Chapter 9. Organic Rxns 2--Alcohols, Ethers, Aldehydes, and Ketones

Alcohols, Ethers, and Related Compounds

Naming of alcohol involves adding -ol at ending. When -SH group is present, which is closely related to alcohol, it is called thiol. Ether is named

# of C	Name	Formula
Ethers
1	methanol
2	ethanol
3	propanol
4	butanol
5	pentanol
6	hexanol
Thiols (Alcohol equivalent of S)
1	methanethiol
2	ethanethiol
Ethers
2	dimethyl ether
4	diethyl ether
3	methylethyl ether
Sulfides (Ether equivalent of S)
2	dimethyl sulfide
4	diethylethyl sulfide

Example: Name the following compounds or write formula. a), b) 2-butanol, c) , and d) 2-butene-1-thiol

a) 3 Carbon chain. OH at #2 carbon. Thus, 2-propanol.

b) buta = 4, OH on #2 carbon.

c) 5 carbon chain. SH on 3rd carbon. Thus, 3-pentanethiol.

d) 2-butene (4 carbon, and double bond on the #2 carbon) and a thiol group. Hence:

The last molecule in the example above, is one of the three main component of the nasty smelling skuk's odor. The three compounds are:

The one on left is 2-butene-1-thiol, the center one is 3-methyl-butanethiol, and the one on right is 2-quinolinemethanethiol. The ring structure is the quinoline functional group.

Preparations

You can prepare alcohol by nucleophilic substitution reaction . For example,

When yellow colored Bordwell-Wellman reagent, K₂Cr₂O₇ (potassium dichromate), is added to alcohols, 1° and 2° alcohols into carboxylic acid and ketones, respectively. Then, the solution turned to green color, due to the Cr³⁺ ion. We used this reaction in the lab this week to test the presence of alcohols. The 1° alcohols are converted to aldehyde and subsequently converted to carboxylic acid. The 2° alcohols are converted to ketone, and the 3° alcohols have no reaction. These are summerized below:

	Yellow → Green fast rxn
	Yellow → Green slow rxn
	stays Yellow no rxn

Dehydration of Alcohols

Alkene can be synthesized by dehydration of alcohol with acid:

If the branching occurs at a carbon next to the carbon attached to OH group is available, then the hydrogen on that carbond is taken off:

Aldehydes and Ketones

Naming of aldehyde ends with -al, and for ketone ends with -one.

# of C	Name	structure
Aldehydes
1	methanal or formaldehyde
2	ethanal or acetaldehyde
3	propanal
5	2-methylpentanal
5	3-methylpentanal
Ketones
3	propanone
6	3-hexanone
8	2,4-dimethyl-3-hexanone

Oxidation of Aldehydes

Aldehyde can be oxydized to produce carboxylic acid using Bordwell-Wellman reagent, as we have seen above.

Then, you can even do this:

Also, Benedict's reagent, which contains Cu²⁺ can oxidize aldehyde to produce the conjugate base of carboxylic acid. Benedict's reagent leave the alcohol unchanged.

Reduction of Aldehydes and Ketones

We have seen that Pt used as a catalyst can hydrogenate alkenes and alkynes. In the presense of H₂, Pt can reduce aldehyde to alcohol, and ketone is reduced to alcohol.