17. Organic II (CARBONYLS)

Aldehydes Ketones Carboxylic acid

No hydrogen bonding - only permanent dipole - dipole forces

Becomes less soluble

[H]

Lithium Aluminium Hydride

Nucleophilic addition reaction Use Lithium Aluminium Hydride (LiALH4) in dry ether We use dry ether as LiAlH4 reacts violently with water 2[H]

Nucleophilic addition React ketone/ aldehyde with hydrogen cyanide (HCN) in an aqueous solution of potassium cyanide (KCN) –> This is a good way of increasing the carbon chain

2,4 Dinitrophenylhydrazine ( 2,4-DNPH or Brady’s reagent) - forms an orange precipitate (hyrazone)

1) Tollens reagent –> aldehydes give a silver mirror as the silver complex is reduced to Ag. Aldehyde can be oxidised, ketone can’t. 2) Acidified potassium dichromate + warm –> aldehydes are oxidised to carboxylic acid so colour change is orange to green. Ketones are not oxidised so stays orange. However, alcohols can also give a positive colour change so its best to do the 2,4 DNPH test first 3) Benedict’s or Fehling’s –> aldehydes give a brick red precipitate 4) Iodoform test - produces a yellow precipitate with any ketone with a CH3 group next to C=O bond and ethanal, AND secondary alcohols . This is a test for a CH3CO group AND CH3CH(OH)

CH3COCH3 + 3I2 + 4NaOH —> CHI3 + CH3COONa + 3NaI + 3H2O

1) Mix 2,4 DNPH and the carbonyl to form the hydrazone 2) Collect solid hydrazone through vacuum filtration 3) Recrystallise the solid hydrazone using the minimum volume of hot ethanol (This is to REMOVE IMPURITIES) Filter again using hot vacuum filtration and collect the filtrate this time. Cool solution. Filter again and collect solid 4) Leave crystals to dry in a watch glass 5) Determine the melting temperature 6) Compare value to known database of values to identify which carbonyl compound it is

LOWERS the MELTING point INCREASES BOILING point AND makes the range wider

1) Dissolved impure solid in minimum volume of appropriate hot solvent. This is to produce a saturated solution of product. The solvent is appropriate if it dissolves product when hot. 2) Carry out a hot filtration to remove insoluble impurities that as they do not dissolve in hot solvent. Collect filtrate. Filtrate contains product and soluble impurities in solution. 3) Cool solution to allow the pure solid to crystallize out of the solution. Soluble impurities remain in solution 4) Filter to separate soluble impurities from product - collect the solid residue 5) Dry the solid

Wash the crystals with a small amount of cold solvent (e.g. cold distilled water) to remove soluble impurities before drying.

1) put a small amount of the dry solid into a sealed capillary tube 2) Place capillary tube in oil with a thermometer attached 3) Heat slowly. Record temperature when solid has completely melted

2-hydroxypropanenitrile You must name it from the nitrile and count the longest chain from there. In the example above there are 3 carbons in the longest chain, including the nitrile. The OH is on the second carbon, so 2-hydroxy