por What are amines?
The amines They are organic compounds derived from ammonia. They produce covalent bonds between carbon and nitrogen. Naturally, the nitrogen molecule is kinetically inert; but thanks to biological fixation, it is transformed into ammonia, which in turn undergoes subsequent alkylation reactions.
When ammonia is «alkylated,» it replaces one, two, or three of its three hydrogens with carbon atoms. These carbons can either come from an alkyl (R) or aryl (Ar) group. Thus, there are aliphatic (linear or branched) and aromatic amines.
Amines are organic bases that are stronger than ammonia itself. They are easily extractable from plant matter, and generally have strong interactions with the neuronal matrix of organisms; hence many drugs and drugs consist of amines with complex structures and substituents.
amine structure
Although it varies depending on the nature of R, the electronic environment of the nitrogen atom is the same for all of them: tetrahedral. But, since there is a pair of unshared electrons on the nitrogen atom (··), the molecular geometry becomes pyramidal. This is so with ammonia and amines.
Amines can be represented by a tetrahedron, just like carbon compounds. Thus, NH3 and CH4 are drawn as tetrahedrons, where the pair (··) is located in one of the vertices above nitrogen.
Both molecules are achiral; however, they begin to show chirality as their H is replaced by R. The amine R2NH is achiral if the two R’s are different. However, it lacks any configuration to differentiate one enantiomer from another (as is the case with chiral carbon centers).
This is because the enantiomers:
R2N-H | H-NR2
they are exchanged at such a rate that neither can be isolated; and therefore, the amine structures are considered achiral even though all the substituents on the nitrogen atom are different.
amine properties
Polarity
Amines are polar compounds, since the NH2 amino group, having an electronegative nitrogen atom, contributes to the dipole moment of the molecule. Note that nitrogen has the ability to donate hydrogen bonds, which makes amines generally have high boiling and melting points.
physical characteristics
In the world of chemistry, when talking about an amine, the involuntary act of holding one’s nose arises. This is because, in general, they tend to have unpleasant odors, some of which even resemble rotten fish.
In addition, liquid amines usually have yellowish tones, which increase the visual mistrust they generate.
Water solubility
Amines tend to be insoluble in water because, despite being able to form hydrogen bonds with H₂O, their majority organic component is hydrophobic. The bulkier or longer the R groups, the lower their solubility in water.
When there is an acid in the medium, however, the solubility is increased by the formation of what are known as amine salts. In them, the nitrogen has a partial positive charge, which electrostatically attracts the anion or conjugate base of the acid.
Basicity
Amines are organic bases stronger than ammonia. The greater the electron density around the nitrogen atom, the more basic it will be; that is, it will deprotonate the acids in the medium more quickly. If the amine is very basic, it can even take the proton from alcohols.
Types (primary, secondary, tertiary)
Although they have not been formally presented, primary, secondary and tertiary amines have been implicitly referred to (top image, from left to right).
The primary amines (RNH2) are monosubstituted; the secondary ones (R2NH) are disubstituted, with two R alkyl or aryl groups; and the tertiary (R3N), are trisubstituted, and lack hydrogen.
All existing amines are derived from these three types, so their diversity and interactions with the biological and neuronal matrix are enormous.
In general, tertiary amines might be expected to be the most basic; however, such a statement cannot be made without knowing the structures of R.
Formation of the amines
ammonia alkylation
At first it was mentioned that amines are derived from ammonia; therefore, the simplest way to form them is through their alkylation. To do this, an excess of ammonia is reacted with an alkyl halide, followed by the addition of a base to neutralize the amine salt:
NH3 + RX => RNH3+X– => RNH2
Note that these steps lead to a primary amine. Secondary and even tertiary amines can also be formed, so the yield for a single product decreases.
Some formation methods, such as the Gabriel synthesis, allow primary amines to be obtained in such a way that other undesirable products are not formed.
Likewise, ketones and aldehydes can be reduced in the presence of ammonia and primary amines, to give rise to secondary and tertiary amines.
catalytic hydrogenation
Nitro compounds can be reduced in the presence of hydrogen and a catalyst to transform into their corresponding amines.
