Amine Properties and Uses || What are the different types of amines?

Interpretation of amine: The product after the substitution of one or more hydrogen atoms in the ammonia molecule with a hydrocarbon group is called an amine. In this lesson, we will discuss Amine Properties and Uses.

According to the number of hydrogen atoms substituted in the amine molecule, the amine can be divided into primary, secondary, and tertiary amines, ammonia Hydrogen in the molecule is replaced by a hydrocarbon group.

Amine Properties and Uses

At the same time, the amine can be regarded as a derivative of H in the ammonia molecule replaced by a hydrocarbon group. Amines are widely present in the biological world and have extremely important physiological and biological activities, such as Protein, nucleic acids, many hormones, antibiotics, and alkaloids. They are all complex derivatives of amines. Most drugs used in clinical practice are also amines or amine derivatives.

Therefore, mastering the properties and synthetic methods of amines is to study these complex natural products and Basis for better maintenance of human health.

Classification of Amines

According to the number of hydrogen substituted, it is divided into:

The tetrahydroxy substitution of ammonium hydroxide or ammonium salt is called quaternary ammonium hydroxide or Quaternary ammonium salt .

NH4+ammonium R4NOH quaternary ammonium base R4NX quaternary ammonium salt

Depending on the type of hydroxyl group attached to the nitrogen atom in the amine molecule. Amines can be divided into fatty amines and aromatic amines. If the amine molecule contains two or more amino groups (-NH 2), they can be divided into diamines and triamines according to the number of amino groups.

Physical and Chemical Properties

Amine Properties and Uses

At room temperature, lower fatty amines are gases, propylamines are liquids, and higher fatty amines are solids. Lower amines have an unpleasant or bad smell.

For example, trimethyl amine has a fishy smell, but succinyl amine (putrescine) and glutamine (cadaverine) have a bad smell after the animal carcass rots.

Higher amines are less volatile and have a lower odor. Aromatic amines are high-boiling liquids or low-melting solids. Although they are less odorous than fatty amines, they are more toxic. They can cause poisoning whether they inhale their vapor or contact the skin. Some aromatic amines, such as β-naphthylamine, and benzidine also have carcinogenic effects.

Because the nitrogen atom in the amine molecule can form a hydrogen bond with water, the solubility of lower fatty amines in water is relatively large.

Primary and secondary amines can form intermolecular hydrogen bonds, but because the electronegativity of the nitrogen atom is less than that of the oxygen atom, the hydrogen bonding ability of the amine is relatively weak, and its boiling point is lower than that of alcohols with similar molecular weight.

Amine is similar to ammonia in that the nitrogen atom in the molecule contains an unshared electron pair, which can be combined with H +to be alkaline.

The basicity of the amine is expressed by the basic ionization constant Kb or other negative logarithmic values pKb. The larger the Kb value or the smaller the pKb value, the stronger the basicity of the amine.

Synthesis of Amines

Ammonolysis of halides

There is a lone pair of electrons on the ammonia or amine nitrogen, which acts as a nucleophile and undergoes a nucleophilic reaction with a haloalkane. Many organic halides are treated with ammonia or ammonia solution to turn into amines:

X is halogen

NH2 + the RX3 → RNH23 + X- RNH23 + X- -→ RNH22 + H2O + X- -

Made with alcohol

The main synthetic method of amines is the alkylation of ammonia. Industrial use of alcohols and ammonia to synthesize organic amines:

ROH + NH3 → RNH2 + H2O

These reactions require the use of catalysts, special equipment, and additional purification, because the mixture of primary, secondary, and tertiary amines is obtained, and the selectivity of the reaction needs to be improved.

Preparation of Amine

Amines are widely distributed in nature, most of which is produced by decarboxylation of amino acids.

Most of the industrial methods for preparing amines are obtained by the reaction of ammonia with alcohol or haloalkanes. The product is a mixture of amines at various levels, and the pure product is obtained after fractional distillation.

The corresponding amines can also be obtained by catalytic reduction of aldehydes and ketones in the presence of ammonia. In industry, amine compounds are often prepared by catalytic reduction of nitro compounds, nitriles, amides or nitrogen-containing heterocyclic compounds.

Application of Amines

Amine has a wide range of uses. The earliest development of the dye industry was based on aniline. Some amines are necessary for life support

Yes, but some are very harmful to life. Many amine compounds have carcinogenic effects, especially aromatic amines, such as naphthylamine and benzidine.

Structure of Amine

The structure of the nitrogen atom in the amine, much like the nitrogen atom in the ammonia molecule, is connected to hydrogen or a hydrocarbon group by three sp hybrid orbitals, forming a pyramid, leaving an sp3 hybrid orbital occupied by a lone electron pair. If an amine has three different groups, there should be a pair of enantiomers (see Enantiomers):

However, due to the low activation energy required for the lone electron pair in the inverted amine molecule, its enantiomers could not be separated.

The experiment proves that the amine and ammonia molecules have a pyramidal structure, the nitrogen atom is sp3 hybrid, and the bond angle is about 109 degrees.

Originally published at on February 7, 2020.



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