Ethers are formed by interaction. Ethers and ethers. Preparation of ethers

Ethers (alkane oxides) can be thought of as compounds formed by replacing both hydrogen atoms of a water molecule with two alkyl radicals or replacing a hydroxyl alcohol with an alkyl radical.

Isomerism and nomenclature. The general formula of ethers is ROR(I) ((C n H 2 n +1) 2 O) or C n H 2 n +1 OC k H 2 k +1, where nk(R 1  OR 2) (II). The latter are often called mixed ethers, although (I) is a special case of (II).

Ethers are isomeric to alcohols (functional group isomerism). Here are examples of such connections:

H 3 C  ABOUT  CH 3 dimethyl ether; C 2 H 5 OH ethyl alcohol;

H 5 C 2  ABOUT  C 2 H 5 diethyl ether; C 4 H 9 OH butyl alcohol;

H 5 C 2  ABOUT  C 3 H 7 ethylpropyl ether; C 5 H 11 OH amyl alcohol.

In addition, isomerism of the carbon skeleton is common for ethers (methyl propyl ether and methyl isopropyl ether). Optically active ethers are few in number.

Methods for preparing ethers

1. Interaction of halogen derivatives with alcoholates (Williamson reaction).

C 2 H 5 ОNa+I  C 2 H 5 H 5 C 2  ABOUT  C 2 H 5 +NaI

2. Dehydration of alcohols in the presence of hydrogen ions as catalysts.

2C 2 H 5 OHH 5 C 2  ABOUT  C 2 H 5

3. Partial reaction to produce diethyl ether.

P first stage:

IN second stage:

Physical properties of ethers

The first two simplest representatives - dimethyl and methyl ethyl ethers - are gases under normal conditions, all the rest are liquids. Their boiling point is much lower than the corresponding alcohols. Thus, the boiling point of ethanol is 78.3C, and H 3 COCH 3 is 24C, respectively (C 2 H 5) 2 O is 35.6C. The fact is that ethers are not capable of forming molecular hydrogen bonds, and, consequently, of molecule association.

Chemical properties of ethers

1. Interaction with acids.

(C 2 H 5) 2 O +HCl[(C 2 H 5) 2 OH + ]Cl  .

Ether plays the role of a base.

2. Acidolysis – interaction with strong acids.

H 5 C 2  ABOUT  C 2 H 5 + 2H 2 SO 4 2C 2 H 5 OSO 3 H

ethylsulfuric acid

H 5 C 2  ABOUT  C 2 H 5 +HIC 2 H 5 OH+ C 2 H 5 I

3. Interaction with alkali metals.

H 5 C 2  ABOUT  C 2 H 5 + 2NaC 2 H 5 ONa+ C 2 H 5 Na

Individual representatives

Ethyl ether (diethyl ether) is a colorless transparent liquid, slightly soluble in water. Mixes with ethyl alcohol in any ratio. T pl =116.3С, saturated vapor pressure 2.6610 4 Pa ​​(2.2С) and 5.3210 4 Pa ​​(17.9С). The cryoscopic constant is 1.79, the ebulioscopic constant is 1.84. Ignition temperature is 9.4С, forms an explosive mixture with air at 1.71 vol. % (lower limit) – 48.0 vol. % (upper limit). Causes rubber swelling. Widely used as a solvent, in medicine (inhalation anesthesia), addictive to humans, poisonous.

Esters of carboxylic acids Preparation of esters of carboxylic acids

1. Esterification of acids with alcohols.

Hydroxyl acid is released in water, while alcohol gives away only a hydrogen atom. The reaction is reversible; the same cations catalyze the reverse reaction.

2. Interaction of acid anhydrides with alcohols.

3. Interaction of acid halides with alcohols.

Some physical properties of esters are given in Table 12.

Table 12

Some physical properties of a number of esters

Esters of lower carboxylic acids and simple alcohols are liquids with a refreshing fruity odor. Used as flavoring agents for preparing drinks. Many ethers (ethyl acetate, butyl acetate) are widely used as solvents, especially for varnishes.

Definition. General formula of ethers. Physical properties

Ethers are organic compounds that contain hydrocarbon radicals $R$ and $R"$ connected by an oxygen atom. Ethers can be considered as derivatives of alcohols.

The general formula of an ether is $R-O-R"$, $Ar-O-R$ or $Ar-O-Ar$. The hydrocarbon radicals may be the same or different.

