4.5- Carboxylic acids and their derivatives

What group do carboxylic acids contain?

COOH

What two functional groups is this comprised of?

Carbonyl (C=O)

Hydroxyl (OH)

What are the physical properties of carboxylic acids governed by?

Their ability to form hydrogen bonds

In a pure carboxylic acid, what can occur?

Hydrogen bonding between two molecules of acid to form a dimer, as the OH groups can hydrogen bond to one another

What does this result in?

Doubles the size of the molecule, so more Van der Waals forces between the dimers, so a higher boiling point

Why is ethanoic acid less volatile than butane?

Molecules of ethanoic acid can hydrogen bond to one another as they have OH group to form a dimer. The size of the dimer increases the VdW forces between dimers, so they have a higher boiling point.

As hydrogen bonds are stronger than VdW and butane only has VdW, carboxylic acid has higher boiling point.

What don't carboxylic acids do in the presence of water?

Form dimers

What form instead?

Hydrogen bonds and permanent dipole-dipole interactions between water molecules and individual molecules of acid

What happens to the solubility of larger acids?

Decreases with size

Why?

The longer hydrocarbon tails get between water molecules and break the hydrogen bonds. The hydrogen bonds are replaced with weaker VdW

Are carboxylic acids strong or weak acids and what does this mean?

weak so partially dissociate

How can they act as weak acids?

Due to the stability of the R-COO- anion

What does the ion have and what does this mean?

A delocalised system so it has a relatively high stability

Are they stronger or weaker acids than phenols?

Stronger

How can this be shown?

By their reaction with NaHCO3 to produce CO2- phenols are not strong enough acids to react

What do both carboxylic acids and phenols react with?

Strong alkalis

What is the order of acidity for water, carboxylic acids, alcohols and phenols?

Most- carboxylic acids, phenols, water/alcohols- least

What don't?

Alcohols and water

How can the acidity of carboxylic acids and phenols be altered?

By the presence of a substituent group- eg. substituting a H with a Cl, which increases its dissociation into ions

What are some typical reactions of carboxylic acids?

Acid + Metal -> Salt + Hydrogen

Acid + Base -> Salt + Water

Acid + Alkali -> Salt + Water

Acid + Carbonate -> Salt + Water + CO2

What type of reaction is acid + metal

Redox

2CH3COOH + Mg

(CH3COO-)2Mg2+ + H2

What type of reaction is acid + base

Neutralisation

Acid + metal hydroxide

ethanoic acid + NaOH

salt + water

sodium ethanoate + water

Acid + metal oxide

2ethanoic acid + CaO

salt + water

calcium ethanoate + water

What is a standard test for the carboxyl group?

Sodium hydrogencarbonate (fizzing)

Why?

Acid + carbonate

Acid + hydrogencarbonate

salt + water + CO2

2CH3COOH + Na2CO3

2CH3COO-Na+ + H2O + CO2

CH3COOH + NaHCO3

CH3COO-Na+ + H2O + CO2

How can carboxylic acids be formed?

Through the complete oxidation of primary alcohols heated under reflux with acidified potassium dichromate (orange to green)

What else could be used?

Acidified potassium manganate purple to colourless

Or?

Alkaline potassium manganate (purple to brown-black sludge of manganese oxide)

Describe the process of the reduction of carboxylic acids

As relatively stable, have to be reduced with LiAlH4 dissolved in ethoxyethane

Propanoic acid + 4[H] -> Propan-1-ol + water

How can an aromatic carboxylic acid be made?

When a primary alcohol or aldehyde attached to a benzene ring is oxidised using acidified potassium dichromate/manganate

What is another method?

Oxidise a methyl chain on a benzene ring with alkaline potassium manganate to form benzenecarboxylic acid

Propan-1-ol + acidified potassium dichromate under reflux?

propanoic acid + water

orange to green

2 methyl propan-1-ol with alkaline potassium manganate

2 methyl propanoic acid + water

purple to brown sludge

phenylethanol with acidified potassium manganate

phenylcarboxylic acid + H2O

orange to green

What is decarboxylation?

The removal of carbon dioxide from a molecule

What is used for this process and why?

As CO2 is an acidic oxide, it will react with a base.

The base used is 'soda lime' (Ca(OH)2 with NaOH)

What will the resulting product contain?

One less carbon

What is the equation for the decarboxylation of benzenecarboxylic acid with Ca(OH)2?

benzenecarboxylic acid + Ca(OH)2 -> benzene + CaCO3 + H2O

Decarboxylation of 3-methyl 3-phenyl propanoic acid with CaO?

benzene with an ethyl group and a methyl group on that?? CaCO3

When can decarboxylation also occur?

