Amine refers to the product in which one or more hydrogen atoms in the ammonia molecule is replaced by a hydrocarbon group. According to the number of hydrogen atoms in the amine molecule, the amine can be divided into primary amine, secondary amine, and tertiary amine; amines are widely found in biology It has very important physiological and biological activities. For example, proteins, nucleic acids, many hormones, antibiotics, and alkaloids are all amine derivatives. Most drugs used in clinical practice are also amines or amine derivatives. Therefore, master amines. The nature and synthetic methods of this are the basis for studying these complex natural products and better safeguarding human health.



Classification of amines

According to the number of hydrogen substituted, it is divided into primary amine (primary amine) RNH2, secondary amine (secondary amine) R2NH, tertiary amine (tertiary amine) R3N, quaternary ammonium salt (quaternary ammonium salt) R4N+X- For example, methylamine CH3NH2, aniline C6H5NH2, ethylenediamine H2NCH2CH2NH2, diisopropylamine [(CH3)2CH]2NH, triethanolamine (HOCH2CH2) 3N, tetrabutylammonium bromide (CH3CH2CH2CH2) 4N+Br-. The tetrahydroxyl 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

According to the different types of hydroxyl groups connected to the nitrogen atom in the amine molecule, amines can be divided into aliphatic amines and aromatic amines. If the amine molecule contains two or more amino groups (-NH2), it can be divided into diamines and triamines according to the number of amino groups.



Physical and chemical properties

At room temperature, lower fatty amine is gas, propylamine and above are liquid, and higher fatty amine is solid. Lower amines have an unpleasant or unpleasant smell. For example, trimethylamine has a fishy smell, but butanediamine (putrescine) and pentamethylenediamine (cadaverine) have the stench of decayed animal carcasses. High-grade amines are not volatile and have little odor. Aromatic amines are high-boiling liquids or low-melting solids. Although their odor is smaller than fatty amines, they are more toxic. Whether they are inhaled in their vapor or contacted with the skin, they can cause poisoning. Some aromatic amines, such as β-naphthylamine and benzidine, also have carcinogenic effects.

Since nitrogen atoms in amine molecules can form hydrogen bonds with water, the solubility of lower aliphatic amines in water is relatively large. Primary and secondary amines can form intermolecular hydrogen bonds, but because the electronegativity of nitrogen atoms is less than that of oxygen atoms, amines have weaker hydrogen bond association ability, and their boiling point is lower than that of alcohols with similar molecular weights.

Amine is similar to ammonia. The nitrogen atom in the molecule contains an unshared pair of electrons, which can combine with H+ to be alkaline.

R-NH2+HCl≒R-NH3++Cl-

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



Synthesis of Amine

Ammonolysis of halides

Ammonia or amine nitrogen has a lone pair of electrons, which acts as a nucleophile to undergo nucleophilic reaction with halogenated alkanes, according to the SN2 mechanism. Many organic halides are treated with ammonia solution or ammonia solution to become amines:

X is halogen

RX + NH3 → RNH3 + X-

RNH3+X- → RNH2 + H2O + X-

Prepared with alcohol

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

ROH + NH3 → RNH2 + H2O

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



Amine preparation method

Amines are widely distributed in nature, and most of them are produced by decarboxylation of amino acids. For example, most of the industrial methods for preparing amines are prepared by the reaction of ammonia with alcohol or alkyl halides. The product is a mixture of various levels of amines, and the pure product is obtained after fractionation. 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 Amine



Amines have a wide range of uses. The earliest developed dye industry was based on aniline. Some amines are necessary for life-sustaining activities, but some are very harmful to life. Many amine compounds have carcinogenic effects, especially aromatic amines such as naphthylamine and benzidine.



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