Protolytic solvent

A linear dependence of log on log rf was found [175] in the case of a one-electron reduction of cobalt(III) complexes with acetylacetone (AcAc) in several aprotic solvents, but the behavior in protolytic solvents was different. 

Kinetics and mechanisms of dissociation of manganese complexes with porphyrins in mixed protolytic solvents 04MI14. 

Much greater effect on the structure of ground water render polar hydrophilic components, among which ions play the main role. For them, water serves as a strong protolytic solvent, which ... 

In order to compare the basic strength of this solution of the quaternairy ethoxide with that of the corresponding hydroxide and sodium ethoxide solutions, we carried out potentiometric titrations of 0.05M solutions of phenol with these titrants in about 0.3M solutions, using protolytic solvents of different basic strength and working under strictly anhydrous conditions. 

The values of the prirrrary medium effect of proton were used by Izmailov to con-stract the common acidity scale for protolytic solvents and for the solvents more basic than water having negative values of logy +, whereas for more acidic solvents these valuesarepositive. It is obviorrs that for the cafe of molten salts values of logy 2- will... 

These complexes sublime between 150 and 250°C (10" mm) and are soluble in some org mic solvents. The methylcyclopentadienides are dimeric in benzene presumably with chloride in the bridging positions and monomeric in THF. They are stable indefinitely in vacuum or under nitrogen but they decompose in a matter of minutes in air. They are also readily decomposed by protolytic solvents. The chloride ion can be easily replaced by alkoxide, aryloxide, amide, or carboxylate ions by reaction with the corresponding sodium salts. 

Chen, S.H. and Kimura, K. (2001) Synthesis of thiolate-stabilized platinum nanoparticles in protolytic solvents as isolable colloids. Journal of Physical Chemistry E, 105, 5397. 

A. Nucleophilic Attack on Carbon. —(/) Activated Olefins. A study of triarylphosphine-catalysed dimerization of acrylonitrile to 2-methylene-glutaronitrile (26) and 1,4-dicyano-l-butene (27) has established a balance between phosphine nucleophilicity and protolytic strength of the solvent. The reaction of methyl vinyl ketone with triphenylphosphine in triethyl-silanol gave only 3-methylene-2,6-heptadienone (28). 

Nonaqueous electrolyte solutions are analogous to aqueous solutions they, too, are systems with a liquid solvent and a solute or solutes dissociating and forming solvated ions. The special features of water as a solvent are its high polarity, e = 78.5, which promotes dissocation of dissolved electrolytes and hydration of the ions, and its protolytic reactivity. When considering these features, we can group the nonaqueous solvents as follows ... 

Aprotic solvents are not protogenic, but can be protophilic, e.g. acetone, 1,4-dioxan, tetrahy drof uran, dimethy If ormamide, hexamethylphos-phortriamide, propylene carbonate and sulpholane. Solvents that do not participate in protolytic reactions, i.e. do not donate or accept a proton, are usually chemically inert, such as benzene, chlorobenzene, chloroform, tetrachloromethane, etc. 

If an amphiprotic solvent contains an acid and base that are neither mutually conjugate nor are conjugated with the solvent, a protolytic reaction occurs between these dissolved components. Four possible situations can arise. If both the acid and base are strong, then neutralization occurs between the lyonium ions and the lyate ions. If the acid is weak and the base strong, the acid reacts with the lyate ions produced by the strong base. The opposite case is analogous. A weak acid and a weak base exchange protons ... 

If the dielectric constant of an amphiprotic solvent is small, protolytic reactions are complicated by the formation of ion pairs. Acetic acid is often given as an example (denoted here as AcOH, with a relative dielectric constant of 6.2). In this solvent, a dissolved strong acid, perchloric acid, is completely dissociated but the ions produced partly form ion pairs, so that the concentration of solvated protons AcOH2+ and perchlorate anions is smaller than would correspond to a strong acid (their concentrations correspond to an acid with a pK A of about 4.85). A weak acid in acetic acid medium, for example HC1, is even less dissociated than would correspond to its dissociation constant in the absence of ion-pair formation. The equilibrium... 

