Michael Robinson Annulation

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Formal writeup for the conversion of the chalcone, (E)-1,3-dip-tolylprop-2-en-1-one into ethyl 2-oxo-4,6-dip-tolylcyclohex-3-enecarboxylate

Transcript of Michael Robinson Annulation

Template for Electronic Submission of Organic Letters

Solvent Free Synthesis of an ,-Unsaturated KetoneAuthors NamePutramica Winarto

[email protected]

ABSTRACTThe 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 124C and the literature melting point is 127C 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 111-112C.3 This of course, indicates that the product isnt 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 Robinsons Annulation: Synthesis of some novel cyclohexanones under solvent free conditions. PDF file.(3) Casale, Kristin. Preparation of an ,-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 (