Hydrogen displacement reaction

An easy way to predict whether a metal or hydrogen displacement reaction will actually occur is to refer to an activity series (sometimes called the electrochemical series), shown in Figure 4.15. Basically, an activity series is a convenient summary of the results of many possible displacement reactions similar to the ones already dis-... 

An easy way to predict whether a metal or hydrogen displacement reaction will actnaUy occur is to refer to an activity series (sometimes called the electrochemical series), shown in Fignre 4.16. Basically, an activity series is a convenient summary of the results of many possible displacement reactions similar to the ones already discussed. According to this series, any metal above hydrogen will displace it from water or from an acid, but metals below hydrogen will not react with either water or an acid. In fact, any metal listed in the series will react with any metal (in a compound) below it. For example, Zn is above Cu, so zinc metal will displace copper ions from copper sulfate. 

Reactions in which hydrogen ion is reduced to hydrogen gas are known as hydrogen displacement reactions. 

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... 

DispEcement. In many of the appHcations of chelating agents, the overall effect appears to be a displacement reaction, although the mechanism probably comprises dissociations and recombinations. The basis for many analytical titrations is the displacement of hydrogen ions by a metal, and the displacement of metal by hydrogen ions or other metal ions is a step in metal recovery processes. Some analytical pM indicators function by changing color as one chelant is displaced from its metal by another. 

Various sources of fluoride ion have been investigated, of which highly nucleophilic tetraalkylammonium fluorides ate the most effective Thuf, fluoro alkyl halides and N (fluoroalkyl)amines are efficiently synthesized by treatment of the corresponding trifluoromethanesulfonic esters with tetrabutylammonium fluoride trihydrate in aprotic solvents [5fl] (equation 34) The displacement reactions proceed quantitatively at room temperature within seconds, but tail with hydrogen fluoride-pyridine and give reasonable yields only with hydrogen fluo ride-alkylamine reagents... 

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 acids and bases come into contact with one another, a chemical reaction called a neutralization reaction takes place. A neutralization reaction is a double displacement reaction. In a double displacement reaction, the positive ions from one reactant take the place of the positive ions in the other reactant. For example, if hydrochloric acid and sodium hydroxide react with one another, the positive sodium ion in sodium hydroxide will take the place of the hydrogen ion in the hydrochloric acid ... 

Remember that an acid-base reaction is a double displacement reaction. Therefore, if sulfuric acid and potassium hydroxide are mixed, the positive ions trade places. The hydrogen ions from the sulfuric acid will react with the negative hydroxide ions to form water. Because a hydrogen ion has a charge of + 1 and a hydroxide ion has a charge of -1, they bond in a 1 1 ratio ... 

Because this is a reaction between an acid and a base, it will be a double displacement reaction, and the positive ions will switch places. The potassium ion will react with the sulfate ion, forming the salt potassium sulfate (K2S04). And the hydrogen ion in the acid will react with the hydroxide ion in the base to form HOH, or water (H20). 

Reaction with sodium Displaces hydrogen No reaction... 

Catalysis by radicals will usually be due to a radical addition or displacement reaction, hydrogen and halogen being the atoms on which the displacement most often occurs. It is usually a chain reaction once the substrate is converted into a radical it carries the reaction to many molecules of substrate. Examples are polymerization and autoxidation. 

Scheme 8 summarizes some of the reactions that have been observed for H2Os3(CO)10 (135,136, 165). A wide range of products may be obtained, but some of the reactions are complicated by hydrogenation of the products, a situation that does not occur in the displacement reactions considered above. This reagent was the first used to prepare vinyl adducts from alkenes and alkynes. 

An elegant design using a based-induced internal SN2 displacement reaction is depicted in Scheme 20.36 [7, 8], Treatment of 176 with triethylamine in the presence of 1,4-CHD triggered the formation of the enyne-allene 177, leading to the biradical 178 and, after hydrogen-atom abstractions, the cycloaromatized adduct 179. 

BioH14 is a mdo-polyborane, therefore, it is expected that it forms adducts with Lewis bases. This is indeed the case but with concomitant loss of hydrogen as shown in Eq. (51). These adducts of the type BioHi2-2L (L = amines, pyridine, phosphines, nitriles, dialkylsulfides inter alia) proved to be versatile reagents. For instance, when triethylamine is used to replace acetonitrile from the adduct not only does the expected replacement occur but in preference also a proton shift (most likely prior to the base displacement reaction) with cluster closure to the decahydro-doso-decaborate(2—) (Eq. 52) ... 

We note that hydrogen as well as methane, ethane and toluene have been reported [25], but do not currently have good explanations in the schemes shown above. For the methane and ethane, one would have to resort to either radical displacement reactions of the methyl ester shown in Scheme 18.3 in the middle... 

The preparation of thiols by nucleophilic displacement reactions using aqueous potassium or sodium hydrogen sulphide under catalytic conditions is not particularly effective. A limited number of simple alkane thiols have been obtained under mild and neutral conditions in moderate yield (70-80%) from the reaction of bis(n-butyltin) sulphide with bromoalkanes in the presence of a ca. twofold amount of tetra-n-butylammonium fluoride [1], but there has been no exploitation of this procedure. 

Hydrogen Ingress in Metals Metal Displacement Reactions 11... 

A similar dependence of the first-order rate constants with respect to the quantity of added water has been reported for the reaction of sodium formate with 1,4-dichlorobutane and related displacement reactions, In these studies tetra- n-butylammonium hydrogen sulphate and tetra- n-butylammonium bromide were used as catalysts and chlorobenzene as the solvent. 

---