Amine vs. Amide vs. Imine

Amines are the organic nitrogen compound derived from ammonia in which one or more hydrogen atoms are replaced by an alkyl or aryl group. Amides are the organic compounds derived from carboxylic acids in which the hydroxyl (-OH) group of a carboxyl group is replaced by the amino group (NH₂). The imines are organic compounds that contain carbon-nitrogen double bond (C=N). They are derived from aldehydes and ketones by replacing the oxygen atom with the (N-R) group.

Organic nitrogen compounds

Nitrogen is an element from group 5-A of the periodic table. It has an atomic number of 7 and exists as a colorless, odorless gas. It shows the properties of non-metals, for example, being a poor conductor of heat and electricity.

Carboxylic acid derivatives

Carboxylic acids are organic compounds that contain a carboxyl functional group (-COOH). The name carboxyl is derived from the combination of carbonyl and hydroxyl groups. They are the parent compounds of many derivatives such as amides, ester, etc.

Carboxylic acid derivatives are produced by the attack of nucleophilic species of carboxylic acids in the presence of acid catalysts. They are partially ionized in the aqueous solutions, hence they are weak acids.

Differences between amines, amides, and imines

Amines are derived from ammonia (NH₃) in which one or more hydrogen atoms are replaced by an alkyl or aryl group. . Amides are the derivatives of carboxylic acid in which -OH of the carboxyl group (-COOH) is replaced by the amino group (NH₂). Imines are derived from aldehyde and ketone by replacing the oxygen atom with the NR group.

Classification of Amines, Amides and Imines

Amines

Amines are classified as primary, secondary, or tertiary amines.

Primary amines

When one hydrogen atom of ammonia is replaced by one alkyl or aryl group is known as primary amines.

Fig 8.1

Secondary amines

When two hydrogen atoms of ammonia are replaced by two alkyl or aryl groups is known as secondary amines.

Fig 8.2

Tertiary amines

When three hydrogen atoms of ammonia are replaced by three alkyl or aryl groups is known as tertiary amines. The alkyl or aryl groups may be the same or different.

Fig 8.3

Amide

Amides are classified into three types:

Primary amide

When the nitrogen atom of amide is directly attached to only one carbon is known as a primary amide.

Fig 8.20

Secondary amide

When the nitrogen atom of amide is attached to two carbons is known as a secondary amide.

Fig 8.21

Tertiary amide

When the nitrogen atom of amide is attached to three carbon atoms is known as a tertiary amide.

Fig 8.22

Nomenclature for Amines, Amides and Imines

Amines

Common names of amines

• The common names of amines consist of names of alkyl or aryl groups ending with the word amine.
• If the alkyl groups are the same then prefixes -di or -tri are used.

Fig 8.4

IUPAC nomenclature

• For primary amines the ending -e of the alkyl group containing -NH₂ is substituted by -amine.

Fig 8.5

• For some more complicated primary amines -the NH₂ group is taken as a substituent. The prefix -amino along with the number of -NH₂ group is used.

Fig 8.6

• For secondary or tertiary amine, the longest chain is selected as the parent chain.

If the chain length is equal then parent alkane is one with the greater number of substituents. The remaining alkyl groups that are attached to the nitrogen atom are named as the substituents by using the prefix N-.

Fig 8.7

The naming of aromatic amines

• Aromatic amines are named as the derivative of aniline. The substituents are named by adding the prefix -N.

Fig 8.8

• Some aromatic amines have special names.

Fig 8.9

Amides

The names of amides are derived from the carboxylic acid by replacing the ending “-oic” of acid with “-amide”.

Fig 8.23

imines

• Imines are named by replacing the ‘-e’ of parent hydride with ‘-imine’.

Fig 8.29

Physical properties for Amines, Amides and Imines

amines

• Amines are polar compounds They are mostly liquids.
• The high molecular weight amines have an unpleasant “fishy” odor.
• They have high boiling points than alkanes but lower than alcohols.
• They are usually colorless but turn brown in the presence of air due to oxidation.
• The primary and secondary amines can form hydrogen bonds with each other and also with water. The tertiary amines cannot form hydrogen bonds with each other but can form with water.

