Pentyl (E)-3-(3,4-dihydroxyphenyl)acrylate

In the molecule of the title compound, C14H18O4, the C=C double bond is in an E configuration. The molecule is almost planar (r.m.s. deviation of all non-H atoms = 0.04 Å). An intramolecular O—H⋯O hydrogen bond occurs. In the crystal, intermolecular O—H⋯O interactions link the molecules into ribbons extending in [110].

In the molecule of the title compound, C 14 H 18 O 4 , the C C double bond is in an E configuration. The molecule is almost planar (r.m.s. deviation of all non-H atoms = 0.04 Å ). An intramolecular O-HÁ Á ÁO hydrogen bond occurs. In the crystal, intermolecular O-HÁ Á ÁO interactions link the molecules into ribbons extending in [110].
The molecule of (I) has an E configuration (Fig. 1); All non-H atoms of (I) are almost coplanar, with a root mean square deviating from the least-squares plane of 0.04 A°. The bond lengths (Allen et al., 1987) and angles are within normal ranges.
In the crystal structure, hydroxy groups contribute to intermolecular O-H···O interactions (Table 1) link the molecules into ribbons extended in the [110] direction (Fig. 2), in which they may be effective in the stabilization of thestructure. On the other hand, the intramolecular O-H···O H-bond also contribute to the stability of the molecular configuration ( Fig. 1 and Table 1).

Experimental
Esterification of caffeic acid with amyl alcohol was performed in a column (inner diameter= 15 mm, length = 200 mm).
Caffeic acid (8.95 g, 0.05 mol) was dissolved in amyl alcohol (100 ml). The mixture was stirred at 80°C for 60 minutes and fed from the top of the reactor with syringe pumps. The feed rate of the mixture was fixed at 10.0 ml/h. Cation exchange resin CD-552 particles(5 g) and molecular sieve(5 g) were packed into the middle of the reactor and glass beads of 2 mm in diameter were loaded into the rest of the column. The reaction temperature continued at 90°C for 20 h. The mixture was evaporated to dryness and followed by the addition of ethanol and extracted with chloroform three times. The chloroform extract was dried over evaporated to give a solid residue, and dissolved in ethanol/petroleum ether (1:1) to crystal. The solution was filtered and concentrated to yield a brown crystalline product (5.3 g, 59.2%). Recrystallization from ethanol gave colourless crystal.

Refinement
The H atoms were placed in calculated positions (O-H = 0.82 A ° and C-H = 0.93-0.97 A °) and constrained to ride on their parent atoms, with U iso (H) = 1.2 or 1.5Ueq(O,C). Fig. 1. The molecular structure of the title molecule, with the atom numbering scheme. Displacement ellipsoids are drawn at 30% probability levels.