Tetrahydrofuran solvent

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. 

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. 

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.)...

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

A number of lower volume chemicals can be obtained from wood hydrolysis. Furfural is formed from the hydrolysis of some polysaccharides to pentoses, followed by dehydration. This process is still used in the Soviet Union. Furfural is used in small amounts in some phenol plastics it is a small minor pesticide and an important commercial solvent. It can be converted into the common solvent tetrahydrofuran (THF) and an important solvent and intermediate in organic synthesis, furfuryl alcohol. 

Wong, Konizer, and Smid (42) find by a proton nuclear magnetic resonance technique that in the solvent tetrahydrofuran, dicyclohexyl-18-crown-6 binds the ion pair Na+, F (F = fluorenyl carbanion) more strongly than it does the K+, F ion pair. Although no K values are given they estimate log K to be larger than 10 for the reaction Na+, F + L = Na+, F L (L = dicyclohexyl-18-crown-6 or dimethyldibenzo-18-crown-... 

The chemical removal of water can be done in several ways. For anionic polymerisations it is customary to rinse all the glassware repeatedly with a solution of sodium naphthalide which reacts with water to form naphthalene and NaOH, both of which are adequately soluble in the usual solvent tetrahydrofuran (THF) at the low concentrations used. This method, however, requires that the whole reactor assembly be detachable from the vacuum line so that it can be tilted around for the sodium naphtalide solution to reach all parts of the system. Care If much water is to be removed and the volume of the purging solution is too small, some NaOH may be precipitated ). 

We then studied the reactions of CH3Mn(CO)5 with triphenylphosphine and triphenylphosphite, using the same solvent, tetrahydrofuran. In these cases the observed rate constant rose with ligand concentration towards a limiting value, which was close to the rate constant obtained using cyclohexylamine (Figure I). 

Use of more efficient solvents (tetrahydrofuran, isopropyl ether, dimethoxyethane) or more soluble metal hydride reagents (sodium borohydride, lithium tributoxy aluminum hydride, sodium bis(2-methoxyethyl) aluminum hydride) favors the alternative reduction pathway to the hydroquinone. 

A similar but smaller intramolecular quenching effect was seen by Phillips and co-workers 44,4S) for 1-vinylnaphthalene copolymers incapable of excimer fluorescence. The monomer fluorescence lifetime of the 1-naphthyl group in the methyl methacrylate copolymer 44) was 20% less than the lifetime of 1-methylnaphthalene in the same solvent, tetrahydrofuran. However, no difference in lifetimes was observed between the 1-vinylnaphthalene/methyl acrylate copolymer 45) and 1-methylnaphthalene. To summarize, the nonradiative decay rate of excited singlet monomer in polymers, koM + k1M, may not be identical to that of a monochromophoric model compound, especially when the polymer contains quenching moieties and the solvent is fluid enough to allow rapid intramolecular quenching to occur. 

The strong dependence of the Si/ICT lifetime on solvent polarity revealed first by transient absorption experiments in the visible region by Bautista et al. [8] was further confirmed by measurement of Si/ICT fluorescence using a streak-camera [11]. The Si/ICT state fluorescence kinetics of peridinin taken at 730 nm in solvents of different polarity are shown in Fig. 2b. The lifetime changes more than one order of magnitude, from 156 ps in n-hexane to 10.5 ps in methanol. In the middle-polarity solvents tetrahydrofuran and 2-propanol, the observed lifetimes are 77 and 54 ps, respectively. In all solvents, kinetic traces could be fitted by a single exponential decay independent of detection wavelength over nearly the entire fluorescence band (650 - 850 nm). The same decay times were also observed in transient absorption [11,12]. 

Salt Solvents Tetrahydrofuran Dimethyl Formamide 1,1 -Dichloroethane... 

Free xanthophylls, both endogenous and present in the saponified samples, are more polar and extract less efficiently into lipophilic solvents. Frequently, the addition of a polar organic solvent (tetrahydrofuran, methylene chloride, diethyl ether) is required to thoroughly extract them from the sample matrix and aqueous phase. 

