Furan Formation Research Articles

Reaction of Tetracyanoethylene with 1,2-Cyclohexanedione and Bis(cyclohexanon-2-yl)methane

The first study on reactions between tetracyanoethylene and carbonyl compounds was published in 1957 [1]. We extended the investigations in this field and established that the arising b,b,g,g-tetracyanoalkanones were very reactive [2, 3]. However in this process were involved only some b-dicarbonyl compounds whose addition to tetracyanoethylene followed by cyclization due to interactions NH^CN and OH^CN resulted in formation of pyrroles, furans, and pyrans [4].

Evidence of furan formation from acetaldehyde over β-UO 3

Furan, C 4H 4O, has been observed from acetaldehyde over β-UO 3 during temperature programmed desorption (TPD) with a high yield (ca. 40%) at low surface coverage. At high surface coverage crotonaldehyde, CH 3CHCHCHO (formed by β-aldolisation of acetaldehyde), was the most dominant product. Flow experiments at P=30 atm have indicated that one can achieve high reaction selectivity to furan. The catalyst deactivated, however, after a few hours of time on stream. X-ray diffraction analyses have shown that β-UO 3 has been reduced to a mixture of α-U 3O 8 and UO 2. The catalysts could be regenerated by gas-phase O 2 at 673–773 K, 30–40 atm for 2 h. The comparison between furan formation from acetaldehyde to that from ethylene as well as from ethanol [J. Catal. 184 (1999) 553; Stud. Surf. Sci. Catal. 110 (1997) 265] over U oxides indicates the following. (1) β-UO 3 was far more active than α-U 3O 8. (2) Acetaldehyde gave the highest reaction yield. (3) The reaction appears to be driven by the high oxidation state of U cations (U +6) as well as the potential presence of these U +6 cations in a sixfold coordination environment, i.e. containing two vacancies to accommodate the coupling of two C2 molecules to the C4 furan product.

A Theoretical Determination of the Heats of Formation of Furan, Tetrahydrofuran, THF-2-yl, and THF-3-yl

Large basis set coupled cluster calculations, with corrections for core/valence, atomic spin−orbit, and scalar relativistic effects, have been used to determine the atomization energies of furan (1A1, C4H4O), tetrahydrofuran (1A, C4H8O), and the THF-2-yl (2A, C4H8O) and THF-3-yl (2A, C4H8O) radicals. For furan and tetrahydrofuran, where gas-phase experimental data is available, the level of agreement between experiment and theory is very good. The 0 K heats of formation (kcal/mol) for the four systems are ΔHf(furan) = −4.6 ± 0.5 (calcd) vs −5.2 ± 0.2 (exptl), ΔHf(tetrahydrofuran) = −37.6 ± 0.7 (calcd) vs −37.6 ± 0.2 (exptl), ΔHf(THF-2-yl) = 5.1 ± 1.0 (calcd), and ΔHf(THF-3-yl) = 8.9 ± 1.0 (calcd). At 298 K the comparable values are ΔHf(furan) = −7.7 ± 0.5 (calcd) vs −8.3 ± 0.2 (exptl), ΔHf(tetrahydrofuran) = −44.0 ± 0.5 (calcd) vs −44.0 ± 0.2 (exptl), ΔHf(THF-2-yl) = −0.5 ± 1.0 (calcd) and ΔHf(THF-3-yl) = 3.6 ± 1.0 (calcd). The principal limitation on the accuracy of the composite coupled cluster approach followed in this work is the high cost of large basis set calculations on chemical systems that lack exploitable elements of symmetry. Three parametrized methods, G2, G3, and CBS-Q, were also found to be in good agreement with experiment.

Rhodium(II) mediated cyclizations of diazo alkynyl ketones

The rhodium(II)-catalyzed reaction of α-diazo ketones bearing tethered alkyne units represents a new and useful method for the construction of a variety of substituted cyclopentenones. The process proceeds by addition of the rhodium-stabilized carbenoid onto the acetylenic π-bond to give a vinyl carbenoid intermediate. The resulting rhodium complex undergoes a wide assortment of reactions including cyclopropanation, 1,2-hydrogen migration, CH-insertion, addition to tethered alkynes and ylide formation. The exact pathway followed is dependent on the specific metal/ligand employed and is also influenced by the nature of the solvent. Sulfonium ylide formation occurred both intra and intermolecularly when the reaction was carried out in the presence of a sulfide. In the case where an ether oxygen was present on the backbone of the vinyl carbenoid, cyclization afforded an oxonium ylide which underwent a [1,2] or [2,3]-sigmatropic shift to give a rearranged product. These cyclic metallocarbenoids were also found to interact with a neighboring carbonyl π-bond to produce carbonyl ylide dipoles that could be trapped with added dipolarophiles. The domino transformation was also performed intramolecularly by attaching an alkene directly to the carbonyl group. When 2-alkynyl-2-diazo-3-oxobutanoates were treated with a Rh(II)-catalyst, furo[3,4-c]furans were formed in excellent yield. The 1,5-electrocyclization process involved in furan formation has also been utilized to produce indeno[1,2-c]furans. Rotamer population was found to play a significant role in the cyclization of α-diazo amide systems containing tethered alkynes. In this account, an overview of our work in this area is presented.

