Solvent, solvents tetrahydrofuran

Wittig reactions may be carried out m a number of different solvents normally tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) is used... 

Solubility and Solvent Resistance. The majority of polycarbonates are prepared in methylene chloride solution. Chloroform, i7j -l,2-dichloroethylene, yy -tetrachloroethane, and methylene chloride are the preferred solvents for polycarbonates. The polymer is soluble in chlorobenzene or o-dichlorobenzene when warm, but crystallization may occur at lower temperatures. Methylene chloride is most commonly used because of the high solubiUty of the polymer (350 g/L at 25°C), and because this solvent has low flammabiUty and toxicity. Nonhalogenated solvents include tetrahydrofuran, dioxane, pyridine, and cresols. Hydrocarbons (qv) and aUphatic alcohols, esters (see Esters, organic), or ketones (qv) do not dissolve polycarbonates. Acetone (qv) promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichioromethane, and chloroben2ene. The relatively broad solubiHty characteristics of PSF have been key in the development of solution-based hoUow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent Hst for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crysta11i2ation in many solvents. When the PES stmcture contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stabiHtyis much improved over that of PES homopolymer. 

A more interesting example is given with PVC and the polycarbonate of bis-phenol A, both slightly crystalline polymers. It is noticed here that whilst methylene dichloride is a good solvent and tetrahydrofuran a poor solvent for the polycarbonate the reverse is true for PVC yet all four materials have similar solubility parameters. It would seem that the explanation is that a form of hydrogen bonding occurs between the polycarbonate and methylene dichloride and between PVC and tetrahydrofuran (Figure 5.7). In other words there is a specific interaction between each solvent pair. 

The solubility parameter is about 19.2MPa and being amorphous they dissolve in such solvents as tetrahydrofuran, mesityl oxide, diacetone alcohol and dioxane. Since the main chain is composed of stable C—C and C—O—C linkages the polymer is relatively stable to chemical attack, particularly from acids and alkalis. As already mentioned, the pendant hydroxyl groups are reactive and provide a site for cross-linking. 

The column used in the upper chromatogram was 24 cm long, 4.6 mm I.D. the solvent was tetrahydrofuran, the solute benzene and the flow rate 1 ml/min. The column used in the lower chromatogram was 1 m long, 1 mm I.D. using the same solvent and solute but at a mobile phase flow rate of 40 ml/min. It is seen that the reduction in cell volume has a dramatic effect on peak shape. The large 25 pi cell... 

Complete exchange of protons in a sterically unhindered position a to a carbonyl group can be achieved by heating a solution of the ketone in O-deuterated solvents in the presence of an acid or base catalyst, the latter being the more effective. The most commonly used solvents are methanol-OD, ethanol-OD, and the aprotic solvent anhydrous tetrahydrofuran or dioxane mixed with deuterium oxide. Under alkaline conditions the exchange rate in 153 2 14,164 stcroids, for example, is usually... 

Halofluoroalkenes may be prepared by using fluorodihalomethanes or fluoro-halomethanes in olefination procedures similar to those descnbed above. Ruoro-trichloromethane treated with tris(dimethylamino)phosphine forms the corresponding phosphomum salt, which can then be used in the Wirtig procedure. The reaction depends on the nature of the solvent in tetrahydrofuran, little olefination if any occurs however, when benzomtrile is added to the mixture, ylide formation is promoted [50] (equation 48) (Table 19). 

The synthesis of T8[OSiMe2H]8 was first reported by Hoebbel et al. from the reaction between TgLONMeJs and chlorodimethylsilane in dimethylformamide (DMF)/heptane (Table 18, entry 1). Other authors have modified the procedure by changing the solvents to tetrahydrofuran (THF) or hexane, or by using TslONMes (C2H40H)]g as the silicate anion source, but without significant improvement in the yield (Table 18). 

