Alcohol

Alcohols in Chemistry
Nomenclature of Alcohols Preparations of Alcohol Reactions with Alcohol

Alcohols in Chemistry


In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is CnH2n+1OH.












After the nature of the hydrocarbons radical (the radical connected to the –OH group), you can distinguish several types of alcohol:

- if the radical derives from a saturated hydrocarbon (acyclic or cyclic), the respective alcohol is a saturated alcohol (for example: ethanol CH3-CH2-OH).
- if the radical has a double bound, the respective alcohol is a unsaturated alcohol (for example: allelic alcohol CH2=CH-CH2OH).
- if the radical contains an aromatic nucleus, the respective alcohol is a aromatic alcohol (for example: benzilic alcohol C6H6-CH2OH).

There are three major subsets of alcohols: primary (1°), secondary (2°) and tertiary (3°), based upon the number of carbon atoms the C-OH group's carbon is bonded to.

Ethanol is a simple 'primary' alcohol. The simplest secondary alcohol is isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is tert-butyl alcohol (2-methylpropan-2-ol).

The alcohols containing 2 hydroxyl groups connected by different carbon atoms are called glycols, for example: CH2OH-CH2OH.


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Nomenclature of Alcohols

All alcohols contain the hydroxyl functional group, -O-H, attached to single bonded hydrocarbons (alkanes). Alcohol have the general formula R-OH where R represents any chain of carbon and hydrogen atoms.
The four most common alcohols are:









Alcohols use the same formats as alkanes. To name alcohols,

• Determine the parent chain. The parent chain must be the longest that includes the carbon holding the OH group.

• Number according to the end closest to the -OH group regardless of where alkyl substituents are.

• The format is as follows:

(location of branch)-(branch name)-(location of OH group)-(parent chain)

• Change the parent chain -e ending and replace it with an -ol.



Example:









Parent chain: Butane
-OH group location: 2
Substituents locations: 3-methyl
Alkane name: 3-methylbutane
Alcohol name: 3-methyl-2-butanol


Alchohols containing more than one hydroxyl group are also called polyalcohols. Polyalcohols are named similarly to alcohols, with the exception of the prefix di-, tri-, etc before the -ol ending.


The denomination of an alcohol must take into the consideration the position of the carbon atom (the one connected to the hydroxyl) and the existence of isomers. For example, taking into consideration the existence of 2 propanols, they are designated as 1-propanol and 2-propanol:

CH3-CH2-CH2OH (1-propanol)
CH3-CH(OH)-CH3 (2-propanol)



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Preparations of Alcohol

From Alkanes


CH4 + O2                         CH3-OH (methylic alcohol)



Water addition at alkenes (hydration)

General Reaction:

R-CH=CH2 + H2O                   R-CH-OH-CH3


Example:

CH3-CH2-CH2=CH2 + H2O                   CH3-CH2-CHOH-CH2


CH3-CH=CH-CH3 + H2O                     CH3-CHOH-CH2-CH3





From Aldehyde and Ketones


Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts like finely divided platinum, palladium, nickel and ruthenium.





This method is called catalytic hydrogenation.

From halogenated derivates

General Reaction

R-X + H2O                    R-OH + HX


Example:

CH3-CH2-Br + H2O                        CH3-CH2-OH + HBr


Cl-CH2-CHCl-CH2-Cl + 3H2O                       OH-CH2-CHOH-CH2-OH + 3HCl





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Reactions with Alcohol

Ssubstitution of H (the alcohols acidity)

General Reaction

R-OH + Na                    R-ONa (Natrium alcoxide) + H2


Attention! The alcohols do not react with NaOX, fenoxizi and carboxils.

Reaction with the Inorganic acids

General Reaction

R-OH + HX                    R-X + H2O

Example:

CH3-OH + HCl                     CH3-Cl + H2O

CH3-CH2-OH + HBr                      CH3-CH2-Br + H2



Reaction with Organic acids

R-OH + R'-COOH                       R'-C=O-OR + H2O

It is equilibrated and reversible reaction and ester is formed

Alcohol + Alcohol


R-OH + R'-OH                       R-O-R' + R'-O-R'

Examples:

CH3-OH + CH3-OH                       CH3-O-CH3 + H2O

CH3-CH2-OH + CH3-CH2-OH                   CH3-CH2-O-CH2-CH3 + H2O


The elimination reaction (Dehydration)


CH3-CH2-OH                      CH2=CH2 + H2O (ethane)




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