Joice Thomas

Catalytic production of levulinic acid from cellulose and other biomass-derived carbohydrates with sulfonated hyperbranched poly(arylene oxindole)s

Innovative catalyst design holds the key to fundamental advances in the transformation of cellulose to chemicals and transportation fuels, both of which are vital to meet the challenge of increasing energy costs and the finite nature of fossil fuel reserves. Here we report on the functionalization, characterization and successful application of sulfonated hyperbranched poly(arylene oxindole)s for the direct catalytic conversion of cellulose to levulinic acid. The use of water-soluble hyperbranched polymers in combination with ultrafiltration is conceptually novel and opens new horizons in the aqueous-phase processing of cellulose substrates with various degrees of crystallinity. Compared to most conventional types of acid catalysts, these highly acidic polymers demonstrate superior catalytic performance in terms of both activity and selectivity. Additionally, this molecular approach can be successfully transferred to the acid-catalyzed degradation of other abundant biomass resources, including starch, inulin and xylan.

A metal-free three-component reaction for the regioselective synthesis of 1,4,5-trisubstituted 1,2,3-triazoles.

A metal-free three-component reaction to synthesize 1,4,5-trisubstituted 1,2,3-triazoles from readily available building blocks, such as aldehydes, nitroalkanes, and organic azides, is described. The process is enabled by an organocatalyzed Knoevenagel condensation of the formyl group with the nitro compound, which is followed by the 1,3-dipolar cycloaddition of the azide to the activated alkene. The reaction features an excellent substrate scope, and the products are obtained with high yield and regioselectivity. This method can be utilized for the synthesis of fused triazole heterocycles and materials with several triazole moieties.

Synthesis and photophysical characterization of chalcogen substituted BODIPY dyes

Synthetic details and stationary and time-resolved photophysical properties of five BODIPY derivatives containing chalcogen atoms are presented. The photophysical data are compared to those of a chlorine atom containing BODIPY, acting as a reference. A strong impact in the HOMO–LUMO transition energy is achieved via nucleophilic substitution with chalcogen based units. Going from oxygen to tellurium a bathochromic shift in both absorption and emission spectra from the green to the near infrared region was observed. By employing fluorescence single photon timing experiments in two solvents of different polarity, the excited state dynamics and their solvent dependence indicate the presence of a mechanism involving a photoinduced charge transfer that dramatically affects the optical radiative processes of these derivatives.

Thiol-promoted catalytic synthesis of diphenolic acid with sulfonated hyperbranched poly(arylene oxindole)s

Acid-catalyzed condensation of levulinic acid and phenol into high yields of diphenolic acid (>50%) is possible with a combination of sulfonated hyperbranched polymers and thiol promotors, either added as a physical mixture or bound to the polymer by ion-pairing.

UV-responsive polymeric superamphiphile based on a complex of malachite green derivative and a double hydrophilic block copolymer.

We have prepared a UV-responsive polymeric superamphiphile, formed by a malachite green derivative and the double hydrophilic block copolymer methoxy-poly(ethylene glycol)(114)-block-poly(l-lysine hydrochloride)(200) (PEG-b-PLKC) on the basis of electrostatic interactions. The malachite green derivative undergoes photo-ionization upon UV irradiation, which makes it more hydrophilic, resulting in changes in the self-assembly behavior of the polymeric superamphiphile. For this reason, the polymeric superamphiphile originally self-assembles to form sheetlike aggregates, which disassemble after UV irradiation because of the increased solubility of the malachite green derivative. By use of Nile red as a probe, the polarity of the polymeric superamphiphile solution is confirmed to be increased after UV irradiation by fluorescence spectra, which also explains the disassembly of the polymeric superamphiphile.

Selenacalix[3]triazines: synthesis and host–guest chemistry

The heteracalixarene series (N/O/S) has been expanded with Se-bridged cyclotrimeric macrocycles. Selenacalix[3]triazines were synthesized by convenient one-pot nucleophilic aromatic substitution reactions and they showed peculiar supramolecular features. The N tridentate binding pocket was capable of coordinating both copper ions and anions.

