Amines: methods of production, structure and properties

Amines are organic derivatives of ammonia in which one, two, or all hydrogen atoms are replaced by hydrocarbon radicals.

Contents

Structure of amines
Classification of amines
Amine isomerism
Nomenclature of amines
Primary amines
Secondary amines
Tertiary amines
Aromatic amines
Isomerism of the carbon skeleton
Diamines and polyamines
Isomerism between types of amines
Isomerism of the position of the amino group
Physical properties of amines
Chemical properties of amines
Basic properties of amines
Interaction with acids
Interaction with water
Salt interaction
Alkylation of amines
Interaction with nitrous acid
Oxidation of amines
Getting amines
Recovery of nitro compounds
Recovery with ammonium sulfide
Hydrogenation with hydrogen
Metals in an acidic environment – iron, tin or zinc in hydrochloric acid
Aluminum in an alkaline environment
Hydrogenation of nitriles
Amine salts
Alkylation of ammonia and amines

Structure of amines

The nitrogen atom is in a sp3-hybridization state, so the molecule has the shape of a tetrahedron.

Also, the nitrogen atom in amines has an unshared electron pair, so amines exhibit the properties of organic bases.

Classification of amines

According to the number of hydrocarbon radicals associated with the nitrogen atom, a distinction is made between primary, secondary and tertiary amines.

The classification of amines can be confusing. The terms “primary“, “secondary” and “tertiary“, in relation to other classes of organic substances, refer to the position of the functional group at the primary, secondary and tertiary carbon atoms respectively, but things are different for amines:

2-methylbutanol-2	2-methylbutanamine-2
tertiary alcohol	primary amine

Amines are classified according to the degree of substitution at the nitrogen atom. If only one hydrogen is replaced, it is a primary amine, two are secondary, and all three are tertiary:


primary	secondary	tertiary

General formula of limiting monoamines :

Primary, secondary and tertiary amines may be isomers of each other.

According to the type of radicals, amines are divided into aliphatic, aromatic and mixed.

Amen	Primary	Secondary	Tertiary
Aliphatic	Methylamine CH₃-NH ₂	Dimethylamine CH₃-NH-CH₃	Trimethylamine (CH₃)₃N
Aromatic	Phenylamine C₆H₅-NH₂	Diphenylamine (C₆H₅)₂NH	Triphenylamine (C₆H ₅ )₃N
Mixed		Methylphenylamine CH ₃-NH-C₆H₅	Dimethylphenylamine (CH ₃ )₂N-C₆H₅

Remember that the basic properties of amines are expressed the stronger, the more electron density is present on the nitrogen atom. However, in tertiary amines, three hydrocarbon radicals create significant difficulties for chemical reactions.

Thus, in tertiary amines, the basic properties are less pronounced than in secondary amines. Basic properties increase in the order: tertiary amines (weak basic properties) → primary amines → secondary amines (basic properties are well expressed).

Amine isomerism

Amines are characterized by isomerism of the carbon skeleton, isomerism of the position of the amino group, and isomerism of various types of amines .

Nomenclature of amines

The names of amines are formed from the names of hydrocarbon radicals and the suffix amine. The different radicals are listed in alphabetical order.

Primary amines can be named as derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms are replaced by amino groups -NH₂.

In this case, the amino group is indicated in the name by the prefix amino:


1-Aminopropane	1,3-Diaminobutane

For mixed amines containing alkyl and aromatic radicals, the name of the first representative of aromatic amines, aniline , is usually taken as the basis for the name .

Primary amines

First, let’s deal with primary amines – they have only one hydrocarbon radical and an amino group NH₂.

but an amine -2

• but – a chain of four atoms,

• an – no multiple bonds,

• amine – the presence of the -NH2 group,

• -2 is its locant.

The radical-functional nomenclature of amines takes the amino group as the basis of the molecule, and considers the hydrocarbon part of the molecule as a radical . The name of the radical is indicated before the root ” amine “:

ethylamine

isopropylamine

benzylamine

Secondary amines

Secondary amines are organic derivatives of ammonia in which two of the three hydrogen atoms are replaced by a hydrocarbon radical.

The systematic name is built as follows: the main one is chosen from two hydrocarbon chains, and its name is built similarly to primary amines (see above), the second chain is considered as a radical , but has a special locant ” -N “:

N-ethylcyclobutanamine

3-methyl-N-ethylpentanamine-2

Although the radical-functional nomenclature is used more often. In it, the nitrogen atom is taken as the basis of the molecule, and the hydrocarbon parts of the molecule are considered as radicals and are listed before the root “ amine ”:

methylethylamine

diphenylamine

Tertiary amines

Tertiary amines are organic derivatives of ammonia in which all three hydrogen atoms are replaced by a hydrocarbon radical.

For tertiary amines, the radical-functional nomenclature is most commonly used. In it, the nitrogen atom is taken as the basis of the molecule, and the hydrocarbon parts of the molecule are considered as radicals and are listed before the root “ amine ”:

triethylamine

diphenylmethylamine

Aromatic amines

Aromatic amines contain a benzene ring in the molecule. The simplest aromatic amine has a trivial name:

aniline

Aromatic amines can also be secondary and tertiary, and when constructing the name, such amines are usually considered as substituted aniline :

N-methylaniline

N,N-diethylaniline

Like arenes , aromatic amines are characterized by core substitution reactions . The amino group in such reactions is a first-class orientant , facilitating substitution in the ortho and para positions. For example, aniline halogenation doesn’t even need a catalyst:

Aniline decolorizes bromine water.

