Acetic acid's chemical properties

Chemical properties of acetic acid

Acidity of acetic acid

The carboxyl hydrogen atom of acetic acid can be partially ionized into hydrogen ions (protons) and released, resulting in the acidity of carboxylic acid. Acetic acid is a monobasic weak acid in aqueous solution, with an acidity coefficient of 4.8, PKA = 4.75 (25 ℃), and the pH of acetic acid solution with a concentration of 1mol / L (similar to that of domestic vinegar) is 2.4, that is, only 0.4% of acetic acid molecules are dissociated.

Reaction with inorganic substances

1. Acetic acid can react with some salts to form corresponding acetate.

Acetic acid and sodium carbonate: 2ch3cooh + Na2CO3 = 2ch3coona + CO2 ↑ + H2O

Acetic acid and calcium carbonate: 2ch3cooh + CaCO3 = (CH3COO) 2ca + CO2 ↑ + H2O

Acetic acid and sodium bicarbonate: NaHCO3 + CH3COOH = CH3COONa + H2O + CO2 ↑

Reaction of acetic acid with weak acid salt: 2ch3cooh + CO32 - = 2ch3coo - + H2O + CO2 ↑

2. Due to the nature of weak acids, acetic acid is corrosive to many metals, such as iron, magnesium and zinc, which react to produce hydrogen and metal acetate. Although the aluminum oxide protective layer will be formed on the surface of the aluminum in the air, the oxide film will be destroyed under the action of acetic acid, and the aluminum inside can directly interact with the acid.

Reaction of acetic acid with iron: Fe + 2ch3cooh = (CH3COO) 2Fe + H2 ↑

Reaction of acetic acid with aluminum: 2Al + 6ch3cooh = 2 (CH3COO) 3Al + 3h2 ↑

Reaction of acetic acid with zinc: Zn + 2ch3cooh = (CH3COO) 2Zn + H2 ↑

Reaction of acetic acid with magnesium: Mg + 2ch3cooh = (CH3COO) 2mg + H2 ↑

3. The metal acetate can also be prepared by reacting acetic acid with the corresponding base, such as the reaction of sodium hydroxide with acetic acid. Except for chromium (II) acetate, almost all acetate can be dissolved in water.

Ionic formula: CH3COOH + OH - = CH3COO - + H2O

Reaction of acetic acid with sodium hydroxide: CH3COOH + NaOH = CH3COONa + H2O

Reaction of acetic acid with ammonia: CH3COOH + NH3 · H2O = CH3COONH4 + H2O [5]

Biochemical reaction

The acetyl group in acetic acid is the basis of all life in biochemistry. When combined with coenzyme A, it becomes the center of carbohydrate and fat metabolism. However, the concentration of acetic acid in cells is strictly controlled within a very low range to avoid damaging changes in the pH of the cytoplasm. Unlike other long-chain carboxylic acids, acetic acid does not exist in triglycerides. However, the artificial triglyceride containing acetic acid, also known as glycerol acetate (glycerol triacetate), is an important food additive and is also used to manufacture cosmetics and local drugs.

Acetic acid is produced or secreted by certain bacteria. It is worth noting that Clostridium acetobutyricum belongs to Clostridium acetobutyricum, which widely exists in food, water and soil all over the world. Acetic acid is also naturally produced when fruit or other food spoils. Acetic acid is also a component of the vaginal lubricant of all primates, including humans, and is used as a mild antibacterial agent.

Decarboxylation reaction

Under the catalysis of copper and heating, acetic acid can undergo decarboxylation reaction to generate carbon dioxide and methane:

Redox reaction

Reduction reaction

Acetic acid can be reduced to acetaldehyde by lithium aluminum hydride: 

oxidation reaction

The combustion reaction of acetic acid is an oxidation reaction in a broad sense. Complete combustion of acetic acid will generate carbon dioxide and water vapor:

Substitution reaction

esterification

Acetic acid and ethanol can be esterified under the catalysis of concentrated sulfuric acid and heated to produce ethyl acetate: 

α- H halogenation reaction

In the presence of red phosphorus, halogen and acetic acid can occur α- H halogenation reaction. For example, acetic acid reacts with chlorine under the action of red phosphorus to produce chloroacetic acid:

Dehydration reaction

Acetic acid can undergo intermolecular dehydration reaction. One acetic acid molecule will remove one - OH group, while the other acetic acid molecule will remove one h, and finally form acetic anhydride: 

Reaction with phosphorus trichloride

When acetic acid and phosphorus trichloride are heated, substitution reaction can occur, and acetyl chloride and phosphorous acid can be generated:

Reaction with ammonia

Under the catalysis of lipase, acetic acid can undergo addition reaction with ammonia, and the hydroxyl group of acetic acid is replaced by amino group to form acetamide.