One step conversion of lignin from intact biomass to two phenol products, improving access to aromatics and fuels.

The development of chemical methods for the direct catalytic conversion of biomass to high value organic molecules is an area of increasing interest. The plant matter component known as lignin is a polymer consisting of aromatic rings that could provide a means of obtaining aromatic materials currently derived solely from petroleum. This report describes a bimetallic Pd/C and Zn catalytic system that can perform selective hydrodeoxygenation (HDO) of monomeric lignin surrogates as well as successfully cleave the b-O-4 linkages found in dimeric lignin model complexes and synthetic lignin polymers with near quantitative conversions and yields between 80-90%. The reaction with lignin polymer was highly selective affording methoxy substituted propylphenol as the major product. These reactions were performed in a Parr reactor operating at relatively mild temperature (150 C) and pressure (20 bar H 2 ) using methanol as a solvent. Reaction products were characterized using high-pressure liquid chromatography coupled to a linear quadrupole ion trap mass spectrometer equipped with an electrospray ionization source using negative ion mode. Hydroxide ions were doped into the analyte solutions to encourage negative ion formation. This method ionizes all the mixture components to yield a single ion/analyte with no fragmentation. The catalyst is fully recyclable without the need for additional zinc. X-ray absorption spectroscopy (EXAFS) is consistent with Pd nanoparticles (4-5 nm) and no evidence of Pd-Zn alloy formation. A mechanistic hypothesis on the synergy between Pd and Zn is presented.

In the search for a replacement for fossil fuel and the valuable chemicals currently obtained from crude oil, lignocellulosic biomass has become a promising candidate as an alternative biorenewable source for crude oil. Hence, many research efforts focus on the extraction, degradation, and catalytic transformation of lignin, hemicellulose, and cellulose. Unfortunately, these processes result in the production of very complex mixtures. Further, while methods have been developed for the analysis of mixtures of oligosaccharides, this is not true for the complex mixtures generated upon degradation of lignin. For example, high-performance liquid chromatography/multiple stage tandem mass spectrometry (HPLC/MS(n)), a tool proven to be invaluable in the analysis of complex mixtures derived from many other biopolymers, such as proteins and DNA, has not been implemented for lignin degradation products. In this study, we have developed an HPLC separation method for lignin degradation products that is amenable to negative-ion-mode electrospray ionization (ESI doped with NaOH), the best method identified thus far for ionization of lignin-related model compounds without fragmentation. The separated and ionized compounds are then analyzed by MS(3) experiments to obtain detailed structural information while simultaneously performing high-resolution measurements to determine their elemental compositions in the two parts of a commercial linear quadrupole ion trap/Fourier-transform ion cyclotron resonance mass spectrometer. A lignin degradation product mixture was analyzed using this method, and molecular structures were proposed for some components. This methodology significantly improves the ability to analyze complex product mixtures that result from degraded lignin.

Method for identification of compounds in organosolv lignin.

No abstract

Seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or β-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with β-O-4 linkages, were evaporated and deprotonated using negative-ion mode ESI in a linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer. The collision-activated dissociation (CAD) fragmentation patterns (obtained in MS and MS experiments, respectively) for the negative ions were studied to develop a procedure for sequencing unknown lignin oligomers. On the basis of the observed fragmentation patterns, the measured elemental compositions of the most abundant fragment ions, and quantum chemical calculations, the most important reaction pathways and likely mechanisms were delineated. Many of these reactions occur via charge-remote fragmentation mechanisms. Deprotonated compounds with only β-O-4 linkages, or both 5-5 and β-O-4 linkages, showed major 1,2-eliminations of neutral compounds containing one, two, or three aromatic rings. The most likely mechanisms for these reactions are charge-remote Maccoll and retro-ene eliminations resulting in the cleavage of a β-O-4 linkage. Facile losses of HO and CHO were also observed for all deprotonated model compounds, which involve a previously published charge-driven mechanism. Characteristic "ion groups" and "key ions" were identified that, when combined with their CAD products (MS experiments), can be used to sequence unknown oligomers.

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Isomeric O- and N-glucuronides are common drug metabolites produced in phase II of drug metabolism. Distinguishing these isomers by using common analytical techniques has proven challenging. A tandem mass spectrometric method based on gas-phase ion/molecule reactions of deprotonated glucuronide drug metabolites with trichlorosilane (HSiCl) in a linear quadrupole ion trap mass spectrometer is reported here to readily enable differentiation of the O- and N-isomers. The major product ion observed upon reactions of HSiCl with deprotonated N-glucuronides is a diagnostic HSiCl adduct that has lost two HCl molecules ([M - H + HSiCl - 2HCl]-). This product ion was not observed for deprotonated O-glucuronides. Reaction mechanisms were explored with quantum chemical calculations at the M06-2X/6-311++G(d,p) level of theory.