Chloroform solvent properties

The solvent dependence of the reaction rate is also consistent with this mechanistic scheme. Comparison of the rate constants for isomerizations of PCMT in chloroform and in nitrobenzene shows a small (ca. 40%) rate enhancement in the latter solvent. Simple electrostatic theory predicts that nucleophilic substitutions in which neutral reactants are converted to ionic products should be accelerated in polar solvents (23), so that a rate increase in nitrobenzene is to be expected. In fact, this effect is often very small (24). For example, Parker and co-workers (25) report that the S 2 reaction of methyl bromide and dimethyl sulfide is accelerated by only 50% on changing the solvent from 88% (w/w) methanol-water to N,N-dimethylacetamide (DMAc) at low ionic strength this is a far greater change in solvent properties than that investigated in the present work. Thus a small, positive dependence of reaction rate on solvent polarity is implicit in the sulfonium ion mechanism. 

How well can continuum solvation models distinguish changes in one or another of these solvent properties This is illustrated in Table 2, which compares solvation energies for three representative solutes in eight test solvents. Three of the test solvents are those shown in Table 1, one is water, and the other four were selected to provide useful comparisons on the basis of their solvent descriptors, which are shown in Table 3. Notice that all four solvents in Table 3 have no acidity, which makes them more suitable, in this respect, than 1-octanol or chloroform for modeling biomembranes. Table 2 shows that the SM5.2R model, with gas-phase geometries and semiempirical molecular orbital theory for the wave function, does very well indeed in reproducing all the trends in the data. 

Finally, inspection of Table 3.2 shows also that there are cases in which Yu can be even smaller than 1. An example is a solution of diethylether in chloroform. Here, the solute is an electron donor (H-acceptor), while the chloroform solvent is an electron acceptor (H-donor). In this case, the solute and solvent both acquire additional inter-molecular interactions that were unavailable to them in their pure liquid forms. The monopolar diethylether (only vdW interactions in its pure liquid) can add polar interactions to its vdW attractions with the molecules of the monopolar chloroform solvent exhibiting a complementary electron acceptor property. 

These substances have excellent solvent properties for nonpolar and slightly polar substances. Chloroform once was used widely as an inhalation anesthetic. However, it has a deleterious effect on the heart and is oxidized slowly by atmospheric oxygen to highly toxic carbonyl dichloride (phosgene, COCl2)-Commercial chloroform contains about 1% ethanol, which destroys any COCl2 formed by oxidation. 

Chloroform (trichloromethane, CHClj). Chloroform was first used as an anaesthetic in 1847 and its narcotic effects on the central nervous are well documented (ref. 4la). It has important applications as an intermediate in the chemical synthesis of a large number of industrial chemicals chlorofluorocarbons, dyes, drugs and pesticides. Its powerful solvent properties and low boiling point (6l°C) have made it a favorite for extractive and purification operations in preparing antibiotics, alkaloids, flavors and vitamins. 

Before discussing the actual pumps, let us consider the mobile phase and its requirements. The mobile liquid must be very pure, and special chromatographic grades are available for most common solvents, including water. Some solvents are routinely stabilized with small amounts of chemicals that can significantly alter their solvent properties for LC use and may absorb in the UV. For example, chloroform is often stabilized with ethanol or pentene. Even particulate matter finds its way into pure solvents requiring the use of a filter in the intake line from the solvent reservoir. 

In contrast, the most common industrial halo-genated solvents such as methylene chloride, chloroform, perchloroethylene, and carbon tetrachloride have long been identified as suspected human carcinogens. Benzene and other aromatic hydrocarbons have also been associated with the causation or promotion of cancer in humans and animals. All of these substances are widely used because of their excellent solvent properties in a wide range of applications. Nevertheless, regulations have been issued in the United States, for example (under the Clean Air Act) to control many of these chemicals... 

Chloroform. The properties of chloroform dissolved in basic solvents furnish a most interesting example. There is a body of opinion on the side that the relatively weak interactions of chloroform should not be classified as H bonds but rather should be attributed to the less specific effects of a polar solvent (e.g., see 349, 347). With reference to the theory of H bonding the case is important because C—H compounds are not usually listed as H bonding acids. 

