References tetrahydrofurans

Synthesis of dienes [1, 169, before references], Tetrahydrofurane solutions of vinylmagnesium halides are readily accessible from vinyl halides by the method of Normant.19 Kauffmann and Sahm20 found that when a THF solution of the vinyl-magnesium compound (1) is treated at —60° to —40° under nitrogen with a suspension of cuprous chloride an intensely green or red solution is obtained which presumably contains a vinylcopper compound. When the mixture is warmed to... 

Articles fabricated from FEP resins can be made bondable by surface treatment with a solution of sodium in Hquid ammonia, or naphthalenyl sodium in tetrahydrofuran (64) to faciUtate subsequent wetting. Exposing the surface to corona discharge (65) or amines at elevated temperatures in an oxidizing atmosphere (66) also makes the resins bondable. Some of the more recent work is described in References 67—69. 

The absence of such a means for indicating hydrogenation of other monocyclic heterocycles forces the use of tetrahydro-, hexahydro- or perhydro- prefixes. The resulting names are, unfortunately, cumbersome, and in practice are inevitably replaced by acronyms, such as THF for tetrahydrofuran, when the substance must be referred to frequently. 

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. ... 

Being slightly crystalline, there are few good solvents, the best known of which are nitrobenzene, cyclohexanone and tetrahydrofuran. When mixed with certain non-volatile solvents such as some phthalates, adipates and phosphates, flexible materials are obtained and which are referred to as plasticised p. v.c. 

The number 10 refers to the diameter of the silica particles in micron and not the pore size. The five solutes (1-5) were largely hydrocarbon in nature having mean molecular diameters of 11,000, 240, 49.5, 27.1 and 7.4 A respectively. The mobile phase employed was tetrahydrofuran (THF). This solvent is adsorbed as a layer on the surface of the silica (a phenomenon that will be discussed in more detail... 

The spectral properties of pentafluorophenylcopper te-tramer are as follows infrared (Nujol) cm. 1630 medium 1391 medium 1353 medium 1275 medium 1090,1081, and 1071 strong triplet 978 strong 785 medium fluorine magnetic resonance (tetrahydrofuran with trichlorofluoromethane as internal reference) 8 (multiplicity, number of fluorines, assignment, coupling constant J in Hz.) 107.2 (20-line multiple , 2, ortho F), 153.4 (triplet of triplets, 1, para F, J= 1.3 and 20), 162.3 (17-line multiplet, 2, meta F). Absorptions at 820-900, 1100-1125, and 1290 cm.- in the infrared spectrum and at 8 3.05 in the proton magnetic resonance spectrum indicate that dioxane is still present. 

To a solution of hexa hydrated aluminum chloride (1.99g, 8.28 mmol, 1.0 equiv.) in tetrahydrofuran (25 mL), precatalyst (R,R)-salenCo (5.0 g, 8.28 mmol, 1.0 equiv. ) was added and stirred in at open atmosphere at room temperature. As soon as the chiral Co (salen) was added color of the solution changes from brick red to dark olive green. The mixture was stirred for 1 h. The resulting solution was concentrated imder reduced pressure. The crude solid was worked up with H2O and CH2CI2. Yield = 98-99 % as a dark green solid powder. The complex have been analyzed by A1 NMR with reference to [A1(D20)6] and... 

P 10] The reaction was performed on 100 mg of Merrifield resin [75]. Absolute tetrahydrofuran was used as solvent and 4 h of agitation was employed. No other details are given in the reference. Generally, about 2 min were needed to perform a complete washing cycle. 

A selective, mild, and facile reduction of aromatic and aliphatic carboxylic acid imida-zolides to primary alcohols is described in reference [33]. The reaction proceeds in water, water/dioxane or water/tetrahydrofuran solution at room temperature with 2-5 molar equivalents of NaBH4 in about 1 h. 

