One-pot chitin pulping using recyclable superbase-based protic ionic liquid.

The application of ionic liquids and deep eutectic solvents offers a promising opportunity for a more environmentally friendly and straightforward chitin purification process from crustacean shells. Nonetheless, the insufficient recyclability of these ionic solvents poses a challenge to the long-term sustainability of such extraction methods. Thus, there is a strong imperative to focus on employing easily recyclable ionic liquids for chitin isolation, enhancing the overall sustainability of the process. In this investigation, a direct chitin purification procedure that utilized pulping liquors consisting of the superbase-based protic ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate and its precursor, acetic acid, was developed. It was demonstrated that these pulping liquors were capable of simultaneously deproteinate and demineralize shrimp shells to generate chitins with higher purity, degree of N-acetylation and crystallinity than commercially obtained chitin. More significantly, the pulping liquors can be recycled to their pure form in high quantity by simple distillation under reduced pressure, allowing the reuse of these mixtures, which give chitin of nearly identical purity.

Methylation with Dimethyl Carbonate/Dimethyl Sulfide Mixtures: An Integrated Process without Addition of Acid/Base and Formation of Residual Salts.

Dimethyl sulfide, a major byproduct of the Kraft pulping process, was used as an inexpensive and sustainable catalyst/co-reagent (methyl donor) for various methylations with dimethyl carbonate (as both reagent and solvent), which afforded excellent yields of O-methylated phenols and benzoic acids, and mono-C-methylated arylacetonitriles. Furthermore, these products could be isolated using a remarkably straightforward workup and purification procedure, realized by dimethyl sulfide's neutral and distillable nature and the absence of residual salts. The likely mechanisms of these methylations were elucidated using experimental and theoretical methods, which revealed that the key step involves the generation of a highly reactive trimethylsulfonium methylcarbonate intermediate. The phenol methylation process represents a rare example of a Williamson-type reaction that occurs without the addition of a Brønsted base.

Hydrothermal Liquefaction of α-O-4 Aryl Ether Linkages in Lignin.

By using lignin model compounds with relevant key characteristic structural features, the reaction pathways of α-O-4 aryl ether linkages under hydrothermal conditions are elucidated. Experimental results and computational modeling suggest that the α-O-4 linkages in lignin undergo catalyzed hydrolysis and elimination to give phenolic and alkenylbenzene derivatives as major products in subcritical water. The decreased relative permittivity of water at these high temperatures and pressures facilitates the elimination reactions. The alkyl group on the α-carbon and the methoxy groups on the phenyl rings both have positive effects on the rate of conversion of α-O-4 linkages in native lignin.

Unravelling Some of the Key Transformations in the Hydrothermal Liquefaction of Lignin.

Using both experimental and computational methods, focusing on intermediates and model compounds, some of the main features of the reaction mechanisms that operate during the hydrothermal processing of lignin were elucidated. Key reaction pathways and their connection to different structural features of lignin were proposed. Under neutral conditions, subcritical water was demonstrated to act as a bifunctional acid/base catalyst for the dissection of lignin structures. In a complex web of mutually dependent interactions, guaiacyl units within lignin were shown to significantly affect overall lignin reactivity.

Masked N-Heterocyclic Carbene-Catalyzed Alkylation of Phenols with Organic Carbonates.

An easily prepared masked N-heterocyclic carbene, 1,3-dimethylimidazolium-2-carboxylate (DMI-CO2 ), was investigated as a "green" and inexpensive organocatalyst for the alkylation of phenols. The process made use of various low-toxicity and renewable alkylating agents, such as dimethyl- and diethyl carbonate, in a focused microwave reactor. DMI-CO2 was found to be a very active catalyst and excellent yields of a range of aryl alkyl ethers were obtained under relatively benign conditions. The observed difference in the conversion behavior of phenol methylation, in the presence of either the carbene or 1,8-diazabicycloundec-7-ene (DBU) catalyst, was rationalized on the basis of mechanistic investigations. The primary mode of action for the N-heterocyclic carbene is nucleophilic catalysis. Activation of the dialkyl carbonate electrophile results in concomitant evolution of an organo-soluble alkoxide, which deprotonates the phenolic starting material. In contrast, DBU is initially protonated by the phenol and thus consumed. Subsequent regeneration and participation in nucleophilic catalysis only becomes significant after some phenolate alkylation occurs.