Carboxylic acid structure
- functional group is carboxyl group
- general formula: RCO2H
- formula for aromatic: ArCO2H
nomenclature for carboxylic acids
- drop -e add -oic acid
- carboxyl group take precedence over most other functional groups
- dicarboxylic acid: add -dioic acid
- if bonded to a ring, -carboxylic acid
- when common names are used, greek letters used
physical properties of carboxylic acids
- significantly higher BP
- polar, strong IMF
- more soluble in water than alcohols, ethers, aldehydes, and ketones of comparable molecular weight.
- They form hydrogen bonds with water molecules through both their C=O and OH groups.
acidity
-weak acids
-electron withdrawing substituents near the carboxyl group increase acidity through their inductive effect.
–The form of a carboxylic acid present in aqueous solution depends on the pH of the solution.
5 ways to prepare a carboxylic acid
- oxidation of 1 alcohols and aldehydes
- organometallic with CO2
- lab version of liver metabolism
- haloform reaction
- PhCN + H30-> Ph COOH
reactions of carboxylic acids
- decarboxylation
- acid-base
- esterification
- conversion to acyl halides
- reduction (use ester instead)
reactions with bases
- Carboxylic acids, whether soluble or insoluble in water, react with NaOH, KOH, and other strong bases to give water-soluble salts.
- They also form water-soluble salts with ammonia and amines.
- react with sodium bicarbonate and sodium carbonate to form water-soluble salts and carbonic acid.
reduction
- The carboxyl group is very resistant to reduction.
- Lithium aluminum hydride reduces a carboxyl group to a 1° alcohol. But, even here, the yield isn’t usually high.
- Nor are carboxyl groups reduced by NaBH4.
Fischer esterification
Esters can be prepared by treating a carboxylic acid with an alcohol in the presence of an acid catalyst, commonly H2SO4, ArSO3H, or gaseous HCl.
-an equilibrium reaction
-A key intermediate in Fischer esterification is the tetrahedral carbonyl addition intermediate (TCAI) formed by addition of ROH to the C=O group.
•Activation of carbonyl group by protonation of carbonyl oxygen
•Nucleophilic addition of alcohol to carbonyl groupforms tetrahedral intermediate
•Elimination of water from tetrahedral intermediate restores carbonyl group
diazomethane
-Diazomethane, CH2N2
–A potentially explosive, toxic, yellow gas; it is best represented as a hybrid of two contributing structures
-Esterification occurs in two steps
.Step 1: Proton transfer to diazomethane.
Step 2: Nucleophilic displacement of N2.
decarboxylation
The loss of CO2 from a carboxyl group.
- Most carboxylic acids, if heated to a very high temperature, undergo thermal decarboxylation.
- carboxylic acids that have a carbonyl group beta to the carboxyl group–This type of carboxylic acid undergoes decarboxylation on mild heating.
- Malonic acid and substituted malonic acids, for example, also undergo thermal decarboxylation.
