Topic 3.9 - Carboxylic Acids and Derivatives

What is a carboxylic acid?

Functional group?

-COOH (C=O and C-OH)

How do you name

carboxylic acids?

-oic acid

Are carboxylic acids soluble

in water? Why? What

influences their solubility

Yes. Acid group can form hydrogen bonds with

water molecules

What are the intermolecular

forces in carboxylic acids?

Hydrogen bonds in solid state - very strong.

What are esters (what are

they formed from)?

Functional group, general

formula?

Formed from carboxylic acids and alcohols.

RCOOR’ (C=O, C-O-C)

Write an equation for the

reaction of ethanoic acid

with propan-1-ol

CH 3 COOH + CH 3 CH 2 CH 2 OH → CH 3 COOCH 2 CH 2 CH 3 + H 2 O

How do you name esters?

Start with the group that has replaced the

hydrogen, then acid part e.g. propyl (from

alcohol) ethanoate (from carboxylic acid).

What characteristic physical

properties do esters have?

Volatile, pleasant fruity smells e.g. apple, pear

drops

What are some uses of

esters?

Flavourings, perfumes (both for longer chains),

solvents (short chains), plasticisers.

What are some common

natural esters?

Fats and oils

In what way is the

carboxylic acid group

polarised? (Diagram)

Write an equation for the

equilibrium formed by a

ethanoic acid in solution

CH 3

COOH (aq) ⇌ CH 3

COO - (aq) + H + (aq)

What happens to the

negative charge on the

ethanoate ion in terms of

electrons?

Electrons delocalise so the negative charge is

shared across the whole of the carboxylate group

How could you distinguish

carboxylic acids from other

-OH containing

compounds?

Add NaHCO 3 , acids will produce sodium

salt, water and carbon dioxide.

Write an equation for the

reaction of ethanoic acid

with NaOH

CH 3

COOH + NaOH → H 2

O + CH 3

COO -

Na +

Write an equation for the

reaction of ethanoic acid

with Na 2 CO 3 .

2CH 3 COOH + Na 2 CO 3 → 2CH 3 COO -

Na + + H 2 O + CO2

What catalyst is needed for

the formation of esters from

alcohols and carboxylic

acids?

Concentrated strong acid e.g. H 2 SO 4

What catalyst is needed for

the hydrolysis of esters?

Dilute strong acid e.g. H 2 SO 4

What is an alternative

method of hydrolysis?

Base hydrolysis

What are the advantages of

base hydrolysis?

Reaction goes to completion due to neutralisation

by base - more product in the mixture than acid

catalysed hydrolysis.

Which alcohol forms the

esters that make up animal

and vegetable oils?

Glycerol / propane-1,2,3-triol

What is the difference

between oil and fat?

Oils are liquid at room temperature, fats are

solids; fats are usually saturated, oils are not

What are the products of

hydrolysing fats and oils?

Propane-1,2,3-triol and sodium salts of the acids

that make up the ester (hydrolysed with NaOH)

What are the uses of these

products

(Propane-1,2,3-triol and

sodium salts)?

Soaps and cleaning products

What does the long

hydrocarbon chain of the

carboxylate ion do?

Mixes with grease

What does the COO - group

do?

Mixes with water

How does the carboxylate ion

with a long carbon chain

make a good cleaning agent?

Means that grease can be removed from

water

What is the systematic

name of glycerol?

propane-1,2,3-triol

What are some common

uses of glycerol?

Used in pharmaceutical and cosmetic preparations e.g. to

stop creams drying out

Solvent in many medicines, present in toothpaste

Solvent in food industry e.g. food colourings

Plasticising various materials like sheets and gaskets,

cellophane and paper

How do you make biodiesel

(general equation and

conditions)?

NaOH catalyst, 60 o

C

Lipids (fats/oils - esters) + 3CH 3

OH → 3 methyl

esters + glycerol

What does

transesterification mean?

Converting one type of ester to another

What kind of crops is

biodiesel made from?

Rapeseed oil or soybean oil

How is the reaction mixture

of biodiesel purified and

separated?

Settling tank or centrifuge; remove remainder

with water. Add acid to neutralise excess alkali

catalyst. Solid soap is formed - easy to remove

What is a problem with

producing biodiesel?

Crops that could be used to make food are being

used to make fuel - are the resources being best

used?

What are carboxylic acid

derivatives?

