Ethers are organic substances in which molecules contain hydrocarbon radicals joined by an oxygen atom. This can be written as follows: R'– O – R ", where R" and R 'are the same or different radicals.
Ethers are considered as derivatives of alcohols. These compounds have compound names. In this case, the name of the radicals is used (in increasing molecular weight) and, in fact, the word "ether" (dimethyl ether 33, methylethyl ether 253 and so on).
Symmetric R – O – R compounds are obtained by intermolecular alcohol dehydration. In one molecule, the O – H bond is broken, and in the other, the C – O bonds. The reaction can be considered as a nucleophilic substitution of the HO group (in one molecule) by the RO group (from another molecule).
Asymmetric R – O – R ′ compounds are formed upon the interaction of halogenated hydrocarbons and alcoholates.
Ethers (unlike alcohols isomeric to them) have lower melting and boiling points. Compounds hardly mix with water. This is due to the fact that ethers do not form hydrogen bonds due to the absence of O — H polar bonds in their molecules.
Compounds are inactive. They have a lower ability to react than alcohols.
Ethers are often used as solvents because of their ability to dissolve many organic substances.
The most important compounds include heterocyclic acid-containing substances: dioxane and epoxide (ethylene oxide).
The first is a good solvent. Dioxane is able to mix with both hydrocarbons and water. Due to these qualities, this compound is also called "organic water". Dioxane is toxic, but its halogen-containing dibenzo derivatives are most dangerous.
Cellulose ethers are products of substitution of the hydrogen atom in the hydroxyl groups of the cellulose macromolecule by alkyl or acid residues. The synthesis is carried out in order to impart new properties to the substance, in particular, thermoplasticity and solubility. When substituted by acid residues, complex compounds are formed, when substituted by alkyl residues, simple compounds are formed.
The first is obtained in the process of acylation and esterification - in the interaction of cellulose with inorganic and organic acids, their acid chlorides and anhydrides. The greatest practical importance is attached to xatogenates. These compounds are prepared by reaction with inorganic acids and are used in the manufacture of cellophane and viscose fibers. Cellulose nitrates are also of industrial importance. They are used to obtain varnishes, films, smokeless gunpowder.
Of the compounds obtained by reaction with organic acids, cellulose acetates are widely used in industry. They are used to produce synthetic fibers, plastics, and films.
Mixed cellulose ethers also exist. They contain various acyl and alkyl substituents.
The properties of all cellulose ethers depend on the nature of the radical. The degree of substitution and polymerization also matters.
Low substituted simple compounds dissolve in aqueous alkaline solutions and water. This allows them to be used as thickeners and stabilizers in emulsions in the oil, paper, textile, food, pharmaceutical and other industries. Highly substituted ethers (complex and simple) are compatible with plasticizers. They are used in the manufacture of plastics and the manufacture of varnishes.
Crown ethers are polyesters containing several oxygen atoms in a cycle. Formally, they are considered as products of cyclooligomerization of ethylene oxide. A unique property of these compounds is the ability to form complexes with salts of various alkali metals. These complexes are formed due to electrostatic interaction.