Ethers
Chapter Name : Alcohols, Phenols And Ethers |
Sub Topic Code : 102_12_11_06_02 |
Topic Name : Ethers |
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Sub Topic Name : Preparation By Williamson's Synthesis |
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Introduction
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'.
Pre-Requisites:
Ethers
Activity:
Polyethers.
Real Life Question:
What are alcohols?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Organic compound | An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Diethyl ether | Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula (C2H5)2O. |
Real life uses :
Used as a starting fluid, in combination with petroleum distillates for gasoline and diesel engines because of its high volatility and low flash point.
Places to visit :
Chemistry laboratory.
Practical examples around us
| Examples | Explainations |
|---|---|
| Paraformaldehyde | Paraformaldehyde (PFA) is the smallest polyoxymethylene, the polymerization product of formaldehyde with a typical degree of polymerization of 8–10 units. Paraformaldehyde commonly has a slight odor of formaldehyde due to decomposition. Paraformaldehyde is a poly-acetal. |
What you learn in Theory:
This reaction is called the Williamson ether synthesis. It involves treatment of a parent alcohol with a strong base to form the alkoxide, followed by addition of an appropriate aliphatic compound bearing a suitable leaving group (R-X). Suitable leaving groups (X) include iodide, bromide, or sulfonates. This method usually does not work well for aryl halides (e.g. bromobenzene (see Ullmann condensation below). Likewise, this method only gives the best yields for primary halides. Secondary and tertiary halides are prone to undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups.
What you learn in Practice:
In a related reaction, alkyl halides undergo nucleophilic displacement by phenoxides. The R-X cannot be used to react with the alcohol. However, phenols can be used to replace the alcohol, while maintaining the alkyl halide. Since phenols are acidic, they readily react with a strong base like sodium hydroxide to form phenoxide ions. The phenoxide ion will then substitute the -X group in the alkyl halide, forming ether with an aryl group attached to it in a reaction with an SN2 mechanism.