Molecules that have the acyl group as part of

their structure, formed from carboxylic acids

Name two acid derivatives

and give their functional

groups

Acyl chlorides: RCOCl

Acid anhydrides: RCOOCR / (RCO) 2 O

Draw the mechanism for the

acylation of a nucleophile by

an acid derivative.

Which factors determine

how readily the acylation of

a nucleophile by an acid

derivative occurs? (3)

Magnitude of the delta + charge on the carbonyl carbon,

which depends on the electronegativity of the atom/group

being substituted.

How easily the atom/group being substituted is lost

How good the nucleophile is (how readily it will donate

electrons)

What effect do the Cl and O

atoms in acyl chlorides/acid

anhydrides have on the

partial charge of the

carbonyl carbon?

Increase the partial + charge by attracting

electrons; this means that they react more readily

with nucleophiles

Are acyl chlorides or acid

anhydrides more reactive?

Acyl chlorides

What is the name of the

mechanism by which acyl

chlorides and acid anhydrides

acylate nucleophiles?

Addition-elimination

If the nucleophile is

ammonia for the acylation of

acyl chlorides or acid

anhydrides, what are the

products of the reaction?

An amide

Write an equation for the

reaction of ethanoyl chloride

and ammonia

CH 3 COCl + 2NH 3 → CH 3 CONH 2 +

NH 4 Cl

Draw the mechanism for the

reaction of ethanoyl chloride

and ammonia

If the nucleophile is a

primary amine, what are the

products of the acylation of

acyl chlorides or acid

anhydrides?

N-substituted amide

Write an equation for the

reaction of ethanoyl chloride

and methylamine

CH 3 COCl + CH 3 NH 2 → CH 3 CONHCH 3 + CH 3 NH 3 Cl

Draw the mechanism for the

reaction of ethanoyl chloride

and methylamine.

If the nucleophile is an

alcohol, what are the

products of the acylation of

acyl chlorides or acid

anhydrides?

An ester

Write an equation for the

reaction of ethanoyl chloride

and ethanol

CH 3 COCl + CH 3 CH 2 OH → CH 3 COOCH 2 CH 3 + HCl

Draw the mechanism for the

reaction of ethanoyl chloride

and ethanol

If the nucleophile is water,

what are the products of the

acylation of acyl chlorides or

acid anhydrides?

Carboxylic acid (hydrolyses ester

linkage)

What is the name of this

reaction (the acylation of

acyl chlorides/acid

anhydrides with water as a

nucleophile)?

hydrolysis

Write an equation for the

reaction of ethanoyl chloride

and water.

CH 3 COCl + H 2 O → CH 3 COOH + HCl

Draw the mechanism for the

reaction of ethanoyl chloride

and water.

What is a commercially

important acylation

reaction?

The manufacture of aspirin

What are the advantages of

using ethanoic anhydride as

an acylating agent over

ethanoyl chloride?

It is cheaper, less corrosive and does not react as readily with

water.

It is safer, as ethanoic acid is produced, rather than HCl,

which is corrosive.

What would you observe in

a melting point

determination if the sample

was not pure?

Sample melts over a large range (more than

3 o

C).

Sample’s melting point is below the accepted

value due to impurities disrupting structure

Why might the melting point

appear different to the true

value?

Temperature of the material in the machine might

be different to the temperature shown on the

thermometer - apparatus error.

When removing flue gases,

what are the issues?

Disposal of large amounts of CaSO 3 and CO 2 is

produced.

What conditions are needed

to form methyl esters from

an acid anhydride or acyl

chloride?

React with methanol and heat gently under reflux

When purifying by

recrystallisation, why is the

minimum volume of hot

solvent used?

So that a saturated solution is created, so that as

many crystals will fall out of solution as possible

when it is cooled

Why is the solution filtered

hot when purifying by

recrystallisation?

To remove insoluble impurities and ensure that

the crystals do not form in the filter paper

Why is the solution cooled

in an ice bath when

purifying by

recrystallisation?

To ensure that as many crystals as possible fall

out of solution - yield is higher

Why are the crystals

washed with cold water

when purifying by

recrystallisation?

To remove soluble impurities

How would you separate the

crystals from the reaction

mixture when purifying by

recrystallisation?

Filter under reduced pressure using a Buchner

funnel

Why might percentage yield

be below 100% (practical

reasons)?

Product is lost during filtration, drying and weighing - spills,

not all transferred from one piece of apparatus to the other

Product is left dissolved in the solution - some does not

crystallise. Some left on filter paper. Sample still wet