3.9 carboxylic acids

functional group of carboxylic acids

-COOH

are carboxylic acids weak or strong

weak

only slightly dissociate

strong enough to displace carbon dioxide from carbonates

solubility of carboxylic acids in water

smaller carboxylic acids (up to C4) dissolve in water in all proportions but after this solubility rapidly reduces

what makes dissociation of carboxylic acids more likely

they are stabilised by delocalisation

what feature does the delocalised ion have

equal C-O bond length

without delocalisation the C=O bond would be shorter than the C-O bond

what does delocalisation do to the pi charge cloud

spreads it out

ion is more stable and more likely to form

why is propanoic acid less acidic than ethanoic acid

increasing chain length pushes electron density on to the COO^- ion making it more negative and less stable

acid is less strong

why is chloroethanoic acid more acidic than ethanoic acid

electronegative chlorine atoms withdraw electron density from the COO^- ion

making it less negative and more stable

this makes the acid more strong

reaction between acid and metal

acid + metal —→ salt + hydrogen

2CH₃CO₂H + 2Na ——> 2CH₃CO₂^-Na⁺ + H₂

reaction between an acid and alkali

acid + alkali ——> salt + water

CH₃CO₂H + NaOH —→ CH₃CO₂^-Na⁺ + H₂O

reaction between an acid and carbonate

acid + carbonate ——> salt + water + carbon dioxide

2CH₃CO₂H + Na₂CO₃ —→ 2CH₃CO₂^-Na⁺ + H₂O + CO₂

which carboxylic acid is the only one that can be oxidised

methanoic acid

why can methanoic acid be oxidised

its structure effectively has an aldehyde group

forms carbonic acid which can decompose to form CO₂

general equation for esterification of carboxylic acids

carboxylic acid + alcohol ——> ester + water

REVERSIBLE

presence of a strong acid catalyst

how to name esters

the -anoate comes from the carboxylic acid

the -yl comes from the alcohol

common uses of esters (4)

perfumes - sweet smelling

food flavourings - sweet smelling

solvent - ethyl ethanoate

plasticisers

esters of glycerol (2)

vegetable oils

animal fats

when vegetable oils and animals fats are hydrolysed what do they give

soaps

glycerol

long chain carboxylic acids

what is biodiesel

mixture of methyl esters of long chain carboxylic acids

how is biodiesel produced

by reacting vegetable oils with methanol in the presence of a catalyst

how can esters be hydrolysed (2)

heating with acid

heating with sodium hydroxide

hydrolysis of esters with acid

product, reagent, conditions

product - alcohol and carboxylic acid

reagents - dilute acid (HCl)
conditions - heat under reflux

hydrolysis of esters with sodium hydroxide

product, reagent, conditions

product - carboxylic acid salt and alcohol

reagent - dilute NaOH

conditions - heat under reflux

how do you ensure the ester is fully hydrolysed

add excess NaOH

why is the hydrolysis of esters with an NaOH not reversible

carboxylic acid salt produced is an anion and resistant to attack by weak nucleophiles

what does the addition of HCl to the carboxylic acid salt do

convert the salt to a carboxylic acid

draw ethanoyl chloride

draw ethanoic anhydride

nucleophilic addition elimination reactions (4)

reaction with water

reaction with alcohol

reaction with ammonia

reaction with primary amines

reaction of acyl chlorides with water

product, reagent, conditions, observation

product - carboxylic acid

reagent - water

conditions - room temp

observation - steamy white fumes of HCl

mechanism of ethanoyl chloride and water

reaction of acid anhydride with water

product, reagent, conditions

product - carboxylic acid

reagent - water

conditions - room temperature

reactions of acyl chloride with alcohol

product, reagent, conditions, observation

product - ester

reagent - alcohol

conditions - room temperature

observation - steamy white fumes of HCl

mechanism between ethanoyl chloride and propanol

reaction between acid anhydride and alcohol

product, reagent, conditions

product - esters

reagent - alcohol

conditions - room temp

reaction between acyl chloride and ammonia

products, reagent, conditions, observations

product - primary amide

reagent - ammonia

conditions - room temperature

observation - white smoke of NH₄Cl is given off

mechanism between ethanoyl chloride and ammonia

reaction between acid anhydride and ammonia

product, reagent, conditions

product - primary amide

reagent - ammonia

conditions - room temperature

reaction between acyl chloride and primary amines

product, reagent, conditions

product - secondary amide

reagent - primary amine

conditions - room temperature

mechanism between ethanamide and ethanoyl chloride

reaction between acid anhydride and primary amine

product, reagent, conditions

product - secondary amide

reagent - primary amine

conditions - room temp