Oxidation Reactions of Alcohols

Question 1

what does oxidation mean in terms of these reactions

Answer 1

the loss of hydrogen from an alcohol molecule

Question 2

what does oxidation affect in these reaction

Answer 2

one carbon atom

Question 3

when an alcohol is oxidised, what atoms are removed from it

Answer 3

• the hydrogen atom from the OH group

- and the hydrogen atom bonded to the carbon atom with the OH group

Question 4

if a hydrogen from the OH group and a hydrogen from the carbon atom with the OH group are removed, what new bond is formed

Answer 4

a double bond between the carbon atom and the oxygen atom

Question 5

what is an organic product that contains a C=O group

Answer 5

carbonyl group

Question 6

what kind of alcohols can be oxidised in this way in order to become a carbonyl group containing molecule and why

Answer 6

• primary and secondary alcohols can be oxidised this way
• this is because primary and secondary ones are only bonded to 1 and 2 other carbon atoms, meaning both of them are bonded to a hydrogen and OH group
• this means that the oxidation can take place

Question 7

what kind of alcohols cant be oxidised in this way in order to have a carbonyl group and why

Answer 7

• tertiary alcohols
• because the carbon atom with the OH group would be bonded to three other carbon atoms
• meaning it isnt bonded with a singular hydrogen in order for the oxidation to take place

Question 8

what is produced when a secondary alcohol is oxidised

Answer 8

a homologous series called ketones

Question 9

what is the simplified formula for a ketone and what does this refer to

Answer 9

• RCOR
• the carbon atoms the main carbon tom is bonded to on the left and right is R
• while it has a double bond with an oxygen atom in the middle

Question 10

what is the first organic product that is produced when a primary alcohol is oxidised

Answer 10

a homologous series called aldehydes

Question 11

what is the simplified formula for an aldehyde

Answer 11

RCHO

Question 12

what is the product for the oxidation of aldehydes

Answer 12

a homologous series called carboxylic acids

Question 13

why does this reaction even occur

Answer 13

• because although aldehydes are the product of the oxidation of primary alcohols
• they are more easily oxidised
• so they can simply oxidise further

Question 14

what happens during the oxidation of aldehydes

Answer 14

• they gain an oxygen atom but dont lose a hydrogen atom

- the gained oxygen atom goes between the C and H of the CHO group (from RCHO)

Question 15

if the O goes in between the CHO group, what is the simplified formula of carboxylic acids

Answer 15

RCOOH

Question 16

what therefore are the products of the oxidation of primary and secondary alcohols

Answer 16

• primary alcohol = aldehyde = carboxylic acid

- secondary alcohol = ketone

Question 17

what is the usual reagent for these oxidation reactions

Answer 17

• a mixture of potassium dichromate (V)

- and sulfuric acid

Question 18

how would you write the mixture of potassium dichromate and sulfuric acid when writing out equations and why

Answer 18

• you would just write [O]
• which represents an oxygen atom supplied by the oxidising agent
• and you write this because writing the equations with the reagents in would be too complicated

Question 19

what colour change should be seen when the oxidising agent is used

Answer 19

orange to green

Question 20

what would be the name and structural equation for the reaction between propan-1-ol and the oxidising agent

Answer 20

• CH3CH2CH2OH + [O] = CH3CH2CHO + H2O

- called propanal

Question 21

what would be the name and structural equation for the oxidation of propanal

Answer 21

• propanoic acid

- CH3CH2CHO + [O] = CH3CH2COOH

Question 22

what would be the name and structural equation for the reaction between propan-2-ol and the oxidising agent

Answer 22

• propanone

- CH3CH(OH)CH3 + [O] = CH3COCH3 + H2O

Question 23

what two techniques are used when trying to collect ketones, aldehydes or carboxylic acids

Answer 23

• heating under reflux

- distillation with addition

Question 24

when is heating under a reflux used

Answer 24

• when the oxidation is intended to be complete

- in order to obtain a ketone or carboxylic acid

Question 25

how does heating under a reflux work

Answer 25

• the reaction mixture is heated until everything reacts
• the products of the oxidation stay in the mixture because if they boil off they condense in the vertical condenser
• then return back down to the heating flask

Question 26

when is distillation with addition used

Answer 26

• when the oxidation is intended to be incomplete

- in order to obtain an aldehyde, not a carboxylic acid

Question 27

how is distillation with addition done

Answer 27

• only the oxidising agent is heated
• while the alcohol is slowly added to the oxidising agent
• when the aldehyde is formed it immediately distills off and is collected in the receiver
• as it has a much lower boiling point than the alcohol used to make it

Question 28

what do the methods of heating under a reflex and distillation with addition involve

Answer 28

• the heating of a reaction mixture with a condenser fitted vertically
• the heating of a reaction mixture, but adding another liquid and distilling off the products as it forms