Home       About Us |  Contact Us |  Login  /


  

Alcohols

Alcohols

Background:


Alcohol is an every day term we use to refer to "ethanol", the intoxicating component found in beer, wine and spirits. However there is in fact an entire family of organic componds known as alcohols, characterized by the fact that they consist of one or more an "OH" groups attached to a hydrocarbon chain.

Alcohols share properties, such as the ability to form esters with organic acids and being more polar and less volotile than their hydrocarbon base molecules, but they differ widely from each other depending on their hydrocarbon frame work.

Some other commonly known alcohols include:
  • methanol - fuel and solvent;
  • iso-propanol - rubbing alcohol;
  • 1-propanol - break fluid;
  • ethelene glycol - car antifreeze;
  • propylene glycol - plumber's antifreeze.

Important Compounds and Derivatives:


Alcohols combust to form carbon dioxide and water. They can also revert to and alkene + water through a dehydration reaction.

Combustion

Alcohols can burn completely in air to leave behind only water and carbon dioxide.

2 C3H2-OH + 9 O2 --> 9 H2O + 8 CO2

Dehydration

Alcohols can be generated by the hydration of an alkene. The reverse reaction is also possible. An alkene can be generated by dehydrating an alcohol using a strong acid.
conc H2SO4
catalyst
C3H7-OH ---------> CH2=CH-CH3 + H2O

Oxidation

An alcohol can be oxidized using an oxidizing agent such as potassium dichromate, or potassium permanganate in order to create an aldehyde or a ketone, depending on the position of the OH group to be removed.

CH3-CH2-CH2-OH + O --> CH3-CH2-CH1=O + H2O

Laboratory Preparation:


Alcohols can be prepared in the lab through the addition reaction know as hydration of alkenes.

Hydration

This process describes the absorption of a water molecule by an alkene, by the opening up of the double carbon carbon bond to allow in the hydrogen and OH ions.

CH3-CH=CH2 + H2O → CH3-CHOH-CH3

The placement of the hydroxyl ion is governed by Markovnikov's Rule which states that the hydrogen ion will be placed on the carbon which had the most hydrogens prior to the reaction.

Industrial Preparation:


In addition to the hydration of alkenes described above, other methods other exist for producing specific types of alcohols.

Fermentation of Sugar

The traditional and widespread preparation of ethanol involves the frementation of sugar C6H12O6 by yeast in order to break sugar down into ethanol and carbon dioxide.

C6H12O6 --> 2 C2H5-OH + 2 CO2

Hydrogenation of Methane

A modern industrial method for the production of methanol is to combine carbon monoxide with hydrogen under pressure in the presence of a calalyst.

CO + 2 H2 --> CH3-OH

Naming Conventions:


Alcohol names can be derived by first naming the longest hydrocarbon chain which contains an OH group and then adding the suffix "ol" and adding then a numerical prefix identifying the number of the carbon on which the OH group is attached. Of course we number the carbon atoms starting from the end of the chain closest to the OH group.

Compound which have more than one OH group are called polyalcohols. They are identifed with the suffix "diol" for two OH groups, "triol" for three OH groups and so on. In their prefix we include the numbers of the carbons to which each one is attached.

Alcohols in which the OH group is attached to a carbon which in turn is attached to only one other carbon is known as a 1° alchohol. If attached to two other it is a 2° alchohol and if the attaching carbon is connected to three other carbons the alcohol is a 3° alcohol.

An alternative naming convention exists for alcohols in the IUPAC nomenclature where the OH molecule is refered to as "hydroxy" and the base name is that of the root hydrocarbon. For example 1-propanol would become: 1-hydroxypropane.

Bibliography:


Wikipedia article on alcohol
Article on the synthesis of alcohols
Article describes synthesis of aldehydes from alcohol
Perdue University - Discussion of Alcohols and Ethers

  A+ Study Secrets 

© 2008 Canada Connects - All rights reserved