Aldehydes and Ketones, 2,4-DNPH / Tollens reagent

Class Practical: Practical: 6 liquids: 4 of which are aldehydes and ketones and 2 of which are not, with test tubes and 2,4-DNPH solution + chemicals required to make Tollens’ – Mills and Boon book for procedure. 

Aldehydes and Ketones, 2,4-DNPH / Tollens reagent  CinC p.116 ex 2            

   HazCArd : 84, 6, 30, 40A, 41,  83, 85A, 85B

To make Tollens's Reagent : (Student will make they own Tollens's Reagent) 

• DRY Boiling/Test tubes, 

• Silver Nitrate 0.05M and 

• Ammonia 1.0 m (use 2.0M from A level cupboard)

• Sodium Hydroxide 1.0 M use 2.0M from A level cupboard)

• 2 X water bath set at 40-60 Degree C

• Filter paper

Items :

• 6 poly-stop bottle (with solid top to limit evaporation) labelled A-F using masking tape as chemical dissolve ink, 

A = Acetaldehyde, (Aldehydes) (2.4-DNPH Deep orange ppt with ketone and aldehyde)-(Tollens's reagent  mirror like appearance in Aldehyde)-(Fehling's solution (need to warm blue turn to orange ppt test for Aldehyde))-(Benedict from Blue to reddish brown colour in Aldehyde)

B/F = Ethanol, (Ethanol witch is either an  an Aldehydes or ketones)

C = Cyclohexanone, (Ketone) (2.4-DNPH Deep orange ppt with ketone and aldehyde) 

D = Acetone (Propanone), (Ketone) (2.4-DNPH Deep orange ppt with ketone and aldehyde) 

E = Propionaldehyde. (Aldehydes) (2.4-DNPH Deep orange ppt with ketone and aldehyde)-(Tollens's reagent  mirror like appearance in Aldehyde)-(Fehling's solution (need to warm blue turn to orange ppt test for Aldehyde))-(Benedict from Blue to reddish brown colour in Aldehyde)

F = Propionic Acid (Non Aldehydes and/or Ketone)

Other Aldehydes: Formaldehyde (methanal), Acetaldehyde (ethanal), Propionaldehyde (propanal), Butyraldehyde (butanal)Benzaldehyde (phenylmethanal)-

Other Ketones : propan-2-one, methyl ketone 

• Container to collect waste labelled "Used 2,4 DNPH  Aldenydes + Ketones"

• 2 X water bath set to 60oC (for Tollens 's Reagent)

• Test tubes,

• Bungs

• Some Spatula

• Either benedict solution (2X bottle from Bio prep.) or/and Fehling's  solution (add kettle and small beaker)

• pipettes

  • • • add 1or 2 bottle of 1.0M HCl to act as a catalyst

Making 2,4 DNPH solution 250ml from CinC p.113 : See bottom page

 2g of 2,4-DNPH(Cupboard 1 ),34ml of Methanol and 4mlH2SO42 Very slowly, produce a lot of heat

Class set use :

Formula (2,4-DNPH): (NO2)2C6H3NHNH2 Molar mass: 198.14 g mol-1

To prepare 25 cm3 of Brady’s reagent (scale quantities as required) Make 50 cc to see if it is enough

Wear splash-proof goggles. Wear gloves.

1. Add 0.5 g of 2,4-DNPH to ~ 12-13 cm3 of 85 % phosphoric(V) acid.

Do not use old phosphoric acid for the preparation of Brady’s reagent. Phosphoric acid undergoes polymerisation during long term storage leading to the build-up of solid at the bottom of the bottle.

2. Stir until the 2,4-DNPH has completely dissolved in the acid before moving on to Step 3. Dissolving may take 10-15 minutes.

3. Once the 2,4-DNPH has dissolved, make up to a total volume of ~ 25 cm3 with ethanol (or IDA). Stir to mix.

DANGER

*Methods using concentrated sulfuric acid and methanol are no longer recommended.

1. 10gram of 2,4-DNPH , 

2. Add 180ml of Methanol (could be put in a freezer to slow down the heat production when adding the Con. sulfuric acid

3. Add slowly 20ml of Conc.Sulfuric acid H2SO4  (lot of heat produce) 

4. = 250ml of 2,4-DNPH pour in a poly-stop bottle with pipette top

organic reactions at advance Level p.35

For 100ml : mix 2g DNPH with  100ml of Freeze methanol then add drop by drop 4ml Con. H2SO4

Non Aldehydes and/or Ketones : Carboxylic acid, Propionic acid, HCl ...

                        Container to collect waste                                                                                2X Ethanol witch is either an  an Aldehydes or ketone

Aldehydes                                                                                                                                       Ketones

Making 2,4 DNPH solution 250ml from CinC p.113 (2g 2,4-DNPH(Cupboard 1 ),4mlH2SO4,30ml Methanol = 34ml 2,4-DNPH solution)

10gram of 2,4-DNPH      Add slowly 20ml of Conc.Sulfuric acid H2SO4            add 180ml of Methanol Very slowly (lot of heat produce) =250ml of 2,4-DNPH pour in a poly-stop bottle with pipette top

for the kid to make Tollen's reagent  with Silver Nitrate 0.05Mol.  and Ammonia sol. 1.0Mol. Sodium Hydroxyde 1.0 M (CinC p.116 ex 2)

Water bath set up at 40°C

plastic bottle  for used solution                                                                                         Silver Nitrate 0.05M and Ammonia 1m