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Reactions of Alcohols

Reactions of Alcohols. Alcohols can be converted into many other functional groups, including alkanes by reduction alkenes dehydration alkyl halides substitution aldehydes or ketones carboxylic acids esters ethers. by oxidation. Reactions of Alcohols. Oxidation: loss of electrons

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Reactions of Alcohols

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  1. Reactions of Alcohols • Alcohols can be converted into many other functional groups, including • alkanes • by reduction • alkenes • dehydration • alkyl halides • substitution • aldehydes or ketones • carboxylic acids • esters • ethers by oxidation

  2. Reactions of Alcohols • Oxidation: • loss of electrons • increase of oxidation number • addition of O or O2 • loss of H2 • addition of X2 (halogens) • Oxidation reactions: • increase the number of oxygens bonded to a carbon • increase the number of bonds between carbon and oxygen Most important definitions for organic compounds

  3. Reactions of Alcohols • Reduction: • gain of electrons • decrease in oxidation number • addition of H2 (or H-) • loss of O or O2 • loss of X2 • Reduction reactions: • decrease the number of oxygens bonded to a carbon • decrease the number of bonds between carbon and oxygen Most important definitions for organic compounds.

  4. Reactions of Alcohols Example: Classify the following reactions as an oxidation or reduction.

  5. Reactions of Alcohols • Primary and secondary alcohols are easily oxidized by a variety of oxidizing agents. • Substances that cause another to be oxidized • Some of the common oxidizing agents for organic compounds include: • chromium reagents • PCC (pyridinium chlorochromate) • KMnO4 • HNO3 • NaOCl

  6. Reactions of Alcohols • Oxidation of 1o Alcohols • Depending on the oxidizing agent used, primary alcohols can be oxidized to either aldehydesor carboxylic acids • The aldehyde that forms initially is easily oxidized to the carboxylic acid by many reagents

  7. Reactions of Alcohols • Oxidation of 1o Alcohols to Aldehydes • The following reagents convert a primary alcohol to the aldehyde without further oxidation. • Pyridinium chlorochromate (PCC) • Swern’s oxidation • DMP

  8. Reactions of Alcohols • Pyridinium chlorochromate (PCC) is used to oxidize a 1o alcohol to the aldehyde • Also oxidizes 2o alcohol to ketone (discussed later) +

  9. Reactions of Alcohols Swern Oxidation is used to convert 1o ROH’s to aldehydes (or 2o ROH to ketones) Conditions: Dimethyl sulfoxide Oxalyl chloride Et3N CH2Cl2 (solvent) -60oC

  10. Reactions of Alcohols • Dess-Martin Periodinane (DMP)can be used to oxidize a 1o ROH to an aldehyde (or 2o ROH to ketone) DMP =

  11. Reactions of Alcohols • Examples:

  12. Reactions of Alcohols • Oxidation of 1o Alcohols to Carboxylic Acids • Common Reagents: • Chromic acid reagent • Na2Cr2O7/H2SO4 or K2Cr2O7/H2SO4 • CrO3 • NaOCl (aq) or or

  13. Reactions of Alcohols • Examples:

  14. Reactions of Alcohols • Oxidation of 2o Alcohols • 2o alcohols are converted to ketones • The oxidizing agents that are used to oxidize primary alcohols can also be used to oxidize a secondary alcohol to a ketone: • Chromic acid reagent • CrO3 • PCC • Swern oxidation • DMP

  15. Reactions of Alcohols • Examples:

  16. Reactions of Alcohols Examples: Predict the major product.

  17. Reactions of Alcohols • Other oxidizing agents can also be used to oxidize alcohols: • KMnO4 (aq), OH- • cold HNO3 • Tertiary alcohols cannot be oxidized easily. • No hydrogen present on carbinol carbon • Oxidation would require breaking C-C bond • severe conditions required Must be carefully controlled because they can also cleave C-C bonds.

  18. H2SO4 D Reactions of Alcohols • Dehydration of Alcohols • removal of water, forming an alkenes • equilibrium process • drive reaction to completion by removing alkene as formed (LeChatelier’s Principle)

  19. Reactions of Alcohols • Typical reaction conditions • acid catalyst • conc. H2SO4 • conc. H3PO4 • heat • Saytzeff’s product • Rearrangements occur if a more stable carbonium ion can be formed.

  20. Reactions of Alcohols Mechanism of Dehydration (E1) • Step 1: Protonation of the hydroxyl group (fast) • Step 2: Ionization (RDS) +

  21. Reactions of Alcohols • Step 3:Deprotonation to form alkene

  22. Reactions of Alcohols Example: Predict the major product formed in the following reactions.

  23. Reactions of Alcohols • Williamson Ether Synthesis • SN2 reaction between an alkoxide ion and an alkyl halide to form an ether. CH3CH2O- Na+ + CH3I CH3CH2OCH3 • Alkyl halide must be primary or methyl.

  24. Reactions of Alcohols • Williamson Ether Synthesis Mechanism

  25. Reactions of Alcohols Example: Give the major product for the following reactions.

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