Acetates

Acetate is a redirect to this article. For plastic see cellulose acetate , for record pressing see dubplate .

Acetate anion

General structure of acetic acid esters with the acetate residue marked in blue . R is an organyl radical, such as an alkyl radical, aryl radical or arylalkyl radical, etc. - in the frequently used solvent ethyl acetate , R is an ethyl radical .

As Acetate (or ethanoates ) which are salts and esters of acetic acid , respectively. The salts have the general structure CH ₃ COO ^- M ⁺ , also abbreviated as: Ac O ^- M ⁺ (M ⁺ is a monovalent cation). The esters have the general structure CH ₃ COOR (sometimes abbreviated AcOR), where R can be an aliphatic , aromatic or a heterocyclic radical.

Salts

The salts are mostly colorless, crystalline solids, generally water-soluble substances that contain the acetate ion (CH ₃ COO ^- , AcO ^- ) in their crystal lattices ( ion lattices ) . This is the anion of acetic acid. Examples of salt-like acetates are sodium acetate (CH ₃ COONa), potassium acetate (CH ₃ COOK) or ammonium acetate (CH ₃ COONH ₄ ). With divalent cations, salts such as calcium acetate [(CH ₃ COO) ₂ Ca] or lead (II) acetate [(CH ₃ COO) ₂ Pb] are formed.

presentation

The salts are obtained by neutralizing acetic acid with metal hydroxides or metal oxides :

${\displaystyle \mathrm {CH_{3}COOH\ +\ NaOH\longrightarrow CH_{3}COONa\ +\ H_{2}O} }$

Acetic acid and sodium hydroxide react to form sodium acetate and water.

${\displaystyle \mathrm {2\;CH_{3}COOH\ +\ PbO\longrightarrow Pb(CH_{3}COO)_{2}\ +\ H_{2}O} }$

Acetic acid and lead (II) oxide give lead acetate and water.

proof

In chemical analysis, acetates can easily be detected by grinding the sample with potassium hydrogen sulfate in a mortar . The proton (H ⁺ ) of the hydrogen sulfate ion is transferred to the acetate ion, creating volatile acetic acid, which can easily be identified by its typical odor:

${\displaystyle \mathrm {CH_{3}COO^{-}\ +\ HSO_{4}^{-}\longrightarrow CH_{3}COOH\ +\ SO_{4}^{2-}} }$

Acetate is protonated by hydrogen sulfate. Acetic acid and sulfate are formed .

Together with silver nitrate, a flaky, white precipitate of silver acetate forms , which, however, easily dissolves again in dilute nitric acid .

${\displaystyle \mathrm {CH_{3}COO^{-}+AgNO_{3}\longrightarrow Ag(CH_{3}COO)+NO_{3}^{-}} }$

It can also be detected as a fruit ester and identified by the typical smell. (see section Presentation of the acetate esters )

Ester

Acetic acid esters (CH ₃ COOR) are often called acetates. Ethyl acetate (ethyl acetate) is the best known of these esters. Esters with low molecular weight residues are usually liquid and are used as solvents. Some of these esters, such as linalyl acetate , are used as a fragrance or flavor . A widely used medicinal substance is acetylsalicylic acid , also an ester of acetic acid.

A macromolecular acetic acid ester is e.g. B. the plastic cellulose acetate .

presentation

The acetates CH ₃ COOR are obtained by esterifying acetic acid with alcohols (R-OH) or by reacting acetyl chloride with alcohols.

${\displaystyle \mathrm {CH_{3}COOH\ +\ R\!-\!OH\longrightarrow CH_{3}COOR\ +\ H_{2}O} }$

Acetic acid and alcohol react in a condensation reaction to form an acetic acid ester and water.

Alternatively, acetic anhydride can also be reacted with alcohols to form acetic esters.

Occurrence

Acetates occur as metabolic products in all biological organisms. In addition, there are some very rare minerals such as hoganite , paceite and calclacite based on acetates. These are grouped into the group of organic minerals by the Strunz mineral systematics and the systematics of minerals according to Dana. Acetates, as naturally occurring minerals, are extremely rare, although acetic acid is widely used in nature. Until hoganite was recognized as a mineral (2002), calclacite was the only known representative of this class of substances, although it is of anthropogenic origin. Up until then it was assumed that calclacite would remain the only representative of the acetates and a purely natural formation of other acetates was considered very unlikely. With the recognition of hoganite and paceite by the IMA , these are the first representatives of this class of substances that were created without anthropogenic influence.

See also

Sometimes the acetate residue is confused with the acetyl residue . The acetyl radical contains one oxygen atom less than the acetate radical and belongs to the group of acyl radicals .

Individual evidence

1. ↑ ^{a b c} Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 145.
2. ↑ DE HIBBS, U. Kolitsch, P. Leverett, JL SHARPE, PA WILLIAMS: Hoganite and paceite, two new acetate minerals from the Potosi mine, Broken Hill, Australia. (PDF; 115 kB) In: Mineralogical Magazine, June 2002, Vol. 66 (3), pp. 459-464.

Web links

Wikibooks: Practical course organic chemistry / acid residue anions # acetate anions  - learning and teaching materials