Chemistry: Acetaminophen (paracetamol) > Phenacetin

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Discussion Overview

The discussion revolves around the reaction mechanism involved in converting acetaminophen to phenacetin using different alkyl halides (Ethyl iodide vs. 2-iodopropane) and how this choice affects the reaction velocity. Participants explore the nature of nucleophilic substitution reactions, specifically whether they follow an SN1 or SN2 mechanism, and the implications of using primary versus secondary alkyl halides.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant questions how the stability of the reaction with NaOH affects the reaction velocity, suggesting it might remain the same.
  • Another participant seeks clarification on whether the nucleophilic substitution reaction is SN1 or SN2.
  • Some participants assert that the reaction with Ethyl iodide is SN1 due to its two-step mechanism, while questioning if the same applies to 2-iodopropane.
  • There is a discussion about the strength of 2-iodopropane as a nucleophile compared to Ethyl iodide.
  • One participant describes the process of neutralization of the hydroxyl group in acetaminophen, leading to a negative oxygen that acts as a nucleophile.
  • Another participant proposes that the reaction with Ethyl iodide might actually be SN2, prompting further exploration of the implications of using a secondary alkyl halide.
  • Concerns are raised about the rate of SN2 reactions being influenced by the substrate and electrophile, particularly regarding stereochemical repulsion with 2-iodopropane.
  • A later reply emphasizes that the rate of reaction depends on the substrate, leaving group, and attacking nucleophile, suggesting that the same leaving group and nucleophile in both cases should simplify the analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the reactions are SN1 or SN2, and there are differing opinions on the impact of using 2-iodopropane compared to Ethyl iodide. The discussion remains unresolved regarding the exact nature of the reaction mechanisms and their effects on reaction velocity.

Contextual Notes

Participants express uncertainty about the mechanisms involved and the factors affecting reaction rates, including the roles of nucleophiles and substrates. There are references to the need for further exploration of the topic in relevant texts.

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Homework Statement



To convert acetaminophen to phenacetin it was added NaOH in ethanol and then Ethyl iodide.
(Nucleophilic substitution). What would be the change in reaction velocity if insted of Ethyl iodide it was added 2-iodopropane (Isopropyl iodide)


Homework Equations





The Attempt at a Solution



what affects the velocity of the reaction? Is it the stability of the reaction of NaOH with Acetaminophen? If it is, then the velocity is the same although I'm not sure..
 
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By velocity, the question asks to compare the rate of the two reactions. What do you think which nucleophilic substitution reaction takes place here? SN1 or SN2?
 
SN1 in both, right? what do i Do next?
 
tsuwal said:
SN1 in both, right? what do i Do next?

Nope, think again.
 
with Ethyl iodide the reaction is SN1 because the reaction is given in two steps: first neutralization and then nucleophic substitution.
with 2-iodopropane i thought it was the same. is it as strong as Ethyl iodide as a nucleophyle?
 
tsuwal said:
with Ethyl iodide the reaction is SN1 because the reaction is given in two steps: first neutralization and then nucleophic substitution.
with 2-iodopropane i thought it was the same. is it as strong as Ethyl iodide as a nucleophyle?

Check the structure of acetaminophen. What happens when NaOH is added to it? (Hint: There is an acidic hydrogen)
 
the hydrogen of the hydroxyl group neutralizes the OH- from NaOH to form water. The oxygen in acetaminophen becomes negative and a good nuclephyle and attacks the iodine in Ethyl iodide or 2-iodopropane. Now that I think of, it is a SN2 reaction, at least with ethyl iodine. What next?
 
tsuwal said:
the hydrogen of the hydroxyl group neutralizes the OH- from NaOH to form water. The oxygen in acetaminophen becomes negative and a good nuclephyle and attacks the iodine in Ethyl iodide or 2-iodopropane. Now that I think of, it is a SN2 reaction, at least with ethyl iodine. What next?

Yes, you have that right. Now what happens when you use secondary alkyl halide instead of a primary one? Does the rate increase or decrease?
 
the rate of a SN2 reaction depends on how stong the nucleophyl is, right? does it depend on the substrate, eletrophyl? Well, if it depends on the eletrophyl, with 2-iodopropane there is more stereochemical repulsion, so, is it slower with 2-iodopropane?
 
  • #10
tsuwal said:
the rate of a SN2 reaction depends on how stong the nucleophyl is, right? does it depend on the substrate, eletrophyl? Well, if it depends on the eletrophyl, with 2-iodopropane there is more stereochemical repulsion, so, is it slower with 2-iodopropane?

Haven't you yet completed this topic? The rate depends on the substrate, the leaving group and the attacking nucleophile. It should be in your text about the rate dependence on the structure of substrate. We have the same leaving group and the attacking nucleophile in both the cases so we need not bother about that.
 

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