Section 11: Colour By Design

Question 1

What reactions do Arenes undergo?

Answer 1

Electrophillic substitution

Question 2

What are the conditions and reagents for making nitrobenzene?

Answer 2

Warm with nitric and sulfuric acid

Question 3

What do nitric and sulfuric acid make which is crucial for the formation of nitrobenzene?

Answer 3

Nitronium ion (NO2+)

Question 4

Draw the mechanism for nitration of benzene

Question 5

What must the conditions specifically be to ensure mononitration occurs, and not many substitutions occur?

Answer 5

<55 C. If 2 nitronium group substitute onto the Benzene, trinitrotoluene forms (TNT)

Question 6

What conditions are needed to make benzenesulfonic acid?

Answer 6

Boil benzene under reflux with concentrated sulfuric acid for several hours
Or
Warm benzene to 40 C with fuming sulfuric acid (sulfuric acid with many SO3 dissolved in the solution) for 30 minutes

Question 7

What does sulfuric acid make that’s crucial for the formation of benzenesulfonic acid?

Answer 7

It forms sulfur trioxide molecules

H2SO4 -> SO3 +H2O

Question 8

Draw the mechanism for sulfonation of benzene

Question 9

Give examples of halogen carriers

Answer 9

Aluminium halides, Iron Halides, and Iron
AlCl3
FeCl3
Fe

Question 10

Haloalkanes react with halogen carriers to form what?

Answer 10

A carbocation and a polarised halogen carriers
R+ + AlCl4-

Question 11

What are examples of friedel crafts reactions?

Answer 11

Alkylation (adding alkane group with one less H onto benzene)
Acylation (adding C double bond O group onto a benzene)

Question 12

Draw an example mechanism of dreidel crafts:
Alkylation
Acylation

Question 13

Conditions required for the following:
Nitrobenzene -> Phenylamine

Answer 13

Sn (Tin) and and concentrated HCl

Question 14

Phenylamine -> 2,4,6-tribromophenylamine
What raegent is needed?

Google if you need to picture them!

Answer 14

Bromine

Question 15

What functional group is contained within an Azo Dye?

Answer 15

An Azo Group which is -N=N-

Question 16

Azo Dyes can be made in coupling reactions. What is the first step?

Answer 16

Making Diazonium Salts

Question 17

What functional group is contained within Diazonium compounds?

Answer 17

-N ≡ N-

Question 18

This can be done by reacting Phenylamine with nitrous acid hydrochloric acid, what does this form?
(C6H5-NH2 + HNO2 +HCl)

Have a go at drawing the reaction.

What conditions are required?

Answer 18

Benzenediazonium Salt

<5 C. This prevents a phenol from being made.

Question 19

The diazonium salt goes on to react with what to form an Azo Dye?

Have a go at drawing this reaction

Answer 19

Phenol

Question 20

Why is Phenol a good coupling agent?

Answer 20

It has lone pairs, which increase the electron density around the benzene ring.

This means that even a weak electrophile like the diazonium salt/ion is able to attack the phenol to produce an Azo Compound.

Question 21

What is meant by the term colourfast?

Answer 21

A dyes ability to not come out during a wash or fade in sunlight

Question 22

Dyes can have specific groups allowing them to form hydrogen bonds with their fibres. Give examples of such groups.

Answer 22

Amine (NH2)

Question 23

Amine groups are especially good at forming hydrogen bonds with certain cellulose fibres (as such fibres contain many -OH groups). What are these fibres?

Answer 23

Cotton
Rayon
Linen

Question 24

COOH and SO3H groups can form what links with alkaline -NH- groups?

How do they do this?

Answer 24

Ionic bonds

Both donate a H+ ion to form an NH2+:
COO- and NH2+ are attracted
SO3- and NH2+ are attracted

Question 25

If there is an ionic salt group present (i.e. SO3-Na+), how would you bind this to an -NH- groups?

Answer 25

Dissolve the ionic salt so that the ions dissociate leaving SO3- group. Acidify the solution (add H+ ions) so that NH can become NH2+. SO3- and NH2+ can now form ionic bonds.

Question 26

What is the most permanent type of dye? Why are they the most permanent/colourfast?

Answer 26

Fiber reactive dyes They form strong covalent bonds with OH and NH groups on fibres.

Question 27

What is a chromophore? How do they do their function as described?

Answer 27

The structure within a molecule that provides the molecule with its colour. The electrons within a chromophore absorb specific frequencies of light. The visible frequencies of light which aren’t absorbed will be perceived as a particular colour

Question 28

What is meant by the term colourfast?

Answer 28

A dyes ability to not wash out of a fibre too easily or fade from a fibre in light

Question 29

Dyes need to be soluble a lot of the time, especially with fibres. How can they be made more soluble?

Answer 29

By adding solubilising groups, such as sulfur trioxide (SO3-) ions, as they have a polar nature which water is able to surround.

Question 30

What is a pigment and what is a dye?

Answer 30

Pigments are insoluble colourings, usually finely ground particles suspended in substance. Pigments are more colourfast than dyes. Dyes are soluble colourings, they actually bind to their fibres to form one product. The fact they are soluble means water can be used to

Question 31

What do molecular orbitals have to do with colour and energy gaps and delocalisation etc.

Answer 31

Molecular orbitals have similar energy levels, and have an energy gap which electrons can jump up when they absorb frequencies of energy to become excited, which they reflect the complementary wavelength. The more molecular orbitals there are, the less of an energy gap there is, and this tends to be in delocalised systems where there are many bonds (crossing over of atomic orbitals to form molecular orbitals) so lesser of an energy gap. So lesser frequencies of light required to excite electrons means the complementary frequency will sit within the visible light spectrum and the complementary colour will be reflected.

Question 32

What is tollens?

Answer 32

Test for aldehyde Add 5-10 drops aldehyde and a silver mirror forms around the test tube

Question 33

What is fehlings

Answer 33

Test for aldehyde Add 5 drops to blue fehlings solution and it will turn to a brick red precipitate

Question 34

Hydrogen cyanide reacts by a what reaction?

Answer 34

Nucleophillic addition