Alcohol

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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:

Types of alcohol.png

Nomenclature

Systematic names

Common names

Chemical Formula IUPAC Name Common Name
Monohydric alcohols
CH3OH Methanol Wood alcohol
C2H5OH Ethanol Alcohol
C3H7OH 2-propanol Rubbing alcohol
C4H9OH 1-Butanol Butanol
C5H11OH 1-Pentanol Amyl alcohol
C16H33OH Hexadecan-1-ol Cetyl alcohol
Polyhydric alcohols
C2H4(OH)2 Ethane-1,2-diol Ethylene glycol
C3H6(OH)2 Propane-1,2-diol Propylene glycol
C3H5(OH)3 Propane-1,2,3-triol Glycerol
C4H6(OH)4 Butane-1,2,3,4-tetraol Erythritol, Threitol
C5H7(OH)5 Pentane-1,2,3,4,5-pentol Xylitol
C6H8(OH)6 Hexane-1,2,3,4,5,6-hexol Mannitol, Sorbitol
C7H9(OH)7 Heptane-1,2,3,4,5,6,7-heptol Volemitol
Unsaturated aliphatic alcohols
C3H5OH Prop-2-ene-1-ol Allyl alcohol
C10H17OH 3,7-Dimethylocta-2,6-dien-1-ol Geraniol
C3H3OH Prop-2-in-1-ol Propargyl alcohol
Alicyclic alcohols
C6H6(OH)6 Cyclohexane-1,2,3,4,5,6-hexol Inositol
C10H19OH 2 - (2-propyl)-5-methyl-cyclohexane-1-ol Menthol

Physical and chemical properties

Applications

Preparation

Reactions

Oxidation

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.

Mechanism of oxidation of primary alcohols to carboxylic acids via aldehydes and aldehyde hydrates

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.

Esterification

The esterification is a reaction of an alcohol with an acid, the result is an ester.

More on this page.

Dehydration

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

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.

Nucleophilic substitution

Toxicity

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.

References

  1. http://en.wikipedia.org/wiki/Alcohol