Determination of stability constant and donor acceptor ratio of PABA-Caffeine complex by solubility method

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BACKGROUND

Few properties of complexes like solubility, light absorption, conductance, partitioning behavior, chemical reactivity and conductance etc are different from their components. Example- PABA and caffeine form complexes in solution.¹

PABA + Caffeine = PABA – Caffeine Complex

For analyzing the complexes it is required to determine the two parameters which are

Aim: To find out the stability constant and donor acceptor ratio of PABA-Caffeine complex by solubility method.

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REQUIREMENTS

Chemicals:    Distilled water

                p-Amino benzoic acid (PABA)

                Caffeine

                Sodium hydroxide

                Phenolpthalein indicator

Apparatus:    Volumetric flask

                Conical flask

                Pipette

                Burette

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PROCEDURE

Prepare stock solutions of caffeine (0.1M) and sodium hydroxide solution (0.025N). Prepare different concentrations of caffeine as per the Table 1. Then add equal quantities of PABA samples to each flask containing caffeine solutions. Then shake all the flasks till equilibrium (approx 30 minutes). The filter the samples with Whattman filter paper. Then titrate 10 ml of the sample against 0.025N sodium hydroxide solution using phenolpthalein indicator. The data should be filled in the observation table.. Then draw the phase solubility PABA by taking concentration of caffeine on X axis and concentration of PABA on Y axis. Then calculate the Stochiometric ratio and Complex stability constant.

Observation table:

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CONCLUSION

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REFERENCES

1. Subramanyam CVS, Laboratory manual of Physical Pharmaceutics, Vallabh Prakashan, 2008: 72-78.