Chloride counterions

Transmetalation of lithium enolate 1 a (M = Li ) by treatment with tin(II) chloride at — 42 °C generates the tin enolate that reacts with prostereogenic aldehydes at — 78 °C to preferentially produce the opposite aldol diastereomer 3. Diastereoselectivities of this process may be as high as 97 3. This reaction appears to require less exacting conditions since similar results are obtained if one or two equivalents of tin(ll) chloride arc used. The somewhat less reactive tin enolate requires a temperature of —42 C for the reaction to proceed at an acceptable rate. The steric requirements of the tin chloride counterion are probably less than those of the diethyla-luminum ion (vide supra), which has led to the suggestion26 44 that the chair-like transition state I is preferentially adopted26 44. This is consistent with the observed diastereoselective production of aldol product 3, which is of opposite configuration at the / -carbon to the major product obtained from aluminum enolates. 

The initial rates in the 2" mns decreased in the following order Co-OTs > Co-OAc > Co-Cl > Co-1 (see Table 43.2), which is consistent with the idea of deactivation by counterion addition to epoxide. As reported by Nielsen et al. (7), the rate of counterion addition to epoxide determines the kinetics of HKR. We suspect that the iodide and chloride counterions undergo such rapid addition to epoxide that most of the HKR reaction in the 2" mn occurred with the much less active Co-OH catalyst formed in situ. In contrast, the weakly nucleophilic tosylate counterion reacted more slowly with the epoxide and was therefore more stable. 

Several trends emerge in these data (1) The reductive elimination of bromine is 6-13kJmol more facile than reductive elimination of chlorine in similar structures, which is consistent with weaker chalcogen-bromine bonds relative to chalcogen-chlorine bonds.(2) The reductive elimination of chlorine is accelerated by the presence of a chloride counterion as opposed to a less nucleophilic counterion such as hexafluorophosphate. (3) The rate of reductive elimination is accelerated by the presence of a more polar solvent (acetonitrile) relative to tetrachloroethane, which is consistent with development of charge in the rate-determining step. These observations suggest mechanisms for oxidative... 

We studied the feasibility of phosphate determination in a low water-soluble API hydrochloride salt. The aim of the work was quantification of phosphate below 0.1% and evaluation of the effect of the high chloride counterion on the determination of phosphate. 

Ion chromatography is a convenient method for simultaneous determination of alkali, alkaline earth and ammonium ion concentrations in solution. The identity of the analytes is set by the retention times and quantation is carried out by a detector. Conductivity is frequently used, after chemical suppression of the eluate, by which chloride counterions were exchanged by hydroxide. UVV spectrophotometric measurement of hydroxide ions at 200 nm was proposed as an alternative method to suppressed conductivity. Both methods... 

Fig. 10 Concentration dependence of the pseudo first-order rate constants in a 100 mM phosphate buffer at pH 7.5 and 37 °C for a niunber of surface active betaine esters with hydrophobic tails of different sizes. For comparison, the rate constant for a non-siuface active compound (ethyl betainate) is included, (o) Oleyl betainate, ( ) tetradecyl be-tainate, ( ) dodecyl betainate, ( ) decyl betainate, (0) ethyl betainate. All compounds have chloride counterions...

Following the discovery of the above solid-state fluoride anion complex, the authors succeeded in crystallizing the bishydrochloride salt of this same system, 3. The X-ray structure of this derivative revealed the presence of two chloride counterions bound via hydrogen bonds to the diprotonated macrocycle (Figure 2). In contrast to what was seen in the case of the fluoride anion structure, in this instance neither of the counteranions is located in the plane of the sapphyrin macrocycle. Rather, they are found in near symmetric fashion ca. 1.8 A above and below the mean Nj plane. This out-of-plane binding reflects, presumably, the fact... 

Fig. 10 Comparison of experimental data of poly electrolyte PPP-2 to the PB-theory [71]. The respective volume fractions (j) of the polyelectrolytes are indicated in the graph. The upper curve refers to Iodide counterions whereas the lower curve refers to Chloride counterions...

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

After washing, the samples were placed in various 0AN sodium salt solutions to exchange the chloride counterion with other anions they were removed after about 3% hours in these solutions, each rinsed several times in fresh deionized water at room temperature, vacuum dried and weighed. 

The a- and /3-isomers of [Ru2(S2CNR2)5]f can be reduced to the paramagnetic a- and /J-[Ru2(S2CNR2)5] respectively by reaction with Na[BH4] in ethanol. For R = Et, the green a-isomer converts in toluene to the purple /S-isomer with a first-order rate constant of 8 x 10-4s-1 at 30°C. Photolysis in CHC13 yields the oxidized cations with chloride counterions and retained a and... 

Similar results are reported using cationic surfactants. The partition coefficient of a-chymotrypsin in Aliquat solutions decreased with increasing NaCl concentration (36). However, in order to interpret these results it is necessary to take into account that alkylmethyl ammonium salts are known to be involved in anion exchanges. Assuming an exchange equilibrium between the protein and chloride counterion, an increase of the chloride ion concentration should disfavor the extraction of the protein, following a mechanism of mass action law. 

Fig. 10.9 Bond length differences between the ground and excited states of ZsZsZa BV, ZsZsZa PCB and ZaZsZa PB in the absence and presence of a chloride counterion. Reproduced from Strambi A, Durbeej B (2011) Initial excited-state relaxation of the bilin chromophores of phytochromes a computational study, Photochem Photobiol Sci 10 569-579, with permission of the Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC...

The product mixture obtained on photolysis of diaryliodonium salts is, in fact, much more complex than these data suggest. DeVoe et al [22] have identified, in addition to iodobenzene, acetanilide, biphenyl, two iodo-biphenyl isomers in the product mixture from photolysis of Ph2I+PFg in AN or HzO at 254 nm. With the chloride counterion, this list expanded to include chlorobenzene and hydroxybiphenyl (presumably the 2-isomer) Ph2I+I, on the other hand, photolyzed cleanly at 313 nm to iodobenzene. A similar mix of products, including benzene and a third iodobiphenyl isomer was observed by Dektar and Hacker [70] on photolysis of the triflate salt under a variety of conditions (see Table 4, below). 

For cation systems, the suppressor membranes are anion exchange polymers, which allow anions to pass freely, but exclude cations. Dilute acids such as HCl are used in the mobile phase. In the suppressor, chloride counterions are replaced by highly conductive OH ions, neutralizing the acidic mobile phase. Tetrabutylammonium hydroxide is used as the regenerant because it is excluded from the anion exchange membranes."... 

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