Synthesis of Lignin Monomers

By:Alexandria N. Tibbs

Introduction

Lignin is the second most abundant organic polymer. It is found in plants, majorly in trees. Its function is to serve in the assistance of water flow throughout the plant. It forms a barrier for the evaporation, trapping the water inside.

The structure of lignin is composed of the seemingly random combination of three monomers: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.

Lignin Precursors

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These lignin monomers are derived from their acid precursors through the reduction of an aldehyde to the corresponding alcohol. While the acid precursors,p-courmaric acid (p-coumaryl alcohol), ferulic acid (coniferyl alcohol), and sinapic acid (sinapyl alcohol) may not be as abundant in nature, when it comes to the lab setting, these chemicals are easier to come by then their alcohol forms. The synthesis of theses alcohols can save a research space a great deal of money, if experiments require the alcohol forms of these monomers.

Materials

Diisobutylaluminum hydride solution (25 wt.% in toluene)

Product Number: 192724-100G

Quantity: 2

Price: $52.20

Toluene (Anhydrous, 99.8%)

Product Number: 244511-1L

Quantity: 1

Price: $60.50

Experimental

The esterfication of ferlic acid was the first step in the reduction of ferulic acid to coniferyl alcohol. First attempt was made using a 0.24M solution of ferulic acid in ethanol (250 mL ethanol, 12.1g ferulic acid). Along with 3 drops of concentrated HCl this was allowed to reflux for two days. The resulting solution

Results

Figure 1: HPLC Results after esterfication of Ferulic Acid

References

Lignin Biosynthesis and Structure

Oxidative Coupling during Lignin Polymerization is Determined by Unpaired Electron Delocalization within Parent Phenylpropanoid Radicals

[Overview from Lignin and Lignans: Advances in Chemistry]

Facile Large-Scale Synthesis of Coniferyl, Sinapyl, and p-Coumaryl Alcohol