Soaponification

mechanism of working of soap

1. Soaponification Ordinary Soap is a simple mixture of sodium salt of long chain fatty acid. Soap made from olive oil is castile soap Alcohol is added to make it more transparent Perfumes dyes and germicide can be added. If Potassium salt is added it is soft soap. Soap dispersed in spherical cluster are called miscelle .

2. A Soap molecule has a polar COONa end and a non polar end, the long carbon chain of 12-18 carbons.

3. Miscelle of soap

4. The polar end is water soluble [ hydrophillic ] Non polar end is water insoluble[hydrophobic] This are called as amphipathic

5. How do soap clean the dirt Water alone cannot dissolve the hydrophobic substance . Oil droplet in contact with water tend to coalesce [join] so that there is a water and oil layer. But in presence of soap the non polar end of soap dissolve the oil droplet, leaving the carboxylate end projecting into the surrounding water layer.

6. Repulsion between similar charges keeps the oil droplet from coalescing; a stable emulsion of oil and water forms and can be removed from the surface being cleaned. Cleansing property not only limited to carboxylate salt but is possessed by other amphiprotic molecule. How do soap clean the dirt

7. Hard water contains calcium and magnesium salt which react with soap to form insoluble calcium and magnesium carboxylate . [ the ring in the bath tub]  A  detergent  is a surfactant or mixture of surfactants that has cleaning properties in dilute solution with water. A  detergent  is similar to soap, but with a general structure R-SO 4 - , Na + , where R is a long-chain alkyl group.

8. Analysis of oils and fats Prepared by Dr. N.GOPINATHAN ASSISTANT PROFESSOR DEPARTMENT OF PHARMACEUTICAL CHEMISTRY FACULTY OF PHARMACY SRIHER [DU] CHENNAI-116 TAMILNADU

9. Saponification value Acid value Ester value Iodine value Peroxide value

10. Determination of saponification value The saponification value is the number of milligrams of KOH necessary to neutralise the free acids and to saponify the esters present in 1 g of the substance

11. Why KOH is preferred over NaOH Potassium hydroxide is also slightly smaller than sodium hydroxide; therefore, it can penetrate oil molecules faster than sodium hydroxide, thus breaking the oil’s hold on surfaces quicker. Since they are also more soluble, the oils can be rinsed away easier, especially when using hotter water or steam equipment

12. TAG + 3KOH---- 3 alkali salt + Glycerol

13. Principle- saponification value The oil sample is saponified by refluxing with a known excess of alcoholic potassium hydroxide solution. The alkali required for soaponification is determined by titration of excess KOH against the standard HCl

14. Saponification value- apparatus required Erlenmeyer flask Round bottomed flask Reflux condenser Hot water bath / hot plate / heating mantle.

15. Alcohol distillation Reflux 1.2 litre of ethanol with 10 g of KOH and 6 g of granulated aluminium or aluminium foil for 30 minutes. Distil it and collect 1 litre of ethanol after discarding first 50 ml.

16. 0.5 m ethanolic KOH 30g of KOH in one litre of distilled alcohol. K eep the temperature below 15 C while dissolving alkali. Allow to stand overnight. Decant the clear liquid and store it in a air tight container.

17. Phenolphthalein indicator Dissolve 1 g of phenolphthaein in 100 ml of rectified spirit.

18. Preparation of 0.5 M HCl Dilute 42.5 ml of concentrated HCl with water to produce 1000 ml.

19. Standardisation of o.5M HCl Weigh accurately 1.5 g of anhydrous sodium carbonate previously heated at about 270 C for one hour. Dissolve it in 100 ml of water and add 0.1 ml of methyl red solution. Add 0.5M HCl from burette with constant swirling. Until the solution becomes faintly pink.

20. Heat the solution to boiling , cool and continue the titration, Heat again to boiling and titrate further as necessary until the faint pink colour is no longer affected by continued boiling. Each ml of 0.5M HCl is equivalent to 0.02649g of sodium carbonate

21. IP procedure Weight of oil mentioned in the individual monograph otherwise Weigh 2 g of sample being examined into a 200 ml flask of borosilicate glass fitted with a reflux condenser. Add 25 ml of 0.5 M ethanolic KOH and a little pumice powder and boil under reflux on a water bath for 3 minutes.

22. IP procedure Add 1 ml of phenolphthalein solution titrate immediatley with 0.5 M HCl . Repeat the operation omitting the substance being examined

23. Calculation Saponification value = 28.05 x ( b-a )/ w W – weight of the sample in grams. B- blank A- titre value

24. Note If the oil purpose of preservation has been saturated with carbon dioxide for the purpose of preservation, gently reflux the solution of the oil in ethanol 95 % and ether for 10 minutes before titration. The oil may be freed from the CO2 by exposing it in a shallow dish in a vacuum desiccator for 24 hours before weighing the sample.

25. Significance of Saponification Value It gives an idea about the average molecular weight of the fat or oil. Higher the molecular weight of the fat , the smaller is its saponification value.

26. Significance of Saponification Value • It indicates the length of carbon chain of the acid present in that particular oil or fat. Higher the saponification value, greater is the percentage of the short chain acids present in the glycerides of the oil or fats

27. Significance To identify the given fatty oil. To distinguish between fatty oils and mineral oils. In detecting the adulteration of fat or oil.

28. It also help to calculate the amount of alkali required to convert a definite amount of fat or oil into soap. Detection of acids containing less than 16 carbon or more than 18 carbon. Significance