Sulphur – Allotropic forms

Allotrope of sulphur is classified in group 16 of the periodic table. It makes up 0.17 % of the earth’s crust. Sulphur is not a metallic, i.e. non-metallic compound produced as a byproduct of natural gas production.

General Properties Sulphur 

Consider the important physical and chemical features of sulphide related to various applications.

Physical Characteristics: Allotrope of sulphur

• Sulphur appears to be yellow.

• Water is unable to dissolve this chemical. In Toluene, it is highly soluble (methylbenzene) and carbon disulfide.

• The allotrope of sulphur is not made of metal, and it is considered a poor conductor of heat and electricity.

• When we reach a certain point in condensing Sulphur vapour, we obtain a powder that, too fine and forms a pattern that resembles a flower. The ‘Flower of Sulphur’ is the name given to this flower.

Chemical Characteristics: Allotrope of sulphur

• Under specific conditions, metals and non-metals do react with sulphur.

• Sulphur (IV) oxide and some Sulphur (VI) oxide are produced when sulphur burns more than air.

S + O2 →SO2

S + O2 →SO3

• A high-temperature reaction between this compound and hydrogen results in the formation of hydrogen sulphide.

S + H2 →H2S

• It is also possible to produce carbon disulphide, a liquid, by combining Sulphuric acid and hot coke.

Different Allotropic forms of Sulphur 

Sulphur creates a variety of allotropes, but let us focus on the two most essential allotropic forms of Sulphur for the time being.

The yellow rhombic Sulphur (α-Sulphur) and the monoclinic Sulphur (β-Sulphur) are Sulphur types. The most exciting aspect is that the thermal stability and allotropes of the sulphur compound are interconvertible, which means that they may be converted into one another. It signifies that the rhombic Sulphur transforms into monoclinic Sulphur when heated to a temperature greater than 369K. Consider the following two allotropes of sulphur in greater depth.

α-Sulphur Or Rhombic Sulphur

It is the most common type of allotrope of sulphur and is made by slowly evaporating a solution of roll Sulphur in CS2 until octahedral Sulphur crystals form. 2.06 g cm3 is its specific gravity. It melts at 385.8 degrees Celsius. This is the most stable state of Sulphur at room temperature, and all other conditions of Sulphur shift to this state when left standing. 

It is insoluble in water and soluble in benzene, alcohol, and ether to a greater or lesser extent. It is solvable in CS2, however. It is a poor conductor of heat and electricity. It has a specific gravity of 2.07 grams per cubic centimetre. The colour is bright yellow. Rhombic Sulphur exists in the form of S8 molecules. Sulphur atoms are grouped in a puckered ring configuration.

Monoclinic Sulphur Or β-Sulphur

The rhombic Sulphur is melted in a dish and allowed to cool until a crust forms, which is how this sulphur is made. The remaining liquid is drained by drilling two wells in the crust. ß-sulphur needle-shaped crystals form when the crust is scraped away. Like rhombic Sulphur, it is soluble in carbon disulfide, a dull yellow crystalline substance. At 1.98 grams per cubic centimetre, it’s the lightest substance in the world. It is a 393-degree Kelvin melting point. Sulphur monoclinic molecules have puckered rings, similar to rhombic Sulphur As S8 molecules. 

However, the crystal symmetry of the two forms differs. Above 369K, it is stable, but below that point, it degrades to α-Sulphur. Instead of β-Sulphur, which remains stable below 369 K, β-Sulphur undergoes a chemical reaction. As a result, both forms can survive and thrive at 369 degrees Celsius. The changeover temperature is a term used to describe this point in time.

As a result, rhombic and monoclinic Sulphur both contain S8 molecules. These S8 molecules are packed to form a variety of crystal structures. The S8 ring is puckered in both variants and has a crown shape. Other allotropes of sulphur are as follows. 

Plastic Sulphur 

Plastic Sulphur is another allotropic form of sulphur. Plastic Sulphur is created by pouring molten Sulphur into cold water, forming a soft rubber-like mass known as plastic Sulphur. It is a Sulphur compound that is amorphous. It is first soft and elastic but progressively hardens and transforms into rhombic Sulphur. It does not have a well-defined melting point. Its specific gravity is 1.95 grams per cubic centimetre. Carbon disulfide is insoluble in it. Plastic Sulphur is classified as a supercooled liquid, which means that it was rapidly cooled below its freezing point and had no chance to crystallise.

Colloidal Sulphur

 Bypassing hydrogen sulphide about a saturated and cooled solution of sulphur dioxide in water, we can create this type of sulphur. Alternatively, water can be treated by adding an alcohol and sulphur solution. Carbon disulfide is also a solvent for it. This compound has the potential to be used in pharmaceuticals.

Sulphur Milk

We can synthesise this sulphur by reacting ammonium sulphide with weak hydrochloric acid. Sulphur and calcium hydroxide are boiled together to produce this milk of sulphur similarly (which becomes an aqueous solution). Sulphur milk can be made by filtering this mixture and adding a small hydrochloric acid.

In terms of appearance, this compound is crystalline and white. Sulphur turns conventional yellow when heated, allowing us to use it as a pharmaceutical ingredient. Carbon disulphide is a solvent for it.

Allotropic forms of sulphur:  Applications

Consider the following significant applications of sulphur

• Sulphur compounds can promote the growth of particular fungi in vines.

• Sulphur is a frequent component in synthesising tetraoxosulphate(VI) acid. Additionally, this is the primary application of Sulphur.

• Sulphur can be used to make calcium hydrogen tetraoxosulphate (IV), Ca(HSO3)2. This compound is also used as a wood pulp bleacher in the papermaking business.

• Sulphur is a critical and frequently used component in the vulcanisation of rubber. This process hardens and toughens the rubber by clustering the rubber molecules together.

• Sulphur is used in the manufacture of colours.

• Sulphur is used extensively to manufacture Sulphur compounds, such as CS2 and Sulphur monochloride and carbon disulfide, S2Cl2.

• It is often used in ointments.

• Sulphur is also a necessary component of sulphides, including phosphorus sulphide. This can be used to make gunpowder, matches, and firecrackers.

Conclusion

Sulphur can be found in various structures in the same physical form. However, the most effective crystal allotrope of sulphur is rhombic or octahedral Sulphur (α– Sulphur) and monoclinic Sulphur (β– Sulphur). At temperatures less than 96°C, we observe the formation of rhombic Sulphur. On the other hand, monoclinic Sulphur occurs at temperatures greater than 96°C.

96°C is the critical temperature for the transition between the two crystalline forms. There is another Sulphur allotrope known as polymeric Sulphur (S8). It is a ring particle composed of eight constituents. This substance is insoluble in organic solvents and synthetic and natural rubber. Additionally, it is insoluble in carbon disulfide.