Effect of Solvent Type on

Some peroxides can be attacked and directly decomposed by the action of solvents. In general ti for an initiator is increased in the presence of solvents in order of chemical type, as shown below. 

Alcohols ethers aliphatic hydrocarbons aromatic hydrocarbons halogenated solvents. 

Factors of two or three between t, in the different solvents are not uncommon. 

Increasing pressure tends to increase t. Under normal polymerisation conditions, the effect of pressure is insignificant when compared with the effect of temperature on free radical generation. However, where gaseous monomers are involved, the polymerisation is often carried out under conditions of high pressure, and the effect of pressure on tv becomes more relevant. 

In practice, an initiator with a t in the range 30 minutes - 2 hours, is preferred for commercial processes. 

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The percent denitrogenation data is shown in Figure 12 on a fresh catalyst basis corrected for catalyst deactivation. Here the effect of solvent type on nitrogen removal is easily observed. The denitrogenation improved with the higher initial boiling solvents. The 580-850°F solvent showed a 7% improvement, the 660-850°F solvent a 13% improvement, and the 740-850°F solvent a 28% improvement when compared to the 500-850°F solvent. 

The effect of solvent type on the curing rate of epoxy reactions has been well defined. Hydroxyl compounds, such as alcohols, act as catalysts and accelerate curing. However, these solvents are not serious competitors with amines for reacting with the epoxy ring. Water, functioning as a hydroxyl compound, also accelerates the reaction, even more than alcohols. Aprotic solvents, such as aromatic hydrocarbons or mineral spirits, have no effect on the amine-epoxy resin and behave as inert diluents. Carbonyl solvents, such as acetone and methyl ethyl ketone, retard the reaction. 

FIGURE 6.2 Effect of solvent type on the pot life of a hydrogenated bisphenol A diglycidyl ether cured with a polyamide.5... 

NOVEL MATERIALS IN HETEROGENEOUS CATALYSIS Table III. Effect of Solvent Type on Product Yields at 450 C Using Ammonium Tetrathiomolybdate ... 

Shukla, J.P., Kumar, A., and Singh, R.K., Effect of solvent type on neutral macrocycle facilitated transport of uranyl ions across supported liquid membranes using dicyclohexano 18-crown-6 as carrier. Radiochim. Acta, 1992, 57 185-194. 

Table 2 Summary of Some Representative Studies on Effects of Solvent Types on Polymer Degradation... 

Unfortunately, few data are available to determine unambiguously the effect of solvent type on the condensation rate. Artaki et al. [89] investigated the effects of protic and aprotic solvents on the growth rates of polysilicates prepared from TMOS (/ = 10) with no added catalyst (pH measured immediately after mixing the reactants equalled 6-7). Using Raman spectroscopy and molybdic acid reagent methods (see, e.g., ref. 1), qualitative information related to the size of the polysilicate species was obtained as a function of the reduced time, r/fgeii for five solvent systems methanol, formamide, dimethylformamide, acetonitrile, and dioxane. Table 9 lists the stabilized... 

Before run ti in g a molecu lar dyn am ics sim ulatioti with solvent and a m olccular median ics meth od, choose the appropriate dielectric con Stan i. You specify th e type an d value of th c dielectric con slari t in thehorce hield Option s dialog box. ITi e dielectric con star t defines the screen irig effect of solvent molecules on nonbonded (electrostalic) in teraction s. 

Before running a molecular dynamics simulation with solvent and a molecular mechanics method, choose the appropriate dielectric constant. You specify the type and value of the dielectric constant in the Force Field Options dialog box. The dielectric constant defines the screening effect of solvent molecules on nonbonded (electrostatic) interactions. 

Scheme 4.4. Effect of Solvent Polarity on Reactions of Various Charge Types...

Effect of resin type on heat resistance of solvent-borne CR adhesives... 

The paddle mill was used to study the effect of surfactant type on a solvent-aqueous-surfactant extraction scheme for the recovery of bitumen from Athabasca tar sand. n the experiments of Figures 4,5 and 6, bitumen recovered from the surface phases was measured as a function of the mole fraction of ethylene oxide in the surfactant and as a function of the extraction step in which the surfactant was added. The results are reported as the % of the total bitumen present in the surface fraction. The amount of surfactant used was that required to give a final aqueous concentration of 0.02% (w/v), but in different sets of experiments the surfactant was added at various stages in the process. 

The use of tailor made additives holds great promise in the area of crystal growth and morphology control. The routine selection and use of these type of additives will require a fundamental understanding of the mechanism which the additives work on a molecular basis. At the same time, the effect of solvent molecules on the crystal growth process is another related and important problem. In both instances, the relationship between internal aystal structure, aystal growth rate, solvent and impurities are needed to predict the habit of a crystal and thus allow seleaion of the proper conditions and components required to obtain a desired habit... 