$CH_3-O-CH_3$ - dimethyl ether;

Figure 2. The simplest alkylaryl ether is methylphenyl ether (anisole). Author24 - online exchange of student work

The following cyclic ethers are of most practical importance:

Ethers can be:

• symmetrical if both radicals are the same (diphenyl, diethyl ethers);
• unsymmetrical if the radicals are different (methyl-ethyl, methylphenyl ethers).

In simple ethers, the angle between $C-O-C$ bonds is not equal to 180$^\circ$С. Therefore, the dipole moments of two $C-O$ bonds do not cancel each other out. As a result, ethers have a small net dipole moment.

Most ethers are gaseous or liquid substances. But there are exceptions, for example, phenoxybenzene.

Ethers and alkanes with the same molecular weight have similar boiling points. However, ethers have much lower boiling and melting points than isomeric alcohols.

For example: boiling point n-heptane - 98$^\circ$С, methyl- n-pentyl ether - 100$^\circ$С and n-hexyl alcohol - 157$^\circ$C.

Figure 6. Melting and boiling points of some ethers. Author24 - online exchange of student work

In ethers, hydrogen is bonded only to carbon and there are no hydrogen bonds, unlike alcohol. Therefore, ethers practically do not mix with water. However, the solubility of alcohols and ethers in water is approximately the same.

For example, n-butyl alcohol and diethyl ether are dissolved in water in a ratio of 8 g per 100 g of water. The solubility of ethers in water is due to the formation of hydrogen bonds between water molecules and ether molecules.

Ethers dissolve organic substances well.

Absolute Ether

An absolute ether is an ether that has no traces of moisture or alcohol (for example, diethyl ether $C_2H_5-O-C_2H_5$ used in the Grignard reaction). Absolute ether can be obtained by distilling ordinary ether over concentrated sulfate acid, which removes alcohol, water, and peroxides. Subsequently, the absolute ether is stored over sodium metal.

Ether Analysis

The chemical behavior of aliphatic and aromatic ethers corresponds to that of related hydrocarbons. Ethers differ from hydrocarbons in solubility in cold concentrated sulfate acid, which is due to the ability of ethers to form oxonium salts.

If an ether has already been described, then it can be identified by physical properties or chemically, by splitting when heated with concentrated hydroiodic acid and subsequent recognition of the reaction products.

Aromatic esters can be converted to solid nitration or bromination products and their melting points compared with previously described derivatives.

Ether cleavage with hydroiodic acid is used to determine the number of alkoxy groups in an alkylaryl ether using the Zeisel method.

To recognize an ether, spectral analysis is carried out. In the infrared spectrum of an ether there is no characteristic $O-H$ band of alcohols, but there is a strong $C-O$ band in the region of 1060-1300 cm$^(-1)$: for alkyl ethers 1060-1150 cm$^(-1)$, for aryl and vinyl esters 1200-1275 cm$^(-1)$:

Figure 7.

Applications of some ethers

The use of ethers is based on their ability to dissolve organic substances (resins, fats, etc.) well.

Diethyl ether (technical name "sulfur ether") is used:

• as a reaction medium when carrying out organic syntheses;
• for the extraction of certain substances (for example, alcohols from aqueous solutions);
• as a solvent for synthetic and natural resins, cellulose salts in the production of gunpowder;
• as a fuel component in aviation;
• in medicine for inhalation and local anesthesia.

Diisopropyl ether:

• is an excellent solvent for animal fats, mineral and vegetable oils, synthetic and natural resins;
• used as an additive to motor fuel, thereby increasing the octane number;
• used to separate uranium from its fission products;
• for extracting acetic acid from aqueous solutions.

Anisole and phenetol are used as intermediate compounds in the production of drugs, dyes, and fragrances. Phenetidine and its derivatives, used in medicine as antipyretic substances, are obtained from phenetol.

Diphenyl ether (diphenyl oxide) is used as a coolant in a dautherm mixture.

Cyclic ether dioxane:

• good solvent for cellulose acetate, vegetable and mineral fats and oils, waxes, paints;
• used as a reaction medium for organic syntheses;
• used to stabilize 1,1,1-trichloroethane for its transportation in aluminum containers and storage.

Classification of ethers and radical functional nomenclature

When the hydroxyl hydrogen in alcohol is replaced by a hydrocarbon residue, an ether is formed.

Ethers can be divided into ethers:

• with open chain;
• cyclic;
• aromatic;
• saturated;
• unsaturated.

