Introduction and Preparation of Salicylic Acid

Guided By:- By:-Shibu.G.Pillai 13BCH012(Asst. Professor) 13BCH013

SALICYLIC ACID(C7H6O3)

It is obtained from the bark of the willow tree which is the substance used to be obtained is a monohydrobenzoic acid, a type of phenolic acid and a betahydroxy acid. It has the formula C7H6O3. This colourless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin.

COOH

OH

The acid was first discovered by H. Piria in 1839, by fusing salicylic aldehyde with potassium hydroxide.

Salicylic Acid is used externally on the skin. It helps in the treatment of athlete’s foot, ringworm of the scalp, and the removal of warts, corns, and calluses. Salicylic acid is also incorporated into preparations for the treatment of acne, dandruff, seborrhea, and insect bites

Molecular

wt.

• 138.12 g/mol

Physical State

• White crystalline solid

Boiling and Melting

point

• B.P-211ºC• M.P-159ºC

• 1.44Specific Gravity

Slightly soluble in water but soluble in organic solvents

Specific Gravity

Autoignition

and Flas

h poin

t

• Auto-ignition-570ºC• Flash Point-157ºC

pH

• 2.4

Stability

• Stable under ordinary conditions but sensitive to light

Major Manufacturers of Salicylic Acid in India

All India Drugs Supply Co.Alliance Global-MumbaiHindustan Chemicals and

Pharmaceuticals.Forbes Pharmaceuticals.Triveni Chemicals-Vapi,GujaratSamrat enterprise-Ahmedabad

Methods of Preparation

By oxidation of or by fusion with potassium hydroxide, or by electrolysis of one of the following substances:- salicin, salicaldehyde, and saligenin.

By heating with water ortho-diazo amidobenzoic acid.

By heating phenol with carbon tetrachloride and alcoholic potash.

By electrolysis of a solution of benzoic acid in acetic acid.

By exposing a solution of benzoic acid to the sunlight in the presence of a ferric salt.

From Methyl Salicylate in presence of Sodium Hydroxide and Sulphuric acid.

By passing dry carbon dioxide into a hot mixture of phenol and sodium.(Kolbe and Lautemann reaction)

Kolbe-Lautemann’s Processfor synthesis of Salicylic Acid.(Commercial

Process)

1. Phenol and sodium hydroxide form sodium phenoxide.

C6H5OH + NaOH C6H5ONa + H2O

2. Carbon dioxide when added to the sodium phenoxide forms sodium phenyl carbonate:

C6H5ONa + CO2 C6H5OCOONa

This stage is completed then the mass is heated to about 110°C for one hour and at about 6 atmosphere.

3. The sodium phenylcarbonate is transformed into sodium salicylate:

C6H5OCO2Na C6H4OHCOONa

The CO2 goes into the Ortho-position between the hydrogen atom and the nucleus, producing a carboxyl group.

4. In the last stage the salt acts with some unchanged sodium phenate and sets free the Phenol in the disodium salt.

C6H4OHCOONa + C6H5ONa C6H5ONaCOONa + C6H5OH

Mechanism

Process Flow Diagram for Kolbe’s Synthesis

From Methyl Salicylate

Mechanism