Potassium Permanganate, Potassium Dichromate – One of the Excellent Tools of

Analysis

Md. Istiqur RahmanID: 111-29-269L2 T2Dept. of PharmacyDaffodil International University

Pharmaceutical Analysis 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 product.

Titration 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 TitrationRedox 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 permanganate.

Oxidizing Agent 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 PermanganatePotassium 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 (permanganometry).

For the standardization of KMnO4 solutions, reduction by oxalic is often used.

Why potassium permanganate is

stronger oxidizing agent

compared to other oxidizing agents?

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 Potassium dichromate, K2Cr2O7, is a

common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications.

It is a crystalline ionic solid with a

very bright, red-orange color. It is also known as potassium bichromate; bichromate of potash etc.

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 dichromate.

Comparison Between - Potassium Dichromate

&

Potassium Permanganate

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 appropriately.

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.