Polar protic and aprotic solvents

A study of column extraction of metals was carried out using pre-packed columns available from Polymer Laboratories (now a part of Varian, Inc.) [6]. Trace metals in these monomers would have a detrimental effect on the stability of anaerobic adhesive products and must be absent prior to use. The columns used are specially coated macroporous polystyrene products that are compatible with polar, non-polar, protic and aprotic solvents. They are designed to remove metals from solvents and monomers. The metal removing SPE product is approximately 45 pm and based on a mono-dispersed macroporous polymeric material. 

Polymer Laboratories (PL), which is now a part of Varian, Inc., has mainly focused its expertise in copolymerization technology to develop a high-performance, mono-dispersed base material. This specially functionalized macroporous polystyrene product has a much higher loading capacity than functionalized silicas and is compatible with all polar and non-polar, protic and aprotic solvents. 

C Solvent Effects on S sj2 Reactions Polar Protic and Aprotic Solvents... 

The use of ILSB in organic solvents has not been challenged. Because ILs are considerably, if not completely, miscible with polar protic and aprotic solvents, the formation of phase-separated systems is not expected. Even in such cases, ILSBs described above presumably work as conventiOTial salt bridges based on diffusion potential, as is the case of KCISB. As ILs are not completely miscible with nonpolar organic solvents, ILSB should work to correlate electrode potentials in such solvents with those in aqueous solutions. 

Bipyridyl-carbazole derivative 2 is an example of a six-membered system that exhibits ESIPT, as evidenced by dual fluorescence observed in nonpolar and polar, protic and aprotic, solvents [36] (Figure 3.8a). At room temperature, the quantum yields of both emission bands are very weak and their fluorescence decays are short-Hved, whereas both emissions become stronger upon lowering the temperature to 88 K, as seen in Figure 3.8b. Deuterium isotope effects on the ESIPT rates indicate an important role of tunnehng. 

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. 

A term, usually referring to a solvent, describing a compound which act neither as a proton donor nor a proton acceptor. Examples of polar aprotic solvents include dimethylformamide, dimethylsulfoxide, acetone, acetonitrile, sulfur dioxide, and hexamethylphosphoramide. Examples of nonpolar aprotic solvents include benzene and carbon tetrachloride. Studies of reactions in protic and aprotic solvents have demonstrated the importance of solvation on reactants, leaving groups, and transition states. Degrees of nucleophilicity as well as acidity are different in aprotic solvents. For example, small, negatively charged nucleophiles react more readily in polar aprotic solvents. It should also be noted that extremely... 

The cis-trans geometry of the alkene is influenced by the nature of the substituents, solvent and dissolved salts. Polar protic or aprotic solvents favor the cis isomer. 

The ammonium salt of /V-l-(8-sulfonato)naphthylaniline (35) is fluorescent and its emission peaks in 22 polar aprotic and protic solvents were studied by Hiittenhain and coworkers44. The solvatochromic shifts (Stokes shifts between absorption and emission peaks) are only moderate, but able to distinguish between protic and aprotic solvents of similar polarity. 

Catalytic oxidation of cyclohexene with cumene hydroperoxide gave 2 cyclohexen-l-ol and 2-cyclohexenone. Cydohexene oxide was not formed under the reaction conditions. The effect of various solvents on the oxidation reactions was smdied. The reaction was performed in polar, nonpolar, protic and aprotic solvents. Si ificant variation in product yield was observed. Table-1 shows the distribution of product yield with different solvents. Maximum conversion was observed in chloroform. The eflSciency of the catalyst for 2-cyclohexen-l-ol formation in chloroform is of the order, catalyst (2) > (3) > (1). When methanol was used as solvent the selectivity fijr epoxide was highest with catalyst (3), In this complex the selectivity fiar the formation of the allylic oxidation products are comparatively low. With catalyst (l),m methanol as solvent, 2-cyclohexen-l-ol was obtained in higher yield than eporade. With catalyst (1) the yield of the product was maximum when benzene was used as the solvent. Percentage conversion was the highest (39%). 

The selectivity as a function of polarity is opposite for protic and aprotic solvents. This is a consequence of compared stability of intermediate conformers. 

Table 2.8 is further divided into two classes of solvents, those that contain an acidic proton (X—H, protic) and those that do not possess an acidic proton (aprotic). With each class, the higher the dielectric constant, the more polar the solvent. The essential difference between protic and aprotic solvents is the ability of protic... 

The rates of the 5 2 reaction between phenacyl bromide and 2-mercaptobenzothia-zole in 17 protic and aprotic solvents have been measured. The effect on the rates is assessed in terms of the electrophilicity, the hydrogen-bond donor ability, the specific polarizability, and a non-specific polarity of the solvent. The relative infiuence of each factor is given and a linear solvation energy equation is proposed. 

Table 13.2 is further divided into two classes of solvents those that contain an acidic proton (X-H, protic) and those that do not possess an acidic proton (aprotic). Within each class, the higher dielectric constant is associated with the more polar solvent. The essential difference between protic and aprotic solvents is the ability of protic solvents to solvate both cations and anions, whereas aprotic solvents efficiently solvate only cations. Ionization is favored only when both ions are solvated, allowing them to be separated. The O and the H atoms of the polarized OH rmit in protic solvents such as water or an alcohol are not sterically encrunbered, which allows the "0 to solvate cations and the to solvate anions via hydrogen bonding. The 6- atom of aprotic... 

A comprehensive conformational analysis by the use of vicinal proton-proton couplings measured in a variety of solvents and at different temperatures has been performed by Roberts and co-workers for 1,2-disubstituted ethane system - Ar////-trimethyl-(3,3-dimethylbulyl)-ammonium iodide. The authors have come to the conclusion that the compound, which contains both an organic and a highly polar substituent and therefore is soluble in a large variety of solvents, exists predominantly in the tram form (about 90% in contrast to the previously assumed 100%) in a wide range of protic and aprotic solvents. This behaviour makes N,N,N-trimethyl-(3,3-dimethylbutyl)ammonium iodide a possibly useful tra s-standard in conformational analysis, much more so than 1,2-ditert-butylethane, which has a poor solubility in many... 

Most organic reactions are done in solution, and it is therefore important to recognize some of the ways in which solvent can affect the course and rates of reactions. Some of the more common solvents can be roughly classified as in Table 4.10 on the basis of their structure and dielectric constant. There are important differences between protic solvents—solvents fliat contain relatively mobile protons such as those bonded to oxygen, nitrogen, or sulfur—and aprotic solvents, in which all hydrogens are bound to carbon. Similarly, polar solvents, those fliat have high dielectric constants, have effects on reaction rates that are different from those of nonpolar solvent media. 

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