References furans

Dioxin or furan refers to molecules or compounds composed of carbon and oxygen. These compounds when reacted with halogens such as chlorine or bromine acquire toxic properties. Most research on halogenated dioxin and furan has been concerned with chlorinated species. It is generally accepted that dioxin and furan are by-products of combustion processes including domestic and medical waste combustion or incineration processes.7 In combustion processes, hydrocar-... 

For reviews on furan chemistry see References 1, 4—7. The monograph by Dunlop and Peters (1), pubHshed in 1953 remains as the most comprehensive review of furan chemistry available. Unfortunately, it has never been revised, has been out of print for many years, and is not readily available. An excellent, review by Dean (7) covers advances in furan chemistry up through about 1982. 

Furfural can be oxidized to 2-furoic acid [88-14-2] reduced to 2-furanmethanol [98-00-0] referred to herein as furfuryl alcohol, or converted to furan by decarbonylation over selected catalysts. With concentrated sodium hydroxide, furfural undergoes the Cannizzaro reaction yielding both 2-furfuryl alcohol and sodium 2-furoate [57273-36-6]. 

Uses. Furan is utilised as a chemical building block in the production of other industrial chemicals for use as pharmaceuticals, herbicides, stabili2ers, and fine chemicals. There are a great many references to the use of furan as an intermediate in these applications. For a recent review, see Reference 104. Several of the principal uses are described below. 

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Given the relatively rare appearance of oxetanes in natural products, the more powerful functionality of the Patemo-Biichi reaction is the ability to set the relative stereochemistry of multiple centers by cracking or otherwise derivitizing the oxetane ring. Schreiber noted that Patemo—Btlchi reactions of furans with aldehydes followed by acidic hydrolysis generated product 37, tantamount to a threo selective Aldol reaction. This process is referred to as photochemical Aldolization . Schreiber uses this selectivity to establish the absolute stereochemistry of the fused tetrahydrofuran core 44 of the natural product asteltoxin. ... 

Unsaturated y-lactones, c.g., a- (23) and / -angelica lactone (24), are well known. Compounds 23 and 24 are both converted by alkaline catalysts into an equilibrium mixture in which 23 predominates, the amount of the hydroxy form (25) present at equilibrium being exceedingly small. True a-hydroxy furans are unknown, and, although the preparation of both a- and / -bydroxyfurans has been reported, these claims have often been refuted (see, e.g., reference 14). 

Very little is known concerning the simple, monocyclic 3-hydroxy-furans (cf. reference 15). Both the oxo and hydroxy forms of the substituted 3-hydroxyfurans 26 and 27 (R = H, CcHn) have been isolated/ but the individual tautomers slowly undergo interconversion. The enol forms give a positive reaction with ferric chloride, react rapidly with bromine, and form a peroxide with oxygen. From chemical evidence, the benzo derivatives of 3-hydroxyfuran, 28 and 29, appear to exist predominantly in the oxo form, and this is further supported by ultraviolet spectral data. Stefanye and Howard- ... 

The pulp and paper industry is the largest industrial process water user in the U.S.5 In 2000, a typical pulp and paper mill used between 15,140 and 45,420 L (4000 to 12,000 gal) of water per ton of pulp produced. 1 2 3 4 General water pollution concerns for pulp and paper mills are effluent solids, biochemical oxygen demand (BOD), and color. Toxicity concerns historically occurred from the potential presence of chlorinated organic compounds such as dioxins, furans, and others (collectively referred to as adsorbable organic halides, or AOX) in wastewaters after the chlorination/ extraction sequence. With the substitution of chlorine dioxide for chlorine, discharges of the chlorinated compounds have decreased dramatically. 

Natural products find a place not as such but at points where, once again, their chemistry illustrates the behavior of their furan nuclei. There are now so many naturally occurring furans (the sea adds its quota to the land plant count every week) that even to make a list, as in the previous review, was too big a task and would have taken too much room happily, reference to almost any issue of Phytochemistry will immediately supply examples and there are already some good lists available elsewhere (eremophilane2 and farnesane23 furans, butenolides,3 furanoid fatty acids,4 marine products5). 

