Objectivesy To be able to observe and know the reaction of

aldehydes and ketones to Oxidation, Tollen s reagent, Fehling s test, Bisulfite additon, Phenylhydrazone derivative, and iodoform test.

Introductiony Reactions of aldehydes and ketones may be grouped

into: y 1. oxidation reduction of carbonyl group y 2. additon of the carbonyl group y 3. condensation and polymerization reactions

Draw the structure of the following compounds:y Formaldehyde

Acetaldehyde

Acetone

Benzaldehyde

Acetophenone

In a table form, use the compounds in number 1 and write the reagents used in each test, the probable carbonyl compounds postive to these reagents and the expected results.

TEST

REAGENTS

CARBONYL EXPECTED COMPOUNDS (+) RESULT TO TESTFormaldehyde Acetaldehyde Benzaldehyde Observed silver mirror

TOLLEN S REAGENT AgNO3 (doesn t react with NaOH ketones) NH4OH

FEHLING S TEST (sucrose doesn t react) BISULFIDE ADDITION

Fehlings A and B

Formaldehyde Aldehyde Benzaldehyde Acetone Formaldehyde Acetaldehyde Acetone Acetophenone Formaldehyde Acetaldehyde Benzaldehyde Acetone Acetophenone

Brick red precipitare Formation of Precipitate Formation of Precipitate (yellow or red)

NaHSO3 alcohol

PHENYLHYDRAZ Phenylhydrazine ONE DERIVATIVE H20 Glacial acetic acid

IODOFORM TEST KI soln

Yellow Precipitate

Draw the structure of glucose. What functional group present in the glucose molecule is indicated by Fehling s and Tollen s test?

Glucose

Write the equation for the following:y Air oxidation of benzaldehyde to benzoic acid y Tollen s reagent with benzaldehyde y N-heptaldehyde with Fehling s reagent y Acetone with bisulfite reagent

y A.) y C6H5 CHO + O2 C6 H5COOH y B.) y C6H5CHO +2Ag(NH3)2OH 2Ag(s) + RCOONH4 + 2Ag + 3NH3 +H2O y C. CH3CH2CH2CH2CH2CH2CH2CHO + 2Cu2+ RCOOH

+ Cu2O(s) D. RCHO + NaHSO3 RCH(OH)(SO2Na)

1.Oxidation Reactiony Procedure: y Put one drop of acetone on a watch glass.Note any

changes and record the observation.y Put a small drop of benzaldehyde on a watch glass

and spread it around on the glass in a thin film. Watch white solid appear mixed in with the oil.

Results:y Acetone: Evaporated y Benzaldehyde: Formation of colorless crystals

Discussion:y Aldehydes are easily to oxidized to yield carboxylic acids, RCHO to

RCO2H, but ketones are unreactive toward oxidation. This reactivity difference is a consequence of structure: aldehydes have CHO proton that can be removed during oxidation, but ketones do not.

+ O2

2. Tollen s testy Clean four test tubes thouroughly y 4ml of5% Silver Nitrate + 2 Drops of 5% NaOH y Brownigsh Precipiate will Form(Ag2O) y Dissolve precipitate by drops of Ammoniun

Hyrdoxide y Divide Tollen s reagent to 5 test tubes equally y Use 3 drops of compound being tested

y If no precipitate or mirror appears, heat the tubes

gently in a warm water bath for 5-10 minutes.

Results

ResultsAcetaldehyde Benzaldehyde Acetone -Silver Mirror Formed w/out heating Formation of white Globules Dark Silvler Mirror formed after heating (Longest time) Acetophenone Glucose Brownish preciptate fromed Silver Mirror formed after heating

Discussiony Mild oxidizing Tollen s Reagent are easily reduced by

aldehydes to silver mirror. Aromatic Aldehydes reduce Tollen s. Ketones do not reduce either of the two reagents. y RCHO + 2Ag(NH3)2OH --> RCOONH4 + 2Ag + 3NH3 H2O

3. Fehling s testProcedure:y Fehling s solution A + Fehling s solution B to four test

tubesAdd 2 drops of acetaldehyde, benzaldehyde, acetone and acetophenone.

