Some reactions of benzene

Question 1

hydrogenation is when

Answer 1

a species gain hydrogen atoms

Question 2

hydrogenation of benzene is carried out by

Answer 2

mixing benzene with hydrogen and heating under pressure with a nickel catalyst

Question 3

the equation for the hydrogenation of benzene is

Answer 3

C6H6 + 3H2 → C6H12 (which is cyclohexane, a hexagon with no circle in the middle)

Question 4

when benzene is burned in air, what is observed

Answer 4

a smoky flame, which is typical of compounds with a high carbon : hydrogen ratio

Question 5

bromination can mean both………….. and……………

Answer 5

a reaction with bromine in UV conditions, or the substitution of bromine

Question 6

the process for the bromination, as in substitution reaction of bromine with benzene, is

Answer 6

heated under reflux

presence of a catalyst called a halogen carrier

Question 7

halogen carries are

Answer 7

catalysts which help to introduce a halogen atom into a benzene ring

Question 8

halogen carriers are usually …………………… such as

Answer 8

metal-halogen compounds such as aluminium chloride (AlCl3), aluminium bromide (AlBr3) or iron (III) bromide (FeBr3)

Question 9

the equation showing the bromination of benzene using iron(III) chloride is:

Answer 9

Br2 + FeCl3 → Br+ + FeCl3Br-

C6H6 + Br+ → C6H5Br + H+

H+ + FeCl3Br- → FeCl3 + HBr (catalyst is regenerated)

Question 10

nitration is

Answer 10

the substitution of a hydrogen atom by a nitro group (NO2)

Question 11

nitration is carried out by

Answer 11

warming benzene with a mixture of CONCENTRATED nitric and CONCENTRATED sulfuric acid

Question 12

in nitration, the concentrated HNO3 acid provides the…………….and the concentrated H2SO4 acts as ……………

Answer 12

HNO3 provides the NO2 (nitro) group

H2SO4 acts as a catalyst

Question 13

the equaiton for the nitration of benzene is

Answer 13

C6H6 + HNO3 → (H2SO4) → C6H5NO2 + H2O

Question 14

both Friedel-Crafts reactions have the following 3 points in common:

Answer 14

• using reagents represented by XY, and one of the hydrogen atoms on benzene is substituted by Y and the other product is HX
• a catalyst is needed, often aluminium chloride, FeBr3 or FeCl3
• anhydrous conditions are needed as H2O would react with the catalysts and sometimes with the organic product

Question 15

the reagents, conditions and catalysts needed for the Friedel-Crafts alkylation reaction is

Answer 15

• reagent is a halogenoalkane
• AlCl3
• anhydrous conditions

Question 16

the equation showing the alkylation of benzene is

Answer 16

C6H6 + CH3Cl → (AlCl3) → C6H5CH3 + HCl

Question 17

the reagents, conditions and catalysts needed for Friedel-Crafts acylation is

Answer 17

• an acyl chloride
• AlCl3
• anhydrous conditions

Question 18

the equation showing the acylation of benzene is

Answer 18

C6H6 + CH3COCl →(AlCl3)→ C6H5COCH3 + HCl