Acid catalyzed synthesis of dimethyl isosorbide via dimethyl carbonate chemistry

Dimethyl isosorbide (DMI) is a bio-based solvent that can be used as green alternative for conventional dipolar media (dimethyl sulfoxide, dimethylformamide, and dimethylacetamide). The main synthetic procedures to DMI reported in the literature are based on the methylation of isosorbide employing different alkylating agents including toxic halogen compounds such as alkyl halides. A more sustainable alternative would be to employ dimethyl carbonate (DMC), a well-known green reagent and solvent, considered one of the most promising methylating agents for its good biodegradability and low toxicity. Indeed, in recent years, DMC-promoted methylation of isosorbide has been extensively exploited although mostly in the presence of a base or an amphoteric catalyst. In this work, we report for the first time a comprehensive investigation on the synthesis of DMI via DMC chemistry promoted by heterogeneous acid catalyst (Amberlyst-36 and Purolite CT275DR). Re- action conditions were optimized and then applied for the methylation of isosorbide and its epimers, isoidide and isomannide. Considerations on the related reaction mechanism were reported highlighting the difference in the preferred reaction pathways among this new synthetic approach and the previously reported base-catalyzed procedures

Dimethyl isosorbide via organocatalyst N-methyl pyrrolidine: scaling up, purification and concurrent reaction pathways

Dimethyl isosorbide (DMI) is a well-known bio-based green replacement for conventional dipolar solvents such as dimethyl sulfoxide and dimethylformamide. The synthesis of DMI mainly relies on the etherification of the bio-based platform chemical isosorbide in the presence of basic or acid catalysts and by employing different alkylating agents. Among them, dimethyl carbonate (DMC) is considered one of the most promising for its good biodegradability and low toxicity. In this work, we report on a comprehensive investigation on high yielding methylation of isosorbide via DMC chemistry promoted by nitrogen organocatalyst N-methyl pyrrolidine (NMPy). Reaction conditions were optimized and then efficiently applied for the methylation of isosorbide epimers, isoidide and isomannide, and for some preliminary scale-up tests (up to 10 grams of isosorbide). The purification of DMI from the reaction mixture was achieved by both column chromatography and distillation at reduced pressure. NMPy demonstrated to be an excellent catalyst also for the one-pot conversion of d-sorbitol into DMI. Furthermore, for the first time, all seven methyl and methoxycarbonyl intermediates observed in the etherification of isosorbide were synthetised, isolated and fully characterised. This has provided an insight on the concurrent reaction pathways leading to DMI and on the role played by NMPy in the methylation of isosorbide. Finally, the reaction mechanisms for the methylation, methoxycarbonylation and decarboxylation promoted by NMPy partaking in the conversion of isosorbide into DMI via DMC chemistry have been proposed

Synthesis of 2,5-furandicarboxylic acid dimethyl ester from galactaric acid via dimethyl carbonate chemistry

A convenient and simple procedure for the one-pot synthesis of 2,5-furandicarboxylic acid dimethyl ester (FDME) from galactaric (mucic) acid via dimethyl carbonate (DMC) chemistry is presented. Optimization of the reaction conditions showed that when galactaric acid was reacted with DMC in the presence of Amberlyst-36 for 2 hours at 200 °C, FDME formed as the main product. The compound was isolated as a pure crystalline powder in 70% yield using a simple custom-made purification protocol. The reaction intermediates of this one-pot procedure were identified and a possible reaction mechanism was proposed

Alkyl carbonate derivatives of furanics: A family of bio-based stable compounds

Several alkyl carbonate derivatives of 5-hydroxymethylfurfural (HMF) and 2,5-bis(hydroxymethyl)furan (BHMF) have been synthesized for the first time. In most cases high yields were achieved using mild reaction conditions and compounds were recovered as pure with none or minimal purification. The new HMF and BHMF derived products resulted stable over time and they are suitable monomers for new bio-based polycarbonates and polyurethanes