Tri-n-butyl phosphate (TBP) is a reactive extractant that has been widely used in the processing of heavy metal ores and spent fuel elements [53]. It is often mixed with a diluent to improve solvent properties (e.g., to reduce viscosity or to control its extraction power). Such diluents include paraffins such as Amsco 125-82 and n-heptane, benzene, and, to a lesser extent, chloroform and carbon tetrachloride. 

Polyvinyl acetate Methanol, Acetone, Chloroform Mechanical properties of the films depended on the solvent and the time of exposure of film at each temperature CHCl was recommended. Mechanical tests [Olayemi and Adeyeye, 1982]... 

Pyridine is highly toxic (OES-TWA 5 ppm) and it is likely that on any plant where it is handled very stringent steps are taken to avoid harm to operatives. In these circumstances the use of an entrainer or an extraction solvent which would not be considered in other circumstances could be evaluated. Chloroform has good solvent properties, as has monochlorobenzene, and both have a significantly lower fire hazard. 

Small amounts of other solvents are added to obtain the desired retention, increase solubility, and improve resolution. Chlorinated solvents (e.g., chloroform, dichloromethane) are frequently used for this purpose on account of their good solvent properties and effects on selectivity, although these solvents can be contaminated with traces of HCl. Other solvents used as modifiers are THF, ethyl acetate, hexane, acetone, and water. In some cases, methanol has been added to an acetonitrile-based mobile phase. Craft [100] investigated nine solvent modifiers and found THF to be the most beneficial modifier of methanol. Analysts tend to... 

The above theories invoke essentially the physical properties of the grafting system to explain the observed copolymerization phenomenon. Swelling either from the solvent or monomer or both is also an important factor in these reactions. However if the data in Figures 1 and 2 are considered, a further theory would appear to be necessary to explain the solvent properties observed, especially the trend in the alcohol data to n-octanol and also the benzene, pyridine, chloroform and carbon tetrachloride results. Thus, as previously proposed for radiation grafting processes, it is necessary to consider the radiation chemistry of the system and in particular the radiolysis products of the solvent in any complete analysis of the copolymerization process. It has been suggested that a contribution to the mechanism of the acceleration effect of methanol can be due to the radiolytic scavenging properties of styrene and hence the relative numbers of styrene... 

Poly(4,4 -dibutoxy-2,2 -bithiophene) and poly(3,3 -dibutoxy-2-2 -bithio-phene) are only partially soluble in common organic solvents, in contrast to asymmetrically disubstituted PBTs like poly(3-butoxy-3 -decyl-2,2 -bi-thiophene) and poly(4-butoxy-4 -decyl-2,2 -bithiophene), which are completely soluble in chloroform. The properties of these asymmetrically disubstituted PBTs are intermediate between those of PAT and poly(dialkyloxy-2,2 -bi-thiophene) [526, 528]. Poly(3-styrylthiophene) films deposited on the anode surface by electropolymerization have conductivites of the order of 10" S cm" and are redox inactive [529]. 

The treatment chemistry of the MMD is based on (1) the hydrolysis of HD and GB with monoethanolamine (MEA) and water or (2) the hydrolysis of VX with MEA-aqueous sodium hydroxide solution. MEA was chosen as the reagent based on previous experience with it in Russian chemical demilitarization programs. The advantages of MEA include good solvent properties for agents, miscibility with water, noncorrosivity to stainless steel under operating conditions, and low flammability. MEA cannot be used in the RRS because it reacts violently with chloroform, the solvent present in many CAIS items. 

The data are reproduced in Table 1.2, below. Note that chloroform seems to be the best solvent, but recall also that it can readily be deprotonated. Dichloromethane and 1,2-dichloroethane seem to be about equally effective in solvating the salts, but methylene chloride is less prone to undergo substitution than dichloroethane, although the latter s higher boiling point can be an advantage. We also note that in at least one case, special solvent properties have been attributed to ethyl acetate [56]. 

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