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Trial Reports

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  1. 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

  2. Experiment 18 Reactions of Aldehydes and Ketones

  3. Introduction • Aldehydes and ketones are carbonyl compounds • Undergo similar types of reactions – addition, condensation and substitution reactions • Aldehydes more reactive then ketones

  4. 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

  5. Fehlings Test • Aldehydes oxidized to carboxylic acids • Ketones not oxidized • Precipitate due to formation of insoluble Cu+1 as Cu2O – indicates presence of aldehyde

  6. 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

  7. Nucleophilic Addition Reaction • Addition of semicarbazine/hydrazine reagent to the carbonyl compound results in semicarbazone/hydrazone formation • Imine functional group is formed

  8. Hydrazone formation

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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