Question

Synthesis of dimedone This lab exercise will give you practical experience with the generation of a malonic ester enolate and subsequent reaction with an a,p-unsaturated carbonyl compound. This sequence is known as the Michael reaction. In the presence of sodium methoxide, dimethyl propanedioate (malonic ester/dimethyl malonate) is converted to the corresponding enolate anion and reaction with 4-methylpent-3-en-2-one (mesityl oxide) affords the Michael adduct 1, as shown in the reaction sequence below. Under the basic reaction conditions, the Michael adduct 1 undergoes an intramolecular reaction and the cyclic diketone 2 forms. Base induced hydrolysis of the ester to the carboxylic acid and decarboxylation yields the final product, 5,5-dimethylcyclohexane-1,3-dione (dimedone) Dimedone may exist as a mixture of keto and enol tautomers NaOCH , HOCH НаСО COOCH 1. NaOH, H20 2. H30, heat но 2 Experimental The glassware for this reaction must be thoroughly dry and set up to exclude air and moisture during the first step. All glassware required for the reaction and measuring will be oven dried prior to the lab session Gather the following equipment: 2 retort stands, 3 clamps, a 100 mL stirring mantle for heating, and a lab jack. Wind the lab jack to its lowest height and place it on the base of one retort stand, then place the stirring mantle on the lab jack. When you set up your glassware, clamp it above the heating mantle so the heat source can be raised and lowered to allow enough clearance to remove and replace the round bottom flask during the procedure The reaction will be carried out in a 100 mL 2-neck round bottom flask fitted with a magnetic stirrer bar, a reflux condenser and pressure equalising addition funnel. A calcium chloride drying tube is placed in the top of the condenser to exclude moisture. Stopper the top of the addition funnel. Clamp the vertical neck of the round bottom flask to the retort stand, and use a second clamp to secure the condenser to the same stand. Use the second retort stand and another clamp to hold the addition funnel in place Synthesis of dimedone Use the addition funnel to add dimethyl malonate (2.8 mL, 25 mmol) to the flask, followed by 25 % sodium methoxide in methanol (6.0 mL, 26 mmol). Heat the solution to boiling and watch for the formation of a solid. Continue heating until any solid that may have formed has dissolved (or has almost completely dissolved) . Lower the heating mantle and ensure the addition funnel tap is closed. Add mesityl oxide (3.0 mL, 26 mmol) to the addition funnel, then add it drop wise over 2 - 3 minutes to the flask. Raise the heating mantle and reflux the reaction mixture for one hour Make good use of this time to prepare as much as possible for the next steps. Think about the chemistry that is occurring in the reaction vessel and discuss it with your peers. Consider the questions to be answered for the report on this experiment Ask the demonstrator questions to clarify your understanding . .After one hour remove the round bottom flask and stopper the angled neck. Use a rotary evaporator to remove the methanol. Continue evaporation until there is no obvious liquid present, but the solid can be wet. Refit the flask to the retort stand with the condenser and addition funnel in place as before. Use the addition funnel to add aqueous NaOH (3.0 mol L-1, 20 mL) to the solid residue in the flask. Heat to reflux and stir for one hour. Again, make productive use of this time . . Place aqueous HCI (6.0 mol L, 15 mL) in a 250 mL conical flask with a magnetic stirrer bar, and heat on a hotplate stirrer. With stirring, add the reaction mixture to the conical flask containing the aqueous acid and heat to boiling. Continue boiling until no more gas evolves, which will take at least 10 minutes . The solid product will crystallise upon cooling the conical flask. This can be facilitated by placing the flask in ice. Scratch the inside of the flask if necessary Collect the crude product using vacuum filtration . The crude product can be recrystallised if you have enough time. Check with the demonstrator to see if you have time. If so, recrystallise the crude product using a 50:50 mixture of water and acetone . Prepare a sample of the product dimedone for analysis by GCMS. Weigh out 20 mg of the crude or recrystallised product (whichever one you have) into a GCMS vial and completely fill the vial with acetone . Prepare 2 samples for analysis by H NMR, one with CDCl3 as the solvent and the other with acetone-ds as solvent Determine the yield and melting point of the product . Question under the readkien Cordithione, the Michael eaction froduch under90os a cyclisalion reoction. wnte the cured arow mechaniem for this

Answer 1

Ch o соо соос COOCH o-ch 2