Animated Clipping of Phenols |
3D Pictures of Different Types of Phenols |
Phenols
Phenol — also known as carbolic acid — is
an aromatic organic compound with the formula C6H5OH. It is a white crystalline
solid that is volatile. The molecule consists of a phenyl group (-C6H5) bonded
to a hydroxyl group (-OH). It is mildly acidic, but requires careful handling
due to its propensity to cause burns.
Through phenols you understand combinations which contain one or
more hydroxyl groups directly connected to the benzoic nucleus. Phenols can be
similar to tertiary alcohols through the fact that they also contain the
hydroxyl group connected to a carbon atom (which is not bound to a hydrogen
atom).
After the number of hydroxyl groups in the molecule, you can
distinguish:
- phenols with a single hydroxyl group, meaning mono hydroxyl
phenols
- phenols with more than one hydroxyl groups in the molecule,
meaning poly hydroxyl phenols
Mono hydroxyl phenols have not isomers because they are produced
by de mono substitution of the benzoic nucleus. Containing more than one
hydroxyl groups bound in different positions to the aromatic nucleus, the poly
hydroxyl phenols exist under the form of isomers. The denomination of phenols
is based on the fact that they are considered the results of the substitution
of the aromatic hydrocarbons. Properly said, C6H5-OH is
called hydroxybenzene.
Phenols 3D Structures |
Structure and nomenclature
Hydroxybenzene, C6H5-OH, is normally called
phenol and is the simplest mono hydroxyl phenol. His homologue is
hydroxytoluene, (CH3)C6H4OH, at which you can
distinguish 3 isomers, after the relative position of the substitutes at the
aromatic nucleus: o-cresol, m-cresol and p-cresol.
Phenols are, normally, solid substances (at the usual temperature), with a pervading and unpleasant smell. Phenols are a little soluble in water, |
Physical properties
Phenols are, normally, solid substances (at the usual
temperature), with a pervading and unpleasant smell. Phenols are a little
soluble in water, but completely soluble in organic solvents.
Phenols |
Obtaining methods
1. Alkaline melting method
Ar-OH + H2SO4 ----> Ar-SO3H
(sulfonic acid)-----> Ar-SO3Na + H2O ------> Na2SO3
+ Ar-OH (phenol)
2. The cumin procedure
Benzene + CH2=CH-CH3---->
Cumin + O2 ------------>
Cumin hydro peroxide -------> Ar-OH + acetone
Preparation of Phenols |
Chemical reactions
1. The reaction with
metals and bases
Ar-OH + Na ----->Ar-ONa(sodium phenoxide) + H2O
Ar-OH + NaOH-------> Ar-ONa + H2O
Ar-ONa + R-X ----> Ar-OR (mix ether) + NaX
2. Substitutions reactions
(at the nucleus)(-OH is a first grade substitute)
Substitutions reactions |
3. Hydrogenation
Ar-OH + 3H2 ------>Ar-OFeCl2 + HCl
4. The identification of
phenols (FeCl3)
Ar-OH + FeCl3------>Ar-OFeCl2 + HCl
- Phenol + FeCl3 violet
- Cresol + FeCl3 blue
- Hydro quinine + FeCl3 blue
- Alfa-naphthol +FeCl3 green
- Beta-naphthol + FeCl3 green
Reaction of Phenols |
5. Phenols oxidation - at
the oxidation, the phenols react different than the alcohols.
Phenols oxidation |
Resonance structures of
phenol
Notice that three of the four contributing structures possess a
positive charge on the oxygen atom of the molecule. Thus, the true hybrid
structure must possess a partial positive charge. Because oxygen is an
electronegative element, the electrons in the oxygen-hydrogen bond orbital are
attracted to the oxygen atom, resulting in a partially positive hydrogen.
Loss of a hydrogen ion to a base creates a phenoxide ion that is
resonance stabilized.Notice that upon removal of the hydroxy hydrogen by a
base, the phenoxide anion results. This anion is resonance stabilized by
delocalization of an electron pair throughout the molecule, as shown by the
contributing structures
Use
» Phenol - plastic masses, medicine industry, coloring industry
and perfumes
» Cresols - plastic masses, explosive industry
» Naphthols - coloring industry
» Hydro quinine - photographic technique, coloring industry
Uses of Phenols |
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