Effect of Solvent Type

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 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. 

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... 

The effect of solvent type was also evaluated in the vibromilling of a polycaprolactam [41]. On milling in methyl alcohol, methanolysis was observed. The percent of residual OMe groups increased with increasing solvent concentration. 

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. 

The details of proton-transfer processes can also be probed by examination of solvent isotope effects, for example, by comparing the rates of a reaction in H2O versus D2O. The solvent isotope effect can be either normal or inverse, depending on the nature of the proton-transfer process in the reaction mechanism. D3O+ is a stronger acid than H3O+. As a result, reactants in D2O solution are somewhat more extensively protonated than in H2O at identical acid concentration. A reaction that involves a rapid equilibrium protonation will proceed faster in D2O than in H2O because of the higher concentration of the protonated reactant. On the other hand, if proton transfer is part of the rate-determining step, the reaction will be faster in H2O than in D2O because of the normal primary kinetic isotope effect of the type considered in Section 4.5. 

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 neutral reactants possess permanent dipoles, the product is ionic, and the transition state must be intermediate in its charge separation, so an increase in solvent polarity should increase the rate. Except for selective solvation effects of the type cited in the preceding section, this qualitative prediction is correct. 

In supported liquid membranes, a chiral liquid is immobilized in the pores of a membrane by capillary and interfacial tension forces. The immobilized film can keep apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10] reported the effects of membrane type (structure and wettability) on the stability of solvents in the pores of the membrane. Examples of chiral separation by a supported liquid membrane are extraction of chiral ammonium cations by a supported (micro-porous polypropylene film) membrane [11] and the enantiomeric separation of propranolol (2) and bupranolol (3) by a nitrate membrane with a A/ -hexadecyl-L-hydroxy proline carrier [12]. 

Once such effects had been noted, it became necessary to interpret the observed results and to classify the solvents. The earliest attempts at this were by Stobbe, who reviewed the effects of solvents on keto-enol tautomers [4]. Since then many attempts have been used to explain solvent effects, some based on observations of chemical reactions, others on physical properties of the solvents, and yet others on spectroscopic probes. All of these have their advantages and disadvantages and no one approach can be thought of as exclusively right . This review is organized by type of measurement, and the available information is then summarized at the end. 

This subject has been associated with the development of the or and type scales almost from the start74 (see Section II.B), but the first paper in which sulfinyl and sulfonyl groups played a part appears to have been one by Taft and coworkers in 196367. The main object of this paper was to study the effect of solvent on the inductive order by 19F NMR measurements on a large number of mcta-substituted fluorobenzenes in a great variety of solvents. The relationship between the NMR shielding parameter and selected systems as equation 10 ... 

In the reaction, it was essential to use an IL as a co-solvent. Lozano, Iborra and co-workers recently reported an interesting stabilizing effect of two types of water-immiscible ILs ([emim][TFSI] and [BuMe3N][TFSI]) for CAL-B-catalyzed transesterification of vinyl butyrate. The synthetic activity and the stability of the enzyme in these IL solvent systems were markedly enhanced as compared to those in hexane. CAL-B maintained its activity higher than 75% after 4 days of incubation in [emim][TFSI] solvent, while it showed an activity of only 25% when incubated in both water and hexane media at 50°C. Comparison of the ratio of a-helix and (3-sheet by CD spectra showed the activity was closely related with a-helix content which reduced to 31% immediately after lipase was added to hexane and had reached only 2% after 4 days in hexane. On the contrary, no significant reduction of a-helix content was... 

An series of alternative, generally parameterized methods for introducing the effects of solvent into semi-empirical calculations are termed SMr, where the value of x represents the type and quality of parameterization27-76 81. These methods have potential value in studying solvation effects on the structure, electronic spectra, and reactivity of biologically... 

Equation 1 implies that solubility is independent of solvent type, and is only a function of the equilibrium temperature and characteristic properties of the solid phase. In real systems the effect of non-ideality in the liquid phase can significantly impact the solubility. This effect can be correlated using an activity coefficient (y) to account for the non-ideal liquid phase interactions between the dissolved solute and solvent molecules. Eq. 1. then becomes [7,8] ... 

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