Procedure 1. In a mortar and pestle place 0.58 mL (-5 mmol) of the aldehyde (if

Question

Procedure 1. In a mortar and pestle place 0.58 mL (-5 mmol) of the aldehyde (if you have aldehyde C, use 0.51 mL) and 0.58 mL (-5 mmol) of the amine you selected using a separate 1 mL syringe for each. 2. Take turns gently mixing the reaction for 15 minutes until a solid (slushy consistency) is obtained. This indicates that you have formed the imine. 3. Weight 5 mmol of p-toluenesulfonic acid (PTSA) and 5 mmol of NaBHs and mix them together well in a watch glass with a glass rod. Add this solid mixture into the agate mortar and take turns gently grinding for 25-30 minutes. 4. Transfer the mixture obtained into a 50 or 100 mL beaker with a spatula and wash the remaining material on the mortar & pestle into the beaker with 20 mL of 5% NaHCO3. Transfer the solution to a separatory funnel and add 20 mL of ethyl acetate 45 5. Remove the aqueous layer and label the beaker with the aqueous layer for proper disposal later 6. Transfer the organic layer to a 50 mL Erlenmeyer and dry the solvent by placing 1-2 scoops of potassium carbonate into the organic layer and swirling the container. Filter through a gravity filter by placing a filter paper and funnel into a previously weighed 50 mL round bottom flask. 7. Concentrate the product to dryness by placing the round bottom flask on the Rotovap and evaporating the ethyl acetate. Get the mass of your round bottom flask containing the product. WASTE DISPOSAL The condensed ethyl acetate from the rotary evaporator should be poured in the bottle labeled "Ethyl Acetate" and located in the side hood. Be certain to reattach the receiving flask from the rotary evaporator WASTE DISPOSAL 8. Add 5 mL of ethanol to your round bottom flask and transfer the product to a 25 mL Erlenmeyer flask using a disposable pipette. DROPWISE, add 0.5 mL of concentrated HCI (CAUTION: concentrated HCl is very corrosive). 9. At this point you should see some crystals forming in the flask. When this occurs, collect the crystals by vacuum filtration using a Buchner or a Hirsh funnel and keep the vacuum on for a few minutes until the crystalline salt is dry 10. Transfer the solid to a 25 mL Erlenmeyer flask and recrystallize with 10 mL of hot ethanol until the solid completely dissolves then let it cool to room temperature 11. Collect the punified crystals by vacuum filtration using a Hirsch funnel, washing them with 1-2 mL of ethanol and allow them to air dry for at least overnight. Make sure you write down the initials of the group on the watch glass where you are placing the product. Next day, obtain a melting point and weigh your final salt.

Explanation / Answer

5. if you take the melting point of the crude salt at the end of step#9, the melting point will be lower than pure compound at the end of step#11 because impure substances in a crystalline solid interrupt the repeating pattern of forces that holds the solid together. So a smaller amount of energy is required to melt the part of the solid surrounding the impurity. This is called melting point depression from impure solids.

6. If you add NaBH4 at the beginning of the reaction (step#1), NaBH4 will reduce the aldehyde to directly alcohol and total reaction won't happen. NaBH4 should add after forming imine.

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