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Alcohols are organic compounds which contain a hydroxyl functional group (-OH) bonded to a saturated carbon atom.
Types of Alcohols
Alcohols are divided according to the type of carbon atom to which the hydroxyl functional group is bonded:
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
- Tertiary alcohols are ones in which the carbon atom that is bonded to a hydroxyl functional group is bounded to three other carbon atom.
- Tertiary alcohols cannot be oxidized.
|Chemical Formula||IUPAC Name||Common Name|
|Unsaturated aliphatic alcohols|
|C10H19OH||2 - (2-propyl)-5-methyl-cyclohexane-1-ol||Menthol|
Physical and chemical properties
Primary alcohols can be oxidized either to aldehydes or to carboxylic acids, while the oxidation of secondary alcohols normally terminates at the ketone stage. Tertiary alcohols are resistant to oxidation.
The direct oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate by reaction with water before it can be further oxidized to the carboxylic acid.
Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include Collins reagent and Dess-Martin periodinane. The direct oxidation of primary alcohols to carboxylic acids can be carried out using potassium permanganate or the Jones reagent.
Dehydration is a process of separating all the water molecules from the alcohol. This is done with a dehydrating agent which is more hygroscopic than the alcohol, one such example are the alkali metals, dehydrated calcium chloride or anhydrous calcium oxide (quicklime) This can also be done with a 3A molecular sieve.
Deprotonation of alcohols by superbases or active metals gives salt-like compounds called alkoxides. Because most alcohols are weaker acids than water, alkoxides are typically hydrolyzed fully and irreversibly into the original alcohol and a hydroxide. Only certain alicyclic keto-alcohols such as rhodizonic acid are acidic enough to make the corresponding alkoxides stable in aqueous solution.
Methanol is poisonous, and ingestion may lead to blindness and death. Longer chain alcohols, such as ethanol, n-propanol and isopropanol, are much less toxic. Higher alcohols, such as butanol, pentanol, and their isomers also display low toxicity.
Except for ethylene glycol, most polyols have low toxicity.
Monohydric alcohols can be absorbed through skin.