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Calcium carbide (CaC2) is a sustainable source of acetylene which plays an important role in organic synthesis due to its active triple bonds and terminal protons. Solid CaC2 has several advantages over acetylene gas such as easy handling, convenient storage and transportation. The CaC2 is considered as a safer and more convenient source of acetylene. The chemistry of the CaC2 is not confined to its use as a source of acetylene and its applications are not limited to the known reactions of acetylene. With the CaC2 chemistry being actively developing recently, it may eventually lead to the development of new transformations of alkyne chemistry. Herein, this mini review is focused on the synthesis and application of the CaC2 in biomass transformations.

Vinyl ethers are essential synthetic building blocks for organic synthesis, especially for polymer synthesis and highly vinylated polyol substrates. Herein, a transition metal-free, mild, and safe protocol has been developed for direct vinylation of natural alcohols with calcium carbide. Various sugar alcohols, phenol and its derivatives were tested and proved successful using this green methodology. Selectivity of full vinylated products of the reaction decreases with increasing hydroxyl groups because of side reactions occurring under the basic medium. Electron-donating substituted phenols work more efficiently than electron-withdrawing substituted phenols in general. This methodology may provide new insights on selective vinylation of electron-rich biomass-derived materials.

The catalytic conversion of 5-hydroxymethyl furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) over a commercial Ru/C catalyst in a base-free aqueous solution was studied with 88% FDCA yield. A self-catalyzed system using FDCA for the dehydration of fructose to HMF followed by base-free conversion of HMF to FDCA was also demonstrated with 53% overall yield.

A mild and easy-to-handle protocol to produce propargylamines with a terminal alkyne through catalytic cross-coupling of tertiary amines and calcium carbide has been developed. The reaction proceeds via sp3 C–H bond activation and C–C coupling. Good to excellent yields were obtained for the corresponding propargylamines with both alkyl and aryl substitutions. The development of these functionalized propargylamines with a terminal alkyne group will offer a wider application for the synthesis of natural or pharmaceutical products due to their unique sp C–H reactivity.

Transition metal complexes play a key role in catalytic carboxylation reactions with CO 2 . Various metal complex catalytic systems have been developed for the carboxylation of different substrates that provide versatile methodologies for green organic synthesis. This review summarizes recent developments of CO 2 carboxylation reactions with C C bond formation catalyzed by transition metal complexes. The contents in this review are arranged based on various transition metals and substrates of various functional groups. The reaction mechanisms and the role of metal catalysts will also be discussed.

An ammonium resin (PBnNH3Cl) was used as a single catalyst for the glucose and polysaccharide dehydration to 5-hydroxymethylfurfural (HMF) in high selectivity (>80%) in a DMSO or biphasic reaction system. The isomerization mechanism was also studied by using the DFT computational method. ASTAR (Agency for Sci., Tech. and Research, S’pore)

Alkyl/amino functionalized silica nanoparticles to create an emulsion in a biphasic system for sugar dehydration to HMF were successfully developed. As a proof-of-concept, more than 10% increase of HMF yield and 20% increase of selectivity were achieved for both fructose and glucose dehydrations in the emulsion system as compared to the conventional biphasic system. The excellent recyclability of the nanoparticles also further widens the potential of the biphasic system to be scaled up for industrial application.

Calcium carbide has been increasingly used as a sustainable, easy-to-handle, and low-cost feedstock in organic synthesis. Currently, methodologies of using calcium carbide as "solid acetylene" in synthesis are strictly limited to activation and reaction with X-H (X=C, N, O, S) bonds. Herein, a mild and transition-metal-free protocol was developed for the vinylation of epoxides and aryl ether linkage (β-O-4 lignin model compound) with calcium carbide through C-O bond cleavage, forming valuable vinyl ether products. Calcium carbide plays a vital role in the C-O bond activation and cleavage, and in providing acetylide source for the formation of vinylated products. These exciting results may provide new methodologies for organic synthesis and new insights toward lignin- or biomassrelated degradation to useful products.

A one-pot conversion of sugars into 2,5-furandicarboxylic acid (FDCA) is demonstrated in a triphasic system: tetraethylammonium bromide (TEAB) or water-methyl isobutyl ketone (MIBK)-water. In this reaction, sugars are first converted into 5-hydroxymethylfurfural (HMF) in TEAB or water (Phase I). The HMF in Phase I is then extracted to MIBK (Phase II) and transferred to water (Phase III), where HMF is converted into FDCA. Phase II plays multiple roles: as a bridge for HMF extraction, transportation and purification. Overall FDCA yields of 78 % and 50 % are achieved from fructose and glucose respectively.

5-hydroxymethylfurfural (HMF) is one of the most promising platform molecules, and can be converted into a variety of interesting chemicals. The production of HMF is essentially targeted at bulk chemicals downstream, such as chemicals for the fuels and plastics industries. One critical challenge in HMF production processes is the link to further value-adding reactions in a simple and efficient way (e.g., fewer isolation and purification steps). Herein, a novel poly-benzyl ammonium chloride (PBnNH3 Cl) resin is developed as a highly efficient and stable catalyst for dehydration of carbohydrates into HMF. In the isopropanol system, PBnNH3 Cl produces high purity HMF that is suitable as feedstock for oxidation to 2,5-furandicarboxylic acid (FDCA). The excellent catalytic properties together with its easy synthesis, low cost, and nontoxic nature make this poly-ammonium resin a promising catalyst for the development of new and efficient processes for biomass-based chemicals.