Sustainable Valorisation of Renewables through Dialkyl Carbonates and Isopropenyl Esters

This review showcases a thorough analysis of reactions and applications of the most widespread linear and alkylene organic carbonates (DACs) as dimethyl-, diethyl-, ethylene-, and propylene- carbonates (DMC, DEC, EC, and PC, respectively), and a representative enol ester as isopropenyl acetate (iPAc), for the chemical functionalisation and upgrading of renewable compounds, both bio-based platform molecules and biopolymers. The work which follows a previous survey published by us in 2018 and limited to DMC only, is organised into five sections where the literature screening encompasses the past 4 years in the case of DMC and a wider timespan of five-six years for other homologues/analogues carbonates and iPAc. After a general introductory section on benign-by-design processes for the conversion of biomass derivatives, a description of synthetic methods of DACs follows. Most of the review content is then focused on reactions in which DACs and iPAc act as alkylating, carboxylating, and acylating agents, respectively, and processes where the same compounds are used as solvents. Topics are grouped starting from the valorisation of small renewable molecules as glycerol, cyclic carbonates, carbonyl derivatives of furfural and HMF, then proceeding with bio-monomers, and ending up with the synthesis and functionalisation of biopolymers. The investigated examples have been detailed by providing conditions and scope, the proposed reaction mechanisms when available, and a rationale behind the choice of reaction/process parameters (T, p, catalyst(s), etc.). Criticism and comments have been put forward on the pros and cons of the described methods and their perspectives, as well as on those studies which still require follow-ups and more in-depth analyses

Synthesis of the fatty esters of solketal and glycerol-formal: biobased specialty chemicals

The caprylic, lauric, palmitic and stearic esters of solketal and glycerol formal were synthesized with high selectivity and yields by a solvent-free acid catalyzed procedure. No acetal hydrolysis was observed notwithstanding the acidic condition

One-pot tandem catalytic epoxidation – CO2 insertion of monounsaturated methyl oleate to the corresponding cyclic organic carbonate

Conversion of unsaturated fatty acids, FAMEs or triglycerides into the corresponding cyclic organic carbonates involves two reaction steps-double-bond epoxidation and CO2 insertion into the epoxide-that are generally conducted separately. We describe an assisted-tandem catalytic protocol able to carry out carbonation of unsaturated methyl oleate in one-pot without isolating the epoxide intermediate. Methyl oleate carbonate was obtained in 99% yield and high retention of cis-configuration starting from methyl oleate using hydrogen peroxide and CO2 as green reagents, in a biphasic system and in the presence of an ammonium tungstate ionic liquid catalyst with KBr as co-catalyst

Reaction of Glycerol with Trimethyl Orthoformate: Towards the Synthesis of New Glycerol Derivatives

The reactivity of glycerol with trimethyl orthoformate is here described with an emphasis on developing a reliable synthetic approach for glycerol valorization. The glycerol based orthoester 4-(dimethoxymethoxy)methyl)-2-methoxy-1,3-dioxolane (3) was synthesized, under catalytic as well as catalyst-free conditions, by taking advantage of the thermodynamically controlled equilibrium between intermediates. Both Brønsted and Lewis acid catalysts accelerated the attainment of such an equilibrium, particularly Brønsted acidic ionic liquids BSMImHSO4 and BSMImBr were the most effective compounds for this reaction. The kinetic profiles allowed the proposal of a mechanism that accounts for the selectivity of the reaction

Advancements and Complexities in the Conversion of Lignocellulose Into Chemicals and Materials

This Perspective describes the challenges and objectives associated to the development of new chemical technologies for the conversion of lignocellulose (non-food or waste) into chemicals and materials; it also provides an outlook on the sources, potential products, and issues to be addresse

Phosphonium salts and P-ylides

The present chapter is aimed at describing the state-of-the-art, for the period January December 2014, of two pillar classes of phosphorus-containing compounds, the phosphonium salts and ylides. Topics are organized to offer an introductory survey on the methods of preparation and characterisation of both types of compounds, followed by an analysis of the most remarkable but also curiosity driven researches for their applications. A special section is devoted to phosphonium-based ionic liquids (PILs) due to the exceptional importance of this subject

Chitin-Derived Nanocatalysts for Reductive Amination Reactions

Chitin, the second most abundant biopolymer in the planet after cellulose, represents a renewable carbon and nitrogen source. A thrilling opportunity for the valorization of chitin is focused on the preparation of biomass-derived N-doped carbonaceous materials. In this contribution, chitin-derived N-doped carbons were successfully prepared and functionalized with palladium metal nanoparticles. The physicochemical properties of these nanocomposites were investigated following a multi-technique strategy and their catalytic activity in reductive amination reactions was explored. In particular, a biomass-derived platform molecule, namely furfural, was upgraded to valuable bi-cyclic compounds under continuous flow condition

Synthesis of Methyl Carbamates from Primary Aliphatic Amines and Dimethyl Carbonate in Supercritical CO2: Effects of Pressure and Cosolvents and Chemoselectivity

At 130 °C, in the presence of CO2 (5-200 bar), primary aliphatic amines react with dimethyl carbonate (MeOCO2Me, DMC) to yield methyl carbamates (RNHCO2Me) and N-methylation sideproducts (RNHMe and RNMe2). The pressure of CO2 largely influences both the reaction conversion and the selectivity toward urethanes: in general, conversion goes through a maximum (70-80%) in the midrange (40 bar) and drops at lower and higher pressures, whereas selectivity is continuously improved (from 50% up to 90%) by an increase of the pressure. This is explained by the multiple role of CO2 in (i) the acid/base equilibrium with aliphatic amines, (ii) the reactivity/solubility of RNHCO2 - nucleophiles with/in DMC, and (iii) the inhibition of competitive N-methylation reaction of the substrates. Cosolvents also affect the reaction: in particular, a drop in selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2 - moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)nNH2, X ) NH2, OH; n ) 1, 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding methyl carbamates [XC6H4(CH2)nNHCO2Me] in 39-65% isolated yields

reactions of p coumaryl alcohol model compounds with dimethyl carbonate towards the upgrading of lignin building blocks

Cinnamyl alcohol 1 and 4-(3-hydroxypropyl)phenol 2, two compounds resembling the lignin building block p-coumaryl alcohol, can be selectively transformed into different products by catalytic methodologies based on dimethyl carbonate (DMC) as a green solvent/reagent. Selectivity can be tuned as a function of the reaction temperature and of the nature of the catalyst. Basic catalysts such as K2CO3, trioctylmethylphosphonium methylcarbonate ([P8881][CH3OCOO]), and CsF/αAl2O3 promote selective transesterification of the aliphatic hydroxyl group at 90 °C. However, amphoteric solids such as alkali metal-exchanged faujasites, NaX and NaY, selectively yield the corresponding alkyl ethers at higher temperatures (165–180 °C). The phenolic hydroxyl group of 2 can be methylated similarly with the faujasites at high temperatures. This preliminary screening for selectivity illustrates reactivity trends and delineates some of what might be among the most promising synthetic pathways to upgrade lignin-derived chemical building blocks