carboxylic acids Flashcards
small Ka
weaker acid
put these in order : CA ethanol phenol water
CA > phenol > water > ethanol
aciditity of CA
C=O weakens O-H
the R-C=O - O (O-H breaks and H leaves)
carboxylate ion is stabilised because of the delocalised electrons, spreads negative charge and reduces charge density.
Less likely for the H+ to bond again, less attracted. more disassociated
the effect of electron withdrawing groups on CA
furhter weaken O-H bond and extend the delocalistion of electrons
carboxylate ion can stablilised when O-H bond breaks and less attracted to H+ so won’t reform acid, more disassociated
which one is more stronger acid; trichloroethanoic acid or ethanoic acid?
trichloroethanoic acid, Cl is an electron-withdrawing groups
3 Cl electronegative atoms
ethanoic acid is the weakest, CH3 is electron donating group, strengthens O-H group = donates negative charge towards the COO- group, concentrated negative and with H+
can methanoic acid be oxidised??
yes, it is a stronger reducing agent than other carboxylic acids so it can undergo oxidation.
oxidation of methanoic acid
HCOOH
warmed with mild oxidising agents like Tollens and Fehlings
Fehlings : Cu2+ becomes a Cu+ and produces a red ppt
Tollens : Ag+ to Ag silver metal
also works with stronger oxidising agents e.g KMnO4 (decolourise purple solution) and K2Cr2O7 (orange –> green)
HCOOH + [O] –> CO2 + H2O
HCOOH –> CO2 + 2e- + 2H+(aq)
oxidation of ethanedioic acid
sulfuric acid with KMnO4; produces CO2 and H2O
solid ethanedioic acid is weighed to produce an accurate solution of a known concentration. tirtrated with KMnO4 in the titration. end point is determined when the addition of the purple KMnO4 solution into pink, all oxidisied
2MnO4 - + 6H+ + 5H2C2O4 –> 2Mn2+ + 10CO2 + 8H2O
Mn2+ acts as a catalyst, autocataylst (products catalyse reaction)
make acyl chlorides
- phosphorous chloride (PCl5)
- phosphorous chloride (PCl3) heat
- sulfur dichloride oxide (SoCl2) liquid product
phosphorous (V) chloride reaction to ethanoic acid
CH3COOH + PCl5 –> CH3COCl + HCl + POCl3
HCl = white fumes
phosphorous (III) chloride reaction to ethanoic acid
3CH3COOH + PCl3 –> 3CH3COCl + H3PO3
heat is required
sulfur dichloride oxide to ethanoic acid
CH3COOH + SOCl2 –> CH3COCl + HCl + SO2
HCl = white fumes
CH3COCl is the only liquid product
reactivity acyl chrlorides vs CA
acyl shloricdes
the electrons of the O and Cl draw it away from the C atom and gives it a large partial positive charge
open for nucleophiles attack
gives off white fumes of HCl
acyl chlorides with water
mechanism: water attaches to the c c=o gives electron to become C-O- C-Cl breaks and C=O forms again COOH and HCl
acyl chlorides with alchol
esters and HCl
acyl chlorides react faster than CA and go into completion (stronger acid)
C=O-Cl completely swapped with alcohol without the H
H and Cl forms HCl
acyl chrlodies with ammonia
NH3 acts as nucleophile on acyl chlorides
the Cl is replaced with an NH2
forms amide and HCl
HCl + NH3 –> NH4+Cl-
aryl chlorides hydrolysis
doesn’t happen
the lone pair of electrons of Cl overlaps with the delocalised p electrons in the benzene ring.
C-Cl double bond character which makes the bond stronger and harder to break
acyl chlorides with phenol
phenol can’t react with CA so acyl chlorides are warmed for phenyl esters
phenol and base = base accepts H so forms O-
this phenoxide ion acts as nucleophile to attack the acyl chloride
acyl chrlodies with amines
primary amines act as nucleophils as the nitrogen has a lone pair of electrons and attacks the acyl chloride
amine removes an H and replaces the Cl to form an amide and HCl
similarly in secondary amines.
both HCl formed are not white fumes. HCl acts as a base with unreacted amine to form an ammonium salt
CH3NH2 + HCl –> CH3NH3+Cl-
(CH3)2 NH2 + HCl –> (CH3)2NH3+Cl-
forming a cooh
CH3CH2CN + HCl + 2H2O = CH3CH2COOH + NH4Cl
reduction of COOH
CH3CH2COOH + 4[H] –> CH3CH2OH + H2O
