Justin K. Mobley

Catalytic oxidation of alcohols to carbonyl compounds over hydrotalcite and hydrotalcite- supported catalysts

The oxidation of alcohols to carbonyl compounds is an important reaction in synthetic organic chemistry. While stoichiometric oxidants are effective for this transformation, they often produce large amounts of toxic waste, which renders them unacceptable from an environmental and economic perspective. Consequently, there is a strong impetus to develop catalytic processes that utilize environmentally friendly, inexpensive primary oxidants, the use of molecular oxygen being particularly attractive. Recently, hydrotalcites have attracted attention as both catalysts and catalyst supports for the selective oxidation of alcohols to ketones and aldehydes, using either oxygen or TBHP as the oxidant. This review is intended to provide a comprehensive summary of work performed in this area to date. The effects of composition and structure on catalyst properties are highlighted, and mechanistic aspects are discussed.

Synthesis, Characterization, and Structure of Some New Substituted 5,6-Fused Ring Pyridazines

Abstract Pyridazines are an important class of heterocyclic compounds as a result of their materials and commercial applications. The synthesis of 5,6-fused ring pyridazines 2a–h from 1,2-diacylcyclopentadienes (fulvenes) 1a–h is described herein. This route was quite general, and features an efficient and convenient two-step synthesis of a series of 5,6-fused ring 1,2-disubstituted pyridazines using enolized 1,2-disubstituted fulvenes in a methanolic solution of hydrazine. Full characterization of newly formed fulvene 1e and pyridazines 2a–h are reported. Single-crystal X-ray analysis confirms the molecular structure of pyridazine 2f, which displayed the expected pyridazine fused to the cyclopentadienyl moiety. Adding to their real world capabilities in electronic devices, compounds 2a–h display reasonably high stability in solution and in air at room temperature.

The Upper Green River Barcode of Life Project

Abstract The DNA barcoding initiative is an international effort to collect standardized DNA sequences from each Eukaryotic species to facilitate taxonomy and specimen identification. DNA barcoding experiments, because they are not technically difficult, are well suited to being used as investigative research experiences in a teaching laboratory. We have implemented a DNA barcoding exercise for our first year “Undergraduate Experience” students in which participants catch arthropods from our university field station, the Upper Green River Biological Preserve. The arthropod specimens were brought to the laboratory, mounted, photographed, and identified via keys and field guides based on morphological characters. This identification served as a working hypothesis for the identity of each specimen. A single leg was removed from each specimen, DNA was extracted, and a fragment of the cytochrome oxidase I gene was PCR amplified and sequenced. Then, using bioinformatics tools, the sequence for each specimen was compared to those in the Barcode of Life and Genbank nucleotide databases. A second species diagnosis based on DNA sequence matches was determined, which could be compared to the original morphological identification, serving as a test of that hypothetical species identity. In its first semester of implementation, 28 arthropod barcodes were produced, which will be augmented by the work of future classes.

Highly Decorated Lignins in Leaf Tissues of the Canary Island Date Palm Phoenix canariensis

Phoenix canariensis leaf lignins vary between tissue region and contain an array of pendent groups. The cell walls of leaf base tissues of the Canary Island date palm (Phoenix canariensis) contain lignins with the most complex compositions described to date. The lignin composition varies by tissue region and is derived from traditional monolignols (ML) along with an unprecedented range of ML conjugates: ML-acetate, ML-benzoate, ML-p-hydroxybenzoate, ML-vanillate, ML-p-coumarate, and ML-ferulate. The specific functions of such complex lignin compositions are unknown. However, the distribution of the ML conjugates varies depending on the tissue region, indicating that they may play specific roles in the cell walls of these tissues and/or in the plant’s defense system.

Oxidation of lignin and lignin β-O-4 model compounds via activated dimethyl sulfoxide

Lignin oxidation reactions are increasingly being utilized in the field of lignin valorization. This is primarily due to the prospect of obtaining high-value aromatic products from cleavage of the Cα–Cβ bond in lignins β-O-4 linkages. In this work activated dimethyl sulfoxide reactions, namely Swern and Parikh–Doering oxidations, were performed both on lignin and on compounds modeling the β-O-4 linkage. When phenolic moieties were present in the model compounds, enol ethers were formed rather than the ketone expected from oxidation of the β-O-4 alcohol moiety. Conversely, in the absence of phenolic moieties, the β-O-4 alcohol was oxidized to a ketone. These results are interpreted in terms of enol ether formation from a quinone methide intermediate formed via deprotonation of the phenolic –OH in the initial sulfur ylide species. When applied to Kraft lignin, alcohol oxidation was observed at both the α and γ positions in lignin under both Swern and Parikh–Doering conditions, although analytical data were unable to shed light on the relative importance of enol ether versus 1,3-diketone formation (or its tautomer). These results emphasize the importance of working with realistic lignin model compounds in order to understand and develop lignin chemistry.

Selective Oxidation of Lignin Model Compounds

Lignin, the planets most abundant renewable source of aromatic compounds, is difficult to degrade efficiently to welldefined aromatics. We developed a microwave-assisted catalytic Swern oxidation system using an easily prepared catalyst, MoO2 Cl2 (DMSO)2 , and DMSO as the solvent and oxidant. It demonstrated high efficiency in transforming lignin model compounds containing the units and functional groups found in native lignins. The aromatic ring substituents strongly influenced the selectivity of β-ether phenolic dimer cleavage to generate sinapaldehyde and coniferaldehyde, monomers not usually produced by oxidative methods. Time-course studies on two key intermediates provided insight into the reaction pathway. Owing to the broad scope of this oxidation system and the insight gleaned with regard to its mechanism, this strategy could be adapted and applied in a general sense to the production of useful aromatic chemicals from phenolics and lignin.

An “ideal lignin” facilitates full biomass utilization

The structural homogeneity and acid stability of linear C-lignins allow their deconstruction to useful monomers in high yield. Lignin, a major component of lignocellulosic biomass, is crucial to plant growth and development but is a major impediment to efficient biomass utilization in various processes. Valorizing lignin is increasingly realized as being essential. However, rapid condensation of lignin during acidic extraction leads to the formation of recalcitrant condensed units that, along with similar units and structural heterogeneity in native lignin, drastically limits product yield and selectivity. Catechyl lignin (C-lignin), which is essentially a benzodioxane homopolymer without condensed units, might represent an ideal lignin for valorization, as it circumvents these issues. We discovered that C-lignin is highly acid-resistant. Hydrogenolysis of C-lignin resulted in the cleavage of all benzodioxane structures to produce catechyl-type monomers in near-quantitative yield with a selectivity of 90% to a single monomer.