what to expect in two different tlc paper and what solvent is used to re crystal
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what to expect in two different tlc paper and what solvent is used to re crystallize the product?
practical exam - 2017 Fall Term (1) Techniques of . 1 KC bbhosted.cuny.edu practical exam - 2017 Fall em xam ane: You will conduct a reduction reaction of a ketone to an alcohol. You don't need to know the mechanism or which ketone you will work with. Assume that 1 mole of NaBH (Mw-38.03) reacts with 1 mole of reactant ketone to generate 1 mole of product alcohol as shown below. This exam is to evaluate your understanding of chemical laboratory skill and your lab skills. Show all the calculations on the back of this page.If you want to get another reactant,you lose 2 points out of 10. The whole experiment must be completed until 5:30 pm. 1. Put a round-bottom flask containing the reagents shown in the picture above a. Measure the weight of the given ketone ( molecular weight of the ketone ( bar into the reaction mixture g, 4.8 mmole) and calculate the ).Then, add 5 mL of ethanol and a stirring b. Calculate how many grams of NaBHs you need ( can consult Aldrich catalogs fo g: less than 0.3g). You r necessary information. Add the reducing agent slowly into the c. Check TLC of the reaction mixture. Copy the outcome on the TLC below. Label (1-c/your name) the actual TLC and Turn it in. 2. Stir the mixture for 20 min. 3. Add5 ml of water, then 2 mL of HCL. Then warm up the mixture to gentle boiling briefly 4. Add additional 1 then, coolit. 5. Filter and dry. Calculate the yield ( 6. Checkthe TLC and duplicate the result on the TLC below. Indicate which spots are the reactant ml of water; and the product. Calculate Rf values. Label (6/your name) the actual TLC and Turn it in 7. Find the best solvent for recrystallization of Type here to searchExplanation / Answer
The first TLC is of your crude reaction mixture TLC hence we can expect minimum two spots in this TLC : 1) Unreacted Ketone (if it is there), 2) Product alcohol. This TLC is to understand rough sepration of product (alcohol) and reactant (ketone).
The second TLC is after acidic workup. In the workup it is expected that unreacted ketone, inorganic salts to be removed in aqueous filtrate. The residue is crude product. In this TLC it is expected that only product alcohol to be present, but there is a chance of unreacted ketone to be present. (That is what it is checked how much pure the crude product is!)
For recrystalization there is no solvent mentioned as such in the given procedure. However, as per the solubility of your product you can chose. The solvent for recrystalization is chosen in such a way that, the alchol product should not be soluble in solvent at room temperature but it should be soluble at little higher temperature. Often for solid alcohols ether, ethylacetate, DCM or CCl4 are used as recrystalization solvents. Please make note that these mentioned solvents may not work with your product, you will have to find out what solvent is suitable in your particular case.
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