Topic 12: carboxylic acid Flashcards
(29 cards)
Define acid dimer
- H-bonds the O+H/O+H between 2 carboxylic acids
Why are carboxylic acids liquids?
- Due to H-bonds
Describe the boiling points of carboxylic acids
- Both alcohols + carboxylic acids = H-bonds BUT carboxylic acid = dimers = 2x as many H-bonds as alcohol
- C-acids have extra O atom = LDF greater
Describe acidic properties of carboxylic acids
- Weak
- Donate protones
- React with bases = salt + H2O = -oate
Define a carboxylate anion
- Produced by dissociation of C-acid
Give the equations of weak acid dissociation
R-C=O-OH + H2O → R-C=O-O + H3O+
Give the Ka for weak acid dissociation
Ka = [R-C=O-O][H3O+]/[R-C=O-OH]
- Lower the Ka = weaker acid
Give the equation for pKa
pKa = -log10Ka
- Higher pKa = weaker acid
Describe the relationship between acid strength + conjugate base
- HA → H+proton + A-conjugate base
- Stability of conjugate = increase acid strength
- Satble base = equilibrium to right = more H+ ions = acid stronger
How does carboxylate anion stabilized?
- Via resonance = delocalizing -ve charge = stable
Compare acidity between formic acid + acetic acid
- Formic acid = stronger
- Acetic = weaker
- Depends on groups attached to base formed
- If methyl group = e- donating = makes base more negative = more unstable = lowers acidity
Compare acidity between chloroacetic acid + acetic acid
- Chloroacetic acid = stronger
- Acetic acid = weaker
- Depends on groups attached to base formed
- If chlorine = electronegative atom = draws e- charge away = stabilizes base = increases acidity
- Also depends on strength of O-H bond
- Methy group = adds e- = stronger O-H bond = less dissociation = weaker acid
- Chlorine = takes e- = weaker O-H bond = more dissociation = stronger acid
Describe the trend in halogens on carboxylic acids
- I→F = electronegativity increases
- pKa reduces = increases strength of acid
Describe the trend in Cl distance to COOH group in acids
- As Cl gets closer to COOH group = e- withdrawing effect increases = acid stronger
Describe the relationship between BP + acidity
- Stronger the acid = lower BP
- Depends on strength of H-bonds between dimers
- R group e- withdrawing = takes e- density from H-bonds = weaken = easier to boil = lower BP
- R group donating = gives e- density to H-bonds = stronger = harder to boil = higher BP
Give methods of making carboxylic acid
1) Oxidative cleavage of alkenes = KMnO4
2) Oxidative cleavage of alkynes = KMnO4/O3
3) Oxidation of primary alcohols/aldehydes
4) Hydrolysis of nitriles
5) Carboxylation of Grignard reagents
Describe alkene oxidative cleavage
- KMnO4 = alkene split into 2 = fully oxidizes all the way when H attached to C
- If termininal alkene = CO2 gas
- If no H attached = ketone
- KMnO4 = purple = reacting with alkene = decolors
Describe alkyne oxidative cleavage
- KMnO4 + O3
- Split through middle = add O+OH
- If terminal = CO2
- If oxidative cleavage = CO2 = molecule has triple bond
Describe oxidation of alcohols
- Alcohol = all carbonyl compounds
- Oxidation agents = KMnO4 + CrO3 + K/Na2Cr2O7
- Primary → aldehyde + carboxylic acid
- KMnO4 in hot HNO3
- CrO3 in acidic conditions
- Tollens’ reagent = alkaline conditions = Ag2O in aq ammonia
Describe hydrolysis of nitriles
- Mild acidic/alkaline solution + heat
- C≡N →remove N + add =O-OH to C
Describe the carboxylation of Grignard reagent
- Add dry ice = CO2 solid
- MgBr → C=O-OH
Give reactions from carboxylic acids
1) Production of acid chloride
2) Production of acid anhydride
3) Production of ester
4) Production of amide
5) Deprotonation = acid base reaction
Describe nucleophilic acyl substitution
- Reaction carboxylic acids undergo
- Nucleophile attacks C=O → attaches
- Kicks off leaving group attaches to C
- Leaving group = OH
- Not a good leaving group initially = acidified = good leaving group
Why do aldehydes/ketones not go through NAS?
- Don’t have good leaving groups
- Go through nucleophilic addition
