Displacement hydrogenation

Like chlorine, bromine can displace hydrogen from saturated hydrocarbons, though not as readily, and adds on to unsaturated ones. 

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... 

In the dual-temperature H2O/H2S process (61,62), exchange of deuterium between H20(l) and H2S(g) is carried out at pressures of ca 2 MPa (20 atm). At elevated temperatures deuterium tends to displace hydrogen in the hydrogen sulfide and thus concentrates in the gas. At lower temperatures the driving force is reversed and the deuterium concentrates in H2S in contact with water on the tiquid phase. 

In the electrochemical series of elements, copper is near the noble end and will not normally displace hydrogen, even from acid solutions. Indeed, if hydrogen is bubbled through a solution of copper salts, copper is slowly deposited (more rapidly if the process is carried out under pressure). (See Section 1.2 for thermodynamic considerations.)... 

Reaction with sodium Displaces hydrogen No reaction... 

The standard cell potential for the reduction of hydrogen ions to hydrogen gas is, by definition, 0.00 V. This potential is for the standard hydrogen electrode, SHE, which is the reference to which we compare all other cell potentials. All metals above hydrogen on the Activity Series will displace hydrogen gas from acids. (See Chapter 4) Metals below hydrogen will not displace hydrogen gas. 

Metals above hydrogen on the Activity Series will displace hydrogen gas from acids. When this happens, the metal undergoes oxidation. Metals below hydrogen will not release hydrogen from acid solutions. 

A metal displacing hydrogen gas (H2) from an acid or from water... 

If a piece of copper metal was placed in a solution of SrfNOj aq) there would be no reaction, since copper is lower than tin on the activity series. This table allows us to also predict that if sodium metal is placed in water, it will displace hydrogen, forming hydrogen gas ... 

The Group IA and IIA elements on the activity table will displace hydrogen from water, but not the other metals shown. All the metals above hydrogen will react with acidic solutions to produce hydrogen gas ... 

Lithium displaces hydrogen from water to form lithium hydroxide. 

It was later proposed that more suitable extractants to overcome, and also measure, the salt effects which displace hydrogen ions in a seasonal manner would be either 0.1 M KCI or 0.01 M CaCl2, with the latter being more widely used (Schofield and Taylor, 1955). 

In the presence of ammonium chloride or a substance that dissolves Mg(OH)2, the above reaction proceeds at ambient temperatures, the metal continues to dissolve in water, displacing hydrogen. 

Single displacement reaction where magnesium is displacing hydrogen in the water molecule. 

Nickel has typical metallic properties it can be readily rolled, drawn into wire, forged, and polished. It is also ferromagnetic and a good conductor of both heat and electricity. Nickel is positioned after hydrogen in the electrochemical series and slowly displaces hydrogen ions from dilute hydrochloric and sulfuric acids. It reacts more rapidly with nitric acid. Nickel is highly resistant to attack by strong alkalis (Hawley 1981). Black nickel oxide readily yields nickel salts... 

Sodium displaces the hydrogen in the water molecule. The displaced hydrogen is liberated from the water resulting in the formation of hydrogen gas and sodium hydroxide. 

Radical cations can be formed by irradiation of unsubstttuted aromatic hydrocarbons such as naphthalene, and this makes possible the photochemical displacement of hydride ion by a nucleophile such ascyanide f3.10). Oxygen is not necessary for the success of this type of reaction if a good electron-acceptor is present, such as p-dicyanobenzene (3.11), which enhances the initial photoionization and also provides for reaction with the displaced hydrogen. 

At the ordinary temperature chlorosulphonic acid dissolves sodium chloride, displacing hydrogen chloride and forming sodium chloro-sulphonate,11 this reaction being due to its acidic nature. It is of interest that ammonium chlorosulphonate can be synthesised by the action of sulphuryl chloride on aminosulphonic acid at 100° C.12... 

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