The general reaction for primary amines is:

(RCO)₂O  +  R'NH₂  ===> RCONHR'  +  RCOOH

where R and R' = alkyl or aryl, to give a secondary amide

 

The general reaction for secondary amines is:

(RCO)₂O  +  R'NHR"  ===> RCONR'R"  +  RCOOH

where R, R' and R" = alkyl or aryl, to give a tertiary amide

 

Again, as with acid chlorides, tertiary amines (NRR'R") cannot react with acid anhydrides to form amides because there is no hydrogen atom to be replaced by an acyl group.

See also

7.13 Examples of aromatic compounds from the pharmaceutical industry and those found in natural products for the synthesis of Paracetamol - a secondary amide

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8.5.3 Polyamides e.g. Nylon and Kevlar

Diamines and dicarboxylic acids (or a derivative like a diacid chloride) can undergo condensation polymerisation to yield polyamides e.g.

(a) n H₂N-R-NH₂  +  n HOOC-R'-COOH  ===>  -(NH-R-NH-CO-R'CO-)_n-  +  2n H₂O

(a) n H₂N-R-NH₂  +  n ClOC-R'-COCl  ===>  -(NH-R-NH-CO-R'CO-)_n-  +  2n HCl

Extra notes on Nylons

NYLONS are formed by condensing together a dicarboxylic acid and a diamine (nylon-x,y) OR polymerising an amino carboxylic acid (nylon-y). [x = length carbon atoms in amine, y = length of carbon atoms in carboxylic acid]

e.g. depicted using structural formulae and skeletal formulae for a nylon-x and nylon-x,y where x and y = 6

nylon-6 ,

nylon-6,6 ,

The next four diagrams depict the formation of a Nylon polymer and then specifically, the synthesis of Nylon-6,6.

The synthesis involves two different monomer molecules, both of which must have a functional group at each end capable of condensing and bonding with the functional group of the other monomer,

e.g. -NH₂ and -COCl  or -NH₂ and -COOH to form a secondary amide linkage H-N-C=O.

This is the same linkage in peptides and proteins formed naturally from the polymerisation of amino acids, structure H₂N-CHR-COOH, which have both condensing functional groups on the same molecule.

The general equation for the condensation polymerisation of a diacid dichloride (of a dicarboxylic acid) and a diamine with the formation of the amide link (H-N-C=O) at both ends of the monomer molecules and the elimination of a hydrogen chloride molecule for each bond that is formed.

 

The general equation for the condensation polymerisation of a dicarboxylic acid and a diamine with the formation of the amide link (H-N-C=O) at both ends of the monomer molecules and the elimination of a water molecule for each bond that is formed.

 

The equation for the condensation polymerisation of hexane-1,6-dioyl dichloride and 1,6-diaminohexane (1,6-hexanediamine, hexane-1,6-diamine, hexamethylenediamine) with the formation of the amide link (H-N-C=O) at both ends of the monomer molecules and the elimination of a hydrogen chloride molecule for each bond that is formed.

This is the equation for the laboratory demonstration of making Nylon-6,6 (See basic Nylon notes)

 

The equation for the condensation polymerisation of a hexane-1,6-dicarboxylic acid (hexanedioic acid, adipic acid) and hexane-1,6-diaminohexane (1,6-hexanediamine, hexane-1,6-diamine, hexamethylenediamine) with the formation of the amide link (H-N-C=O) at both ends of the monomer molecules and the elimination of a water molecule for each bond that is formed.

This is the equation for the actual manufacture of Nylon-6,6 and n is around 20 000 repeating units.

 

It is possible to make a Nylon with just one monomer, as long as the molecule has two functional groups, one at each end of the molecule that can condense together to give the polyamide bond e.g. Nylon-6 from 6-aminohexanoic acid.

 

A brief note on the manufacturing, structure and uses of Nylon

In the manufacturing process the strength of Nylon fibres are increased by a technique called cold-drawing.

The threads are tensioned to encourage the polymer molecules to line up and therefore increasing the surface-surface contact and increasing the intermolecular bonding forces of attraction.

(i) Increase in instantaneous dipole - induced dipole forces, AND

(ii) allows increased hydrogen bonding (llll) between the C=O and the NH groups of adjacent polymer molecules that have become more closely aligned with each other i.e. >C=O^δ-llll^δ+H-N<.

The resulting strong fibres are used in stockings and fabrics for carpets.

Nylon is a tough strong material that doesn't melt until ~250^oC.

Nylon is actually strong enough to be used to make mechanical parts for machines including bearings and rollers.

Nylon has a high electrical resistance and is used to make safe switches operating electrical circuits.

To avoid over repetition of notes PLEASE note where to read more on the details of POLYAMIDES ...

Basic notes on Condensation polymers including school demonstration making Nylon

The properties and uses of Nylon

Basic notes on High performance polymers like KEVLAR

An introduction to the structure, properties and uses of Kevlar.

7.12 The structure, properties and uses of polyamides including more advanced notes on Nomex & Kevlar

Includes hydrogen bonding diagrams.

For addition polymerisation (polymers from alkene monomers) see

for basic notes: Addition polymers - plastics, poly(ethene),  PVC etc., uses, problems, recycling

and includes a comparison of addition and condensation polymerisation,

and for more advanced notes see Advanced Organic Chemistry Notes section 2.8:

Polymerisation of alkenes - addition polymers - structure, properties and uses of poly(alkenes)

 

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INDEX of Organic Nitrogen Compound NOTES

 All Advanced Organic Chemistry Notes

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