Amide

Amids have a conjugated system on the atoms of O, C, N, consisting of molecular orbitals occupied by delocalized electrons. One of the "molecular obitals π" in formamida is shown above.

An amide is a compound that is formed conceptually or chemically by replacing the hydroxyl of an oxacid with an amino substituent. In organic chemistry, it is called par excellence as "amide" to amides of carboxylic acids (strictly, carboxamide). It can be considered as a derivative of a carboxylic acid by substituting the —OH group of the acid for a —NH₂, —NHR or —NRR' (called an amino group). For this reason, its functional group is of the RCONR'R'' type, with CO being a carbonyl, N a nitrogen atom, and R, R' and R'' organic radicals or hydrogen atoms:

Formed (formal acid friend)	Amida (carboxamide) (carboxylic acid friend)	Urea or carbamide (charcoal acid friend)	Cianimida (sic acid friend)	Hexametilfosforamida (hexamethylated acid)	Sulfamida (sulfuric acid friend)	Nitramida (Nitric acid friend)

When the amide group is not the main one, it is named using the prefix carbamoil:

CH₃-CH₂-CH(CONH₂)-CH₂-CH ₂-COOH → 4-carbamoylhexanoic acid.

All amides except the first in the series are solid at room temperature and have high boiling points, higher than those of the corresponding acids. They have excellent solvent properties and are very weak bases. One of the main methods of obtaining these compounds consists of reacting ammonia (or primary or secondary amines) with esters. Amides are common in nature, and one of the best known is urea, a diamide that does not contain hydrocarbons. Proteins and peptides are made up of amides. An example of a long chain polyamide is nylon. Amides are also widely used in the pharmaceutical industry.

Polyamides

Carbonic acid amide is called urea and its derivatives are the ureido functional group.

Diacylamines are denominated as imide functional group and are analogous to carboxylic anhydrides, for example carboxyl

Functional group imida

Polyamides are compounds that contain amide groups. Some are synthetic, such as nylon, but they are also found in nature, in proteins, formed from amino acids by reaction of a carboxyl group of an amino acid. with one amino group from another. In proteins, the amide group is called a peptide bond.

ε-caprolactama

Nylon is a polyamide due to the characteristic amide groups in the main chain of its formulation. For example, nylon 6 is obtained by polymerization of ε-caprolactam.

Nailon 6

Certain nylon-type polyamides are polyamide-6, polyamide-11, polyamide-12, polyamide-9,6, polyamide-6,9, polyamide-6,10, and polyamide-6, 12. As an example of non-linear polyamides, the condensation products of dimerized acids of vegetable oils with amines may be mentioned.

Peptides, including proteins like silk, which nylon replaced, are also polyamides. These amide groups are highly polar and can be linked together by hydrogen bonding. Because of this, and because the nylon chain is so regular and symmetrical, nylons are often crystalline, making excellent fibers.

Oligopeptide (tetrapéptide)

Synthesis of amides

The synthesis of amides can be carried out by various methods. The simplest method is the condensation of a carboxylic acid with an amine. This reaction is thermodynamically favorable in general, but has a high activation energy, mainly due to the first deprotonation of the carboxylic acid and the protonation of the amine, which forms a stable product, the amino carboxylate. This reduces the reactivity. Also, high temperatures are required.

RCO₂H + R′R′NH RCO−
2 + R′R′NH+
2 RC(O)NR′R′ + H₂O

Many methods are known to drive the equilibrium to the right. For the most part, these reactions involve "activating" the carboxylic acid by first making it a better electrophile; such as esters, acid chlorides (Schotten-Baumann reaction) or anhydrides (Lumière-Barbier method). Conventional methods in peptide synthesis use coupling agents such as HATU, hydroxybenzothiazole (HOBt) or PyBOP. Recently, novel boron-based reagents have emerged for CO-N bond formation, including the use of acid catalysts. 2-iodophenylboronic acid, MIBA, and tris(2,2,2-trifluoroethyl) borate.

Name of reaction	Substrate	Details
Transfer of Beckmann	Cetona cyclica	Reactive: hydroxylamine in acid medium. It forms a lactama.
Schotten-Baumann's Reaction	Acelogenide	Reactivo: amina con un halogenuro de acilo en medio basic
Schmidt reaction	Cetonas	Reactive: Hydrazoic acid
Nitrile hydrolysis	Nitrilo	Reactivo: Agua en medio acid RCN + H2O → RC(O)NH2
Willgerodt-Kindler's reaction	Aril alquil cetonas	Sulphur and morfoline
Passerini Reaction	Carboxylic acid, ketone or aldehyde	Reaction of three components between a carboxylic acid, a carbonyl compound, such as a ketone or aldehyde, and an issocianide, to form α-hydroxycarboxamides.
Ugi reaction	Isocianide, carboxylic acid, cetona, primary amine	Condensation of four components between aldehyde, amine, carboxylic acid and issocianide to prepare derivatives of α-aminoacil amides.
Bodroux reaction	Carboxylic acid, reactive of Grignard with an aniline derivative ArNHR′
Transposition of Chapman	Arilo, imino ether	Stop. N,N- a loved one. The reaction mechanism is based on an aromatic nucleophilic substitution.
Syntesis de amidas de Leuckart	Isocianato	Reaction of a sandstone with an issocyanate catalyzed by aluminum chloride. It forms a benzamide.
Reaction of Ritter	Wholes, alcohols, or any other source of carbocations	Loved with nitrogen linked to a tertiary carbon by means of an addition reaction between a nitrile and a tertiary carbocation in the presence of concentrated acids.
Photolithic addition of a form of olefins	To the terminals	Reaction of radical approval between an alcheno ends and forms.
Aminolysis of esters	_	Reaction of acid aminolysis of esters.

Reactions of amides

The main reactions of amides are:

• Acid or basic hydrolysis: The amide is hydrolyzed in the basic medium by forming a metal carboxylate or in the acid medium forming a carboxylic acid.
• Dehydration: In the presence of a dehydrant such as tionyl chloride or phosphorus pentoxide a nitrile is produced.
• Reduction: Amids can be reduced with lithium and aluminium amines.
• Hofmann's Transposition: In the presence of a halogen in the basic medium, a complex reaction is produced that allows to obtain amine with a less carbon in its main chain.

Mechanism of acid hydrolysis of a carboxamide.

Example of amide

• Acrylamide is used in different applications, although it is best known for being probably carcinogenic and being present in enough foods as it is formed by natural processes when cooking them.
• They are a source of energy for the human body.
• They can be vitamins in the body or painkillers.

Importance and uses

Amides are common in nature and are found in substances such as amino acids, proteins, DNA and RNA, hormones, and vitamins.

Urea is used for the excretion of ammonia (NH₃) in humans and mammals. It is also widely used in the pharmaceutical industry and in the nylon industry.