Lab IV
Aldehydes and ketones
Structures:
Aldehyades:
Formaldehydes
Benzaldehyde
Acetaldehydes
Chloral hydrate
Ketones:
Acetone
Acetophenone
I-Physical properties:

State:
Formaldehydes: liquid, mobile, true liquid.
Acetaldehydes:
Benzaldehyde:
Chloral hydrate: solid
Acetone:
Acetophenone :

Color:
Colorless except chloral hydrate which is white in color.

Odor
1.
2.
3.
4.
5.
6.

Formaldehyde :Pungent odor
Acetaldehyde:
Benzaldehyde: bitter almond odor.
Chloral hydrate:
Acetone : characteristic odor of ketones .
Acetophenone:
Ignition test :
1. Inflammability :
Formaldehyde & acetaldehyde :
Benzaldehyde :
Chloral hydrate : non inflammable,
Acetone & acetophenon :
2.
3.
4.
5.
Change in appearance :
Color imparted to the flame:
Odor of gas evolved :
Residue :
Comment :
II- tests for Acid- base properties (solubility or miscibility)


Formaldehyde, acetaldehyde, acetone and chloral hydrate: miscible in water.
Effect on L.P : NO CHANGE .
Benazaldehyde : immiscible in water ( oil droplet )
COMMENT :
III-Preliminary general chemical tests:
1. Soda lime :
on cold
Few granules soda lime+ few mg of chloral hydrate
chloroform odor ( sweaty odor)
2. 30 % NAOH:
formaldehyde
acetaldehyde
benzaldehyde
Chloral hydrate
Acetone
acetophenon
ON COLD
No reaction
Yellow resin
ON HOT
Cannizzaro’s reaction
No reaction
Chloroform odor
+oil droplet
No reaction
No reaction
Cannizzaro’s reaction
comment
Dilute it with water(aldol
condensation)
No reaction
No reaction
Cannizzaroe’s reaction: self oxidation reduction reaction
3. Fecl3 : no reaction either on cold or hot.
4. Conc. H2SO4:
Few mg. chloral hydrate + 2 drops conc. H2SO4 Shaking
separation and the formation of
Chloral layer
IV-Class general test:
1-2,4-Dinitrophenylhydrazine test ( brady’s reagent )
Reagent used:
1-Reagent A
2- Reagent B
aldehydes and ketone miscible in water
aldehydes and ketones immiscible in water.
Reaction :
1 ml of aldehyde or ketone + 3 drops of reagent A or B
shaking
Results:
Formaldehydes :
Acetaldehyde :
Chloral hydrate:
Acetone :
yellow ppt.
orange ppt.
no reaction.
orange ppt.
Benzaldehyde : orange ppt.
Acetophenone : orange ppt.
2- Silver mirror test ( tollens’ reagent test) or ammoniacal silver nitrate test :
Reaction :
1- 5 mls of silver nitrate + 1 drop 10% NAOH
Black ppt.
hydroxide(drop by drop ) shaking
clear solution .
add
dilute ammonium
2- add 1 ml of aldehyde or ketone + 1 ml of tollens’ reagent
heat on W.B. ( 1O\ )
Cool on the rack.
Results:
Formaldehyde: rapidly gives silver mirror.
Acetaldehyde: rapidly gives silver mirror.
Benzaldehyde: silver mirror after longer time on the water bath.
Chloral hydrate: silver mirror after longer time on the water bath.
Acetone acetophenone:
-v reaction.
3- Fehling reagent:
Reaction:
1-2 mls of fehling A solution + 2 mls of fehling B solution
fehling reagent ( blue color
2- 1 ml of aldehyde or keton + 1 ml of 10% NAOH + 1 ml of fehlling reagent
RESULTS:
Any chang of the blue color to red is a +v result.
Formaldehyde , acetaldehyde : rapidaly gives +v reslut.
Chloral hydrate, benzaldehyde : takes longer time to give +v results.
Aceton , acetophenon : -v reaction.
on W.B FOR 10\
v- specific tests :
1- Aldehydes:
a- formaldehyde & acetaldehyde :
Test
steps
Na-nitroprusside 1ml of aldehyde+3 drops of Na- nitroprusside +
1 ml of 10 % NaoH
acetaldehyde
Red color
formaldehyde
-v
Iodoform
1 ml of aldehyde (diluted with water) +1 ml
10% NaoH + excess I2 shake & wait 5\
Yellow resin
-v
Salicylic acid
2 drops of aldehyde + few mg of salicylic acid+2 -V
drops of conc. H2SO4 on the wall of T.T
Crimson red
color on the
wall of the T.T
b- Chloral hydrate:
1- conc. H2SO4.
2- Soda lime test.
3- 30% NaoH.
C- Benzaldehyde :
- auto-oxidation test :
on a watch glass add few drops Benzaldehyde leave it for 20\ crystals of benzoic acid.
2-Ketones:
TEST
Iodoform
steps
As before
Na- nitroprusside
metadinitrobenzen
As before
1 ml of keton+ few mg of
metadinitrobenzen + 1 ml 10% NaoH
Acetone
Yellow
precipitant
Red color
Violet color
rapidly
disappear
N.B: acetophenone should first be dissolved in ethanol or methanol.
Acetophenone
Yellow precipitant
Red color
Persistent Violet
color