Conformational factors in the photolysis of N-acylimidazoles leading to Norrish type II products or cyclobutanols have been discussed in reference [7]. 7V-Acylimidazoles have been irradiated in tetrahydrofuran using a low-pressure mercury lamp (quartz well,... 

Diborane, Bis(2-methoxyethyl) ether See Borane-tetrahydrofuran (reference 3)... 

On each of the curves, the points at lowest X represent swelling in cyclohexane, the next in tetrahydrofuran and the last in benzene. In all cases, the samples were swollen in the pure solvent. The curves are reproduced from Figure 13 of Reference 19. The networks were made from anionically polymerized polyr-styrene using a bifunctional initiator crosslinked subsequently by divinyl benzene. The curves correspond to different ratios of divinyl benzene (DVB) per polystyrene living end (LE),... 

These equilibria give directly only acidity differences between RH and R H and can vary with solvent and counterion. The corresponding — log f values have been converted to pK scales by choosing one compound as the standard and referring others to it. The standard chosen for tetrahydrofuran (THF) solutions is fluorene and it is assigned a pK of 22.9, its value in the DMSO scale (statistically corrected per hydrogen for fluorene the measured pK is 22.6)3,4. 

The selective oxidation of ra-butane to give maleic anhydride (MA) catalyzed by vanadium phosphorus oxides is an important commercial process (99). MA is subsequently used in catalytic processes to make tetrahydrofurans and agricultural chemicals. The active phase in the selective butane oxidation catalyst is identified as vanadyl pyrophosphate, (V0)2P207, referred to as VPO. The three-dimensional structure of orthorhombic VPO, consisting of vanadyl octahedra and phosphate tetrahedra, is shown in Fig. 17, with a= 1.6594 nm, b = 0.776 nm, and c = 0.958 nm (100), with (010) as the active plane (99). Conventional crystallographic notations of round brackets (), and triangular point brackets (), are used to denote a crystal plane and crystallographic directions in the VPO structure, respectively. The latter refers to symmetrically equivalent directions present in a crystal. 

Apart from the qualitative observations made previously about suitable solvents for study, the subject of solvates has two important bearings on the topics of thermochemistry which form the main body of this review. The first is that measured solubilities relate to the appropriate hydrate in equilibrium with the saturated solution, rather than to the anhydrous halide. Obviously, therefore, any estimate of enthalpy of solution from temperature dependence of solubility will refer to the appropriate solvate. The second area of relevance is to halide-solvent bonding strengths. These may be gauged to some extent from differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) solvates of "aprotic solvents such as pyridine, tetrahydrofuran, and acetonitrile will give clearer pictures here than solvates of "protic solvents such as water or alcohols. 

This is not the first time that the kinetics of bulk polymerizations has been analysed critically. Szwarc (1978) has made the same objection to the identification of the rate constant for the chemically initiated bulk polymerization of tetrahydrofuran as a second-order rate constant, k, and he related the correct, unimolecular, rate constant to the reported by an equation identical to (3.2). Strangely, this fundamental revaluation of kinetic data was dismissed in three lines in a major review (Penczek et al. 1980). Evidently, it is likely to be relevant to all rate constants for cationic bulk polymerizations, e.g., those of trioxan, lactams, epoxides, etc. Because of its general importance I will refer to this insight as Szwarc s correction and to (3.2) as Szwarc s equation . 

Figure 18 Cyclic voltammetric responses at different temperatures of ferrocene in a 16 17 1 chloroethane tetrahydrofuran 2-methyl-tetrahydrofuran solution containing LiBF4 (0.6 mol dm 3) as supporting electrolyte, (a) Platinum electrode (b) Tl 1223 ( Tl0.sPbo.s Sr2Ca2Cu306). Scan rate 0.025 V s. Potential values are referred to a pseudo-reference silver wire...

FIGURE IS Plots of log k vs. % organic solvent modifier for methanoi, acetonitrile, and tetrahydrofuran. Reprinted with permission from Reference 7. 

