Hydration of propylene: reaction equation

Organic matters occupy an important place in our life. They are the main constituent of polymers that surround us everywhere: these are plastic bags, and rubber, as well as many other materials. Polypropylene is not the last step in this line. It is also part of a variety of materials and is used in a number of industries, such as construction, has household use as a material for plastic cups and other small (but not for production scale) needs. Before talking about a process such as the hydration of propylene (thanks to which, incidentally, we can get isopropyl alcohol), let us turn to the history of discovery of this necessary for the industry substance.

History

As such, the date of discovery is not propylene. However, its polymer, polypropylene, was actually discovered in 1936 by the famous German chemist Otto Bayer. Of course, it was theoretically known how one could get such an important material, but in practice it was not possible. This was only possible in the middle of the twentieth century, when German and Italian chemists Ziegler and Nutt discovered a catalyst for the polymerization of unsaturated hydrocarbons (having one or more multiple bonds), which was later called the Ziegler-Natta catalyst. Up to this point, it was decidedly impossible to make the polymerization reaction of such substances go. Polycondensation reactions were known where, without the action of the catalyst, the substances were combined in a polymer chain, thereby forming a by-product. But it was not possible to do this with unsaturated hydrocarbons .

Another important process associated with this substance was its hydration. Propylene in the years of its application was quite a lot. And all this thanks to the invented by various oil and gas processing companies ways of curing propene (this is sometimes also called the described substance). When cracking oil, it was a by-product, and when it turned out that its derivative, isopropyl alcohol, is the basis for the synthesis of many useful substances for mankind, many firms, such as BASF, patented their way of production and started mass trade in this compound. Hydration of propylene was tested and applied before polymerization, that is why acetone, hydrogen peroxide, isopropylamine began to be produced before polypropylene.

A very interesting process is the separation of propene from oil. It is to him that we now turn.

Isolation of propylene

In fact, in the theoretical interpretation, the main method is only one process: the pyrolysis of oil and associated gases. But the technological realizations are just the sea. The fact is that each company seeks to obtain a unique method and protect it with a patent, while other similar companies also look for their ways to still produce and sell propene as raw materials or turn it into various products.

Pyrolysis ("pyro" - fire, "lysis" - destruction) is the chemical process of decay of a complex and large molecule into smaller ones under the action of high temperature and a catalyst. Oil, as is known, is a mixture of hydrocarbons and consists of light, medium and heavy fractions. Of the first, the most low-molecular, and get propene and ethane in pyrolysis. Conduct this process in special ovens. Among the most advanced manufacturers, this process is technologically different: some use sand as a coolant, others - quartz, others - coke; It is also possible to divide the furnaces according to their structure: there are tubular and conventional reactors, as they are called.

But the process of pyrolysis makes it possible to obtain insufficiently pure propene, since, besides it, a huge number of hydrocarbons are formed there, which then have to be separated by energy-consuming methods. Therefore, to obtain a cleaner substance for subsequent hydration, dehydrogenation of alkanes is also used: in our case, propane. Just like polymerization, the above process just does not happen. Cleavage of hydrogen from the mollusc of the ultimate hydrocarbon occurs under the action of catalysts: trivalent chromium oxide and aluminum oxide.

Well, before we go on to the story of how the hydration process is going on, let's look at the structure of our unsaturated hydrocarbon.

Features of the structure of propylene

Propene itself is only the second member of a series of alkenes (hydrocarbons with one double bond). By its lightness it is second only to ethylene (from which, as you might guess, polyethylene is the most massive polymer in the world). In the usual state, propene gas, like its "relative" from the alkane family, is propane.

But the essential difference between propane and propene is that the latter has a double bond in its composition, which fundamentally changes its chemical properties. It allows to connect other substances to the molecule of unsaturated hydrocarbon, resulting in compounds with completely different properties, often very important for industry and everyday life.

It's time to talk about the theory of reaction, which, in fact, this article is devoted to. In the next section, you will learn that when hydrating propylene, one of the most industrially important products is formed, as well as how this reaction occurs and what nuances there are in it.