The Noell Conversion Process – a gasification process for the pollutant-free disposal of sewage sludge and the recovery of energy and materials

The Noell Conversion Process was developed to guarantee the safe disposal of sewage sludge and other waste materials by means of thermal treatment, evenwith very strict emission standards. The center piece of this process is a pressurized entrained flow gasifier. The reactin conditions in this gasifier does not only suppresses the formation of dioxins and furans, but also completely destroys any dioxins and furans contained in the waste materials. Another advantage of the Noell Conversion Process referring the thermal treatment of sewage sludge is the recovery of marketable substances such as synthesis gas, sulphur and vitrified slag. To demonstrate this advanced technology in the field of sewage sludge treatment, Noell-KRC has built a pilot plant in Freiberg/Germany. This plant was designed for a throughput of 0.5 Mg/h (dry base) of sewage sludge. During the operation of the plant from 1996 until 1998, it was possible to demonstrate that there are no problems with emissions of heavy metals like Mercury or organic components like Dioxins and Furans. The H2 rich gas produced in the process can be utilized as a power source. The vitrified slag produced in the process is of a quality suitable for use as a construction material with a wide range of applications.

Selective isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran using CO-modified, supported Pd catalysts

The selective isomerization of 2,5-dihydrofuran (2,5-DHF) to produce 2,3-dihydrofuran (2,3-DHF) over 1% Pd/SiO 2 requires the addition of low levels of CO to the reaction feedstream. In the absence of CO, the selectivity is approximately 70%, with equimolar amounts of furan and tetrahydrofuran forming the balance of the products. At 50 ppm CO in the feedstream, selectivity increases to >94% with virtually no decline in activity. Higher levels of CO lower overall activity with only marginal improvements in selectivity. These results, based on statistical modeling, CO chemisorption measurements, and DRIFTS experiments, are best explained by the preferential adsorption of CO on basal planes, such as (111) facets, on the surface of the Pd crystallites to change the average ensemble sizes of contiguous Pd atoms. These ensembles are too small to catalyze the formation of furan and tetrahydrofuran, but not the isomerization to 2,3-DHF. The role of CO does not appear to be linked to preferential adsorption of CO on Pd defect sites, such as those at the corners and edges of Pd crystallites. DRIFTS results indicate low concentrations of CO are preferentially-adsorbed on the low index planes, such as (111) facets in different bridged modes. Linearly-bonded CO on edge and corner Pd sites is detected only at levels of CO higher than used during isomerization conditions.

Effect of dichlorophenol substitution pattern on furan and dioxin formation

The gas-phase formation of tetrachlorodibenzofurans (T 4 CDFs) and dichlorodibenzo- p -dioxins (DCDDs), and trichlorodibenzofuranols (T 3 CDF-ols) from combinations of 2,3-, 2,4-, and 2,5-dichlorophenols (DCPs), each of which have one ortho site chlorinated, was studied to assess the effect of chlorine substitution pattern on reactivity. Benzene containing DCP, dissolved individually and in mixtures of equal amounts, was vaporized when combined with a heated gas stream (1% total organic vapor, 8% oxygen) and passed through a 10s flow reactor. Maximum gas phase formation of furan and dioxin occurs at temperatures between 500 and 700 °CC. Results confirm that chlorine substitution at ortho sites it is necessary for dioxin formation via carbon-oxygen coupling, whereas formation of both dibenzofurans and dibenzofuranols occurs via carbon-carbon coupling at unsubstituted ortho sites Effects of the second chlorine substituent were complex. In single DCP precursor experiments, 2,3-DCP strongly favored T 4 CDF formation, whereas the greatest DCDD yield was from 2,4-DCP. T 3 CDF-ol was produced only from 2,5-DCP, consistent with a reaction mechanism that rquires a chlorine meta substitutent adjacent to an unsubstituted ortho site in the phenol precursor. In DCP mixture experiments, T 4 CDF yields were greatest from 2,3- and 2,5-DCP, two 2,3-DCP, and 2,3- and 2,4-DCP, consistent with these combinations of phenoxy radicals having at least steric hindrance in carbon-carbon coupling, DCDD yields were greater from combinations of 2,3- and 2,4-DCP and 2,3- and 2,5-DCP than from combinations of two 2,3-DCP, two 2,4-DCP, and two 2,5-DCP. In all cases, homogeneous gas-phase formation of furan was favored over dioxin from DCP containing one ortho chlorine substituent. Moreover, secondary furan products, but not dioxin products, were formed by reactions involving phenol, produced from benzene, and monochlorophenols, produced from DCP. This work contributes to a better understanding of factors that control the distribution of furan and dioxin products formed in the gas phase of combustion exhaust streams.