ResultsAcetaldehyde Benzaldehyde Acteone Acetophenone

Green No change No change No change solution Red precipitate

y Precipitate is due to formation of insoluble Cu+1 as

Cu2O indicates the presence of aldehyde

y Precipitate is due to formation of insoluble Cu+1 as Cu2O indicates the presence of aldehyde.

Fehlings Test

Aldehydes oxidized to carboxylic acids Ketones not oxidized Precipitate due to formation of insoluble Cu+1 as Cu2O indicates presence of aldehydeO

O

+R H

2Cu2+ +

H 2OR OH

+

Cu2O +

2H+

4 .Bisulfite Addition Producty 2ml of saturated NaHSO3 + 0.5 ml alcohol y Filter off any precipitate then add 0.5 ml of samples.

Shake vigorously y Place tube in a freezing mixture Observe any change in color and appearance y Place in freezing mixture

Results

ResultsFormaldehyde Clear Solution Benzaldehyde 2 Layers formed Yellowish Layer on Top White Layer below Acetone Clear Solution with Crystalline White precipitate at the bottom Acetophenone White Murky Solution

Discussiony Aldehydes and Methyl Ketones give solid addition

products with NaHSO3. The addition compounds may be reconverted to the original carbonyl compound by treatment with acid. The reaction may therefore be used to separate carbonyl compounds from mixtures with other substances.

5. Phenylhydrazoney Procedure:

y To 1 ml of phenylhyrdazine add 2ml water and 1ml

glacial acetic acid. Mix well. y Add 0.5ml of the sample. Stopper tube tightly. y Shake contents vigorously for 2-3 minutes y Allow to stand with occasional stirring for 10 min.

Results:Formaldehyde orange solution yellowish solution Formation of yellow precipitate

Benzaldehyde

Acetone

Acetophenone

orange solution cream orange solution Formation of white precipitate Warm

2 layers are formed: Brownish red on top and clear at the bottom Warm

orange solution brownish orange solution Light orange precipitate are formed Warm

For a closer look..

Discussiony Addition of hydrazine reagent to the carbonyl

compound results in hydrazone formationy Imine functional group is formed

For ketones: With hydrazine,

The product is a "hydrazone" with phenylhydrazine,

the product is a "phenylhydrazone".

What happened:

The reaction is known as a condensation reaction. A condensation reaction is

one in which two molecules join together with the loss of a small molecule in the process. In this case, that small molecule is water.

In

terms of mechanisms, this is a nucleophilic additionelimination reaction. The 2,4-dinitrophenylhydrazine first adds across the carbon-oxygen double bond (the addition stage) to give an intermediate compound which then loses a molecule of water (the elimination stage).

6. Iodoform testy 3ml of 10% KI solution each to four test tubes.

Add 2 drops of the sample to each test tube. Add 3ml of 5% NaClO soultion Heat in water bath

ResultsAcetaldehyde Golden yellow solution Benzaldehyde Yellow solution Acetone Colorless solution with yellow precipitate Acetophenone Yellow orange layer on top Yellow precipitate formed

Discussiony Formation of solid iodoform (yellow precipitate)

indicates a positive test. RCOCH3 + 3I2 + 4OH- = RCOO- + CHI3 + 3I- + 3H2O Acetone and acetophenone formed yellow precipitate indicating a positive test.

Questions:y 1. Acetaldehyde and ethanol gives a positive iodoform test.

Structure: Acetaldehyde O

Ethanol O

y y y y

CH3-C-H H-C-C-OH 2. Which of the following compounds would give a positive iodoform test? a.CH3COCH2CH3 - YES b.CH3OCH2CH2CH3 -NO c.CH3CH2CH3CHOHCH3 YES

One should have CH3C=O in the compund to be positive in a iodoform test.

y 3. Explain how you could use the simple laboratory test perfomed in

this experiment to distinguish between: y a. 2-pentanone and 3-pentanone Performing the Iodoform test. 2-pentatone will have a positive result in an iodoform test but 3 pentatone will not. This is because of the methyl ketone present in 2-pentanone.y b. benzaldehyde and acetophenone

Performing the Fehling s test. Benzaldehyde will be oxidized and the Acetophenone doesn t. Precipitate due to formation of insoluble Cu+1 as Cu2O indicates presence of aldehyde.y c. acetaldehyde and propionaldehydey Performing the Iodoform test. Acetaldehyde will be positive and

propionaldehyde will be negative.