Fig 8.10

amides

• All amides are solids except formamide which is a liquid.
• They have high melting and boiling points due to strong intermolecular hydrogen bonding. If we replace the amino hydrogen with the methyl group it decreases the formation of hydrogen bonds so the compound has low melting and boiling point.
• The lower amides are soluble in water due to the formation of a hydrogen bond.

Comparison of Basicity of Amines, Amides and Imines

amines

Amines are basic in nature due to the presence of lone pair on the nitrogen atom so that amines can accept a proton from an acid.

Fig 8.11

Amines are more basic than water because oxygen is more electronegative than nitrogen. So that lone pair on the nitrogen atom is more available for the protonation.

The order of basicity of amines is:

(CH₃)₃N > (CH₃)₂NH＞CH₃NH₂＞NH₃

The greater the alkyl group in amines, the greater is the basicity. This is because the alkyl group increases electron density on the nitrogen atom, therefore, increases the basicity.

amide

Amides are less basic relative to amines. This is because in amides lone pair on the nitrogen atom is delocalized between nitrogen and the carbonyl oxygen through resonance. It decreases the availability of lone pair for donation. However, the lone pair in amines is localized on the nitrogen atom.

Fig 8.24

Preparation of Amines, Amides and Imines

amines

There are two types of methods for the preparation of amines:

• General method
• Special method

The general method gives a mixture of primary, secondary, and tertiary amines whether the special method gives the only special type of amines.

Alkylation of ammonia (Hofmann reaction)

In this reaction, ammonia is treated with the alkyl halide and the salt of primary amines are prepared. Salt of primary amines converted into primary amines on treatment with a base.

It follows the S_N2 mechanism.

Fig 8.12

Reductive amination

It is a reaction in which aldehyde and ketones are converted into amines through the reduction in the presence of ammonia.

This reaction consists of two steps. In the first step, imine is formed which is later reduced to amines.

Fig 8.13

amide

Reaction of a carboxylic acid with ammonia

Amides are prepared by the reaction of the carboxylic acid with aq. ammonia. It is a two-step reaction. In the first step, the ammonium salt is formed. In the second step, it undergoes dehydration on heating to form amides.

Fig 8.25

imines

The reaction of ammonia and its derivatives with aldehyde and ketone.

Imines are formed by the reaction of ammonia and its derivatives with aldehyde or ketones in the presence of an acid. The rate of formation of imine is high at pH of 4 and 5 and it is slow at very low and high pH.

Reaction

Fig 8.28

Reactions of Amines, Amides and Imines

Amines

Acylation of Amines

The replacement of hydrogen in amines by an acyl group is known as acylation.

In this reaction, primary and secondary amines react with acyl chloride or acid anhydride to form substituted amide.

Reaction

Fig 8.14

Mechanism

Fig 8.15

Alkylation of Amines

The replacement of hydrogen in amines by an alkyl group is known as alkylation.

In this reaction, amines react with the alkyl halide to form another amine of the next higher class.

Fig 8.16

amide

Hydrolysis of amide

When amides are heated with acid or alkali, they are hydrolyzed into carboxylic acid and ammonia.

Fig 8.26

Dehydration of amide

When amides are heated with a strong dehydrating agent, they form nitriles.

Fig 8.27

imines

Imines are used as intermediate in the synthesis of heterocyclic compounds.

For example

N-Methanimine (CH₃N=CH₂) trimerizes to the hexahydrotriazine.

Distinction among primary, secondary, and tertiary amines, amides, and imines

Reaction with nitrous acid

This reaction is used to distinguish between primary, secondary, and tertiary amines.

Nitrous acid is formed by the reaction of sodium nitrite(NaNO₂) with dilute hydrochloric acid (HCl).

• Primary amines

Primary amines react with nitrous acid to form alcohol.

Fig 8.17

• Secondary amines

Secondary amines react with nitrous acid to form N-nitrosamines

Fig 8.18

• Tertiary amines

Tertiary amines react with nitrous acid to form N-nitrosoammonium salts.

Fig 8.19

Related Topics

• Keto enol tautomerism
• Enol vs Enolate vs Enamine

Uses of Amines, Amides and Imines

amines

• Amines are used in the synthesis of many organic compounds such as amino acids which are the building blocks of proteins.
• They are used in the synthesis of drugs.

For example, Citalopram (antidepressant), isoetharine, etc.

