aldehydes and ketones Flashcards
Aldehyde FG
CHO - think of ariella. C=O is on the end of the chain with an H attached
Ketone FG
If the C=O is in the middle
aldehydes and ketones are known as
carbonyls
carbonyls and solubility
The smaller carbonyls are soluble in water because they can form hydrogen bonds with water. The longer the chain, the more insoluble
intermolecular forces
pure carbonyls do not make Hydrogen bonds but permanent dipole forces
what causes carbonyl reactions
the polar C=O bond, this bond is stronger than the alkene bond and is less prone to addition reactions
three main reactions
addition, reduction, oxidation
Oxidation reaction (primary)
primary alcohol–> aldehyde—> carboxylic acid
Oxidation reaction (secondary)
secondary alcohol—> ketone
Oxidation reaction (tertiary)
do not oxidise
If you want to get a carboxylic acid from a primary alcohol
potassium dichromate (VI) solution and dilute sulphuric acid. Heat under reflux
If you want to get an aldehyde from a primary alcohol
potassium dichromate (VI) solution and dilute sulphuric acid. distill
observation in oxidation of propanal
the orange dichromate ion (Cr2O72-) reduces to the green Cr 3+ ion
other ways of oxidising aldehydes
Tollen’s Reagent, Fehling’s solution
how to make tollen’s
formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+ .
Tollen’s Reagent (conditions)
heat gently
Tollen’s Reagent (observation)
with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
Fehling’s solution (conditions)
heat gently
Fehling’s solution (reaction)
aldehydes only are oxidised by Fehling’s Solution into a carboxylic acid and the copper ions are reduced to copper(I) oxide .
Fehling’s solution (observation)
Aldehydes :Blue Cu 2+ ions in solution change to a red precipitate of Cu2O. Ketones do not react.
what are aldehydes reduced to
primary alcohols
what are ketones reduced to
secondary alcohols
reagent and conditions for reducing aldehydes and ketones
NaBH4 or LiAlH4 at RTP
what is the mechanism for reducing carbonyls
nucleophilic addition
Propanal reduction equation
CH3CH2CHO + 2[H] = CH3CH2CH2OH
propanone reduction equation
CH3COCH3 + 2[H] = CH3CHOHCH3
how else can aldehydes and ketones be reduced
catalytic hydrogenation (H2 and Ni catalyst) high pressure
how to make a hydroxynitrile from carbonyls
NaCN or HCN and dilute H2SO4
RTP
nucleophilic addition
