LAB+Report+for+Green+Synthesis+of+Fluorescent+Natural+Product


 * __Green synthesis of a fluorescent natural product__**

Douglas M. Young, Jacob J. C. Welker, and Kenneth M. Doxsee[|*] Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, United States J. Chem. Educ., 2011, 88 (3), pp 319–321 Publication Date (Web): December 8, 2010 Copyright © 2010 The American Chemical Society and Division of Chemical Education, Inc.
 * DOI:** 10.1021/ed1004883

__Introduction__- Synthesis of 4-methylumbelliferone via the acid-catalyzed Pechmann condensation. The Pechmann condensation: Discovered by the German chemist Hans von Pechmann. Is a synthesis of coumarins via the acid-catalyzed reaction of a phenol with a b-keto ester. The condensation is performed under acidic conditions. This synthesis introduces students to several types of organic reactions: transesterification, electrophonic aromatic substitution, and alcohol dehydration. Performed with a recyclable, solid catalyst and under solvent-free conditions, the experiment illustrates many of the principles of green chemistry and additionally illustrates the potential of green chemistry to yield not only safety and environmental benefits, but positive economic impacts as well. With high regioselectivity, complex yet interpretable IR and, and unusual pH-dependent fluorescence, the synthesis of 4-methylumbelliferone provides a rich learning platform. The Pechmann condensation: Discovered by the German chemist Hans von Pechmann. Is a synthesis of coumarins via the acid-catalyzed reaction of a phenol with a b-keto ester. The condensation is performed under acidic conditions.

The Pechmann condensation experiment will have some positive modification of a chemical process through green chemistry. Dowex 50W20 beads will be used as the acid catalyst instead of H2SO4 and POCL3, Dowex it’s easy to handle (the nonvolatile beads make it safer to use). Dowex under solvent-free provides many green chemistry principles to make the experiment without the use of any solvent, thus avoiding the requirement of a rotary evaporator and the use of a volatile solvent as toluene with highly activated phenols such as resorcinol, the reaction can be performed under much milder conditions. This provides a useful route to umbelliferone derivatives.

__**Procedure:**__ In a 50ml Erlenmeyer flask combine ethyl aceoactate (1.0ml, 7.8 mmol), resorcinol (.08 g, 7.3mmol) and Dowex 5W20 beads (1.0 g). In two additional 50ml erlenmeyer flask add 20ml water to one and 15ml ethanol (95%) to the other. Place all three flasks on a hot plate and set to level 5 occasionally stirring and swirling the mixtures until the substance stops bubbling and becomes a solid red matter. (20- 30 min) When reaction is complete add 2ml warm ethanol (95%) to dissolve the solid. Using a Pasteur Pipette, pipette the warm ethanol solution from the dowex beads into a clean Erlenmeyer flask. If necessary, repeat warm ethanol wash two to three more times to produce a greater yield. While heating the ethanol solution add hot water until the solution becomes cloudy and then allow ethanol solution to cool slowly to room temperature. Collect white to off white preciptate by the vacuum filtration and wash with distilled water. Allow substance to dry before taking a melting point and characterizing by IR spectrum. After samples have been measured and processed dissolve a small amount (20mg) of the product into 2-3ml of ethanol (95%) into three separate test tubes. Alter the pH of two of the test tubes by adding 2 ml of a 10% HCl solution into one tube and then adding 10%Na2CO3 to the other and place under a UV Lamp.

Step 1



Step 2 -3 Step 4.

Step 5 Step 6. Final Step

__**Data:**__ Final Product: 1.35mmol % yield=(Actual yield)/(theoretical yield) x 100% = 1.35mmol/7.3mmol x 100%= 18% yield melting point of final product: 128.8C-182.6C melting point of the original 7-hydroxy-4-methylcoumarin: 190-192C
 * Dowex 50X4 || 1.0g ||
 * Resorcinol || 7.3mmol(800mg ||
 * Ethyl Acetoacetate || 7.8mmol(1.0ml) ||
 * Water || 12.0ml ||
 * Ethanol (95%) || 6.0ml ||

Change of pH: Change of color Acidic pH: Green Basic pH: Blue Product: Bluish

__**IR Spectrum:**__

__**<< http://webbook.nist.gov/cgi/cbook.cgi?Scan=cob2732&Type=IR >>**__

Different characteristics can be observed comparing the IR spectrum and the melting points from the original 7-hydroxy-4-methylcoumarin and the one made it in lab. The absence of a round peak around 3000cm-1 on the IR spectrum indicates a lack of OH group attached to the compound, this could indicates that the procedure was not as accurate as a could be (in the moment of extracting the hot ethanol from the Dowex some residue of Dowex could of end up in the ending precipitate) and this would also explain the large range of melting point obtained from the sample. As the sample was being observed in the Mel Temp you could easily see that the impurities that came from the Dowex liquidized at lower temperature that started at around 122.6 degree Celsius, however the major product remained intact until the higher temperatures where reached which completely melted at 182.6 degree celsius which was very similar to lab manuals projected melting point for the product. Though the fluorescent ending product indicates the presence of a coumarin.This Pechmann condensation introduces the students to numerous types of organic reactions, such as Transesterification. Transesterification is the process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst in this experiment the Dowex was used as the catalyst and ether was used to replace the alcohol. Electrophilic aromatic substitution was observed when the addition of the warm ethanol was added to the mixture to extract the dowex from the pure mixture. Alcohol dehydration is also easily observable from the filtration of the mixture as it dried and was used for the IR spectrum and to determine a melting point for our final substance. To clarify that the procedure has been followed correctly by using a simple handheld long-wave UV lamp, adds attractiveness and potential utility of this experiment. This experiment is also consider to be a green chemistry experiment because you are able to recycle the Dowex after it has been heated extracted and processed in this experiment. By using these chemical sources it also has economic and environmental benefits because you do not need to obtain hazardous and dangerous chemicals from laboratories to help in the extraction and the energy used to produce this produce has alot less impact on behalf of the researchers and on the environment around them. For this lab group it was fairly easily to look at the mechanism and IR spectrum and understand at which step in the procedure each part of this experiment underwent and how the molecule had materials added and extracted to find a solid mixture for a final product. The data and results gathered from this lab were very similar to the ones expressed in the lab manual and this can be credited to exact measurements, slowly heating and cooling the mixture, carefully extracting the Dowex, and multiple attempts of filtering the final product which allowed similar results compared to those express in the lab manual.
 * Conclusion:**

Thanks, Sol, for finding this page for me. I have evaluated this lab now. July 7