Carboxylic Acids and Derivatives Flashcards
What is the functional group of carboxylic acids?
-COOH
What is general formula of carboxylic acids?
CnH2n+1COOH / RCO2H
where
R = H, alkyl, aryl grp
Describe nomenclature of carboxylic acids
- take alkane name, remove ‘-e’ and replace w -oic acid
eg butane –> butanoic acid - if >1 -COOH in molecule, retain ‘e’ and add suitable prefix for no of -COOH
eg ethanoic acid –> ethanedioic acid - parent chain = longest carbon chain w -COOH grp
- C atom of carboxylic acid grp is ALWAYS assigned pos n 1
Explain why boiling points of carboxylic acids are higher than those of corresponding alcohols?
- Presence of e- withdraw carbonyl grp in RCOOH cause more polar O-H bond, so stronger H bonding
- Most carboxylic acid exist as cyclic dimers held tgt by 2 H bonds => immediately double size of molecule, increase id-id forces btw one of these dimers & its neighbours, cause higher bp than corresponding alcool
Why can’t carboxylic acids form dimers in aqueous state?
- RCOOH form H bond w water molecules instead (since more H2O molecules so less probability of dimer n)
Explain solubility of carboxylic acids in water
- small molecular size RCOOH are soluble
bcos
- energy released by form n H bond btw RCOOH & H2O molecules enough overcome intermolecular H bond btw RCOOH & H2o molecules respectively - as molecular size increase, RCOOH bcome increasingly insoluble
bcos
- larger non-polar R grp make RCOOH more hydrophobic
- main interact n btw larger RCOOH & H2O molecules bcome id-id attract n instead
so
- energy released fr id-id attract n btw RCOOH & H2O molecules insufficient overcome intermolecular H bonds btw H2O & RCOOH molecules respectively (& id-id btw RCOOH molecules)
Name reagent, conditions, type of reaction for primary alcohol/aldehyde and oxygen
R&C: KMnO4 (aq), H+, heat OR K2Cr2O7, H+, heat
type: oxidat n
Name reagent, conditions, type of reaction for alkyl side chain of benzene ring and oxygen
R&C: KMnO4, H+, heat (CANNOT USE K2Cr2O7)
type: oxidat n
NOTE: need at least one H bonded to immediate C to benzene ring; whole alkyl bcome oni -COOH
Name reagent, conditions, type of reaction for nitrile and acid
R&C: HCl(aq)/H2SO4(aq), heat
type: acidic hydrolysis
Name reagent, conditions, type of reaction for nitrile and base and then acid
R&C:
NaOH(aq)/KOH(aq), heat
THEN, HCl (aq)/H2SO4(aq)
type: basic hydrolysis then neutralisat n
Why are carboxylic acids generally stronger than alcohols and phenols?
- In RCOO- anion, delocal n of -ve charge is over C atom & both electro-ve O atom
- -ve charge on RCOO- more delocalised than that of phenoxide & alkoxide ion/ intensity of -ve charge on RCOO- is less
=> RCOO- ion more stable than phenoxide/alkoxide ion - greater tendency for carboxylic acid to ionise
In general, substituents may … or … electrons (as compared to o-H group)
donate or withdraw
How do electron-donating substituents affect acidity?
- cause decrease acidity
bcos, - e-donate grp increase intensity of -ve charge on carboxylate anion
- anion/conj base is less stable
(the bulkier R grp, slight increase in e- donate effect)
How do electron-withdrawing substituents affect acidity?
increase acidity
bcos,
- e-withdraw grp reduce intensity of -ve charge on carboxylate anion to greater extent
- anion/ conj base is more stable
How do number, strength and distance (from charge position) of substituent groups affect electron withdrawing/ donating effect?