Theory of hydration

First, let's turn to a more general process - solvation - which also includes the reaction described above. This chemical transformation, which consists in the attachment of solvent molecules to the molecules of the dissolved substance. In this case, they can form new molecules, or so-called solvates, - particles consisting of molecules of dissolved substance and solvent, connected by electrostatic interaction. We are only interested in the first kind of substances, because with the hydration of propylene, it is mainly this product that is formed.

When solvating in the manner described above, the solvent molecules are attached to the dissolved substance, a new compound is obtained. In organic chemistry, hydrates mainly produce alcohols, ketones and aldehydes, but there are several other cases, for example the formation of glycols, but we will not touch them. In fact, this process is very simple, but at the same time it is rather complicated.

Hydration mechanism

The double bond, as is known, consists of two types of compounding atoms: pi and sigma bonds. Pi-bond during the hydration reaction is always broken first, as it is less strong (has a lower binding energy). When it breaks, two vacant orbitals form at two neighboring carbon atoms, which can form new bonds. A water molecule that exists in a solution in the form of two particles: a hydroxide ion and a proton, is capable of joining via a broken double bond. In this case, the hydroxide ion is attached to the central carbon atom, and the proton to the second, extreme. Thus, upon hydration of the propylene, propanol 1 or isopropyl alcohol is predominantly formed. This is a very important substance, because when it is oxidized, you can get acetone, mass used in our world. We said that it is formed mainly, however it is not quite so. I must say so: the only product is formed when hydrating propylene, and this is isopropyl alcohol.

This, of course, all the subtleties. In fact, everything can be described much easier. And now we find out how the process of hydration of propylene is recorded in the school course.

Reaction: how it happens

In chemistry, everything is usually called simply: with the help of reaction equations. So the chemical transformation of the substance under discussion can be described in this way. The hydration of propylene, the equation of the reaction of which is very simple, proceeds in two stages. First breaks the pi-link, which is part of the double. Then a water molecule in the form of two particles, hydroxide-anion and hydrogen cation, comes to a molecule of propylene, which currently has two vacant sites for bonding. The hydroxide ion forms a bond with a less hydrogenated carbon atom (i.e., with one to which a smaller number of hydrogen atoms are attached), and the proton, respectively, with the remaining extreme. Thus, we obtain a single product: the limiting monohydric alcohol isopropanol.

How to record a reaction?

Now we learn how to write down a chemical reaction that reflects a process, such as the hydration of propylene. The formula that will come in handy for us: CH ₂ = CH - CH ₃ . This is the formula of the starting substance - propene. As you can see, he has a double bond marked with the "=" sign, and it is in this place that water will be attached when hydration of propylene takes place. The reaction equation can be written as: CH ₂ = CH-CH ₃ + H ₂ O = CH ₃ -CH (OH) -CH ₃ . The hydroxyl group in the brackets means that this part is not in the plane of the formula, but lower or higher. Here we can not show the angles between the three groups that depart from the average carbon atom, but we say that they are approximately equal to each other and make up 120 degrees.

Where does this apply?

We have already said that the substance obtained during the reaction is actively used for the synthesis of other substances vital to us. It is very similar in structure to acetone, which differs only in that instead of the hydroxo group there is a keto group (that is, an oxygen atom connected by a double bond to a nitrogen atom). As is known, acetone itself finds its application in solvents and varnishes, but, in addition, it is used as a reagent for the further synthesis of more complex substances, such as polyurethanes, epoxy resins, acetic anhydride, and so on.

Acetone Production Reaction

We think it would be superfluous to describe the conversion of isopropyl alcohol to acetone, especially since this reaction is not so complicated. To begin with, propanol is evaporated and at 400-600 degrees Celsius oxygenates with a special catalyst. A very pure product is obtained by carrying out the reaction on a silver grid.

The reaction equation

We will not go into details of the mechanism of the reaction of oxidation of propanol to acetone, since it is very complex. We shall confine ourselves to the usual chemical transformation equation: CH ₃ -CH (OH) -CH ₃ + O ₂ = CH ₃ -C (O) -CH ₃ + H ₂ O. As can be seen, everything is quite simple on the diagram, but it's worth digging into the process, And we will encounter a number of difficulties.

Conclusion

So we disassembled the process of hydration of propylene and studied the equation of the reaction and the mechanism of its flow. The considered technological principles underlie the real processes occurring in production. As it turned out, they are not very complicated, but they have a real benefit for our daily life.