What is Raney Nickel?
Raney nickel, also known as spongy nickel, is a solid substance that is made up of nickel obtained from an alloy of nickel and aluminium.
The primary application of this solid is its use as a reagent & catalyst for many hydrogenation reactions in the field of organic chemistry. This solid has a fine-grained texture. Among the different known grades of this substance, the majority exist as grey solids under ambient conditions. Raney nickel is named after its developer – the American mechanical engineer Murray Raney.
It can be noted that Raney nickel is sometimes referred to as “sponge metal catalyst” and as “skeletal catalyst”.
Table of Contents
- Preparation of Raney Nickel
- Properties of Raney Nickel
- Catalytic Applications of Raney Nickel
- Frequently Asked Questions – FAQs
Preparation of Raney Nickel
In order to prepare Raney nickel, a nickel-aluminium alloy must be prepared first. This can be done by heating aluminium into a molten state and subsequently dissolving nickel into it. This molten mixture must now be cooled in a process known as quenching. The activity of the catalyst can be enhanced by adding small quantities of chromium or zinc to the mixture during the quenching process.
Once the alloy is obtained, it must be ground into a fine powder and then treated with concentrated sodium hydroxide. This results in the formation of sodium aluminate and hydrogen gas, as shown in the chemical equation provided below.
2Al + 6H2O + 2NaOH → 2Na[Al(OH)4] + 3H2
Via the process of leaching, a sizable amount of aluminium present in the nickel-aluminium alloy is extracted. This leaves behind the required catalyst. Before storing the catalyst, it must be cleaned with distilled water under room temperatures in order to remove any leftover sodium aluminate.
Properties of Raney Nickel
The properties of Raney nickel are highly dependent on the activation process followed during the production phase. This catalyst is known to be structurally and thermally stable. On a macroscopic level, it appears to be a fine powder that is grey in colour. However, upon microscopic inspection, it can be observed that each grain of the powder is, by itself, a 3-Dimensional mesh containing pores that are irregular in shape and size. These pores are usually created during the leaching phase of the production process.
When BET measurements are conducted with the help of a gas that tends to get preferentially adsorbed on the surface of certain metals (such as hydrogen), it is usually observed that the majority of the surface area of Raney nickel grains is made up of nickel. The larger the concentration of nickel in the surface, the greater the catalytic activity of the catalyst. Typically, one gram of Raney nickel has an active nickel surface of 100m2.
The density of Raney nickel is 6.5 grams per cubic centimetre. It is not very soluble in many common laboratory solvents. This catalyst is, however, highly soluble in many mineral acids (hydrochloric acid, for example).
Catalytic Applications of Raney Nickel
Owing to its relatively high catalytic activity and its ability to adsorb hydrogen within its pores, Raney nickel is a very good catalyst for hydrogenation reactions. For example, this catalyst can be used for the conversion of benzene into cyclohexane (which can, in turn, be oxidised into adipic acid).
Raney nickel also has the ability to catalyse certain desulfurization reactions. For example, hydrocarbons can be obtained from the reduction of thioacetal with the help of Raney nickel (illustrated below).
Additionally, Raney nickel can be used as a catalyst for the following reactions:
- Conversion of dextrose to sorbitol
- Obtaining amines from nitro compounds
- Conversion of alkenes and alkynes to alkanes
- Obtaining amines from nitriles
Frequently Asked Questions – FAQs
What is the difference between nickel and Raney nickel?
The key difference between Raney nickel and nickel is that Raney nickel is a mixture of several chemical elements whereas nickel is a chemical element we categorise as a metal. However, nickel is a metal and Raney nickel is a finely powdered solid which has nickel as the major component.
What does H2 Raney nickel do?
Raney nickel is used in a large number of industrial processes and in organic synthesis because of its stability and high catalytic activity at room temperature. It is typically used in the reduction of compounds that have multiple bonds, such as alkynes, alkenes, nitriles, dienes, aromatics and carbonyls.
Can Raney nickel reduce amides?
Most known examples of nickel-catalysed amide reduction require the use of Raney nickel, high temperatures, and high pressures of H2 gas.
Does Raney nickel reduce ketone?
Raney nickel in refluxing 2-propanol containing a trace of HCl is an effective catalytic system for the reduction of ketones to secondary alcohols.
What does nickel bond with?
Compounds of nickel are chemical compounds containing the element nickel which is a member of group 10 of the periodic table. Nickel forms simple binary compounds with non-metals including halogens, chalcogenides, and pnictides.
To learn more about Raney nickel and other important catalysts in organic chemistry (such as Wilkinson’s catalyst), register with BYJU’S and download the mobile application on your smartphone.
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