This experiment uses H2TTP made during the last lab and hydrated copper (II) acetate to convert the H2TTP to Cu(TTP). The reaction proceeds by being refluxed for 30 minutes. The final product is a non-iridescent purple color, unlike the vivid, shimmering purple color of the starting H2TTP. Introduction Thin layer chromatography, or TLC, is used as a prerequisite for column chromatography.
When performing types of chromatography, like TLC, the polarity of solvents is extremely important. This lab uses TLC plates, five solvents (hexane, toluene, ethyl acetate, dichloromethane, and acetone), and small evaporating dishes to determine which solvent would be best to use in column chromatography. The least polar solvent is hexane, which has a polarity index of 0.1. Toluene has a polarity index of 2.4, while ethyl acetate’s is almost twice that at 4.4. By comparing the polarity indexes, you can tell what solvent will separate your dots of product on your TLC plates the best (Skoog 761).
Experimental Section The equipment needed for this experiment is as following: 100 mL round bottom flask, stir bar, water condenser, hot plate, UV light, Pasteur pipet, ice bath, separatory funnel, rotary evaporator, evaporating dish, cotton for filtering, and UV-vis spectrometer. Quinn 2 The chemicals required are: 0.1 g. of H2TTP made previously, 20 mL N,N-dimethylformamide, 0.16 g. hydrated copper acetate, distilled water, 75 mL dichloromethane, hexane, toluene, ethyl acetate, dichloromethane, and acetone for TLC plates.
Procedure 1. Measure out 0.1 g. of the H2TTP made previously into a 100 mL round bottom flask with a stir bar. 2. Add 20 mL of N,N-dimethylformamide (a bright blue powder) and let the solution stir. 3. Add 0.16 g. of hydrated coppe (II) acetate, cover with a water condenser and allow to reflux for 30 minutes. 4. Spot the solution on a TLC plate and check with UV light to see if there is any red on or around the spot. Add additional copper (II) acetate and allow to reflux for 10 more minutes if any red is visible.
5. When the reaction is complete, cool in an ice bath for 5-10 minutes then add 50 mL of distilled water. 6. Transfer into a separatory funnel and wash three times with 25 mL of dichloromethane. Collect the bottom layer each time. Discard the top layer properly. 7. Pour the collected solution back into the separatory funnel and add 50 mL of distilled water. Shake. Drain off the bottom layer. 8. Dry the bottom layer using a rotary evaporator. 9. Make five TLC plates spotted on a line drawn near the bottom, once with the beginning product and once with the final product. Dissolve in dichloromethane to make the spots. Put one of each into the five solvents: hexane, toluene, ethyl acetate, dichloromethane, and acetone.
10. Dilute the product once again with dichloromethane and filter with a pipet stuffed with cotton. Make sure the product is a very light pink color; it will need to be very diluted. 11. Take a UV-vis spectrum of the product. Data By looking at the TLC plates (attached) of the starting and final products, it is easy to see that dichloromethane would be the best solvent for column chromatography.
The ethyl acetate moved the final product up leaving just one spot near the top of the plate, but it left one wide band for the starting product. Toluene left two lines from top to bottom for both products, with no clear distinction of a certain spot. Hexane didn’t move the products at all from the beginning line. Acetone separated the starting product, but not the final product. Dichloromethane clearly separated both products. The reason for this separation is because dichloromethane is more polar than the other solvents.