carbonyls and carboxylic acids Flashcards
(19 cards)
Write a balanced equation (using [O] as the oxidising agent) for the oxidation of ethanal. What is used as the oxidising agent? What colour change would you see?
CH3CHO + (O) > CH3COOH
acidified potassium dichromate
orange > green
Write balanced equations for the reduction of (1) propanal and (2) propanone. What is the reducing agent (name and formula) and reaction conditions? What type of product is formed in each equation?
- CH3CH2CHO + 2(H) > CH3CH2CH2OH (primary alcohol)
-CH3COCH3 + 2(H) > CH3CH(OH)CH3 (secondary alcohol)
NaBH4 - sodium tetrahydridoborate warm, aq
reaction conditions of ethanal with HCN
H2SO4 + KCN produce the HCN ‘in situ’ as HCN is toxic
What is the name of the compound that you use to detect the presence of a carbonyl group qualitatively? What would the result of a positive test be?
2,4-DNP
You’d see a brightly coloured (red/orange/yellow) precipitate
How can you use the resulting derivative from carbonyl test to identify the specific carbonyl identity?
-recrystallise the precipitate and dry
-find the melting point
-compare to data book values of known derivatives
When you use Tollen’s reagent to distinguish between aldehydes and ketones, what happens to the organic reagent and the silver ions?
Organic reagent oxidises to carboxylic acid
Ag+ ion is reduced to Ag
silver mirror effect formed
Ag+(aq) + e- > Ag(s)
Explain why carboxylic acids are water soluble. What happens to the solubility of carboxylic acids as the carbon chain length increases.
Carboxylic acid group can H bond to water
Solubility decreases as chain length increases.
Alkyl chain is non-polar and so cannot H-bond to water
What are the advantages of using an acid anhydride over a carboxylic acid?
More reactive molecule, so can make unreactive alcohol groups, like those in phenol react.
Reaction goes to completion so better yield. However, water sensitive, so need anhydrous conditions
do aldehydes or carboxylic acids have lower boiling point?
aldehydes,
aldehydes do not form H bonds, instead permanent dipole-dipole forces.
H bonds are stronger, require more energy to overcome
how to test for aldehyde?
-create Tollens reagent (silver nitrate, one drop sodium hydroxide and ammonia solution brown ppt dissolves)
-warm tollens reagent and add aldehyde (few drops and stir)
aldehyde produces a silver mirror with tollens
reactions for testing of aldehyde
CH3CH2CHO +［O) > CH3CH2COOH
Ag(aq) + e- > Ag(s)
how to name esters:
start with alcohol group eg propyl
then acid part eg ethanoate
how could you distinguish carboxylic acids from other -OH containing compounds?
add NaHCO3
acids will produce sodium salt, water and CO2
acid anhydride+ alcohol>
carboxylic acid + ester
nucleophile
electron pair donor
why can acyl chlorides react with nucleophiles?
there is a lone pair on the N that can accept a proton to form a dative covalent bond. ammonia acts as a base.
what is 2,4-DNP used for
turns aldehydes and ketones to orange ppt
how to make 2,4-DNP
-filter to get impure 2,4-DNP derivative
-recrystallise impure derivative
-measure the melting point if purified derivative
-compare to known data values
what is the advantage of using ethanoyl chloride over ethanoic acid?
more reactie (use with phenols), go to completion, higher yield
