Tetrahydrofuran, acid-base

Borane is very reactive because the boron atom has only six electrons in its valence shell. In tetrahydrofuran solution, BH3 accepts an electron pair from a solvent molecule in a Lewis acid-base reaction to complete its octet and form a stable BH3-THF complex. 

Fluorine at the equatorial 6a position also results in an increase in potency. One scheme for the production of such a compound relies on the shift of the double bond from the 4,5 to the 5,6 position, which follows the formation of an acetal at position 3. The scheme starts with the selective reduction of the 11 ketone in the cortisone intermediate (13-2). Epoxidation of the product (18-1) with a peracid takes place selectively at the unconjugated double bond to give the 5a,6a oxirane (18-2). Treatment of that with hydrogen fluoride in tetrahydrofuran leads to fluorohydrin (18-3). (There is evidence to indicate that the reagent involves an HF THF acid base complex since the omission of THF in at least some cases leads to a complex mixture of rearrangement products [15].) The side chain in fluorohydrin (18-3) is then converted... 

The same synthetic acid-base strategy has been employed to prepare AuVTl1 polymeric species. The simplest one is that resulting from treatment of NBu4[Au(C6 Cl5)2] with T1PF6 in tetrahydrofuran [Eq. (56)].152... 

Diborane is the dimer of the hypothetical BH3 (horane) and, in the reactions that concern us, acts much as though it were BH3. Indeed, in tetrahydrofuran, one of the solvents used for hydroboration, the reagent exists as the monomer, in the form of an acid-base complex with the solvent. 

Various approaches for the O-methylation of coals have appeared. These include reaction with diazomethane (7) and, more recently, base-promoted methylation in which coal is first neutralized with an aqueous tetrahydrofuran (THF) base solution followed by reaction with methyl iodide (8-10) or methyl p-toluenesulfonate (II). Instead, we opted to O-methylate PSOC 1197 with 13,14C double-labeled dimethyl sulfate at various pH values. This approach was taken to evaluate the distribution of acidic OH sites and to determine an acceptable set of O-methylation conditions. Briefly, the coal was neu-... 

Esters aldehydes, ketones aromatic hydrocarbons chloroform ethers acids bases Higher alcohols (e.g., isoamyl and isopropyl alcohol) esters ethers strong acids and bases aliphatic and aromatic hydrocarbons chlorinated solvents Ketones methyl alcohol dioxane ethers aldehydes tetrahydrofuran... 

A nonpetrochemical route to tetrahydrofuran is based on pentoses (natural sugars). The chemistry involves digestion of the pentoses with sulfuric acid to produce furfural, which is successively decarbonylated and hydrogenated to tetrahydrofuran. 

LNA, which is an acid, can adsorb on alumina via acid-base interaction or hydrogen bonding. The structural formula of LNA and those of other organic dispersants are given in Fig. 2. The interaction between the solvent and LNA cannot be responsible for the viscosity curves because the most basic solvent, tetrahydrofuran (THF) [11], would interact with LNA the most. The acid-base interaction is based on Drago s work on Lewis acid-base interaction energies [12]. Fowkes [2,13,14] expanded the concept to ceramic processing. The relative acidity and basicity of solvents used are listed in Table 1. The ceramic powders used are listed in Table 2. 

The solubility of PLA is dependent on the molar weight and the crystallinity degree of the polymer. For the enantiopure PLA, chloroform and other chlorinated organic solvents, such as furan, dioxane, dioxolane and pyridine are good solvents. In addition to these organic solvents, the non-enantiopure PLA is soluble in ethyl acetate, dimethylsulfoxide, tetrahydrofuran, acetone, xylene, methyl ethyl ketone, ethyl lactate and dimethylformamide. However, lactic acid based polymers are not soluble in water, alcohol (e.g. ethanol, methanol), isopropyl ether, or unsubstituted hydrocarbons (e.g. cyclohexane, heptane) [19]. 

Ionic equilibria in solvents of low relative permittivity have been described in the literature and equations for calculating titration curves have also been proposed. The equations involve the partial dissociation of the acids, bases, and salts in these media, and the effect of the activity coefficients. The equations can be applied to pH and titration curve computation in solvents such as t-butyl and isopropyl alcohols, ethylene diamine, pyridine, or tetrahydrofuran. 

Hydroboration is the addition of borane, BH3, to an alkene to form a trialkyl-borane. Borane cannot be prepared as a pure compound because it reacts with itself (2BHj B2H0) to form diborane BgHe, a toxic gas that ignites spontaneously in air. However, BH3 forms a stable Lewis acid-base complex with ethers and is most commonly used as a commercially available solution of BH3 in tetrahydrofuran (THF). 

The choice of solvent is also important, as the enthalpy measured is essentially that of the displacement of the solvent from the filler surface by the probe molecule. For acid-base characterisation a non-polar solvent such as n-heptane is ideal. However, poor solubility of the desired probe molecule may demand the use of a polar solvent, when this is the case the enthalpy of interaction of the solvent with the filler must be considered when interpreting the results. If the probes in question are only capable of weak physical adsorption, (i.e., not via hydrogen bonding), and are only soluble in highly polar solvents such as tetrahydrofuran and dimethyl formamide, situations can arise where apparently no adsorption occurs. This is due to the solvent having equal or stronger interaction with the substrate than the probe. In such cases the value of performing FMC experiments should be questioned and the use of more soluble model compounds considered. If chemical adsorption of the probe occurs the polarity of the solvent is somewhat less critical, provided the solubility of reaction products is not enhanced. 

Two of the early nitrogen derivatives of borane were NR3 -BHa and [(NH3)2BHJ][BH4 ]. These resulted, respectively, from symmetric cleavage of B2H6 (BH3 - -BH3) and unsymmetric cleavage of B2H6 (BHj + BH4). Many studies have shown that Lewis acid-base (BH3 base) products are common in borane chemistry due to the electron-deficient nature of boron. Phosphorus, arsenic, oxygen, and sulfur acid-base adducts are aU known. Borane (BH3) is commonly stored and marketed as its tetrahydrofuran adduct. 

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