The Formation of VOC, PAH and Dioxins During Incineration

The formation of polynuclear aromatic hydrocarbons (PAH) dioxins and furans which arise from incinerators and coal-fired combustion systems has been the focus of attention for many years. Some of these compounds are considered to be formed in the combustion region and other in the cooler post-combustion environment. The accurate measurements of trace emissions such as those of dioxins are difficult and expensive; consequently it is useful to examine these from a modelling and thermodynamic point of view in order to make design predictions and derive a full analytical specification from incomplete experimental data. The thermodynamic properties combined with the kinetic pathways have been used to examine the likely routes of formation of dioxins. These processes were modelled using the Sandia National Laboratories code PSR (Perfectly Stirred Reactor). The properties demonstrated that formation of these compounds occurred during the quenching process for the species which were thermodynamically favoured. Proper insight into the chemical features may help to improve incinerator installation so as to reduce, or eliminate, these emissions.

A novel thiopyran-4-thione synthesis and crystal structure of a thiopyran-4-thione

The zinc(II) chloride catalysed reaction between ethylene trithiocarbonate (1) and dibenzoylacetylene (3) gave the novel 2,3,5,6-tetrabenzoylthiopyran-4-thione (4a) and its structure was elucidated by X-ray crystallography. Treatment of 2,3,5,6-tetrabenzoylthiopyran-4-chalcogenones (4a,b) with triethyl phosphite afforded the bis-annelated furans 1,3,5,7-tetraphenylthiopyrano[2,3-c∶5,6-c′]difuran-8-chalcogenones (5a,b) in almost quantitative yields. The mechanism for this furan formation is discussed.

Asymmetric synthesis of the northern segment of ephedradine C. A novel dihydrobenzo[ b]furan formation

An asymmetric synthesis of the dihydrobenzo[ b]furan segment of ephedradine C has been achieved utilising a chiral oxazolidinone in an aldol reaction to form a β-hydroxy ester, followed by a novel debenzylation and concomitant intramolecular cyclisation with iodotrimethylsilane as key steps. An asymmetric Michael reaction with a homochiral lithium amide was used to form the third and final chiral centre.

Thermodynamic evaluations on the formation of dioxins and furans in combustion gas

The formation of toxic PCDD/Fs are discussed thermodynamically for COHCl quaternary combustion gas to elucidate the effects of temperature and gas composition. In most cases, these toxic gases are formed at a temperature below 400°C, representing the isomers of furans and tetra dioxin (4CDD) in similar amounts, but those of other dioxin isomers are much lower.The amounts of PCDD/Fs species formed depend greatly on the gas composition, but are always associated with the formation of chlorobenzenes. When the system contains excess oxygen such as O/C > 1, PCDD/Fs decrease sharply.Hydrogen and water vapor are quite effective in decomposing dioxins and furans to form benzene and hydrocarbons. The derived amounts of PCDD/Fs are much higher than those observed in practice because of kinetic reasons. Taking account of kinetic factors, reasonable amounts of these toxic gases are derived.Especially, the reaction of carbon deposition has always been neglected in thermodynamic calculation of PCDD/Fs because of kinetic reason, but both of solid carbon and PCDD/Fs must be coexisting in small amounts.

Theozymes for Intramolecular Ring Cyclization Reactions

A complex of the five-membered transition structure for intramolecular cyclization of 4,5-epoxyhexan-1-ol with the “Houk” theozyme which is 3.5 kcal/mol lower in energy than the complex previously reported as a model for the antibody IgG26D9 catalyzed intramolecular cyclization reverses the preference of that theozyme to favor furan formation. This shows the reported theozyme complex was not a global minima and therefore not a satisfactory model for the antibody reaction. We report a new theozyme favoring pyran formation consistent with the antibody result and the recently published crystal structure of the antibody Fab 5C8 with hapten.

