The Modification of Lignin at Positions 2 and 6 of the Phenylpropanoid Nucleii - Part II<sup>1</sup>: Hydroxymethylation of Lignin Model Compounds

Klashorst, G. H. Van Der

doi:10.1080/02773818808070680

Cited by 5 publications

(4 citation statements)

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“…Additionally, formaldehyde also partially blocks the electron-rich meta positions through the formation of m-hydroxymethyl groups (relative to the phenolic position). [226][227][228][229][230] Noteworthy, the subsequent formation of methylene cross-linkages such as in phenol formaldehyde resins does not occur, thanks to the optimised processing conditions. 229,230 A side-reaction of the formaldehyde-assisted delignification process is the incorporation of formaldehyde into the residual carbohydrate pulp.…”

Section: Fractionation Based On Delignificationmentioning

confidence: 99%

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

et al. 2018

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In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon-carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.

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Section: Fractionation Based On Delignificationmentioning

confidence: 99%

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

et al. 2018

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“…The hydroxymethylation of the hardwood model (13) was first attempted by using a 20 molar excess formaldehyde in 1,1N HC1 in 50% aqueous dioxane (14). Since IS has two reactive sites (2 and 6), this means a ten-fold excess of formaldehyde per reactive site.…”

Section: Meta Hydroxymethylationmentioning

confidence: 99%

Modification of Lignin at the 2- and 6-Positions of the Phenylpropanoid Nuclei

Klashorst

1989

ACS Symposium Series

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Lignin model compounds were reacted with formaldehyde in acid medium at positions meta to the aromatic hydroxy groups. Both phenolic and etherified phenolic lignin model compounds were shown to give fast polymerization or hydroxymethylation of the meta positions depending on the conditions used. This reaction differs from the reaction of formaldehyde with phenolic lignin model compounds under alkaline conditions, where the reaction with formaldehyde always occurs at positions ortho/para to the aromatic hydroxy group. The conditions developed for the polymerization and hydroxymethylation were also evaluated on industrial lignin. The reaction of formaldehyde with the meta positions of lignin clearly have considerable potential for the use of lignin, particularly heavily condensed alkali lignin, in polymeric applications.Lignin, present as a waste material in the spent liquors of the pulping industry, constitutes a potentially useful raw material for the production of various polymeric products. This has repeatedly been demonstrated in the past by its application in products ranging from wood adhesives to plastics (1). In these applications the lignin is crosslinked to increase its molecular mass or to form a rigid three-dimension ally crosslinked structure.The features on lignin that were utilized for these polymerization or modification reactions are as follows (compare Fig. 1):1. phenolic hydroxy group; 2. aliphatic hydroxy group; 3. unsubstituted 3-or 5-positions on C9 units; and 4. structures that can form quinonemethide intermediates.

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“…Usually, the reaction progress is monitored through the disappearance of formaldehyde. However, other techniques have been used, such as differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV-vis) spectroscopy [ 23 , 24 , 25 , 26 , 27 ]. The reaction has been described as being a second-order reaction [ 24 ].…”

Section: Introductionmentioning

confidence: 99%

“…In an older study, the methylolation of lignin model compounds in their meta positions was studied using 1 H NMR. Both phenolic and non-phenolic softwood and hardwood model compounds were modified with formaldehyde in an acidic medium with dioxane [ 27 ].…”

Section: Introductionmentioning

confidence: 99%

The Potential of Visible Spectroscopy as a Tool for the In-Line Monitoring of Lignin Methylolation

et al. 2022

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Out of the 50 to 70 million tons of lignin that are produced annually, only 1 to 2% are used for value-added products. Currently, 90% of the total market of this compound corresponds to lignosulphonates (LS). The most successful industrial attempts to use lignin for wood adhesives rely on using it as a partial substitute in phenol–formaldehyde or urea–formaldehyde resins. However, lignin’s aromatic ring presents a low number of reactive sites. Several methods have been proposed to improve its reactivity, such as prior methylolation with formaldehyde. Off-line methods are commonly applied to monitor this reaction’s progress, but this introduces a significant delay in the analysis. This study proposes a new method for in-line monitoring of the methylolation reaction using visible spectroscopy. In order to monitor the reaction progress, principal component analysis was applied to the spectra, and the obtained scores were analyzed. When these results were plotted against those obtained by the off-line methods, a satisfactory regression was obtained at 50 °C (R2 = 0.97) and 60 °C (R2 = 0.98) for two different LS samples. Therefore, it was concluded that visible spectroscopy is a promising technique for studying lignin methylolation.

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The Modification of Lignin at Positions 2 and 6 of the Phenylpropanoid Nucleii - Part II¹: Hydroxymethylation of Lignin Model Compounds

Abstract: Phenolic hardwood and softwood lignin model compounds were hydroxyme-ihylated with formaldehyde at positions rneta to the aromatic hydroxy group. 0-alkylated phenolic model compounds were hydroxymethylated at the same relative positions.

Cited by 5 publications

References 3 publications

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Modification of Lignin at the 2- and 6-Positions of the Phenylpropanoid Nuclei

The Potential of Visible Spectroscopy as a Tool for the In-Line Monitoring of Lignin Methylolation

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The Modification of Lignin at Positions 2 and 6 of the Phenylpropanoid Nucleii - Part II1: Hydroxymethylation of Lignin Model Compounds

Abstract: Phenolic hardwood and softwood lignin model compounds were hydroxyme-ihylated with formaldehyde at positions rneta to the aromatic hydroxy group. 0-alkylated phenolic model compounds were hydroxymethylated at the same relative positions.

Cited by 5 publications

References 3 publications

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Modification of Lignin at the 2- and 6-Positions of the Phenylpropanoid Nuclei

The Potential of Visible Spectroscopy as a Tool for the In-Line Monitoring of Lignin Methylolation

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The Modification of Lignin at Positions 2 and 6 of the Phenylpropanoid Nucleii - Part II¹: Hydroxymethylation of Lignin Model Compounds