The amines they are organic compounds derived from ammonia. In them there are 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 may well come from an alkyl (R) or aryl (Ar) group. Thus, there are aliphatic amines (linear or branched), and aromatic.
The general formula for aliphatic amines is shown above. This formula can be used for aromatic amines, considering that R can also be an aryl group Ar. Note the similarity between amine and ammonia, NH3. Practically, an H has been replaced by an R side chain.
If R consists of aliphatic chains, you have what is known as an alkylamine; while if R is aromatic in nature, an arylamine. Of the arylamines, the most important of all is alanine: an amino group, -NHtwo, bonded to the benzene ring.
When there are oxygenated groups in a molecular structure, such as OH and COOH, the compound is no longer called an amine. In that case, the amine is considered a substituent: the amino group. For example, this happens in amino acids, as well as in other biomolecules of enormous importance for life..
Because nitrogen is found in many of the essential compounds for life, those were considered vital amines; ie 'vitamins'. However, many of the vitamins are not even amines, and furthermore, not all of them are vital for life. However, this does not negate its great importance in living organisms..
Amines are stronger organic bases 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.
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What is its 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 tetrahedra, where the pair (··) is located at one of the vertices above the nitrogen.
Both molecules are achiral; however, they begin to present chirality as their H's are replaced by R. The amine RtwoNH 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:
RtwoN-H | H-NRtwo
they are exchanged at such a rate that neither of them can isolate themselves; and therefore, the structures of amines are considered achiral even though all the substituents on the nitrogen atom are different.
Amines are polar compounds, since the amino group NHtwo, by having an electronegative nitrogen atom, it contributes to the dipole moment of the molecule. Note that nitrogen has the ability to donate hydrogen bonds, which causes amines to generally have high boiling and melting points..
However, when this property is compared with that of oxygenated compounds, such as alcohols and carboxylic acids, they result in lower magnitudes..
For example, the boiling point of ethylamine, CH3CHtwoNHtwo (16.6ºC) is lower than that of ethanol, CH3CHtwoOH (78ºC).
Thus, it is shown that O-H hydrogen bonds are stronger than those of N-H, even though an amine can form more than one bridge. This comparison is only valid if R has the same molecular weight for the two compounds (CH3CHtwo-). On the other hand, ethane boils at --89ºC, CH3CH3, being a gas at room temperature.
As an amine has less hydrogen, it forms fewer hydrogen bonds and its boiling point is lowered. This is observed by comparing the boiling point of dimethylamine, (CH3)twoNH (7ºC), with that of ethylamine (16.6ºC).
In the world of chemistry, when you talk about an amine, the involuntary act of holding your nose arises. This is because in general, they tend to have unpleasant odors, some of which come to resemble that of rotten fish..
In addition, liquid amines tend to have yellowish tones, which increase the visual mistrust they generate..
Amines tend to be insoluble in water because, despite being able to form hydrogen bonds with HtwoOr, its major 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, nitrogen has a positive partial charge, which electrostatically attracts the anion or conjugate base of the acid..
For example, in a dilute solution of HCl, the amine RNHtwo reacts as follows:
RNHtwo + HCl => RNH3+Cl- (primary salt of amine)
RNHtwo It was insoluble (or slightly soluble) in water, and in the presence of acid it forms a salt, whose solvation of its ions favors its solubility.
Why does this happen? The answer lies in one of the main properties of amines: they are polar and basic. As they are basic, they will react with acids strong enough to protonate them, according to the Brönsted-Lowry definition..
Amines are stronger organic bases than ammonia. The higher the electron density around the nitrogen atom, the more basic it will be; that is, it will deprotonate the acids in the environment more quickly. If the amine is very basic, it can even steal the proton from alcohols.
The R groups contribute electron density to nitrogen by inductive effect; since, we must not forget that it is one of the most electronegative atoms in existence. If these groups are very long or bulky, the inductive effect will be greater, which will also increase the negative region around the electron pair (··).
This causes (··) to accept the H ion more quickly+. However, if R are very bulky, the basicity decreases due to the steric effect. Why? For the simple reason that the H+ must cross a configuration of atoms before reaching nitrogen.
Another way to reason about the basicity of an amine is by stabilizing its amine salt. Now, the one that decreases by inductive effect can decrease the positive charge N+, it will be a more basic amine. The reasons are the same just explained.
Alkylamines are much more basic than arylamines. Why? To understand it simply, the structure of aniline is shown:
Above, in the amino group, is the pair of electrons (··). This pair "travels" inside the ring in the ortho and para positions with respect to NHtwo. It means that the two upper vertices and the opposite to NHtwo are negatively charged, while the nitrogen atom, positively.