99/03307 Enhanced formation of dioxins and furans from combustion devices by addition of trace quantities of bromine

99/03307 Enhanced formation of dioxins and furans from combustion devices by addition of trace quantities of bromine

In Situ Kinetics and Mechanism of Furan Decomposition and Desorption with CO Formation on Pd(111)

The work presented here uses kinetic studies under conditions of varying temperature, coverage, and isotopic substitution to elucidate the energetics and mechanism of furan decomposition and desorption on Pd(111). Laser-induced thermal desorption with Fourier transform mass spectrometry detection is used as a sensitive tool for measuring the in situ kinetics of furan decomposition simultaneously with the formation of CO. The kinetics of both furan loss and CO formation have been studied for 0.17 and 0.32 Langmuir exposures of furan on Pd(111) at 100 K. This corresponds to about 2 and 4% of a monolayer and approximately 15 and 30% of a saturation monolayer, respectively. Total observed furan loss follows two processes involving a competition between desorption and decomposition. The kinetic factors for each process are extracted yielding an activation barrier of approximately 60 kJ/mol and preexponential factor of 107 s-1 for decomposition, and an activation barrier of approximately 95 kJ/mol and preexpone...

Organization of the biosynthetic gene cluster for the polyketide anthelmintic macrolide avermectin in Streptomyces avermitilis.

Analysis of the gene cluster from Streptomyces avermitilis that governs the biosynthesis of the polyketide anthelmintic avermectin revealed that it contains four large ORFs encoding giant multifunctional polypeptides of the avermectin polyketide synthase (AVES 1, AVES 2, AVES 3, and AVES 4). These clustered polyketide synthase genes responsible for avermectin biosynthesis together encode 12 homologous sets of enzyme activities (modules), each catalyzing a specific round of polyketide chain elongation. The clustered genes encoding polyketide synthase are organized as two sets of six modular repeats, aveA1-aveA2 and aveA3-aveA4, which are convergently transcribed. The total of 55 constituent active sites makes this the most complex multifunctional enzyme system identified to date. The sequenced DNA region contains 14 additional ORFs, some of which encode polypeptides governing other key steps in avermectin biosynthesis. Between the two sets of polyketide synthase genes lie two genes involved in postpolyketide modification, one of which encodes cynthochrome P450 hydroxylase that probably catalyzes furan ring formation at C6 to C8a. Immediately right of the large polyketide synthase genes is a set of genes involved in oleandrose biosynthesis and its transglycosylation to polyketide-derived aglycons. This cluster includes nine genes, but one is not functional in the biosynthesis of avermectin. On the left side of polyketide synthase genes, two ORFs encoding methyltransferase and nonpolyketide synthase ketoreductase involved in postpolyketide modification are located to the left of the polyketide synthase genes, and an adjacent gene encodes a regulatory function that may be involved in activation of the transcription of avermectin biosynthetic genes.

ChemInform Abstract: Direct Furan Formation by Treatment of Alkynyl Ketones with Strong Potassium Bases.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ab Initio Study of Intramolecular Ring Cyclization of Protonated and BF(3)-Coordinated trans- and cis-4,5-Epoxyhexan-1-ol.

The potential energy surface for the rearrangement of cis- and trans-4,5-epoxyhexan-1-ol with acid and the Lewis acid BF(3) to five- and six-membered cyclic ethers has been investigated by ab initio methods. The transition structures involving both inversion and retention of configuration at the reaction center at the HF/6-31G and B3LYP/6-31G levels are characterized. The preference for furan formation over pyran is attributed to the more favorable O-C(ep)-O bond angles at the transition structures for furan formation. The torsional O-C(ep)-C(ep)-O angles associated with tetrahydrofuran and tetrahydropyran formation vary with structure and do not directly correlate with the preferred pathway.

Evidence of Furan Formation from Ethanol over β-UO3

Furan formation during ethanol-TPD over β-UO3 is observed. Previous work has shown the formation of furan from ethylene-TPD over β-UO3 (13). The negligible activity of α-U3O8 (containing U6+ cations representing 86% of total U cations) indicates that the surface structure of β-UO3 contains the necessary sites. These sites are proposed to be U6+ cations with double vacancies to accommodate two ethoxide species followed by coupling to CH2CH2OU6+OCH2CH2. Flow experiments of ethanol also indicated the formation of furan, besides acetaldehyde, over β-UO3 (while α-U3O8 was inactive).

Novel secosteroids arising from acid catalysed rearrangement of fluocinonide acetonide in the presence of Tf 2O and TMSOTf

Treatment of 6α,9α-difluoro-11β,21-dihydroxy-3,20-dioxo-16α,17α-isopropylidenedioxypregna-1,4-diene-21-yl acetate (fluocinonide acetonide) with trifluoromethanesulfonic anhydride in the presence of trimethylsilyl trifluoromethanesulfonate as catalyst gave the ketone 3 and furan 4 arising from cleavage of the C9–C10 bond and aromatisation of the A ring, and fluocinonide 5. The ketone 3 was shown to be an intermediate in the formation of furan 4.

Application of a thermochemical selectivity criterion to the catalytic oxidation of butadiene to furan and maleic anhydride

It is shown that the selectivity of furan formation from butadiene is not limited by the C−H bond strengths of the molecules involved and that ring fission energies are not suitable data for the criterion applied.