Cyclic ethers are classified according to the number of atoms in the ring into:

• oxiranes (epoxides);
• oksana;
• dioxanes;
• oxolans;
• crown polyesters.

Aliphatic ethers can have the same radicals - symmetrical ethers or different radicals - unsymmetrical ethers.

Ethers, according to the rules of radical functional nomenclature, are named by radicals that are associated with an oxygen atom and add the word “ether”:

$(CH_3)_2-O-C_2H_5$ - isopropyl ethyl ether, $(CH_3)_2CH-O-CH(CH_3)_2$ - diisopropyl ether, $CH_3-O-CH_2CH_2CH_2CH_3$ - n-butyl methyl ether.

IUPAC nomenclature

According to IUPAC nomenclature, ethers are considered alkoxyalkanes (for aliphatic groups) and aryloxyalkanes (for aromatic groups).

For example, methylcyclohexyl ether is called methoxycyclohexane by IUPAC nomenclature. The name 2-ethoxyhexane is made up of hexane and an ethoxy group:

Figure 1.

The longest alkyl group (senior hydrocarbon radical) will determine the root of the ether name:

Figure 2.

For some ethers, trivial names are retained:

Figure 3.

Figure 4.

When one of the constituent radicals is much larger than the other or there are several alkoxy groups, it becomes more convenient to use alkoxy-prefix names than names using the word "ether".

Example 1

3$\beta$-methoxy-5$\alpha$-cholestane, 2,3,5-trimethoxyquinoline.

Names using the word “ether” are convenient for simple compounds, with a small number of carbon atoms, for symmetrical compounds (for example, dibutyl ether is more convenient than 1-butoxybutane); for phenol esters or polyols having known trivial names (for example, glycerol 1,3-dimethyl ether or phloroglucinol trimethyl ether).

Rules for the nomenclature of polyethers

In the case of partial esters of polyhydroxy compounds, alternatively, substitutive names can be applied by using the name of the radical $R$ as a prefix to the name of the polyhydroxy compound $R"OH$, together with positional locants and multiplying prefixes. The italicized capital $O$ indicates substitution at the atom oxygen.

This nomenclature is most often used for carbohydrate derivatives. The introduction of an alkyl group at $O$-1 of a cyclic sugar produces an acetal rather than an ester, and these derivatives are called alkyl glycosides.

Partial esters of polyhydroxy compounds can be named by combining the name of the esterifying radical (or radicals) and the name of the polyhydroxy compound and the necessary positional indications or multiplying prefixes, followed by the word "ester".

1. If two identical groups are connected by an ether bridge and they contain a group that has an advantage over the ether group in the right to be indicated as a suffix, then the ether bridge is indicated by the prefix “oxy”.
2. In $RO-X-OR$ compounds, where the parent compounds $RH$ are identical and contain a group that has an advantage over the ether group in the right to be indicated as a suffix, the name is constructed according to the method used to designate groups of identical units.
3. Linear polyethers are named using open chain substitutive nomenclature, where the structure is considered to result from the substitution of oxygen atoms for methylene groups in the parent compound. The name is derived from the name of the original molecule, and the prefix “oxa”, together with the necessary positional locants and multiplying prefixes, indicates which methylene groups are replaced by oxygen atoms.
4. If polyesters have a symmetrical linear structure, then they are called derivatives of the central part of the molecule. The role of the central part in molecules with an odd number of ether oxygen atoms is played by an ether bridge, and with an even number - a hydrocarbon radical.

Now let's talk about the difficult ones. Esters are widely distributed in nature. To say that esters play a big role in human life is to say nothing. We encounter them when we smell a flower whose aroma is due to the simplest esters. Sunflower or olive oil is also an ester, but of high molecular weight - just like animal fats. We wash, wash and wash with products that are obtained by the chemical reaction of processing fats, that is, esters. They are also used in a variety of areas of production: they are used to make medicines, paints and varnishes, perfumes, lubricants, polymers, synthetic fibers and much, much more.

Esters are organic compounds based on oxygen-containing organic carboxylic or inorganic acids. The structure of the substance can be represented as an acid molecule in which the H atom in the hydroxyl OH- is replaced by a hydrocarbon radical.

Esters are obtained by the reaction of an acid and an alcohol (esterification reaction).

