1. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 Chapter 17 Lipids 17.4 Chemical Properties of Triacylglycerols

2. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.2 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.  In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme. Chemical Properties of Triacylglycerols

3. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.3 Hydrogenation of Glyceryl Trioleate

4. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 Hydrogenation of Oils The hydrogenation of oils  converts double bonds to single bonds  adds hydrogen (H 2 ) to the carbon atoms of double bonds  increases the melting point  produces solids such as margarine and shortening

5. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 What product(s) is obtained from the complete hydrogenation of glyceryl trioleate? 1) glycerol and 3 oleic acids 2) glyceryltristearate 3) glycerol and 3 stearic acids Learning Check

6. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 What product(s) is obtained from the complete hydrogenation of glyceryl trioleate? 2) glyceryltristearate Solution

7. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7 Olestra, A Fat Substitute Olestra don’t consume much in a short term  used in foods as an artificial fat: potato chips, etc.  sucrose linked by ester bonds to several long-chain fatty chains  not broken down, not absorbed (too big) in the intestinal tract: Side effects: abdominal cramp, carries fat-soluble Vitamin (A, D, E & K) with it to waste them.

8. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Unsaturated fatty acids can be  Cis with bulky groups on the same side of C═C  Trans have bulky groups on opposite sides of C═C 8 Cis and Trans Fatty Acids

9. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.9 Trans Fatty Acids and Hydrogenation Trans fatty acids  are formed during hydrogenation when cis double bonds are converted to trans double bonds  in the body behave like saturated fatty acids  are estimated to make up 2 to 4% of our total calories  in several studies are reported to raise LDL- cholesterol and lower HDL-cholesterol

10. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.10 Trans Fats In vegetable oils,  the unsaturated fats usually contain cis double bonds  during hydrogenation, some cis double bonds are converted to trans double bonds (more stable), causing a change in the fatty acid structure  a label states “partially” or “fully hydrogenated” if the fats contain trans fatty acids

11. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. Formation of Trans Fats 11

12. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.12 Learning Check Identify each statement as true (T) or false (F). 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.

13. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.13 Solution Identify each statement as true (T) or false (F). T A. There are more unsaturated fats in vegetable oils. F B. Vegetable oils have higher melting points than fats. T C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds. T D. Animal fats have more saturated fats.

14. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.14 Hydrolysis In acid or enzyme hydrolysis,  water adds to the ester bonds  triacylglycerols split into glycerol and three fatty acids  an acid or enzyme catalyst is required

15. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.15 Base Hydrolysis (Saponification ) In base hydrolysis (saponification),  a triacylglycerol reacts with a strong base  a triacylglycerol splits into glycerol and the salts of fatty acids  soaps (salts of fatty acids) form

16. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.16 Saponification

17. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.17 What products are obtained from the complete hydrolysis of glyceryl trioleate? 1) glycerol and 3 oleic acids 2) glyceryl tristearate 3) glycerol and 3 stearic acids Learning Check

18. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.18 What products are obtained from the complete hydrolysis of glyceryl trioleate? 1) glycerol and 3 oleic acids Solution

19. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.19 Learning Check Draw the condensed structural formula of the product of the following reaction.

20. General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.20 Solution