What are Amines?

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Amines are organic molecules containing nitrogen and are relatives of ammonia. In amines one of the hydrogen atoms on the nitrogen is replaced with a hydrocarbon group. Depending on how many hydrogens have been replaced by the hydrocarbon group they have been classified into Primary, secondary and tertiary amines. Amines have single bonds between carbon and nitrogen. Nitrogen can form a covalent bond with three other atoms. When all three side groups are hydrogen the compound is called ammonia (NH3). When one or more of the hydrogen’s are substituted by organic groups (containing carbon) they are called “amines”.


What is the nomenclature followed in Amines ?

The nomenclature of amines follows the IUPAC  as other organic chemicals. The IUPAC method follows the naming by considering the base group to be an alkane and the attached  -NH2 group as the amino group. For example, CH3-NH2 in IUPAC method is, amino methane. The other way is by naming the  alkyl group attached to the nitrogen in the amine. For example, CH3-NH2 in this method is named as methyl amine.The amines are found in different kinds of vital bio-molecules and significant pharmaceutical agents. They are used to make azo-dyes, many drugs and medicines which are based on amino compounds.


What are the different types of Amines?

There are 2 classes of amines. They are as below.

  • Aliphatic amines: These aliphatic amines are classified into 3 types.

        A) Primary amines: Primary amines are formed when one of three hydrogen atoms in ammonia is substituted by an alkyl group which means the formula of the primary amine will be RNH2 where "R" is an alkyl group. Significant primary alkyl amines encompass methylamine (CH3NH2), ethanolamine (2-aminoethanol).

        B) Secondary amines: In a secondary amine, two of the hydrogen atoms in an ammonia molecule have been replaced by hydrocarbon groups. Major examples include dimethylamine, (CH3)2 NH and diethylamine.

        C) Tertiary amines: In a tertiary amine, all of the hydrogen atoms in an ammonia molecule have been replaced by hydrocarbon groups. The naming is analogous to secondary amines. An example of tertiary amine is trimethylamine, (CH3)3 N, that has a characteristically fishy stink.

  • Aromatic amines: Aromatic amines are also known as Analines. These are obtained as byproducts in the  manufacturing compounds of dyes, pesticides, polyurethane foams etc. They are three types of aromatic amines, the monocyclic, polycycluc and heterocyclic amines. Heterocyclic amine are formed when meat and fish are grilled. 

    Examples are, benzidine, pyridine, 1,2 Diphenylhydrazine.


What are the properties of Amines?

  • The properties of primary and secondary amines are mainly altered by the Hydrogen bonding. The reason for the elevated boiling points of the primary amines is that they can form hydrogen bonds with each other as well as van der Waals dispersion forces and dipole-dipole interactions. The boiling point of the secondary amine is a little lower than the primary amine with the identical number of carbon atoms. The lower boiling point is due to the lower dipole-dipole attractions in the dimethylamine compared with ethylamine.
  •  The boiling point of amines is usually lower than those of the alcohols. In standard conditions, methylamine and ethylamine are gases, but the analogous methyl alcohol and ethyl alcohols are liquids.
  •  Gaseous amines acquire a distinguishing ammonia smell whereas  liquid amines have a characteristic "fishy" smell.
  •  The majority of aliphatic amines exhibit some solubility in water, because of their ability to form hydrogen bonds. Solubility decreases with the increase in the number of carbon atoms.
  •  Primary amines react with ketones such as acetone.
  • Aliphatic amines exhibit momentous solubility in organic solvents, particularly in polar organic solvents.
  • The aromatic amines such as aniline, do not take part in the hydrogen bonding. Due to this, their boiling points are high and their solubility in water is very low.


How are amines synthesized?

  • Alkylation : The majority of industrially important amines are synthesized by alkylation of alcohols from ammonia. These reactions need catalysts, specific equipment, and supplementary purification procedures, as the selectivity can be a difficult task. 

    The chemical reaction that take place is,

 ROH + NH3 → RNH2 + H2O 


Treatment of Halo alkanes with amines give the resultant alkyl-substituted amine, with the discharge of a halogen acid, which sequentially reacts with the amine product as follows, 

RX + 2 R'NH2 → RR'NH + (RR'NH2) X

  •  Hydrogenation : By hydrogenation of nitriles, an organic compound that has a triple bond between carbon and nitrogen which are reduced to amines using hydrogen in the presence of a nickel catalyst. Lithium aluminum hydride, LiAlH4, is generally used for the reduction of nitriles in the laboratory and LiAlH4 reduces amides to amines.
  •  Several amines are produced from aldehydes and ketones through a process called “Reductive amination” that make use of either catalytic hydrogenation or stoichiometric reagents.
  •  The aromatic amine, Aniline and its derivatives are prepared by reduction of the Nitro aromatics.
  •  Hydrogen is the favored reductant, in industry level, but in the laboratory, iron and tin are the mostly used reagents.
  •  Other methods : Numerous laboratory methods are available for the preparation of amines. One such method is Gabriel synthesis. Gabriel reaction has been widespread to include the alkylation of sulfonamides and imides, followed by de protection, to produce amines.


What are the Applications of amines?

  • The industrially used amines for eliminating carbon dioxide (CO2) and hydrogen sulfide (H2S) from natural gas streams and refinery procedure streams are aqueous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), diisopropanolamine (DIPA) and methyldiethanolamine (MDEA). They may also be used to eliminate CO2 from combustion gases and are likely for the reduction of greenhouse gases.
  •  Primary aromatic amines are employed as a preliminary material to produce azo dyes. It reacts with Nitric (III) acid to form diazonium salt, which can experience coupling reaction to form azo compound. They are extensively used in dyeing industries, as azo-compounds are extremely coloured. Some examples are: Methyl orange, sunset yellow FCF, Direct brown 138, etc.,
  •  Amines are used in the production of drugs and medicines too.


What are the effects of amines?

Many higher molecular weight amines are highly active biologically. Naturally, vital amines are amino acids which the human body utilizes to produce proteins that are very important in the biochemistry of the human body system. Low molecular weight amines are poisonous, where few are simply absorbed through the skin. Amines themselves might not be harmful but they could react with compounds to form nitrosoamines and nitramines which affect the environment and humans and animals alike. Several of the amino compounds are also known  to be carcinogenic, ex, Nitrosodimethylamine is a carcinogen.In some of the industries there has been a continuous rise in bladder infection which is due to the aromatic amines but there is not enough study done on the toxicology of these amines but hopefully there will be an increase in their studies with an increase in realization of their effects.

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