Ch. 4 Synthesis Of Acetophenetidin

24 July 2022
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question
What is recrystallization?
answer
It is technique to purify organic solids by removing the impurities in it. Impurities hinder the crystal lattice structure of these compounds. So in order to do recrystallization you should choose a solvent which dissolves the compound along with the impurities at boiling point and only the impurities at cold temperature, otherwise the impurities will crystallize with the pure material.
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How does recrystallization work?
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An impure sample is first dissolved in a minimum amount of solvent at the boiling point. Any insoluble impurities are typically removed by hot gravity filtration. The hot saturated solution is then allowed to cool to room temp. Crystallization starts here, where seed crystals start forming nucleation sites where more molecules of the desired compound deposit themselves in layers. Once put in ice bath the process becomes rapid. These crystals can then be collected through vacuum filtration, and a small rinse with ice cold solvent can remove any trace impurities. The filtrate can go through the whole process again to get a second crop.
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Amide synthesis recap:
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p-phenetidin + dilute HCL and then decolorizing carbon to take out impurities. Then sodium acetate and anhydride to create the amide bond.
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Why is HCl used instead of plain deionized water in p-phenetidine in amide synthesis of acetophenetidin?
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HCl is used for the acid-base reaction rather than water because HCl's polarity contributes to a reaction driven to the right. It protonates the amine group, making it easy to dissolve.
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What is the purpose of the sodium acetate solution in the amide synthesis of acetophenetidin?
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It is used to buffer the reaction mixture because control of acidity is important in maximizing yield. Protonation activates acetic anhydride toward nucleophilic attack, but if the pH is too low the starting amine will will be converted to its conjugate acid.
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Williamson-ether synthesis recap:
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p-acetamidophenol + sodium methoxide in methanol replaces the OH with ONa (williamsom ether). Then bromoethane to replace the Na with the ethyl.
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What does the reflux condenser do? What did we use it for?
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Allows the reaction to be carried out at the boiling point of the solvent and yet it prevents loss of solvent or reagent due to evaporation. The vapors condense as they rise up the condenser and thus prevent them from escaping. We used it for Williamson Ether synthesis of acetophenetidin. ( In the assembly water flows into the condenser from bottom and out from top.)
question
Why should you always use a boiling chip whenever you heat any liquid in the lab?
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Boiling chips provide a large surface area and give the gas that forms from the hot liquid a place to form and then release. To summarize, it prevents bumping.