Discussion+of+green+synthesis+of+fluorescent


 * Introduction: ** The Pechmann condensation 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 had some positive modification of a chemical process through green chemistry. This synthesis uses Dowex 50 WX5 as the acid catalyst. In the past less green acids have been used including H2SO4 and POCL3. Resorcinol is used as the phenol. Dowex was 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. The condensation introduces students to numerous types of organic reactions, Transesterification, electrophilic aromatic substitution, alcohol dehydration and will provide the opportunity to interpret IR spectra to help elucidate the structure. Easily observable using a simple handheld long-wave UV lamp, adds attractiveness and potential utility of this experiment.


 * The experiment in brief: ** Ethyl acetoacetate (1 ml), resorcinol (.08 g) and Dowex 5W20 beads (1g) was combined in a 50ml Erlenmeyer flask. In two additional 50ml Erlenmeyer flask 20ml of water was added to one and 15ml ethanol (95%) to the other. The three flasks were placed on a hot plate and set to level 5 occasionally stirring for (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 into a clean Erlenmeyer flask. Hot water was added until the solution becomes cloudy and then allowed the ethanol solution to cool slowly to room temperature. The white precipitate was collected by the vacuum filtration and washed with distilled water. The substance was allowed to dry before taking a melting point and IR spectrum. After samples have been measured, a small amount (20mg) of the product into 3ml of ethanol (95%) was collected into three separate test tubes. The pH of two of the test tubes by was altered 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.


 * Our results: ** The products purity was determined by taking melting point and IR spectrum data. While comparing the IR spectrum and the melting point of the product and the actual results, the suppositions that may explain why the product shows different characteristics; The absence of a round peak around 3000cm-1 on the IR spectrum indicates a lack of OH group attached to the compound indicating that some residue of Dowex could of end up in the final product. The large range of melting point can also be explained for the same reasons of the presence of Dowex, as the sample was being observed in the Mel Temp some impurities from the Dowex liquidized at lower temperature 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. The observable color of the product is a mixture of the acidic and basic colors, which could mean that there is a combination of the final mechanistic product and an earlier version of the product. The green color of the product could represent the sigma bond between oxygen and hydrogen, the presence of this bond can be observed in the IR spectrum. Mentioning the environmental factors; Dowex catalyst is easily recoverable though recycling the catalyst requires three times the amount of acid to regenerate its original charge.

Heating the three Erlenmeyer flasks be sure to slowly heat the flask with the Dowex, otherwise the mixture of the Dowex and other components will boil and jump out the flask. We also learned when to when extracting the Dowex to be very careful just to extract the solution and not the particles of Dowex because will alter the final result. While filtering it’s a good idea to set up a double filter which will give a higher yield for the end up product.
 * We learned when: **

This is experiment is highly suitable for an organic chemistry lab. The visual fluorescent end up product adds attractiveness to the Pechmann reaction due to the presence of coumarins. In addition, students are introduced to the Pechmann reaction with some modification of a chemical process through green chemistry.
 * This experiment is highly suitable: **

Thank you, Sol, for your comments. +10