Microwave-Assisted Aminoalkylation of Phenols via Mustard Carbonate Analogues

A microwave-assisted chlorine-free direct phenol substitution is presented, which is indicated as a key green chemistry research area for pharmaceuticals manufacturers. The reaction of -aminocarbonates (mustard carbonates) with several substituted phenols in the presence of a polar solvent (acetonitrile or butanol) led to the related aminoalkylated products via the anchimeric assistance of the nitrogen incorporated in the organic carbonate backbone. The aminoalkylation required short reaction time (7 min) and the related products were isolated in high yields (90%) via quick liquid-liquid extraction or column chromatography depending on the solvent employed. Furthermore, microwave irradiation also promoted the one-pot aminoalkylation of phenol in excellent yield. In this approach a -aminoalcohol was reacted with phenol in the presence of diethyl carbonate, used for the in situ formation -aminocarbonate, key intermediate in the consequent anchimerically driven alkylation. The resulting product, namely N,N-dimethyl-2-phenoxyethanamine, was isolated as pure in almost quantitative yield

A Green Synthesis of 5,5 '-[Oxybis(methylene)]bis-2-Furfural: from By-Product to Attractive Bio-Based Platform Chemical

In this work, a green synthetic approach to 5,5'-(oxybis(methylene)]bis-2-furfural (OBMF) from 5-hydroxymethyl-2-furfural (HMF) is reported for the first time. In the optimized reaction conditions, dimethyl carbonate (DMC) is used as the preferred green solvent and iron(III) sulfate as the best catalyst, recyclable up to three times. The HMF self-etherification reaction is conducted both in milligram- and gram-scale with isolated yields up to 99% and 81% respectively. OBMF is further derivatized via reduction to achieve 5,5'-oxybis(methylene)bis(furan-5,2-diyl)dimethanol (OBMF-H), a potential bisphenol-A biobased alternative. Thus, methoxycarbonylation of OBMF-H leads to the biscarboxymethylated derivative (OBMF-DC) employing, once again, DMC as solvent and reagent. Both OBMF-H and OBMF-DC are achieved in high yields and are fully characterized. Furthermore, thermogravimetric analysis of OBMF, OBMF-H, and OBMF-DC establishes that these compounds are more thermally stable than HMF and its derivatives. In fact, they can withstand up to 200 degrees C before undergoing complete degradation rendering OBMF and its derivatives valuable bio-based monomers for bioplastics prepared via polycondensation reaction

Fully renewable photocrosslinkable polycarbonates from cellulose-derived monomers

Cellulose-derived photocrosslinkable polycarbonates (PCs) with renewable citronellol pendant chains were synthesised through the polycondensation of Triol-citro, a recently developed levoglucosenone-based triol monomer, and dimethoxycarbonyl isosorbide. The polymer structures were unveiled through NMR spectroscopy and four repeating units were identified: three hydroxy-functional linear units (Ln, Lo and Lp) and one dendritic unit (Dq). The relative percentages of the repeating units, as well as the molecular weights of the corresponding polymers, can be finely tuned by varying the catalyst and reaction conditions (i.e., polycondensation temperature and monomer concentration). Thermal analyses demonstrated that the novel PCs exhibited low glass transition temperatures (Tg as low as −72 °C) and Td5% up to 159 °C. These hydroxy-functionalised PCs are not only fully biobased with a controlled extent of branching, but they also bear citronellol side chains that were successfully crosslinked via ultraviolet irradiation to further control the polymer properties

Sustainable Hyperbranched Functional Materials via Green Polymerization of Readily Accessible Levoglucosenone-Derived Monomers

The homopolymerization in basic conditions of the recently reported bis(γ-lactone), 2H-HBO-HBO, is herein described for the first time. The solvent-free polymerization of this pentafunctional levoglucosenone (LGO) derivative affords fully renewable poly(vinyl-ether lactone) copolymers with a highly hyperbranched structure. This investigation stems from the polycondensation trials between 2H-HBO-HBO and di(methyl carbonate) isosorbide (DCI) that fails to give the anticipated polycarbonates. Such unexpected behavior is ascribed to the higher reactivity of the 2H-HBO-HBO hydroxy groups toward its α,β-conjugated endocyclic C═C, rather than the DCI methylcarbonate moieties. The different mechanistic scenarios involved in 2H-HBO-HBO homopolymerization are addressed and a possible structure of poly(2H-HBO-HBO) is suggested. Furthermore, the readily accessible (S)-γ-hydroxymethyl-α,β-butenolide (HBO) is also polymerized for the first time at a relatively large scale, without any prior modification, resulting in a new hyperbranched polymer with an environmental factor (E factor) ≈0. These new HBO-based polymers have a great potential for industrial-scale production due to their interesting properties and easy preparation via a low-cost, green, and efficient process