Yields Of Furans Research Articles

Strapped Calix[2]furan[4]pyrroles, Novel Examples of Ditopic Molecular Receptors

The cyclocondensation of polyether chains functionalised with dipyrromethane units at both ends with 2,5-bis[(α-hydroxy-α,α-dimethyl)methyl]furan yield novel strapped calix[2]furan[4]pyrroles. These receptors were studied for their ability to act as ion-pair ligands towards fluoride salts.

Quantitation of Furan and Methylfuran Formed in Different Precursor Systems by Proton Transfer Reaction Mass Spectrometry

Furan has recently received attention as a possibly hazardous compound occurring in certain thermally processed foods. Previous model studies have revealed three main precursor systems producing furan upon thermal treatment, i.e., ascorbic acid, Maillard precursors, and polyunsaturated lipids. We employed proton transfer reaction mass spectrometry (PTR-MS) as an on-line monitoring technique to study furan formation. Unambiguous identification and quantitation in the headspace was achieved by PTR-MS/gas chromatography-mass spectrometry coupling. Ascorbic acid showed the highest potential to generate furan, followed by glyceryl trilinolenate. Some of the reaction samples generated methylfuran as well, such as Maillard systems containing alanine and threonine as well as lipids based on linolenic acid. The furan yields from ascorbic acid were lowered in an oxygen-free atmosphere (30%) or in the presence of reducing agents (e.g., sulfite, 60%), indicating the important role of oxidation steps in the furan formation pathway. Furthermore, already simple binary mixtures of ascorbic acid and amino acids, sugars, or lipids reduced furan by 50-95%. These data suggest that more complex reaction systems result in much lower furan amounts as compared to the individual precursors, most likely due to competing reaction pathways.

The influence of chemical transport via vapour phase on the properties of chloride and caesium-doped V–Fe mixed oxide catalysts in the oxidation of butadiene to furan

Chloride and caesium-doped V–Fe mixed oxides prepared by different methods and calcined under vapour-phase transport-restricted conditions showed a high initial furan yield of up to 40 mol% in the oxidation of butadiene. However, after only a few hours on stream a significant loss of activity and selectivity was observed. The reason for this undesirable property was investigated using different bulk and surface-sensitive characterisation methods such as X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and chemical methods. The data obtained for the structure, morphology, and composition of the fresh and used catalysts were correlated with their activity and selectivity properties. The presence of chloride ions was found to be surprisingly necessary for the origin of furan selectivity even up to 50%, which was however stable only for a short period of time. Chemical transport via chlorides or bromides was observed to be essential for the formation as well as the maintenance of the activity and selectivity properties of the system. The results obtained are interpreted with an assumption that the formation of volatile halides is necessary to form disperse VO x species, which act as active and selective centres for the present reaction. Models for the formation and deactivation of these centres are discussed in this work. In addition, the possible roles of caesium and iron oxides in the catalytic system are also described and disputed.

Pyrolysis of biomass in the presence of Al-MCM-41 type catalysts

Al-MCM-41 type mesoporous catalysts were used for converting the pyrolysis vapours of spruce wood in order to obtain better bio-oil properties. Four Al-MCM-41 type catalysts with a Si/Al ratio of 20 were tested. The catalytic properties of Al-MCM-41 catalyst were modified by pore enlargement that allows the processing of larger molecules and by introduction of Cu cations into the structure. Spruce wood pyrolysis at 500 °C was performed and the products were analysed with the help of on-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). In addition, thermogravimetry/mass spectrometry (TG/MS) experiments were applied for monitoring the product evolution under slow heating conditions (20 °C/min) from 50 to 800 °C. Levoglucosan is completely eliminated, while acetic acid, furfural and furanes become quite important among cellulose pyrolysis products over the unmodified Al-MCM-41 catalyst. The dominance of phenolic compounds of higher molecular mass is strongly cut back among the lignin products. Both the increase of the yield of acetic acid and furan and the decrease of large methoxyphenols are repressed to some extent over catalysts with enlarged pores. The Cu modified catalyst performed similarly to the catalyst with enlarged pore size in converting the pyrolysis vapours of wood, although its pore size was similar to the unmodified Al-MCM-41.

