Can just gently reflux o/n. In the morning, conc to a low volume on buchi and partition ether/bicarb as above

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