The condensation reactions of silanols are catalyzed by acids [19, 25-27,63—68, 72], Grubb measured the hydrogen chloride catalyzed silanoi condensation reaction of trimethylsilanol in methanol [19]. Lasocki and Michalska studied the effect of acid type on the condensation of dialkylsilanediols in dioxane [68]. Under anhydrous conditions, the rate of acid catalysis by strong acids (such as hydrogen bromide and perchloric acid) was directly related to the acid concentrations. The catalytic effects of weaker acids, such as hydrogen chloride, were not linearly related to the concentration. They postulated that in anhydrous dioxane, the strong acids were completely ionized while the weaker acids were not [68]. When small amounts of water were added to the solvent, all the acids behaved in a similar manner. Lasocki [64-67] extended the studies to examine the effects of alkyl or aryl substitution of silanediols on the condensation rate in aqueous dioxane [64-67]. The rate constants for acid catalyzed condensation of... 

These predictions of effect of solvent polarity on reaction rates were first made by Hughes and Ingold in 1935. They searched the literature of direct displacement reactions and found that for charge types 1-3 the experimental facts agreed with their predictions. For example, the reaction of ethyl iodide with triethylamine (Equation 4.9) an SN2 displacement of type 2, does proceed more... 

The effect of solvent type and aminosilane concentration has been evaluated. The third component in the reaction system is the silica substrate. The surface of the silica gel carries the active sites for adsorption. The concentration of these sites varies with varying silica type, its specific surface area and pretreatment temperature. Additionally, surface adsorbed water has a clear effect on the reaction mechanism. Isotherm data, reported in the previous paragraph, only accounted for fully hydrated or fully dehydrated silica. The effect of the available surface area and silanol number remains to be assessed. Information on these parameters allows the correlation of data from studies in which different silica types have been used. In this part the effect of these parameters in the loading step is discussed. Silica structural effects on the ultimate coating, after curing, are evaluated in the next paragraph. 

Two types of solvent effects have been determined for prolyl isomerization and amide rotation (1) the effect of solvent deuterium on reaction rate and (2) the effect of organic solvents on reaction rate. Solvent deuterium isotope effects are useful tools in probing the role of proton transfer... 

The Effect of Solvent and Solute Concentration. The effect of solvent concentration on selectivity is qualitatively described by three types (2, 11) shown in Figure 3. 

These Hughes-Ingold rules can be used for making qualitative predictions about the effect of solvent polarity on the rates of all heterolytic reactions of known mechanisms. For nucleophilic substitution reactions of types (5-11) and (5-12)... 

In this study, three types of solvents, alcohol, ketones and alkane were used to study the effects of solvent polarity on hydrogenolysis activity. As shown in Table 4 the debenzylation (hydrogenation) reaction is favored by the use of high polarity (high dielectric constants, e) solvents. Under the same reaction conditions, methanol (with the highest dielectric constant) is the best solvent among the three alcohol solvents for N-phenylbenzylamine (NPBA) conversion. Table 4 also shows that under the same reaction conditions, using non-polar solvent cyclohexane (dielectric constant e is 2.02 at ambient temperature), results in low NPBA conversion, 27.1%. 

In summary, we are primarily concerned with two classes of reactions (/) bimolecular reactions with a steep chemical barrier or possibly a steric constraint to reaction, and (2) recombination reactions in which motion of the atoms in the strongly attractive well must be treated. In both instances we assume that only the strongly repulsive solute-solvent and solvent-solvent forces need to be taken into account. We present a type of kinetic theory that is capable of handling more general cases, but the two reaction classes suffice to illustrate the use of the theory without overly elaborate calculations. Our goal is a detailed treatment of the effects of solvent dynamics on the reaction. 

As with other chiral stationary phases, dispersive interactions with the cyclodextrin structure are controlled with polar solvents, polar interaction controlled with dispersive solvents and, if ionic interactions are present, these will be controlled by both the pH and the type of buffer that is employed. Small changes in pH can be quite critical and a the effect of buffer type on chiral selectivity, under certain circumstances can be quite profound, an example of the effect of pH and buffer type is depicted in figure 8.20. 

There are two cases to consider when predicting flie effect of solvent polarity on copolymerization propagation kinetics (1) the solvent polarity is dominated by an added solvent and polarity is thus independent of the comonomer feed ratio, or (2) the solvent polarity does depend on the comonomer feed ratio, as it would in a bulk copolymerization. In the first case, the effect on copolymerization kinetics is simple. The monomer reactivity ratios (and additional reactivity ratios, depending on which copolymerization model is appropriate for that system) would vary fi om solvent to solvent, but, for a given copolymerization system they would be constant as a function of the monomer feed ratios. Assuming of course that there were no additional types of solvent effect present, fliese copolymerization systems could be described by their appropriate base model (such as the terminal model or the explicit or implicit penultimate models), depending on the chemical structure of the monomers. 

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