Catalytic Oxidation of Lignins into the Aromatic Aldehydes: General Process Trends and Development Prospects

Catalytic oxidation of biorefinery corncob lignin via zirconium(IV) chloride and sodium hydroxide in acetonitrile/water: A functionality study

In order to realize the efficient utilization of biorefinery corncob lignin, the promising catalytic oxidation strategy was carried out by using ZrCl₄ and NaOH as the co-catalyst and dioxygen as the oxidant in MeCN/H₂O. GC/MS, GC-FID, and MALDI-TOF/MS were employed to recognize the produced monomers and oligomers, and GPC was used to monitor the molecular weight changes of lignin fragments. In addition, specific structural evolution of corncob lignin during ZrCl₄/NaOH-catalyzed oxidation were revealed by quantitative ¹³C (Q¹³C) and 2D HSQC NMR techniques. Results showed that the total yields of produced oxidation monomers reached 6.8 wt%, and aromatic aldehydes were the major species, in which vanillin and 4-hydroxybenzaldehyde were the two dominant products. After ZrCl₄/NaOH-catalyzed oxidation, the weight-average molecular weight of corncob lignin and its products decreased from 2000 Da to 300 Da after oxidation with 16 h. Moreover, Q¹³C NMR analysis showed the decrease percentage of CO aliphatic carbons (including methoxyl carbons), the increase percentage of CC aliphatic and carbonyl carbons, and the relative stable percentage of aromatic carbons with reaction prolonged. These results combined with the further confirmation from HSQC indicated the oxidative cleavage of CO aliphatic linkages and removal of methoxy groups within corncob lignin, as well as the formation of CC aliphatic bonds and carbonyl groups. The work presented a comprehensive insight into the catalytic oxidative depolymerization of biorefinery corncob lignin.

Primary Benzylamines by Efficient N-Alkylation of Benzyl Alcohols Using Commercial Ni Catalysts and Easy-to-Handle Ammonia Sources

Primary benzylamines are highly important building blocks in the pharmaceutical and polymer industry. An attractive catalytic approach to access these compounds is the direct coupling of benzyl alcohols with ammonia via the borrowing hydrogen methodology. However, this approach is usually hampered by a series of side-reactions, one of the most prominent being the overalkylation of the formed primary amine. Herein, we describe a robust catalytic methodology, which utilizes commercially available heterogeneous Ni catalysts and easy-to-handle ammonia sources, such as aqueous ammonia or ammonium salts, for the formation of primary benzylamines with good selectivity and scope. Notably, our method enables the conversion of potentially lignin-derived vanillyl alcohol to vanillylamine, which can be used to produce emerging biobased polymers or as pharma building blocks. Important sugar derived platform alcohols as well as long chain aliphatic primary alcohols can be successfully aminated. Moreover, we provide an alternative, sustainable route to p-xylylenediamine and m-xylylenediamine, important components of heat resistant polyamides such as Kevlar.

Microwave-Assisted Knoevenagel-Doebner Reaction: An Efficient Method for Naturally Occurring Phenolic Acids Synthesis

The common chemical method to synthesize Phenolic Acids (PAs) involves a relatively considerable energy intake. In order to solve this issue, microwave-assisted Knoevenagel-Doebner condensations were developed. Nevertheless, these synthetic procedures prove difficult to reproduce. Herein, we developed and optimized—by using a combination of a Design of Experiment and a standard optimization approach—a reliable procedure that converts naturally occuring p-hydroxybenzaldehydes into the corresponding PAs with conversions of 86–99% and in 85–97% yields.

The sustainable heterogeneous catalytic reductive amination of lignin models to produce aromatic tertiary amines

A sustainable and heterogeneous catalytic reductive amination process is developed in the presence of heterogeneous zirconium-based catalysts, in which N,N-dimethylformamide (DMF) is used as the solvent, the low-molecular-weight amine source, and the reductant.