6.1.3 carboxylic acids and esters

Question 1

acidity

Answer 1

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

Question 2

solubility in water

Answer 2

smaller carboxylic acids (up to 4C) dissolve in water but after this solubility rapidly reduces

dissolve as they form hydrogen bonds to water molecules

Question 3

strength of carboxylic acids

Answer 3

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

makes the acid less strong

Question 4

halide ion effect on strength of carboxylic acid

Answer 4

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

makes the acid more strong

Question 5

acid + metal

Answer 5

salt + hydrogen

Question 6

acid + alkali

Answer 6

salt + water

Question 7

acid + carbonate

Answer 7

salt + water + CO2

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

Question 8

oxidation of carboxylic acid

Answer 8

cannot be oxidised using oxidising agent but methanoic acid is exception as structure effectively an aldehyde

forms H2CO3 which can decompose to give CO2

Question 9

esterification

Answer 9

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

Question 10

esterification using acid anhydrides

Answer 10

acid anhydride > ester

alcohol reagent

room temp

anhydride more reactive than carboxylic acid
- not reversible > higher yield

Question 11

hydrolysis of esters (2)

Answer 11

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

Question 12

acyl chlorides

Answer 12

much more reactive than carboxylic acids

Question 13

formation of acyl chloride

Answer 13

carboxylic acid > acyl chloride + SO2 + HCl

reagent: SOCl2 (thionyl chloride, liquid)

room temp

Question 14

acyl chloride + water

Answer 14

carboxylic acid + HCl

reagent: water

room temp

steamy white fumes of HCl are given off

Question 15

acyl chloride + alcohol

Answer 15

acyl chloride > ester + HCl

reagent: alcohol

room temp

steamy white fumes of HCl given off

quicker than making ester with COOH and not reversible

Question 16

acyl chloride + ammonia

Answer 16

acyl chloride > primary amide + NH4Cl (s)

reagent: ammonia

room temp

white smoke of NH4Cl given off

Question 17

acyl chloride + primary amine

Answer 17

acyl chloride > secondary amide

reagent: primary amine

room temp

Question 18

acyl chloride + phenol

Answer 18

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