How Can You Distinguish Between Propanone and Propanal?

Click For Summary

Discussion Overview

The discussion centers on distinguishing between propanone and propanal through chemical tests, outlining reactions of propanone with various reagents, and identifying isomers with the molecular formula C4H8O. The scope includes theoretical and practical aspects of organic chemistry reactions and mechanisms.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests using an ammoniacal solution of silver to distinguish between propanone and propanal, expecting propanone to show a white precipitate while propanal does not.
  • Another participant agrees with the use of Tollens reagent but notes that only aldehydes react with it, indicating a misunderstanding in the initial claim.
  • There is a discussion about the reaction of propanone with hydrogen cyanide, with one participant incorrectly stating that N-bonds will break, while another clarifies that CN- acts as a nucleophile attacking the carbonyl carbon to form a cyanohydrin.
  • Participants discuss the reduction of the cyanohydrin product by sodium borohydride, but there is uncertainty regarding the mechanism involved.
  • For the isomers of C4H8O, it is noted that all compounds give a positive test with 2,4-dinitrophenylhydrazine, but only aldehydes react with Tollens reagent, leading to a request for structural formulae of the isomers.

Areas of Agreement / Disagreement

Participants express differing views on the reactions and mechanisms involved, particularly regarding the use of Tollens reagent and the nature of the reactions with hydrogen cyanide. There is no consensus on the correct interpretation of the reactions or the mechanisms at play.

Contextual Notes

Some claims about the reactions and mechanisms lack clarity and may depend on specific definitions or assumptions about the reagents and products involved. The discussion does not resolve the uncertainties surrounding the mechanisms or the structural representations of the isomers.

nathaniell
Messages
8
Reaction score
0
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.
 
Last edited:
Physics news on Phys.org
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?
 

Similar threads

How do you study Organic Chemistry?
  • · Replies 10 ·
Replies
10
Views
9K