Toluene- system

Another issue important to the success of this chiral titanium reagent 31 was the discovery of a marked solvent effect. When the fumaric acid derivative is reacted with isoprene in the presence of 10 mol% of the titanium reagent 31 in toluene, poor optical purity results (36-68% ee). Interestingly the optical purity of the adduct greatly increased in the order benzene, toluene, xylenes, and mesitylene, with 92% ee obtained in the last. Mesitylene is difficult to remove, because of its high boiling point, and other solvents were screened in detail. As a result, the mixed solvent system toluene petroleum ether (1 1) was discovered to be very effective. 

A special technique was necessary to obtain good yields of ethyl pyrrole-3-acetate from ethyl pyrrole-3-glyoxalate. Reduction over W-7 Raney Ni in 50% aq ethanol was accompanied by major ring reduction and tarring. By use of a two-phase system, toluene and 50% aq ethanol, these side reactions could be curtailed. Apparently the desired product was removed effectively from the aqueous layer into the toluene as soon as it was formed (26). 

In contrast to oxoesters, the a-protons of thioesters are sufficiently acidic to permit continuous racemization of the substrate by base-catalyzed deprotonation at the a-carbon. Drueckhammer et al. first demonstrated the feasibility of this approach by performing DKR of a propionate thioester bearing a phenylthiogroup, which also contributes to the acidity of the a-proton (Figure 4.14) [39a]. The enzymatic hydrolysis of the thioester was coupled with a racemization catalyzed by trioctylamine. Owing to the insolubility of the substrate and base in water, they employed a biphasic system (toluene/H2O). Using P. cepacia (Amano PS-30) as the enzyme and a catalytic amount of trioctylamine, they obtained a quantitative yield of the corresponding... 

The interaction of carotenoids with cigarette smoke has become a subject of interest since the results of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group 1994 (ATBC) and CARET (Omenn et al. 1996) studies were released. P-Carotene has been hypothesized to promote lung carcinogenesis by acting as a prooxidant in the smoke-exposed lung. Thus, the autoxidation of P-carotene in the presence of cigarette smoke was studied in model systems (toluene) (Baker et al. 1999). The major product was identified as 4-nitro-P-carotene, but apocarotenals and P-carotene epoxides were also encountered. 

Shang et al. [7] studied the effect of different additives (NaAc, NaOH, NaCl, NH4Ac) on analyte signal intensity and they found that the relative intensity of NPEO adduct ions may be enhanced by all additives, but NaAc produced the most abundant adduct ions for the entire ethoxylate series with good reproducibility. Additionally, the intensity of adducts, especially for mono- and diethoxylates was found to depend on reaction time prior to LC-ESI-MS analysis and concentration of NaAc. They recommended 0.5 mM NaAc for normal-phase separation with solvent system toluene-MeOH-water. In reversed-phase systems the highest abundance of sodium adducts for NPEOs ( iEO = 1-10) was observed at concentrations higher than 10 xM, while any further increase in concentration had very low influence on signal intensity [10,11],... 

Figures 8 and 9 show, by way of examples, the I.B. spectra of the ternary systems toluene-HCl-GaCls and m-xylene-HCl-GaCla. The pronounced changes can be interpreted if the formation of a proton addition complex is assumed. A detailed discussion of the I.B. spectra...

Fio. 8. I.R. spectra of toluene (broken line) and of its proton addition complex (solid line) in the system toluene-GaCls-HCl at 77°K. (Perkampus and Baumgeu ten, 1964a.)... 

Utilization of zeolite acidic strength in Cg-aromatics (xylens) systems is illustrated next. In the presence of strong acids, xylene isomers have varying basicity (Table 6.5), with m-xylene being the most basic and p-xylene the least basic among the Cg-aromatics [27]. Based on the basicity of the xylenes, the acidity of each zeolite can be properly adjusted to selectively adsorb m-xylene or p-xylene. As demonstrated in Figure 6.4, a more acidic zeolite such as NaY will selectively adsorb m-xylene from other Cg-aromatics [28, 29], In contrast. Figure 6.5 shows that a weaker acidic zeolite such as KY will selectively adsorb p-xylene from other Cg-aromatics [30, 31]. In both systems, toluene was used as the desorbent. 

