Initial Products and Reaction Mechanisms for Fast Pyrolysis of Synthetic G‐Lignin Oligomers with β‐O‐4 Linkages via On‐Line Mass Spectrometry and Quantum Chemical Calculations

Abstract

The products of fast pyrolysis that first leave the hot pyrolysis surface were identified for three G‐lignin model compounds, a trimer, a tetramer and a synthetic polymer, all containing β‐O‐4 linkages, by using a very fast heating pyrolysis probe coupled with a linear quadrupole ion trap mass spectrometer or a linear quadrupole ion trap coupled with an orbitrap detector. High‐resolution measurements were used to determine the elemental compositions of the deprotonated pyrolysis products. Their structures were examined using collision‐activated dissociation experiments and via comparison to the dissociation reactions of ionized authentic compounds. The initial pyrolysis products for all model compounds range from monomers to tetramers. Even for the polymer, no products larger than tetramers were observed. None of the products were radicals. The observed trimers and tetramers were formed directly from the intact model compounds rather than from repolymerization of initially formed monomers. Both the observed product distributions and quantum chemical calculations suggest that the mechanism(s) of the major reactions occurring under the conditions employed here are Maccoll and/or retro‐ene eliminations rather than radical reactions. Based on a comparison of the behavior of the smaller β‐O‐4 model compounds to the synthetic β‐O‐4 lignin polymer, the smaller model compounds appear to be good surrogates for further studies of the mechanisms of fast pyrolysis of lignin.

Studies of the Fragmentation Mechanisms of Deprotonated Lignin Model Compounds in Tandem Mass Spectrometry

“…This epoxide ion can undergo further activating collisions and isomerize to BAK (Scheme ). Previous theoretical studies suggest that this reaction mechanism may also rationalize the elimination of the B-end unit of similar neutral β-O-4 type lignin model compounds upon pyrolysis. , In other studies wherein pyrolysis was coupled with MS, the formation of product ions analogous to ionized BAK was observed, although no mechanisms were proposed to explain these reactions. , …”

“…34,35 In other studies wherein pyrolysis was coupled with MS, the formation of product ions analogous to ionized BAK was observed, although no mechanisms were proposed to explain these reactions. 36,37 To test the new mechanism (Scheme 3), a simple dideuterated β-O-4 type lignin model compound DO4-S2H (Figure 2) containing only one (aliphatic) hydroxyl group, that on the α-carbon (Figure S4), was ionized, transferred into the ion trap, isolated, and subjected to CAD. As expected, the elimination of the B ring-containing charge-remote end unit (formation of fragment ions of m/z 165) was observed (Figure S4).…”

Effect of Temperature and MgCl2 Concentration on the Catalytic Pyrolysis of Malt Waste Using Response Surface Methodology

“…[3,4] This process is normally carried out in the total or partial absence of oxygen, at a temperature range of 400-600 °C. [5] Many industrial wastes, such as plastic waste, [6,7] spent tire, [8] tetra pak residue, [9] cellulose, [10,11] lignin, [12] sugarcane bagasse, [13][14][15] coffee residues, [16,17] corncob, [18] fruit residue, [19] oilseed shells, [20] microalgae, [21,22] seeds [23,24] and pine wood, [25] among others, have been evaluated as sources for the pyrolysis process.…”

Fast Determination of the Lignin Monomer Compositions of Genetic Variants of Poplar via Fast Pyrolysis/Atmospheric Pressure Chemical Ionization Mass Spectrometry

“…4,5 On the basis of recent studies on the fast pyrolysis of dimeric and oligomeric lignin model compounds, monomeric phenolic compounds are the most abundant primary fast pyrolysis products of lignin, and they are formed predominantly via cleavages of the β-O-4 linkages. 18 However, other linkages are also cleaved (with the exception of the 5−5 linkage). High-resolution tandem mass spectrometry based on collision-activated dissociation (CAD) has been used to identify these primary fast pyrolysis products.…”

“…18,21 The ionization method, (−)APCI with NH 4 OH dopant, has been demonstrated to nearly equally efficiently deprotonate different lignin model compounds with little to no fragmentation. 18 The py/(−)APCI MS experiment involves the transfer of the deprotonated fast pyrolysis products from the ion source into a linear quadrupole ion trap and their detection by ejecting them in a mass-selective manner to two external electron multiplier detectors (low-resolution detection). Alternatively, all ions were transferred from the linear quadrupole ion trap into the orbitrap for high-resolution measurements.…”