Polar solvents methylene chloride

Intersystem crossing rate constants of ortho- and meta-substituted singlet phenylni-trenes are presented in Table 1Mono- and di-o-fluorine substituents have no influence on ISC rate constants.No effect with meta, meta-difluoro substitution is observed either. Pentafluoro substitution has no effect on fcisc in pentane although a modest acceleration is observed in the more polar solvent methylene chloride.i° - i... 

In order to test the above proposition two other experiments were performed (25). One was to use a more polar solvent, methylene chloride (e = 9.73), such that interaction between the charge and its counterion in the dilute regime is weaker. In contrast to P3HT in chloroform, spins are obsoved suggesting that part of the charge is stored in a polaron structure in the ute regime. The oAer concerns a common test used for polyelectrolyte... 

Specific examples illustrate that similar principles affect the absorption spectra. For example, as we have pointed out above, the neutral form of the C-2 benzyl ester is red in MeOH and orange in methylene chloride. Thus it has the spectrum of the ionized form in the polar, protic solvent and of the nonionized form in the nonpolar solvent methylene chloride [248]. The tributyl ammonium salt of the C-2 octyl ester is soluble in solvents ranging from ethanol-water to toluene. Its spectrum in an essentially nonionizing solvent such as toluene is that of the ionized xanthene [249], The spectrum of the pyrillium salt in ethanol is concentration dependent. In dilute solution the compound is totally ionized and is red, whereas in concentrated solution the compound is not fully ionized and the orange form predominates, as predicted by the law of mass action. 

It is for this reason, and because they are generally non-specific and possess an acceptable polarity, that methylene chloride and ethylene chloride are by far the most frequently employed solvents in cationic polymerisation. 

For these reasons, normal-phase SPE does not use polar solvents, such as water or alcohols, but works extremely well with nonpolar solvents such as hydrocarbons (hexane), chlorinated solvents (methylene chloride), or ether solvents (petroleum ether). Thus, normal-phase SPE is a popular method for applications that require the removal of organic analytes from nonpolar... 

Martinez-Oharriz et al. [24] found that Form III of diflunisal is obtained from polar solvents, whereas Forms I and IV are obtained from nonpolar solvents. Likewise, Wu et al. [25] observed that when moricizine hydrochloride is recrystallized from relatively polar solvents (ethanol, acetone, and acetonitrile), Form I is obtained, whereas nonpolar solvents (methylene chloride or methylene chloride/ethyl acetate) yield Form II. 

In liquid-solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett s original work the stationary phase was finely divided CaCOa, but modern columns employ porous 3-10-)J,m particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is... 

Aluminum chloride dissolves readily in chlorinated solvents such as chloroform, methylene chloride, and carbon tetrachloride. In polar aprotic solvents, such as acetonitrile, ethyl ether, anisole, nitromethane, and nitrobenzene, it dissolves forming a complex with the solvent. The catalytic activity of aluminum chloride is moderated by these complexes. Anhydrous aluminum chloride reacts vigorously with most protic solvents, such as water and alcohols. The ability to catalyze alkylation reactions is lost by complexing aluminum chloride with these protic solvents. However, small amounts of these "procatalysts" can promote the formation of catalyticaHy active aluminum chloride complexes. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Dichloromethane (CH2C12, methylene chloride), trichloromethane (CHCI3, chloroform), and tetrachloromethane (CCI4, carbon tetrachloride) are often used as solvents for nonpolar and moderately polar compounds. 

Colostrum or AG-secretions of three different women were separately mixed with Florisil (Merck 1 3 w/w). This material (6 samples) was transferred to a small column that already contained about the same amount of Florisil and enough methylene chloride to cover the two Florisil-batches. Subsequently, organic components adsorbed on the Florisil were eluted with solvents of increasing polarities (hexane to methanol). The fractions were concentrated and analysed by coupled gas chromatography/mass spectrometry (Francke 1988). 

Methylene chloride This solvent is a slightly polar solvent also known as dichloromethane, CH2C12. Its solubility in water is 1.32 g/100 mL. It is denser than water (density = 1.33 g/mL) thus it would be the bottom layer when used with a water solution in a separatory funnel. It may form an emulsion when shaken in a separatory funnel with water solutions. It is not flammable and is considered to have a low toxicity level. 

A solvent-dependent chemoselectivity, pointing to a dependence of the relative reactivities of the 1,2- and 1,1-disubstituted double bonds on solvent polarity and nucleophilicity, has been observed in the reaction of benzeneselenenyl chloride with 2-methylenebicyclo[2.2.1]hept-5-ene (159) which gives products 160-163140. In methylene chloride the reaction occurs with a moderate chemoselectivity, attack on the endocyclic bond being preferred over that on the exocyclic one in a 60 40 ratio. In methanol, the addition is completely chemoselective and the attack occurs exclusively on the endocyclic double bond (equation 132). It may be further noted that 162 and 163 isomerize and solvolyze at high temperatures, leading to the homoallylic products 160 and 161. 

As noted in Table 21, for a given boron ligand there is a small but consistent improvement in aldol diastereoselection when the less polar solvents are employed. This trend is observed for both enolates 60 and 61. In subsequent studies it has been noted that aldol diastereoselection in methylene chloride is comparable to that observed... 

Quaternary ammonium and phosphonium permanganates exist as intimate ion pairs in nonpolar solvents such as methylene chloride and toluene (1). However, in more polar solvents, such as acetone, nmr studies indicate that they are better described as being solvent separated ion pairs (37). In water, these salts separate completely and exist as individual ions. 

Solvent Effects. Information on the effect of solvent polarity of the phase transfer assisted permanganate oxidation of alkenes has been obtained by studying the oxidation of methyl cinnamate by tetrabutylammonium permanganate in tv/o different solvents, acetone and methylene chloride (37). 

Taken together these results suggest that the quaternary ammonium ions must not form closely associated ion pairs in acetone solutions. In this more polar solvent, it appears as if the reactants are present as solvent separated ion pairs and that the rate of reaction is, consequently, not effected by the structure of the quaternary ammonium ion. In methylene chloride solutions, where theory predicts tighter ion pairs (61), the ions must be intimately associated in either (or both) the ground state and the transition... 

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