1. Chapter 6 Alcohols and Ethers

2. Nomenclature of Alcohols
Examples
Common Names of simple alcohols are still often used and are approved by IUPAC
Chapter 4

3. Nomenclature Nomenclature of Ethers Common Names IUPAC Chapter 6
The groups attached to the oxygen are listed in alphabetical order
IUPAC
Ethers are named as having an alkoxyl substituent on the main chain
Chapter 6

4. Cyclic ethers can be named using the prefix oxa-
Three-membered ring ethers can be called oxiranes; Four-membered ring ethers can be called oxetanes
Chapter 6

5. Physical Properties of Alcohols and Ethers
Ether boiling points are roughly comparable to hydrocarbons of the same molecular weight
Molecules of ethers cannot hydrogen bond to each other
Alcohols have considerably higher boiling points
Molecules of alcohols hydrogen bond to each other
Both alcohols and ethers can hydrogen bond to water and have similar solubilities in water
Diethyl ether and 1-butanol have solubilites of about 8 g per 100 mL in water
Chapter 6

6. 1- Synthesis of Alcohols from Alkenes
Acid-Catalyzed Hydration of Alkenes
This is a reversible reaction with Markovnikov regioselectivity
Chapter 6

7. Reactions of Carbonyl Compounds with Nucleophiles
Carbonyl groups can undergo nucleophilic addition
The nucleophile adds to the d+ carbon
The p electrons shift to the oxygen
The carbon becomes sp3 hybridized and therefore tetrahedral
Hydride ions and carbanions are two examples of nucleophiles that react with the carbonyl carbon
Chapter 12

8. 2- Synthesis of Alcohols by Reduction of Carbonyl Compounds
A variety of carbonyl compounds can be reduced to alcohols
Carboxylic acids can be reduced to primary alcohols
These are difficult reductions and require the use of powerful reducing agents such as lithium aluminum hydride (LiAlH4 also abbreviated LAH)
Chapter 12

9. Esters are also reduced to primary alcohols
LAH or high pressure hydrogenation can accomplish this transformation
Aldehydes and ketones are reduced to 1o and 2o alcohols respectively
Aldehydes and ketones are reduced relatively easily; the mild reducing agent sodium borohydride (NaBH4) is typically used
LAH and hydrogenation with a metal catalyst can also be used
Chapter 12

10. Carboxylic acids and esters are considerably less reactive to reduction than aldehydes and ketones and require the use of LAH
Lithium aluminium hydride is very reactive with water and must be used in an anhydrous solvent such as ether
Sodium borohydride is considerably less reactive and can be used in solvents such as water or an alcohol
Chapter 12

11. 3- Synthesis of Alcohols from Grignard Reagents
Organometallic Compounds
Carbon-metal bonds vary widely in character from mostly covalent to mostly ionic depending on the metal
The greater the ionic character of the bond, the more reactive the compound
Organopotassium compounds react explosively with water and burst into flame when exposed to air
Chapter 12

12. Grignard Reagents
Grignard reagents are prepared by the reaction of organic halides with magnesium turnings
An ether solvent is used because it forms a complex with the Grignard reagent which stabilizes it
Chapter 12

13. 3- Synthesis of Alcohols from Grignard Reagents
Aldehydes and ketones react with Grignard reagents to yield different classes of alcohols depending on the starting carbonyl compound
Chapter 12

14. Chapter 12

15. Alcohols as Acids Alcohols have acidities similar to water
Sterically hindered alcohols such as tert-butyl alcohol are less acidic (have higher pKa values)
Why?: The conjugate base is not well solvated and so is not as stable
Alcohols are stronger acids than terminal alkynes and primary or secondary amines
An alkoxide can be prepared by the reaction of an alcohol with sodium or potassium metal
Chapter 6

16. Reactions of alcohols
Carbonyl groups and alcohols can be interconverted by oxidation and reduction reactions
Alcohols can be oxidized to aldehydes; aldehydes can be reduced to alcohols
Chapter 6

