Chemistry - 3.3.9: Carboxylic acid and derivatives

Carboxylic acid functional group?

-COOH

When numbering side chains/substituents on a carboxylic acid, where do you start numbering from?

The carbon of the carboxylic acid (the one with the carboxyl group)

Suffix for carboxylic acids?

-oic acid

What do you call a benzene ring with a -COOH group attached to it?

Benzenecarboxylic acid/ benzoic acid

2 physical properties of carboxylic acids

1. High MP/BP - higher than alkanes (-COOH group can form hydrogen bonds with other acids)
2. Completely soluble in water (-COOH group can form hydrogen bonds with water molecules)

General formula of esters

RCOOR'

R = hydrogen atom / alkyl group / aryl group
R’ = alkyl group / aryl group

How do you name esters?

Alcohol carboxylate e.g. methyl ethanoate (produced from methanol and ethanoic acid)

2 properties of esters

Volatile and sweet smelling (pleasant and fruity scent)

4 common uses of esters

Perfumes, food flavourings, solvents and plasticisers

What are fats and oils?

Esters of the alcohol propane-1,2,3-triol with longer carbon chains

What happens when the carboxylic acid group loses a proton?

- Proton is lost from -OH group, forming a negatively-charged carboxylate ion
- The negative charge is shared over the whole carboxylate group (between the two oxygens), causing the ion to be more stable

What type of acids are carboxylic acids?

Weak acids

Name of salts derived from carboxylic acids?

Carboxylates

What can carboxylic acids do that not all weak acids can?

Liberate CO2 from carbonates

What catalyst is needed for carboxylic acids to react with alcohols to form esters?

A strong acid catalyst e.g. concentrated sulfuric acid

Reaction to form esters

Carboxylic acid + alcohol ⇌ ester + water

2 reactions for the hydrolysis of esters

1. With water and an acid catalyst
2. With warm, dilute, aqueous NaOH

What does the hydrolysis of an ester catalysed by an acid produce?

A carboxylic acid and an alcohol

What does the hydrolysis of an ester catalysed by a base produce?

A carboxylate salt and an alcohol

Formula for the hydrolysis of an ester with an acid catalyst

ester + water ⇌ carboxylic acid + alcohol

Formula for base hydrolysis of an ester

ester + base -> base carboxylate (a carboxylate salt) + alcohol

What is the difference between fats and oils?

Oils are liquid at room temperature, while fats are solid

Non-systematic name for propane-1,2,3-triol?

Glycerol

What are fats and oils made of?

3 carboxylic acids (fatty acids) and propane-1,2,3-triol (glycerol)

What are fats and oils called collectively?

Triglycerides

What is produced when triglycerides are hydrolysed by boiling with sodium hydroxide?

Soap (the sodium salts) and glycerol

Saponification

The reaction where triglycerides are hydrolysed by boiling with NaOH, producing soaps

What conditions are needed for saponification?

Boiling + NaOH

Soap

Salts of long-chain carboxylic acids

3 uses of glycerol

1. As a solvent
2. As a plasticiser
3. In pharmaceutical and cosmetic preparations (e.g. to prevent creams from drying out)

Biodiesel

A renewable fuel that is a mixture of methyl esters of long-chain carboxylic acids

What type of esters are biodiesels made of?

Methyl esters

How are biodiesels produced?

Vegetable oils are reacted with methanol with a strong alkali catalyst

2 important acid derivatives

Acyl chlorides and acid anhydrides

General formula for acid chloride

RCOCl

General formula for acid anhydride

RCOOCOR'

What is special about the carbonyl group of an acid derivative?

