Aqueous solutions displacement reactions

The stability constants for the 2o/10 species seem to be mainly controlled by the activation energies and, in turn, rate constants for the dissociation of the three-electron bond (back reaction of eq. 40/40a). The respective values, for the two systems with all-methyl and all-i-propyl substitution are 57 and 17 kJ mol and 1.5x10 and 5.6x10 s . 6 xhe latter are certainly in line with the S S bond energies but, again, a direct correlation is not justified because in aqueous solution the reaction of interest is not simply the dissociation of the 3-e-bond but, in fact, a displacement process which involves also a water molecule. (See section on sulfur-oxygen interactions ). 

Correlation of the S—S Bond Distance and the Activation Energy of Various Displacement Eeactions in Aqueous Solution General reaction X + YSSZ YSX + SZ... 

The general characteristics of all these elements generally preclude their extraction by any method involving aqueous solution. For the lighter, less volatile metals (Li, Na, Be, Mg, Ca) electrolysis of a fused salt (usually the chloride), or of a mixture of salts, is used. The heavier, more volatile metals in each group can all be similarly obtained by electrolysis, but it is usually more convenient to take advantage of their volatility and obtain them from their oxides or chlorides by displacement, i.e. by general reactions such as... 

This is an acid-base reaction, in which the base is the oxide ion (p. 89) the acidic oxide SiOj displaces the weaker acidic oxide CO2 in the fused mixture. But in aqueous solution, where the 0 ion cannot function as a strong basefp. 89),carbon dioxide displaces silica, which, therefore, precipitates when the gas is passed through the aqueous silicate solution. In a fused mixture of silica and a nitrate or phosphate, the silica again displaces the weaker acidic oxides N2O5 and P4OJ0 ... 

Many of the reactions of halogens can be considered as either oxidation or displacement reactions the redox potentials (Table 11.2) give a clear indication of their relative oxidising power in aqueous solution. Fluorine, chlorine and bromine have the ability to displace hydrogen from hydrocarbons, but in addition each halogen is able to displace other elements which are less electronegative than itself. Thus fluorine can displace all the other halogens from both ionic and covalent compounds, for example... 

From the data in Fig. 4.8b, estimate the shift factors required to displace the data at 0 = 0.5 (consider only this point) so that all runs superimpose on the experiment conducted at 128 C at 0 = 0.5. Either a ruler or proportional dividers can be used to measure displacements. Criticize or defend the following proposition Whether a buffered aqueous solution of H2O2 and 1. containing small amounts of S2O3 and starch, appears blue or colorless depends on both the time and the temperature. This standard general chemistry experiment could be used to demonstrate the equivalency of time and temperature. The pertinent reactions for the iodine clock are... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Displacement Reactions. The reactions RCl RCN are carried out by heating a threefold excess of concentrated aqueous NaCN solution with the alkyl chloride and 2 mol % tributyUiexadecylphosphonium bromide for 2 h (1) (see Nitriles). 

Figure 1 illustrates the complexity of the Cr(III) ion in aqueous solutions. The relative strength of anion displacement of H2O for a select group of species follows the order perchlorate < nitrate < chloride < sulfate < formate < acetate < glycolate < tartrate < citrate < oxalate (12). It is also possible for any anion of this series to displace the anion before it, ie, citrate can displace a coordinated tartrate or sulfate anion. These displacement reactions are kineticaHy slow, however, and several intermediate and combination species are possible before equiUbrium is obtained. 

O- Alkylation is comparable to A/-alkylation, but since the sodium salts are water-soluble it is most convenient to treat the phenol or naphthol in aqueous caustic solution with dimethyl sulfate or diethyl sulfate. These are comparatively expensive reagents, and therefore, alkoxy groups are introduced at a prior stage by a nucleophilic displacement reaction whenever possible. 