When a calcium salt of an acid is heated in the absence of soda lime (CH3CH2COO-)2Ca2+

What will be formed?

pentan-3-one and CaCO3

What functional group do esters have?

RCOOR'

The one bonded to the C=O is from the...

acid

General name for ester: methyl methanoate.

If you reacted propanol with ethanoic acid, what would the name be?

Propyl ethanoate

methyl ethanol with methanoic acid

methylethyl methanoate

How are acid chlorides formed?

By reacting carboxylic acid with sulfur dichloride oxide (SOCl2)

What does them being extremely reactive mean?

That due to the instability of methanoyl chloride, ethanoyl chloride is the simplest acid chloride

How do you name acid chlorides?

Remove the 'oic acid' part and replace it with 'oyl chloride'

eg

propanoic acid -> propanoyl chloride

What is the skeletal formula of propanoyl chloride?

How are acid anhydrides formed?

removal of water from two carboxylic acid molecules

How do you name them?

Remove the 'acid' and replace with 'anhydride'

eg. ethanoic acid-> ethanoic anhydride

What are the 3 ways of making esters?

Carboxylic acids + alcohol -> ester + water

acid anhydride + alcohol -> ester + carboxylic acid

acid chloride + alcohol/phenol -> ester + hydrogen chloride

What conditions are carboxylic acids and alcohols reacted under?

Heated under reflux with concentrated H2SO4 as a catalyst

What is this reaction know as?

Esterification

What is it an example of?

Condensation

Is it reversible?

Yes

ethanoic acid + methanol ->

Methyl ethanoate + H2O

What are the conditions that acid anhydrides are reacted with alcohols and phenols under?

Gently heated

What are the advantages?

Non-reversible, high yield, occurs readily

Acid anhydride + alcohol ->

ester + carboxylic acid

methanol + ethanoic anhydride ->

methyl ethanoate + ethanoic acid

propanoic anhydride + ethanol ->

ethyl propanoate + propanoic acid

What are the conditions for acid chloride + alcohol/phenol and what is formed?

ester + hydrogen chloride

react readily without need for catalyst

ethanoyl chloride + butan-1-ol ->

butyl ethanoate + HCl

propanoyl chloride + phenol ->

phenyl propanoate + HCl (g)

What are the two types of hydrolysis of esters?

Acid and alkaline hydrolysis

What does acid hydrolysis entail?

Refluxing an ester with an acid

What is the equation?

Ester + H2O -> carboxylic acid + alcohol

Why is it not ideal?

Not got a good yield as reversible

Alkaline?

Ester + NaOH -> Carboxylate salt + alcohol

What is it also known as?

Saponification

What are the conditions?

Heated under reflux with aqueous NaOH

Why is it good?

Irreversible so high yield

What can be done after cooling?

Carboxylate ion can be acidified to form a carboxylic acid

What are the properties and uses of esters?

Sweet smelling

Used in food flavourings and perfume

Methyl propanoate + water ->

methanol + propanoic acid

propyl methanoate + water ->

propanol + methanoic acid

methyl propanoate + NaOH ->

sodium propanoate + methanol

propyl methanoate + NaOH->

sodium methanoate + propan-1-ol

How do you prepare acid chlorides?

React a carboxylic acid with SOCl2

Where must this reaction be carried out?

In a fume cupboard

Why?

As harmful gases SO2 and HCl are evolved

What is the reaction between propanoic acid and sulfur dichloride oxide?

Propanoyl chloride + sulfur dioxide + hydrogen chloride

What reagents can be used instead?

PCl3 and PCl5

What are the equations for these reactions with propanoic acid?

3CH3COOH + PCl3 -> 3CH3COCl + H3PO3

CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl

What are the 3 reactions of acid chlorides?

1. Reaction of acid chlorides to form esters

2. Reaction of acid chlorides with water to form carboxylic acids

3. Reaction of acid chlorides with ammonia and amines to form amides

Are acid chlorides very reactive?

Yes

What do acid chlorides react with?

Nucleophiles, substituting the chlorine through the loss of a chloride ion whilst retaining the carbonyl bond

What can acid chlorides form esters with and what will they form?

Alcohols/phenols and will form

What does the reaction between ethanoyl chloride and water form?

Ethanoyl chloride + water -> ethanoic acid + hydrogen chloride

Why are acid chlorides not described as soluble in water?

Because they react so vigourously

Why can acid chlorides react with ammonia and amines?

Because they are both good nucleophiles as they have a lone pair of electrons which can readily be donated

Ammonia reacts with acid chlorides to form what?

A primary amide

Ethanoyl chloride + ammonia ->

Ethanamide + NH4Cl