Carboxylic acids and derivatives

Acid definition

Proton donor/releases H+

What type of intermolecular forces are present in carboxylic acids?

Hydrogen bonding

Describe the acidity of carboxylic acids

Weak acids in water and only slightly dissociate, but they are strong enough to displace carbon dioxide from carbonates

Describe the solubility of carboxylic acids in water

Smaller acids (up to C4) dislocate in water in all proportions but after this solubility rapidly reduces (dissolve because they can hydrogen bond to water molecules)

Describe how strength of carboxylic acids changes as alkyl chain length increases

Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable, making the acid less strong

Give the reaction of carboxylic acids with metals to form salts (ethanoic acid and sodium as example)

2CH3COOH + 2Na —> 2CH3COO-Na+ + H2

Give the reaction of carboxylic acids with alkali to form salt (ethanoic acid and NaOH as example)

CH3COOH + NaOH —> CH3COO-Na+ + H2O

Give the reaction of carboxylic acids with carbonates to form salt (ethanoic acid and sodium carbonate as example)

2CH3COOH + Na2CO3 —> 2CH3COO-Na+ + H2O + CO2

What is the standard test for carboxylic acids?

Add Na2CO3 - fizzes if carboxylic acid due to CO2 produced

Why are carboxylic acids susceptible to nucleophilic attack?

They have regions of slightly positive charge (carbon in COOH group)

Give the general equation for making esters out of carboxylic acids and alcohols

Carboxylic acid + alcohol —> ester + water

What conditions are needed for esterification?

Strong acid catalyst

What catalyst is used when reaction carboxylic acids and alcohols?

Sulfuric acid

Is the reaction between carboxylic acids and alcohols to make esters reversible?

Yes

Give the general equation for ester hydrolysis

Ester + water —> carboxylic acid + alcohol

What happens during ester hydrolysis under acidic conditions?

The carboxylic acid and alcohol are formed, but the reaction is slow and reversible

What happens during ester hydrolysis under alkaline conditions?

Reaction goes to completion and forms a salt of the carboxylic acid and an alcohol

What is the name given to ester hydrolysis under alkaline conditions?

Saponification

Give 3 uses of esters

Flood flavourings, perfumes, solvents for polar organic substances, plasticisers

Why don’t esters form hydrogen bonds?

There is no hydrogen bonded to a highly electronegative atom

Explain the difference in boiling points between esters and carboxylic acids

Carboxylic acids have higher boiling points as they form hydrogen bonds

What effect to plasticisers have on polymers?

Allows the chains to move more easily so the polymer can become flexible

Give the reagents and conditions for hydrolysis of esters with acid

Dilute acid (HCl), heat under reflux

Give the reagents and conditions needed for hydrolysis of esters using sodium hydroxide

Dilute NaOH, heat under reflux

Give the equation for hydrolysis of esters using NaOH (methyl propanoate as example)

CH3CH2COOCH3 + NaOH —> CH3CH2COO-Na+ + CH3OH

Give the word equation for the hydrolysis of esters using acid (ethyl propanoate example)

Ethyl propanoate + water <=> propanoic acid + ethanol

give the equation for the dissociation of carboxylic acids (using ethanoic acid as example)

CH3COOH <=> CH3COO- + H+

why are carboxylic acids with longer alkyl chains less stable than those with shorter chains?

increasing chain length pushes electron density onto the COO- ion, making it more negative and less stable

why is CH2ClCOOH a stronger acid than unsubstituted carboxylic acids?

electronegative chlorine atoms withdraw electron density from COO- ion, making it less negative and more stable

what are fats and oils made up of?

esters of glycerol and long chain carboxylic acids

describe how soaps work

polar COO- end is hydrophilic and mixes with water, non-polar hydrocarbon chain is hydrophobic and mixes with grease (allowing grease and water to mix and be washed away)

how are soaps and biodiesel different?

soaps are sodium salts of long chain carboxylic acids, biodiesels are methyl esters of long chain carboxylic acids

How can vegetable oils be converted into biodiesel?

