Solvent effects chloride

Solvent Effects on the Rate of Substitution by the S l Mechanism Table 8 6 lists the relative rate of solvolysis of tert butyl chloride m several media m order of increasing dielectric constant (e) Dielectric constant is a measure of the ability of a material m this case the solvent to moderate the force of attraction between oppositely charged par tides compared with that of a standard The standard dielectric is a vacuum which is assigned a value e of exactly 1 The higher the dielectric constant e the better the medium is able to support separated positively and negatively charged species 8olvents... 

The preparation of perfluoroalkylzinc compounds has been achieved earlier 111 ethereal solvents [26] However, solvent effects play a significant role in the course of this reaction When a mixture of acetic anhydride and methylene chloride is used, coupled and cross-coupled products can be formed [27, 28] (equations 19 and 20) However, the cross-coupling reaction often gives mixtures, a fact that seriously restricts the synthetic applicability of this reaction [27, 28, 29]... 

The dissolving of electrolytes in water is one of the most extreme and most important solvent effects that can be attributed to electric dipoles. Crystalline sodium chloride is quite stable, as shown by its high melting point, yet it dissolves readily in water. To break up the stable crystal arrangement, there must be a strong interaction between water molecules and the ions that are formed in the solution. This interaction can be explained in terms of the dipolar properties of water. 

Levy (Chapter 6) has also explored the use of supercomputers to study detailed properties of biological macromolecule that are only Indirectly accessible to experiment, with particular emphasis on solvent effects and on the Interplay between computer simulations and experimental techniques such as NMR, X-ray structures, and vltratlonal spectra. The chapter by Jorgensen (Chapter 12) summarizes recent work on the kinetics of simple reactions In solutions. This kind of calculation provides examples of how simulations can address questions that are hard to address experimentally. For example Jorgensen s simulations predicted the existence of an Intermediate for the reaction of chloride Ion with methyl chloride In DMF which had not been anticipated experimentally, and they Indicate that the weaker solvation of the transition state as compared to reactants for this reaction In aqueous solution Is not due to a decrease In the number of hydrogen bonds, but rather due to a weakening of the hydrogen bonds. 

Fluoride ion catalyzes the hydrosilylation of both alkyl and aryl aldehydes to silyl ethers that can be easily hydrolyzed to the free alcohols by treatment with 1 M hydrogen chloride in methanol.320 The most effective sources of fluoride are TBAF and tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF). Somewhat less effective are CsF and KF. Solvent effects are marked. The reactions are facilitated in polar, aprotic solvents such as hexamethylphosphortriamide (HMPA) or 1,3-dimethyl-3,4,5,6-tetrahydro-2(l //)-pyrirnidinone (DMPU), go moderately well in dimethylformamide, but do not proceed well in either tetrahydrofuran or dichloromethane. The solvent effects are dramatically illustrated in the reaction of undecanal and dimethylphenylsilane to produce undecyloxyphenyldimethylsi-lane. After one hour at room temperature with TBAF as the source of fluoride and a 10 mol% excess of silane, yields of 91% in HMPA, 89% in DMPU, 56% in dimethylformamide, 9% in tetrahydrofuran, and only 1% in dichloromethane are obtained (Eq. 164).320... 

Carbodiimides are, in general, useful compounds for effecting certain dehydrative condensations, e.g., in the formation of amides, esters, and anhydrides. These two crystalline water-soluble carbodiimides are especially useful in the synthesis of peptides and in the modification of proteins. The excess of reagent and the co-product (the corresponding urea) are easily separated from products with limited solubility in water. The hydrochloride is best employed in nonaqueous solvents (methylene chloride, acetonitrile, dimethylformamide). The methiodide is relatively stable in neutral aqueous systems, and thus is recommended for those media. 

The solvent effect on the azo-hydrazone equilibrium of 4-phenylazo-l-naphthol has been modelled using ab initio quantum-chemical calculations. The hydrazone form is more stable in water and in methylene chloride, whereas methanol and iso-octane stabilise the azo form, The calculated results were in good agreement with the experimental data in these solvents. Similar studies of l-phenylazo-2-naphthol and 2-phenylazo-l-naphthol provided confirmation. Substituent effects in the phenyl ring were rationalised in terms of the HOMO-LUMO orbital diagrams of both tautomeric forms [53]. 

A full report has now appeared of solvent effects on the rates of hydrolysis of benzyltriphenylphosphonium bromide. The remarkable increase in rate in media of low polarity is largely attributable to a shift of the pre-equilibrium between phos-phonium and hydroxide ions in favour of the intermediate hydroxyphosphorane.129 In a similar vein, a study of medium and deuterium isotope effects on the rate of hydrolysis of tetraphenylphosphonium chloride in acetone-water mixtures has been reported.130... 

