Catalytic Transfer Hydrogenation of Cooking Oil, and Fatty Acid Content of the Hydrogenated Cooking Oil | CH 344, Lab Reports of Organic Chemistry

Download Catalytic Transfer Hydrogenation of Cooking Oil, and Fatty Acid Content of the Hydrogenated Cooking Oil | CH 344 and more Lab Reports Organic Chemistry in PDF only on Docsity! Catalytic Transfer Hydrogenation of Cooking Oil, and Fatty Acid Content of the Hydrogenated Cooking Oil Reference: A. M. Schoffstall, B. A. Gaddis, and M. L. Druelinger, Microscale and Miniscale Organic Laboratory Experiments, 2nd Edition, McGraw-Hill: New York, 2004, Experiment 6.1C, page 241. Introduction: Oils are triesters derived from plants, and are usually liquids. They contain cis C=C’s. They are not uniform in structure. They are biosynthesized formed from long-chain carboxylic acids (“fatty acids”) and a triol, glycerol. An example structure is shown below. HC H2C H2C O C O (CH2)7 O C O (CH2)7 O C O (CH2)7 C C C C (CH2)7CH3 C (CH2)7CH3 C (CH2)7CH3 H H H H HH E x a m p l e o f a C o o k i n g O i l M o l e c u l e Some of the C=C’s in oils are reduced to form semisolid products, which can be used in margarines, for example. These reductions are usually carried out using hydrogen gas, and a catalyst such as platinum or palladium. Since hydrogen gas is highly flammable, and the glassware to do the reductions is highly specialized, hydrogenations are usually not done in organic labs. There is another process, called catalytic transfer hydrogenation (CTH), which avoids the use of hydrogen gas. Since addition of hydrogen to an alkene is reversible, CTH uses an organic compound as the source of hydrogen. In our experiment, we will use cyclohexene as the hydrogen source. Cyclohexene is a good source of hydrogen, since it can produce the stable aromatic compound, benzene, as a byproduct when two equivalents of hydrogen are lost from it. You can learn more about the stability of benzene in chapter 16 of your lecture text. The palladium removes hydrogens from the cyclohexene, and transfers them to the olive oil. Since the palladium is just transferring hydrogens from cyclohexene to the cooking oil, we only need a small amount of it, so it is functioning as a catalyst. We are using an excess of cyclohexene to drive the reaction toward products, since the reaction could be an equilibrium reaction. See the reaction scheme below. An Example Reaction Scheme: HC H2C H2C O C O (CH2)7 O C O (CH2)7 O C O (CH2)7 C C C C (CH2)7CH3 C (CH2)7CH3 C (CH2)7CH3 H H H H HH HC H2C H2C O C O (CH2)7 O C O (CH2)7 O C O (CH2)7 CH2 C CH2 CH2 (CH2)7CH3 C (CH2)7CH3 CH2 (CH2)7CH3 H H + e x c e s s P d - C c a t a l y s t r e f l u x + E x a m p l e C o o k i n g O i l M o l e c u l e E x a m p l e P a r t i a l l y H y d r o g e n a t e d M o l e c u l e Procedure: To 25 mL round-bottomed flask containing a magnetic stirring bar, add 600 mg of olive oil (record exactly what you use), 2-4 mL of cyclohexene, and 40-50 mg of 10% Pd on charcoal. Fit the vial with a water condenser. Reflux the mixture using a thermowell for at least 50 minutes. Cool the mixture to room temperature. Prepare a Pasteur filter pipette with cotton, and add a small portion of Celite, until you have a layer of Celite that is about 2-3 cm. Place the filter pipette into a one-hole stopper that fits into your filter flask. Clamp the filter flask to a support bar. Add 1-2 mL of methyl t-butyl ether (MTBE) to the filter pipette using another pipette. Attach the hose to the aspirator to the side arm of the filter flask, and apply gently suction, to draw the MTBE through the Celite to wet it completely. Disconnect the suction hose from the side arm, and pipette 1-2 mL of the reaction mixture into the top of the filter pipette. Reattach the suction hose, and pull the solvent through the filter pipette: the black palladium on carbon catalyst should remain in the filter pipette. Continue adding the reaction mixture to the filter pipette until you have transferred all of it. Rinse the reaction flask with 1-2 mLs of MTBE, and filter it through the filter pipette. Transfer the filtrate to a pre-weighed 50 mL round-bottomed flask (rinse your filter flask with 1- 2 mL of MTBE, and transfer that to the round-bottomed flask as well), and remove the solvents