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Preparation &Reactions of alcohols

Preparation &Reactions of alcohols. Lec.9. Preparation of alcohols:. Reactions of Alcohols. 1-Reaction of Alcohols with Active Metals

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Preparation &Reactions of alcohols

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  1. Preparation &Reactions of alcohols Lec.9

  2. Preparation of alcohols:

  3. Reactions of Alcohols 1-Reaction of Alcohols with Active Metals Alcohols react with Li, Na, K, and other active metals to liberate hydrogen and form metalalkoxides. In this oxidation/reduction reaction, Na is oxidized to Na+and H+ is reduced to H2.

  4. 2-Dehydration of Alcohols to Alkenes • Alcohols can be dehydrated by heating them with a strong acid. • It is an elimination reaction. • Examples:

  5. Example: • The alkene with the most substituted double bond usually predominates. • By “most substituted,” we mean the alkene with the greatest number of alkyl groups on the doubly bonded carbons. • Thus, in the example shown, the major product is • 2-methyl-2-butene.

  6. 3-The Reaction of Alcohols with Hydrogen Halides • Alcohols react with hydrogen halides (HCl, HBr, and HI) to give alkyl halides (chlorides, bromides, and iodides). • It is a substitution reaction • Tertiary alcohols undergo substitution reactions with hydrogen halides faster than do secondary alcohols because tertiary carbocations are easier to form than secondary carbocations

  7. Thus, the reaction of a tertiary alcohol with a hydrogen halide • proceeds readily at room temperature, whereas the reaction of a secondary alcohol with a hydrogen halide would have to be heated to have the reaction occur at the same rate

  8. 4-Oxidation of alcohols • Alcohols with at least one hydrogen attached to the hydroxyl-bearing carbon can be oxidized to carbonyl compounds. • Primary alcohols give aldehydes, which may be further oxidized to carboxylic acids. • Secondary alcohols give ketones

  9. Important Note: • Tertiary alcohols, having no hydrogen atom on the hydroxyl-bearing carbon, do not undergo this type of oxidation. Examples: for 1st alcohol, the type of oxidizing agent control the product

  10. Note : • A solution of chromic acid in aqueous sulfuric acid • is known as the Jones reagent. • Dissolving CrO3 in aqueous HCl and adding pyridine to precipitate • pyridinium chlorochromate (PCC) as a solid.

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