Deprotection of 2,2-disubstituted-l,3-dithiolanes to give carbonyl compounds can be achieved using Oxone with KBr in aq. MeCN <06TL8559> and a review of silylated heterocycles as formyl anion equivalents includes reference to 64 <06CC4881>. A method for transformation of propargylic dithiolanes 43 into tetrasubstituted furans has been reported <06SL1209> and Michael addition of enolates to the chiral dithiolane dioxide 65 takes place... 

Alkyl furans are another class of naturally occurring compounds with insecticidal activity (Fig. 13)- This group of compounds, commonly referred to as avocado furans is present in avocados, Persea americana (Lau-raceae) and related plants. When tested against beet armyworm, Spodoptera... 

Verb tense Verb tenses in conference abstracts are consistent with conventions described elsewhere in the textbook (e.g., see tables 4.1, 5.1, 6.5). For example, past tense is used to describe work done in the past (e.g., The rates were measured ), and present tense is used to make statements of fact or state information that is expected to be true over time (e.g., Furans are found in natural products ). Some authors use future tense (in active or passive voice) in conference abstracts to refer to the work that will be presented (e.g., We will present these Endings and The synthesis will be presented ). Others prefer to state such intentions in present tense—passive voice (e.g., The Endings are presented ). 

The following important conclusions can be drawn from the above results [88JST(163)173]. First, the values of [2A ]n are nearly equal for furan and pyrrole hence the correct aromaticity trend can be ascertained only if the [XAE], contributions are also taken into account. Thus, the relative aromatic character of the compounds under discussion is determined by the sum of the stabilizing effects of the two electron interactions. These are the stabilization energy AE, referring to the interaction be-... 

The lability of thieno[3,4-6]thiophene (3) and other iso-annelated systems, such as benzo[c]thiophene and benzole] furan, may be due to the strain effect (Mills-Nixon effect see also Zwanenburg et alP and references therein) in the condensed five-membered ring. The stability of the iso-annelated dithienothiophenes 7—9 is noteworthy. Simple LCAO MO method calculations on benzo[c]thiophene indicate that its instability is due to low specific delocalization energy and high free valence index at position 1. 

V-containing silicalite, for example, has been shown to have different catalytic properties than vanadium supported on silica in the conversion of methanol to hydrocarbons, NOx reduction with ammonia and ammoxidation of substituted aromatics, butadiene oxidation to furan and propane ammoxidation to acrylonitrile (7 and references therein). However, limited information is available about the characteristics of vanadium species in V-containing silicalite samples and especially regarding correlations with the catalytic behavior (7- 6). 

Caution. The reaction should be carried out in a well-ventilated hood and away from flames, since BMS, 1,3-butadiene, organoborane by-products, and methyl sulfide are flammable, odoriferous, and possibly toxic substances. BMS and the initial hydroboration product are sensitive to air and moisture. The inert atmosphere technique8 is therefore recommended. Peroxide-free tetrahydro-furan (THF) should be distilled from a small quantity of lithium tetrahydro-aluminate according to the procedures in Reference 8. BMS is a very concentrat-... 

The term charge tranter refers to a succession of interactions between two molecules, ranging from very weak donor-acceptor dipolar interactions to interactions that result in the formation of an ion pair, depending on the extent of electron delocalization. Charge transfer (CT) complexes are formed between electron-rich donor molecules and electron-deficient acceptors. Typically, donor molecules are p-electron-rich heterocycles (e.g., furan, pyrrole, thiophene), aromatics with electron-donating substiments, or compounds... 

As examples of the conformational behavior of these derivatives, a number of selected experimental results have been gathered in Table I Those referring to furan-2-carboxaldehyde show the wide range of conformational composition found in different solvents. 

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