It is polarised, so can be attacked by nucleophiles

Acylation

A reaction where an acyl group is added to a compound

3 factors that affect the rate of the nucleophilic addition-elimination reactions

1. The magnitude of the δ+ charge on the carbon of C=O (depends on electron-releasing/attracting power of Z)
2. How easily the leaving group (Z) is lost
3. How good the nucleophile is

Acyl group formula

R-C=O and C-Z

R = hydrocarbon chain. Z = the leaving group (e.g. Cl)

4 nucleophiles that can react with acyl chlorides / acid anhydrides (in order of reactivity, from most to least)

Primary amines, ammonia, alcohol, water

Product of nucleophilic addition-elimination reaction with ammonia

An amide + HCl

Product of nucleophilic addition-elimination reaction with a primary amine

An N-substituted amide + HCl

Amide structure

R-C=O and C-NH2

N-substituted amide structure

R-C=O and C-N-R' and N-H

R = hydrogen atom / alkyl group / aryl group
R’ = alkyl group / aryl group

Product of nucleophilic addition-elimination reaction with water

A carboxylic acid + HCl

Product of nucleophilic addition-elimination reaction with an alcohol

An ester + HCl

Mechanism for the nucleophilic addition-elimination reactions

1. Electrons transfer from C=O bond to Oδ-, forming O-. From nucleophile, electrons transfer from nucleophile to Cδ+ (carbon on C=O) (main nucleophile atom positively charged)
2. Electrons from O- to C to reform C=O. Electrons from C-Cl bond to Cl, forming Cl- ion
3. Electrons from H bond with nucleophile to the main nucleophile atom, forming H+ ion

What is special about the reaction of ethanoyl chloride and ammonia?

The H+ ion lost then reacts with a second molecule of ammonia to form NH4+ (and so NH4Cl)

4 reasons why ethanoic anhydride is used instead of ethanoyl chloride as an acylating agent (e.g. to produce aspirin)

1. It is less corrosive
2. It is cheaper
3. It does not react with water as readily
4. It is safer as the by-product of the reaction is ethanoic acid instead of hydrogen chloride

What is the difference between nucleophilic addition-elimination reactions with acyl chlorides and acid anhydrides?

Acyl chlorides produce HCl as a by-product, while acid anhydrides produce carboxylic acids as a by-product

One use of nucleophilic addition-elimination reactions

To produce aspirin

How do you produce aspirin? (8)

1. Add salicylic acid to weighing boat and weigh its mass with a balance

2. Tip the weighing boat into a 100cm³ conical flask

3. Reweigh the empty weighing boat and record the mass to calculate the actual mass of salicylic acid added

4. Add ethanoic anhydride to the conical flask and stir

5. Add 5 drops of concentrated phosphoric acid

6. Warm the flask for 20 minutes

7. Add ice-cold water to the reaction mixture and place the flask in an ice bath

8. Filter off the crude aspirin from the mixture and leave it to dry

2 differences in melting point between pure aspirin and crude aspirin

1. Lower melting point

2. Melting point over a range of values

Difference in physical appearance between pure aspirin vs crude aspirin

Pure product has larger crystals / needle-like crystals / lighter in colour crystals

How can you test if an ester was produced in a reaction? (2)

There is a sweet-smelling liquid if liquid ester / misty/steamy fumes if gaseous ester

Conditions for base hydrolysis

Warm, dilute, aqueous NaOH

What are drying agents + give 2 examples

Compounds that readily hydrate in the presence of water so can be used to remove traces of water from an organic product - usually inorganic salts e.g. CaSO4, MgSO4

When producing crystals, why should the minimum quantity of hot water be used?

To ensure the hot solution would be saturated / that crystals would form on cooling

When producing crystals, why should the flask be left to cool before the crystals are filtered off?

The yield will be lower if warm (more soluble if warm)

When producing crystals, why should the crystals be compressed in the funnel?

So air passes through the sample, not just around it

When producing crystals, why should a little cold water be poured through the crystals?

To wash away soluble impurities

When producing crystals, why might the melting point be slightly lower than the data book value?

Water is present

How can you purify an organic solid? (5)

1. Dissolve the product in a minimum volume of hot solvent

2. Filter to remove insoluble impurities

3. Cool to recrystallise

4. Filter under reduced pressure with a Buchner funnel

5. Wash with cold solvent and dry