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B-Glucose Pentaacetate through the
acetylation of glucose with acetic anhydride
in the presence of a basic catalyst (sodium
acetate). Methods The procedure of this experiment incorporated
the mixture of sodium acetate and acetic anhydride
in a 10 mL round bottom flask. A small amount of
glucose was added, and the solution was stirred and
refluxed using a Microscale condenser for one hour.
The solution was heated in a hot water bath for 35 minutes, and then poured into 10 mL of ice cold DI water while stirring. A small amount of ethanol was added, and an extraction was performed with 3 X 5 mL of diethyl ether.
The ether layer was evaporated off through a hot
water bath, and the final product was collected. Results Observations: Conclusion Table 1: Compounds Used and their Respective Properties/ Hazards (2) Background Information:
*In solution, sugars exist in more than one form. Open straight chain and cyclic hemiacetal are most common.
*In forming the cyclic isomer, the carbonyl carbon becomes a chiral center.
*This forms two stereoisomeric configurations (anomers). The alpha-anomer and the beta-anomer (1). D-Glucose Alpha-D-Glucose Beta-D-Glucose Open Straight Chain Haworth Projections Figure 1: Figure 1: *The anomer in which the -OH group at Carbon-1 is below the ring (down) in the Haworth projection, is called the alpha-anomer.
*The anomer in which the -OH group at Carbon-1 is above the ring (up) in the Haworth projection is called the beta-anomer (1). Reaction Importance:
*This experiment helped to demonstrate the effects of a catalyst on the formation of the anomers.
*In the presence of an acidic catalyst like zinc chloride, the alpha-anomer is formed.
*In the presence of a basic catalyst like sodium acetate, the beta-anomer is formed (1). D-Glucose B-Glucose Pentaacetate Figure 2: Figure 2:
*This experiment used a basic catalyst (sodium acetate) for the purpose of forming the beta anomer. Green Chemistry! *The principles of green chemistry were incorporated in the following ways: 1. Use of Microscale kit to limit reagents used and wastes.
2. Using a small amount of glucose (about 0.200 g) for environmental sustainability.
3. Ethanol was used as a solvent to perform the recrystallization. Most experiments use methanol. We replaced methanol with ethanol because it is less flammable and more environmentally friendly.
3. Acidic catalysts like zinc chloride are often used in acetylation of glucose exploratory experiments. Besides the purpose of specifying the beta-anomer, the basic catalyst (sodium acetate) was used in this experiment because it is a safer chemical than zinc chloride.
*Zinc chloride often reacts with moisture in the atmosphere (2). O-H Peak Contaminant
Remaining Solvent Slight C-H Methyl Peak
Typical Range 2960 cm-1 Ester Carbonyl Groups Peak
Typical Range 1700 cm-1 C-O Functional Group Peak
Typical Range 1100 cm-1 Figure 4: IR Spectrum of Product (3) -After reflux, the liquid was a clear, slightly
-Recrystallization would not occur. Extraction
had to be performed with diethyl ether.
-Small amount of final liquid product remained which appeared oily and thick.
-Melting point could not be measured because the final product was a liquid. Figure 3: Masses/Data Obtained During the Experiment Figure 5: HNMR Spectrum for Final Product *Procedure had to be modified to obtain a product
which limited the available data from the experiment.
*The calculated percent yield (84%)
was relatively high, but could be attributed to the extraction process.
*The IR analysis indicates the desired functional groups are present on the product. A contaminant was present which could be from the ethanol or possible glucose remaining.
*The NMR indicates the possibility that the target product is missing at least one peak normally associated with Beta-glucose pentaacetate. NMR indicated contaminant. Experimental Errors: *Too much D.I. water.
*Did not heat product enough.
*Adaptation to Microscale experiment. Self-Reflection A) We have learned that it can be rather difficult attempting to design your own experiment in comparison to performing a procedure already written.
B) From the content, we learned the importance of a catalyst in an acetylation reaction. We found it very interesting that the catalyst not only helps to speed the reaction, but can also play a role in different formations of the product.
C) We learned this procedure does not work well with Microscale kits, and is not as simple as it appears.We would like to explore this reaction using an acidic catalyst, or using a higher quantity of reagents to more closely form the desired product. What Others Are Doing! Debaraj Mukherjee of the Indian Institute of Integrative Medicine
Manipulated the amount of acetylation, the presence of solvent, and the reaction temperature.
Molecular iodine catalyst and enol acetate
Low temperatures produced acetonide acetate and high temperatures produced peracetate (4) References 1) Nicholas, S. D., and F. Smith. "Acetylation of Sugars." Nature 161 (1948): 349. Nature. Web. 17 Apr. 2013. <http://www.nature.com/nature/journal/v161/n4088/abs/161349b0.html>.
2) Chemical Search/Sigma Aldrich. http://www.sigmaaldrich.com/catalog/search?interface=All&term=glucose&lang=en®ion=US&focus=product&N=0+220003048+219853269+219853286&mode=match%20partialmax
3) Spectra Database/B-D-Glucose Pentaacetate. http://www.chemicalbook.com/SpectrumEN_604-69-3_IR2.htm
4) Mukherjee D, Bhahwal Au S, Gupta P, Taneja S. Tandem Acetalation—Acetylation of Sugars and Related Derivatives with Enolacetates under Solvent-Free Conditions. Journal Of Organic Chemistry [serial online]. November 9, 2007;72(23):8965-8968. Available from: Academic Search Complete, Ipswich, MA. Accessed April 17, 2013.