6E: Alcohols

Question 1

What is the general formula of alcohols?

Answer 1

C_nH_2n+1OH

Question 2

How can halogenoalkanes be made from alcohols?

Answer 2

Substitution reactions with different reactions depending on the halogenoalkane wanted

Question 3

How are chloroalkanes formed from alcohols?

Answer 3

React with phosphorus pentachloride: ROH + PCl₅ → RCl + HCl + POCl₃

React with hydrochloric acid: ROH + HCl -> RCl + H₂O

Question 4

What are the relative rates of reactions with hydrochloric acid between the reactions of tertiary to primary alcohols?

Answer 4

Fastest when tertiary alcohols are reacted with HCl

Slowest when primary alcohols are reacted with HCl

Question 5

How are bromoalkanes formed from alcohols?

Answer 5

Alcohols reacted with a source of bromide ions (e.g. KBr) in a substitution reaction

This requires an acid catalyst such as 50% conc H₂SO₄

Question 6

How are iodoalkanes formed from alcohols?

Answer 6

Reacts with phosphorus triiodide (PI₃)

PI₃ usually made in situ

3ROH + PI₃ → 3RI + H₃PO₃

Question 7

What is the elimination reaction to form alkenes from alcohols?

Answer 7

Alcohol mixed with acid catalyst (conc phosphoric acid) and then heated

C₂H₅-OH → C₂H₄ + H₂O

Water is made from OH group and H from adjacent carbon to that which the OH was bonded to (two possible alkene products

Question 8

What are the products from the elimination of alcohols to alkenes?

Answer 8

Two different alkene products at hydrogen can be taken from the carbon on either side

However there can be E/Z forms

Question 9

How are alcohols most easily oxidised?

Answer 9

Burn them to form carbon dioxide and water

Combustion reaction

Question 10

What is the oxdising agent used on alcohols?

Answer 10

Acidified dichromate ions H⁺/Cr₂O₇^2-
E.g. from K₂Cr₂O₇/H₂SO₄

Question 11

What are the terms primary, secondary and tertiary someimtes replaced with?

Answer 11

Primary - 1°

Secondary - 2°

Tertiary - 3°

Question 12

What can 1º alcohols be oxidised to?

Answer 12

Partially oxidised to aldehydes

Can be fully oxidised to carboxylic acids

Question 13

What can 2º alcohols be oxidised to?

Answer 13

Ketones

Question 14

What can 3º alcohols be oxidised to?

Answer 14

They will not be oxidised by potassium dichromate

Question 15

What do aldehydes and ketones contain?

Answer 15

Contain the funcitonal group C=O which is a carbonyl

Question 16

What is the general formula of ketones and aldehydes?

Answer 16

C_nH_2nO

Question 17

What is the functional group found in aldehydes?

Answer 17

R-C(O)-R

C=O is a double bond

Question 18

What is the functional found in ketones?

Answer 18

R-C(O)-R

C=O present

Question 19

How are aldehydes produced from primary alcohols?

Answer 19

Gently heating with potassium dichromate and sulphuric acids

Distil the product as soon as it is formed

Use excess alcohol

Question 20

How are carboxylic acids produced from primary alcohols?

Answer 20

Alcohol is oxidised under reflux with excess potassium dichromate

Question 21

How are ketones produced from secondary alcohols?

Answer 21

2º alcohol oxidised under reflux with excess oxidising agents as ketones can’t easily be further oxidised

Question 22

What is the colour change when potassium dichromate is reduced?

Answer 22

Orange -> green solution

Question 23

What happens when potassium dichromate is added to a ketone?

Answer 23

No oxidation so no colour change