• They are used in the preparation of azo dyes.
• They are used in the industries for pest control and tanning of leather.
• They are used in the production of detergents.

amides

• Some substituted amides are used as solvents

For example, dimethylformamide is used as solvents in organic synthesis.

• Some unsaturated aliphatic amides are monomers. They are used in polymer synthesis.

For example, acrylamide is used in the synthesis of polyacrylamide.

• They are used in the metal industry for ore processing.
• Aromatic amides are used in the synthesis of dyes.
• Some amides have insect repellent properties.

For example, DEET ( N, N-Diethyl-meta-toluamide) is used as the insect repellent.

imines

• Imines are used in the preparation of dyes.
• They are used in the synthesis of drugs.
• They are used in the synthesis of coordination polymers.

Key Takeaway(s)

Concepts berg

Which is more basic amide or amine?

Amine is more basic than amide because in amine lone pair of nitrogen is more available for donation. Whether in amide carbonyl group is highly electron-withdrawing it pulls electron density towards itself which makes lone pair of amide nitrogen less available for donation.

What is the amine formula?

Amines are derived from ammonia (NH₃) in which one or more hydrogen atoms are replaced by an alkyl or aryl group. They have the general formula RNH₂.

What is substituted imine is called?

The substituted imine is called Schiff base. It is obtained by the reaction of an aromatic aldehyde with amines. It is unstable.

What is a primary amine?

When one hydrogen atom of ammonia is replaced by one alkyl or aryl group is known as primary amines.

What are amines used for?

• Amines are used in the synthesis of many organic compounds such as amino acids which are the building blocks of proteins.
• They are used in the synthesis of drugs.

For example:

Citalopram (antidepressant), isoetharine, etc.

• They are used in the preparation of azo dyes.
• They are used in the industries for pest control and tanning of leather.
• They are used in the production of detergents.

What is the functional group of amine?

The functional group of amine has a nitrogen atom with the lone pair of electrons bonded to one or more alkyl groups.

Why is amine more nucleophilic than amide?

Amines are more nucleophilic because in amine lone pair of nitrogen is available and can be easily donated to electron-deficient species. But in amides, the lone pair of nitrogen is delocalized with the carbonyl oxygen so they are less nucleophilic.

Which test is used to distinguish between amines and amides?

When amides are heated with caustic soda, ammonia is evolved.

CH₃CONH₂ + NaOH → CH₃COONa + NH₃

Amines are basic so they do not react with alkalis.

Which one is more reactive primary secondary or tertiary amine?

Tertiary amines are more reactive than secondary or primary amines. This is because in tertiary amines nitrogen atom is attached to three alkyl groups. They are electron-donating so they increase electron density on the nitrogen atom and make it more reactive.

What are amine hormones?

Amine hormones are derived from amino acids. For example, the melatonin hormone is derived from tryptophan( amino acid). It helps to control the circadian rhythm.

What is an unsubstituted amide?

The functional group of an amide has a carbonyl group bonded to the amine and alkyl group. If one or both bonds of the nitrogen atom of the amide is attached to the alkyl or aryl group it is known as a substituted amide.

How can we differentiate primary secondary and tertiary amines?

Reaction with nitrous acid

This reaction is used to distinguish between primary, secondary, and tertiary amines.

• Primary amines

Primary amines react with nitrous acid to form alcohol.

• Secondary amines

Secondary amines react with nitrous acid to form N-nitrosoamines

• Tertiary amines

Tertiary amines react with nitrous acid to form N-nitrosoammonium salts.

What are the physical properties of amines?

• Amines are polar compounds They are mostly liquids.
• The low molecular weight amines have an odor like amines whereas the high molecular weight amines have an unpleasant “fishy” odor.
• They have high boiling points than alkanes but lower than alcohols.
• They are usually colorless but turn brown in the presence of air due to oxidation.
• The primary and secondary amines can form hydrogen bonds with each other and also with water. The tertiary amines cannot form hydrogen bonds with each other but can form with water.

Is 2 butylamine a primary secondary or tertiary amine?

When the nitrogen atom of amine is directly attached to only one carbon is known as a primary amine. 2-Butylamine is the primary amine because the nitrogen atom is attached to only one carbon.

What products are formed when amides are hydrolyzed?

When amides are heated with acid or alkali, they are hydrolyzed into carboxylic acid and ammonia.