- Post Lab Discussion Percent Yield Weight Of Product Melting Point Atom Economy Experimental M P 154 1 161 4 Carbon E 1 (32.73 KiB) Viewed 48 times
- Post Lab Discussion Percent Yield Weight Of Product Melting Point Atom Economy Experimental M P 154 1 161 4 Carbon E 2 (60.14 KiB) Viewed 48 times
- Post Lab Discussion Percent Yield Weight Of Product Melting Point Atom Economy Experimental M P 154 1 161 4 Carbon E 3 (61.89 KiB) Viewed 48 times
- Post Lab Discussion Percent Yield Weight Of Product Melting Point Atom Economy Experimental M P 154 1 161 4 Carbon E 4 (41.58 KiB) Viewed 48 times
- Post Lab Discussion Percent Yield Weight Of Product Melting Point Atom Economy Experimental M P 154 1 161 4 Carbon E 5 (32.99 KiB) Viewed 48 times
Experiment # 20 Schiff Base w/ TLC (Tender Loving Care) Techniques thin-layer chromatography, reaction monitoring Introduction Many organic reactions can be viewed as the addition or removal of water. In alkenes for example, water may be added across the double bond in a Markovnikov addition either by acid catalyst, or by oxymercuration-demercuration, and in an anti-Markovnikov fashion by hydroboration-oxidation. Oppositely, an alcohol may be dehydrated to an alkene by removing an OH and an H to give a double bond, either by E1 or by E2 mechanism. In this laboratory, an imine will be synthesized by dehydrating an aldehyde (or a ketone) with an amine. Imines are also called Schiff bases. A seminal example of an imine functional group Is found in the retinylidene protein in our eyes, where the amino group in lysine binds with the aldehyde moiety of the photosensitive retinal. Herein, o-vanillin (aldehyde) will be condensed with p-nitroaniline. An acid catalyst, para- toluenesulfonic acid (p-TSA) will be used to promote the solventless reaction. Ho Meo Moo OH HN -NO D-TSA OH The reaction will be monitored by thin-layer chromatography (TLC). In TLC, silica (SiO2) is admixed with a binder and an even layer is deposited onto a plate. The principle of attraction furnishes the rationale for the TLC technique. Polar compounds are attracted by the polar silica and therefore stick to the TLC. When a polar solvent moves up the plate by capillary action, it takes with it the adsorbed compounds. How far the compound travels up the TLC plate is governed by the interaction of its functional groups with the silica and with the solvent. As a general rule of thumb, more polar compounds stick to the TLC, and less polar compounds move up with the solvent.
Procedure o-Vanillin p-Nitroaniline P-TSA Schiff Base Theo. Substance Mass (8) MW (g/mol) Mmol Equivalents 5 5 0.05 Prepare a pre-cut TLC plate by lightly marking a line 1-2 cm from the bottom with a pencil. Handle only the edges of the TLC. On this line, mark three ticks where the starting materials and reaction will be spotted. Prepare a TLC sample by dissolving a few crystals (1-2 mg) of o-Vanillin in a small test tube with ethyl acetate (1 ml). Using a wooden applicator stick or a capillary TLC spotter, apply a small spot of the o-Vanillin solution onto the TLC plate. Make the spot as small as possible. Visualize under UV to make sure that the spot is present, if not re-apply. Label and keep the test tube for other TLC analyses. Do the same sample preparation for the aniline and spot this on the same TLC plate. To a mortar add vanillin (5 mmol) followed by p-nitroaniline (5 mmol). Grind the the mixture for 5 min or until it is as homogeneous as possible, you may need to use a spatula to aid in mixing. Record your observations. Using a spatula, take a small amount of the mixture and dissolve in a small test tube using ethyl acetate. Spot this mixture onto the TLC plate. Now the plate will have three spots, the two starting materials, and the reaction mixture. Prepare the developing chamber by placing 3 mL of chloroform (CHCI) in a 50 ml beaker. Using a pair of tweezers, place the TLC plate inside the beaker, making sure that the solvent is below the pencil mark so as not to dissolve away the spots. Cover the beaker with a watch glass and allow the solvent to rise up the plate by capillary action. Once the solvent is about 1 cm away from the top of the TLC, remove the plate from the chamber using a pair of tweezers and quickly mark with a line where the solvent front traveled before it evaporates. Visualize the TLC under a UV lamp and circle the spots. Measure the distance of the spots from the bottom line using a ruler. Measure the distance from the bottom line to the solvent front line. These two values will allow you to calculate the retention factor, Re: dist traveled by spot RF- dist traveled by solvent Draw the TLC in your notebook, label as "5 min mixing", and record all the Rf values for the spots.
mixture thoroughly until it is homogeneous. Use a spatula to ensure even mining, To the mortar containing the reaction mixture, add p-TSA (0.05 mmol). Grind the this may take 15-20 minutes. Record your observations. Continue grinding untila dry, homogenous solid is obtained. Prepare a TLC sample and obtain a new TLC plate. Spot this product sample along with the o-vanillin and p-nitroniline starting materials. Develop the plate and record your observations as before. If a significant amount of starting material is detected by TLC. continue grinding the reaction mixture and monitor the reaction by TUC. Once there is very little starting material left as determined by TLC, add water (5 ml) to the mortar andre homogenize the mixture gently. Mix for 5 minutes to ensure all of the PTSA is dissolved in the water. Prepare a vacuum filtration setup using a small Buchner funnel and wet the filter paper with water. Vacuum filter the reaction mixture and wash the precipitate with water (2x10 mL) Discard the filtrate in the acid waste container. Lastly, wash the precipitate with ice coid ethanol. Discard the filtrate in the organic waste container and let the scilids air- dry for 15 min in your bench top. Weigh the product to calculate the percent yield and obtain the melting point of the product. O-vanillin reaction p-nitroaniline TLC spots before developing Hypothetical movement of spots after developing Em 118
Pre-lab #20: Schiff Base w/ TLC (Tender Loving Care) Name: Calculate the theoretical yield and fill in the reagents table below: o-Vanillin p-Nitroaniline P-TSA Substance Mass (9) MW (g/mol) Mmol Equivalents Schiff Base Theo. 5 5 0.05 Fill in the safety precautions: o-Vanillin p-Nitroaniline para-toluenesulfonic acid Draw the mechanism for the acid-catalyzed imine formation of RCHO and ZNH2.