Investigate The Relationship Between Structure And Properties Of Nitrogen Containing Organic Compounds

Amines are organic compounds that contain a nitrogen atom bonded to carbon atom of alkyl group or aryl group. They are derived from ammonia by replacing one or more hydrogen atoms with alkyl group or aryl group. The bonding in amines are covalent. Amines can be divided into aliphatic amines and aromatic amines. Aliphatic amines have alkyl groups attached to the nitrogen atom. Aromatic amines have aryl groups attached to the nitrogen atom.

Amines can be further classified into primary-amines, secondary-amines, and tertiary-amines. Primary-amines have one alkyl group or aryl group bonded to the nitrogen atom. Primary-amines are formed by replacing one hydrogen atom of ammonia with an alkyl group or an aryl group. An example of primary-amine is methylamine.

secondary-amines have two alkyl groups or aryl groups bonded to the nitrogen atom. secondary-amines are prepared by replacing two hydrogen atoms of ammonia with alkyl group or aryl group. The two alkyl groups or aryl groups attached to nitrogen atom in secondary-amines can be same or different. An example of aliphatic secondary-amine is dimethylamine. Diphenylamine is an example of a aromatic secondary-amine.

Tertiary-amines have three alkyl groups or aryl groups bonded to the nitrogen atom. They are formed by replacing three hydrgen atoms of ammonia with alkyl groups or aryl groups. An example of aliphatic tertiary amine is triethylamine. Tertiary-amines are widely used as catalysts and intermediates in organic synthesis.

Primary-amines can participate in nucleophilic substitution reactions. Amino group acts as a nucleophile. These reactions involve the substitution of the amino group with another atom or group. Alkylation of amines is an example of nucleophilic substitution reaction of amines. In this reaction primary-amines react with alkyl halides to form secondary-amines and tertiary-amines. The reaction involves the displacement of the halide by the amino group.

Primary-amines can undergo acylation reactions with acyl chlorides to form amides. The amino group displaces the chloride ion of acid chloride to form the amide. The reaction takes place in the presence of pyridine and heat. For example, ethylamine can react with acetyl chloride to form N-ethyl acetamide.

The Gabriel synthesis is a method used to prepare primary-amines from alkyl halides. It involves several steps. The first step involves the preparation of phthalimide. Phthalimide is an important reagent used in the Gabriel synthesis. Phthalimide is obtained by the reaction of phthalic anhydride with ammonium hydroxide. This reaction leads to the formation of a phthalimide.

In the next step, the phthalimide is reacted with an alkyl halide. The reaction is carried out in the presence of a strong base, such as potassium hydroxide. Under basic conditions, the phthalimide ion acts as a nucleophile. It attacks the alkyl halide. This nucleophilic attack results in the displacement of the halide ion. As a result, an intermediate is formed which is known as an alkyl phthalimide. The alkyl phthalimide is then treated with a hydrazine. This causes the alkyl phthalimide to break apart and form primary-amine as the main product.

Diazotization is a chemical process that involves the conversion of primary aromatic amines into diazonium salts. In diazotization, a primary aromatic amine reacts with nitrous acid, resulting in the formation of a diazonium salt. During diazotization, the amino group of the primary aromatic amine is replaced by a diazonium group. This substitution results in the formation of diazonium salt.

We know that a base is a specie that can donate a lone pair of electrons and accept hydrogen ions easily. In amines, the nitrogen atom has a lone pair of electrons. It can easily accept hydrgen ions. This makes amines basic in their nature. For example, when alkyl amine is dissolved in water, it dissociates into alkyl ammonium ion and chloride ion. Alkyl ammonium ion is formed by accepting hydrogen ion.

Basicity of amines increases due to presence of alkyl groups in amines. This is due to electron donating inductive effect of alkyl groups. nitrogen atom already has a lone pair of electrons. The alkyl group further increases electron density at nitrogen atom. For example, propylamine is more basic in its nature than methylamine. This is because propyl group in propylamine has three carbon atoms. While methyl group in methylamine has only one carbon atom. So the electron donating inductive effect of propyl group is greater than methyl group.

Secondary-amine is more stable than primary-amine. This is because in secondary-amine, two alkyl groups are attached to the nitrogen atom. Meanwhile, in primary-amine, only one alkyl group is attached to nitrogen atom. Therefore, the two alkyl groups in secondary-amine increases electron density on nitrogen atom greatly as compared to only one alkyl group in primary-amine.

The primary-amines are more basic than tertiary-amines. But we have recently discussed that basicity of amines increases by increasing alkyl groups. Then why tertiary amine is less basic than primary-amine? The tertiary amine is less basic due to steric hindrance. Steric hindrance means the bulky alkyl groups in tertiary amine block the incoming hydrogen ion. Due to this reason tertiary-amines cannot easily accept a hydrogen ion. This makes them less basic as compared to primary-amines.

Aliphatic amines are generally more basic than amides. The basicity of nitrogen atom in amines and amides differs due to their electronic properties. In amines, the nitrogen atom possesses a localized lone pair of electrons. This makes it highly basic. However, in amides, the lone pair of electrons on the nitrogen atom is delocalized through resonance. This delocalization stabilizes the electron density. The lone pair of electrons on the nitrogen atom is less likely to bond with a proton because it is already involved in the stable delocalized pi bonding system. This makes amides less basic than amines.

Amines are also more basic than alcohols. Although they are in alcohols, a lone pair of electrons is also seen on oxygen atom. But in alcohols, oxygen atom is more electronegative as compared to nitrogen atom in amines. The highly electronegative oxygen atom in alcohols withdraws electron density from hydrogen atom attached to it. In this way hydrogen atom is released. This makes alcohols weakly acidic. However in amines, the lone pair of electrons on nitrogen atom can be used to accept hydrogen ion. This makes amines more basic than alcohols.