PRPM112 LAB: EX 10

• ALDEHYDES AND KETONES


  • organic compounds both containing a carbonyl functional group - (C=O)
  • has two more bonds that may be occupied by hydrogen or alkyl or aryl substituents
• aldehyde


  if one R is hydrogen
• ketone


  If both R are neither H
• ALDEHYDES

  
• ALDEHYDES

  
• KETONES

  
• KETONES

  
• ALDEHYDES AND KETONES


  naturally occurring organic

  can be found in plants, animals, and even microorganisms
• CARBONYL GROUP


  • highly polarized group because of the greater electronegativity of the oxygen
  • susceptible to nucleophilic attack
• SYNTHESIS OF ALDEHYDES AND KETONES

  • synthesized in the laboratory through oxidation reaction of alcohols

  1. primary alcohols are oxidized to aldehydes
  2. secondary alcohols are oxidized to ketones
• TEST FOR CARBONYL GROUP

  1. 2,4-DNPH TEST
  2. SODIUM BISULFITE TEST
• 2,4-DNPH (BRADY’S) TEST

  • acetone

  1. clear orange solution

  • acetophenone

  1. yellow-orange precipitate

  • benzaldehyde

  1. orange precipitate

  • formaldehyde

  1. reddish-orange precipitate
• 2,4-DNPH (BRADY’S) TEST


  • function of test: detect the presence of carbonyl group
  • reagent: Brady’s reagent (2,4- dinitrophenylhydrazine in methanol);
  • named after Oscar Brady
  • positive result:

  1. yellow to orange precipitate for aldehydes
  2. red to orange precipitate for ketones
• condensation reaction; aldehyde reacts with 2,4-DNPH to forms an aldehyde 2,4- dinitrophenylhydrazone while ketone reacts with to form a ketone 2,4-dinitrophenylhydrazone
• SODIUM BISULFITE TEST

  • acetone

  1. white precipitate

  • acetaldehyde

  1. white precipitate
• SODIUM BISULFITE TEST


  • function of test: used to determine if a compound is an aldehyde or an aliphatic methyl ketone
  • Reagent: sodium bisulfite
  • positive result: white precipitate
• the aldehyde or the methyl ketone reacts with sodium bisulfite by breaking the pi bond of the carbonyl group through nucleophilic attack; the bisulfite ion then attaches to the original carbonyl group to form the bisulfite addition compound
• only methyl ketones will yield positive result
• TEST FOR ALDEHYDES


  SCHIFF’S TEST

  TOLLEN’S TEST

  FEHLING’S TEST
• SCHIFF’S TEST

  • acetone

  1. clear colorless solution

  • acetophenone

  1. clear colorless solution

  • benzaldehyde

  1. magenta-red solution

  • formaldehyde

  1. magenta-red solution
• SCHIFF’S TEST


  • function of test: used to differentiate aldehydes from ketones
  • reagent: Schiff’s reagent (sodium bisulfite with the organic dye pararosaniline hydrochloride);
  • named after Hugo Schiff
  • positive result: magenta red solution
• oxidation of aldehyde to carboxylic acid; reaction involved is the same as explained in the sodium bisulfite test
• TOLLENS’ TEST

  • acetone

  1. clear colorless solution

  • 5% glucose

  1. silver mirror precipitate

  • benzaldehyde

  1. turbid gray solution

  • formaldehyde

  1. silver mirror precipitate
• TOLLENS’ TEST


  • function of test: used to differentiate aldehydes from ketones
  • reagent: Tollens’ reagent (silver nitrate with sodium hydroxide and excess ammonium hydroxide to render solution colorless);
  • named after Bernhard Tollens
  • positive result: silver mirror precipitate
• oxidation of aldehyde to carboxylic acid; the ammoniacal silver nitrate is reduced to silver while producing the carboxylic acid-ammonium salt product

  • Tollens’ test can detect both aliphatic and aromatic aldehydes
• FEHLING’S TEST

  • acetone

  1. clear blue solution

  • 5% glucose

  1. brick red precipitate

  • benzaldehyde

  1. clear blue solution

  • formaldehyde

  1. brick red precipitate
• FEHLING’S TEST


  • function of test: used to differentiate aldehydes from ketones
  • reagent: Fehling’s reagent ;
  • named after Hermann von Fehling
  • positive result: brick red precipitate
• oxidation of aldehyde to carboxylic acid; aldehyde reduces the cupric ions in complex with tartrate ions to cuprous ions; forming cuprous oxide 

  • Fehling’s test is very specific to produce the positive result with an aliphatic aldehyde; aromatic aldehydes and ketones give a negative result with this test
• Fehling’s A 


  prepared by mixing concentrated sulfuric acid with aqueous solution of copper sulfate pentahydrate
• Fehling’s B 


  prepared by mixing sodium hydroxide with potassium tartrate
• TEST FOR METHYL KETONES

  SODIUM NITROPRUSSIDE TEST

  IODOFORM TEST
• SODIUM NITROPRUSSIDE TEST

  • acetone

  1. wine red solution

  • ethyl methyl ketone

  1. wine red solution
• SODIUM NITROPRUSSIDE TEST


  • function of test: identify the presence of an acetyl group (CH3C=O)
  • reagent: sodium nitroprusside
  • positive result: wine red solution
• sodium nitroprusside test is also used in clinical tests to detect the presence of acetone in urine
• IODOFORM TEST

  • acetone

  1. canary yellow precipitate

  • ethyl methyl ketone

  1. canary yellow precipitate

  • ethyl acetate

  1. clear colorless solution
• IODOFORM TEST


  • function of test: used to identify methyl ketones or secondary alcohols adjacent to a methyl group
  • reagent: Wagner’s reagent (iodine in potassium iodide) in sodium hydroxide
  • positive result: canary yellow precipitate
• TEST FOR SACCHARIDES


  MOLISCH’S TEST

  BIAL’S TEST
• MOLISCH’S TEST

  • 5% glucose

  1. purple ring at junction of two layers

  • 5% starch

  1. purple ring at junction of two layers

  • benzaldehyde

  1. dark red solution
• MOLISCH’S TEST


  • function of test: general test for saccharides
  • reagent: Molisch’s reagent (10% α-naphthol in 95% ethanol);
  • named after Hans Molisch
  • positive result: purple ring at junction of two layers
• Molisch reagent dehydrates pentoses to furfural derivatives and hexoses to 5-hydroxymethyl furfural derivatives; furfural compounds further react with α-naphthol producing a purple-colored product