ACS 2022 JWS

Lignin is a complex organic polymer that's found in the cell wall of plants. It's a hydrophobic organic molecule with a molecular weight over 10,000 g/mol. Each lignin polymer is made up of three monomeric precursors: Coniferyl alcohol (4-hydroxy-3-methoxyphenylpropane), Sinapyl alcohol (3,5-dimethoxy-4-hydroxyphenylpropane), and Coumaryl alcohol (4-hydroxyphenylpropane). Each monomer is made up of an aromatic ring with a hydroxyl group and a propanol group each attached to the ring in the para position. Coniferyl alcohol has one methoxy group attached to the ring in a position ortho to the hydorxyl group while Sinapyl alcohol has two methoxy groups each attached ortho to the hydroxyl group. Because each lignin monomer is neutrally charged and consists of an aromatic ring, the entire polymer is hydrophobic and therefore insoluble in water. This allows lignin to form a semi-permeable membrane that can regulate the flow of water into plant cells. The goal of this project is to create a synthetic pathway to synthesize each of the lignin monomers from their carboxylic derivatives. This will allow further chemical analysis to study the properties of each monomer.

Ferulic acid, Sinapic acid, and Coumaric acid are the carboxylic acid derivatives of Coniferyl alcohol, Sinapyl alcohol, and Coumaryl alcohol. They serve as the starting materials for this project. Each acidic derivative will be synthesized in two steps: first, the carboxylic acid group will be converted into an ethyl ester and then the ester will be reduced into its alcoholic monomer. The kinetics (rate) of each reaction will be monitored at different time intervals using High-Performance Liquid Chromatography (HPLC) instrumentation. This not only determines the reaction's velocity, but also confirms whether product is being formed or not. Other instruments such as Mass Spectrometry and Nuclear Magnetic Resonance (NMR) will be used to confirm the presence of unknown product.