Solvent types protic

While most of the solvents of interest here are aprotic, in the sense defined in the introduction, they may be further classified with regard to their solvent type. Kolthoff [4] has categorized these solvents in a useful way. Only the classifications useful for nonaqueous studies have been included below. That is, the protic solvents (amphiprotic solvents in Kohltoff s terminology) are not included in this chapter. The classes and definitions are as follows ... 

Other examples of this type of reaction are Sn2 reactions between azide ion and 1-bromobutane [67], bromide ion and methyl tosylate [68], and bromide ion and iodoethane [497]. In changing the medium from non-HBD solvents (HMPT, 1-methylpyrrolidin-2-one) to methanol, the second-order rate constants decrease by a factor of 2 10 [67], 9 10 [68], and 1 10 [497], respectively. The large decrease in these rate constants in going from the less to the more polar solvent is not only governed by the difference in solvent polarity, as measured by dipole moment or relative permittivity, but also by the fact that the less polar solvents are dipolar aprotic and the more polar solvents are protic cf. Section 5.5.2). 

These results reflect the importance of the employment of these types of binary solvent systems can be, for instance, as reaction media. Additionally, the experimental data of n, P and a parameters of 15 binary mixtures of the type [protic molecular solvent + IL] at various compositions have been fitted to the CNIBS/R-K model. The model proved to be statistically valuable, showing a strong correlation between predicted and experimentally measured values. 

Fortunate G, Mancini PME, Bravo V, Adam C (2010) New solvent designed on the basis of the molecular-microscopic properties ob binary mixtures of the type protic molecular solvent + l-butyl-3-methylimidazolium-based ionic liquids. J Phys Chem B 114 11804-11819... 

Solubility sol hydrocarbon and ethereal solvents, but should be used at low teir ierature in the latter solvent type half-lives in diethyl ether and THF have been reported reacts violently with H2O and other protic solvents. 

Fortunate, G., Mancini, P.M.E., Bravo, V., Adam, C. (2010). New solvent designed on the basis of molecular microscopic properties of binary mixtures of the type protic molecular solvent + l-butyl-3-methylimidazolium-based ionic liquids. The Journal of Physical Chemistry B, 114,11804-11817, ISSN 1520-5707 Hitchcock, P.B., Mohammed, T.J., Seddon K.R., Zora, J.A., Hussey, C.L., Ward, E.H. (1986). 

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... 

Thickeners. Thickeners are added to remover formulas to increase the viscosity which allows the remover to cling to vertical surfaces. Natural and synthetic polymers are used as thickeners. They are generally dispersed and then caused to swell by the addition of a protic solvent or by adjusting the pH of the remover. When the polymer swells, it causes the viscosity of the mixture to increase. Viscosity is controlled by the amount of thickener added. Common thickeners used in organic removers include hydroxypropylmethylceUulose [9004-65-3], hydroxypropylceUulose [9004-64-2], hydroxyethyl cellulose, and poly(acryHc acid) [9003-01-4]. Thickeners used in aqueous removers include acryHc polymers and latex-type polymers. Some thickeners are not stable in very acidic or very basic environments, so careful selection is important. 

Solvent effects on chemical equilibria and reactions have been an important issue in physical organic chemistry. Several empirical relationships have been proposed to characterize systematically the various types of properties in protic and aprotic solvents. One of the simplest models is the continuum reaction field characterized by the dielectric constant, e, of the solvent, which is still widely used. Taft and coworkers [30] presented more sophisticated solvent parameters that can take solute-solvent hydrogen bonding and polarity into account. Although this parameter has been successfully applied to rationalize experimentally observed solvent effects, it seems still far from satisfactory to interpret solvent effects on the basis of microscopic infomation of the solute-solvent interaction and solvation free energy. 

Majeti11 has studied the photochemistry of simple /I-ketosulfoxides, PhCOCH2SOCH3, and found cleavage of the sulfur-carbon bond, especially in polar solvents, and the Norrish Type II process to be the predominant pathways, leading to both 1,2-dibenzoylethane and methyl methanethiolsulfonate by radical dimerization, as well as acetophenone (equation 3). Nozaki and coworkers12 independently revealed similar results and reported in addition a pH-dependent distribution of products. Miyamoto and Nozaki13 have shown the incorporation of protic solvents into methyl styryl sulfoxide, by a polar addition mechanism. 

Here, the relative stability of the anion radical confers to the cleavage process a special character. Thus, at a mercury cathode and in organic solvents in the presence of tetraalkylammonium salts, the mechanism is expected16 to be an ECE one in protic media or in the presence of an efficient proton donor, but of EEC type in aprotic solvents. In such a case, simple electron-transfer reactions 9 and 10 have to be associated chemical reactions and other electron transfers (at the level of the first step). Those reactions are shown below in detail ... 

Aprotic polar solvents such as those listed in Table 8.1 are widely used in electrochemistry. In solutions with such solvents the alkali metals are stable and will not dissolve under hydrogen evolution (by discharge of the proton donors) as they do in water or other protic solvents. These solvents hnd use in new types of electrochemical power sources (batteries), with hthium electrodes having high energy density. 

It has also been shown that dimethylsilyl enolates can be activated by diisopropylamine and water and exhibit a high reactivity toward iV-tosyl imines to give Mannich-type reaction products in the absence of a Fewis acid or a Bronsted acid.51 For example, the reaction of [(1-cyclohexen-l-yl)oxy]dimethylsilane with 4-methyl-A -(phenylmethylene)benzene sulfonamide gave re/-4-methyl-N- (f )-[(15)-(2-oxocyclohexyl)phenyl-methyl] benzenesulfonamide (anti-isomer) in 91% yield stereoselectively (99 1 anti syn) (Eq. 11.30). On the other hand, Fi and co-workers reported a ruthenium-catalyzed tandem olefin migration/aldol and Mannich-type reactions by reacting allyl alcohol and imine in protic solvents.52... 

Furthermore, it is often possible to extract from the structural analysis of solid solvates a significant information on solvation patterns and their relation to induced structural polymorphism. An interesting illustration has been provided by crystal structure determinations of solvated 2,4-dichloro-5-carboxy-benzsulfonimide (5)35). This compound contains a large number of polar functions and potential donors and acceptors of hydrogen bonds and appears to have only a few conformational degrees of freedom associated with soft modes of torsional isomerism. It co-crystallizes with a variety of solvents in different structural forms. The observed modes of crystallization and molecular conformation of the host compound were found to be primarily dependent on the nature of the solvent environment. Thus, from protic media such as water and wet acetic acid layered structures were formed which resemble intercalation type compounds. 

This type of charge reduction by charge transfer to the solvent molecule occurs in general when SI are polar solvent molecules of aprotic character such as dimethyl-sulfoxide, dimethyl formamide, and acetonitrile. Protic solvents such as water lead to charge reduction which involves an intracluster proton transfer reaction ... 

Trialkyl phosphites readily undergo conjugate addition with a,(3-unsaturated carbonyl compounds in the presence of a proton source, such as a protic solvent.359 The use of a protic solvent, such as an alcohol, obviates the difficulties found in the performance of the simple Abramov-type reaction with a,(3-unsaturated carbonyl compounds.189198 In alcohol medium, an ether is generated as a by-product in the dealkylation process (Equation 3.22). 

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