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Ch.9 - Alkynes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.9 - AlkynesProblem 23c
Chapter 9, Problem 23c

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO4 and (2) warm basic KMnO4, then dilute acid.
(c) hex-3-yne

Verified step by step guidance
1
Step 1: Understand the reaction conditions. Neutral KMnO4 (dilute, neutral potassium permanganate) is a mild oxidizing agent that typically adds hydroxyl groups across double or triple bonds, resulting in diols. Warm, basic KMnO4 followed by acidification is a stronger oxidizing agent that cleaves double or triple bonds, producing carboxylic acids or ketones depending on the substituents attached to the carbons involved in the bond.
Step 2: Analyze the structure of hex-3-yne. Hex-3-yne is an alkyne with a triple bond between carbons 3 and 4 in a six-carbon chain. The structure can be written as CH3-CH2-C≡C-CH2-CH3.
Step 3: Predict the product with dilute, neutral KMnO4. Neutral KMnO4 will add hydroxyl groups across the triple bond, converting it into a diol. The triple bond will first be oxidized to a double bond, and then hydroxyl groups (-OH) will be added to each carbon of the former triple bond, resulting in a vicinal diol (a compound with two hydroxyl groups on adjacent carbons).
Step 4: Predict the product with warm, basic KMnO4 followed by acidification. Under these conditions, the triple bond in hex-3-yne will be cleaved completely. Each carbon of the triple bond will be oxidized to a carboxylic acid group (-COOH). Since the triple bond is symmetrically located in the middle of the chain, the products will be two molecules of propanoic acid (CH3-CH2-COOH).
Step 5: Summarize the results. For dilute, neutral KMnO4, the product is a vicinal diol. For warm, basic KMnO4 followed by acidification, the product is two molecules of propanoic acid. Ensure you understand the difference in reactivity between the mild and strong oxidizing conditions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Alkyne Reactivity

Alkynes, characterized by a carbon-carbon triple bond, undergo various reactions due to their high reactivity. In the presence of oxidizing agents like KMnO4, alkynes can be converted into carbonyl compounds or carboxylic acids, depending on the reaction conditions. Understanding the structure and reactivity of alkynes is crucial for predicting the products of their reactions.
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Alkyne Hydration

Oxidation with KMnO4

Potassium permanganate (KMnO4) is a strong oxidizing agent used in organic chemistry to oxidize alkenes and alkynes. In dilute, neutral conditions, KMnO4 typically leads to syn-dihydroxylation, while warm basic KMnO4 can cleave the triple bond, resulting in the formation of carboxylic acids. The conditions of the reaction significantly influence the outcome, making it essential to consider them when predicting products.
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Acidic Workup

An acidic workup, often involving dilute acid, is a common step following oxidation reactions to neutralize any remaining reagents and stabilize the products. In the case of KMnO4 oxidation, this step can help convert intermediate products into their more stable forms, such as converting alkoxide ions into alcohols or carboxylic acids. Understanding the role of the acidic workup is vital for accurately determining the final products of the reaction.
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Related Practice
Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO4 and (2) warm basic KMnO4, then dilute acid.

(e) cyclodecyne

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Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO4 and (2) warm basic KMnO4, then dilute acid.

(a) hex-1-yne

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Textbook Question

Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamyl groups. Disiamylborane is prepared by the reaction of BH3·THF with an alkene.

a. Draw the structural formulas of the reagents and the products in the preparation of disiamylborane.

b. Explain why the reaction in part (a) goes only as far as the dialkylborane. Why is Sia3B not formed?

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Textbook Question

Oxidative cleavages can help to determine the positions of the triple bonds in alkynes.

(a) An unknown alkyne undergoes oxidative cleavage to give adipic acid and two equivalents of acetic acid. Propose a structure for the alkyne.

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Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO4 and (2) warm basic KMnO4, then dilute acid.

(d) 2-methylhex-3-yne

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Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO4 and (2) warm basic KMnO4, then dilute acid.

(b) hex-2-yne

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