Pharmaceutica Analytica Acta

Abstract

Microwave Assisted Degradation of Lignin to Monolignols

Shaveta, Harshpinder Kaur and Palwinder Singh

Objective: To carry out lignin degradation under very mild conditions using microwave technique.
Methods: Lignin salt purchased from HiMedia laboratories was dissolved in distilled water and the solution was
introduced to Biotage Initiator microwave. The reaction temperature was varied between 100-150°C with average
power 85-90 W. Mass spectra were recorded in ACN-H2O (3:7) solution on BrukermicroTOF QII mass spectrometer
in +ve ESI mode. Acetonitrile and water were HPLC grade and were bought from Sigma Aldrich while Sodium
fluoride was purchased from Spectrochem. SEM images were recorded on ZEISS EVO LS10 scanning electron
microscope with prior coating of silver using Quorum Q150R ES coating machine.
Results: 1 g of lignin dissolved in 10 ml distilled water was irradiated under microwaves. Aliquots of samples
were withdrawn and mass spectra were recorded after every 10 min. Maximum conversion of lignin to monolignols
was observed after 90 min. Effect of NaF was also observed when catalytic amount of NaF (10 mg) was used in
each reaction. Surprisingly, the results obtained in the previous conditions after 90 min were achieved only after 30
min in the presence of NaF.
Conclusion: Lignin was degraded to its monomeric units when its aqueous solution in presence of catalytic
amount of NaF was irradiated under microwaves at 150°C for 30 min. Hence, this technique could be used to
degrade lignin into various lower lignols along with monolignols. Using this technique, revolutionary change could
be made in paper, pulp and leather industry. Above all, several pharmaceutical raw materials could be synthesized
efficiently from important monolignols produced from lignin degradation.