Protolytic reactions can also occur in fused salts. The solvent participates in these reactions provided that at least one of its ions has protogenic and/or protophilic character. An example of a solvent in which the cation is aprotic and the anion protophilic is ethylpyridinium bromide (m.p. 114°C). The acid HA is protolysed in this solvent (HA -I- Br HBr + A"). Hydrogen bromide acts as a solvated proton and the acidity is expressed as... 

Products of organic reactions, magnetic field and magnetic isotope effects on, 30, 1 Protic and dipolar aprotic solvents, rates of bimolecular substitution reactions in, 5, 173 Protolytic processes in H20-D20 mixtures, 7, 259... 

If two conjugate acid-base pairs are coupled with one another, then, depending on the magnitude of the constants (2a, b) a proton exchange can take place and this is described as a protolytic reaction. In general, the solvent itself is one acid-base pair. 

K thus represents the quotient of two acidity constants. If water is the solvent the protolytic reaction is described as the dissociation of an acid or base. 

Chemoselective reduction of methyl ester 7 to aldehyde 2 is possible with DIB AH. The metallatcd hemiacetal that results from addition of DIBAII to the carbonyl group of ail ester usually decomposes rapidly in polar solvents like THF to an intermediate aldehyde This then competes with the ester and, as a result of its higher clcctrophilicity. js reduced by DIBAH to an alcohol. However, ester 7 bears a methoxymethyl residue in its a-position, which stabilizes the metallated hemiacetal by chelate formation. Chelate complex 22 is protolytically cleaved by way of the hemiacetal only in the course of aqueous workup, so in this case the DIBAH reaction produces only aldehyde 2, not the alcohol (see also Chapter 3), DIBAH, THF, -78 C 100. ... 

The rate of hydrogen exchange depends on the protolytic properties of both the solvent and the substrate. In fact there is a correspondence between the magnitude of the rate constants for deuterium exchange with ND3 and the conventional ionization constants of hydrocarbons which were used by Conant and Wheland (1932) and by McEwen (1936) to obtain the first quantitative estimates of the acidity of hydrocarbons. To do this, they determined the equilibrium of metallation of hydrocarbons by organo-alkali metal compounds. This reaction was described by Shorygin (1910) and is represented by the equation... 

Halonium ions are an important class of onium ions.43 The dialkylchloro, bromo, and iodohalonium ions can be prepared and even isolated as stable salts (i.e., 46), as shown by Olah et al. by reacting an excess of haloalkane with strong Lewis acid halides in solvents of low nucleophilic-ity (eq 14). In superacid solution, dialkylhalonium ions show enhanced alkylating reactivity.44 It is considered that this enhanced reactivity is due to further protolytic (or electrophilic) activation involving the non-bonded... 

The dissociation of acetic acid in aqueous solution is an example of the simplest type of protolytic process. The dissociation constant was one of the first chemical parameters to be studied as a function of isotopic composition of the solvent (La Mer and Chittum, 1936 Homel and Butler, 1936), and the determinations have been repeated by several groups of workers. Conductivity measurements (La Mer and Chittum, 1936), potentiometry using the quinhydrone electrode (Korman and La Mer, 1936) or glass electrodes (Salomaa et al., 1964a Gold and Lowe, 1968), and measurements of the rate of a hydrogen-ion... 

Moreover, as has been recognized, pyridine is strongly hydrogen bonded in protolytic media (hence, for example, its high water solubility). Such hydrogen bonding substantially reduces the reactivity toward electrophiles, and as a consequence reactivity parameters determined for the free base in solution in H-donor solvents differ markedly from those determined in the gas phase. This difference is —0.3 ct units at each position. 

THE PROTOLYSIS OF ACIDS. STRENGTHS OF ACIDS AND BASES It is of interest to examine the processes which take place when an acid is dissolved in a solvent, first of all in water. According to the Br0nsted-Lowry theory this dissolution is accompanied by a protolytic reaction, in which the solvent (water) acts as a base. To elucidate these processes, let us examine what happens if a strong acid (hydrochloric acid) and a weak acid (acetic acid) undergo protolysis. 

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