Disulfuric acid: characteristics and functions of this substance

We have all heard of sulfuric acid, even in passing. This extremely corrosive and dangerous substance is the most widely produced chemical compound in the world. It is particularly important in the petroleum industry, the treatment of steel, the manufacture of explosives, detergents and plastics, and in the synthesis of fertilizers.

Without sulfuric acid, it would also not be possible to power the wood and paper industry, many processes in the textile factories or the production of batteries. Nor can we forget its role in the chemical industry, since it is necessary for the synthesis of other acids and sulfates vital for certain processes.

In other words, society would not be as we know it without sulfuric acid, since it plays essential tasks in the chemical industry, in the oil industry and in the agricultural field, among many others things. However, not all sulfur compounds are equally well known. Here we pay attention to one much less familiar to the general population: disulfuric acid..

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What is disulfuric acid?

Disulfuric acid, also known as pyrosulfuric acid or oleum, is an oxacid of sulfur. The term "oxacid" refers to any acid that contains oxygen in its composition, especially those that They have in their chemical structure at least one hydrogen atom (H), one oxygen atom (O) and a variable element, be it this X.

Disulfuric acid is the main component of fuming sulfuric acid or oleum, whose properties and uses we will explain in future sections. For now, we are left with that its chemical structure is H2SO7. This means that it is made up of two hydrogen atoms (H2), 7 oxygen (O7) and two sulfur (S2). Sulfuric acid to use, for its part, has two hydrogen atoms, one sulfur and four oxygen (H2SO4).

It is also of interest to emphasize that this acid has a molar mass of 178.13 g · mol − 1 and that its melting point is 36 degrees, a temperature that marks the change from a solid to a liquid state. There are other acids with the same formula "H2O · (SO3) x", although these cannot be isolated under experimental conditions today.

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Oleum characteristics

As we have said, disulfuric acid is the main component of fuming sulfuric acid, also known as oleum. The formula of this solution is ySO3 · H2O, where “y” is the total molar mass of the sulfur trioxide (SO3) part. However, it can also be designated by the nomenclature "H2SO4 · xSO3", where "x" refers to the content of molar free sulfur trioxide. When x = 1 and y = 2, the formula H2S2O7 is obtained, or what is the same, that of disulfuric acid.

It may sound complex, but keep the following idea: an oleum solution can have different properties depending on the percentage of concentration of sulfuric acid and the aforementioned conformation gives rise to disulfuric acid, which occurs in solid form up to 36 degrees of temperature environmental. As interesting as this whole conglomerate sounds at a chemical level, in any case, it is necessary to emphasize that disulfuric acid is rarely used in laboratory settings or industrial processes.

Oleum is synthesized through a “contact process”, where oxygen groups are added to sulfur (S + O3, SO3) and then it is dissolved in a sulfuric acid concentrate (H2SO4). Perhaps a chemist would pull his hair to see such a great oversimplification, but for informative purposes, we take the license to show you the union of both concepts:

Thus, the typical oleum or disulfuric acid is built with sulfur to which oxygen and concentrated sulfuric acid have been added. In the world of chemistry, in the end everything is also a matter of mathematical knowledge.

Functions and utilities of this substance

Once we have dissected the chemical nature of this complex solution, we can explore its uses, albeit briefly.

1. Sulfuric acid production

Although it sounds counterintuitive, a solution that requires sulfuric acid for its synthesis can be useful for the production of sulfuric acid itself.

Due to its high enthalpy of hydration (change in enthalpy when one mole of ions dissolves in enough water to give a dilute solution), the oleum can be diluted in water to produce concentrated sulfuric acid additional.

On the contrary, if SO3 were added directly to the water, it would form a gaseous film of sulfuric acid that is very difficult to handle.

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2. Transport intermediary

As oleum is presented in a solid state up to 36 degrees of temperature, can be useful for transportation of sulfuric acid in tank trucks, between oil refineries and various industries. Once it reaches its destination, the oleum can revert to its liquid state. In any case, this process must be carried out very carefully, as overheating of the material (overheating) exceeds the safety limits.

In addition, oleum or disulfuric acid is less corrosive than sulfuric acid in use when it comes into contact with metals, since there are no free water molecules that can attack these surfaces. For this reason, liquid disulfuric acid is sometimes also chosen to be synthesized for transport between complex pipelines. Due to its ability to "revert" to concentrated sulfuric acid and its ease of changing from a solid to a liquid state, oleum has many uses in the field of transportation.

3. Disulfuric acid in the explosives industry

The oleum also used in the synthesis of explosives, with the notable exception of nitrocellulose. This is due to the fact that solutions of nitric acid (NO3) and sulfuric acid (H2SO4, which may or may not be obtained using the disulfuric acid) contain significant amounts of water, making them of little use in many manufacturing processes of explosives.

4. Use in the study of organic chemistry

Oleum is an aggressive and highly corrosive reactive agent, useful as an intermediate in certain chemical reactions.

Resume

In summary, disulfuric acid can be seen as an intermediate of sulfuric acid, despite being derived from reactions that require it in the first instance. As it occurs naturally in a solid state, it is suitable for safe transport in many sectors of the industry that handle H2SO4 naturally. The use of this compound in its liquid form is also very interesting, since being less corrosive than sulfuric acid, it generates less damage to pipes and other metallic coatings.

Again, we return to the idea that sulfuric acid is essential in the agricultural, wood, textile, oil industry and many other branches. Thus, although disulfuric acid is not very useful as a directly applicable compound in the field laboratory, it does provide a certain plasticity when transporting, refining and treating the acid itself sulfuric.