6.1.3 carboxylic acids and esters

weak acids in water and only slightly dissociate but strong enough to displace CO2 from carbonates

smaller carboxylic acids (up to 4C) dissolve in water but after this solubility rapidly reduces dissolve as they form hydrogen bonds to water molecules

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

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

salt + hydrogen

salt + water

salt + water + CO2 effervescence caused by production of CO2 - can be used as functional group test for carboxylic acids

cannot be oxidised using oxidising agent but methanoic acid is exception as structure effectively an aldehyde forms H2CO3 which can decompose to give CO2

carboxylic acid + alcohol (H+)> ester + water name alcohol (e.g. methyl) then acid (e.g. ethanoate) reversible, slow and need heating under reflux - low yields, acid catalyst H2SO4 needed

acid anhydride > ester alcohol reagent room temp anhydride more reactive than carboxylic acid - not reversible > higher yield

can be hydrolysed and split up by either heating with acid or NaOH i) with acid reagent: dilute acid (HCl) conditions: heat under reflux - reverse reaction of ester formation > carboxylic acid and alcohol formed - reversible so low yield ii) with NaOH reagent: dilute NaOH conditions: heat under reflux - sodium salt + alcohol formed - not reversible > high yield

much more reactive than carboxylic acids

carboxylic acid > acyl chloride + SO2 + HCl reagent: SOCl2 (thionyl chloride, liquid) room temp

carboxylic acid + HCl reagent: water room temp steamy white fumes of HCl are given off

acyl chloride > ester + HCl reagent: alcohol room temp steamy white fumes of HCl given off quicker than making ester with COOH and not reversible

acyl chloride > primary amide + NH4Cl (s) reagent: ammonia room temp white smoke of NH4Cl given off

acyl chloride > secondary amide reagent: primary amine room temp

acyl chloride > ester + HCl phenol reagent room temp steamy white fumes of HCl given off phenols don’t easily form esters with carboxylic acids but do so readily with acyl chlorides