An Improved Synthesis of 3-Substituted Furans from Substituted Butene-1,4-diols

A two-phase mixture of water and hexanes improves the yields of furans produced by the oxidation of butene-1,4-diols.

Influence of methoxy and nitro groups in the oxidative metabolism of naphtho[2,1- b]furan

In the present study, we have investigated the role of methoxy and nitro groups in the oxidative metabolism of naphtho[2,1- b]furan. Hepatic microsomes were used to investigate the aerobic metabolism of naphtho[2,1- b]furan (compound A), 2-nitro-naphtho[2,1- b]furan (compound B) and 7-methoxy-naphtho [2,1- b]furan (compound C) and comparison of the metabolites formed was made using HPCL analysis and NMR, mass and UV-visible spectrometry. The different metabolic pathways investigated were compared with the previously reported metabolism of 7-methoxy-2-nitro-naphtho[2,1- b]furan (compound D). Naphtho[2,1- b]furan yield metabolites of both the furan and benzene rings, while metabolites formed from 7-methoxy-naphtho[2,1- b]furan and 2-nitro-naphtho [2,1- b]furan were derived entirely as a result of enzymic attack on the first benzene ring.

Partial oxidation of hydrocarbons on silver: conversion of 1-butene to maleic anhydride by atomically adsorbed oxygen on Ag(110)

The reaction of 1-butene with atomically adsorbed oxygen on Ag(110) has been studied using temperature-programmed reaction mass spectrometry (TPRS) and high-resolution electron-energy-loss vibrational spectroscopy (HREELS). The reaction was studied as a function of oxygen coverage from 0.00 to 0.50 ML. 1-Butene is oxidized by atomically chemisorbed oxygen via a sequence of reactions on the surface to 1,3-butadiene, 2,5-dihydrofuran, furan, carbon dioxide, and small amounts of maleic anhydride. 1,3-Butadiene is the principal oxidation product; the 2,5-dihydrofuran and furan yields are approximately 50% and 10%, respectively, of the 1,3-butadiene yield for oxygen atom coverages of 0.50 monolayers. 1,3-Butadiene is formed from 1-butene via C-H bond activation of the acidic allylic C-H bonds by atomically chemisorbed oxygen, a reaction that has a precedent in the oxidation of cyclohexene on Ag(110). The oxygen-containing products are formed via oxygen atom addition to 1,3-butadiene; this addition resembles the epoxidation of norbornene and styrene on Ag(110) and the epoxidation of styrene and 3,3-dimethylbutene on Ag(111).

Furan derivatives. part 11 [1]. on substituent effects in the synthesis of 3,4,5,6‐tetrahydrocyclohepta[cd]benzofurans

AbstractTetrahydrocyclohepta[cd]benzofurans 7a‐e were synthesized by the treatment of (5‐oxo‐tetrahydro‐5H‐benzocyclohepten‐4‐yloxy)acetic acids 5a‐e with sodium acetate in acetic anhydride or by heating of their esters 6a‐e with sodium hydroxide or sodium hydride in dioxane. The yield of furans 7 decreased as a substituent R of acids 5 or esters 6 was changed from hydrogen to a methyl, ethyl, or isopropyl group. When R was a phenyl group furan 7e was always prepared in good yield. Sodium hydride was a useful base for synthesis of tetrahydrocyclohepta[cd]benzofurans.

Furan production by oxygen insertion in the 1–4 position of butadiene on V-P-O-based catalysts

Furan formation from butadiene on a vanadium-phosphorus catalyst prepared in an organic medium is examined. The furan yield can be increased up to about 30%, operating at low conversion and at oxygen/butadiene ratios in the 1.5 – 2.0 range. This value cannot be increased further, due to the similarity of the mechanism of furan formation from butadiene and further furan oxidation to maleic anhydride and due to the self-inhibition of butadiene on the formation of furan. Comparison of the butadiene oxidation with that of furan and 2,5-dihydrofuran suggests that the mechanism of oxidation occurs through an electrophilic oxygen attack on the 1,4 butadiene positions to give 2,5-dihydrofuran, which is further converted by allylic dehydrogenation to furan. This intermediate, in turn, is further converted to maleic anhydride by the insertion of oxygen in the 2–5 furan positions and subsequent allylic dehydrogenation.

