Aldehydes and ketones ii oxidation and reduction synthesis
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Aldehydes and Ketones. II. Oxidation and Reduction; Synthesis. Chapter 17. Assignment for Chapter 17. Skip the following sections: Section 17.3 Sections 17.13 through 17.15 . Problem Assignment. In-Text Problems 17-1, 2, 3, 4 5 (NH 2 -NH 2 is misssing from the problem!!)

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Aldehydes and ketones ii oxidation and reduction synthesis l.jpg

Aldehydes and Ketones. II.Oxidation and Reduction;Synthesis

Chapter 17


Assignment for chapter 17 l.jpg
Assignment for Chapter 17

  • Skip the following sections:

  • Section 17.3

  • Sections 17.13 through 17.15


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Problem Assignment

  • In-Text Problems

    • 17-1, 2, 3, 4

    • 5 (NH2-NH2 is misssing from the problem!!)

    • 6 - 11 15, 17, 18

  • End-of-Chapter Problems

    • 1, 2, 3


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Oxidation and reduction -- an overview

  • Oxidation: add O or remove H2

  • Reduction: remove O or add H2

  • Oxidation numbers are relatively useless for carbon!



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Reactions of sodium borohydride

  • Aldehydes yield primary alcohols

  • Ketones yield secondary alcohols

  • Esters give no reaction!

  • Amides give no reaction!


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Keep water away from lithium aluminum hydride!

LiOH + Al(OH)

+ 4 H2

+ 4 H

O

LiAlH

4

2

3


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Reactions of lithium aluminum hydride

  • Aldehydes give primary alcohols

  • Ketones give secondary alcohols

  • Esters give primary alcohols from the

    carboxylic acid part of the ester

  • Amides give primary amines!!


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Sect. 17.2: Reduction of carbonyl groups with hydrogen

  • You really have to “pound” on carbonyl compounds to reduce them by using hydrogen under high pressure!

  • Aldehydes give primary alcohols

  • Ketones give secondary alcohols

  • Other carbonyl compounds, such as esters are virtually unreactive.


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Selective reduction of C=C and C=O bonds

  • Hydrogen/ Pt (low pressure): reduces C=C but not the C=O group

  • Sodium borohydride: reduces C=O but not the C=C group





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Sect. 17.7: Oxidations

NOTE: A dehydrogenationis also a form of oxidation!


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Oxidation: an overview

Mild oxidizers: CrO3 in pyridine

CrO3 in acetone

pyridinium chlorochromate (PCC)

Primary alcohols give aldehydes

Secondary alcohols give ketones

Strong oxidizers: K2Cr2O7 in acid

CrO3 in acid

KMnO4

Primary alcohols give carboxylic acids

Secondary alcohols give ketones






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Important!!

  • Sarrett reaction: Primary alcohols get oxidized to aldehydes

  • Aldehydes are not further oxidized to carboxylic acids



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Important!!

  • PCC reactions: Primary alcohols get oxidized to aldehydes

  • Aldehydes are not further oxidized to carboxylic acids


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Sect. 17.11: Silver and Copper oxidation of aldehydes

  • Tollens: oxidation with silver ion yields a carboxylic acid; Ag+ is reduced to Ago (silver mirror)

  • Benedict’s: oxidation with copper ion yields a carboxylic acid; Cu2+ is reduced to Cu+ (Cu2O)


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Sect. 17.12: Reducing and non-reducing sugars

  • Carbohydrates that have hemi acetal structures are in equilibrium with a “free” aldehyde ---- reducing sugars

  • Carbohydrates that are in the acetal form, do not have free aldehyde --- non-reducing

  • Reducing sugar =positive Tollens/Benedicts

  • Non-reducing sugar = negative tests







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Sect. 17.18: Ketone Synthesis using Organometallic Reagents

  • Acid chlorides give ketones with lithium dialkyl cuprates

  • Acid chlorides give ketones with Grignard reagents, but only at low temperatures