Amines are molecules and functional groups in organic chemistry that have a lone pair on a basic nitrogen atom. Amines are officially ammonia derivatives with one or more hydrogen atoms replaced by an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of the substituent are attached to one nitrogen atom may be called alkyl arylamines). Amino acids, biogenic amines, trimethylamine, and aniline are all important amines; a complete list of amines may be found in Category: Amines. Monochloramine and other inorganic ammonia derivatives are referred to as amines (NClH2). An amino group refers to the substituent -NH2.
Structure of Amines
Amines, like ammonia, have a trivalent nitrogen atom with an unshared pair of electrons. As a result, amines’ nitrogen orbitals are sp3 hybridised, and their geometry is pyramidal.
Depending on the amine composition, each of the three sp3 hybridised orbitals of nitrogen overlaps with orbitals of hydrogen or carbon. All amines have an unshared pair of electrons in the fourth orbital of nitrogen. The angle of C–N–E (where E is C or H) is less than 109.5∘ due to the presence of an unshared pair of electrons; for example, it is 108∘ in the case of trimethylamine, as illustrated in fig.
Classification of Amines
Amines are chemical compounds that are derived from ammonia (NH3). The hydrogen groups from the ammonia are replaced to generate these derivatives. The Alkyl or Aryl groups are responsible for replacing the hydrogen atom in ammonia. Amines, in their natural state, behave like bases. This is because the Nitrogen atom itself has 2 valence electrons in its orbital. The chemical also has Alkyl groups, Aryl groups, and Hydrogen atoms connected to it. As a result, the amine group functions as a base and an electron donor.
The number of Hydrogen atoms in the parent Ammonia that are replaced by Alkyl or Aryl groups in the amine might be used to classify it. Amines are not the same as alkyl halides or alcohols in terms of classification. The fundamental reason for this is that in amines, the nitrogen atom forms three neutral single bonds and has a lone pair with it. Other groups could take the place of up to three hydrogen atoms in ammonia. However, the lone pair could be deleted and a new group added by subsequent treatment with a Halide.
- Primary, Secondary, Tertiary, and Quaternary Amines are the four types of amines. 1°, 2°, 3°, 4° amines are the primary, secondary, tertiary, and quaternary amines, respectively.
- 1° amine is another name for primary amino acids. The primary amines are made by replacing one of the hydrogen atoms in ammonia. Amino is another name for primary amine. Because it contains two hydrogen atoms and an alkyl group, this amine is extremely basic. Furthermore, nitrogen has two valence electrons, making the molecule very basic.
Primary Amine
- 2° amines are also referred to as secondary amines. Secondary amines are made by substituting two hydrogen atoms in an ammonia molecule. Alkyl or Aryl groups are used to replace the compound’s two hydrogen atoms.
Secondary amine
- 3° amines are another name for tertiary amines. The substitution of all three hydrogen atoms in ammonia produces these amines. Alkyl or aryl groups would be used to replace the hydrogen atoms. Because no hydrogen atoms remain in the molecule, it has a lower boiling point than other amine derivatives. This is due to their inability to form hydrogen bonds with one another.
Tertiary amine
- 4° amines are another name for quaternary amines. Quaternary amines are quaternary ammonium compounds that form bonds with halides.
Quaternary amine
Nomenclature of Amines
Amines are also known as alkylamines. In alphabetical order, the alkyl groups linked to the N-atom are identified, followed by amine. In the IUPAC nomenclature system, they are referred to as Alkanamine. The parent compound with the longest carbon atom chain attached to the N-atom is chosen, and the suffix amine substitutes the last letter “e” in the parent hydrocarbon’s name.
In alphabetical order, the substituents are called prefixes. The names of the alkyl groups in mixed amines are listed in alphabetical order. The prefix di- or tri- is added to the name of an alkyl group when two or three identical alkyl groups are connected to a nitrogen atom. Below are the IUPAC names (in bold letters) and common names (in parenthesis) of a few well-known amines.
- Primary Amines: Primary amines are formed when one of the three hydrogen atoms in ammonia is replaced with an alkyl or aromatic group. Methylamine and most amino acids are important fundamental alkylamines, while aniline is a primary aromatic amine.
The names of most secondary and tertiary amines are similar. We denote the organic groups individually if they are distinct or use the prefixes di- or tri- if they are the same in the common language. The locant N is used in systematic nomenclature to identify substituents bonded to a nitrogen atom.
- Secondary Amines: Secondary amines are those with two organic substituents, which can be alkyl, aryl, or both. They are joined to the nitrogen via a hydrogen atom. Secondary amines are more basic than primary amines and tertiary amines. The stability of the chemical generated after receiving a proton is used to explain the basicity of amines (donating the lone pair on the nitrogen atom to a proton). Electron donating groups are alkyl groups. The positive charge on the nitrogen atom in a secondary amine with two alkyl groups is lowered due to the electron-donating ability of alkyl groups. As a result, secondary amines are more basic than other amines.
e.g. Dimethylamine is a well-known example. Diphenylamine, on the other hand, is an aromatic amine.