As the nitrogen is positively charged, +N, will repel ion H+. And if this is not enough, the electron pair is delocalized within the aromatic ring, making it less accessible to deprotonate acids..
The basicity of aniline can increase if groups or atoms that give it electronic density are linked to the ring, competing with the pair (··) and forcing it to be located with greater probability on the nitrogen atom, ready to act as a base.
Although not formally presented, reference has been implicitly made to primary, secondary, and tertiary amines (top image, left to right).
Primary amines (RNHtwo) are the monosubstituted; the secondary ones (RtwoNH), are disubstituted, with two R alkyl or aryl groups; and the tertiary ones (R3N), are trisubstituted, and lacks 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 could be expected to be the most basic; however, such a statement cannot be made without knowing the structures of R.
At first it was mentioned that amines are derived from ammonia; therefore, the simplest way to form them is by alkylating them. 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- => RNHtwo
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 training methods, such as the Gabriel synthesis, make it possible to obtain primary amines so that other undesirable products are not formed..
Also, ketones and aldehydes can be reduced in the presence of ammonia and primary amines, to give rise to secondary and tertiary amines..
Nitro compounds can be reduced in the presence of hydrogen and a catalyst to their corresponding amines.
ArNOtwo => ArNHtwo
Nitriles, RC≡N, and amides, RCONRtwo, are also reduced to give primary and tertiary amines, respectively.
How are amines named? Most of the time they are named based on R, the alkyl or aryl group. To the name of R, derived from its alkane, the word 'amine' is added at the end.
Thus, CH3CHtwoCHtwoNHtwo is propylamine. On the other hand, it can be named considering only the alkane and not as an R group: propanamine.
The first way of naming them is by far the best known and most used.
When there are two NH groupstwo, the alkane is named and the positions of the amino groups are listed. Thus, the HtwoNCHtwoCHtwoCHtwoCHtwoNHtwo is called: 1,4-butanediamine.
If there are oxygenated groups, such as OH, it should be given priority over NHtwo, which happens to be named as a substituent. For example, HOCHtwoCHtwoCHtwoNHtwo It is called: 3-Aminopropanol.
And with regard 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 the ch3NHCHtwoCH3 is called: N-Methylethylamine.
Primary aromatic amines can serve as starting material for azo dye syntheses. Initially, amines react to form diazonium salts, which form azo compounds through azo coupling (or diazo coupling)..
These, due to their intense coloration, are used in the textile industry as a dyeing material; for example: methyl orange, direct brown 138, sunset yellow FCF and ponceau.
Many drugs work with agonists and antagonists of natural amine neurotransmitters. Examples:
-Chlorpheniramine is an antihistamine used in the control of allergic processes due to the ingestion of some foods, hay fever, insect bites, etc..
-Chlorpromazine is a sedative, not a sleep-inducing agent. Relieves anxiety and is even used in the treatment of some mental disorders.
-Ephedrine and phenylephedrine are used as airway decongestants.
-Amitriptyline and imipramine are tertiary amines that are 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.
Several amines, including diglycolamine (DGA) and diethanolamine (DEA), are used in the elimination of carbon dioxide (COtwo) and hydrogen sulfide (HtwoS) present in natural gas and refineries.
Methylamines are intermediate compounds in the synthesis of chemicals that are used in agriculture as herbicides, fungicides, insecticides, and biocides..
Methylamines are used during the production of ion exchange resins, usable in the deionization of water.
Trimethylamine (TMA) is used primarily in the production of choline chloride, a vitamin B supplement used in the feed of chickens, turkeys and pigs..
Dimethylamine oleate (DMA) is an emulsifier for use in the production of synthetic rubber. DMA is used directly as a polymerization modifier in the vapor phase of butadiene, and as a stabilizer for natural rubber latex in place of ammonia
Dimethylamine (DMA) and monomethylamine (MMA) are used to synthesize the polar aprotic solvents dimethylformamide (DMF), dimethylacetamide (DMAc) and n-methylpyrrolidone (NMP).
DMF applications include: urethane coating, acrylic yarn solvent, reaction solvents, and extraction solvents.
DMAc is used in the manufacture of yarn dyes and solvent. Lastly, NMP is used in the refining of lubricating oils, paint stripper and enamel coating..
Cocaine is used as a local anesthetic in certain types of eye, ear, and throat surgery. As seen, it is a tertiary amine.
Nicotine is the primary agent of tobacco addiction and chemically it is a tertiary amine. Nicotine in tobacco smoke is rapidly absorbed and highly toxic.
It is one of the most effective pain relievers to relieve pain, especially cancer. It is, again, a tertiary amine.
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.
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