Solvent Free Synthesis of an α,β-Unsaturated KetoneAuthors Name

Putramica Winarto

putrahhh@gmail.com

ABSTRACT

The formation of ethyl 2-oxo-4,6-dip-tolylcyclohex-3-enecarboxylate stemmed from the Microwave Irradiation of the

chalcone (E)-1,3-dip-tolylprop-2-en-1-one that resulted in a Robinson Annulation and the formation of the product was not completely successful.

This experiment consisted of two parts, first among which involved the creation of the chalcone by grinding equimolar 4-methylbenzaldehyde and 4-methylacetophenone in porcelain mortar with the use of solid sodium hydroxide as the base catalyst.1 After the chalcone was created the melting point and the IR was obtained. The melting point of the chalcone was 124°C and the literature melting point is 127°C which indicates that the product was relatively pure. IR of the chalcone presented peaks at 1652.87 cm-1 which is indicative that the product has a conjugated ketone. There is also a peak at 1591.09 cm-1 which belongs to the aromatic rings and at 809.36 cm-1 there is a peak that suggests the benzene is disubstituded and the groups are para to each other. Once the chalcone product was verified, converting the chalcone via Robinson Annulation could proceed. In the second part of the experiment, the product was placed into a microwave after being mixed with ethyl acetoacetate and potassium carbonate.2 After mixing the reactents together, the solid was microwaved for 3 minutes on medium power which changed the color of the solid to more a white color rather than a yellow color. Robinson Annulation via microwave irradiation resulted in a 33.33% product yield. IR of the product presented a

peak at 1738.73 cm-1 which comes from the carbonyl of an ester and one at 1653.91 cm-1 from the conjugated ketone carbonyl. At 1241.69 cm-1 there is a carbon to oxygen stretch that arises from the ester as well as a peak that results from the aromatic rings at 1594.11 cm-1. The IR of the crude procut was obtained and it offered a peak at 1715.81 cm-1 which indicates that the crude contains unreacted ethyl acetoacateate. Because it was so, recrystallization of the product in 95% ethanol was necessary as ethanol-dioxane solvent was not readily available. The crude was recrystallized using an ice bath, cold ethanol, and a vacuum filtration and the IR obtained lacked the 1715.81 cm-1 peak which means recrystallization of the crude was successful. Obtaining the crude was a journey in and of its own because the crude product melted in the oven after being filtered and turned into a yellow, pasty, goopy liquid/solid mix. As a result, the crude had to be dried through other means. First the crude was dissolved completely in dichloromethane and then it was dried with anhydrous magnesium sulfate. After the crude was dried and decanted, the remaining liquid was evaporated off in the hood through the use of a stream of air until only solid remained. The solid was then dissolved in hot ethanol and

recrystallized as stated above. The final solid was not dried in the oven at first for fear that the end result would mimic that of the crude, and the IR was taken after letting it air dry. The IR showed an OH peak because of the ethanol and an executive decision to put the final product in the oven was made. After being in the oven for an entire day the IR of the final product was taken once again and it revealed a smaller OH peak which means the ethanol has yet to dry completely. After the IR was taken, the melting point followed suit. However, this proved to be a problem as well.The final product did not melt at all, instead it burned inside the melting point device; it changed from a white-yellow color to a solid yellow color before turning into a golden yellow color. The yellow got darker and darker until eventually it turned black. Because the first melting point was not successful another melting point was taken and unfortunately the results were the same. It can be deduced from the experiment form that the melting point of the product should be in the 110s-120s as the form indicated a compound of similar build (except it had OH instead of methyl for its R group) and the melting point was 111-112°C.3 This of course, indicates that the product isn’t pure at all and something must have happened during the procedure, chief among which, the microwave irradiation bit. The crude was set in the 500-wat microwave for 3 minutes on medium and resulted in little color change, however, when the crude was set in the oven on high for 4-5 minutes, a massive color change was observed. This lack of color chang e indicates that perhaps the crude did not react completely with the ethyl acetoacetate. Regarldess of the result, the final product is at least, not the chalcone that was used as a reactant in this experiment.

(1) Palleros, Daniel R. “Solvent-free Synthesis of Chalcones.” PDF file.

(2) Priya V Frank, B'alakrishna Kalluraya, and Shobhitha Shetty. “Microwave Assisted Robinson’s Annulation: Synthesis of some novel cyclohexanones under solvent free conditions.” PDF file.

(3) Casale, Kristin. “Preparation of an α,β-unsaturated ketone via Michael and Aldol Condensation Reactions.” Chemistry 421 Lab Manual. Chemistry Department, American River College.

Experimental Procedure. This experiment started off with the addition of 0.00286 moles of ethyl acetoacetate

(0.360 mL) to .3362 grams (.00142 moles) compound 1. 0.00571 moles or .7897 grams of potassium carbonate was also added. All three reactants were crushed by a pestle in a mortar and then put inside a microwave under medium heat for 3-4 minutes. Afterwards the crude product was put under vacuum filtration and a small amount of cold water was ran through it (<20 mL). After letting the solid dry under suction for 3 minutes, place the crystals in the oven to dry for 20-30 minutes. Chop up the solid to ensure even drying. After 20-30 minutes have passed, take the product out of the oven and let it cool to room temperature before placing it inside a small beaker or Erlenmeyer flask. As the product is cooling, acquire 20-30 mL of 95% ethanol and set some aside to put into a centrifuge tube as cold ethanol will be needed. Prepare an ice bath to put the centrifuge tube in. Place the remaining ethanol on a hot plate and wait until it bubbles. Once the solution is bubbling or near bubbling, use a Pasteur pipette to transfer minute amounts of hot solvent to the crude. Remember that the crude shold be dissolved in the minimum amount of solvent to lessen yield loss. Once the crude is completely dissolved by the hot ethanol, allow the mixture to room to cool temperature. At this point you may fill a beaker up with room temperature water and place the beaker or Erlenmeyer flask inside for faster cooling. After the product is cooled to room temperature, place the beaker or flask inside the ice bath and swirl it around. To aid in the recrystallization process, proceed to scratch the inside of the beaker or flask with a glassrod to induce crystallization. Repeat this process as many times as necessary while swirling the beaker or flask when required. You may also add in tiny tiny chunks of ice to help. When the mixture has recrystallized completely, pour the contents onto a Buchner funnel and vacuum filtrate the solid. Wash the glassware with small portions of cold ethanol and pour contents over the funnel. You may also wash the solid inside the funnel with cold ethanol. Allow solid to be under suction for at least 3 minutes. Place the solid in a preweighed beaker or watch glass and place it inside the oven. Let it dry for 20-30 minutes again. Remove the product from the oven and

allow it to cool to room temperature before taking the mass. Obtain the IR and melting point once the mass has been taken. The IR and melting point should indicate that compound 2 has been created.

Acknowledgment I would like to acknowledge Michael Tomolillo who encountered the same unfortunate fate as I when drying the crude product. I’d also like to thank Ariel, Beverly, Carol, and Don who were all more than willing to share the vacuum filtration system that they had set up. And to Kristin Casale who hath put up with onslaughts of questions and “is this ok?”