Isomerism of the carbon skeleton

Amines are characterized by isomerism of the carbon skeleton (starting with C₄H₉NH₂).

Isobutylamine (1-amine-2-methylpropane)

n- Butylamine (1-aminobutane)

Diamines and polyamines

Polyamines are compounds containing two (diamines) or several amino groups (NH₂).

The systematic name of polyamines is constructed similarly to monoamines, but a multiple prefix is indicated before the root ” amine ” :

cyclohexanthriamine-1,3,5

ethane-1,2

Trivial names for some diamines:

putrescin

cadaverine

Isomerism between types of amines

For example. The formula C ₃ H ₉ N corresponds to primary, secondary and tertiary amines.


propylamine (primary amine)	Methylethylamine (secondary amine)	Trimethylamine (tertiary amine)

Isomerism of the position of the amino group

Amines are characterized by isomerism of the position of the amino group (starting from C₃H₉N).

For example. The formula C₄H₁₁N corresponds to the amines of the position of the amino group.

1-Aminobutane (n- butylamine)

2-Aminobutane

Physical properties of amines

At ordinary temperature, lower aliphatic amines CH₃NH₂, (CH₃)₂NH and (CH₃)₃N are gases (with the smell of ammonia), medium homologues are liquids (with a sharp fishy odor), higher ones are odorless solids.

Aromatic amines are colorless liquids with a high boiling point or solids.

Primary and secondary amines form weak intermolecular hydrogen bonds:

This explains the relatively higher boiling point of amines compared to alkanes with similar molecular weights.

Amines are also capable of forming hydrogen bonds with water:

Therefore, lower amines are highly soluble in water.

With an increase in the number and size of hydrocarbon radicals, the solubility of amines in water decreases. Aromatic amines do not dissolve in water.

Chemical properties of amines

Amines have a structure similar to ammonia and exhibit similar properties. In both ammonia and amines, the nitrogen atom has a lone pair of electrons:

*Ammonia* *:NH3*	*Primary amine* *R–:NH ₂*

Therefore, amines and ammonia have the properties of bases.

Basic properties of amines

Like ammonia, amines in aqueous solutions are able to form ammonium ions, more precisely, substituted ammonium (alkylammonium) and create an alkaline environment in the solution:

Due to this, amines have basic properties and form salts with acids:

ethylamine → ethylammonium bromide

The reaction is also possible with secondary and tertiary amines:

dimethylamine → dimethylammonium hydrosulfate

dimethylethylamine → dimethylethylammonium chloride

Interaction with acids

Amines react with acids , both mineral and carboxylic, and amino acids to form salts (or amides in the case of carboxylic acids):

When amines interact with polybasic acids, the formation of acid salts is possible:

Interaction with water

In aqueous solution, amines react reversibly with water. The medium of an aqueous solution of amines is weakly alkaline:

Salt interaction

Amines are capable of precipitating heavy metal hydroxides from aqueous solutions.

For example , when interacting with iron (II) chloride, a precipitate of iron (II) hydroxide is formed:

Alkylation of amines

Primary amines are able to interact with haloalkanes to form a secondary amine salt:

From the resulting salt, a secondary amine is isolated with alkali, which can be further alkylated to a tertiary amine.

Interaction with nitrous acid

Primary aliphatic amines are converted into alcohols by the action of nitrous acid:

This is a qualitative reaction to primary amines – the release of nitrogen.

Secondary amines (aliphatic and aromatic) form nitroso compounds – yellow substances:

Oxidation of amines

Amines burn in oxygen to form nitrogen, carbon dioxide and water. For example, the combustion equation for ethylamine:

Getting amines

Recovery of nitro compounds

Primary amines can be obtained by reduction of nitro compounds.

Recovery with ammonium sulfide

Hydrogenation with hydrogen

Metals in an acidic environment – iron, tin or zinc in hydrochloric acid

In this case, not amines themselves are formed, but amine salts:

Amines are isolated from a salt solution using alkali:

Aluminum in an alkaline environment

Aluminum reacts with alkalis to form hydroxo complexes. In an alkaline and neutral environment, amines are obtained . Aniline is obtained by reduction of nitrobenzene.

Hydrogenation of nitriles

Thus, primary amines are obtained. It is possible to reduce nitriles with hydrogen on a catalyst:

Amine salts

Amine salts are odorless solids, highly soluble in water, but insoluble in organic solvents (unlike amines).

Amine salts enter into exchange reactions in solution:

Under the action of alkalis on amine salts, free amines are released:

Interaction with amines:

A salt of an amine with weaker basic properties can react with another amine to form a new salt (stronger amines displace weaker ones from salts):

Alkylation of ammonia and amines

When ammonia reacts with haloalkanes, the formation of a salt of the primary amine occurs, from which the primary amine itself can be isolated by the action of alkali.