Nature of the Solvent

The chemical polymerization of aniline at the interface between two immiscible solvents provides an attractive alternative route to PAn s. Such interfacial polymerization was first demonstrated in 1994 by Michaelson and McEvoy,82 who produced a freestanding PAn film at the interface between a solution of aniline/sodium dodecylsulfate in carbon tetrachloride and an aqueous oxidant solution containing ammonium persulfate/HCl. The analogous interfacial polymerization of a range of /V-alkylanilincs and o-alkylanilines using hexane and water phases for chemical oxidation with ammonium persulfate has also been briefly described.83 

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The use of Henry s constant for a standard-state fugacity means that the standard-state fugacity for a noncondensable component depends not only on the temperature but also on the nature of the solvent. It is this feature of the unsymmetric convention which is its greatest disadvantage. As a result of this disadvantage special care must be exercised in the use of the unsymmetric convention for multicomponent solutions, as discussed in Chapter 4. 

According to the nature of the solvent employed, the yields and constitutions of the asphaltenes are different. In the United States, asphaltenes are obtained by precipitation from normal pentane. 

Drying of crystals. Whenever possible crystals should be dried in a smdl vacuum desiccator containing a suitable desiccant. The latter depends upon the nature of the solvent used c/. p. 19). However for most purposes anhydrous calcium chloride is satisfactory. If a hydrocarbon has been used in the recrystallisation, a few thin fresh shavings of paraffin wax are efficacious. 

It seems now established by NMR spectroscopic investigations that a change can take place in electronic structures and atomic configuration of the dyes depending on the polarity of the solvent. Parameters describing the transition from one single bond to more double bond character vary according to the nature of the solvent (107). 

This suggests that polymerizations should be conducted at different ratios of [SX]/[M] and the molecular weight measured for each. Equation (6.89) shows that a plot of l/E j. versus [SX]/[M] should be a straight line of slope sx Figure 6.8 shows this type of plot for the polymerization of styrene at 100°C in the presence of four different solvents. The fact that all show a common intercept as required by Eq. (6.89) shows that the rate of initiation is unaffected by the nature of the solvent. The following example examines chain transfer constants evaluated in this situation. 

The nature of the solvent is as important as the polymer in determining , as is apparent from the wide range of values for poly (dimethyl siloxane) in different solvents. 

The liquid medium is assumed to be continuous. This makes the results suspect when applied to spheres which are so small that the molecular nature of the solvent cannot be ignored. 

This relationship with a = 1 was first proposed by Staudinger, but in this more general form it is known as the Mark-Houwink equation. The constants k and a are called the Mark-Houwink coefficients for a system. The numerical values of these constants depend on both the nature of the polymer and the nature of the solvent, as well as the temperature. Extensive tabulations of k and a are available Table 9.2 shows a few examples. Note that the units of k are the same as those of [r ], and hence literature values of k can show the same diversity of units as C2, the polymer concentration. 

Under 0 conditions occurring near room temperature, [r ] = 0.83 dl g for a polystyrene sample of molecular weight 10. f Use this information to evaluate tg and for polystyrene under these conditions. For polystyrene in ethylcyclohexane, 0 = 70°C and the corresponding calculation shows that (tQ /M) = 0.071 nm. Based on these two calculated results, criticize or defend the following proposition The discrepancy in calculated (rQ /M) values must arise from the uncertainty in T>, since this ratio should be a constant for polystyrene, independent of the nature of the solvent. 

Chemical Equilibria. In many cases, mass transfer between two Hquid phases is accompanied by a chemical change. The transferring species can dissociate or polymerize depending on the nature of the solvent, or a reaction may occur between the transferring species and an extractant present in one phase. An example of the former case is the distribution of benzoic acid [65-85-0] between water and benzene. In the aqueous phase, the acid is partially dissociated ... 

Donoi—acceptoi chromogens in solution are often strongly affected by the nature of the solvent or the resinous substrate in which they are dissolved. The more polar the solvent or resin, the longer the wavelength of the fluorescent light emitted. Progressing from less polar to more polar solvents, the bathochromic, or reddening, effect of the solvents on the dye increases in the order of aUphatics < aromatics < esters < alcohols < amides. 

Nuclear Magnetic Resonance. The nmr spectmm of aromatic amines shows resonance attributable to the N—H protons and the protons of any A/-alkyl substituents that are present. The N—H protons usually absorb in the 5 3.6—4.7 range. The position of the resonance peak varies with the concentration of the amine and the nature of the solvent employed. In aromatic amines, the resonance associated with N—CH protons occurs near 5 3.0, somewhat further downfield than those in the aliphatic amines. 

The ortho para isomer ratio depends on several factors, including the nature of the diazo component, the nature of the solvent, the pH of the medium, the temperature of coupling, the presence of catalysts, and the position of substituents. Simple benzenediazonium compounds couple to... 

