Colour by Design - Azo Compounds and Dyes Flashcards
what is the functional group for diazonium compounds?
what is the functional group for diazonium compounds also known as?
diazo groups
what is the stability of diazo groups on their own?
very unstable
why are diazo groups unstable on their own?
electronically unfavourable - electrons easily move onto positive nitrogen to produce N2 which then leaves the molecule
how can diazo groups be made more stable?
by attaching them to benzene rings
draw the product of a diazo group attaching to a benzene ring
how are diazonium salts prepared?
normally made in situ to form intermediates
in cold conditions
made from sodium nitrate
what does it mean if a reactant is made in situ?
it is made in a solution containing the other reactants, so as soon as it forms it will react
why must diazonium salts be prepared in cold conditions?
they are explosive
what is the process of reacting diazo groups with aromatic molecules called?
diazotisation
why are diazonium salts more stable when added to benzene rings?
(not on spec but helps to understand)
the electrons can delocalise to form part of the conjugated system
what is the functional group of an azo compound?
what reaction occurs to convert diazonium salts into azo compounds?
coupling reaction
what happens in a coupling reaction?
the diazonium compounds reacts with a coupling agent to produce an azo compound and H+
what are usually the properties of coupling agents?
contain hydroxy or amino groups attached to a benzene ring
why are coupling agents good nucleophiles in coupling reactions?
The lone pairs on the hydroxy and amion groups increase the electron density of the benzene ring and so make it more reactive towards electrophiles
draw the general equation for a coupling reaction
where does the proton in the products of a coupling reaction come from?
where the diazonium salt attaches to the coupling agent
what are the reaction conditions for coupling reactions?
ice cold solution of diazonium salt
what is different about the reaction conditions for coupling reactions when phenols are used?
coupling agent dissolved in alkali
what are the properties of azo compounds?
usually coloured
wide range of these compounds so colour, solubility and ability to bind to fabrics all vary
how can you identify which section of an azo compound originated from the coupling agent?
it will have a phenol or amino group attached
what do dye molecules contain?
chromophore
functional groups which modify colour of chromophore
functional groups which allow molecule to bind to clothing fibres
functional groups which alter solubility
what is a chromophore?
the section of a molecule that is responsible for its colour
how do chromophores determine the colour of dye molecules?
it contributes to delocalisation of electrons and therefore responsible for absorption of light
what are permanent dipole - permanent dipole bonds?
pd - pd bonds are the strong bonds formed between molecules with permanent dipoles
what are permanent dipole - induced dipole bonds?
pd - id bonds are the bonds formed between molecules with permanent dipoles and non-dipolar molecules that are close
what are instantaneous dipole - induced dipole bonds?
id - id bonds are the weak bonds formed between any molecules
what are 3 types of fibre?
polyamide protein fibres
cellulose fibres
polyesters
what are examples of polyamide protein fibres?
wool
silk
fur
what side groups are present in polyamide fibres?
NH2 that are ionised to NH3+
what are examples of cellulose fibres?
cotton
hemp
bamboo
what side groups are present in cellulose fibres?
- OH groups
- NH2 groups
what bonds are formed between polyamide protein fibres and dyes?
ionic
what bonds are formed between cellulose fibres and dyes?
hydrogen bonds
what bonds are formed between polyester fibres and dyes?
id-id bonds
what type of dye fibre can bond to polyamide protein fibres?
containing SO3H groups
how are dye molecules bonded to polyamide protein fibres?
NH2 on fibre goes to NH3+ on addition of acid
SO3H loses H when dissolved in water, forming SO3-
ionic bond forms between the 2 ions
what type of dye molecules can bond to cellulose fibres?
containing OH and NH2 groups
linear molecules
how are dye molecules bonded to cellulose fibres?
hydrogen bond between NH2 and OH groups on each molecule
why are linear molecules usually used to bind dyes to cellulose fibres?
only bonded with H bonds so have to be very strong or will be broken in water
what type of dye molecules can bond to polyesters?
with very few polar groups
how are dye molecules bonded to polyesters?
dyes are insoluble and so are ‘dispersed’ through water
polyesters contain few polar groups so are bonded with id-id forces
what are the 2 ways of attaching dyes with covalent bonds?
mordanting
adding fibre reactive groups
what is mordanting?
using a metal ion to join a dye to a fabric
groups on the fabric and dye form dative covalent bonds to the central ion, forming a chelate
what is a chelate?
a complex ion in which the metal ion is bonded to two or more atoms in the same molecule
what is the fibre reactive dyes method of attaching dyes through covalent bonding?
reactive groups on the dye form a bridge between the dye and fibre