- number
eg more e-withdraw grp => greater e- withdraw effect - strength
eg the more electro-ve atom => greater e-withdraw effect - distance
eg nearer to carboxylate grp => greater e-withdraw effect
Compare acid strength of chloroethanoic acid and ethanoic acid
- for CH2ClCOOH, e- withdraw Cl atom reduce intensity of -ve charge on carboxylate anion to greater extent
=> stabilise anion - stability of carboxylate anion: CH2ClCOO- > CH3COO-
- tendency for acid to dissociate: chloroethanoic acid > ethanoic acid
- acid strength: chloroethanoic acid > ethanoic acid
Compare acid strength of trichloroethanoic acid and chloroethanoic acid
- no of chlorine atoms: trichloroethanoic acid > chloroethanoic acid
- extent of e- withdraw effect: CCl3COO- > CH2ClCOO-
- stability of carboxylate anion: CCl3COO- > CH2ClCOO-
- tendency for acid to dissociate: trichloroethanoic acid > chloroethanoic acid
- acid strength: trichloroethanoic acid > chloroethanoic acid
Name reagent, condition and type of reaction of carboxylic acid and metal
R&C: reactive metals (eg Na, Mg, Ca)
type: acid-metal displacemt
*form carboxylate salt & H2 gas
Name reagent, condition and type of reaction of carboxylic acid and base
R&C: NaOH(aq)/KOH(aq)/Ca(OH)2(aq)
type: acid-base rxn/ neutral n
Name reagent, condition, type of reaction AND observation of carboxylic acid & carbonates/ hydrogencarbonates
R&C: Na2CO3(s)/(aq) OR NaHCO3(s)/(aq)
type: acid-base rxn/ neutral n
observ n: effervescence CO2 observed, forms white ppt in Ca(OH)2
*oni RCOOH react w carbonates/hydrogencarbonates, not phenol or alcohol
* mol ratio: 2RCOOH = Na2CO3 = CO2
Compare reactions of alcohol, phenol & carboxylic acids with Na, NaOH and Na2CO3/NaHCO3
carboxylic acid reacting with:
- Na: effervescence H2 observed
- NaOH: form n salt, H2O
- Na2CO3/NaHCO3: effervescence CO2, form white ppt in limewater
phenol reacting with
- Na: effervescence H2 observed
- NaOH: form n salt & H2O
- Na2CO3/NaHCO3: no effervescence
alcohol reacting with
- Na: effervescence H2 observed
- NaOH: no react n
- Na2CO3/NaHCO3: no effervescence
Explain acidity of ethanol, phenol and ethanoic acid
- ethanol
- e-donate grp intensify -ve charge on O atom in conj base
- destabilises conj base
- ethanol is weaker acid, lower tendency dissociate in aq medium to give H+ - phenol
- lp of e- on O atom of conj base delocalised into benzene ring
- dispersal of -ve charge on O atom of conj base, stabilising conj base
- phenol is stronger acid than ethanol, higher tendency dissociate in aq medium give H+ - ethanoic acid
- delocal n of -ve charge over C atom & both electro-ve O atom in conj base
- -ve charge on conj base more dispersed than phenoxide ion/ intensity of -ve charge of conj base less than of phenoxide ion
- more stable than phenoxide ion
- greater tendency for ethanoic acid ionise vs phenol
(logically, if phenol more acidic vs ethanol and ethanoic acid more acidic vs phenol, ethanoic acid more acidic vs ethanol. Thus, no need make last comparison explicitly)
Name reagent, condition and type of reaction of carboxylic acid and alcohol
R&C: alcohol, R’OH, conc H2SO4 catalyst, heat
type: condensat n
* forms ester
* H2SO4 acts as catalyst (increase rate rxn) & dehydrating agent (increase pdt yield by LCP)
*phenols no react w carboxylate acids
Name reagent, condition and type of reaction of carboxylic acid and chlorine compounds
R&C:
1. anhydrous PCl5
or
2. anhydrous PCl3
or
3. anhydrous SOCl2
type: Nu sub n
*NOT Nu acyl sub n!
