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THF-System

Because the boiling temperature of 1,4-BD is much higher than of the two reaction products and the reaction is irreversible, the bifurcation behavior is only affected by the mass transfer coefficient ratio Kwater/KTHF, if kbd is not extremely high or low. There exists a critical value of Kwater/KTHF = 2.1, above which the stable node branch approaches the THF-vertex. [Pg.142]


The Mark-Houwink equation for the linear polystyrene/THF system at 25 C was determined accurately by W. Graessley et al. We used their equation as follows ... [Pg.256]

We shall discuss now the variation of the three main thermodynamic functions with solvent composition for the case of n-Bu4NBr-water-acetone system and shall extend this discussion to the n-Bu4NBr-water-THF system. Figure 4 and Table IV present the results obtained. The figure was constructed as follows first the standard enthalpy of transfer AH°t, obtained by Ahluwalia and co-workers (12) from pure water to Z2 = 0.30, was used in order to get the standard entropy of transfer function from the relation ... [Pg.316]

The observation of an ESR signal does not necessarily mean dissociation to ion-radicals. The nitrobenzene-THF system gives ESR signals under photoirradiation, but this is due to hydrogen abstraction from THF. [Pg.326]

Reductive cleavage, using the NaCNBHj-HCl-THF system to produce 2 -pro-penylidene acetals, produced the same regioselectivity as that found in benzylidene acetals [27] (Scheme 11), and also for the p-methoxybenzylidene acetals (Scheme 12) [27]. These observations open the way to further strategies for protecting group manipulations. [Pg.61]

Since THF is a much stronger base than ether, (36, 38) it doesn t matter whether gaseous BF3 is used or if it is charged in the form of BF3 etherate. It will very rapidly be present in a bulk THF system in the form of the BF3 THF complex. It is this complex, then, which must... [Pg.538]

Figure 17.2 illustrates our model for splitting water by solar energy. I" is important that all the redox reactions involved in thf system be reversible. The quinone compound in the organic solvent combines the two photocatalytic reactions, and its function can be compared to the electron relaying molecules in thylakoid membranes of chloroplasts. Electron transfer reactions via quinone compouncs in artificia systems have been studied as a model of photosynthesis22-23 and in an electrochemical system for acid concentration.24 ... [Pg.323]

In order to assess the synthetic potential of enzymatic oxidations for organosilicon chemistry, the (hydroxyalkyl)silanes 95, 97 and 99 have been studied for their oxidation (dehydrogenation) with horse liver alcohol dehydrogenase (HLADH E.C. l.l.l.l)79. For this purpose, these compounds were incubated with HLADH in a TRIS-HC1 buffer/THF system in the presence of NAD+. As monitored spectrophotometrically (increase of absorbance of the NADH formed), the (2-hydroxyethyl)silane 97 and the (3-hydroxypropyl)silane 99 were better substrates for HLADH than ethanol, whereas the related (hydroxymethyl)silane 95 was not a substrate under the experimental conditions used. Interestingly, the corresponding carbon analogue 101 was found to be accepted by HLADH. On the other hand, the (2-hydroxyethyl)silane 97 was found to be a better... [Pg.2394]

Carbonyl ylides of type 94 were generated, as illustrated in Scheme 8.28, by irradiating a, (3-unsaturated-y, 8-epoxynitrile 93 in acetonitrile at 254 nm upon trapping with ethyl vinyl ether, these produced THF system 95 with high regioselectivity. [Pg.257]

Residue curve maps of the THF system were predicted for reactive distillation at different reaction conditions (Fig. 4.29). The topology of the map at nonreactive conditions (Da = 0) is structured by a binary azeotrope (unstable node) between water and THF. Pure water and pure THF are saddle nodes, while the 1,4-BD vertex is a stable node. [Pg.134]

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... [Pg.84]

The composition of the solid precipitate which was found in some of the mixtures of the potassium chloride-water-THF system was determined by using Schreinemakers wet residue method (6) as modified by Hill and Ricci (7). [Pg.186]

All such points formed smooth curves when plotted on the three-component triangular graphs used for each system investigated except that of the potassium chloride-water-THF system. In the latter case, two solubility curves appeared which met in an invariant point. The solubility plots are shown in Figures 1, 2, and 3. [Pg.186]

Solid—Liquid Tie-Lines. Tabulated in Table III are the weight percentages of the originally prepared complexes which were chosen as points within the two-phase, solid-liquid region in the potassium chloride-water-THF system. The weight percentages of the saturated solutions for each of the original complexes are presented also in this table. [Pg.187]

Formic acid salts can also be prepared by the reaction of CO2 and II2 with an alkali metal manganese pcntacarbonyK such as NaMn(CO). in an inert solvent [164]. Magnesium format was synthesized directly from CO2, II3 and Mg under mild conditions 165], The catalytic fixation of Hj and CO2 was carried out in the TiCU 2THF/Mg/THF system and the following mechanism has been proposed (Scheme 4). [Pg.186]

On the other hand, the TiCl4-Sm-THF system was applied for the preparation of selenol esters from diaryl diselenides and acid chlorides (Scheme 14) [20]. [Pg.62]

The mechanism of initiation was carehilly studied for the PFs-THF system ). Reichert ) used the P-NMR method and claimed the following set of reactions ) ... [Pg.29]

If p and A (Cl)/Ar(Br) were the only mechanistic tests performed on the ArC=CX— (EtO)3P-THF systems, then it would have been concluded that substitution occurs via intermediate 45. The addition of ethanol to the phenylchloroacetylene reaction produced no phenylacetylene, confirming the supposition that steps (a) (ratedetermining), (c) and (f) occur in the process (equation 260). When phenylbromo-acetylene was treated with triethylphosphite in THF with added ethanol, phenylacetylene was produced. This fact indicates that step (b) of equation (260) occurs in the phenylbromoacetylene reaction. [Pg.405]

The anionic ROP of cyclotrisiloxane in THF initiated with lithium trialkylsilanolate or butyl lithium is our system of choice for the controlled synthesis of functionalized polysiloxanes. The polymerization proceeds in a selective way. The undesired reactions of back biting, chain transfer and terminal unit exchange may be eliminated. The initiation is fast and complete, and the quenching of polymerization by triorganochlorosilanes is fast and clean. The polymerization may be performed at low temperatures, which increases its selectivity [4, 5]. In addition, the SiOLi/THF system tolerates many functional groups in the monomer. [Pg.621]

It should be noted that this reported chemistry was performed with Rieke magnesium prepared by the MgCl2—KI—K—THF system. Rieke magnesium prepared by the safer lithium naphthalenide reduction approach should be expected to give the same or even improved results compared with what is reported here. [Pg.69]

Bezbarua, M. S., Bez, G., Barua, N. C. A facile procedure for the conversion of nitroolefins to carbonyl compounds using the AI-NiCl2.6H20-THF system. Chem. Lett. 1999, 325-326. [Pg.637]


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