Xylose-lysine model systems: The effect of pH on the volatile reaction products

Aqueous molal solutions of xylose and lysine (initial pH 4–9) were refluxed either with control of the pH at 5–0 or without pH control (final pH 2–6). Analysis by gas chromatography (GC) and GC-mass spectrometry resulted in the identification of 58 and 28 compounds, respectively, from the two systems. Furans were the main reaction products in both systems and 2-furfural alone comprised 522 and 999 g kg^?1 of the volatiles, respectively, from the systems with final pH values of 5–0 and 2–6. Maintaining the pH at 5–0 resulted in a higher yield and greater numbers of nitrogen-containing compounds, and monocyclic pyrroles, pyridines and 2,3-dihydro-l H-pyrrolizines were identified only in that system. Aliphatic compounds, alicyclic compounds, benzene derivatives. l-(2–furfuryl)pyrroles and pyrazines were also identified. This investigation is the first report of the formation of 2.3-dihydro-l H-pyrrolizines in a model system containing lysine as the amino compound; a possible mechanism is proposed.     

Asymmetric Synthesis of Bioxindole‐Substituted Hexahydrofuro[2,3‐b]furans via Hydroquinine Anthraquinone‐1,4‐diyl Diether‐Catalyzed Domino Annulation of Acylidenoxindoles/Isatins,Acylidenoxindoles and Allenoates

Hydroquinine anthraquinone‐1,4‐diyl diether [(DHQ)₂AQN]‐catalyzed unprecedented asymmetric domino annulation reactions of acylidenoxindoles/isatins, acylidenoxindoles and allenoates are disclosed in this communication, providing a facile access to hexahydrofuro[2,3‐b]furans containing four contiguous chiral centers in good to excellent yields along with good to excellent ee values and moderate to good dr values. Based on theoretical investigations, a concerted [3+2] ring‐closure process was proposed, in which steric hindrance and π–π stacking interaction between catalyst and substrate subtly co‐control the diastereoselectivity of the reaction.

     

Synthesis of Difurylmethane Derivatives via the Gold‐Catalyzed Tandem Cycloisomerization/Dimerization of Epoxide Alkynes

A simple and convenient synthetic approach to difurylmethane derivatives has been developed via gold‐catalyzed cycloisomerization of 1‐oxiranyl‐2‐alkynyl esters and dimerization of the 2‐(α‐hydroxyalkyl)furans. The reaction takes place in the presence of 2 mol% of tetrachloroauric acid tetrahydrate (HAuCl₄⋅4 H₂O) under very mild conditions.     

Gold Catalysis: Mild Conditions for the Transformation of Alkynyl Epoxides to Furans

Gold(III) chloride catalyzes the isomerization of alkynyl epoxides to furans under mild conditions. Additional functional groups like hydroxy groups or aryl bromides do not need to be protected.     

Base‐Catalyzed Cascade 1,3‐H Shift/Cyclization Reaction to Construct Polyaromatic Furans

A convenient new method was developed to prepare unfused polyaromatic furan derivatives from diynyl‐1,6‐diols through a novel base‐catalyzed cascade 1,3‐H shift/cyclization process. Deuterium experiments were performed to determine that the 1,3‐H shift was the rate‐determining step.     

Tuning of Regioselectivity in Inorganic Iodide‐Catalyzed Alkylation of 2‐Methoxyfurans via Electronic and Steric Effects

In the presence of inorganic iodide, the methoxy C O bond in 2‐methoxyfurans may be cleaved to afford the corresponding lactonic anion. Due to the presence of an electron‐withdrawing group at the 3‐position, the alkylation with normal organic iodides occurred at the 3‐position highly regioselectively. However, when electron‐deficient allylic iodides with an electron‐withdrawing group at the 2‐position were used the 5‐alkylation products were formed as the major products with sodium iodide as the catalyst. With magnesium iodide as the catalyst, the 5‐allylation occurred highly regioselectively. As a whole, the 3‐ vs. 5‐alkylation selectivity may be determined by the relative steric hindrance at the 3‐ and 5‐positions and the electronic effect of the allylic iodides. A rationale was proposed.     

Copper(II) Triflate‐Catalyzed Nucleophilic Substitution of Propargylic Acetates with Enoxysilanes. A Straightforward Synthetic Route to Polysubstituted Furans

A novel and efficient procedure for the synthesis of γ‐alkynyl ketones by the nucleophilic substitution of propargylic acetates with enoxysilanes in the presence of a catalytic amount of Copper(II) triflate, has been developed. The substitution reaction can be followed by a 4‐toluenesulfonic acid‐catalyzed cyclization without purification of the γ‐alkynyl ketone intermediates, offering a straightforward synthetic route to polysubstituted furans.     

辽东栎和蒙古栎心材挥发性成分分析

通过液液萃取-气相色谱-质谱联用法以法国产橡木（Quercus acutissima Caruth）为对照，对原产于我国的辽东栎（Quercus liaotungensis Koidz）和蒙古栎（Quercus mongolica Fisch）2 种橡木树种心材的挥发性成分进行分析，鉴定出呋喃、挥发性酚、酚醛、内酯和其他5 类组分，其中，国产辽东栎心材的挥发性成分在种类和含量上最高（88 种、75 113.03 μg/kg），法国橡木次之（79 种、70 940.18 μg/kg），国产蒙古栎心材最低（77 种、52 967.62 μg/kg）。主成分分析和热图分析结果表明，辽东栎在愈创木酚及其衍生物、香草醛和丁香醛等成分上具有较高相关性，具有明显的花香、果香特征，表现出较好的应用潜力，因此可能作为传统橡木的替代资源。     

Characterization of palm acid oil

Palm acid oil (PAO) is a by-product obtained from the alka-line refining of palm oil. It is used for making laundry soaps and for producing calcium soaps for animal feed formulations. The properties and composition of PAO may differ according to variations in the palm oil feedstock and the alkaline refining process. Because information on the characteristics of PAO is limited, this investigation aims to establish the properties of this product. Quality and oxidative parameters of 27 samples of PAO were determined. The six parameters analyzed were moisture and free fatty acid content, peroxide value, iodine value, saponification value and unsaponifiable matter. Headspace-gas-chromatographic (HSGC) analysis and gas-chromatographic analysis of the extract from Likens-Nickerson steam distillation of the samples were also carried out. Mean moisture content was 0.98%, free fatty acids 62.6% (palmitic acid), peroxide value 4.1 meq/kg, iodine value 50.2, saponification value 186 and unsaponifiable matter 0.53 HSGC profiles of a few samples showed the presence of one to three peaks, while the steam distillation extract showed the presence of aldehydes, ketones, furans and acids.     

Hazardous Emissions from Combustion of Biomass

Abstract

The main objective of this study is to identify the possible hazerdous emissions deriving from uncontrolled and incomplete combustions of biomass fuels that are reviewed based on the results of some investigations. Biomass combustion is a contributor of toxic air pollutants, particulate matter (PM), and greenhouse gases. PM emissions and detrimental metal emissions from biomass combustion, emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from the combustion of different biomass and solid wastes are reviewed.