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Ch.11 - Reactions of Alcohols
Wade - Organic Chemistry 9th Edition
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Tutti i libri di testoWade 9th EditionCh.11 - Reactions of AlcoholsProblema 6a,b,c
Capitolo 11, Problema 6a,b,c

Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent.
(a) butan-1-ol → butanal, CH3CH2CH2CHO
(b) but-2-en-1-ol → but-2-enoic acid, CH3CH=CH–COOH
(c) butan-2-ol → butan-2-one, CH3COCH2CH3

Guida verificata passo dopo passo
1
Step 1: For part (a), converting butan-1-ol to butanal involves oxidation of a primary alcohol to an aldehyde. A chromium reagent such as PCC (Pyridinium Chlorochromate) can be used for this purpose as it selectively oxidizes primary alcohols to aldehydes without further oxidation to carboxylic acids. A chromium-free alternative is Dess-Martin periodinane, which also selectively oxidizes primary alcohols to aldehydes.
Step 2: For part (b), converting but-2-en-1-ol to but-2-enoic acid involves oxidation of a primary alcohol to a carboxylic acid while preserving the double bond. A chromium reagent such as Jones reagent (CrO3 in H2SO4) can be used for this purpose as it oxidizes primary alcohols to carboxylic acids. A chromium-free alternative is KMnO4 (potassium permanganate) under mild conditions, which can achieve the same transformation without affecting the double bond.
Step 3: For part (c), converting butan-2-ol to butan-2-one involves oxidation of a secondary alcohol to a ketone. A chromium reagent such as PCC or Jones reagent can be used for this purpose as both are effective in oxidizing secondary alcohols to ketones. A chromium-free alternative is the use of DMP (Dess-Martin periodinane) or Swern oxidation, which are mild and efficient methods for this transformation.
Step 4: When selecting reagents, consider the functional group sensitivity and the need to avoid over-oxidation or side reactions. Chromium reagents are strong oxidizers and may require careful handling, while chromium-free alternatives are often milder and more environmentally friendly.
Step 5: Ensure proper reaction conditions for each reagent. For example, PCC is typically used in dichloromethane (DCM) as a solvent, Jones reagent requires acidic aqueous conditions, and Dess-Martin periodinane is used in non-aqueous solvents like DCM. Adjust conditions based on the specific reagent chosen.

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Oxidation Reactions

Oxidation reactions involve the loss of electrons or an increase in oxidation state by a molecule. In organic chemistry, this often refers to the conversion of alcohols to aldehydes, ketones, or carboxylic acids. Understanding the specific conditions and reagents that facilitate these transformations is crucial for selecting appropriate methods for synthesis.
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Benzylic Oxidation

Chromium Reagents

Chromium reagents, such as chromium trioxide (CrO3) or Jones reagent (CrO3 in sulfuric acid), are commonly used in organic synthesis for the oxidation of alcohols. These reagents are effective but can be hazardous and environmentally unfriendly, making it important to consider alternatives in laboratory settings.
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Jones Reagent Mechanism

Chromium-Free Reagents

Chromium-free reagents, such as pyridinium chlorochromate (PCC) or the use of oxidizing agents like potassium permanganate (KMnO4) or sodium hypochlorite (NaOCl), provide safer and more environmentally friendly options for oxidation reactions. Understanding these alternatives is essential for synthesizing compounds while minimizing toxic waste and adhering to green chemistry principles.
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Jones Reagent Mechanism
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