Synthesis of Ethers

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Formation of Ether

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Ether is a class of organic compounds consisting of an oxygen atom that is chemically bonded to two alkyl groups or aryl groups. Ether, alcohol, and water have similar chemical structures. In alcohol, a single hydrogen atom of a water molecule is replaced by the alkyl functional group. In ether, two hydrogen atoms of the water molecule are replaced either by alkyl or aryl groups. In subsequent sections, we will also look at the formation of ether. 

In normal temperature conditions, ether exists as a colourless liquid that has a pleasant smell. Unlike alcohols, ethers have low density, lower boiling points, and low solubility in water. Ethers by themselves are not too reactive and are hence used as solvents for other chemical compounds such as oils, perfumes, waxes, fats, gums, dyes, and resins. In the gaseous state, ethers are used as fumigating agents, pesticides, and insecticides to keep the soil healthy. 

Application as Solvents

As mentioned above, ethers are good solvents. They are used in a variety of extraction processes and other chemical reactions. Since they are volatile, they are used to start diesel and gasoline engines in places where the weather is cold. 

A type of ether called MTBE is added to gasoline to increase the level of octane and decrease the level of nitrogen oxide pollutants. Dimethyl ether is used as a refrigerant while ethylene glycol is used in the formation of plastic.  

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Applications in Pharmacology

Ethers have their applications in the field of medicine too. Ethyl ether was traditionally used as an anesthetic. The first application of ether as an anesthetic can be traced back to 1842. Ethers are also used in pain relief medications. Codeine which is a well-known pain relief medicine is an etherized form of morphine. 

Properties of Ethers

Ethers are similar in structure to alcohols. While alcohols have a chemical bond between the hydrogen and the oxygen atom which is highly polarized, ethers do not. Due to this, ethers cannot form hydrogen bonds with each other. 

The oxygen atoms in ether, however, have non-bonded electron pairs which can be used to form hydrogen bonds with other molecules that are not ethers. For instance, hydrogen bonds can be formed with alcohols or amines, i.e., O―H or N―H bonds. 

The ability to create hydrogen bonds with other compounds gives ether its application as solvents for other organic and inorganic compounds. Ethers cannot form hydrogen bonds among themselves. This is the reason why they have a lower boiling point than alcohols of the same molecular weight.  

Preparation of Ethers

In this section, we will take a closer look at various methods of synthesis of ethers. There are two methods by which ethers can be synthesized:

  1. Williamson ether synthesis

  2. Dehydration of alcohols

Let us study the reaction mechanisms of both these methods.

Williamson Synthesis 

This is one of the most flexible methods of ether synthesis. It was discovered by and named after chemist Alexander Williamson. In the Williamson synthesis reaction, the alkoxide ion reacts with the alkyl halide to substitute the (―O―R) group with the halide. For this method, the alkyl halide should be unhindered for the substitution to occur instead of an elimination reaction. 

Williamson Ether Synthesis Mechanism

The Williamson synthesis mechanism occurs in the following steps:

  • The reaction of the nucleophile with alkyl halide from the back to form an ether.

  • The entire reaction happens in one go

  • Cleavage of the molecule and formation of the bond takes place simultaneously 

  • The products depend on whether elimination or substitution reaction occurs.

Crown Ether Synthesis

Crown ethers are synthesized by a modified version of the Williamson ether synthesis reaction. These compounds are created using the same steps as in a Williamson ether reaction when a templating cation is present. 

Dehydration of Alcohol

If a protic acid reacts with alcohol then its two molecules lose water to form either ether or alkene, the product formed depends on the temperature conditions. Mostly, the dehydration of a single molecule of alcohol competes with the dehydration of two molecules. The dehydration of a single molecule is easier and leads to the formation of alkenes. The loss of two molecules can create ethers with primary alkyl groups. 

Fun Facts

Ethers should be stored in small quantities in airtight containers and used as soon as possible. This is because when ethers are exposed to the air, they explode. The reason behind this is the process of autoxidation. Air contains oxygen. Ethers react with oxygen present in the air to form dialkyl peroxides or hydroperoxides. If these compounds exist at a concentrated level or if they are exposed to heat, they lead to an explosion. 

FAQ (Frequently Asked Questions)

1. What are the Uses of Ether?

Ans: Ether is a chemical that normally exists in a liquid state. It has a pleasant smell, a colourless appearance, and is highly inflammable. When ethers are converted into vapours, these vapours can be used as proto- anesthetic. They do not manage to make a patient unconscious, but they do help in reducing pain during an operation. Ethers were used during surgeries when anesthetics were not discovered. Historically, in the field of medicine, ether was used to alleviate pain symptoms and treat various diseases such as inflammation in the lung or scurvy. It was also used as anesthesia for surgeries.

2. How are Ethers Prepared by Dehydration of Alcohols?

Ans: Using protic acids such as sulphuric acid, primary, secondary and tertiary alcohols are dehydrated to produce alkenes and ethers. The conditions of dehydration may vary. An ideal dehydration method is when ethanol (primary alcohol) reacts with sulphuric acid at 413K temperature to create ethoxyethane. If the temperature is varied and kept at 443K then the product form is an alkene instead of an ether. The dehydration of alcohols to yield ethers is a reaction which is also known as a substitution reaction that involves nucleophiles. The nucleophilic substitution occurs through two different chemical pathways. While primary alcohols follow one pathway, secondary and tertiary alcohols follow the other. This was the procedure of preparation of ether.