Solving H2/Pd/C Reduction for #5 & #6 Questions

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    Pd Reduction
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Discussion Overview

The discussion revolves around the chemical reactions involved in solving specific problems related to the reduction of compounds using H2/Pd/C, particularly focusing on the effects of this reduction on ketal and ester groups. Participants explore the implications of these reactions in a multi-step synthesis process.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • One participant questions whether the addition of H2/Pd/C will affect the ketal group during the reduction process, expressing uncertainty about the steps required to complete the exercise.
  • Another participant asserts that esters and acyclic aliphatic ketals are generally non-reactive to Pd/C hydrogenation unless specific conditions are met, such as using activated esters or high pressure and temperature.
  • There is a suggestion that multiple methods exist for deprotecting ketals/acetonides, with a caution about the potential formation of water during cyclization reactions.
  • A participant raises concerns about the reversibility of transesterification reactions and seeks clarification on how to ensure the formation of a cyclic product without excess reactants.
  • Discussion includes the use of a Dean-Stark apparatus for removing water during the reaction process, with some participants questioning the feasibility of achieving this in a single step.
  • Another participant expresses a lack of lab experience but seeks feedback on their proposed reaction setup involving Dean-Stark for Fischer esterification.

Areas of Agreement / Disagreement

Participants express differing views on the reactivity of esters and ketals under hydrogenation conditions, with no consensus reached on the best approach for the synthesis steps discussed. The discussion remains unresolved regarding the optimal method for achieving the desired reactions.

Contextual Notes

Participants mention limitations related to the conditions required for reactions, such as the need for activated esters or specific temperatures and pressures, as well as the challenges posed by water formation in certain steps.

duchuy
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Homework Statement
Find the mechanism
Relevant Equations
x
Hi,
I'm trying to solve the number 5 and 6. Now I'm wondering what happens when I add H2/Pd/C on the 4th (after the question 4) molecule. I know that it will reduce pi bonds to sigma bonds, but will it affect the cetal group? Because if it does't I'm not quite sure that I'll be able to do the exercice with the steps given. My solution :
After adding Hd/Pd/C :
1) H+/H20, I will form 2 alcohol molecules (with the ester group) and acetone
2)Saponification : NaOH : Here I'm turning ester to carboxylate
3Intramolecular esterification : H+/H20 : I have to reacidify my environement in order to perform the esterification.

This would take 3 steps, while I only have step to do this (if H2/pd/C doesn't interact with the ketal group.
And if H2/Pd/C does give me my alcohol, it would also take me 2 extra steps to form my lactone.
Please help me find the solution for this.

By the way, what are the groups that H2 reduce?
I know that they reduce alcyne, alcene, cetone, aldehyde, ... the rest google is giving me mixed answers.
So what about : Nitrile, imine, carboxylic acid, ester, RCOCl, and acid anhydride?

Thank you so so much for your help!
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Unless you have an activated ester, or use high pressure and temperature, consider esters non-reactive to Pd/C hydrogenation. Acyclic aliphatic ketals are also non-reactive to Pd/C hydrogenation.

There is more than one way to deprotect ketals/acetonides. Remember if we have a carboxylic acid in 5 the cyclization reaction will produce a molecule of water…. and we don’t want water in this step. Think in terms of trans-esterification.
 
Last edited:
chemisttree said:
Unless you have an activated ester, or use high pressure and temperature, consider esters non-reactive to Pd/C hydrogenation. Acyclic aliphatic ketals are also non-reactive to Pd/C hydrogenation.

There is more than one way to deprotect ketals/acetonides. Remember if we have a carboxylic acid in 5 the cyclization reaction will produce a molecule of water…. and we don’t want water in this step. Think in terms of trans-esterification.
chemisttree said:
Unless you have an activated ester, or use high pressure and temperature, consider esters non-reactive to Pd/C hydrogenation. Acyclic aliphatic ketals are also non-reactive to Pd/C hydrogenation.

There is more than one way to deprotect ketals/acetonides. Remember if we have a carboxylic acid in 5 the cyclization reaction will produce a molecule of water…. and we don’t want water in this step. Think in terms of trans-esterification.

Ok I see, but from what I see from writing the reaction, is that if I were to do transesterification to from 5 to 6 in acidic conditions, that would be a totally reversible reaction and how could I ensure the formation of the cycle? Since I can't use an excess of reactants right? Unless I remove the alcohol at the end?
But if I were to do saponification in order to do Fischer's esterification, I could easily remove water at the end and ensure the formation of the cycle by using a Deanstark or may be ZnCl2 no?
 
Dean-Stark in a single step?
 
chemisttree said:
Dean-Stark in a single step?
I would make my reaction in a Deanstark for the final fischer esterification? I honestly don't know, I'm just doing chemistry on paper I really don't have much lab experience. But what do you think about my proposition?
 
Why I wrote, “Dean stark in a single step?” …
You want aqueous acid to deprotect the ketal and then turn around and do an internal transesterification in the absence of water… in one step.
 
chemisttree said:
Why I wrote, “Dean stark in a single step?” …
You want aqueous acid to deprotect the ketal and then turn around and do an internal transesterification in the absence of water… in one step.
Oooh ok I see thank you so so much you're absolutely amazing
 

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