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[Chemical Knowledge]：Why is vinyl alcohol unstable?

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Vinyl alcohol is one of the most common organic compounds, made from the reaction of carbon dioxide and water. Vinyl alcohol plays a very important role in the industrial preparation of many chemicals. It can be used as a chemical solvent, adhesive and diluent, and it is also one of the ingredients of some fragrances. However, it has been found that vinyl alcohol is not very stable and decomposes easily, so why is vinyl alcohol unstable? This article will explain in detail the instability of vinyl alcohol and the possible decomposition reactions. The hydroxyl group (-OH) in

vinyl alcohol molecule is very polar, and has good hydrophilicity and induction effect. This makes the vinyl alcohol and other polar substances easy to react. Among them, a typical reaction is the etherification reaction, that is, under the action of an acid catalyst, vinyl alcohol can react with another organic compound containing a reactive hydrogen atom by losing a water molecule to form an ether. For example, vinyl alcohol and propylene oxide can react to form 1,2-propylene oxide:

CH2 = CHOH C3H6O → CH2OCH2CH2OC2H5

This reaction is one of the causes of the instability of vinyl alcohol.

In addition, vinyl alcohol can also cause polymerization reactions by their own electrophilic attack with each other. When a vinyl alcohol molecule is added to other vinyl alcohol molecules, a reaction of share cleavage and discharge of water molecules occurs, that is, a hydroxyl group pair as an initiating mechanism may undergo an addition reaction to form a polymer. This polymerization phenomenon is another cause of the instability of vinyl alcohol.

In addition, vinyl alcohol is also susceptible to an oxidative decomposition reaction. Vinyl alcohol is susceptible to oxidation by oxygen in the air to form aldehydes and acids. This decomposition reaction is also called oxidative decomposition reaction, and its composition is as follows:

2CH2CHOH → CH2 = CHCHO CH3CHO

This reaction is often caused by vinyl alcohol exposed to air. The usual way is to add antioxidants to prevent the occurrence of oxidation reactions.

finally, vinyl alcohol is also susceptible to thermal decomposition. When vinyl alcohol absorbs heat or is stimulated by external high temperature, a decomposition reaction occurs to produce ethylene and water. Ethylene is a very reactive monomer that easily initiates other reactions, and the presence of water also promotes ethylene production. Therefore, great care must be taken with the high temperature pyrolysis of vinyl alcohol, as it may produce some undesirable chemicals that are difficult to control.

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