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Experimental Reports. Today is the final practical Get dry weights for % yield, melting points by next week All reports must be handed up to your demonstrators no later than one week from today – otherwise marks will be lost. Experiment 18. Reactions of Aldehydes and Ketones. Introduction.

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Experimental reports l.jpg
Experimental Reports

  • Today is the final practical

  • Get dry weights for % yield, melting points by next week

  • All reports must be handed up to your demonstrators no later than one week from today – otherwise marks will be lost


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Experiment 18

Reactions of Aldehydes and Ketones


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Introduction

  • Aldehydes and ketones are carbonyl compounds

  • Undergo similar types of reactions – addition, condensation and substitution reactions

  • Aldehydes more reactive then ketones


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Introduction

  • Aldehydes can be oxidized, ketones can not be oxidized

  • Fehlings test uses this principle to distiguish between the two types of compound

Accompanied by formation of a red precipitate


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Fehlings Test

  • Aldehydes oxidized to carboxylic acids

  • Ketones not oxidized

  • Precipitate due to formation of insoluble Cu+1 as Cu2O – indicates presence of aldehyde


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Derivative Formation

  • One derivative of each class of compound will be prepared

  • A semicarbazone derivative of a ketone will be formed

  • A phenylhydrazone derivative of an aldehyde will be formed


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Nucleophilic Addition Reaction

  • Addition of semicarbazine/hydrazine reagent to the carbonyl compound results in semicarbazone/hydrazone formation

  • Imine functional group is formed



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Experimental – Fehlings Test

  • To 6 drops of Fehlings solution in a test tube add 3 drops of propanal

  • Heat in the water bath for 2 mins

  • Red precipitate indicated oxidation of aldehyde

  • Repeat with butanone – record observations & comment on the results


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Experimental – Semicarbazone Formation

  • Dissolve 2.0 g of semicarbazide hydrochloride and 2.0 g of sodium acetate in 10 ml water

  • Add 2 ml butanone and heat for 15 min on the water bath

  • Cool to room temperature & collect the crude crystals


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Experimental – Semicarbazone Formation

  • Wash with water

  • Recrystallise from aqueous ethanol

  • Allow to dry on the Hirsch funnel

  • Record the yield in g, the melting point, and % yield of the dry crystals

  • Include a mechanism for the reaction in your experimental report


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Experimental – hydrazone formation

  • To 1.0 ml of propanal add 10 ml ethanol and 25 ml of the 2,4-dinitrophenylhydrazine solution

  • Heat for 5 mins and allow to cool

  • Isolate the crystals on the Hirsch funnel

  • Allow to dry, record the yield in g, the melting point and % yield of crystals


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Report

  • Introduction

  • Observsations & conclusions from Fehlings tests & derivative formation

  • % yield & mp of semicarbazone

  • Mechanism of semicarbazone formation

  • % yield & mp of phenylhydrazone

  • Discussion of all results and reactions


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Experimental Reports

  • Today is the final practical

  • Get dry weights for % yield, melting points by next week

  • All reports must be handed up to your demonstrators no later than one week from today – otherwise marks will be lost


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