MODULE 6: Carbonyls and Carboxylic Acids
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What is an aldehyde group?
H-C=O
What is a ketone group?
R-C(=O)-R
How are carbonyls oxidised?
Acidified potassium dichromate under reflux
What is the features of the C=O bond?
Reactive due to polarity
What is the difference between the species that attack C=C and C=O?
Electrophilic addition = C=C Nucleophilic addition = C=O
How are carbonyls reduced?
Using NaBH4, which reduces them into alcohols
How does cyanide react with carbonyls?
With sulfuric acid to form a hydroxynitrile
What tests are there for carbonyl tests?
• 2,4-DNP (brady’s reagent), forms an orange precipitate when a carbonyl group is present. • Tollens reagent, silver nitrate and ammonia. If an aldehyde is present, a silver mirror is formed. • With the precipitate formed from DNP, test boiling/melting point and compare to known values
Why are carboxylic acids more water soluble than carbonyls?
More opportunities to hydrogen bond with water
Why are carboxylic acids weak acids?
Because they only partially dissociate the hydrogen ions
What reactions do carboxylic acids undergo?
Redox reactions with metals and neutralisation reactions with bases
What are the products of reactions with carboxylic acids and metals?
Carboxylate salt (RCOO-X+) and hydrogen gas
What are the products of carboxylic acids in neutralisation reactions?
• Metal oxides: carboxylate salt (RCOO-X+) and water • Alkalis: carboxylate salt (RCOO-X+) and water • Carbonates: carboxylate salt (RCOO-X+), carbon dioxide and water
What are the main derivatives of a carboxylic acid?
Esters, acid anhydrides, acyl chlorides, amides
What are esters?
A hydrocarbon that has a double bonded oxygen to a carbon, and then another oxygen single bond linking two carbons together
What are acyl chlorides?
Similar to esters, except with a double bonded oxygen and a chloride group attached. PropanOYL CHLORIDE
What are acid anhydrides?
Two carboxylic acids that have bonded to form a double bonded oxygen on each carbon around a single bonded oxygen
What is esterification?
A method of making esters using alcohols and carboxylic acids. Concentrated sulfuric acid acts as a catalyst and the solution is added to 80oc water bath to allow the reaction. It is a condensation reaction, so forms a mole of water.
What are some physical properties of esters?
Sweet/fruity smells and tastes
What are the two types of hydrolysis for esters?
Acid and alkaline
What is acid hydrolysis for esters?
Reverse esterification, reversible reaction. Ester heated under reflux with dilute acid.
What is alkaline hydrolysis for esters?
Also known as saponification; irreversible. Ester is heated under reflux with OH- to form a carboxylate ion and an alcohol.
How are acyl chlorides prepared?
Carboxylic acid with thionyl chloride (SOCl2) to form an acyl chloride, SO2 and HCl gas.
Why are acyl chlorides useful in organic synthesis?
Can be converted into other carboxylic derivatives with a good yield, as well as being much more reactive which increases the rate of reaction. Can react with phenols.