Table 3.20 lists examples of the preparation of oxygen-containing heterocycles by RCM. Further examples, including lactones [895], pyrans [896,897], chromenes [839], tetrahydrofurans [838], phosphonates [898], and oxepines [856,899-902], have been reported. For references to macrocyclizations see Scope and Limitations in this section. 

Another highly active non-pyrophoric nickel catalyst is prepared by reduction of nickel acetate in tetrahydrofuran by sodium hydride at 45° in the presence of tert-amyl alcohol (which acts as an activator). Such catalysts, referred to as Nic catalysts, compare with P nickel boride and are suitable for hydrogenations at room temperature and atmospheric pressure, and for partial reduction of acetylenes to civ-alkenes [49]. 

Combinations of a Lewis acid, protogen or cationogen, and a reactive cyclic ether (e.g., oxirane or oxetane) have been used to initiate the polymerization of less reactive cyclic ethers such as tetrahydrofuran [Saegusa and Matsumoto, 1968]. Initiation occurs by formation of the secondary and tertiary oxonium ions of the more reactive cyclic ether, which then act as initiators for polymerization of the less reactive cyclic ether. The reactive cyclic ether, referred to as a promoter, is used in small amounts relative to the cyclic ether being polymerized and increases the ability of the latter to form the tertiary oxonium ion. 

Analysis of adrenaline (adr), noradrenaline (nadr) and dopamine (DA) in urine using (A) An ODS column with ionpairing agent in citrate buffer pH 5.0 with 2% tetrahydrofuran (THF) as the mobile phase (B) a strong cation exchange column with citrate buffer pH 5.0 with 7% THF as the mobile phase. The eluent was monitored by electrochemical detection at a potential of 0.7 V. Methyidopamine (MDA) was used as an internal standard and added to the urine before extraction. Reproduced with permission from J. Chromatogr. Biomed. Apps. (see Reference 10). 

Satake et al. reported the use of a coated wire electrode sensitive to procaine and other local anesthetic cations, and their application to potentiometric determination [73]. Electrodes were constructed from a copper wire (0.8 mm diameter), coated with a PVC membrane comprising a mixture of the drug-tetraphenylborate ion-pair, dioctyl phthalate, polyvinyl chloride, and tetrahydrofuran. Potential measurement was made with respect to a Ag-AgCl reference electrode. The electrodes showed linear responses with a Nemstian slope for procaine over the concentration range investigated. The method was used for analyses of the drug in pharmaceutical preparations. 

Hamada et al. used a poly (vinyl chloride) matrix membrane ion-selective electrode for the analysis of procaine [76]. Procaine flavianate (10 mg, prepared by precipitation from an equimolar mixture of procaine hydrochloride and flavianic acid), was mixed with PVC powder (150 mg), dioctyl phthalate (370 mg), and tetrahydrofuran (4 mL). This mixture was used to produce membranes (3 cm diameter), from which discs were cut to prepare ion-selective electrodes. The electrodes were used in conjunction with a double-junction Ag-AgCl (KNO3) reference electrode for the potentiometric determination of procaine hydrochloride at 25°C. 

After the amalgam is cooled, 400 mL of tetrahydrofuran (THF) distilled from lithium tetrahydridoaluminate is added to the flask, followed by 50.0 g (142 mmole) of W(CO)6. "Caution. The THF should be checked for peroxide and high water content before LiAlH4 is added. The distillation procedure is given in Reference 6. 

In this reaction purified tetrahydrofuran (THF) is required, as well as a standardized solution of Li[AlH4] in tetrahydrofuran. The THF from freshly opened bottles is distilled from Li [A1H4]. ("Caution. Li[AlHJ is a hazardous material and must be handled in dry conditions and in small quantitites. Serious explosions can occur when impure THF is purified if it contains peroxides (see Reference 7). 

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