In mordant dyes, phenols, naphthols, and enolizable carbonyl compounds, such as pyrazolones, are generally the couplers. As a rule, 2 1 metal complexes are formed ia the afterchroming process. A typical example of a mordant dye is Eriochrome Black T (18b) which is made from the important dyestuff iatermediate nitro-l,2,4-acid, 4-amiQO-3-hydroxy-7-nitro-l-naphthalenesulfonic acid [6259-63-8]. Eriochrome Red B [3618-63-1] (49) (Cl Mordant Red 7 Cl 18760) (1, 2,4-acid — l-phenyl-3-methyl-5-pyrazolone) is another example. The equiUbrium of the two tautomeric forms depends on the nature of the solvent. 

Some 4,5-disubstituted pyridazines exhibit ring-chain isomerism involving heterospiro compounds. For example, 5-(o-aminophenylcarbamoyl)pyridazine-4-carboxylic acid exists in a zwitterionic form in the solid state, but in a solution of DMSO it is almost exclusively 3, 4 -dihydro-3 -oxospiro[pyridazine-5(2//),2 (l //)-quinoxaline]-4-carboxylic acid (134). The equilibrium is strongly influenced by the nature of the solvent, the substituents on the pyridazine ring and the nucleophilicity of the group attached to the phenyl ring (Scheme 48) <80JCS(P2)1339). 

All stated pK values in this book are for data in dilute aqueous solutions unless otherwise stated, although the dielectric constants, ionic strengths of the solutions and the method of measurement, e.g. potentiometric, spectrophotometric etc, are not given. Estimated values are also for dilute aqueous solutions whether or not the material is soluble enough in water. Generally the more dilute the solution the closer is the pK to the real thermodynamic value. The pK in mixed aqueous solvents can vary considerably with the relative concentrations and with the nature of the solvents. For example the pK values for V-benzylpenicillin are 2.76 and 4.84 in H2O and H20/EtOH (20 80) respectively the pK values for (-)-ephedrine are 9.58 and 8.84 in H2O and H20/Me0CH2CH20H (20 80) respectively and for cyclopentylamine the pK values are 10.65 and 4.05 in H2O and H20/EtOH (50 50) respectively. pK values in acetic acid or aqueous acetic acid are generally lower than in H2O. 

The properties of the varnish, such as the nature of the solvent and the viscosity and resin content of the varnish. 

The pK values determined are influenced by the solvent and other conditions of the measurement. The nature of the solvent in which the extent or rate of deprotonation is determined has a significant effect on the apparent acidity of the hydrocarbon. In general. 

Generally, the stereochemistry of the products obtained on hydrogenation of isolated olefins is not affected by the nature of the solvent. However, an example of product dependence on the nature of the reaction medium which... 

The product stereochemistry obtained on hydrogenation of a, -unsaturated ketones is generally the same as that observed on saturation of the corresponding desoxy olefin. However, the stereochemistry of hydrogenation of these polarized species can be affected by the nature of the solvent (see section II-C). 

The behavior of simple and molecular ions at the electrolyte/electrode interface is at the core of many electrochemical processes. The complexity of the interactions demands the introduction of simplifying assumptions. In the classical double layer models due to Helmholtz [120], Gouy and Chapman [121,122], and Stern [123], and in most analytic studies, the molecular nature of the solvent has been neglected altogether, or it has been described in a very approximate way, e.g. as a simple dipolar fluid. Computer simulations... 

Halofluoroalkenes may be prepared by using fluorodihalomethanes or fluoro-halomethanes in olefination procedures similar to those descnbed above. Ruoro-trichloromethane treated with tris(dimethylamino)phosphine forms the corresponding phosphomum salt, which can then be used in the Wirtig procedure. The reaction depends on the nature of the solvent in tetrahydrofuran, little olefination if any occurs however, when benzomtrile is added to the mixture, ylide formation is promoted [50] (equation 48) (Table 19). 

These isomerization processes may be dependent on the nature of the solvent. For example, the rotational barrier of the tetrazathiapentalenes 15.15 (ca. 16 kcal moF ) is influenced by the donor or acceptor ability of the substituents X and Y through the S N short contacts.Solvents with acidic protons increase the magnitude of the barrier, whereas solvents that are good Lewis bases decrease the size of the barrier, owing to solvation of the transition state. 

As in the freezing-point method, the molecular weight is calculated from the weight of substance lequired to raise the boiling-point of too grams of solvent i°, and the result multiplied by a coefficient which depends upon the nature of the solvent. The following is a list of solvents commonly employed and their coefficients and boiling-points —... 

Adsorption is influenced by the surface area of the adsorbent, the nature of the solvent being adsorbed, the pH of the operating system, and the temperature of operation. These are important parameters to be aware of when designing or evaluating an adsorption process. 

The delicate balance between ionic and covalent forms is influenced not only by the state of aggregation (solid, liquid, gas) or the nature of the solvent, but also by the effect of substituents. Thus PhPCl4 is molecular with Ph equatorial whereas the corresponding methyl derivative is ionic, [MePClsl+Cl". Despite this the [PhPCl3]+... 

A general solvent dependence of the a y ratio similar to that noted above is also probable for piperidino-dehalogenation of A-oxides. 4-Bromoquinoline and its A-oxide show a strong and nearly identical dependence on the nature of the solvent, the rate increases on going from benzene to 95% ethanol, being in the order of 10 at 120°. 

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