Carboxylic acids Flashcards
Carboxylic acid
COOH (image)
Carboxylic acids are
Dimeric
Dimeric
Consisting of two similar molecules that have been linked together
Low Pka
strong acid
high pka
weak acid
strength of alkanes as an acid
very weak acid
are carboxylic acids strong or weak acids
most are weak acids
pKa table
draw table out
electronegativity
a measure of the ability of an atom in a chemical compound to attract electrons
inductive effects
stabilize charge through sigma bonds
electron-withdrawing substituents increase
acidity of nearby atom
electron withdrawing groups effect increases with ____ and decreases with ______
electronegativity, distance
Rank chlorine, iodine, fluorine and bromine in order of increasing electronegativity
F > Cl > Br > I
A carboxylic acid with F as a substituent is ___ acidic than one without
more
two methods of preparing carboxylic acids
1) oxidation in aqueous conditions 2) addition of Grignard or alkyl lithium reagents to CO2
carboxylic acids ____ undergo nucleophilic substitution with negatively charged nucleophiles
do NOT
LiAlH4 will reduce _____ to _____
carboxylic acids, primary alcohols
reduction using LiAlH4
1) deprotonation
2) addition of hydride
3) elimination
4) addition of hydride
5) protonation
(Image)
Acid chloride
Image
Anhydride
Image
Ester
Image
Amide
Image
Nucleophilic substitution
A type of substitution reaction in which a nucleophile is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond.
Addition elimination mechanism
1) add to carbonyl
2) elimination of leaving group
Nucleophilic acyl substitution
1) Nucleophilic addition
2) elimination of the leaving group and reformation of the carbonyl (Image)
Golden rule of acid base reactions
stronger acids and stronger base should react to give a weaker acid and a weaker base
Four derivatives ranked by reactivity
Acid Chloride > anhydride > ester > amide
Two nucleophilic acyl substitutions that don’t work
Anhydride into acid chloride ester into anhydride
Conversion of carboxylic acids to acid halides
1) chloride is a bad nucleophile
2) leaving group must be worse than chloride
3) leaving group disintegrates making the reaction irreversible
4) requires SOCl2, HCl, and SO2 gas
Mechanism of carboxylic acids to acid halides
1) attack on thionyl chloride
2) additon of Cl- to carbonyl carbon
3) elimination of SO2Cl
4) deprotonation
Reaction of carboxylic acid with alcohols to make esters
Requires an acid catalyst (H2SO4) and an alcohol
Esterfication
The reaction of an alcohol with a carboxylic acid to produce an ester and water (Image)
Using an excess of alcohol drives the esterification equilibrium towards the
Ester product
Equal concentrations of alcohol and acid
65% ester
10 fold excess of alcohol to acid
97% ester
100 fold excess of alcohol to acid
99% ester
Mechanism of esterfication
Image
Backwards reaction of esterfication
Hydrolysis
Mechanism of hydrolysis
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