Alcohols

Question 1

alcohol to alkene : reagents , conditions and reaction type

Answer 1

Reagents : concentrated H3PO4 (you can also use H2SO4 but spec says H3PO4)
conditions : heat

elimination reaction (or dehydration in this case - as you’re removing OH)

+ forms a molecule of water

Question 2

Alcohol to chloroalkanes : reagents, conditions and reaction type

Answer 2

reagents : PCl5
conditions: room temp , completely alcoholic

reaction type : substitution

Question 3

Give the equation for turning an alcohol into a chlorolalkane

Answer 3

R-OH + PCl5(l) —> R-Cl + POCl3 + HCl(g)

Question 4

Why is reacting alcohols with PCl5 Seen as a test for alcohols?

Answer 4

• misty white fumes of HCl gas are produced, confirming the presence of the -OH group

Question 5

Alcohol to bromoalkane : reagents, conditions and reaction type

Answer 5

reagents : KBr in 50% conc. H2SO4
conditions : warm under reflux( distill off product)
Reaction type : substitution

Question 6

Give the two steps in turning an alcohol into a bromoalkane

Answer 6

1. KBr reacts with H2SO4 to form HBr
   2KBr + H2SO4 —> KHSO4 + HBr
2. HBr reacts with R-OH to form R-Br
   R-OH + HBr —> R-OH + H2O

Question 7

Alcohol to iodoalkane : reagents, conditions and reaction type

Answer 7

Reagents : Red phosphorus, iodine
conditions : heat under reflux (then distill off product)
Reaction type : substitution

Question 8

Give the two steps in turning an alcohol into an iodoalkane

Answer 8

1. Red phosphorus reacts with iodine to form PI3
   2P + 3I2 —> 2PI3
2. Phosphorous (III) iodide reacts with alcohol to form iodoalkane
   3R-OH + PI3 —> 3 R-I + H3PO3 (phosphorous acid )

Question 9

Which oxidising
agent is used to oxidise alcohols?

Answer 9

[O] = acidified K2Cr2O7 (potassium dichromate) , acidified with dilute H2SO4

Question 10

What affects how many times an alcohol can be reduced?

Answer 10

The amount of Hydrogens bonded to the carbon bonded to the OH group ( as these are removed during oxidation)

Question 11

Which alcohols can be oxidised, and how many times can they be oxidised

Answer 11

Primary alcohols - twice

Secondary alcohols - once

Tertiary alcohols - cannot be oxidised as the carbon bonded to the OH group is not bonded to any hydrogen aroma

Question 12

How do you produce a ketone from an alcohol. Reagents and conditions AND state which alcohol it comes from

Answer 12

reagents : SECONDARY alcohol, acidified potassium dichromate
conditions : heat , reflux

Question 13

How do you produce an aldehyde from an alcohol : reagents and conditions

Answer 13

Reagents : PRIMARY alcohol, acidified K2Cr2O7
conditions : heat then distill out aldehyde
(If this is not done under distillation it will be oxidised to a COOH)

aldehydes have lower bps than carboxylic acids and alcohols

Question 14

How do you produce a carboxylic acid from an alcohol? Reagents and conditions

Answer 14

Reagents : PRIMARY alcohol, acidified K2Cr2O7 (in dilute H2SO4)
—> actually need 2[O] : alcohol to aldehyde aldehyde to COOH

Conditions : heat under reflux

Question 15

What is the colour change when K2Cr2O7 oxidises an alcohol

Answer 15

Orange to green

Question 16

Give the ionic equation for the reduction of Cr2O7(2-) in K2Cr2O7 (it acts as an oxidised agent, so it’s reduced)

Answer 16

Cr2O7(2-) + 14H+ + 6e- —> 2Cr3+ + 7H2O