6.1.3 Carboxylic Acids And Esters

Question 1

carboxylic acids acidity

Answer 1

weak acids
only partially dissociate
can displace carbon dioxide from carbonates

Question 2

carboxylic acids solubility in water

Answer 2

smaller (up to C4) dissolve in water in all proportions but after this the solubility rapidly reduces
dissolve as they can hydrogen bond to the water molecules

Question 3

delocalisation of a carboxylic acid

Answer 3

stabilised by delocalisation, makes dissociation more likely
delocalised ion has equal C-O bond lengths, if delocalisation didn’t occur then C=O is shorter than C-O
pi charge cloud has delocalised and spread out, makes ion more stable and more likely to form

Question 4

explain the drawing of the delocalisation of a carboxylic acid

Answer 4

draw normal carboxylic acid
then break the double bond C=O and lose the H on OH
draw a dotted c shaped curve with a - inside of a small circle

Question 5

factors that affect strength of a carboxylic acid

Answer 5

chain length

electronegativity

Question 6

effect of chain length on the strength of a carboxylic acid

Answer 6

decreases the acidity 
alkyl groups are electron donating 
pushes the electron density on to the COO- ion 
makes it more negative and less stable 
makes the acid less strong

Question 7

effect of electronegativity on the strength of a carboxylic acid

Answer 7

more electronegative atom added then the stronger the acidity of the acid
electronegative chlorine withdraw electron density from the COO- ion
makes it less negative and more stable
makes the acid more strong

Question 8

what reactions can carboxylic acids also take part in

Answer 8

acid + metal -> salt + hydrogen
acid + base -> salt + water 
acid + alkali -> salt + water 
acid + carbonate -> salt + water + CO2
acid + ammonia -> ammonium salt

Question 9

example of a functional group test for a carboxylic acid

Answer 9

effervescence caused by the production of CO2 with carboxylic acids with solid Na2CO3 or aqueous NaHCO3

Question 10

oxidation of methanoic acid

Answer 10

forms carbonic acid H2CO3

which can decompose to give CO2

Question 11

why can methanoic acid be oxidised using an oxidising agent

Answer 11

as its structure effectively has an aldehyde group

Question 12

esterification

Answer 12

carboxylic acids react with alcohols in the presence of a strong sulfuric acid catalyst to form esters and water

carboxylic acid + alcohol (reversible with H+) ester + water

Question 13

naming an ester

Answer 13

2 parts to their name
name them right to left
bit ending in -yl comes from alcohol that has formed it, next to the single-bonded oxygen
bit ending in -anoate comes from the carboxylic acid and includes the C in C=O bond

Question 14

conditions of esterification

Answer 14

requires a strong sulfuric acid catalyst
reversible reaction
quite a slow reaction and needs heating under reflux for several hours or days
low yields are achieved

Question 15

esterification using acid anhydrides

Answer 15

acid anhydride -> water 
reagent: alcohol 
conditions: room temperature 
NOT REVERSIBLE
(RCO)2O + CH3CH2OH -> RCO2CH2CH3 + RCO2H

React with alcohols to form esters as the main product and a carboxylate salt as a side product

Question 16

acid anhydrides

Answer 16

more reactive than carboxylic acids
not reversible
higher yield achieved

Question 17

hydrolysis of esters reagents

Answer 17

acid reagents- dilute HCl

sodium hydroxide reagents- dilute sodium hydroxide

Question 18

hydrolysis of esters with acid reagents

Answer 18

dilute HCl 
heat under reflux 
reversible reaction 
forms a carboxylic acid and an alcohol 
not a good yield

Question 19

hydrolysis of esters with sodium hydroxide reagents

Answer 19

dilute sodium hydroxide NaOH
heat under reflux
reaction goes to completion
forms carboxylate salt and alcohol

salt is the anion of the carboxylic acid
anion is resistant to attack by weak nucleophiles such as alcohols so the reaction isn’t reversible

Question 20

acyl chlorides reactivity, explain

Answer 20

much more reactive than carboxylic acids
Cl group is classed as a good leaving group (to do with less effective delocalisation), makes acyl chlorides much more reactive than carboxylic acids and esters

Question 21

formation of acyl chlorides from a carboxylic acid

Answer 21

carboxylic acid -> acyl chloride
reagent: SOCl2
conditions: room temperature
forms acyl chloride, SO2 + HCl

CH3COOH + SOCl2 -> CH3COCl + SO2 + HCl

Question 22

what is SOCl2

Answer 22

sulfur dichloride oxide (thionyl chloride)

it is a liquid

Question 23

what do acyl chlorides react with

Answer 23

water 
alcohol 
ammonia
primary amines 
phenol

Question 24

acyl chlorides reaction with water

Answer 24

acyl chloride -> carboxylic acid

reagent: water
conditions: room temperature
observation: steamy white fumes of HCl are given off

example:
RCOCl (l) + H2O -> RCO2H + HCl (g)

Question 25

acyl chlorides reaction with alcohol

Answer 25

acyl chloride -> ester and hcl
reagent: alcohol
conditions: room temperature
observation: steamy white fumes of HCl are given off
(better to make esters this way than with carboxylic acid as reaction isn’t reversible and is much quicker)

example:
RCOCl (l) + CH3CH2OH -> RCO2CH2CH3 + HCl (g)

Question 26

acyl chlorides reaction with ammonia

Answer 26

acyl chloride -> primary amide

reagent: ammonia
conditions: room temperature
observation: white smoke off NH4Cl is given off

example:
RCOCl (l) + 2NH3 -> RCONH2 + NH4Cl (s)

Question 27

acyl chlorides reaction with primary amines

Answer 27

acyl chloride -> secondary amine

reagent: primary amine
conditions: room temperature

examples:
RCOCl + 2 CH3NH2 -> RCONHCH3 + CH3NH3+Cl-

Question 28

acyl chlorides reaction with phenol

Answer 28

acyl chloride -> ester

reagent: phenol
conditions: room temperature
observation: steamy white fumes off HCl are given off

example:
RCOCl (l) + C6H5OH -> RCO2C6H5 + HCl (g)

Question 29

phenols reactivity with carboxylic acids vs acyl chlorides

Answer 29

don’t easily form esters with carboxylic acids but do with acyl chlorides