Ananda S. Amarasekara

Mechanism of the dehydration of D-fructose to 5-hydroxymethylfurfural in dimethyl sulfoxide at 150 °C: An NMR study

The anomeric composition of d-fructose in dimethyl sulfoxide changes when the solution is heated from room temperature to 150 degrees C, with a small increase in the alpha-furanose form at the expense of the beta-pyranose tautomer. Additionally, a small amount of alpha-pyranose form was also observed at 150 degrees C. A mechanism is proposed for the dehydration of D-fructose to 5-hydroxymethylfurfural in DMSO at 150 degrees C, where the solvent acts as the catalyst. A key intermediate in the reaction was identified as (4R,5R)-4-hydroxy-5-hydroxymethyl-4,5-dihydrofuran-2-carbaldehyde by using (1)H and (13)C NMR spectra of the sample during the reaction.

Acidic Ionic Liquids

Ionic liquid with acidic properties is an important branch in the wide ionic liquid field and the aim of this article is to cover all aspects of these acidic ionic liquids, especially focusing on the developments in the last four years. The structural diversity and synthesis of acidic ionic liquids are discussed in the introduction sections of this review. In addition, an unambiguous classification system for various types of acidic ionic liquids is presented in the introduction. The physical properties including acidity, thermo-physical properties, ionic conductivity, spectroscopy, and computational studies on acidic ionic liquids are covered in the next sections. The final section provides a comprehensive review on applications of acidic ionic liquids in a wide array of fields including catalysis, CO2 fixation, ionogel, electrolyte, fuel-cell, membrane, biomass processing, biodiesel synthesis, desulfurization of gasoline/diesel, metal processing, and metal electrodeposition.

Zinc chloride mediated degradation of cellulose at 200 °C and identification of the products

The effect of ZnCl(2) on the degradation of cellulose was studied to develop conditions to produce useful feedstock chemicals directly from cellulosic biomass. Cellulose containing 0.5 mol of ZnCl(2)/mol of glucose unit of cellulose was found to degrade at 200 degrees C when heated for more than 60 s in air. The major non-gaseous products of the degradation were identified as furfural, 5-hydroxymethylfurfural and levulinic acid. The maximum yields for furfural and 5-hydroxymethylfurfural are 8% and 9%, respectively, based on glucose unit of cellulose. These yields are reached after 150 s of heating at 200 degrees C. A cellulose sample containing 0.5 mol of ZnCl(2)/mol of glucose unit of cellulose and 5.6 equivalents of water when heated for 150 s at 200 degrees C produced levulinic acid as the only product in 6% yield. The ZnCl(2) mediated controlled degradation of cellulose at 200 degrees C is shown to produce useful feedstock chemicals in low yield.

Vanillin based polymers: I. An electrochemical route to polyvanillin

Electrochemical reductive polymerization of divanillin in aqueous sodium hydroxide using a lead cathode gives polyvanillin in 91% yield. The product was characterized by elemental analysis, UV-Vis, FT-IR, 1H, 13C NMR, TGA-DTGA, and GPC.

Mechanism of 1-(1-propylsulfonic)-3-methylimidazolium chloride catalyzed transformation of d-glucose to 5-hydroxymethylfurfural in DMSO: an NMR study

The conversion of D-glucose to 5-hydroxymethylfurfural (HMF) in the presence of 5.48 mol% 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalyst in DMSO at 150°C was studied using (1)H, (13)C NMR, and visible spectroscopy. The HMF yield rapidly increases in the first 100 min of reaction, however yield drops beyond 100 min and levels off to a maximum yield of about 15.7% around 600 min. The visible spectroscopy study of the reaction mixture suggests that rate of HMF formation slows down after 100 min due to increase in the rate of humin formation after first 100 min. A mechanism has been proposed and key intermediates in the pathway could be identified by studying the (13)C NMR spectra of acidic ionic liquid catalyzed transformations of C-1 and C-2 (13)C labeled d-glucose under identical conditions. The proposed mechanism involves the isomerization of d-glucose to d-fructose via the complexation of the open chain sugar with the imidazolium cation of the acidic ionic liquid catalyst.

