Solvent furans

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

The synthesis of 168 has also been completed by using other reaction conditions (Scheme 22). 6,7-Dimethoxyisoquinoline (162) was reacted with potassium cyanide and 2-chloromethylbenzoyl chloride in the presence of a catalytic amount of benzyltriethylammonium chloride, resulting in 164 which on treatment with lithium diisopropylamide in hexamethylphosphoramide-tetrahydro-furan solvent mixture afforded the cyclized product 168 in high yield (40). 

Scheme 4.2 Syntheses of homoerythrina alkaloids by domino alkylation/Michael addition. 6b with iodide 7 gave spiro compound 8b in 48% yield, which could be subsequently increased to 80% by using cesium t-butoxide as a base in t-BuOH/THF (tetrahydro-furan) solvent [5]. The ketoesters 8a,b were found to be useful precursors for Homoerythrina alkaloids such as 10. Thus, ( )-3-demethoxy-l,2-dihydrocomosidine 10b was obtained in good yield in four steps form ketoesters 8b, involving a Schmidt rearrangement as the final step (Scheme 4.2) [6].

Among the important oxygenated solvents that are not covered above are furan solvents and organic carbonates. Furan solvents of commercial interest include furfuryl alcohol, tetrahydrofuran, and tetrahydrofurfuryl alcohol. They are characterized by strong solvency for some synthetic polymers. Tetrahydrofuran has an evaporation rate between that of acetone and methyl ethyl ketone. Organic carbonate solvents include ethylene and propylene carbonates, diethyl carbonate and dimethyl carbonate, which are good solvents for many polymers. 

Propylene Carbonate (solvent) Tetra-Hydro Furan (solvent)... 

CH3COCH2CH1COCH3. Colourless liquid which becomes yellow on standing b.p. I9PC. Obtained by boiling 2,5-dimethylfuran with dilute sulphuric acid. It readily condenses with a variety of substances to give derivatives of furan, thiophen and pyrrole, and is a solvent for cellulose acetate. 

The 7, i5-unsaturated alcohol 99 is cyclized to 2-vinyl-5-phenyltetrahydro-furan (100) by exo cyclization in aqueous alcohol[124]. On the other hand, the dihydropyran 101 is formed by endo cyclization from a 7, (5-unsaturated alcohol substituted by two methyl groups at the i5-position. The direction of elimination of /3-hydrogen to give either enol ethers or allylic ethers can be controlled by using DMSO as a solvent and utilized in the synthesis of the tetronomycin precursor 102[125], The oxidation of the optically active 3-alkene-l,2-diol 103 affords the 2,5-dihydrofuran 104 in high ee. It should be noted that /3-OH is eliminated rather than /3-H at the end of the reac-tion[126]. 

Reinforced furan resias have been used for many years in process piping and in underground sewer or waste-disposal systems. With a wide range in pH acceptability and good solvent resistance, furan piping has been a logical choice for many services. 

Physical Properties. Furan, a colorless Hquid with a strong ethereal odor, is low-boiling and highly flammable. It is miscible with most common organic solvents but only very slightly soluble in water. The physical properties of furan are Hsted in Table 1. 

Other furan compounds, best derived from furfural, are of interest although commercial volumes are considerably less than those of furfural, furfuryl alcohol, furan, or tetrahydrofurfuryl alcohol. Some of these compounds are stiU in developmental stages. Apphcations include solvents, resin intermediates, synthetic mbber modifiers, therapeutic uses, as well as general chemical intermediates. 

Since double bonds are no longer present, these compounds are more stable than the corresponding furan derivatives. Tetrahydrofurfuryl alcohol—ethylene oxide adducts [31692-85-0] are also usehil solvents for paint stripping formulations (136,141,143). 2-Methylfuran is a good solvent, but... 

Lubricating Oil Extraction. Aromatics are removed from lubricating oils to improve viscosity and chemical stabihty (see Lubrication and lubricants). The solvents used are furfural, phenol, and Hquid sulfur dioxide. The latter two solvents are undesirable owing to concerns over toxicity and the environment and most newer plants are adopting furfural processes (see Furan derivatives). A useful comparison of the various processes is available (219). 

Aqueous mineral acids react with BF to yield the hydrates of BF or the hydroxyfluoroboric acids, fluoroboric acid, or boric acid. Solution in aqueous alkali gives the soluble salts of the hydroxyfluoroboric acids, fluoroboric acids, or boric acid. Boron trifluoride, slightly soluble in many organic solvents including saturated hydrocarbons (qv), halogenated hydrocarbons, and aromatic compounds, easily polymerizes unsaturated compounds such as butylenes (qv), styrene (qv), or vinyl esters, as well as easily cleaved cycHc molecules such as tetrahydrofuran (see Furan derivatives). Other molecules containing electron-donating atoms such as O, S, N, P, etc, eg, alcohols, acids, amines, phosphines, and ethers, may dissolve BF to produce soluble adducts. 

Only the potentially 2,4-dihydroxy derivatives of furan and thiophene are known and these exist in the solid state and in polar solvents as the monoenols (82) (71T3839). However, in non-polar solvents the furan derivatives exist predominantly in the dioxo form (83). The 2,5-dioxo structure (84) is well established for X=0, NR, S and Se (71BSF3547) and there is no evidence for intervention of any enolic species. The formal tautomer (85) of succinimide has been prepared and is reasonably stable (62CI(L)1576). 

A number of cement materials are used with brick. Standard are phenolic and furan resins, polyesters, sulfur, silicate, and epoxy-based materials. Carbon-filled polyesters and furanes are good against nonoxidizing acids, salts, and solvents. Silica-filled resins should not be used against hydrofluoric or fluosihcic acids. Sulfur-based cements are limited to 93°C (200°F), while resins can be used to about 180°C (350°F). The sodium silicate-based cements are good against acids to 400°C (750°F). 

Examples of mono-layer adsorption isotherms obtained for chloroform and butyl chloride are shown in Figure 5. The adsorption isotherms of the more polar solvents, ethyl acetate, isopropanol and tetrahydro-furan from -heptane solutions on silica gel were examined by Scott and Kucera [4]. Somewhat surprisingly, it was found that the experimental results for the more polar solvents did not fit the simple mono-layer... 

Furane resins are superior to polyesters and epoxies for resistance to ketones, chlorinated solvents and carbon disulfide. However, as they are... 

D) Preparation of 2-(1-Hydroxyethyi)-3-Methyi-5-(2-Oxo-2,5-Dihydro-4-Furyi)Benzo[b] Furan (3574 CB) 13,2 grams of compound 3556 CB of which the preparation is described in (C) are treated successively with 66 ml of methylene chloride, 27 ml of methanol and, with stirring, 1.6 grams of sodium borohydride added in stages. The reaciton takes 1 hour. The mixture is poured into water acidified with a sufficient amount of acetic acid, the solvents are stripped under vacuum, the crystalline product removed, washed with water, and recrystallized from ethyl acetate. Yield 90%. MP <=158°C. 

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