Potassium permanganate, potassium dichromate – one of the excellent tools of analysis
Md. Istiqur Rahman
Dept. of Pharmacy
Daffodil International University
Pharmaceutical analysis may be defined as a process or
sequences of processes to identify and/or quantify a
substance or drug, the components of a
pharmaceutical solution or mixture or the
determination of the structures of chemical
compounds used in the formulation of pharmaceutical
Titration, also known as titrimetry, is a common
laboratory method of quantitative chemical
analysis that is used to determine the unknown
concentration of an identified analyte.
Because volume measurements play a key role in
titration, it is also known as volumetric analysis.
A reagent, called the titrant or titrator is prepared
as a standard solution. A known concentration and
volume of titrant reacts with a solution of analyte
or titrand to determine concentration.
Redox titrations are based on a reduction-oxidation
reaction between an oxidizing agent and a reducing agent.
A potentiometer or a redox indicator is usually used to
determine the endpoint of the titration, as when one of the
constituents is the oxidizing agent potassium dichromate.
The color change of the solution from orange to green is
not definite; therefore an indicator such as sodium
diphenylamine is used.
Some redox titrations do not require an indicator, due to
the intense color of the constituents. For
instance, in permanganometry a slight faint persisting pink
color signals the endpoint of the titration because of the
color of the excess oxidizing agent potassium
An oxidizing agent (also called
an oxidant, oxidizer or oxidiser) can be defined as a
substance that removes electrons from another
reactant in a redox chemical reaction. The oxidizing
agent is "reduced" by taking electrons onto itself and
the reactant is "oxidized" by having its electrons taken
away. Oxygen is the prime example of an oxidizing
agent, but it is only one among many –
1. KMnO4 (potassium permanganate)
2. K2Cr2O7 (potassium dichromate)
3. O3 (ozone)
4. F2 (fluorine)
Potassium permanganate is an inorganic chemical
compound with the formula KMnO4. It is
a salt consisting of K+ and MnO4
− ions. Formerly known
as permanganate of potash or Condy's crystals, it is a
strong oxidizing agent. It dissolves in water to give
intensely purple solutions.
Potassium permanganate can be used to quantitatively
determine the total oxidizable organic material in an
aqueous sample. The value determined is known as the
permanganate value. In analytical chemistry, a
standardized aqueous solution of KMnO4 is sometimes
used as an oxidizing titrant for redox titrations
For the standardization of KMnO4 solutions, reduction
by oxalic is often used.
compared to other
Because it contains Manganese in its highest
oxidation state of +7.
This compound is a strong oxidizing agent
because elements become more electronegative
as the oxidation states of their atoms increase.
The permanganate in potassium permanganate
has the anion MnO4- that is the reason for its
strong oxidizing properties.
KMnO4, being a very strong oxidizing agent, can
react with a variety of groups.
Potassium permanganate oxidizes
aldehydes to carboxylic acids, such as the
conversion of n-heptanal to heptanoic acid:
5 C6H13CHO + 2 KMnO4 + 3 H2SO4 → 5
C6H13COOH + 3 H2O + K2SO4 + 2 MnSO4
Even an alkyl group (with a benzylic
hydrogen) on an aromatic ring is
oxidized, e.g. toluene to benzoic acid.
5 C6H5CH3 + 6 KMnO4 + 9 H2SO4 → 5
C6H5COOH + 14 H2O + 2 K2SO4 + 6 MnSO4
Potassium dichromate, K2Cr2O7, is a
common inorganic chemical reagent, most
commonly used as an oxidizing agent in
various laboratory and industrial
It is a crystalline ionic solid with a very
bright, red-orange color. It is also known
as potassium bichromate; bichromate of
In organic chemistry, potassium dichromate is a mild
oxidizer compared with potassium permanganate.
It is used to oxidize alcohols. It converts primary
alcohols into aldehydes, or into carboxylic acids if
heated under reflux.
In contrast, with permanganate, carboxylic acids are
the sole products. Secondary alcohols are converted
into ketones — no further oxidation is possible.
For example, menthone may be prepared by
oxidation of menthol with acidified dichromate.
Tertiary alcohols are not oxidized by potassium
Comparison Between -
ξ Both are powerful oxidants, but typically if one can use
manganate you do so with preference over chromate.
Chromate is dangerously toxic stuff.
ξ Dichromate is +6 oxidation state, and this rapidly
converts to chromate +5 which is one of the most
powerful inorganic carcinogens.
On the other hand, manganese is not that bad.
ξ Unlikely to Potassium Permanganate, Potassium
Dichromate is acutely and chronically harmful to
health and must be handled and disposed of
ξ Potassium dichromate is carcinogenic and should be
handled with gloves and appropriate health and safety
protection; permanganate is not carcinogenic.
ξ Unlikely to Potassium Permanganate, Potassium
Dichromate is corrosive and exposure may produce
severe eye damage or blindness. Human exposure
further encompasses impaired fertility, heritable
genetic damage and harm to unborn children.
ξ As an oxidizer, potassium permanganate is stronger
than potassium dichromate.