# data[].attributes.body
An amine is generally a functional group with a nitrogen atom having a lone pair. Amines resemble ammonia structurally where nitrogen can bond up to 3 hydrogen atoms. It is also characterized by various properties that are based on carbon connectivity.

# data[].attributes.body
Amines are used in making azo-dyes and nylon apart from medicines and drugs. They are widely used in developing chemicals for crop protection, medication and water purification.

They also find use in products of personal care. Ethanol amines are the most common type of amine used in the global market.

As antioxidants for rubber and roofing asphalt (diarylamines), as stabilizers for cellulose nitrate explosives (diphenylamine), as protectants against damage from gamma radiation (diarylamines), as developers in photography (aromatic diamines), as flotation agents in mining, as anticling and waterproofing agents for textiles, as fabric softeners, in paper coating, and for solubilizing herbicides

# data[].attributes.body
The lower aliphatic amines are gaseous in nature. They have a fishy smell.

Primary amines with three or four carbon atoms are liquids at room temperature whereas higher ones are solids.

Lower aliphatic amines can form hydrogen bonds with water molecules. Therefore, such amines are soluble in water.

Increase in the size of hydrophobic alkyl part increases the molar mass of amines. This usually 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.

# data[].attributes.attachment_link.title
Amines: Crash Course Organic Chemistry #46

# data[].attributes.body
byjus.com

# data[].attributes.attachment_link.readable_text
Amine, any member of a family of nitrogen-containing organic compounds that is derived, either in principle or in practice, from ammonia (NH ₃).

Encyclopædia Britannica, Inc.

Naturally occurring amines include the alkaloids, which are present in certain plants; the catecholamine neurotransmitters (i.e., dopamine, epinephrine, and norepinephrine); and a local chemical mediator, histamine, that occurs in most animal tissues.

Aniline, ethanolamines, and several other amines are major industrial commodities used in making rubber, dyes, pharmaceuticals, and synthetic resins and fibres and for a host of other applications. Most of the numerous methods for the preparation of amines may be broadly divided into two groups: (1) chemical reduction (replacement of oxygen with hydrogen atoms in the molecule) of members of several other classes of organic nitrogen compounds and (2) reactions of ammonia or amines with organic compounds.

Amines are classified as primary, secondary, or tertiary depending on whether one, two, or three of the hydrogen atoms of ammonia have been replaced by organic groups. In chemical notation these three classes are represented as RNH ₂, R ₂NH, and R ₃N, respectively. A fourth category consists of quaternary ammonium compounds, which are obtained by replacement of all four hydrogen atoms of the ammonium ion, NH ₄⁺; an anion is necessarily associated (R ₄N⁺X −). Amines are also classified as aliphatic, having only aliphatic groups attached, or aromatic, having one or more aryl groups attached. They may be open-chain, in which the nitrogen is not part of a ring, or cyclic, in which it is a member of a ring (generally aliphatic).

The older and most widely used system for naming amines is to identify each group that is attached to the nitrogen atom and then add the ending -amine, as in methylamine, CH ₃NH ₂; N-ethyl-N-propylamine (or ethyl(propyl)amine), CH ₃CH ₂NHCH ₂CH ₂CH ₃; and tributylamine, (CH ₃CH ₂CH ₂CH ₂) ₃N. Two or more groups cited are in alphabetical order; to clarify which groups are attached to nitrogen rather than to each other, Ns or internal parentheses are used. A few aromatic amines and most cyclic amines have trivial (nonsystematic) names (e.g., aniline, C ₆H ₅NH ₂), which may be used as a parent (basic structural unit) on which to specify any other groups attached, as in N,N-dimethylaniline.

An alternative method replaces the terminal -e of a hydrocarbon name by the suffix -amine to indicate the functional group ―NH ₂. With secondary and tertiary amines, the largest group is chosen as the parent, and the other groups are named as substituents. The names in this system for the previous examples are methanamine, N-ethylpropanamine, and N,N-dibutylbutanamine. Dimethylaniline is named N,N-dimethylbenzenamine. When another functional group of the compound has a higher priority than the amino group (―NH ₂, ―NHR, or ―NR ₂), the latter is named as a substituent, as in aminoacetic acid, NH ₂―CH ₂COOH, and 2-(dimethylamino)ethanol, (CH ₃) ₂N―CH ₂CH ₂ OH. (The simple guidelines given here may not be adequate for more-complex structures.)

