carboxylic acids and derivatives

How are carboxylic acids produced?

oxidation of primary alcohols or aldehydes

What are the two types of carboxylic acids?

Aliphatic and aromatics

What is the characteristic functional group of a carboxylic acid?

-COOH

What is the strongest intermolecular force between water and a carboxylic acid?How does a

Hydrogen bonding

How do carboxylic acids form hydrogen bonds between each other and what is it called?

They form dimers, two hydrogen bonds between each molecue

Are carboxylic acids soluble in water?

Yes, up to 6 carbons per water molecule

Why does the solubility of carboxylic acids decrease as the chain length increases?

The non-polar chain increases

What type of acid is carboxylic acid?

weak acid

They react as acids to form salts called...

Carboxylates

Why do carboxylic acids have higher boiling points than similar chain alcohols and aldehydes?

Carboxylic acids have two hydrogen bonds between the molecules (dimer) And alcohols form one hydrogen bond between molecules Aldehydes have permanent dipole-dipole forces between molecules which is weaker than hydrogen bonding so carboxylic acids require the most energy to overcome the IMFs

What two distinct functional groups are found in a carboxylic acid?

Carbonyl and hydroxyl group

How do carboxylic acids react with carbonates?

The carboxylate ion displaces the CO3 ion making a salt + CO2 + H2O

How does a salt and carboxylic acid react?

Metal + acid --> salt + 1/2H2

How does alkali and carboxylic acid react?

Alkali + acid --> salt + water

Metal carbonate + acid gives...

salt + carbon dioxide + water

Metal hydrogen carbonate + acid gives...

salt + carbon dioxide + water

Why may a substance NOT show hydrogen bonding despite it having H with F,O or N atoms in it?

The F,O or N is not directly bonded to the H

How does the carboxylate ion become delocalised?

The 2p orbital electrons in the pi bond of the C=O and one of the lone pairs of electrons on the oxygen atom will delocalise

Why does this delocalisation lead to stability?

The negative charge on the carboxylate ion is shared over the whole carboxylate group which leads to more stability of the carboxylate ion The two C-O bonds are equal in length now

What are electron withdrawing groups?

Atoms/ groups of atoms which draw electron density towards itself

What are examples of this?

Cl F -COOH

How do electron withdrawing groups affect the carboxylate ion?

EWGs stabilise the carboxylate ion so the ion is more likely to form and the O-H bond is weaker therefore it is a stronger acid

What are electron donating groups?

Atoms/ groups of atoms which donate electron density away from itself

For example...

Alkyl groups

What effect do EDGs have on the carboxylate ion?

EDG destabilises the carboxylate ion so the ion is less likely to form and the O-H bond is stronger therefore weaker acid as the H+ is less easily dissociated

Why are the acid strengths of ethanoic acid and ethanedioic acid different?

In ethanoic acid R is -CH3 whereas in ethanedioic acid R is -COOH The COOH group contains two very electronegative oxygen atoms therefore has a negative inductive effect CH3 is an alkyl group which has a positive inductive effect The O-H bond in ethanedioic acid is more polarised so the H becomes more delta positive Ethanedioic acid dissociates more into H+ ions so it is a stronger acid than ethanoic acid

How can benzoic acid be formed?

Refluxing methyl benzene with alkaline KMnO4

What is the equation for producing benzoic acid from methyl benzene?

C6H5CH3 + [O] --> C6H5COOH

What is benzoic acid also called and why?

glacial acetic acid because when it freezes it forms needle shaped crystals

How does benzoic acid look like?

A white crystalline solid

What is an esterification reaction?

when an alcohol and carboxylic acid react to form an ester and water in the presence of a CONCENTRATED acid catalyst

What acid catalysts could be used here?

HCl H2SO4 H3PO4

What do we not use HNO3?

It is explosive with some alcohols

What type of reaction is esterification? why?

condensation reaction because a water molecule is removed AND reversible The reaction is reversible since ester and water can react to form the carboxylic acid and alcohol again.

State the role of a catalyst

Increases the rate of reaction

Explain how a catalyst works

Provides an alternative reaction pathway Lowers the activation energy

How can a higher yield of esters be obtained?

reacting acid and acyl chloride/acid anhydride (acylations)

What are esters used for?

-food flavourings -plasticisers -perfume

Why don't esters form hydrogen bonds?

There are no Hydrogens bonded to Oxygen

Why do esters have lower boiling points than carboxylic acids?

polar so have dipole-dipole forces and vdw's between molecules But they do not form hydrogen bonds so weaker IMFs than in carboxylic acids

How does solubility of esters change as chain length increases?

decreases

How are plasticisers used to modify properties of polymers?

They get between polymer molecules pushing them further apart This weakens the strength of the IMF between molecules The material is more flexible as layers can slide past each other more easily The more plasticisers added the more flexible the polymer

What is acid hydrolysis of esters?