Aqueous solutions are not suitable solvents for esterifications and transesterifications, and these reactions are carried out in organic solvents of low polarity [9-12]. However, enzymes are surrounded by a hydration shell or bound water that is required for the retention of structure and catalytic activity [13]. Polar hydrophilic solvents such as DMF, DMSO, acetone, and alcohols (log P<0, where P is the partition coefficient between octanol and water) are incompatible and lead to rapid denaturation. Common solvents for esterifications and transesterifications include alkanes (hexane/log P=3.5), aromatics (toluene/2.5, benzene/2), haloalkanes (CHCI3/2, CH2CI2/I.4), and ethers (diisopropyl ether/1.9, terf-butylmethyl ether/ 0.94, diethyl ether/0.85). Exceptionally stable enzymes such as Candida antarctica lipase B (CAL-B) have been used in more polar solvents (tetrahydrofuran/0.49, acetonitrile/—0.33). Room-temperature ionic liquids [14—17] and supercritical fluids [18] are also good media for a wide range of biotransformations. 

Accordingly GPC analysis of dried latex samples were carried out. The carrier solvent was tetrahydrofuran and peaks were monitored by a Waters dual absorbance detector at wavelengths of 2 h and 3U0 nm. The latter detection was the closest to 350 nm available. 

The effect of sodium hydride on nitromethane forms a sait that detonates if the reaction is carried out without using a solvent. When tetrahydrofuran is present, the reaction is violent if the temperature is greater than 40 C. 

KHC03, NaOAc, K2HP04, Na3P04, triethyl amine) and finally sodium carbonate was selected as the base of choice. Fluoride initiated Suzuki coupling with KF was unsuccessful. Dimethoxy ether was selected as the solvent after screening a variety of solvents (acetone, tetrahydrofuran, methanol, isopropyl alcohol, and methyl-i-butyl ether). 

In a study looking at solvent stability [424], various aqueous-miscible solvents (tetrahydrofuran, acetonitrile, isopropanol, methanol, and A,A-dimethylformamide) were used with pinacyanol chloride as substrate. Although a PAH was not used as a substrate, the results may be extrapolated to PAH reactions. The greater impact of peroxide as compared to the solvent on biocatalyst stability was reported in this study and the need to control peroxide concentration was noted. 

Effect of Solvent and Base on the Ruthenium Carbonyl/Tri-methylamine System. Solvent plays an important role in the rate of hydrogen production. The ideal solvents are tetrahydrofuran, diglyme, and dimethoxyethane. Alcohols are only slightly less effective. Apparently the solvent must be miscible with water, promote ion formation, and be capable of weakly coordinating with the coordinately unsaturated species formed in the course of the reaction. 

Figure 3.13 Scavenging of palladium using three different quantities of Si-Thiol scavenger. (Complex Pd(AcO)2 solvent tetrahydrofuran scavenger Si-Thiol initial concentration 1000 ppm room temperature.) (Reproduced from ref. 6, with permission.)...

Water is, of course, a particularly difficult solvent to remove from solvates (i.e., hydrates). Thermal decomposition patterns for solvates containing such solvents as tetrahydrofuran suggest that thermal treatment of such solvates may prove a feasible route to anhydrous trihalides. 

FIGURE 7.31 Aminolysis of a succinimido ester by (A) an amino-acid anion generated by base [Anderson et al., 1974] and (B) a peptide anion that is in equilibrium with the peptide.114 Pg = protecting group. Appropriate solvents are tetrahydrofuran, acetone, or dimethylforma-mide with water. 

The existence of an ion pair stabilized by a solvent molecule in the product-determining step of the reaction has been established by calculations and also supported by the product composition (equation 89). While the formation of the diiodo derivative is characteristic of all the cited solvents, in tetrahydrofuran this iodination takes place with the predominant formation of l-iodomethyl-3-(4-iodobutoxy)adamantane (equation 89). 

The major use of this chemical is in the manufacture of polyesters. It is also used to make an industrial solvent, tetrahydrofuran (THE). 

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