Properties of amines

Physical properties

Distinctive odours that are fishy to putrid characterize the lower-molecular-weight amines. They are gases at room temperature or are easily vaporized liquids. Aliphatic amines are less dense than water, having densities in the range 0.63 to 0.74 gram per cubic cm; aromatic amines are typically slightly heavier than water (e.g., the density of aniline is 1.02 grams per cubic cm). With increasing size, they become less volatile; the odour decreases and eventually becomes unnoticeable, although some diamines have offensive odours. For example, H ₂N(CH ₂) ₄NH ₂, called putrescine, and H ₂N(CH ₂) ₅NH ₂, called cadaverine, are foul-smelling compounds found in decaying flesh. Amines are colourless; aliphatic amines are transparent to ultraviolet light, but aromatic amines display strong absorption of certain wavelengths. Amines with fewer than six carbons mix with water in all proportions. The aliphatic amines are stronger bases than ammonia, and the aromatic ones are substantially weaker. The basicity is measured in terms of the pK b value, which is equal to −logK b, where K b is the equilibrium constant for the reaction B + H ₃O⁺ ⇌ BH⁺ + H ₂O (B is the amine). Thus, a larger pK b value indicates greater strength as a base. For comparison, the pK b of ammonia is 4.75. Quaternary ammonium hydroxides are very strong bases, but the chlorides are not basic.

Most aliphatic amines are not highly toxic, and many are harmless, natural components of foods and pharmaceuticals. In high concentrations, however, the smaller amines are highly irritating to the skin and especially to the mucous membranes of the eyes, nose, throat, and lungs, to which they can cause acute damage upon prolonged exposure. Larger amines (12 or more carbon atoms) are usually less irritating. Aromatic amines are also irritants and can be absorbed through the skin. They may be dangerous poisons. Aniline, for example, destroys the hemoglobin of blood, and prolonged exposure has been linked with cancer. Amines can be corrosive to some metals and plastics; they should therefore be stored in glass or steel containers.

Molecular shape and configuration

An amine molecule has the shape of a somewhat flattened triangular pyramid, with the nitrogen atom at the apex. An unshared electron pair is localized above the nitrogen atom. In quaternary ammonium ions this region is occupied by a substituent, forming a nearly regular tetrahedron with the nitrogen atom at its centre.

Encyclopædia Britannica, Inc.

Left-handed and right-handed forms (mirror-image configurations, known as optical isomers or enantiomers) are possible when all the substituents on the central nitrogen atom are different (i.e., the nitrogen is chiral). With amines, there is extremely rapid inversion in which the two configurations are interconverted. The process is like an umbrella turning inside out in the wind; the substituents move in one direction ("up") and the nitrogen atom in the other ("down"). Quaternary ammonium ions do not undergo such equilibration short of conditions where they decompose; their optical isomers are indefinitely stable and isolable, and the physiological effects of the two enantiomers may be profoundly different.

# data[].attributes.attachment_link.description
Amine, any member of a family of nitrogen-containing organic compounds that is derived, either in principle or in practice, from ammonia (NH3). Naturally occurring amines include the alkaloids, which are present in certain plants; the catecholamine neurotransmitters (i.e., dopamine, epinephrine,

# data[].attributes.attachment_link.readable_text
Amines as Nucleophiles

Amines seldom serve as leaving groups in nucleophilic substitution or base-catalyzed elimination reactions. Indeed, they are even less effective in this role than are hydroxyl and alkoxyl groups. While we will see another section that it is possible to coax the amine to serve as a leaving group. As weak bases, amines are good nucleophiles.

Amines and Carbonyls

The reaction of aldehydes and ketones with ammonia or 1º-amines forms imine derivatives, also known as Schiff bases (compounds having a C=N function). Water is eliminated in the reaction, which is acid-catalyzed and reversible in the same sense as acetal formation. The pH for reactions which form imine compounds must be carefully controlled. The rate at which these imine compounds are formed is generally greatest near a pH of 5, and drops at higher and lower pH's. At high pH there will not be enough acid to protonate the OH in the intermediate to allow for removal as H ₂ O. At low pH most of the amine reactant will be tied up as its ammonium conjugate acid and will become non-nucleophilic.

Imine formation is reversible. Imines can be hydrolyzed back to the corresponding primary amine under acidic aqueous conditions.

Most aldehydes and ketones react with 2º-amines to give products known as enamines.

It should be noted that, like acetal and imine formation, these are acid-catalyzed reversible reactions in which water is lost. Consequently, enamines are easily converted back to their carbonyl precursors by acid-catalyzed hydrolysis.

Amines and Acid Chlorides

Acid chlorides react with ammonia, 1 o amines and 2 o amines to form amides.

Amines and Sulfonyl Chloride

The sulfonyl group is the sulfur-analog to the carbonyl group. Both groups contain an electrophilic carbonyl carbon with chloride as an excellent leaving group. Because sulfur is a third shell element it can form "expanded octets".

Amines react with sulfonyl groups to form sulfonamides. Sulfonamides are used as antimicrobial agents therapeutically and called sulfa drugs. The reaction to form sulfonamides occurs under alkaline conditions to keep the amine nucleophilic. Any time amines are present in an aqueous solution, measurable hydroxide is present. The mechanism for the sulfonation reaction is analogous to the acylation mechanism as is shown below.

