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Chemistry A2 > Colour by Design - Azo Compounds and Dyes > Flashcards

Colour by Design - Azo Compounds and Dyes Flashcards

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1
Q

what is the functional group for diazonium compounds?

A
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2
Q

what is the functional group for diazonium compounds also known as?

A

diazo groups

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3
Q

what is the stability of diazo groups on their own?

A

very unstable

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4
Q

why are diazo groups unstable on their own?

A

electronically unfavourable - electrons easily move onto positive nitrogen to produce N2 which then leaves the molecule

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5
Q

how can diazo groups be made more stable?

A

by attaching them to benzene rings

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6
Q

draw the product of a diazo group attaching to a benzene ring

A
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7
Q

how are diazonium salts prepared?

A

normally made in situ to form intermediates

in cold conditions

made from sodium nitrate

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8
Q

what does it mean if a reactant is made in situ?

A

it is made in a solution containing the other reactants, so as soon as it forms it will react

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9
Q

why must diazonium salts be prepared in cold conditions?

A

they are explosive

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10
Q

what is the process of reacting diazo groups with aromatic molecules called?

A

diazotisation

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11
Q

why are diazonium salts more stable when added to benzene rings?

(not on spec but helps to understand)

A

the electrons can delocalise to form part of the conjugated system

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12
Q

what is the functional group of an azo compound?

A
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13
Q

what reaction occurs to convert diazonium salts into azo compounds?

A

coupling reaction

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14
Q

what happens in a coupling reaction?

A

the diazonium compounds reacts with a coupling agent to produce an azo compound and H+

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15
Q

what are usually the properties of coupling agents?

A

contain hydroxy or amino groups attached to a benzene ring

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16
Q

why are coupling agents good nucleophiles in coupling reactions?

A

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

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17
Q

draw the general equation for a coupling reaction

A
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18
Q

where does the proton in the products of a coupling reaction come from?

A

where the diazonium salt attaches to the coupling agent

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19
Q

what are the reaction conditions for coupling reactions?

A

ice cold solution of diazonium salt

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20
Q

what is different about the reaction conditions for coupling reactions when phenols are used?

A

coupling agent dissolved in alkali

21
Q

what are the properties of azo compounds?

A

usually coloured

wide range of these compounds so colour, solubility and ability to bind to fabrics all vary

22
Q

how can you identify which section of an azo compound originated from the coupling agent?

A

it will have a phenol or amino group attached

23
Q

what do dye molecules contain?

A

chromophore

functional groups which modify colour of chromophore

functional groups which allow molecule to bind to clothing fibres

functional groups which alter solubility

24
Q

what is a chromophore?

A

the section of a molecule that is responsible for its colour

25
Q

how do chromophores determine the colour of dye molecules?

A

it contributes to delocalisation of electrons and therefore responsible for absorption of light

26
Q

what are permanent dipole - permanent dipole bonds?

A

pd - pd bonds are the strong bonds formed between molecules with permanent dipoles

27
Q

what are permanent dipole - induced dipole bonds?

A

pd - id bonds are the bonds formed between molecules with permanent dipoles and non-dipolar molecules that are close

28
Q

what are instantaneous dipole - induced dipole bonds?

A

id - id bonds are the weak bonds formed between any molecules

29
Q

what are 3 types of fibre?

A

polyamide protein fibres

cellulose fibres

polyesters

30
Q

what are examples of polyamide protein fibres?

A

wool

silk

fur

31
Q

what side groups are present in polyamide fibres?

A

NH2 that are ionised to NH3+

32
Q

what are examples of cellulose fibres?

A

cotton

hemp

bamboo

33
Q

what side groups are present in cellulose fibres?

A
  • OH groups
  • NH2 groups
34
Q

what bonds are formed between polyamide protein fibres and dyes?

A

ionic

35
Q

what bonds are formed between cellulose fibres and dyes?

A

hydrogen bonds

36
Q

what bonds are formed between polyester fibres and dyes?

A

id-id bonds

37
Q

what type of dye fibre can bond to polyamide protein fibres?

A

containing SO3H groups

38
Q

how are dye molecules bonded to polyamide protein fibres?

A

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

39
Q

what type of dye molecules can bond to cellulose fibres?

A

containing OH and NH2 groups

linear molecules

40
Q

how are dye molecules bonded to cellulose fibres?

A

hydrogen bond between NH2 and OH groups on each molecule

41
Q

why are linear molecules usually used to bind dyes to cellulose fibres?

A

only bonded with H bonds so have to be very strong or will be broken in water

42
Q

what type of dye molecules can bond to polyesters?

A

with very few polar groups

43
Q

how are dye molecules bonded to polyesters?

A

dyes are insoluble and so are ‘dispersed’ through water

polyesters contain few polar groups so are bonded with id-id forces

44
Q

what are the 2 ways of attaching dyes with covalent bonds?

A

mordanting

adding fibre reactive groups

45
Q

what is mordanting?

A

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

46
Q

what is a chelate?

A

a complex ion in which the metal ion is bonded to two or more atoms in the same molecule

47
Q

what is the fibre reactive dyes method of attaching dyes through covalent bonding?

A

reactive groups on the dye form a bridge between the dye and fibre

48
Q
A

Chemistry A2 (20 decks)

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