1. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 15 Lipids 15.4 Chemical Properties of Triacylglycerols 1

2. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chemical Properties of Triacylglycerols The chemical reactions of triacylglycerols are similar to those of alkenes and esters. In hydrogenation, double bonds in unsaturated fatty acids react with H 2 in the presence of a Ni or Pt catalyst hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme 2

3. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Hydrogenation of Oils The hydrogenation of oils adds hydrogen (H 2 ) to the carbon atoms of double bonds converts double bonds to single bonds increases the melting point produces solids, such as margarine and shortening 3

4. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Hydrogenation When hydrogen adds to all the double bonds of glyceryl trioleate (triolein) using a nickel catalyst, the product is the saturated fat glyceryl tristearate (tristearin). 4

5. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check What products are obtained from the complete hydrogenation of glyceryl trioleate? A. glycerol and three oleic acids B. glyceryltristearate C. glycerol and three stearic acids 5

6. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution What products are obtained from the complete hydrogenation of glyceryl trioleate? B. glyceryltristearate 6

7. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Olestra, a Fat Substitute Olestra is used in foods as an artificial fat sucrose linked by ester bonds to several long-chain fatty chains not broken down in the intestinal tract 7

8. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Cis and Trans Fatty Acids Unsaturated fatty acids can be cis, with bulky groups on same side of C=C trans, with bulky groups on opposite sides of C=C 8

9. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Hydrogenation and Trans Fatty Acids Most naturally occurring fatty acids have cis double bonds. During hydrogenation, some cis double bonds are converted to trans double bonds. In the body, trans fatty acids behave like saturated fatty acids. It is estimated that 2–4% of our total calories are in the form of trans fatty acids. Several studies reported that trans fatty acids raise LDL-cholesterol and lower HDL-cholesterol. 9

10. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Hydrogenation of Unsaturated Fats 10

11. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Which of the following statements are true and which are false? A. There are more unsaturated fats in vegetable oils. B. Vegetable oils have higher melting points than fats. C. Hydrogenation of oils converts some cis double bonds to trans double bonds. D. Animal fats have more saturated fats. 11

12. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Which of the following statements are true and which are false? A. True There are more unsaturated fats in vegetable oils. B. False Vegetable oils have higher melting points than fats. C. True Hydrogenation of oils converts some cis double bonds to trans double bonds. D. True Animal fats have more saturated fats. 12

13. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Hydrolysis In hydrolysis, triacylglycerols split into glycerol and three fatty acids an acid or enzyme catalyst is required 13

14. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Saponification and Soap Saponification is the reaction of a fat with a strong base splits triacylglycerols into glycerol and the salts of fatty acids is the process of forming “soaps” (salts of fatty acids) with KOH gives softer soaps 14

15. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Saponification 15

16. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Summary of Organic and Lipid Reactions 16

17. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check What products are obtained from the complete hydrolysis of glyceryl trioleate? A. glycerol and three oleic acids B. glyceryl tristearate C. glycerol and three stearic acids 17

18. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution What products are obtained from the complete hydrolysis of glyceryl trioleate? A. glycerol and three oleic acids 18

19. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Write the product of the following reaction: 19 + 3

20. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 20 C O (CH 2 ) 14 CH 3 C (CH 2 ) 14 CH 3 O C O (CH 2 ) 14 CH 3 CH 2 O CH CH 2 O O