How Can You Distinguish Between Propanone and Propanal?

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SUMMARY

The discussion focuses on distinguishing between propanone and propanal using chemical tests, specifically the Tollens' reagent and 2,4-dinitrophenylhydrazine (2,4-DNP). Propanone does not react with Tollens' reagent, while propanal does, producing a silver mirror. The reaction of propanone with hydrogen cyanide results in the formation of a cyanohydrin, facilitated by the nucleophilic attack on the carbonyl carbon. Additionally, the discussion addresses the structural isomers of C4H8O, highlighting that only aldehydes react with Tollens' reagent.

PREREQUISITES
  • Chemical properties of carbonyl compounds
  • Understanding of nucleophilic addition reactions
  • Knowledge of organic reaction mechanisms
  • Familiarity with reagent tests such as Tollens' and 2,4-DNP
NEXT STEPS
  • Study the mechanism of nucleophilic addition reactions in carbonyl chemistry
  • Learn about the properties and reactions of aldehydes and ketones
  • Research the synthesis and applications of cyanohydrins
  • Explore the structural isomerism of organic compounds with the formula C4H8O
USEFUL FOR

Chemistry students, organic chemists, and laboratory technicians involved in organic synthesis and analysis will benefit from this discussion.

nathaniell
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1)Give a chemical test that can be used to distinguis between separate samples of propanone and propanal. Give a suitable reagent for the test and describe what you would obsrve with propanone and with propanal.

2) Outline the reaction of propanone with the following reagents. Give the equation for the reaction, the conditions, and the name of the organic product.
(i)Hydrogen cyanide
(ii)dodium tetrahydridoborate(III) (sodium borohydride)
(iii)what type of mechanism is this
(iv) what feature of the carbonyl group makes this type of mechanism possible? Explain how this feature arises?

3)Three isomers A,B, and C have the molecular formula C4H8O. All three compouds give an orange precipitate with 2,4-dinitrophenylhydrazine reagent. B and C give a silver mirror when waremed in ammoniacal silver nitratesolution. Write the strcutural formulae of A,B and C.
 
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You need to show some work before we will help. What have you tried with this problem?
 
My idea to the separate samples of propanone and propanal is to use an ammoniacal solution of silve which propanone should show some change(a white precipitate) and propanal does not

While when propanone reacts with hydrogen cynaide the N-bonds will break and will be attached to propanone

While the last one I have had no ideas
 
Youre right on the tollens reagent test. Propanal will also give a red ppt with benedicts solution and felhings reagent (of Cu2O).

On the cyanide reaction, the N-bonds won't break, CN- will act as a nucleophile and attack the carbonyl carbon to form a cynohydrin.

The NaBH4 will reduce it to alcohol, but I don't know what mechanism makes it possible.

For the last one, if they give red ppt with 2,4-DNP, then they have a hydroxy group (OH). If they react with tollens reagent (ammonical silver nitrate), then they are aldehydes.
 
nathaniell said:
My idea to the separate samples of propanone and propanal is to use an ammoniacal solution of silve which propanone should show some change(a white precipitate) and propanal does not

While when propanone reacts with hydrogen cynaide the N-bonds will break and will be attached to propanone

While the last one I have had no ideas

You have that backwards. Only aldehydes react with the Tollens reagent.
 
nathaniell said:
...While when propanone reacts with hydrogen cynaide the N-bonds will break and will be attached to propanone

While the last one I have had no ideas

What is name of the product of cyanide reacting with a ketone?

The last question only distinguishes the aldehydes from the ketones. All will react with 2,4-DNP but only an aldehyde(s) can react with the Tollen's reagent. Obviously there are two isomers of aldehydes with the empirical formula C4H8O. Can you draw the two isomers?
 

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