Disulfuric acid: characteristics, properties and functions

Chemistry is one of the most important sciences in the world because, basically, everything around us is chemistry. From nuclear fusion reactions that take place in the heart of stars, to the process by which our cells consume energy, to how plants photosynthesize, to how we cook our dishes, it is all chemistry.

And in this context, of the millions of different chemicals, there are some better known and others less well known. Today, in this article, we will focus on one that is perhaps not as famous as others but is undoubtedly chemically amazing: disulfuric acid.

With importance in the oil industry, in the manufacture of explosives, in the manufacture of plastics, in the synthesis of fertilizers, in the treatment of steel, in the production of batteries, in the synthesis of other acids and sulfates, in the industry. of wood, in textile factories, etc, this disulfuric acid is present in more areas than we think.

And if you want to know its characteristics, chemical properties, nomenclature, uses and functions, you have come to the right place. In today's article we will explore, in the hands of the most prestigious scientific publications in the world of Chemistry, the most interesting characteristics of disulfuric acid. Let's go there.


    What is disulfuric acid, oleum or pyrosulfuric acid?

    Disulfuric acid, oleum or pyrosulfuric acid is an oxacid, that is, an acid that contains oxygen in its chemical composition. More concretely, is an oxacid of sulfur whose chemical formula is H2S2O7, so it is composed of two hydrogen atoms (H), two sulfur (S) and seven oxygen (O).

    Disulfuric acid is the main component of fuming sulfuric acid and has a molar mass of 178.13 g / mol and a melting point (transition from solid to liquid) of 36 ° C, so at room temperature, this pyrosulfuric acid it is solid.

    It is known as oleum due to its oily consistency and its crystalline color., although sometimes it can be yellowish or even dark brown (depends on the concentration of SO3). It is an anhydrous acid, that is, it does not contain water and it is difficult to isolate it in a pure form.

    In this sense, disulfuric acid is a "dense" form of sulfuric acid that is formed when a molecule of H2SO4 reacts with one of SO3, thus giving rise to this disulfuric acid that can be formulated as H2S2O7 or, due to the formation reaction , as H2SO4 · SO3.

    As far as its molecular structure is concerned, at both ends we find each hydroxyl group. And due to the inductive effect of the oxygen atoms, the hydrogens increase their positive partial charge, something that explains why they present even higher acidity than sulfuric acid.

    A disulfuric acid solution can have different properties depending on the percentage of sulfuric acid it contains and its conformation. Even so, it is necessary to emphasize that, although it seems very interesting at the laboratory level, the truth is that it is rarely used in these environments and its uses are intended for other frameworks that we will comment on later.

    Properties of disulfuric acid

    Disulfuric acid, oleum or pyrosulfuric acid It is obtained through what is known as the “contact process”, which consists of adding oxygen groups to sulfur (SO3) and then dissolving in concentrated sulfuric acid (H2SO4). As we can see, Chemistry has a lot of Mathematics.

    In any case, it is important to bear in mind that its properties are not very well described due to the difficulties of isolating it in its pure form. And it is that in this oleum there may be other compounds with similar chemical formulas but not exactly those of disulfuric acid.

    Be that as it may, in a state of almost total purity, it is about a fuming crystalline solid (which is unstable) at room temperature that melts at 36 ° C, although this phase change point depends on purity. Similarly, depending on the SO3 concentration, it can be yellowish and even dark brown in color.

    Another of its properties is the ability to form disulfate salts, also known as pyrosulfate. An example of this is what happens with potassium hydroxide (KOH), a substance with which this disulfuric acid reacts to give rise to potassium pyrosulfate (K2S2O7).

    It also has two H + ions that can be neutralized with a strong base and, as we discussed earlier, a molar mass of 178.13 g / mol. Chemically, it is considered an anhydride of sulfuric acid, because, due to the condensation between two acid molecules, it loses a water molecule.

    And although it is known as pyrosulfuric acid because heat intervenes in its formation, the IUPAC (International Union of Pure and Applied Chemistry) simply recommends the nomenclature of disulfuric acid. Be that as it may, its -ico prefix is ​​due to the sulfur atom having a valence of +6.

    Functions and uses of disulfuric acid

    Now that we have understood the chemical nature of disulfuric acid and its properties, we are more than ready to see what applications this substance has on a practical level. So let's discuss the functions and uses of disulfuric acid.

    1. Synthesis of sulfuric acid

    One of its most important uses is in the production of sulfuric acid. Yes, it may sound counterintuitive, as we have seen that disulfuric acid is obtained from sulfuric acid, but it can also be useful for the synthesis of this sulfuric acid (H2SO4).

    And is that if we add water to the solution, the disulfuric acid reacts forming more sufuric acid and increasing its concentration. If there is still water, more SO3 is added, which reacts with the sulfuric acid to produce disulfuric acid, which can be rehydrated to dry out the sulfuric acid. This process can be repeated several times until obtaining an isolated sulfuric acid with a concentration of 100%..

    2. Sulfuric acid warehouse

    A very interesting use is that it can serve as a safer and more practical store for sulfuric acid. Thanks to its property of being solid at room temperature, it is a good way to “store” sulfuric acid and to transport it safely.. Then, when it is necessary to have the sulfuric acid as such, the previous process is carried out to obtain it in a 100% concentration.

    This is very interesting for the transport of sulfuric acid in tank trucks, between different industries and between oil refineries. Obviously, it must be done extremely carefully, as overheating of the material can cause problems.

    It is safer because it can be transported in a solid form and, in addition, disulfuric acid is less corrosive to metals than sulfuric acid, since there are no free water molecules that can attack surfaces. For all this, disulfuric acid is very interesting for the storage and transport of what can be converted, by the reaction that we have analyzed before, into sulfuric acid.

    3. Sulfonation of chemicals

    Sulfonation is any chemical reaction in which a sulfonic group (SO2OH) is introduced to a chemical substance, thus obtaining a sulfonic acid. This is very interesting in the textile industry, since disulfuric acid is used to stimulate the sulfonation of coloring chemical compounds. The addition of the sulfonic group causes them to lose an acidic proton and that they can be anchored to the polymers of the textile fiber and thus improve the coloring process.

    4. Chemical reaction intermediary

    Beyond this sulfonation, disulfuric acid can be used as an intermediate for different chemical reactions. In fact, its acidity is used to achieve the second nitration (addition of NO2 groups) in chemicals with aromatic rings, especially nitrobenzene, a toxic oily liquid. Its first nitration occurs in the presence of nitric acid, but for the second a stronger reagent such as this disulfuric acid is needed.

    And its corrosive power and aggressive reactivity can be interesting in different organic chemistry reactions. In the same way, disulfuric acid is also used to obtain trinitrotoluene, a chemical compound explosive and part of various explosive mixtures, by promoting the oxidation of the dinitrotoluene ring and the addition of a third nitro group.

    5. Uses in industry

    Finally, we end with its industrial use. Disulfuric acid is very important, thanks to its chemical properties and / or corrosive power, as we have commented in the introduction, in the oil industry, in the manufacture of explosives (we have just analyzed its role in obtaining trinitrotoluene), in the chemical treatment of steel, in the manufacture of different types of plastics, in the production of batteries, in the synthesis of other acids (including, of course, sulfuric) and sulfates (by sulfonation), in textile factories (especially in what has to do with the binding of colorants to textile polymers), in the synthesis of fertilizers and in the wood and paper industry. As we see, its industrial uses have an impact on almost all areas of our lives.

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