What are Amines?
Amines are organic compounds having functional groups which contain a nitrogen atom with a lone pair of electrons. They are the derivatives of ammonia where one or more hydrogen atom can be replaced by substituent groups such as alkyl or aryl. Amino acids, biogenic amine, trimethylamine, and aniline are examples of some significant amines.
Classification of Amines
Amines are classified into four categories namely, primary, secondary, tertiary and cyclic. When one of the three hydrogen atoms is replaced by an alkyl or aryl group, the amine is primary. In case of replacing two out of three hydrogen atoms we get secondary amine and when all the three hydrogen atoms are replaced tertiary amines are formed. Only secondary or tertiary amines can be cyclic, 3 – member ring aziridine is an example of cyclic amine.
Physical Properties of Amines
- The lower aliphatic amines are gaseous in nature with a fishy smell. Primary amines with three or four carbon atoms are liquids at room temperature whereas higher ones are solids.
- Aniline and other arylamines are generally colourless, but they get coloured if stored in open due to atmospheric oxidation.
- Lower aliphatic amines can form hydrogen bonds with water molecules hence they are soluble in water. Increase in size of hydrophobic alkyl part increases the molar mass of amines which results in a decrease in its solubility in water. Higher amines are insoluble in water.
- Organic solvents like alcohol, benzene, and ether readily dissolve amines. Alcohols have higher polarity as compared to amines and hence they form stronger intermolecular hydrogen bonds.
- Primary and secondary amines are often engaged in the intermolecular association as a result of hydrogen bonding between nitrogen of one and hydrogen of the other molecule.
- The intermolecular association is more prominent in case of primary amines as compared to secondary due to the availability of two hydrogen atoms.
- In tertiary amines, there is no intermolecular association due to the absence of free hydrogen atom for bonding. The order of boiling point of amines is as follows: Primary > Secondary > Tertiary.
Frequently Asked Questions – FAQs
What are amines used for?
Amines, aside from narcotics and medications, are used in producing azo-dyes and nylon. They are commonly used in the production of crop safety, medicine and water purification chemicals. They also find use in personal care goods. The most popular form of amine used in the global market is ethanol amine.
Which amine is more reactive?
Secondary amines are more reactive to the S-O bond fission than primary amines of equivalent fundamentality. For reactions with secondary amines, the k(1) value was estimated to be larger than for primary amines with equivalent basicity, which completely accounts for their greater reactivity.
Is amine flammable?
In general, amines, phosphines, and pyridines are high-boiling liquids or solids that are combustible, but not extremely flammable, at room temperature. An exception is methylamine, since it is a gas with a large spectrum of flammability. Noxious NOx gases are formed by the combustion of amines.
Why are aromatic amines carcinogenic?
The carcinogenic aromatic multi-ring amines are thought to be partially directed at the urinary bladder when the ultimate electrophilic form, a nitrenium ion, is transferred to the bladder in a stable form, where it becomes accessible by a shift in acidity.
What are the chemical properties of amine?
Amines are organic compounds that contain one or more nitrogen atoms and are often actually dependent on them. Structurally, amines mimic ammonia in that up to three hydrogens may be bound by nitrogen, but amines also have extra properties dependent on their connectivity to carbon.
This article covers the basic details of the physical properties of amines. For any further query on this topic install BYJU’S the learning app.