Classification

- Fruit esters are liquids with a fruity odor, the molecule contains no more than eight carbon atoms. Obtained from monohydric alcohols and carboxylic acids. Esters with a floral scent are obtained using aromatic alcohols.
- Waxes are solid substances containing from 15 to 45 C atoms per molecule.
- Fats - contain 9-19 carbon atoms per molecule. Obtained from glycerin a (trihydric alcohol) and higher carboxylic acids. Fats can be liquid (vegetable fats called oils) or solid (animal fats).
- Esters of mineral acids, in their physical properties, can also be either oily liquids (up to 8 carbon atoms) or solids (from nine C atoms).

Properties

Under normal conditions, esters can be liquid, colorless, with a fruity or floral odor, or solid, plastic; usually odorless. The longer the chain of the hydrocarbon radical, the harder the substance. Almost insoluble. They dissolve well in organic solvents. Flammable.

React with ammonia to form amides; with hydrogen (it is this reaction that turns liquid vegetable oils into solid margarines).

As a result of hydrolysis reactions, they decompose into alcohol and acid. Hydrolysis of fats in an alkaline environment leads to the formation not of acid, but of its salt - soap.

Esters of organic acids are low-toxic, have a narcotic effect on humans, and mainly belong to the 2nd and 3rd hazard classes. Some reagents in production require the use of special eye and breathing protection. The longer the ether molecule is, the more toxic it is. Esters of inorganic phosphoric acids are poisonous.

Substances can enter the body through the respiratory system and skin. Symptoms of acute poisoning include agitation and impaired coordination of movements, followed by depression of the central nervous system. Regular exposure can lead to diseases of the liver, kidneys, cardiovascular system, and blood disorders.

Application

In organic synthesis.
- For the production of insecticides, herbicides, lubricants, impregnations for leather and paper, detergents, glycerin, nitroglycerin, drying oils, oil paints, synthetic fibers and resins, polymers, plexiglass, plasticizers, reagents for ore dressing.
- As an additive to motor oils.
- In the synthesis of perfumery fragrances, food fruit essences and cosmetic flavors; medicines, for example, vitamins A, E, B1, validol, ointments.
- As solvents for paints, varnishes, resins, fats, oils, cellulose, polymers.

In the assortment of the Prime Chemicals Group store you can buy popular esters, including butyl acetate and Tween-80.

Butyl acetate

Used as a solvent; in the perfumery industry for the production of fragrances; for tanning leather; in pharmaceuticals - in the process of manufacturing certain drugs.

Twin-80

It is also polysorbate-80, polyoxyethylene sorbitan monooleate (based on olive oil sorbitol). Emulsifier, solvent, technical lubricant, viscosity modifier, essential oil stabilizer, nonionic surfactant, humectant. Included in solvents and cutting fluids. Used for the production of cosmetic, food, household, agricultural, and technical products. It has the unique property of turning a mixture of water and oil into an emulsion.

Ethers have the general formula. All esters listed in table. 19.5, with the exception of phenoxybenzene, are gases or volatile liquids under normal conditions. Their boiling points are approximately the same as those of alkanes with similar relative molecular weights. However, since ether molecules are not associated by forming hydrogen bonds between them, ethers have much lower boiling points compared to their isomeric alcohols (Table 19.6).

Table 19.5. Examples of ethers

Table 19.6. Boiling points of alkane, ether and alcohol with similar relative molecular weights

Laboratory methods for obtaining esters

Symmetric ethers, such as ethoxyethane (diethyl ether), can be prepared by partial dehydration of alcohols with concentrated sulfuric acid under excess alcohol conditions:

Dehydration of alcohols was discussed above.

Both symmetric ethers, such as ethoxyethane, and unsymmetrical esters, such as methoxyethane (methyl ethyl ether) and ethoxybenzene (ethyl phenyl ether) can be prepared from the corresponding haloalkanes and alcohols using the Williamson synthesis (see above).

Chemical properties of ethers

Esters are much less reactive than alcohols. Since there is no hydrogen atom attached to the oxygen atom in ethers, ethers do not have the acidic properties that alcohols have. For example, they do not interact with sodium. However, ethers exhibit weakly basic properties, which are due to the presence of lone pairs of electrons on the oxygen atom.

Aliphatic esters behave as Lewis bases in acidic conditions. They dissolve in strong mineral acids, forming disubstituted hydronium salts:

When aliphatic ethers are heated in a mixture with concentrated hydroiodic acid, the formation of iodoalkanes occurs:

For example, the reaction of ethoxyethane with hydroiodic acid leads to the formation of dometane.