A process performance study has been conducted by David et al. [47] taking the coupling of pervaporation with the esterification reactions of 1-propanol and 2-pro-panol with propionic acid as a model system. Toluene sulfonic acid was appHed as the homogeneous acid catalyst A PVA-based composite membrane from GFT was used. Fig. 13.5 shows the comparison between the esterification reaction with and without pervaporation. Without pervaporation, the conversion factor reaches a hm-it, which corresponds to the equihbrium of the esterification reaction. Coupling of the esterification to pervaporation allows the reaction to reach almost complete conversion. 

Figure 9.7a shows values of stable drop diameters that are calculated with Eqs. (9.3) and (9.4) for special conditions for the liquid system toluene-water as a function of the product of pulse amplitude, a, and frequency, /, the so-called pulse intensity. Figure 9.7b is a parity plot and shows that Eq. 9.4 describes the measured drop sizes for a wide range of velocities and parameters of the sieve tray geometry quite well. 

Clear-cut evidence on the intermolecular nature of the excitation step and the need for in-cage radical annihilation has been gained from a study on the solvent-cage effect in the peroxyoxalate reaction. The viscosity effect on the singlet quantum yields was verified using the binary solvent system toluene-diphenyhnethane. A rise in solvent viscosity from 0.50 cP (toluene) to 2.67 cP (diphenylmethane) leads to an up to tenfold increase in the quantum yields, demonstrating the intermolecular nature of the excitation step. 

Thus, an opposite sense of asymmetric induction was found in the solvent system toluene/HM-PA compared to toluene/ tetrahydrofuran, dioxolane or trimethylamine. Optimized conditions for each electrophile are tetrahydrofuran for iodomethane, dioxolane for allyl and benzyl bromide, and trimethylamine for methyl bromoacetatel8. Starting from a-substituted fl-oxo esters, quaternary asymmetric centers arc generated (see Table 6). 

Solvent acetone Solvent system toluene/ethyl acetate (97 3)... 

A diastereomeric guanidine-bisthiourea bifunctional organocatalyst gives high ees (g) and des in nitroaldols in a biphasic system toluene-water at 0°C.146... 

A nonagueous medium was chosen in this procedure, as in the work of Gangneux et al (11), to inhibit diffusion of CAS out of the fiber, thus lessening homopolymer formation in the solution, and to increase the availability of the acrylic acid. Selective experiments were performed to examine the potential of homopolymer formation. A mixture of CAS solution, water and acrylic acid was found to form homopolymer throughout whereas a mixture of CAS solution, toluene and acrylic acid formed homopolymer only in the aqueous CAS phase. This offers evidence of the advantages of using a two phase system. Toluene was used instead of benzene, as employed in the French work (11), for safety considerations. 

Julia, S., Masana, J. and Vega, J. C. Synthetic enzyme highly stereoselective epoxidation of chalcone in the three-phase system toluene-water-poly-(5)-alanine, Angew. Chem., 1980, 92, 968-969. 

A typical experimental phase diagram for the system toluene-benzene is sketched in Figure 34.4 from which it can be seen that this diagram corresponds exactly in form to a superposition of the liquid and vapour curves derived in Figures 34.2 and... 

Fig. 10.17. Simulated and experimental Sauter diameters in RDC columns with (C—>D D— C) and without mass transfer (system toluene/acetone/water at 298 K).

In contrast, anodic cyanation of diphenylacetylene occurs exclusively at the aromatic ring and the triple bond remains intact 4-cyanodiphenylacetylenc is formed in 60% yield. The reaction was run at 2 V (vs. S.C.E.) for 3-9 F mol" using a platinum anode in methanol containing sodium cyanide. Anodic cyanation results in preferred attack at the aromatic nucleus in other systems toluene, mesitylene and hexamethylbenzene give nuclear substitution and little side-chain cyanation under similar conditions in contrast with the corresponding acetoxylation or methoxylation reactions. 

Suzuki-type C-C-coupling reactions (cf. Section 2.11) with Pd phosphine complexes as catalysts can also be promoted by amphiphiles in an aqueous biphasic system (toluene/water). The amphiphile should have a phase-transfer function, with the best effect being observed with micelle-forming amphiphiles [27]. 

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