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Chapter 4: Problem 36

Write equations for the reaction of each compound with \(\mathrm{H}_{2} \mathrm{SO}_{4}\), a strong protic acid. (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SCH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{3}\) (f) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\)

Short Answer

Expert verified
Question: Write short equations for the reactions of the following compounds with H鈧係O鈧�: 1. CH鈧僌CH鈧� 2. CH鈧僀H鈧係CH鈧侰H鈧� 3. CH鈧僀H鈧侼HCH鈧侰H鈧� 4. CH鈧僀H鈧� 5. CH鈧僀OCH鈧� Answer: 1. CH鈧僌CH鈧� + H鈧係O鈧� 鈫� CH鈧僌CH鈧僅鈦� + HSO鈧勨伝 2. CH鈧僀H鈧係CH鈧侰H鈧� + H鈧係O鈧� 鈫� CH鈧僀H鈧係CH鈧侰H鈧僅鈦� + HSO鈧勨伝 3. CH鈧僀H鈧侼HCH鈧侰H鈧� + H鈧係O鈧� 鈫� CH鈧僀H鈧侼HCH鈧侰H鈧僅鈦� + HSO鈧勨伝 4. CH鈧僀H鈧� + H鈧係O鈧� 鈫� No reaction 5. CH鈧僀OCH鈧� + H鈧係O鈧� 鈫� CH鈧僀OCH鈧僅鈦� + HSO鈧勨伝

Step by step solution

01

Reaction of CH鈧僌CH鈧� with H鈧係O鈧�

The lone pair electrons on the oxygen atom in CH鈧僌CH鈧� will react with the acidic hydrogen atom of H鈧係O鈧�, forming a protonated ether, which is an intermediate. The reaction will be: \(\mathrm{CH}_{3} \mathrm{OCH}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CH}_{3} \mathrm{OCH}_{3}\mathrm{H}^{+} + \mathrm{HSO}_{4}^{-}\)
02

Reaction of CH鈧僀H鈧係CH鈧侰H鈧� with H鈧係O鈧�

The sulfur atom in CH鈧僀H鈧係CH鈧侰H鈧� has lone pair electrons and is nucleophilic. It will react with the acidic hydrogen atom of H鈧係O鈧�, forming an intermediate thioether. The reaction will be: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SCH}_{2} \mathrm{CH}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{SCH}_{2} \mathrm{CH}_{3}\mathrm{H}^{+} + \mathrm{HSO}_{4}^{-}\)
03

Reaction of CH鈧僀H鈧侼HCH鈧侰H鈧� with H鈧係O鈧�

The nitrogen atom in CH鈧僀H鈧侼HCH鈧侰H鈧� has lone pair electrons and is nucleophilic. It will react with the acidic hydrogen atom of H鈧係O鈧�, forming an intermediate amine. The reaction will be: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{3}\mathrm{H}^{+} + \mathrm{HSO}_{4}^{-}\)
04

Reaction of CH鈧僀H鈧� with H鈧係O鈧�

There are no nucleophilic atoms in \(\mathrm{CH}_{3} \mathrm{CH}_{3}\), so there will be no direct reaction with H鈧係O鈧�. Hence, the equation is: \(\mathrm{CH}_{3} \mathrm{CH}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow\) No reaction
05

Reaction of CH鈧僀OCH鈧� with H鈧係O鈧�

The oxygen atom in the carbonyl group of CH鈧僀OCH鈧� has lone pair electrons and is nucleophilic. It will react with the acidic hydrogen atom of H鈧係O鈧�, forming a protonated ketone, an intermediate. The reaction will be: \(\mathrm{CH}_{3} \mathrm{COCH}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CH}_{3} \mathrm{COCH}_{3}\mathrm{H}^{+} + \mathrm{HSO}_{4}^{-}\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Protonation of Ethers
Ethers are organic compounds where an oxygen atom is connected to two alkyl or aryl groups. When an ether, like dimethyl ether (\(\text{CH}_3\text{OCH}_3\)), is treated with sulfuric acid (\(\text{H}_2\text{SO}_4\)), the oxygen in the ether uses its lone pairs of electrons to attack the hydrogen ion provided by the acid. This results in the creation of a protonated ether, an intermediate species.

The reaction can be represented as:\[\text{CH}_3\text{OCH}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CH}_3\text{OCH}_3\text{H}^+ + \text{HSO}_4^- \]

Key points to remember:
  • Protonation increases the oxygen's positive charge, making it less stable and more reactive in subsequent reactions.
  • The protonated ether can readily undergo further reactions due to its positive charge.
Protonation of Thioethers
Thioethers resemble ethers in structure but contain a sulfur atom instead of an oxygen. In the case of the thioether \(\text{CH}_3\text{CH}_2\text{SCH}_2\text{CH}_3\), protonation occurs when the lone pair electrons on sulfur interact with a hydrogen ion from sulfuric acid. This is similar to the reaction with ethers, but due to sulfur's larger size and higher nucleophilicity, it reacts slightly differently.

