Reactions of β-O-4-type Non-phenolic Lignin Model Compounds in Various Basic Systems using tert-Butoxide and Other Bases under Mild Conditions
Xu Zeng, Tomoya Yokoyama
Published online: 23 Feb 2021
- and C6
-type lignin model compounds with the β-O-
4 bond were treated in tert
-butyl alcohol (t
BuOH) or dimethyl sulfoxide (DMSO) containing potassium tert
Bu) or various other bases under mild conditions (at a base concentration of 0.5 mol/L and 30ºC) to examine how the reactions differ between these systems.
4 bond cleavage in KOt
BuOH was slower than that in KOt
Bu/DMSO owing to the greater solvation of t
BuO¯ in t
BuOH than in DMSO.
4 bond cleavage of the erythro
isomer of the C6
-type compound was slower than that of the threo
isomer in all the reactions.
This is explained by the preferred formation of a strong hydrogen bond between the α-hydroxy and the dissociated γ-alkoxy groups (or vice versa
) of theformer, which interferes with the cleavage.
The rates of the β-O-
4 bond cleavages in DMSO were in the order of the systems containing: NaOt
Bu > KOt
Bu >> LiOt
Bu, which seems to relate to whether each base dissolves as an ion pair or free ions in DMSO.
Those in DMSO were in the order of the systems containing KOt
Bu >> potassium hydride (KH) >> potassium iso
-propoxide > potassium ethoxide, which is consistent with their basicities except for KH.
Production of Vanillin and Vanillic Acid by Aerobic Oxidation of Polyethylene Glycol (PEG)-modified Glycol Lignin in Tetrabutylammonium Hydroxide
Takashi Hosoya, Daiki Okamoto, Hisashi Miyafuji, Tatsuhiko Yamada
Published online: 20 May 2021
Aerobic oxidation of lignin in reaction media containing Bu4
facilitates efficient production of vanillin
(4-hydroxy-3-methoxybenzaldehyde) and vanillic acid
(4-hydroxy-3-methoxybenzoic acid). This study presents production of these
compounds from polyethylene glycol (PEG)-modified glycol lignin
(PEG-lignin) from Japanese cedar (Cryptomeria japonica
). A Bu 4
NOH-based reaction medium was prepared by the addition of
NaOH(s) to 1.25 mol/L Bu4
NOH aq. Degradation of the PEG-lignin
(14 mg) in 2.0 mL of the medium at 120 o
C under O2
a sealed test tube produced vanillin and vanillic acid with 9.1 and 2.6 wt%
yields, respectively, based on the Klason lignin amount of the PEG-lignin.
The total yield of vanillin and vanillic acid reached 79.6 % of that in the
corresponding alkaline nitrobenzene oxidation (14.7 wt%), indicating high
performance of the medium. Bench-scale aerobic oxidation of the PEG-lignin
(100 g /1.0 L) under O2
pressurized at 0.7 MPa gave the products
with their maximum yields similar to those in the above lab-scale
experiment. Further increase in the O2
pressure to 2.5 MPa
significantly shortened the reaction time to achieve the maximum product
yield. This pressure increase did not affect the vanillin yield, but
suppressed the formation of O2
-sensitive vanillic acid, by which
selective vanillin production was achieved.
A Microscale Protocol for Alkaline Nitrobenzene Oxidation of Lignins Using a Readily Available Reactor
Masaomi Yamamura, Takuji Miyamoto, Rie Takada, Dwi Widyajayantie, Vincentia Esti Windiastri, Satya Nugroho, Toshiaki Umezawa
Published online: 12 July 2021
Nitrobenzene oxidation of lignin has long been one of the typical lignin chemical degradation methods. Previously, we reported a high-throughput and microscale protocol for the method. However, the reactor used in the protocol was available only in Japan and not supported outside Japan. In this study, we prepared an alternative protocol of alkaline nitrobenzene oxidation using an alternative reactor, which is available in many countries. Using the new protocol almost the same product yields as the previous protocol were obtained using a stable-isotope-dilution method. In addition, ethylvanillin, which is readily and commercially available, was also found to be usable as an alternative internal standard.