Substitution Reactions For Alkanes (LEC)

Question 1

What is Sulfonation?

Answer 1

This is a reaction of organic compounds/alkanes with sulfuric acid (SO3) and H2O (water)

RH+ HOSO3H -> RSO3H + HOH

Question 2

Alkanes react with SO3 to form:

Answer 2

Alkyl sulfonic acid or RSO3H

Question 3

How is Sulfonation a Substitution Reaction?

Answer 3

RH+ HOSO3H -> RSO3H + HOH

SO3 is substituted in between alkane and its last H atom—therefore, the last H atom is joined to SO3 instead

Question 4

What is Vapor Phase Nitration (Temp 400 C)?

Answer 4

It is the reaction between an alkane and hydroxized nitric acid (HONO2)

RH + HONO2 -> RNO2 + H2O

Question 5

How is Vapor Phase Nitration a Substitution Reaction?

Answer 5

An H atom in the alkane and NO2 switch places

RH + HONO2 -> RNO2 + H2O

Question 6

What is formed in Vapor Phase Nitration?

Answer 6

Nitroalkane (RNO2) and Water (H2O)

Question 7

What is Halogenation?

Answer 7

Substitution of Halogens for Hydrogen

RH + X2 -> [heat or uv light] RX + HX

or RHX + X2 -> [heat or uv light] RX2 + HX

Question 8

Halogenation is initiated by catalysts:

Answer 8

Heat or UV light

Question 9

How is substitution present in Halogenation?

Answer 9

RH + X2 -> [heat or uv light] RX + HX

• One halogen atom switches with an H atom from the alkane

Question 10

Halogens differ in their ability to undergo Halogenation.

What is the order of halogen reactivity and what does this entail?

Answer 10

F2 > Cl2 > Br2 > I2

• Fluorine is too reactive and Iodine is too unreactive
• Only Chlorine and Bromine are capable of being used

Question 11

What does Halogenation yield?

Answer 11

Alkyl halides (RX)

Question 12

In Halogenation, the reaction of methane and chlorine will give a mixture of:

Answer 12

Mono- di- tri- and tetra- substituted chloromethanes

Question 13

However, if an excess of Cl is used, the reaction can be controlled to give all _____

Answer 13

Tetrachloromethane

Question 14

However, if a large ratio of CH4 to Cl is used, the product will be predominantly _____

Answer 14

Chloromethane

Question 15

What is Pyrolysis or Cracking?

Answer 15

It is the breaking down of alkanes into smaller molecules by heating them in high temperatures but without air.

Question 16

In what temperature is Pyrolysis/Cracking achieved?

Answer 16

400-700 C

Question 17

What happens if air is present during Pyrolysis/Cracking?

Answer 17

The mixture will catch fire; combustion occurs

Question 18

What are alkanes’ relationship with addition reactions?

Answer 18

Because alkanes are saturated, they do not undergo addition reactions