Nonpolar solvents benzene

This reaction gives us an opportunity to consider the roles of the salt additive, the solvent polarity, the stilbene concentration, the temperature level, and the intensity of potoirradiation. The reaction is facilitated by the replacement of a nonpolar solvent (benzene) by a polar one (acetonitrile), a rise in reaction temperature, an increase in the stilbene concentration, a decrease in the irradiation intensity, or the addition of alkali metal salts. All of these factors intensifying the process are directly related to the mechanism just described. It is substantial enough to analyze the effects of these factors on the efficiency of the photoreaction. 

The effect of the medium on the rates and routes of liquid-phase oxidation reactions was investigated. The rate constants for chain propagation and termination upon dilution of methyl ethyl ketone with a nonpolar solvent—benzene— were shown to be consistent with the Kirkwood equation relating the constants for bimolecular reactions with the dielectric constant of the medium. The effect of solvents capable of forming hydrogen bonds with peroxy radicals appears to be more complicated. The rate constants for chain propagation and termination in aqueous methyl ethyl ketone solutions appear to be lower because of the lower reactivity of solvated R02. .. HOH radicals than of free RO radicals. The routes of oxidation reactions are a function of the competition between two R02 reaction routes. In the presence of water the reaction selectivity markedly increases, and acetic acid becomes the only oxidation product. 

For water at 25 °C, e (which is dimensionless) is 78.5, and for the very nonpolar solvent benzene, e is 4.6. Thus, ionic interactions are much stronger in less polar environments. The dependence on r2 is such that ionic attractions or repulsions operate only over short distances—in the range of 10 to 40 run (depending on the electrolyte concentration) when the solvent is water. 

The simple diastereoselectivity of the photocycloaddition of electronically excited carbonyl compounds with electron rich olefins was studied as a function of the substituent size—at identical starting conditions ignoring the electronic state involved in the reaction mechanism [123], The [2+2] photocycloaddition of 2,3-dihydrofuran with different aldehydes in the nonpolar solvent benzene resulted in oxetanes 118 with high regioselectivity and suprising simple diastereoselectivites the addition to acetaldehyde resulted in 45 55 mixture of endo and exo diastereoisomer, with increasing the size of the ot-carbonyl substituent (Me, Et, i-Bu, t-Bu), the simple diastereoselectivity increased with preferential formation of the endo stereoisomer (Sch. 37). 

When sodium chloride dissolves in water, the H2O molecules orient their dipoles around the Na and Cl ions so that their oppositely charged ends are adjacent to each ion (Figure 15.1). Each sodium or chloride ion in solution is sur-ronnded by many water molecules, lessening the attractions between the ions. Silver chloride, AgCl, does not dissolve in water. Evidently, the ion-dipole attractions are not sufficient to overcome the ion-ion attractions of this solid lattice. The nonpolar solvent benzene, CgHg, cannot dissolve either of these ionic compounds. 

Alkylution of cyclic I J-diketones The reaction of cyclic 1,3-diketones with thallium(l) ethoxidc, thallium(l) carbonate, or thallium(l) cyclopentadienide gives colorless, crystalline thallium(l) salts (2,408). These salts can be alkylated in nonpolar solvents (benzene, DME) to give products of O-alkylation in high yield, as illustrated... 

A detailed study was carried out on (benzophenonylmethyl)-tri- -butylammonium triphenylbutylborate (BTAB). Nano- and picosecond laser photolysis demonstrated electron transfer from the borate counteranion to the excited triplet state of the benzophenone moiety. This leads to formation of a benzophenone moiety and a boranyl radical that dissociates rapidly to form butyl radicals. In the nonpolar solvent benzene the short lifetime of the triplet state (300 ps) suggests an intra-ion-pair process. The addition of 1 % MeCN caused an increase in the triplet lifetime to 1.2 ns, suggesting formation of a solvent-separated ion pair. For a lO" m solution in neat MeCN triplet decay is a function of tetrabutylammonium triphenyl- -butylborate concentration. 

Because both homolytic and heterolytic cleavages readily occurs with C—I bonds, plausible reaction mechanisms can be written with either radical or ionic intermediates. However, in the nonpolar solvent benzene, the radical mechanism is more likely because the ionic mechanism requires the... 

For the determination of benzoylecgonine from plasma, the compound was extracted after basification (pH 9.5) with ethanol-chloroform (20 80), then it was immediately reacted with pentafluorobenzyl bromide and the pentafluorobenzyl-benzoylecgonine partitioned into a nonpolar solvent (benzene) leaving the more polar interfering substances behind. This is the important step in the procedure. 

A waxy solid obtained from roses by extraction with nonpolar solvents (benzene) after trace quantities of solvent have been removed. When the concrete is dewaxed by a properly chosen second solvent (alcohol), the desired essential oil remains. This is called an absolute. See absolute perfume. 

The r-BuOK-catalyzed reaction of a terminal alkyne with cyclohexanone in DMSO to give a tertiary alcohol in 91% yield (eq 47) provides a straightforward illustration of an addition to a carbonyl compound. The same type of addition takes place in the nonpolar solvent benzene but the rate is slower and the yield lower. Treatment of cyclohexanone with ethynylbenzene under the same reaction conditions yields l-(phenylethynyl)cyclohexanol in 83% yield when the reaction is carried out using 1.0 equiv of r-BuOK in the absence of solvent the yield of the tertiary alcohol is 93%. Other aliphatic and aromatic ketones give similar results. Ketones with relatively acidic a hydrogens are capable of undergoing intermolecular aldol additions in the presence of the base but, apparently, the reversibility of this reaction allows the irreversible addition of the acetyUde anion to compete favorably. ... 

SEC) analysis, the star polymer exhibited a bimodal distribution. This was attributed to the strong association effects of the trifunctional initiator in the nonpolar solvent benzene. The problem has been overcome when s-BuOLi was added in the reaction mixture in a ratio of [s-BuIi]/[s-BuOLi] = 2. s-BuOIi was shown to be capable of breaking the initiator association without appreciably affecting the miaostmcture of the PBd chains. Therefore, a well-defined star polymer with low-molecular-weight distribution was obtained. 

One way to protect polymers from solvents is copolymerisation. For example, polystyrene can be attacked by the nonpolar solvent benzene. Copolymerisation with a polar group (for example acrylonitrile) stops the nonpolar... 

Dichloroanthracene absorbs at longer wavelength than simple dienes. It reacts photochemically with 2,5-dimethyl-2,4-hexadiene by two pathways in nonpolar solvents (benzene) a photocycloadduct forms by way of a singlet exciplex, whereas in polar solvents reduction to 9-chloroanthracene is observed and a triplex (C,4H8Cl2 2DMH) is implicated. Experiments with added DjO show that in polar solvent the reduction involved transfer of a proton to the exciplex rather than loss of chloride ion. 

For example, 4-methyl-4-phenyl-2-cyclohexeiioiie upon irradiation yields several products (Scheme 14). Two of these products derive from a triplet of njt character and three of them from a triplet of TiK character. As indicated in the scheme, in the nonpolar solvent benzene, only nJt -derived products are formed whereas in more polar acetonitrile and formamide, Jt7t -derived products are also obtained. 

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