Consider the alkylation of acetaminophen: acetaminophen + K 2 CO 3 + butyl iodid
ID: 1028298 • Letter: C
Question
Consider the alkylation of acetaminophen:
acetaminophen + K2CO3 + butyl iodide ----> 4-butoxyacetanilide
When the 4-butoxyacetanilide-solution is made, 5 mL of water is added and the solution is extracted to a test tube. 1 mL diethylether is added to the round-bottomed flask (contains filler from the tablet) and the solution is extracted to the same test tube. The contents in the tube is transferred to a seperating funnel and the phases are extracted (water phase in another test tube). The water phase is extracted with 2.5 mL diethylether two times, and the ether-phase is added to the first test tube. The ether-phase is then washed with NaOH (5%, 2.5 mL) 3 times, and the water-phase is extracted to a new test tube. The ether-phase is then extracted using a saturated NaCl-solution, and dryed using MgSO4. The solvent is then removed using reduced pressure.
A) Which impurities is it possible to find the final product?
B) Why are the ether-phases washed with NaOH and extracted with a saturated NaCl-solution?
C) TLC-analysis shows unreacted acetaminophen. What steps can be taken to improve purity in the final product?
Explanation / Answer
A) Unreacted acetaminophen and butyl IOdide (reactants) may be present as impurities in the product
B)Ether phase contains the product 4-butoxyacetanilide(non-polar soluble only in non-plar solvent ether),so it is washed with NaOH to wash away any unreacted acetaminaphen as its sodium salt.
[acetaminophen]-OH +NaOH ---->[acetaminophen]-O-Na+ +H2O
it is extracted with saturated NaCl,as a salt solution helps in separation of water layer from the organic layer ,(water moves into salt solution due to osmosis)
3)The organic layer must be extracted with NaOH several times ,until all the polar component(unreacted reactants ) get extracted from the organic layer leaving behind purest possible product.