CHEMICAL PROPERTIES

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CHEMICAL PROPERTIES
VIDEO 1
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Objective

• To explain the chemical properties with reference
  to these reactions
• a) oxidation with KMnO4, K2Cr2O7,Tollens,
  Fehling, Benedict and Schiff reagents to
  differentiate between aldehydes and ketones.
• b) reduction to alcohol using LiAlH4,NaBH4 and
  catalytic hydrogenation.

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CHEMICAL PROPERTIES

• Oxidation
• Reduction
• Nucleophilic addition reaction
• Condensation
• Haloform reaction

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1. OXIDATION

• Aldehydes are easy to oxidize.
• Strong oxidizing agents such as potassium
  permanganate, potassium dichromate, readily
  oxidize aldehydes and they are also oxidized by
  such mild oxidizing agents as silver oxide.

VIDEO 2
VIDEO 3
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EXAMPLE

O
ll CH3(CH2)4-C-H hexanal
H
K2Cr2O7
O
ll CH3(CH2)4-C-OH hexanoic acid
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a) TOLLENS TEST

• Tollen reagent is use to differentiate aldehydes
  and ketones.
• Tollen reagent is prepared by mixing aqueous
  silver nitrate with aqueous ammonia.
• The reagent contains the diamminosilver ion,
  Ag(NH3)2.
• Although this ion is a very weak oxidizing
  agent, it oxidizes aldehydes to carboxylate
  anions.

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• As it does this, silver is reduced from the 1
  oxidation state to metallic silver.
• If the rate of reaction is slow and the walls of
  the vessel are clean, metallic silver deposits on
  the walls of the test tube as a mirror.
• If not, it deposits as a grey to black
  precipitate.
• Tollens reagent gives a negative result with
  all ketones except a-hydroxy ketones.

VIDEO 4
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O ll R-C-H 2Ag(NH3)2 OH-
2Ag? RCOO- 2NH4 2NH3
Silver mirror
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silver mirror
Example
silver mirror
silver mirror
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b) FEHLING TEST

• Fehlings solution consists of Cu(II) ion, as a
  complex ion in a basic solution.
• Fehlings solution also can be used to
  distinguish aliphatic aldehyde and aromatic
  aldehyde.

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• It oxidizes aldehydes to carboxylate ions as the
  Cu2, which forms a brick-red precipitated, Cu2O.
• Fehlings solution has the characteristic blue
  colour of Cu2 which fades as the red
  precipitated of Cu2O forms.

VIDEO 5
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RCHO Cu2
Fehlings solution (blue)
RCOO- 2Cu2O? 3H2O
Copper (I) oxide (brick red precipitate)
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c) BENEDICT TEST

• For Benedict test, citrate complex are used.

VIDEO 6
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d) SCHIFFS REAGENT

• Aldehyde reacts with Schiffs reagent giving a
  pink colourisation.
• This shows a positive test for aldehyde with
  Schiffs reagent.
• But do not shows positive test with ketone.

VIDEO 7