6.1.3 Carboxylic Acids And Esters Flashcards
carboxylic acids acidity
weak acids
only partially dissociate
can displace carbon dioxide from carbonates
carboxylic acids solubility in water
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
delocalisation of a carboxylic acid
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
explain the drawing of the delocalisation of a carboxylic acid
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
factors that affect strength of a carboxylic acid
chain length
electronegativity
effect of chain length on the strength of a carboxylic acid
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
effect of electronegativity on the strength of a carboxylic acid
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
what reactions can carboxylic acids also take part in
acid + metal -> salt + hydrogen acid + base -> salt + water acid + alkali -> salt + water acid + carbonate -> salt + water + CO2 acid + ammonia -> ammonium salt
example of a functional group test for a carboxylic acid
effervescence caused by the production of CO2 with carboxylic acids with solid Na2CO3 or aqueous NaHCO3
oxidation of methanoic acid
forms carbonic acid H2CO3
which can decompose to give CO2
why can methanoic acid be oxidised using an oxidising agent
as its structure effectively has an aldehyde group
esterification
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
naming an ester
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
conditions of esterification
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
esterification using acid anhydrides
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
acid anhydrides
more reactive than carboxylic acids
not reversible
higher yield achieved
hydrolysis of esters reagents
acid reagents- dilute HCl
sodium hydroxide reagents- dilute sodium hydroxide
hydrolysis of esters with acid reagents
dilute HCl heat under reflux reversible reaction forms a carboxylic acid and an alcohol not a good yield
hydrolysis of esters with sodium hydroxide reagents
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
acyl chlorides reactivity, explain
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
formation of acyl chlorides from a carboxylic acid
carboxylic acid -> acyl chloride
reagent: SOCl2
conditions: room temperature
forms acyl chloride, SO2 + HCl
CH3COOH + SOCl2 -> CH3COCl + SO2 + HCl
what is SOCl2
sulfur dichloride oxide (thionyl chloride)
it is a liquid
what do acyl chlorides react with
water alcohol ammonia primary amines phenol
acyl chlorides reaction with water
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)
acyl chlorides reaction with alcohol
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)
acyl chlorides reaction with ammonia
acyl chloride -> primary amide
reagent: ammonia
conditions: room temperature
observation: white smoke off NH4Cl is given off
example:
RCOCl (l) + 2NH3 -> RCONH2 + NH4Cl (s)
acyl chlorides reaction with primary amines
acyl chloride -> secondary amine
reagent: primary amine
conditions: room temperature
examples:
RCOCl + 2 CH3NH2 -> RCONHCH3 + CH3NH3+Cl-
acyl chlorides reaction with phenol
acyl chloride -> ester
reagent: phenol
conditions: room temperature
observation: steamy white fumes off HCl are given off
example:
RCOCl (l) + C6H5OH -> RCO2C6H5 + HCl (g)
phenols reactivity with carboxylic acids vs acyl chlorides
don’t easily form esters with carboxylic acids but do with acyl chlorides
