When the alloy of aluminium and nickel gives a solid entity, this result is called the Raney Nickel. Raney or Spongy Nickel plays a key role in organic chemistry, where the element is used as a catalyst or reagent during hydrogenation chemical reactions. Upon inspection of its microparticles, this Raney Nickel is said to be a finely grated powder-like substance, where each of its pores forms a 3-dimensional shape. From understanding its properties to the preparation and applications, let us learn everything important about Raney Nickel.
The Basic Information about Raney Nickel
Spongy Nickel, Skeletal Catalyst, Sponge Metal Catalyst, are all the different names of one compound which is Raney Nickel. The credits for the discovery of this compound goes to Murray Raney in 1926, who was an American mechanical engineer and developed this element for hydrogenation of vegetable oils.
Deriving from the Aluminium-Nickel’s alloy, the Raney Nickel is said to be a solid substance but present as a fine powdery element. This is a compound that is given high importance in the fields of organic chemistry, for hydrogenation reactions in particular.
A vast majority of the available Raney Nickel grades are noted to be a grey substance, strictly under ambient temperature conditions. Let’s now see how one can prepare Raney Nickel using a few chemical elements.
Preparing Raney Nickel Chemically
The primary conditions to prepare Raney Nickel is the alloy of nickel and aluminium. First, heat the aluminium until getting a molten stage and then mix nickel into this mixture. Then, with a method known as ‘quenching’, the molten state of the aluminium-nickel alloy is cooled down for some time.
Meanwhile, the catalyst’s activity can be intensified by adding a third metal, such as zinc or chromium into the mixture obtained. Chromium and zinc here are stated to be the ‘promoters’. Concentrated Sodium Hydroxide is then added to the final alloy, forming hydrogen gas and sodium aluminate. This step can be equated as follows:
2Al + 6H2O + 2NaOH → 2Na[Al(OH)4] + 3H2
After this process, filter out a minimal amount of aluminium from the alloy as NiAl3 and Ni2Al3 using the leaching process. This will result in leaving only the catalyst behind and this Raney Nickel catalyst is cleansed using distilled water in room temperature. This final step is important before storing the result, to remove the sodium aluminate that is leftover from the reaction.
Note that the water used should be oxygen-free (degassed).
Raney Nickel and its Important Properties
Given below are the important physical and chemical properties regarding Raney Nickel and its structure:
Grey coloured-powder under macroscopic conditions but appears solid externally.
Irregularly sized shapes and 3-D figures were observed inside every single grain of the power under an electron microscope and formed using the leaching process.
Both Thermally and Structurally stable.
Raney Nickel is labelled as both ‘harmful’ and ‘flammable’.
Mineral acids like that of the Hydrochloric Acid solute Raney Nickel completely.
6.5 grams per cubic centimetre is the density.
The pH level of this Nickel form is 8.5-12.0.
A few grades of this Nickel form is said to be a Pyrophoric substance.
The catalytic activity of the substance is directly proportional to the amount of Nickel present in it. Which means, the more nickel available, the higher is the catalyst’s activity.
The commercial form of Raney Nickel is available in both active and inactive modes.
Stable grade forms are used in air slurries.
100m2 of Active Raney Nickel surface is noted to be from a 1 gram of the same substance.
Less soluble with other chemical compounds present in a clinical laboratory.
With measurement processes of BET, more than half the structure of the Raney Nickel consists of Nickel only.
The phase of production plays a vital role in deciding the activation level of this Nickel form.
Applicability of the Raney Nickel Catalyst
As stated before, hydrogenation reactions majorly prefer Raney Nickel for its good reactivity and high range of oxygen absorption capacity inside its pores. Let us consider the example of benzene conversion.
Raney Nickel Catalysts is used in producing cyclohexane by the conversion of benzene. Again, this can be oxidized with the same element to create adipic acid.
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This element further catalyzes organic reactions such as desulfurization. To state an example, Raney Nickel Catalyst is used in the Mozingo reduction of thioacetal into the hydrocarbon Ethane.
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Adding to the stated, Raney Nickel is also preferred in the removal of Sulfides and Thiols from the heteroaromatic, aromatic and aliphatic compounds. The result of removing the thiophene and sulfur from the reaction is the formation of an alkane.
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Furthermore, Raney Nickel is also an important catalyst for the reactions including, nitro compounds conversion into amines (vice-versa), getting different kinds of paraffin from olefins, in the formation of sorbitol from dextrose, converting acetylenes to paraffin, and even to obtain alkanes from alkynes and alkenes.
Spongy Nickel, Skeletal Nickel, or Raney Nickel is obtained from the alloy of aluminium and nickel, discovered by Murray Raney, a mechanical engineer in America. This appears solid grey but is a fine powdery material under microscopic conditions. Raney Nickel is available in different grades and can be sold commercially both as an inactive and active reagent. Organic chemistry gives high importance to this compound since hydrogenation, reduction, oxidation, and many other chemical reactions are enhanced and prepared using the Raney Nickel Catalyst.
1. Give the safety and health hazards, if any, linked with the usage of Raney Nickel.
The activated dry form of Raney Nickel is Pyrophoric. Meaning under certain aerated conditions, this element can quickly catch fire. It has to be handled strictly under inert atmospheric conditions. Even acute levels of exposure to Raney Nickel develops health issues such as nasal cavity damage, respiratory tract irritation, and even triggers pulmonary fibrosis when inhaled deeply. As per the International Agency for Research on Cancer (IARC), Nickel is also to be handled with good care since it might lead to serious life hazards such as cancer.
2. What are the applications of Raney Nickel for industries and other chemical procedures?
Raney Nickel has plenty of applications both industrially as well as for chemical synthesis. To name a few, reducing the chemical compounds with a triple bond such as nitriles, alkynes, aromatics, alkanes, carbonyls, alkenes, dienes, nitrosamines, heteroatom-heteroatom reduction, amination of alcohols, desulfurization, hydrogenation, are some of the common applications of Raney Nickel.
3. How to store Raney Nickel safely?
Raney Nickel has to be safely stored by keeping the substance always submerged in water. Even a slighter presence of air can trigger fire as this material is highly flammable and pyrophoric. Dioxane, ethanol, and even cyclohexane can be substituted for water.
4. Mention the primary stage of preparing Raney Nickel using the 2 alloys.
The 2 alloys, Nickel and Aluminium are the key factors to primarily create Raney Nickel. Starting by heating the Aluminium compound and adding Nickel to the process at its molten stage, the preparation of Raney Nickel ends by removing the aluminium through a process called and cooling down the mixture using the procedure of quenching. The resulting substance possesses a high surface area with flammable properties and hence is the Raney Nickel formed.
5. Mention at least 3 uses of Raney Nickel Catalyst apart from its application inside organic chemistry.
Raney Nickel Catalyst, apart from its organic chemistry-related applications, is used in areas such as the production of pesticide intermediates, creating rubber additives and in the manufacturing of Caprolactam.