Organic Chemistry I CHM 336 PRE-LAB 9 PDF

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Samantha Truckly (2654185) Pre-lab Assignment: Experiment Title: Stereochemistry of Alkenes Statement of Purpose:  Microscale cis-trans isomerization of an alkene.  Microscale addition of bromine to fumaric acid.  Determine the mechanism of the isomerization of dimethyl maleate to dimethyl fumarate. Reagents: CHEMICAL

STRUCTURE

MELTING POINT

HAZARD

DISPOSAL

0C

No hazards

Drain

135C

Avoid skin and eye contact, do not inhale

Solid Organic Waste

Fumaric Acid

287C

Avoid skin and eye contact, do not inhale

Solid Organic Waste

Hydrochloric Acid

-26C

Avoid skin and eye contact, do not inhale or ingest, can be fatal

Halogenated waste

-118.5C

Flammable, do not inhale or ingest

Liquid Organic Waste

173.5C

Flammable

Liquid Organic Waste

Water

O

Maleic Acid HO

Ethyl Acetate

O OH

O

O

Absolute Ethanol

Procedure Outline: Part A: 1. Place 1g of maleic acid in 1.5mL of water in a 5mL conical vial equipped with a spin vane and a water jacketed reflux condenser then add add 1.3mL of concentrated HCl. 2. Reflux mixture gently for 15-30 minutes. 3. A precipitate will separate. Cool and collect product by vacuum filtration using a Hirsch funnel. 4. Air dry solid and measure weight. Part B: 1. Add 100mg of fumaric acid to and 1.25mL of stock bromide to a 5mL conical vial equipped with a spin vane.

Samantha Truckly (2654185) 2. Swirl to mix and attach an air condenser. 3. Heat solution on warm sand bath, the color will turn orange. 4. After 10 minutes a white precipitate will form and the mixture will turn yellow. If solution is colorless add a few more drops of bromide. 5. Continue heating for 15 minutes then remove the solution from heat and cool in an ice bath. 6. Cool and collect product by vacuum filtration using a Hirsch funnel then rinse in cold water. 7. Air dry solid and measure weight. Part C: 1. Obtain a TLC plate and cut it in half. Draw a line 1cm from bottom and draw eight spots. 2. Mark these spots with dimethyl maleate, dimethyl fumarate, and 2,3 dibromosuccinate. Then mark four spots for reaction mixture when initially mixture, after 2 minutes, 5 minutes, and 20 minutes. The final spot is for the isolated product. 3. Obtain 2 10mL Erlenmeyer flasks one for light reaction mixture and one for dark reaction mixture. 4. Add 4mL of methylene chloride and 0.75mL of dimethlyl maleate to the flasks and swirl to mix. 5. Add 10 drops 0.5M Br2 into the methylene chloride of one of flasks and swirl to mix. 6. Immediately spot an aliquot of the reaction mixture on both TLC plates. 7. Stopper the flasks and place one in the dark and one in the light. After 2 minutes spot each of the reaction mixtures on the TLC plate. Repeat after 5 minutes and 20 minutes. 8. Add a boiling chip to any flask that indicates dimethyl fumarate has been produced and reduce the volume by half on an aluminum heat block or steam bath. 9. Chill in an ice bath and add 6mL of ice-cold hexanes. Cool until crystallization is complete. 10. Suction filter the crystals, washing with small amounts of cold hexanes, and air dry. If no product crystallizes after adding cold hexanes, set the reaction flask aside. 11. Spot solutions of the isolated crystals or uncrystallized reaction solution. 12. Develop plates in 1:3 ethyl acteate: hexanes mixture in TLC chambers. Develop plates until the solvent in front is 1-2cm from top of plates. 13. Remove plates, air dry, and view the spots under a UV light. 14. Weight the crystals and obtain a melting point. Reflux apparatus: See attached. Citation: Mohrig, J.R.; Alberg, D.G.; Hofmeister, G.E.; Schatz, P.F.; Hammond, C.N.; Laboratory Techniques in -Organic Chemistry; Freeman, New York, 2014, 86-89; Mohrig, J.R.; Alberg, D.G.; Hofmeister, G.E.; Schatz, P.F.; Hammond, C.N.; Laboratory Techniques in -Organic Chemistry; Freeman, New York, 2014, 132-140; 231-232; 255-269 Pre-lab questions: 1. What is a cis and a trans alkene? If two groups are bonded on the same side as the double bond on an alkene, it is cis. If the groups are bonded to opposite sides of the double bond, then it is trans. 2. What is E and Z alkenes? What is the criteria used for define E and Z alkenes? The general strategy of the E-Z system is similar to the cis-trans system. At each end, rank the two groups, using the Cahn-Ignold-Prelog priority rules. Then, see whether the higher priority group at one end of the double bond and the higher priority group at the other end of the double bond are on the same side (Z) or on opposite sides (E) of the double bond. 3. Explain the difference of stability of cis and trans alkenes. Trans alkenes are more stable than cis alkenes because they have fewer steric interactions....