Green Chemistry
Cite this: Green Chem., 2012, 14, 2395
COMMUNICATION
Vanillin based polymers: I. An electrochemical route to polyvanillin†
Ananda S. Amarasekara,* Bernard Wiredu and Ashfaqur Razzaq
Received 27th April 2012, Accepted 3rd July 2012
DOI: 10.1039/c2gc35645g
Electrochemical reductive polymerization of divanillin in
aqueous sodium hydroxide using a lead cathode gives poly-
vanillin in 91% yield. The product was characterized by
elemental analysis, UV-Vis, FT-IR, 1H, 13C NMR,
TGA-DTGA, and GPC.
Current interest in the development of renewable resources based
Fig. 1 Synthesis of polyvanillin (3). a = 3% H2O2, 1% w/w horse-
polymeric materials has opened up a new area of research into
abundant natural products that can be utilized as monomers
or monomer precursors for the polymer industry.1 Vanillin
(4-hydroxy-3-methoxybenzaldehyde, 1, Fig. 1) is one of these
renewable resources based building blocks gaining increasing
attention in this area of research as a potential monomer or pre-
cursor,2 in addition to its present applications in the food and
pharmaceutical industries. Currently, approximately half of the
vanillin produced in the world is used as a flavoring material in
the food industry, and the remaining half is utilized as an inter-
mediate in the chemical and pharmaceutical industries for the
production of herbicides, antifoaming agents or drugs such as
papaverine, L-dopa, L-methyldopa and the antimicrobial agent
trimethoprim.3
This eight carbon phenolic-aldehyde was initially isolated from
the vanilla bean extract derived from orchids of the genus Vanilla,
and primarily from the Mexican species, Vanilla planifolia. Until
the 1920s, vanillin was commercially produced from another
natural product eugenol. Later it was synthesized from the lignin-
containing paper industry by-product called “brown liquor”. Even
though this process uses industrial waste materials, the “brown
liquor” based process is no longer popular because of environ-
mental concerns, and today most of the vanillin is produced from
the petroleum based raw material guaiacol.3 However the recent
advancements4 in the production of vanillin by catalytic air oxi-
dation of abundant lignin have made this an easily accessible
material, and have promoted the status of this flavor chemical to
another promising feedstock material.
radish peroxidase, pH = 4.0, b = electrolysis in 1 M aqueous NaOH,
Pb electrodes, 1.1 A, 12 V, 3 h.
Fig. 2 meso-Hydrovanilloin (4).
is also a flavor chemical found in roasted vanilla beans at very
low concentrations. Fortunately, this symmetrical dimer of vanil-
6
lin can be easily prepared by FeCl3 or enzyme7 catalyzed oxi-
dative dimerization of vanillin, and the polyfunctional divanillin
is a very attractive molecule as a monomer due to its symmetrical
arrangement of functional groups.
In addition to the free radical promoted oxidative dimerization
to produce divanillin, vanillin can be reductively dimerized at
the aldehyde function using low-valent titanium generated via
TiCl4–Mn8 or by electrochemical9 methods. In 1952 Pearl
first reported9 this electrochemical dimerization of vanillin to
hydrovanilloin (1,2-bis-(4-hydroxy-3-methoxy-phenyl)-ethane-
1,2-diol, 4, Fig. 2) in basic media; later, Grimshaw and Ramsey
showed10 that electrochemical coupling is a highly stereo-
selective reaction, and gives the meso compound. Our inter-
est11,12 in the synthesis of novel polymeric materials from
biomass derived monomers has led us to examine the application
of vanillin (1) and divanillin (2) as building blocks for the
preparation of new renewable polymeric materials. While re-
investigating this classical electrochemical coupling reaction, we
envisioned that a combination of oxidative and reductive coup-
lings of vanillin could be used to produce polyvanillin (3), and
in this communication we report the first preparation of poly-
vanillin (3) by electrochemical polymerization of the vanillin
dimer, divanillin (2) prepared by enzymatic dimerization of
vanillin.
Alternative biotechnology-based approaches applying fungi,
bacteria, plant cells, and genetically engineered microorganisms
are also currently under study5 for the large scale production of
this highly functionalized versatile building block.
The related dimer of vanillin, or divanillin (6,6′-dihydroxy-
5,5′-dimethoxy-(1,1′-biphenyl)-3,3′-dicarboxaldehyde, 2, Fig. 1),
Department of Chemistry, Prairie View A&M University, Prairie View,
Texas 77446, USA. E-mail: asamarasekara@pvamu.edu; Fax: +1 936
261 3117; Tel: +1 936 261 3107
†Electronic supplementary information (ESI) available: Procedures,
characterization data, spectra. See DOI: 10.1039/c2gc35645g
During this study meso-hydrovanilloin (4) (m.p. 232–233 °C,
lit.9 233–234 °C) was prepared as a model compound to
collect spectroscopic data that can be used as tools in the
This journal is © The Royal Society of Chemistry 2012
Green Chem., 2012, 14, 2395–2397 | 2395