Dehydration of Alcohols

Alcohols are compounds with one or more -OH groups that bond with the carbon atoms and are widely used in pharmaceuticals and many industries. The dehydration of alcohol means the removal of water to form alkenes and other products. The best way to make alkenes is by dehydration of alcohol. It is a process through which alcohol undergoes E1 or E2 mechanisms, which helps them to form a double bond and lose water. 

Dehydration of Alcohol forms alkenes

The dehydration reaction of alcohol starts by heating it at a high temperature along with phosphoric or sulfuric acid or any strong acid in this case.

If the dehydration process is not carried out at sufficient temperature, they react with each other and form ethers instead of forming alkenes. For example,

Amphoterism is the property of a substance to react with both acid and base. They act as a base in the presence of acid and as the acid in the presence of a base, and since alcohol has such properties, it can act both as an acid and a base. For example, 

Mechanism of Dehydration of an alcohol

Every type of alcohol has different ways of mechanisms to dehydrate. The basic process of alcohol dehydration includes the -OH group donating two electrons to H+ from the acid reagent, which forms alkyloxonium ions. The secondary and the tertiary groups undergo the E1 mechanism, and the primary group of alcohol undergoes the E2 mechanism. The primary reaction undergoes the process in which the hydroxyl oxygen donates two electrons to a proton from sulphuric acid, resulting in an alkyloxonium ion. The secondary and tertiary alcohol dehydration results in the -OH protonate forming alkyloxonium ions. 

Dehydration of alcohols using an acid catalyst

In this dehydration process of alcohols, the acid catalysts are either concentrated phosphoric acid or concentrated sulphuric acid. Concentrated sulphuric acid can be tricky because it is not only acid but also a strong oxidising agent. Because of this, when reacting with alcohol, it reduces itself into sulphur dioxide. Also, it oxidises some of the alcohol into carbon dioxide, and both of these gases need to be removed from the alkene. 

Dehydration of alcohols to ethers

Alcohols can undergo intermolecular dehydration to produce ethers under strictly controlled conditions. But this reaction is only effective in ethanol methanol and other primary alcohols. It is also the cheapest way to make ethyl ether which is widely used in industries as solvents. 

Physical properties of alcohol

Most of the pure forms of alcohol are colourless liquids at room temperature. Compounds alcohols such as methyl, isopropyl, and ethyl have a fruity odour. The compounds that contain 4-10 carbon atoms are most likely viscous or oily. The boiling point of alcohol is higher than alkanes. 

Alcohol and water have indistinguishable properties because alcohol molecules can form hydrogen bonds with water and other alcohol molecules. Similarly, water molecules contain hydroxyl groups through which they can form hydrogen bonds with other water molecules and alcohol molecules. Because of this, the alcohol molecules tend to be soluble in water. 

Importance of alcohol in industries

Ethanol 

Ethyl alcohol goes way back in time because it has been produced mainly by fermentation of fruit juices since prehistoric times. The process was to store the fermented juice in an airtight container and was safe to drink throughout winter. The fermentation process also included breaking down sugar and starch into simpler components. 

The common name of ethanol is a grain alcohol, as it is mainly produced with grains like wheat, corn and barley. These grains are first boiled in water to produce mash and include malt. The malt converts the starches into sugar maltose. 

Then the liquid extracted from the mashing process is then incubated with yeast, which helps convert the maltose to glucose and then convert the glucose to ethanol. Ethanol has been widely used as a fuel for motos since they have low emissions and high octane rating.

Methanol 

The common term used for methanol is wood alcohol, as methyl alcohol is made by heating the wood chips in the absence of air. When this is done, the carbohydrates from the wood are broken down into methanol, and then the vapour is condensed. Methanol undergoes a catalytic reaction of carbon monoxide with hydrogen gas under high temperature and pressure.

This mixture can be generated in the presence of water by partially burning the coal. Methanol is mainly used in industries as a solvent and is more harmful than ethanol as it can also cause blindness or death if inhaled in large quantities. 

Glycerol 

Glycerol is also known as glycerine and can be produced by fermentation from sugar and molasses. It was widely used in world war II to produce glyceryl trinitrate. Glycerine is also used to make nitroglycerin, an explosive material used in blasting gelatin and dynamites. 

Nitroglycerin is also used as a drug that expands and relaxes the blood vessels to relieve chest pain because of poor circulation of blood to the heart. Glycerol is used as a plasticiser, antifreeze, water-soluble lubricant, moisturising agent and solvent. It is widely found in foods, cosmetics, hydraulic fluids, pharmaceuticals, soaps and printing inks. 

Conclusion 

Alcohol is a group of organic compounds that contains one or more -OH groups attached to the carbon atom of a hydrocarbon chain. When you heat the alcohol with strong acid catalysts, they undergo a 1,2 elimination reaction to produce alkene and water. The relative reactivity order of alcohol is 3°>2°>1°. The familiar sources of alcohol are ethanol, isopropyl alcohol and ethanol. Since alcohols can be easily transformed into other compounds and are easily synthesised, it serves as crucial intermediates in organic synthesis. They can also be oxidised to give aldehydes, carboxylic acids and ketones.