CD 5

Question 1

why are substitution reactions important to chemists that design dyes

Answer 1

they affect kep properties in the dye and provide a way pf making an important class of synthetic dyes

Question 2

what is an azo group

Answer 2

N=N

Question 3

what were azo dyes originally produced from, what was the process

Answer 3

phenylamine
By a two step process involving diazotisation them a coupling reaction

Question 4

what is the sulfonic group and what are they derived from (give the formula)

Answer 4

another group of the azo dyes
they are derived from sulfonic acid SO3H -

Question 5

what are the properties of the sulfonic group

Answer 5

The ionic group SO3 - helps make the dye more soluble in water as well as providing a way for the molecule to attach to fabric (by bonding to the positively charged molecules in the fabric)

Question 6

what is nitration and what are the products

Answer 6

• The reaction of benzene with concentrated nitric acid and a concentrated sulfuric acid - this is a nitrating mixture
• If the reaction is kept below 55 degrees, then the product is nitrobenzene
  -if the reaction is kept above 55 degrees, further substitution takes place to give di and tri substituted compounds

Question 7

what reacts with benzene in a nitration reaction, and how is this reactant formed

Answer 7

NO2 + cation, which is formed in the nitrating mixture

Question 8

what is the effect of nitration reactions

Answer 8

the nitro groups inserted into a benzene ring that is part of a chromophore will change the wavelength of light that it absorbs and the molecule will have a different colour

Question 9

describe the reaction of the sulfonation of benzene

Answer 9

Benzene + sulfuric acid (H2SO4) —– REFLUX —-> benzene sulfonic acid + H+ ions

Question 10

what is the electrophile in sulfonation and where does it come from

Answer 10

SO3 which is present in concentrated sulfuric acidwh

Question 11

does benzene sulfonic acid react with alkali?

Answer 11

Yes, it forms salts in alkaline solution

Question 12

define coupling

Answer 12

coupling is a reaction between a diazonium compound and a phenol or aromatic amine to produce an azo dye

Question 13

how are azo compounds formed

Answer 13

they are the result of a coupling reaction between a diazonium salt and a coupling agent

Question 14

what makes an azo compound stable and why

Answer 14

• If the R groups on an azo compound are arene then the azo compound is much more stable than it would be if they were alkyl groups
• this is because the azo group is stabilised by becoming part of delocalised system involving the arene groups
• this stability enables the highly coloured aromatic azo compounds to be used as dyes

Question 15

whats the other name for diazonium compounds

Answer 15

diazonium salts

Question 16

Usually, what is the stability of diazonium salts and why

Answer 16

They are usually very unstable because the diazonium group is very easily lost, forming nitrogen gas

Question 17

what happens when the R group of a diazonium salt is a benzene ring

Answer 17

The electrons in the N+ TRIPLE BOND N will become part of the delocalised system in the benzene ring which stabilises it enough to allow the diazonium compounds to be formed as intermediated in synthesis.

Question 18

how are diazonium compounds attached to benzene typically used

Answer 18

• used in synthesis and are prepared in ice cold solutions and used immediately

Question 19

what are aromatic diazonium compounds made from, and describe the process of diazotization

Answer 19

aromatic amines e.g. phenylamine
1. aromatic amine is dissolved in dilute hydrochloric acid
2. cold solution of sodium nitrite (sodium nitrate III) NaNO2 is added
3. The temperature is kept below 5 degrees by performing the reaction in 5 degrees C

Question 20

what is the reactant in diazotization

Answer 20

unstable acid nitrous acid, HNO2

Question 21

what are the reactants in a coupling reaction

Answer 21

diazonium compound and a coupling agent (compound with a relatively large benzene ring)

Question 22

what is the electrophile in a coupling reaction
and what is the coupling agent

Answer 22

• electrophile is diazonium ion and reacts with the benzene ring of the coupling agent
• coupling agents generally contain phenol or amino groups attached to the benzene ring as their lone pairs increase the electron density of the benzene ring, increasing its reactivity towards electrophiles

Question 23

describe the process of a coupling reaction

Answer 23

1. a solution of a coupling agent is made up
2. an ice cold solution of diazonium salt is added to iy
3. a coloured precipitate of the azo compound immediately forms

Question 24

describe the process of a coupling reaction with phenols

Answer 24

• coupling agent is dissolved in alkali