1. Para amino benzoic acid
Identification Of
Para amino benzoic acid
Pharmacist
Omar abdulrahman
Pharmaceutical Chemistry Department
College Of Pharmacy-HMU

2. Para amino benzoic acid
Act as chemical sun screen, Sunscreens are used to protect the skin from the harmful effects of the sun. They help to prevent sunburn and premature aging (e.g., wrinkles).
Sunscreens also help to decrease the risk of skin cancer and also of sunburn-like skin reactions (sun sensitivity) caused by some medications.

3. The active ingredients in sun screens work either by absorbing the sun's ultraviolet (UV) radiation, preventing it from reaching the deeper layers of the skin, or by reflecting the radiation.
PABA absorb and scatter U.V.B rays which are ranged from nm that are responsible for sun burn and photo toxicity but allow longer wave length to penetrate the skin so that tanning will occur .

4. Ultraviolet A rays (UVA) (Longer wave length or black light)
Types of UV Rays
Ultraviolet A rays (UVA)
(Longer wave length or black light)
( nm)
Most of the sun’s natural light.
Penetrates deep into the skin causing wrinkles & increased aging.
Concerns over long term hazards.

5. Ultraviolet B rays (UVB)
(Medium wave Length)
( nm)
Needed for vitamin D production.
Most damaging to skin.
1000 times stronger than UVA rays.
Main cause of sunburns.

6. Ultraviolet C rays (UVC)
(Short wave length)
( nm)
Never reach the earth surface.
Filtered out by the atmosphere.

7. Chemical structure of Para amino benzoic acid

8. Identification of para amino benzoic acid
Diazonium salt formation

9. Coupling reaction

10. Reaction of PABA with Nitrous Acid
Nitrous acid, HNO2, is a weak unstable acid formed from NaNO2 and a strong acid like HCl.
In the presence of acid, nitrous acid decomposes to +NO, the nitrosonium ion. This electrophile then goes on to react with the nucleophilic nitrogen atom of amines to form diazonium salts (RN2+Cl¯) from 10 amines and N-nitrosamines (R2NN=O) from 20 amines.

11. Nitrous acid reacts with 10 alkylamines and arylamines to form diazonium salts. This reaction is called diazotization.
The mechanism for this reaction consists of many steps.
It begins with nucleophilic attack of the amine on the nitrosonium ion, and it can conceptually be divided into two parts: formation of an N-nitrosamine, followed by loss of H2O. Mechanism

12. Mechanism

13. Procedure
Disssolve 1.14 gm of PABA in a mixture of 2.5ml of conc.HCl and 5 ml of water,cool the solution in an ice bath (0-5⁰C).
Dissolve 1gm of sodium nitrite in 5 ml of water then cool the solution to (0-5⁰C), add this solution to the first solution (slowly), cool the solution (0-5⁰C).
Dissolve 1.5 gm of B-napthol in 15ml of 10℅ sodium hydroxide solution ,cool the solution (0-5⁰C).
Add the diazotization solution to B-naphthol solution a red to orange colour is observed.