Cyclohexane, solvent

Diketones can be reduced usually in high selectivity to either an intermediate ketol or thediol (72). Selectivity to the ketol depends in large measure on both catalyst and solvent. In cyclohexane solvent, the maximal yield of ketol obtained on partial hydrogenation of biacetyl fell in the order 5% Pd-on-C (99%), 5% Rh-on-C (92%), 5% Pt-on-C (88%), 5% Ru-on-C (63%) from acetylacelone the descending order was 5% Pd-on-C (86%), 5% Rh-on-C (60%), 5% Ru-on-C(35%), 5% Pt-on-C (27%)(56) from 1,4-cyclohexanedione in isopropanol initial selectivity to the ketol fell in the sequence 5% Pd-on-SiO, (96%), 5% Ir-on-C (95%), 5% Ru-on-C (92%), 5% Pt-on-C (67%) (73). Generalizing from these data, it appears palladium is a good first choice to achieve maximal selectivity. 

Figure 3.24 Resonance Raman Stokes and anti-Stokes difference spectra of the photochemical ring opening of 1,3-cyclohexadiene. Anti-Stokes spectra were obtained with 284-nm pump and probe wavelengths, while the two-color Stokes spectra were generated with a 284-nm probe and a 275-nm pump. The line at 801 cm is due to the cyclohexane solvent. (Reprinted with permission from reference [122]. Copyright (1994) American Chemical Society.)...

Compound (cone. 5 mole %) Cyclohexane Solvent Benzene Pyridine DjO... 

Rate constants for the reaction of thiyl radicals with the t-BuMePhSiH were also extracted from the kinetic analysis of the thiol-catalysed radical-chain racemization of enantiomerically pure (S)-isomer [34]. Scheme 3.2 shows the reaction mechanism that involves the rapid inversion of silyl radicals together with reactions of interest. The values in cyclohexane solvent at 60 °C are collected in the last column of Table 3.5. 

The ligand (S)-N-methylprolinol was used in a 2 1 molar ratio to the Mo02(acac)2 catalyst (1 mol % on the allylic alcohol (43) in the epoxidation of 3-methyl-2-buten-l-ol (43) with cumene hydroperoxide in cyclohexane solvent. 

This work by Jonah et al. is at variance with the study of Beck and Thomas [400] who did not observe the slower rise of fluorescence intensity when scintillator solutions were radiolytically stimulated rather than photoexcited. Bech and Thomas suggested that the scintillator was excited by excitation transfer from excited state cyclohexane solvent... 

An opposite effect is obtained with increasing hydrogen pressure in cyclohexane solvent. Due to the difference in the adsorption constant, PE is more easily displaced than AC by hydrogen, therefore yield in EB decreases as tne hydrogen pressure increases. 

This useful procedure, whereby solvent anisotropy is measured in terms of an S value defined by the ratio t(X)— r(CaHu)/60, where t(X) is the difference in chemical shift between cyclohexane and acetonitrile in solvent X and t(C Hi3) is the analogous difference in cyclohexane solvent, was developed by F. A. L. Anet and G. E. Schenclc, J. Am. Chem. Soc. 93, 556 (1971). 

In addition, studies indicate that Zn(CH3)2 undergoes rapid exchange with Cd(CH3)2, and various postulates concerning the mechanism of this reaction have been made (57, 87). Recent studies of this system in methyl-cyclohexane solvent have clearly shown that the reaction is first order in each of the components and proceeds with an activation energy of 17 kcal/mole (57). This study indicates that the exchange process proceeds through a four-centered transition state... 

Such metal-complexed nitrenes were also generated by the reaction of (tosyliminoio-do)benzene (106) with Mn(m)- or Fe(n)-tetraphenylporphyrin, 107, in a mimic of cytochrome P-450 but with a tosylimino group instead of an oxygen atom on the metals (108) [179]. It was able to functionalize cyclohexane solvent, by nitrogen insertion into a C-H bond to form 109. Furthermore, the metalloporphyrins also catalyzed an intramolecular nitrogen insertion converting 110 into 111 [180]. 

The reaction is found to be zeroth order with respect to a-methylstyrene and approximately first order with respect to hydrogen in all solvents as shown in Table I. Reaction dependence on hydrogen in cyclohexane solvent is shown in Figure 2 and a typical Arrhenius plot is presented in Figure 3. Reaction rate is independent of Pd concentration (structure insensitive) in pure nonpolar solvents (cyclohexane, hexane (U.V.)) but becomes structure sensitive (i.e. dependent on Pd concentration) in solvents with impurities or which are more polar. The activation energy of 10.2 kcal/mol found in cyclohexane agreed well with the one determined by Germain et al. (6). 

Figure 3. Reaction rate as function of reaction temperature in cyclohexane solvent.

Polymers and blends were worked up by evaporating the cyclohexane solvent and massing the polymer on a 140°C roll mill. Films were then prepared by compression molding (5 min at 200°C) or, in one set of experiments, by extrusion through a slit die. Dynamic viscoelastic meas-... 

As we have noted the data reported in Table 7-3 refer to Franck-Condon ICT states it thus becomes interesting to analyze the effects of both the solute and the solvent relaxation. For the apolar cyclohexane, solvent relaxation effects are null whereas they are large for the polar acetonitrile, as shown in Table 7-4 in which we report the evolution of the dipole moment and of the NBO charges of the ICT state of PNA in acetonitrile when we allow both solvent relaxation and solute geometry relaxation. 

At the end of polymerization the mixture was treated with an additional 100 ml of cyclohexane solvent to fluidify the medium, 1 ml of 1M acetylacetone in cyclohexane added to stop the reaction, and A-l,3-dimethylbutyl-A -phenyl-p-phenylenediamine (0.02 g) added as an antioxidant. Polyisoprene was then extracted by steam stripping for 30 minutes in the presence of calcium tamolate. Each extraction was then dried for approximately 18 hours in an oven at 50°C under 200 mmHg vacuum for 72 hours. Reaction scoping results are provided in Table 1. 

Organized media have also been used to influence the regiochemical outcome in the reactions. Photoaddition of 3-n-butylcyclopentenone with various terminal alkenes has shown a pronounced preference for the alignment of the enone and the alkenes with their polar groups toward the surface of the micelle. This effect is most pronounced in the case of 1-acetoxy-I-heptene, which gives exclusively the head-to-tail adduct in cyclohexane solvent but a 2.3 1 mixture in favor of the head-to-head isomer in the presence of potassium dodecyl sulfate (equation 13). 

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