Molecular design of sulfonated hyperbranched poly(arylene oxindole)s for efficient cellulose conversion to levulinic acid

This contribution is about the design and synthesis of various sulfonated hyperbranched poly(arylene oxindole)s (SHPAOs) with different substituents via a convenient A2 + B3 polycondensation and subsequent sulfonation as water-soluble and recyclable acid catalysts for the conversion of cellulose to levulinic acid (LA). Whereas their molecular weight (from 2.7 × 103 to 20.2 × 103), acid density (from 3.4 to 4.8 mmol H+ per g) as well as the polymer structure, viz. hyperbranched or linear analogues, only slightly affect the catalytic performance, the presence of electron-withdrawing substituents on the isatin polymer building block is key to their catalytic efficiency. Among all polymer catalyst designs studied, the use of 5-Cl-SHPAO provided the highest LA yield of almost 50%, directly obtained from ball-milled cellulose in aqueous medium at 165 °C, being twice the LA yield of that of unsubstituted SHPAOs. The presence of the 5-chloro-substituent substantially facilitates the hydrolysis of the glycoside bonds. The close vicinity of the oxindole functionality to the sulfonic acid group seems essential to realize such high hydrolysis rates, as chemical protection of the NH group or sulfonation at other positions lead to substantially lower LA yields. The presence of the 5-chlorine substituent also retards the glucose isomerisation rate, while slightly increasing the HMF conversion rate to LA. As a result, the catalytic reaction progresses in conditions of low concentrations of the most reactive intermediates, fructose and HMF, that otherwise could lead to considerable humin formation. Though hydrophobic interactions are usually invoked to explain such catalytic effects, this contribution suggests also a significant role of the steric proximity of the sulfonic acid group to the oxindole NH group, enabling a kinetic optimization of the reaction cascade through molecular design of the catalytically active acid site.

Homoselenacalix[n]arenes.

A novel family of homoselenacalix[n]arenes (n = 3-8), with bridging CH(2)SeCH(2) groups connecting the aryl subunits, has been synthesized via two different approaches employing nucleophilic Se species. The macrocycles are adequately characterized, including single-crystal X-ray structures for the homoselenacalix[4]- and homoselenacalix[6]arene homologues. The combined features of a calixarene-like macrocyclic scaffold and the presence of multiple selenium atoms create appealing (biomimetic) supramolecular opportunities.

Sustainable bisphenols from renewable softwood lignin feedstock for polycarbonates and cyanate ester resins

The selective reductive catalytic depolymerisation of softwood lignin (e.g. pine, spruce) yields predominantly 4-n-propylguaiacol (4PG; 15–20 wt% on lignin basis), an interesting platform chemical for bio-based chemistry. This contribution specifically shows promising technical, sustainable and environmental advantages of such a bio-phenol for various polymer applications. The bisphenolic polymer precursor, 5,5′-methylenebis(4-n-propylguaiacol) (m,m′-BGF-4P), was therefore first synthesized by acid-catalysed condensation, and its synthesis and isolation are compared with shorter chain analogs, viz. 4-methyl- and 4-ethylguaiacol. A thorough GC-GPC/SEC analysis of the crude condensation mixture was developed to assess the purity of the isolated dimers. Isolation is done by a single-step crystallization, yielding 57 wt% of m,m′-BGF-4P in >99% purity. This pure m,m′-BGF-4P bisphenol displays a notably reduced potency to activate human estrogen receptor alpha (hERα; EC50 at 10−5 M) in comparison with commercial bisphenols, and is therefore useful for future polymer applications. As a proof of concept, polycarbonates and cyanate ester resins were prepared from m,m′-BGF-4P and compared to other bisphenols. The polycarbonate had Mn = 5182 g mol−1, Tg = 99 °C, Tm = 213 °C, Td,5% = 360 °C, and displayed improved processability in common solvents, as opposed to the methylated and ethylated bisguaiacols. A fully cured resin disk exhibited a Tg = 193 °C, Td,5% = 389 °C and a water uptake of only 1.18% after being immersed in 85 °C water for four days. These results underscore the potential of the intrinsic functionality of lignin-derived building blocks to transcend the scope of renewability.

Metal-Free Route for the Synthesis of 4-Acyl-1,2,3-Triazoles from Readily Available Building Blocks

Functionalized 1,2,3-triazole heterocycles have been known for a long time and hold an extraordinary potential in diverse research areas ranging from medicinal chemistry to material science. However, the scope of therapeutically important 1-substituted 4-acyl-1H-1,2,3-triazoles is much less explored, probably due to the lack of synthetic methodologies of good scope and practicality. Here, we describe a practical and efficient one-pot multicomponent reaction for the synthesis of α-ketotriazoles from readily available building blocks such as methyl ketones, N,N-dimethylformamide dimethyl acetal, and organic azides with 100 % regioselectivity. This reaction is enabled by the in situ formation of an enaminone intermediate followed by its 1,3-dipolar cycloaddition reaction with an organic azide. We effectively utilized the developed strategy for the derivatization of various heterocycles and natural products, a protocol which is difficult or impossible to realize by other means.