Kinetic data on acetate displacement from C-3 using a number of sulfur and nitrogen nucleophiles in aqueous solution at near neutral pH demonstrate that the reaction proceeds by an 5 1 mechanism (B-72MI51004). The intermediate in this reaction is depicted as a dipolar allylic carbonium ion (9) with significant charge delocalization. Of particular significance in this regard is the observation that the free carboxylate at C-4 is required since... 

It is usual to choose a container metal for fused salts sufficiently noble for the displacement reaction (2.16) to be negligible, and the most important aspects of corrosion are, as in aqueous solutions, those which involve reducible impurities, although in a salt melt there is also the additional possibility of a reducible anion (see above). All such factors can be described as controlling the oxidising power of the melt, which can be defined in terms of a redox potential just as in aqueous solutions The redox potential is expressed by relationships of the form... 

In 0-level qualitative analysis, unknown cations are identified by reacting them with aqueous sodium hydroxide and/or aqueous ammonia. For example, zinc salt solutions react with aqueous sodium hydroxide to form a white precipitate, zinc hydroxide, which in turn will react with excess aqueous sodium hydroxide to form a colourless solution of sodium zincate, a complex salt. However, 25% of the 915 students thought that when sodium hydroxide solution was added to a solution of a zinc salt, a displacement reaction resulted leading to the formation of a precipitate... 

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

Zinc metal displaces copper ions from aqueous solution. The blue color signals the presence of copper ions. The color fades and copper metal appears as the reaction proceeds. 

Many other metal displacement reactions can be visualized, but not all of them occur. Some metals are oxidized readily, but others are highly resistant to oxidation. Likewise, some metal cations are highly susceptible to reduction, but others resist reduction. Zinc displaces copper ions from aqueous solutions, but copper will not replace zinc ions, because Cu is easier to reduce than Zn . Zinc will not displace ions, because... 

Stability of the bidentate and multidentate complexes in aqueous solution [16] compared with monodentate complexes. Kinetic studies of gold(III) reactions with ethylenediamine and related ligands show that the initial displacement of one end of the chelate is most often followed by rapid reclosure of the ring, rather than displacement of the second bond to the metal ion [15]. 

Extractive alkylation is used to derivatize acids, phenols, alcohols or amides in aqueous solution [435,441,448,502]. The pH of the aqueous phase is adjusted to ensure complete ionization of the acidic substance which is then extracted as an ion pair with a tetraalkylammonium hydroxide into a suitable immiscible organic solvent. In the poorly solvating organic medium, the substrate anion possesses high reactivity and the nucleophilic displacement reaction with an alkyl halide occurs under favorable conditions. 

The principle of the displacement of one metal by another, or in other words of the displacement of nobler by base or not so noble metals, as described earlier, must be applied with due caution, without neglecting other effects that may not be immediately obvious from consideration of the electrochemical series. Some of these effects are illustrated in the following. Although the position of lithium is above that of sodium in the series, lithium cannot displace sodium from common salt solutions since both of these metals occupy positions higher up than hydrogen and will displace this element from the solution. It must be borne in mind, therefore, that the series applies to aqueous solutions, and the hydrogen ion, which is present in these solutions, can also take part in the displacement reactions. 

When an octahedral complex such as [Cr(CO)6] reacts with pyridine, only three CO ligands are replaced. In the product [Cr(CO)3(py)3], the CO and py ligands are trans to each other. Replacement reactions are important because frequently one type of complex is easily prepared and then can be converted to another that cannot be obtained easily. Gaseous butadiene will react with an aqueous solution of K2[PtCl4] to give a bridged complex in which Cl ligands are displaced. 

Zn, Fe and Ni are more active metals than Cu and will displace Cu from an aqueous solution of CuS04. Hg(Z) + CuS04( ) - no reaction... 

Displacement reactions involve one element displacing another element from solution The element that dissolves in the solution is more active than the element supplanted from solution. Within the halogen group the activity decreases from top to bottom. Thus, each halogen is able to displace the members of the group below it, but not those above it. For instance, molecular bromine can oxidize aqueous iodide ion but molecular iodine is incapable of oxidizing bromide ion ... 

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