This is reverse esterification ester + water --> carboxylic acid + alcohol

What is base hydrolysis of an ester?

ester + OH- --> carboxylate ion + alcohol

What reagent and conditions are required for acid hydrolysis?

dilute acid catalyst eg. HCl and heat under reflux

What conditions are required for base hydrolysis?

aqueous alkali eg. NaOH and heat under reflux

How can you deduce from acid hydrolysis equations that the reaction does not go to completion?

reversible reaction

How can you deduce from base hydrolysis equations that the reaction goes to completion?

irreversible reaction

Explain why the base hydrolysis reactions are irreversible

The salt produced in the reaction is an anion of the carboxylic acid The anion is resistant to attack by weak nucleophiles such as alcohol so the reaction is irreversible

Suggest why an excess of base is used in base hydrolysis

To ensure the ester is completely hydrolysed

Suggest why reflux is used in both acid and base hydrolysis

allows reactant vapours to be returned to the reaction mixture

How can yield of product be maximised in acid hydrolysis?

Add large amounts of water to shift equilibrium to the right to maximise yield of acid and alcohol

Base hydrolysis has taken place and a carboxylate salt and an alcohol is formed. Suggest how you could obtain a sample of alcohol from the reaction mixture

Fractional distillation

Suggest why an electric heater is used in hydrolysis reactions

Alcohols are flammable

Why is benzoic acid insoluble in cold water?

despite polarity of the COOH group, the benzene ring is non polar

What is the IUPAC name for glycerol?

Propane-1,2,3-triol

what does glycerol and fatty acids make?

esters

What happens when glycerol reacts with fatty acids?

a tri-ester is formed which is a 3 ester bond and water

How do oils and fats differ in structure?

fats are saturated so have strong vdw forces between them and solid at RTP oils are unsaturated so have weaker vdw forces between them and liquid at RTP

How is glycerol soluble in water?

they form hydrogen bonds with water

What is glycerol used for?

solvent glues cosmetics

What is saponification?

oils and fats are hydrolysed (base hydrolysis) with alkali to form sodium/potassium carboxylate salt (soap) and glycerol

How do soaps work?

they are ionic and dissociate to form Na+ and RCOO- ions. The RCOO- ion has two ends the long hydro chain in attracted to oil (hydrophobic) for cleaning purposes The COO- end is hydrophilic and mixes with water

How can the sodium salt be converted back into a carboxylic acid?

reaction with an acid such as HCl, HNO3, H2SO4etc

Why is the salt soluble in water?

salt is ionic

How is biodiesel formed?

reacting vegetable oils (esters) with methanol forms a mixture of methyl esters and glycerol AND strong alkali catalyst eg. KOH/NaOH

What is biodiesel?

a mixture of methyl esters of long chain carboxylic acids

What is rapeseed oil?

A triglyceride ester

What type of reaction is making biodiesel?

trans esterification

What is a biofuel?

A fuel produced from plants

What does carbon neutral mean?

There is no net carbon dioxide emission to the atmosphere

Why is making biodiesel not carbon neutral?

energy is required, unless renewable energy then it is not carbon neutral (extra energy from transport, irrigation should be accounted for) energy usually comes from fossil fuel burning

what is the functional group of an acyl chloride?

-COCl

What is the suffix for acyl chlorides?

-oyl chloride

What makes acyl chlorides very reactive?

Both the chlorine and oxygen atom are very electronegative Cl has negative inductive effect making the C atom very electron deficient Therefore it is extremely susceptible to attacks from nucleophiles

What mechanisms do acyl chlorides usually undergo?

nucleophilic addition elimination mechanism

What byproduct is produced?

HCl

Where should this reaction be carried out and why?

HCl is toxic so fume hood should be used

What is observed when HCl is produced?

White misty fumes

Define a nucleophile

an electron pair donor

How do acyl chlorides react with water?

they form carboxylic acids and hydrogen chloride

What removes the H+ in the reaction mechanism?

The Cl-

Why does ethanoyl chloride react readily with nucleophiles?

The Cl and O bonded to the C atom are both electronegative This makes the C atom of the carbonyl group very electron deficient Nucleophiles have electron pairs which are donated to the carbon atom

How do acyl chlorides react with alcohols?

They react with alcohols to form esters and HCl at RTP

Give an advantage of using ethanoyl chloride and methanol to produce esters instead of carboxylic acid and methanol

Faster Greater yield Pure product No acid catalyst required Not reversible

Give disadvantages of using ethanoyl chloride over ethanoic acid and methanol to make esters

reaction is dangerous HCl produced is corrosive and toxic

How do acyl chlorides react with ammonia?

they form an amide and ammonium chloride at RTP

How do acyl chlorides react with primary amines?

form N - substituted amides and a chlorine containing salt which depends on the primary amine that reacts

In what order are nucleophiles most reactive with acyl chlorides?

primary amine > ammonia > alcohol > water

How are acid anhydrides formed?

removal of water from two carboxylic acid molecules

What does anhydride mean?

without water

How do you name if two different carboxylic acids make an anhydride?

place acids in alphabetical order

Do acid anhydrides dissolve in water?

No they react with water to form an aqueous solution of carboxylic acids

What IMFs are found in acid anhydrides?

VdW and dipole-dipole forces

How do the electron deficient carbons in acyl chlorides and acid anhydrides compare?

C in acyl chloride is more electron deficient

What is a nucleophile without charge?

a neutral nucleophile ie. NH3 H2O ...

How do acid anhydrides react with water?

they form carboxylic acids at RTP

How can a carboxylic acid be reduced to alcohol?

NaBH4 in methanol nucleophilic addition

How do acid anhydrides react with alcohols?

they form esters, higher yield than acyl chlorides

How do acid anhydrides react with ammonia?

they form an amide and carboxylic acid