Solvent Effects. Information on the effect of solvent polarity of the phase transfer assisted permanganate oxidation of alkenes has been obtained by studying the oxidation of methyl cinnamate by tetrabutylammonium permanganate in tv/o different solvents, acetone and methylene chloride (37). 

Ab initio SCRF/MO methods have been applied to the hydrolysis and methanol-ysis of methanesulfonyl chloride (334). ° The aminolysis by aromatic amines of sulfonyl and acyl chlorides has been examined in terms of solvent parameters, the former being the more solvent-dependent process.Solvent effects on the reactions of dansyl chloride (335) with substituted pyridines in MeOH-MeCN were studied using two parameters of Taft s solvatochromatic correlation and four parameters of the Kirkwood-Onsager, Parker, Marcus and Hildebrand equations. MeCN solvent molecules accelerate charge separation of the reactants and stabilize the transition... 

The solvent effects on the C-Cl bond cleavage in the aromatic radical anions of 9-chloroanthracene, 3-nitrobenzyl chloride, and 3-chloroacetophenone were described by applying the Saveant model. The results showed that the bond dissociation energy is not strongly solvent dependent. 

Such drastic changes in selectivity may also occur with eluents pre-l lllCll imiii Iwti Qolvnila uf similiii elution slrmalh, such dichlor(>-methane and ethyl acetate. In Fig. 6 the effect of ethyl aceta concentration in dichloromethane on the retention behavior of some (steroids and barbiturates is illustialed (/). The k values of the sleRiids ate reduced drastically by the addition of 1% of ethyl acetate to methylene chloride. Some barbiturates behave similarly, whereas the behavior of others is dominated by other solvent effects that also manifest themselves in the widely different solubilities of the substances in methylene chloride and ethyl acetate. j... 

There is an ongoing controversy about whether there is any stabilization of the transition state for nucleophilic substitution at tertiary aliphatic carbon from interaction with nucleophilic solvent." ° This controversy has developed with the increasing sophistication of experiments to characterize solvent effects on the rate constants for solvolysis reactions. Grunwald and Winstein determined rate constants for solvolysis of tert-butyl chloride in a wide variety of solvents and used these data to define the solvent ionizing parameter T (Eq. 3). They next found that rate constants for solvolysis of primary and secondary aliphatic carbon show a smaller sensitivity (m) to changes in Y than those for the parent solvolysis reaction of tert-butyl chloride (for which m = 1 by definition). A second term was added ( N) to account for the effect of changes in solvent nucleophilicity on obsd that result from transition state stabilization by a nucleophilic interaction between solvent and substrate. It was first assumed that there is no significant stabilization of the transition state for solvolysis of tert-butyl chloride from such a nucleophilic interaction. However, a close examination of extensive rate data revealed, in some cases, a correlation between rate constants for solvolysis of fert-butyl derivatives and solvent nucleophicity. " ... 

Intersystem crossing rate constants of ortho- and meta-substituted singlet phenylni-trenes are presented in Table 1Mono- and di-o-fluorine substituents have no influence on ISC rate constants.No effect with meta, meta-difluoro substitution is observed either. Pentafluoro substitution has no effect on fcisc in pentane although a modest acceleration is observed in the more polar solvent methylene chloride.i° - i... 

Domariska, U. and Mazurowska, L., Solubility of 1,3-dialkylimidazolium chloride or hexafluorophosphate or methylsulfonate in organic solvents. Effect of the anions on solubility. Fluid Phase Equilib., 221, 73, 2004. 

The preceding sections have shown the complexity of solvent effects in the solvolysis of acyl chlorides, and how ambiguities in the role of the solvent, particularly in its apparent reaction order, critically affect the assignment of detailed mechanism. It is the intention in this brief section to point to some of... 

Since isomerization and propagation are both ionic processes, solvent polarity was expected to affect their rates and in turn polymer composition. The effect of solvent polarity on I using a polar solvent, ethyl chloride, and a nonpolar solvent, n-pentane, and EtAlCl2 and BF3 coinitiators at various temperatures is shown in Table 10. 

Effects of Substitution on Spectra Solvent Effects. Solvent effects on the absorption spectra can be summarized as follows if the compound is soluble in water, alcohols, and polar, protic solvents such as DMSO, DME, and DMF, the /.max is most red shifted in polar, nonprotic solvents. Compounds that are soluble in nonpolar solvents such as CH2C12 are generally not soluble in water, and their absorption lies at about the same place in both alcohols and methylene chloride, but is shifted to the red in polar, nonprotic solvents. The value of Amax also reflects the hydrogen bonding ability of the... 

---