ArNO2 => ArNH2
Nitriles, RC≡N, and amides, RCONR2, are also reduced to primary and tertiary amines, respectively.
Nomenclature
How are amines named? Most often they are named after R, the alkyl or aryl group. To the name of R, derived from its alkane, the word ‘amine’ is added at the end.
Thus, CH3CH2CH2NH2 is propylamine. On the other hand, it can be named considering only the alkane and not as a group R: propanamine.
The first way of naming them is by far the best known and used.
When there are two NH2 groups, the alkane is named and the amino group positions are listed. Thus, H2NCH2CH2CH2CH2NH2 is called: 1,4-butanediamine.
If there are oxygenated groups, such as OH, it should be given priority over NH2, which is named as a substituent. For example, HOCH2CH2CH2NH2 is called: 3-Aminopropanol.
And with respect to secondary and tertiary amines, the letters N are used to indicate the R groups. The longest chain will remain with the name of the compound. Thus, CH3NHCH2CH3 is called: N-Methylethylamine.
Uses of amines
dyes
Primary aromatic amines can serve as starting material for azo dye syntheses. Initially, the amines react to form diazonium salts, which form the azo compounds by azo coupling (or diazo coupling).
Due to their intense coloration, they are used in the textile industry as a dyeing material; for example: Methyl Orange, Brown 138 Direct, Sunset Yellow FCF, and Ponceau.
drugs and drugs
Many drugs work with agonists and antagonists of natural amine neurotransmitters. Examples:
-Chlorpheniramine is an antihistamine used to control allergic processes due to the ingestion of some foods, hay fever, insect bites, etc.
-Chlorpromazine is a sedative agent, not a sleep inducer. It relieves anxiety and is even used in the treatment of some mental disorders.
-Ephedrine and phenylephedrine are used as decongestants of the respiratory tract.
-Amitriptaline and imipramine are tertiary amines used in the treatment of depression. Due to their structure they are classified as tricyclic antidepressants.
-Opioid pain relievers such as morphine, codeline and heroin are tertiary amines.
Gas Treatment
Several amines, including diglycolamine (DGA) and diethanolamine (DEA), are used to remove carbon dioxide (CO2) and hydrogen sulfide (H2S) gases from natural gas and refineries.
agricultural chemistry
Methylamines are intermediate compounds in the synthesis of chemical products that are used in agriculture as herbicides, fungicides, insecticides, and biocides.
Resin manufacturing
Methylamines are used during the preparation of ion exchange resins, usable in the deionization of water.
animal nutrients
Trimethylamine (TMA) is used primarily in the production of choline chloride, a B vitamin supplement used in chicken, turkey, and pig feed.
rubber industry
Dimethylamine oleate (DMA) is an emulsifier for use in the production of synthetic rubber. DMA is used directly as a vapor phase polymerization modifier for butadiene, and as a natural rubber latex stabilizer in place of ammonia.
solvents
Dimethylamine (DMA) and monomethylamine (MMA) are used to synthesize the aprotic polar solvents dimethylformamide (DMF), dimethylacetamide (DMAc), and n-methylpyrrolidone (NMP).
Applications for DMF include: urethane coating, acrylic yarn thinner, reaction solvents, and extraction solvents.
DMAc is used in the manufacture of dyes and spinning solvent. Lastly, NMP is used in the refining of lubricating oils, paint stripper and enamel coating.
Examples of amines
Cocaine
Cocaine is used as a local anesthetic in certain types of eye, ear, and throat surgery. As you can see, it is a tertiary amine.
Nicotine
Nicotine is the primary agent of tobacco addiction and is chemically a tertiary amine. The nicotine present in tobacco smoke is rapidly absorbed and highly toxic.
Morphine
It is one of the most effective analgesics to relieve pain, especially from cancer. It is, again, a tertiary amine.
serotonin
Serotonin is an amine neurotransmitter. In depressed patients the concentration of the main metabolite of serotonin is decreased. Unlike the other amines, this one is primary.
References
Methylamines: uses and applications. Recovered from: chemours.com
Transparency Market Research. (nd). Amines: important facts and uses. Retrieved from: transparencymarketresearch.com