17. 1- Oxidation of Alcohols
Oxidation of Primary Alcohols to Aldehydes
A primary alcohol can be oxidized to an aldehyde or a carboxylic acid
The oxidation is difficult to stop at the aldehyde stage and usually proceeds to the carboxylic acid
A reagent which stops the oxidation at the aldehyde stage is pyridinium chlorochromate (PCC)
PCC is made from chromium trioxide under acidic conditions
It is used in organic solvents such as methylene chloride (CH2Cl2)
Chapter 12

18. Oxidation of Primary Alcohols to Carboxylic Acids
Potassium permanganate (KMnO4) is a typical reagent used for oxidation of a primary alcohol to a carboxylic acid
The reaction is generally carried out in aqueous solution; a brown precipitate of MnO2 indicates that oxidation has taken place
Oxidation of Secondary Alcohols to Ketones
Oxidation of a secondary alcohol stops at the ketone
Many oxidizing agents can be used, including chromic acid (H2CrO4) and Jones reagent (CrO3 in acetone)
Chapter 12

19. A Chemical Test for Primary and Secondary Alcohols
Chromium oxide in acid has a clear orange color which changes to greenish opaque if an oxidizable alcohol is present
Chapter 12

20. 2- Conversion of Alcohols into Alkyl Halides
Hydroxyl groups are poor leaving groups, and as such, are often converted to alkyl halides when a good leaving group is needed
Three general methods exist for conversion of alcohols to alkyl halides, depending on the classification of the alcohol and the halogen desired
Reaction can occur with phosphorus tribromide, thionyl chloride or hydrogen halides
Chapter 6

21. Oxidation-Reduction Reactions in Organic Chemistry
Reduction: increasing the hydrogen content or decreasing the oxygen content of an organic molecule
A general symbol for reduction is [H]
Oxidation: increasing the oxygen content or decreasing the hydrogen content of an organic molecule
A general symbol for oxidation is [O]
Oxidation can also be defined as a reaction that increases the content of any element more electronegative than carbon
Chapter 12

22. Alkyl Halides from the Reaction of Alcohols with Hydrogen Halides
The order of reactivity is as follows
Hydrogen halide HI > HBr > HCl > HF
Type of alcohol 3o > 2o > 1o < methyl
Mechanism of the Reaction of Alcohols with HX
SN1 mechanism for 3o, 2o, allylic and benzylic alcohols
These reactions are prone to carbocation rearrangements
In step 1 the hydroxyl is converted to a good leaving group
In step 2 the leaving group departs as a water molecule, leaving behind a carbocation
Chapter 6

23. Primary and methyl alcohols undergo substitution by an SN2 mechanism
In step 3 the halide, a good nucleophile, reacts with the carbocation
Primary and methyl alcohols undergo substitution by an SN2 mechanism
Primary and secondary chlorides can only be made with the assistance of a Lewis acid such as zinc chloride
Chapter 6

24. Alkyl Halides from the Reaction of Alcohols with PBr3 and SOCl2
These reagents only react with 1o and 2o alcohols in SN2 reactions
In each case the reagent converts the hydroxyl to an excellent leaving group
No rearrangements are seen
Reaction of phosphorous tribromide to give alkyl bromides
Reaction of thionyl chloride to give alkyl chlorides
Often an amine is added to react with HCl formed in the reaction
Chapter 6

25. Synthesis of Ethers Ethers by Intermolecular Dehydration of Alcohol
Primary alcohols can dehydrate to ethers
This reaction occurs at lower temperature than the competing dehydration to an alkene
This method generally does not work with secondary or tertiary alcohols because elimination competes strongly
Chapter 6

26. Williamson Ether Synthesis
This is a good route for synthesis of unsymmetrical ethers
The alkyl halide (or alkyl sulfonate) should be primary to avoid E2 reaction
Substitution is favored over elimination at lower temperatures
Chapter 6

27. Reactions of Ethers
Acyclic ethers are generally unreactive, except for cleavage by very strong acids to form the corresponding alkyl halides
Dialkyl ethers undergo SN2 reaction to form 2 equivalents of the alkyl bromide
Chapter 6