Alcohols ✅

define the term functional group

atom or group of atoms that determine the chemical properties of a compound

what functional group do alcohols contain

-OH

what is the general formula for alcohols

C_nH_2n+1OH

give 3 properties of alcohols

1. soluble in water

2. neutral pH

3. toxic

what is the molecular formula of ethanol

C₂H₆O

naming alcohols:

suffix: -ol

prefix: hydroxy-

show position of -OH

e.g. Butan-2-ol

shape of alcohols:

• what is the bond angle in the C-O-H bond in an alcohol

• why?

• 104.5

• oxygen atom has 2 bonding pairs and 2 lone pairs

• two lone pairs repel more than electron pairs

Classification of alcohols:

1. primary alcohol

2. secondary alcohol

3. tertiary alcohol

1. -OH group attached to a C with at least 2 H atoms on it and 1 alkyl group

2. -OH group attached to a C with only 1 H atom on it and 2 alkyl groups

3. -OH group attached to a C with 0 H atoms on it and 3 alkyl groups

which primary alcohol will have 3 Hs on the carbon bearing the OH?

methanol

use formula C₃H₈O to draw a primary alcohol

CH3–CH2–CH2–OH

use formula C₃H₈O to draw a secondary alcohol

CH₃-CH(OH)-CH₃

use formula C₅H₁₂O to draw a tertiary alcohol

CH₃C(CH₃)(OH)CH₂CH₃

Properties of alcohols:

explain why alcohols have a relatively high mp and bp

• due to presence of strong hydrogen bonds between alcohol molecules

Summary of oxidation of alcohols:

• Primary alcohols can be oxidised to form aldehydes, which can undergo further oxidation to form carboxylic acids

• Secondary alcohols can be oxidised to form ketones only

• Tertiary alcohols do not undergo oxidation

• Common oxidising agents for alcohols include acidified potassium dichromate(VI), K₂Cr₂O₇ and acidified potassium manganate(VII), KMnO₄

Oxidation of alcohols: PRIMARY (heating under distillation)

1. what is the oxidising agent used to oxidise primary alcohols

2. what are primary alcohols oxidised to when using limited oxidising agent?

3. give the equation to show this reaction with ethanol

4. what type of conditions is this mixture heated under in this reaction

5. why is this important

6. what is the colour change for this reaction and why

1. acidified potassium dichromate (K₂Cr₂O₇)

2. aldehydes

3. CH₃CH₂OH + [O] → CH₃CHO + H₂O

4. distillation

5. aldehyde has a lower boiling point than alcohol → it can be distilled off as soon as it forms otherwise further heating under reflux with excess oxidising agent will oxidise it to a carboxylic acid

6. orange → green, dichromate is being reduced to chromium (III) and gains electrons

Oxidation of alcohols: PRIMARY (heating under reflux)

7. what happens if the oxidising agent is used in excess

8. what is formed?

9. what type of conditions is this mixture heated under for this to occur?

10. reagents?

11. give the equation to show the oxidation from ethanal to ethanoic acid

12. give the equation to the show oxidation from ethanol to ethanoic acid

7. further oxidation occurs

8. carboxylic acid

9. heat under reflux (so that any aldehyde initially made goes back into the flask to be further oxidised)

10. reagents?

11. CH₃CHO + [O] → CH₃COOH

12. CH₃CH₂OH + 2[O] → CH₃COOH + H₂O

DIAGRAM- Oxidation of ethanol by acidified potassium dichromate(VI) to form an aldehyde by distillation

Oxidation of alcohols: SECONDARY (heating under reflux)

1. what product is formed when secondary alcohols are oxidised

2. what is the oxidising agent used

3. what condition is the mixture heated under

4. can further oxidation of secondary alcohols occur

5. give the equation to show the the oxidation of propan-2-ol to propanone

1. ketone

2. acidified potassium dichromate

3. under reflux

4. no- ketones can’t be oxidised as there is no H attached to C with OH attached

5. CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ +H₂O

DIAGRAM- Further oxidation of the aldehyde via reflux can be done to produce a carboxylic acid

when heating under reflux, why is it critical that the top of the condenser is never sealed

to avoid pressure buildups and explosions

what would the observation be when acidified potassium dichromate is added to a tertiary alcohol

no colour change

• tertiary alcohols can’t be oxidised

give 4 uses of ethanol

1. alcoholic drinks

2. fuel

3. antiseptics

4. solvent

Fermentation

1. give the word equation for this reaction

2. give the chemical equation for this reaction

3. name the catalyst for this reaction

4. name the conditions for this reaction

5. why can’t temp be too low

6. why can’t temp be too high

1. glucose → ethanol + carbon dioxide

2. C₆H₁₂O₆ → 2C₂H₅OH _(aq) + 2CO_{2 (g)}

3. yeast

4. anaerobic, temp 30

5. ROR is too slow

6. enzymes in yeast are denatured

why does a fermentation reaction to produce ethanol require anaerobic conditions

needs no oxygen- if oxygen were present, ethanol would be converted to ethanoic acid

name 1 problem with fermentation

as ethanol is produced, concentration of ethanol in mixture increases

15% conc of ethanol will kill yeast

name 2 methods that produce ethanol

1. fermentation

2. hydration of ethene

hydration of ethene

1. give the word equation for this reaction

2. give the chemical equation for this reaction

3. name the catalyst for this reaction

4. name the conditions for this reaction

5. type of reaction

1. ethene + steam → ethanol

2. C₂H_{4 (g)} + H₂O _(g) → C₂H₅OH _(g)

3. conc phosphoric acid H₃PO₄

4. pressure- 60-70 atmospheres, temperature- 300

5. electrophilic addition

Comparison of Methods of ethanol production

Fermentation vs hydration of ethene

1. renewable vs non renewable

2. type of process

3. rate of reaction

4. quality of product

5. reaction conditions

1. renewable vs non renewable

2. batch reaction = inefficient vs continuous reaction = efficient

3. slow vs fast

4. impure ethanol- purify using fractional distillation = expensive vs purer product

5. low temp + pressure = lower cost vs higher temp + pressure = lots of energy = high cost

define the term dehydration

removal of H₂O from a molecule

what do alcohols form when they are dehydrated

alkenes

dehydration of an alcohol

1. how are alcohols dehydrated

2. name 2 good dehydrating agents / catalysts for this reaction

3. name the conditions for reaction

4. what is made

5. what structure does the alcohol need in order to be dehydrated

1. Alcohol vapour passed over a hot aluminium oxide (Al₂O₃) powder (or pieces of porous pot)

2. excess, hot conc H₂SO₄ or conc H₃PO₄

3. heat under reflux

4. alkene

5. contain an H atom on the C atom adjacent to the C atom with OH group

draw the mechanism for the dehydration of propan-2-ol and name the product formed

product = propene

(for stage 3 add +H₂O when drawing mechanism)

(for stage 4 add H⁺ when drawing mechanism)

what functional group do aldehydes and ketones both have in common

C=O (carbonyl group)

in aldehydes, where is the carbonyl group in the hydrocarbon chain

at the end

in ketones, where is the carbonyl group in the hydrocarbon chain

in the body of the chain

draw propanal vs propanone

okay

what is a primary alcohol

C with OH attached to it is only attached to 1 other carbon i.e. OH group on end carbon

what is a secondary alcohol

C with OH attached to it is attached to 2 other carbon

what is a tertiary alcohol

C with OH attached to it is attached to 3 other carbon

1. draw out the displayed formula of dimethylpropanol

2. why can’t it be dehydrated

1. okay

2. no H attached to C adjacent to C with OH attached