Chapter 20: Carboxylic Acids and Their Derivatives Flashcards
Naming carboxylic acids
- Identify and name the parent chain that includes the carboxyl group
- Identify and name substituents
- Assign locant to each substituent giving the carboxyl carbon the lowest number
- Assemble substituents alphabetically
- Assign configurations to any chiral centers
- Replace “e” with suffix −oic acid
Cyclohexanecarboxylic acid
Formic acid
Acetic acid
Propionic acid
Butyric acid
Benzoic acid
Naming deprotonated carboxylic acids
Replace the “ic acid” with the suffix −ate
Average pKa for carboxylic acids
4−5
Henderson-Hasselbach equation
Preparing a carboxylic acid from an alkyne
Reagents
- O3
- H2O
Preparing a carboxylic acid from a primary alcohol
Reagents
Na2Cr2O7 (sodium dichromate) & H2SO4/H2O
or
xs CrO3 (chromium trioxide) & H3O+/acetone
Preparing a carboxylic acid from an alkylbenzene
Reagents
Na2Cr2O7 (sodium dichromate) & H2SO4/H2O
Preparing a carboxylic acid from a nitrile
Reagents
H3O+ & heat
Preparing a carboxylic acid from a Grignard reagent
Reagents
- Mg
Followed by
- CO2
- H3O+
Mechanism
Replaces the leaving MgX group withe the carboxyl group; resulting in the addition of one carbon atom
Reduction of carboxylic acids
Reagents
- LiAlH4
- H3O+
or
BH3 (borane) & THF
Mechanism
Borane is chemoselective and only reduces carboxyl groups in the presence of other carbonyl groups
What is a heteroatom
Any atom that is not carbon or hydrogen
Naming acid halides
Replace “ic acid” with suffix −yl halide
Naming acid anhydrides
Replace “acid” with suffix −anhydride
If molecule is asymmetrical then the compound is called −oic −oic anhydride
Naming esters
- Add name of the oxygen R −yl group before the parent chain −ate
- Replace “ic acid” with suffix −ate
Naming amides
- Replace “ic acid” with suffix −amide
- If the nitrogen has substituents, then name them with locant “N”
Naming nitriles
Replace “ic acid” with suffix −nitrile
Reactivity of carboxylic acid derivatives
Carboxylic acid derivatives are electrophilic at the carbonyl carbon
Acid chlorides are the most reactive derivatives
Amides are the least reactive derivatives
Nucleophilic acyl substitution
Basic reaction mechanism
Can occur under acidic or basic conditions
Mechanism
A nucleophile attacks a carbonyl carbon and forms a tetrahedral intermediate, the carbonyl can then be reformed by the expulsion of the best leaving group
C− and H− are generally not expelled as leaving groups
Preparing an acid chloride from a carboxylic acid
Reagents
SOCl2 (thionyl chloride)
Preparing a carboxylic acid from a acid chloride
Reagents
H2O & Pyridine
Mechanism
Water functions as a nucleophile and the chloride is ejected as a LG
Pyridine is used as a base to react with the HCl byproduct and prevent it from performing unwanted side reactions
Alcoholysis of acid chlorides
Reagents
ROH & Pyridine
Mechanism
Alcohol oxygen and R group are acylated to produce an ester
Reaction can also be viewed from the perspective of the acid chloride
Aminolysis of acid chlorides
Reagents
NH3, RNH2, or R2NH (two equivalents)
Mechanism
An amide is formed through the acylation of the amine group with the loss of one hydrogen atom from the amine reagent
Pyridine is not required because the amine is sufficiently basic enough to neutralize the HCl as it forms; hence why two equivalents are required
Reduction of acid chlorides
Forming a primary alcohol
Reagents
- LiAlH4
- H2O
Mechanism
Carbonyl carbon is reduced to form a primary alcohol