By reaction with methanol in the presence of a strong alkali catalyst

why is biodiesel described as carbon neutral?

any CO2 given of when biodiesel is burnt would have been extracted from the air by photosynthesis when the plant grew

what are methyl esters made up of?

mixture of methyl esters of long chain carboxylic acids

give the equation for the industrial manufacture of aspirin

salicylic acid + ethanoic anhydride —> aspirin + ethanoic acid

Acid + metal —>?

salt and hydrogen

acid + alkali —> ?

salt + water

acid + metal carbonate —> ?

salt + water + CO2

describe what you would see when acid and metal carbonate react

effervescence caused by production of CO2

what is the rule for oxidation of carboxylic acids?

generally carboxylic acids cannot be oxidised using oxidising agents but methanoic acid is an exception

give the equation for the oxidation of methanoic acid

methanoic acid (CH3COOH) + [O] —> carbonic acid (CO(OH)2)

what is formed when carboxylic react with alcohols in the presence of a strong acid catalyst?

ester and water

what are the conditions needed for the hydrolysis of esters using an acid?

dilute acid (HCl), heat under reflux

give the equation for the hydrolysis of esters using an acid catalyst and water

ester + water <=> carboxylic acid + alcohol

why is the hydrolysis of esters using NaOH instead of water and acid catalyst preferred?

reaction with NaOH goes to completion, while reaction with acid and water is reversible and does not give good yield of product

give the conditions needed for the hydrolysis of esters using NaOH

dilute NaOH, heat under reflux

give the equation for the hydrolysis of esters using NaOH

ester + NaOH —> carboxylic acid salt + alcohol

why is the reaction of esters using NaOH not reversible?

the anion (of carboxylic acid COO-) is resistant to attack by weak nucleophiles such as alcohols

general formula of acyl chloride

R-CO-Cl

general formula of amides

R-CO-NH2

general formula for anhydrides

R-CO-O-CO-R

general formula for esters

R-CO-O-R

describe in general how nucleophilic addition-elimination takes place in acyl compounds

nucleophilic addition of small molecule across the C=O bond followed by elimination of a small molecule

Give the reagent and conditions needed to convert acyl chloride to carboxylic acid

Water and room temp

Give the equation for the conversion of acyl chloride to carboxylic acid

RCOCl + H2O —> RCOOH + HCl

Give the observation when acyl chloride and water react

Steamy white fumes of HCl are given off

Give the reagent and conditions needed to convert acid anhydride to carboxylic acid

Water, room temp

Give the equation for conversion of acid anhydride to carboxylic acid

(RCO)2O + H2O —> 2RCOOH

Give the reagents and conditions needed to convert acyl chloride to ester

Alcohol, room temp

Give the equation for the conversion of acyl chloride to ester

RCOCl + CH3CH2OH —> RCOOCH2CH3 + HCl

Give the observation when acyl chlorides are converted to esters

Steamy white fumes of HCl are given off

Give the reagent and conditions needed to convert acid anhydride to ester

Alcohol, room temp

Give the equation for the conversion of acid anhydride to ester

(RCO)2O + CH3CH2OH —> RCO2CH2CH3 + RCOOH

Why is making esters using acyl chlorides much better than using carboxylic acids?

The reaction is much quicker and it is not reversible

Give the change in functional group when acyl chloride reacts with ammonia

Acyl chloride → primary amide

Give the change in functional group when acid anhydride reacts with ammonia

Acid anhydride → primary amide

Give the equation for the conversion of acyl chloride to primary amide

RCOCl + 2NH3 —> RCOHN2 + NH4Cl

Give the observation when acyl chlorides react with ammonia

White smoke of NH4Cl is given off

Give the equation for the conversion of acid anhydride to primary amide

(RCO)2O + 2NH3 —> RCONH2 + RCOO- NH4+

Describe the change in functional group when acyl chlorides react with primary amines

Acyl chloride → secondary amide

Give the equation for the conversion of acyl chloride to secondary amide

RCOCl + 2CH3NH2 —> RCONHCH3 + CH3NH3+Cl-

Give the change in functional group when acid anhydride reacts with primary amines

Acid anhydride → secondary amide

Give the equation for the conversion of acid anhydride to secondary amide

(RCO)2O + 2CH3NH2 —> RCONHCH3 + [CH3NH3]+ [RCOO]-