CD5 - Benzene rings + dye molecules

Question 1

benzene –> nitrobenzene

Answer 1

conc. nitric acid + conc. H2SO4
below 55oC

(higher temp = di- + tri-)

Question 2

How is the NO2+ cation formed in a nitration reaction?

Answer 2

sulfuric acid + nitric acid

HNO3 + 2H2SO4 –> NO2+ + 2HSO4- + H3O+

Question 3

affects of nitrating a chromophore?

Answer 3

change the wavelength of light it absorbs

molecule will have a different colour

Question 4

benzene –> benzenesulfonic acid

Answer 4

SULFONATION
conc. H2SO4 + reflux

• electrophile = SO3 from H2SO4

Question 5

benzene acid is a strong acid and forms _______ in ALKALINE solution

Answer 5

salt + water

Question 6

dyes are often made more soluble by adding….

Answer 6

SULFONIC ACID groups

sulfonic acid groups are able to form ionic salts

Question 7

what are azo compounds?

Answer 7

contain azo functional group

R1 - N = N - R2

formed by coupling beween diazonium salt + coupling agent

Question 8

how can an azo compound become more stabilised?

Answer 8

If R1 + R2 are arene groups, the -N=N- group becomes part of an extended delocalised system involving the arene groups

= aromatic azo compounds –> highly coloured = used as dyes

Question 9

what are diazonium compounds/salts?

Answer 9

R - N+ = N Cl-

triple bond

Question 10

How can unstable diazonium compounds become more stable?

Answer 10

attach to benzene ring
N=N –> part of delocalised system

• stabilised enough to form intermediates in synthesis
• compounds prepared in ice-cold solvents + used immediately (explosive)

Question 11

How do you prepare an aromatic diazonium compound?

Answer 11

• aromatic amine dissolved in dilute HCl
• add cold sodium nitrite (NaNO2)
• temp below 5oC (ice bath)

= DIAZOTISATION

Question 12

what is a coupling reaction?

Answer 12

diazonium compound reats with a coupling agent (compound with a reactive benzene ring)

• diazonium ion = electrophile + reacts with benzene ring/ coupling agent

Question 13

How do you perform a coupling reaction?

Answer 13

• sol, of coupling agent made
• • ice cold diazonium salt
• coloured precipitate of azo compound

Question 14

with PHENOLS, the COUPLING AGENT is usually dissolved in ____ to enable the reaction to occur

Answer 14

ALKALI

Question 15

what is affected by altering the structure of a diazonium compound + coupling agent in a coupling reaction?

Answer 15

forms a range of diff. coloured azo compounds

• colours
• water solubility
• ability to bind to fabrics