* anhydrous bcos reactive w water
Name reagent, condition and type of reaction of carboxylic acid and LiAlH4
R&C: LiAlH4 in dry ether
type: reduct n
*NaBH4 in ethanol & H2 gas CANNOT reduce RCOOH
What reactants react with LiAlH4 in dry ether, NaBH4 in ethanol, H2 gas w Pd/Pt or H2 gas w Ni at high temp, Pa
- LiAlH4 in dry ether
- nitrile (-CN)
- aldehyde, ketone
- RCOOH
- ester
- amide - NaBH4 in ethanol
- aldehyde, ketone - H2 gas w Pd/Pt or H2 gas w Ni at high temp, Pa
- alkene
- nitrile (-CN)
- aldehyde, ketone
Name reagent, condition and type of reaction of methanoic acid and oxygen
R&C: KMnO4(aq)/K2Cr2O7(aq), H+, heat
type: oxidat n
*HCOOH + [O] –> CO2 + H2O
* can oso oxidise HCOOH using Tollens’ reagent, Fehling’s solut n
Name reagent, condition and type of reaction of ethanedioic acid and oxygen
R&C: KMnO4(aq), H+, heat
type: oxidat n
* decompose to 2CO2 + H2O
Describe chemical tests for carboxylic acids
- rxn w carbonate
test: add Na2CO3(aq)/(s)
observ n: effervescence of CO2 observed forming white ppt w Ca(OH)2
type: neutral n - rxn w PCl5
test: add ANHYDROUS PCl5
observ n: white fumes HCl evolved
type: Nu Sub
NOTE:
- alcool oso give similar observ n w PCl5; cnt use this to distinguish fr alcool
- PCl5 oso hydrolyse w water form white fume, so rxn must b conducted in anhydrous environ
Name some carboxylic acid derivatives
- acyl chloride/ acyl halide
- ester
- amide
Describe nomenclature of esters
- formula: write acid grp first, then alcohol grp
- name: name alcohol grp, then acid grp
eg ethanol + benzoic acid –> ethyl benzoate
Explain boiling point of acyl chloride and ester
acyl chloride and ester:
- polar molecules w weak intermolecular pd-pd attract n
- lower bp than RCOOH
- more volatile
Explain solubility in water of acyl chloride and ester
- acyl chloride
- readily undergo hydrolysis form acidic sol n HCl
- solubility decrease as size of -R increase (more hydrophobic) - ester
- extremely slow hydrolysis in water
- solubility tends to be limited due to 2 -R grp (bigger R grp, less soluble)
Explain acidity of carboxylic acids and acyl chlorides
acyl chloride is stronger acid
RCOOH:
- in conj base, delocal n of -ve charge is over C atom & both O atom
- stabilise conj base
acyl chloride:
- undergo hydrolysis in water, form strong acid HCl
Name reagent, condition and type of reaction of acyl chloride & water
R&C: H2O
type: hydrolysis
Explain difference in reactivities of acyl chloride, aryl chloride and alkyl chloride
reactivity towards Nu Sub: acyl chloride > alkyl chloride > aryl chloride
acyl:
- carboxyl C bonded to electro-ve O, Cl
- makes C highly e- deficient
- C vv susceptible to Nu sub, occur readily
alkyl:
- oni 1 electro-ve Cl bonded to alkyl C
- alkyl C is less e- deficient
- less susceptible to Nu sub vs acyl chloride
aryl:
- lp e- on Cl delocalised into benzene ring
- strengthens C-Cl bond due to presence of partial double bond character
- Nu sub no occur under normal condit n
Name reagent, condition and type of reaction of alcohol/phenol and acyl chloride
R&C: alcohol/phenol
type: condensat n
NOTE:
- irreversible rxn, unlike RCOOH + alcool
- oni method to prepare phenyl ester (phenol no react w RCOOH)
- when reacting phenol, common to use base eg NaOH to form phenoxide ion, acts as stronger Nu than phenol (for faster rxn)
Name reagent, condition and type of reaction of acyl chloride and ammonia and amines
R&C: amines (eg R’NH2) or NH3
type: condensat n
NOTE:
- Do not use RCOOH as neutral n can occur btw RCOOH & NH3 or amine (forms ionic salt instead)
Name reagent, condition and type of reaction of ester and acid
R&C: HCl(aq)/H2SO4(aq), heat
type: acidic hydrolysis
- ester + H2O ⇌ RCOOH + alcohol
Name reagent, condition and type of reaction of ester and base
R&C: NaOH(aq)/KOH(aq), heat
type: basic hydrolysis
*ester + NaOH –> carboxylate salt + alcohol
* salt can b converted to acid by neutral n w strong acid
Explain difference in speed of reaction of basic hydrolysis vs acidic hydrolysis of esters
- acidic slow, reversible as reverse rxn oso enabled by acidic condit n
- basic faster bcos OH- is stronger Nu than H2O, & reverse rxn no compete, so complete rxn
Name reagent, condition and type of reaction of ester and H
R&C: LiAlH4 in dry ether
type: reduct n
*mole ratio
ester = 4[H]
