Ethers

Physicochemical features

Ethers differ radically from alcohols in physical properties, even though they are frequently isomers. The main reason lies in their structure: no hydrogen bonds are formed between ether molecules.

This directly affects their thermodynamic characteristics. Ethers possess significantly greater volatility. For example, ethanol boils at 78 °C, whereas its structural isomer — dimethyl ether ($CH_3OCH_3$) — turns into a gas at as low as -24.8 °C.

Chemically, ethers are notable for their inertness. They do not decompose or hydrolyze back to the initial alcohols even upon prolonged boiling in concentrated alkali solutions.

Mechanisms of formation: dehydration

One of the classical preparation methods is intermolecular dehydration of alcohols. The reaction proceeds by heating an alcohol in the presence of a sulfuric acid ($H_2SO_4$) catalyst. The process follows a nucleophilic substitution mechanism in three stages:

1. Protonation: the oxygen atom of the first alcohol molecule attaches a hydrogen ion ($H^+$).
2. Nucleophilic attack: the oxygen of the second alcohol molecule donates its electron pair to the carbon of the protonated molecule.
3. Elimination of water: a $H_2O$ molecule is eliminated, the catalyst ($H^+$) is regenerated, forming an ether.

Important: reaction conditions must be controlled. If parameters change (e.g., heating to ~150 °C with a sulfuric acid mixture), a different process is triggered — intramolecular dehydration of the alcohol yielding an alkene (ethylene).

Synthesis of unsymmetrical ethers (Williamson synthesis)

Intermolecular dehydration is convenient for producing symmetrical ethers. For the synthesis of compounds with different hydrocarbon radicals, the reaction of alcoholates (alcohol salts, such as ethoxides or methoxides) with haloalkanes is used.

During the reaction, the metal of the alcoholate binds with the halogen to form a salt, while the radicals link via oxygen. Example: the reaction of sodium ethoxide with chloropropane yields unsymmetrical ethoxypropane and sodium chloride as a byproduct.

Safety and medical aspect

Special attention is paid to safety rules when handling ethers in medicine, primarily ethoxyethane (medical ether, $C_2H_5OC_2H_5$). Under the influence of atmospheric oxygen, the process of peroxide formation is initiated in such organic liquids.

Peroxides are unstable and highly explosive substances. They retain relative safety only in a heavily diluted form. Over time, the concentration of peroxide impurities in the preparation inevitably increases. This is precisely why a strict rule applies: long-term storage of medical ether is prohibited, as this may lead to a spontaneous explosion of the container.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Intramolecular dehydration of alcohols (elimination)
• Synthesis of alcohols using Grignard reagents
• Oxidation of primary and secondary alcohols
• Qualitative reactions for polyhydric alcohols (formation of copper chelates)
• Esters of inorganic acids (nitroglycerin)

Other topics in "Chapter 16. Oxygen-containing organic substances"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.