The reaction can be outlined as:\[\text{CH}_3\text{CH}_2\text{SCH}_2\text{CH}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CH}_3\text{CH}_2\text{SCH}_2\text{CH}_3\text{H}^+ + \text{HSO}_4^-\]

Considerations:
  • Sulfur is more nucleophilic than oxygen, which can affect the rate and mechanism of reactions involving thioethers.
  • The resulting protonated thioether is also a reactive intermediate, capable of further chemical transformations.
Protonation of Amines
Amines contain a nitrogen atom, characterized by having lone pair electrons that can act as a nucleophile. When dimethylamine like compound \(\text{CH}_3\text{CH}_2\text{NHCH}_2\text{CH}_3\) meets sulfuric acid, the nitrogen atom can easily interact with the hydrogen ion of the acid.

The catalytic step of protonation is portrayed as:\[\text{CH}_3\text{CH}_2\text{NHCH}_2\text{CH}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CH}_3\text{CH}_2\text{NHCH}_2\text{CH}_3\text{H}^+ + \text{HSO}_4^-\]

Important notes:
  • The interaction renders the nitrogen's lone pairs unavailable, affecting the basicity of the amine.
  • The protonated amine is more likely to participate in various types of chemical reactions, such as nucleophilic substitution.
Protonation of Ketones
Ketones feature a carbonyl group made up of a carbon double-bonded to an oxygen. In acetone \(\text{CH}_3\text{COCH}_3\), the oxygen atom in the carbonyl group, having lone pairs, can serve as a nucleophile. When exposed to sulfuric acid, the ketone undergoes protonation at the oxygen locus.

This protonation process is depicted by:\[\text{CH}_3\text{COCH}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CH}_3\text{COCH}_3\text{H}^+ + \text{HSO}_4^-\]

What to keep in mind:
  • Protonation at the oxygen reduces the electron density at the carbonyl carbon, making it more electrophilic.
  • The protonated ketone can lead to different reactions, such as hydration or nucleophilic addition, due to its increased electrophilicity.

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Most popular questions from this chapter

If the \(\Delta G^{\circ}\) for a reaction is \(-4.5 \mathrm{kcal} / \mathrm{mol}\) at \(298 \mathrm{~K}\), what is the \(K_{\text {eq }}\) for this reaction? What is the change in entropy of this reaction if \(\Delta H^{\circ}=-3.2 \mathrm{kcal} / \mathrm{mol}\) ?

Predict the position of equilibrium, and calculate the equilibrium constant, \(K_{\text {cq, }}\), for each acid-base reaction. (a) \(\mathrm{CH}_{3} \mathrm{NH}_{2}+\mathrm{CH}_{3} \mathrm{COOH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{NH}_{3}^{+}+\mathrm{CH}_{3} \mathrm{COO}^{-}\) \(\begin{array}{ccc}\text { Methylamine Aceticacid } & \begin{array}{c}\text { Methylammonium } \\ \text { ion }\end{array} & \begin{array}{c}\text { Acetate } \\ \text { ion }\end{array}\end{array}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{NH}_{3} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{NH}_{2}{ }^{-}\) Ethoxide ion Ammonia Ethanol Amide ion

Write an equation for the reaction between each Lewis acid-base pair, showing electron flow by means of curved arrows. (a) \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{3} \mathrm{~B}+\mathrm{OH}^{-} \longrightarrow\) (b) \(\mathrm{CH}_{3} \mathrm{Cl}+\mathrm{AlCl}_{3} \longrightarrow\)

Following is a structural formula for the tert-butyl cation. (We discuss the formation, stability, and reactions of cations such as this one in Chapter 6 .) C[C+](C)C tert-Butyl cation (a carbocation) (a) Predict all \(\mathrm{C}-\mathrm{C}-\mathrm{C}\) bond angles in this cation. (b) What is the hybridization of the carbon bearing the positive charge? (c) Write a balanced equation to show its reaction as a Lewis acid with water. (d) Write a balanced equation to show its reaction as a Br酶nsted-Lowry acid with water.

Following is a structural formula for guanidine, the compound by which migratory birds excrete excess metabolic nitrogen. The hydrochloride salt of this compound is a white crystalline powder, freely soluble in water and ethanol. (a) Write a Lewis structure for guanidine showing all valence electrons. (b) Does proton transfer to guanidine occur preferentially to one of its \(-\mathrm{NH}_{2}\) groups \((\) cation A) or to its = NH group (cation B)? Explain.
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