Furan derivatives. Part 8 On substituent effects in the synthesis of 4,5‐dihydro‐3H‐naphtho[1,8‐bc]furans

Abstract4,5‐Dihydro‐3H‐naphtho[1,8‐bc]furans 4 and 6 which have various substituents (R1 and R2) have been synthesized from 8‐oxo‐5,6,7,8‐tetrahydro‐1‐naphthyloxyacetic acids 1 and 3 or their ethyl esters 2. The reaction of acids 1 and 3 with sodium acetate in acetic anhydride gave a mixture of furans 4 and 6 and lactones 5 and 7. The ratios of the products were varied according to the types of substituents (R1 and R2) in acids 1 and 3. As the substituent R1 (R2 = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, production of furans 4 became more difficult. However, when a phenyl group was used as the substituent, furan 4 was obtained in good yield. Similarly, as the substituent R2 (R1 = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, furan formation was more difficult. In contrast, acids 3 which had electron‐withdrawing substituents such as chlorine, bromine or a nitro group at the 4‐position afforded furans 6 in good yield. 4,5‐Dihydro‐3H‐naphtho[1,8‐bc]furans 4 and 4,5‐dihydro‐3H‐naphtho[1,8‐bc]furan‐2‐carbocylic acids 8 were synthesized from the reaction of esters 2 and potassium hydroxide in dioxane. When the substituents R1 or R2 in esters 2 were varied from hydrogen to a methyl, ethyl or isopropyl group the total yields of furans 4 and furancarboxylic acids 8 were reduced.

A simple synthesis of 3-substituted furans. The preparations of dendrolasin, perillene and congeners

The Grignard reagent 7 , derived from 3-chloromethyl furan, reacts with various alkyl- and allylic halides, in the presence of Li 2CuCl 4, to provide high yields of 3-substituted furans.

Improvement of Furan Yield in Oxidation of Crotonaldehyde by Modifying 12-Molybdophosphoric Acid Catalysts

Abstract 12-Molybdophosphoric acid effective for oxidation of crotonaldehyde to furan was modified in two ways; by adding various cations and by replacing Mo with V or W. Among cations caesium was proved to be most effective in improving the furan yield, by decreasing reactivity of product furan relative to crotonaldehyde, thus minimizing the secondary oxidation of furan to maleic anhydride. The highest efficiency of caesium is associated with its high basicity, while the active catalyst species responsible for the furan formation is acidic in nature. The replacement of Mo by V or W gave rise to decreased activity, in contrast to other oxidations on the same catalyst. The unique character of crotonaldehyde oxidation is discussed.

The production of furan by the vapor-phase oxidation of butadiene using heteropoly compounds as catalysts

Supported heteropoly compounds, such as salts of 12-molybdophosphoric acid (H 3PMo 12O 40), were found to be effective as catalysts for the synthesis of furan in the vapor-phase oxidation of 1,3-butadiene. The rate of the reaction increases with the contents of oxygen and steam in the feed gas, whereas it decreases with the butadiene content. The yield of furan attains a maximum at a conversion of about 70%, regardless of the reaction conditions and the catalysts. From tests on 18 salts of 12-molybdophosphoric acid with an M n+ Mo atomic ratio of 1 12n ( M 1 n H 2PMo 12O 40 ) as catalysts, it was found that the best results for furan formation are obtained with the cesium, sodium, and ammonium salts. The effect of cesium content was also studied. The best results for both the yield of furan and the oxidation activity are obtained at a Cs Mo atomic ratio of from 1 12 to 1.5 12 . The results were discussed in the light of the acid-base properties of the cataysts.