Hashimoto et al.1 have concluded that reaction (6) (RMgX = EtMgBr) follows third-order kinetics in solvent tetrahydrofuran (THF) and write the mechanism as... 

Aresta and Quaranta focused on the direct synthesis of carbamate esters by the reaction of aliphatic primary amines with alkyl halides in the presence of C02. Under the conditions used (293-353 K 0.1 MPa C02 solvent = tetrahydrofuran (THF), MeOH, PhCH3/CH2Cl2 mixtures), the formation of carbamate ester was... 

Furfural is used in small amounts in some phenol plastics it is a small minor pesticide and an important commercial solvent, ft can be converted into the common solvent tetrahydrofuran and an important solvent and intermediate in organic synthesis, furfuryl alcohol. 

Irradiation of a ferf-butyl alcohol solution of 2-ethoxy-pyrroline-5-one (12) with Vycor filtered light from a 450-W mercury lamp results in formation of ferf-butyl N-(ethoxycyclopropyl) carbamate (13) in 73% isolated yield17,18 When the irradiation is conducted in the non-hydroxylic solvent, tetrahydrofuran, 1-ethoxycyclo-propyl isocyanate (20) can be isolated in 78% yield. Both 13 and 20 can be prepared in synthetically useful quantities. 

These results indicate that the naphthalene radical anion is not stable to the solvent tetrahydrofuran at room temperature on a time scale of 100 hours. Decomposition pathways are alkali metal dependent. Sodium and potassium naphthalene attack THF through a proton abstraction, cycloreversion mechanism, as previously described by Bates for the butyllithium/THF system (27). Lithium naphthalenide attacks the THF not only by the Bates mechanism but also by a nucleophilic ring opening, as is implicit in earlier high temperature work on lithium naphthalenide in THF (28) and in work on the attack of THF by tritylmagnesium bromide (29). The two smaller alkali metals, lithium and sodium, leave behind a... 

Light scattering measurements were carried out on a Brice-Phoenix photometer in three solvents—tetrahydrofuran, toluene, and methyl isobutyl ketone. The values of Hc/t and sin2 0/2 -f- 10c were calculated, where c is concentration, with the aid of a computer. 

Solvent, tetrahydrofuran precipitating agent, petroleum ether. 

A more recent application is the calculation of the absorption and emission spectrum of a pyrenyldeoxyuridine nucleoside model [155] (see Figure 3-8). The interest was here to find an explanation for the stronger pyrenyl emission quenching in the polar solvents (MeCN and MeOH) than in the less polar solvent tetrahydrofuran (THF) [156], This is consistent with the formation of intramolecular Py +/dlT charge transfer (CT) states. 

The reaction can be carried out in two solvents, tetrahydrofuran and 1,2-dime-thoxyethane (DME). DME allows condensations at lower temperatures but also favors the formation of benzocyclobutenoates IV/108. The non-nucleo-... 

Vinyltrimethylsilane (97%), trimethylchlorosilane (98%), chlorodimethylsilane (97%), bromoform (96%), 5-bromo-l-pentene (95%), nBuLi (2.5M solution in hexanes), MeLi (1.6M solution in diethyl ether), n-decane (puriss. p.a., standard for GC, > 99.8%) and hexachloroplatinic(lV) acid hydrate were purchased from Aldrich. Platinum divinyltetramethyldisiloxane complex (Karstedt s catalyst, 3% solution in xylenes), hexamethyl-cyclotrisiloxane (95%), vinylmethyldichlorosilane (97%) and 1,1,3,3-tetramethyldisiloxane (97%) were bought from ABCR. Bromine (puriss) was bought from Eluka. Triethylamine (pure for analysis) and zinc oxide (pure) was purchased from Chempur. Solvents (tetrahydrofurane, diethyl ether, methylene chloride, pentane, ethyl acetate) were supplied by POCh (Polish Chemical Reagents). 

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