Reduction of acid chlorides
Forming an aldehyde
Reagents
- LiAl(OR)3H (lithium hydride)
- H2O
Mechanism
A bulky lithium hydride reagent will slow down reduction at an aldehyde
Preparing a tertiary alcohol from an acid chloride
Reagents
- Excess RMgBr
- H2O
Mechanism
Gringnard reagent R groups are added to the carbonyl carbon with the ejection of the chloride ion
Preparing a ketone from an acid chloride
Reagents
R2CuLi (dialkyl lithium cuparate)
Mechanism
One of the two alkyl groups adds to make a ketone
Nucleophilic acyl substitution reactions of acid anhydrides
Anhydrides undergo many of the same reactions as acid chlorides
The leaving group is a carboxylate ion rather than a chloride ion
Acetic anhydride
Acetylation of an alcohol or an amine
Reagents
Acetic anhydride
Preparing an ester from a carboxylic acid
Reagents
- NaOH
- RX
Mechanism
The carboxylic acid is first deprotonated to yield a carboxylate ion which then functions as a nucleophile and attacks the alkyl halide in an SN2 process
A tertiary alcohol cannot be used due to SN2 mechanism
Fischer esterfication
Reagents
[H+] & ROH
Mechanism
A carboxylic acid is converted into an ester when treated with an alcohol
Can be reversed with an excess of water under acidic conditions such as in an acid catalyzed ester hydrolysis
Can also be reversed via soaponification
Preparing an ester from an acid chloride
Reagents
ROH & Pyridine
Mechanism
Alcohol performs a nucleophilic attack on an acid chloride
Reaction can also be viewed from the perspective of the alcohol via alcoholysis reaction
Ester hydrolysis
Basic conditions
Reagents
- NaOH
- H3O+
Mechanism
Esters undergo hydrolysis in basic conditions through the hydration of the ester bond in a reaction called saponification
Ester hydrolysis
Acidic conditions
Reagents
H3O+
Mechanism
The mechanism is a reverse Fischer esterification
Aminolysis of esters
Reagents
NH3
Mechanism
Ammonia attacks carbonyl carbon to form an amide
Very slow process, easier to make amides from acid chlorides
Reduction of esters
Forming an alcohol
Reagents
- LAH (LiAlH4)
- H2O
Esters are NOT sensitive towards NaBH4 reduction
Reduction of esters
Forming an aldehyde
Reagents
- DIBAH
- H2O
Preparing a tertiary alcohol from an ester
Reagents
Mechanism
Esters can react with excess Grignard reagent to form a tertiary alcohol via the addition of two R groups
Preparation of amide trends
Amides are most efficiently prepared from acid chlorides
Hydrolysis of amides
Acidic conditions
Reagents
H3O+ & heat
Hydrolysis of amides
Basic conditions
Reagents
- NaOH & heat
- H3O+
Reduction of amides
Reagents
- Excess LAH (LiAlH4)
- H2O
Mechanism
Produces a primary amine
Water is used to prevent the formation of an ammonium ion
Preparing a nitrile from an alkyl halide
Reagents
NaCN
Mechanism
Transformation proceeds via an SN2 mechanism so a tertiary alkyl halide CANNOT be used
Preparing a nitrile from a primary amide
Reagents
SOCl2 (thionyl chloride)
Mechanism
Can be used to prepare tertiary nitriles which cannot be preparred via an SN2 mechanism
Hydrolysis of a nitrile
Basic conditions
Reagents
- NaOH, H2O
- H3O+
Hydrolysis of a nitrile
Acidic conditions
Reagents
H3O+ & heat
Preparing a ketone from a nitrile
Reagents
- RMgBr
- H3O+
Mechanism
The Grignard reagent first forms an imine which can then he hydrolyzed to form the ketone
Reduction of a nitrile
Reagents
- Excess LAH (LiAlH4)
- H2O
Mechanism
Produces a primary amine
Water is used to prevent the formation of an ammonium ion