CARBONYLS KETONES (ONE) ALDEHYDES (al)

PHYSICAL PROPERTIES Boiling Point: Higher than alkanes due to permanent dipole dipole interactions, but less than alcohols (no H-bonds IMF between molecules ) Water Solubility Not water soluble due to inability to form H-bonds with H 2 O State at RT Probably liquids (see BP)

Preparation What reagents are needed? Alcohols (Primary for aldehydes, secondary for ketones) and acidified Potassium Dichromate Conditions? Need sulphuric acid and distil off product as formed to remove the chance of further oxidation if aldehydes are being made Possible impurities Carboxylic acid or unreacted alcohol for aldehyde synthesis, only unreacted alcohol for ketone synthesis as ketones cannot be further oxidised How detected? IR (OH bond seen between cm -1 )

Expected Chemistry Nucleophile or electrophile? Addition or substitution? Mechanism (Click here for mechanism)Click here for mechanism Nucleophile (δ+ on C as O more electronegative) Addition (C accepts electron pair and C=O breaks and nucleophile adds on)

Expected Chemistry: Redox reactions Oxidation? Reduction? Yes BOTH TO CORRESPONDING ALCOHOL- CLICK HERE FOR MECHANISMCLICK HERE FOR MECHANISM Ketones: NO there is no spare H to remove off functional group Carbon Aldehydes: YES there is a spare H to remove off functional group Carbon CLICK HERE FOR CONDITIONSCLICK HERE FOR CONDITIONS

Identification of Carbonyl 2,4 nitrophenylhydrazone (Bradys reagent) Product with butan-2-one Orange crystals Product with propanone Orange crystals Product with Ethanal Orange crystals The MP of these crystals are dependant on the carbonyl used The following can be used to identify a carbonyl Add Bradys reagent to carbonyl Filter of crystals formed Recrystallise the crystals (to purify) by dissolving in minimum quantity of hot solvent Filter of crystals that form when the solution is cooled Dry the crystals in a warm oven Determine the MP Check with book values ALL Carbonyls give orange crystals with Bradys reagent

Chemical detection How can I prove it is a carbonyl? CLICK HERE FOR ANSWER CLICK HERE FOR ANSWER How can I prove it is an aldehyde? CLICK HERE FOR ANSWER CLICK HERE FOR ANSWER

Nucleophilic Addition RCHO + 2[H] RCH 2 OH Conditions / Reagents Room temperature and pressure RCOR + 2[H] RCH(OH)R Reduction of Carbonyls to form the corresponding alcohol Aqueous NaBH 4 or LiAlH 4

Nucleophilic Addition Mechanism Reduction of propanone NaBH 4 or LiAlH 4 is the source of H - CH 3 COCH 3 + 2[H] CH 3 CH(OH)CH 3 CH 3 C O C O H C O H H Propan-2-ol ++ -- H OH OH H

Nucleophilic Addition Mechanism Reduction of propanal NaBH 4 or LiAlH 4 is the source of H - CH 3 COCH 3 + 2[H] CH 3 CH(OH)CH 3 CH 3 H C O H C O H H C O H H Propan-1-ol ++ -- H OH OH H

Oxidation of Aldehydes Reagents UsedObservations made if aldehyde present Organic Product Tollins Reagent (Ammoniacal silver nitrate) Made by adding a few drops of sodium hydroxide to aqueous silver nitrate and then dissolving the Ag 2 O formed in Ammonia Silver Mirror formsCorresponding Carboxylic acid (eg Ethanal  Ethanoic acid) Acidified Potassium Dichromate (Made by adding sulphuric acid to solution of potassium dichromate) Solution turns from orange to green Corresponding Carboxylic acid (eg Ethanal  Ethanoic acid) NB KETONES DO NOT UNDERGO THESE REACTIONS AS THEY CANNOT BE OXIDISED