The end of this chapter includes some additional information on sulfonamides.

It is instructive to examine nitrogen substitution reactions using common alkyl halides as the electrophiles. Thus, reaction of a primary alkyl bromide with a large excess of ammonia yields the corresponding 1º-amine, presumably by an SN2 mechanism. The hydrogen bromide produced in the reaction combines with some of the excess ammonia, giving ammonium bromide as a by-product. Water does not normally react with 1º-alkyl halides to give alcohols, so the enhanced nucleophilicity of nitrogen relative to oxygen is clearly demonstrated.

2 RCH ₂Br + NH ₃ (large excess) RCH ₂NH ₂ + NH ₄⁽⁺⁾ Br⁽⁻⁾

It follows that simple amines should also be more nucleophilic than their alcohol or ether equivalents. If, for example, we wish to carry out an S N 2 reaction of an alcohol with an alkyl halide to produce an ether (the Williamson synthesis), it is necessary to convert the weakly nucleophilic alcohol to its more nucleophilic conjugate base for the reaction to occur. In contrast, amines react with alkyl halides directly to give N-alkylated products. Since this reaction produces HBr as a co-product, hydrobromide salts of the alkylated amine or unreacted starting amine (in equilibrium) will also be formed.

2 RNH ₂ + C ₂H ₅Br RNHC ₂H ₅ + RNH ₃⁽⁺⁾ Br⁽⁻⁾ RNH ₂C ₂H ₅⁽⁺⁾ Br⁽⁻⁾ + RNH ₂

Unfortunately, the direct alkylation of 1º or 2º-amines to give a more substituted product does not proceed cleanly. If a 1:1 ratio of amine to alkyl halide is used, only 50% of the amine will react because the remaining amine will be tied up as an ammonium halide salt (remember that one equivalent of the strong acid HX is produced). If a 2:1 ratio of amine to alkylating agent is used, as in the above equation, the HX issue is solved, but another problem arises. Both the starting amine and the product amine are nucleophiles. Consequently, once the reaction has started, the product amine competes with the starting material in the later stages of alkylation, and some higher alkylated products are also formed. Even 3º-amines may be alkylated to form quaternary (4º) ammonium salts. When tetraalkyl ammonium salts are desired, as shown in the following example, Hünig's base may be used to scavenge the HI produced in the three S N 2 reactions. Steric hindrance prevents this 3º-amine (Hünig's base) from being methylated.

C ₆H ₅NH ₂ + 3 CH ₃I + Hünig's base C ₆H ₅N(CH ₃) ₃⁽⁺⁾ I⁽⁻⁾ + HI salt of Hünig's base

You get a complicated series of reactions on heatingprimary amines with halogenoalkanesto give a mixture of products - probably one of the most confusing sets of reactions you will meet at this level. The products of the reactions include secondary and tertiary amines and their salts, and quaternary ammonium salts.

Making secondary amines and their salts

In the first stage of the reaction, you get the salt of a secondary amine formed. For example if you started with ethylamine and bromoethane, you would get diethylammonium bromide

In the presence of excess ethylamine in the mixture, there is the possibility of a reversible reaction. The ethylamine removes a hydrogen from the diethylammonium ion to give free diethylamine - a secondary amine.

Making tertiary amines and their salts

But it doesn't stop here! The diethylamine also reacts with bromoethane - in the same two stages as before. This is where the reaction would start if you reacted a secondary amine with a halogenoalkane.

In the first stage, you get triethylammonium bromide.

There is again the possibility of a reversible reaction between this salt and excess ethylamine in the mixture.

The ethylamine removes a hydrogen ion from the triethylammonium ion to leave a tertiary amine - triethylamine.

Making a quaternary ammonium salt

The final stage! The triethylamine reacts with bromoethane to give tetraethylammonium bromide - a quaternary ammonium salt (one in which all four hydrogens have been replaced by alkyl groups).

This time there isn't any hydrogen left on the nitrogen to be removed. The reaction stops here.

Exercise

10. Draw the products of the following reactions.

11. Draw the structure of the reactant needed to produce the indicated product.

12. Draw the products for the following reactions.

13. Draw the missing reactant to complete each reaction below.
Answer
10. 11. 12. 13.

Contributors and Attributions

# data[].attributes.attachment_link.description
Amines seldom serve as leaving groups in nucleophilic substitution or base-catalyzed elimination reactions. Indeed, they are even less effective in this role than are hydroxyl and alkoxyl groups. While we will see another section that it is possible to coax the amine to serve as a leaving group.

# data[].attributes.body
Amines play an important role in the survival of life – they are involved in the creation of amino acids, the building blocks of proteins in living beings. Many vitamins are also built from amino acids. Serotonin is an important amine that functions as one of the primary neurotransmitters for the brain