Brönsted Acidic Ionic Liquid 1-(1-Propylsulfonic)-3-methylimidazolium-Chloride Catalyzed Hydrolysisof D-Cellobiose in Aqueous Medium

Bronsted acidic ionic liquid 1-(1-propylsulfonic)-3-methylimidazolium chloride (PSMIMCl) shows a higher catalytic activity than sulfuric acid in the hydrolysis of D-cellobiose to D-glucose in water at 90–120°C. This catalytic activity enhancement is more significant at higher temperatures, and at 120°C, PSMIMCl produced 64.5% glucose yield, whereas H2SO4 produced only 42.2% after 40 min. reaction, and this is a 52.8% enhancement of catalytic activity due to the alkylimidazolium group attached to the sulfonic acid group. 1H NMR monitoring of the D-cellobiose hydrolysis in PSMIMCl and sulfuric acid mediums failed to reveal intermediates in the hydrolysis reaction, and this is probably due to rapid conversion of the intermediate(s) to a mixture of D-glucose anomers with .

Vanillin-Based Polymers—part II: Synthesis of Schiff Base Polymers of Divanillin and Their Chelation with Metal Ions

Condensation of renewable resources-based monomer divanillin with alkyl diamines gives Schiff base polymers with degree of polymerization (DP) ~25–32 in 88–95% yield. These yellow polymers are insoluble in water and common organic solvents, slightly soluble in warm DMSO, DMF and dissolves in aqueous NaOH. The polymers were characterized using FT-IR, 1H, and 13C NMR spectroscopy and by comparison with the model compound N,N′-bis(vanillidene)-1,3-propanediamine. Polymer prepared by condensation of divanillin and 1,6-diaminohexane is shown to chelate with Cu(II), Fe(II), and Co(II) metal ions in basic aqueous methanol.

A comparison of dilute aqueous p-toluenesulfonic and sulfuric acid pretreatments and saccharification of corn stover at moderate temperatures and pressures.

Single step pretreatment-saccharification of corn stover was investigated in aqueous p-toluenesulfonic and sulfuric acid media. Dilute aqueous solution of p-toluenesulfonic acid was a better catalyst than aqueous sulfuric acid of the same H(+) ion concentration for single step pretreatment-saccharification of corn stover at moderate temperatures and pressures. For example, 100mg corn stover heated at 150°C for 1h in 0.100 M H(+) aqueous sulfuric acid produced 64 μmol of total reducing sugars (TRS), whereas the sample heated in 0.100 M H(+)p-toluenesulfonic acid produced 165 μmol of TRS under identical conditions. Glucose yield showed a similar trend, as aq. sulfuric acid and p-toluene sulfonic acid media produced 29 and 35 μmol of glucose respectively after 2.5h. Higher catalytic activity of p-toluenesulfonic acid may be due to an interaction with biomass, supported by repulsion of hydrophobic tolyl group by the aqueous phase.

The effect of metal ions as co-catalysts on acidic ionic liquid catalyzed single-step saccharification of corn stover in water

The effects of adding Cr(3+), Mn(2+), Fe(3+), Co(2+) Ni(2+), Cu(2+), Zn(2+) and La(3+) chlorides as co-catalysts to 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalyzed saccharification of corn stover in aqueous medium was studied at 140-170 °C, by measuring the total reducing sugar (TRS) and glucose yields. The samples with Mn(2+), Fe(3+), Co(2+) as co-catalysts produced higher TRS yields compared to the sample without the metal ions. The Mn(2+) produced the highest catalytic effect enhancements and produced TRS yields of 68.0%, 72.9%, 90.2% and 87.9% at 140, 150, 160 and 170 °C respectively; whereas the corn stover samples without the Mn(2+) produced TRS yields of 42.9%, 52.3%, 54.4% and 53.5% at the same four temperatures. At higher temperatures of 160 and 170 °C, all metal ions studied produced significant enhancements in glucose yields, except Cr(3+). The addition of La(3+) as a co-catalyst produced the highest glucose yield improvement.

Synthesis of 4-acylpyrazolone Schiff base ligand grafted silica and selectivity in adsorption of lanthanides from aqueous solutions

Abstract The Schiff base form of the 4-acylpyrazolone ligand was immobilized on the silica surface by reaction of 3-aminopropyl silica with 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one in 97% yield, producing grafted silica with 0.77 mmol/g ligand loading. This surface modified silica was shown to be selective in the adsorption of Yb 3+ ions from dilute aqueous solutions, for which 98% adsorption was observed from a 1.0×10 −5 mol/L aq. solution at pH 6.7, after 24 h at room temperature. Six other lanthanides studied Eu 3+ , Gd 3+ , Nd 3+ , Tb 3+ , Sm 3+ and La 3+ showed moderate to weaker adsorptions of 39%, 28%, 16%, 12%, 11% and 5% respectively under similar conditions.