4.4 Aldehydes & Ketones Flashcards
Draw the mechanism for reduction of an aldehyde
Draw reflux and distillation apparatus
Reduction of butanone with NaBH4
Draw a hydroxy nitrile group
How do you test for the presence of a carbonyl?
2,4-DNP
- orange solution to orange ppt
Describe the test for differentiating between aldehyde and ketone
- Tollens reagent (silver mirror test)
- aldehydes reduce Tollens to silver
- ketones don’t react
What is the organic product produced from Tollens?
Carboxylic acid
How do you test for an aldehyde?
- Fehlings test (same as Benedict’s)
- brick red when aldehyde present
Describe the Iodoform test
- add NaOH and iodine
- detects ketones with carbonyl on carbon 2, 2° alcohols with OH on carbon 2, and ethanol
—> yellow ppt!
What is meant by a nucleophile?
Electron pair donor
Describe what happens to electron pairs in first step of nucleophilic addition
- electron pair on H- attracted to the delta + carbon forming a dative covalent bond
- electron pair breaks
- electron pair now on O-
How can the orange ppt from 2,4-DNP be used to distinguish between aldehydes and ketones?
- recrystallise the ppt
- measure melting point
- compare to known values
Why does Tollens give a different result with aldehydes than ketones?
- aldehyde can be oxidised to carboxylic acid
Describe how Tollens is made
- AgNO3
- ammonia
- heat
- silver mirror
What happens to the Tollens reagent and the aldehyde?
- Ag ions are reduced
- aldehyde oxidised to carboxylic
Explain why 2,4-DNPH is an appropriate reagent to use in ketone and aldehyde identification
- derivatives formed using 2,4-DNP have suitable melting temperatures for identification
Equation for the colour change in fehlings
Cu2+ + e- —> Cu+
—> copper ions oxidise the aldehyde and are reduced
—> blue to red