- Tertiary Amines: All of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups in a tertiary amine. Again, you’re more likely to run across simple ones with all three hydrocarbon groups being alkyl and all three being the same. The name is akin to that of secondary amines.
e.g. Two examples are trimethylamine (which has a distinct fishy odour) and EDTA.
- Arylamines: The NH2 group is directly linked to the benzene ring in arylamines. Aromatic amines are known as arylamines in the common naming system, and are named by adding the suffix amine to the name of the aryl group. They are also known as derivatives of aniline, the most basic aromatic amine.
e.g. The simplest aromatic amine is benzenamine, and the other amines are designated derivatives of benzenamine in the IUPAC system. An amine’s full name is always written as a single word. Some aromatic amines are listed below with their common and IUPAC designations.
- Heterocyclic Amines: Heterocyclic amines (HCAs) are carcinogenic and mutagenic compounds that are generated when muscle meats like beef, hog, poultry, and fish are cooked. When amino acids and creatine combine at high cooking temperatures, HCAs occur, and they form in higher numbers when meats are overdone or blackened. Seventeen different HCAs have been identified as a result of cooking muscle meats, and they may pose a cancer risk to humans.
When HCAs are activated by cytochrome P450 1A2-mediated oxidation of the amino group, which is followed by acetylation or sulfation to generate direct-acting reactive mutagens that attack critical sites in DNA, they gain a high carcinogenic potential. Several of these HCAs have been shown to cause cancer of the mammary glands, colon, and pancreas in rats. Avoiding high-temperature cooking, adding high-antioxidant-containing foods, or adding soy protein can all help to reduce HCAs in food. Nonetheless, there is no conclusive evidence that the degree of cooking affects the risk of colorectal cancer.
Sample Questions
Question 1: Describe the structure of amines.
Answer:
The nitrogen atom of amines is trivalent and bears an unshared pair of electrons in its structure. As a result, amines’ nitrogen orbitals are sp3 hybridised, and their geometry is pyramidal. Each of the three hybridised orbitals of nitrogen overlaps with orbitals of hydrogen or carbon, depending on the amine composition. In the fourth orbital of nitrogen, all amines have an unshared pair of electrons. Due to the presence of an unshared pair of electrons, the angle C–N–E (where E is C or H) is less than 109.5∘ ; for example, in the case of trimethylamine, it is 108∘ .
Question 2: Describe the classification of amines?
Answer:
Amines are divided into several categories. Amines are ammonia-based organic compounds with alkyl or aryl groups replacing one or more hydrogen atoms. Depending on whether alkyl groups replace one, two, or all three hydrogen atoms in ammonia, they are classified as primary, secondary, or tertiary (R). Amines are ammonia derivatives that are made by substituting alkyl and/or aryl groups for one, two, or all three hydrogen atoms.
Question 3: How the naming of amines is done?
Answer:
The amines can be named in a variety of ways. Amines are also known as alkylamines. In alphabetical order, the alkyl groups linked to the N-atom are identified, followed by amine. In the IUPAC nomenclature system, they are referred to as Alkanamine. The parent compound with the longest carbon atom chain attached to the N-atom is chosen, and the suffix amine substitutes the last letter “e” in the parent hydrocarbon’s name. Prefixes are the names given to the substituents in alphabetical sequence.
Question 4: What are primary amines? Give IUPAC names and common names of some common amines.
Answer:
Primary amines are formed when one of the three hydrogen atoms in ammonia is replaced with an alkyl or aromatic group. Methylamine and most amino acids are important fundamental alkylamines, while aniline is a primary aromatic amine.
Question 5: What is the order of basicity of Amines?
Answer:
Amine has the ability to contribute a pair of electrons to form a base due to the presence of lone pair electrons on the nitrogen atom. The basicity of amines is determined by the following criteria: structural, electronic, and solvent considerations.
In the gaseous state the order of basicity of amine, when R = Me, 3°>2°>1°
In the aqueous solution the order of basicity of amine, when R = Me, 2°>1°>3°
In the aqueous solution the order of basicity of amine, when R = Et, 2°>3°>1°
Question 6: How do amines get prepared?
Answer:
Some of the important methods of preparation of amines are:
- Alkylation of Ammonia
- Alkylation of Azide Ion and Reduction
- Gabriel Phthalimide Synthesis
- Reduction of Nitro Compounds
- Reduction of Nitriles, Isonitriles, and Oximes
- Reductive Amination of Carbonyl Compounds
- From Amides
- Hoffmann Bromamide Degradation