Question

I'm quite new to organic chemistry and want to try menshutkin reaction. Like the reaction in an attachment. I use that recipe: I do everything in a 60ml beaker. I dissolve 18 mmol of pyridine in 35 ml of acetone. I add 115 mmol of 1,6-dibromohexane and stir for 30 minutes. Then I add 76.6 mmol KOH (in the form of crushed pre-flakes). Stir for the next 24 hours. Then I put the whole thing into a solution of 50 ml of dichloromethane and 100 ml of water. I mix for 1 hour, then pour into a funnel (I have a small 25ml one, so I do it several times). I evaporate the whole thing using a 60-80 degree water bath until all the dichloromethane evaporates. Then, after cooling down, I wash it a few times with pentane (it cleans the material from the residual dibromohexane, unfortunately I don't have a vacuum pump). Unfortunately, I only got 5% yield and the product still look little reddish, what am I doing wrong?

Answer 1

To improve the yield and purity of the Menshutkin reaction product, verify the ratios and purity of reactants, consider optimizing reaction conditions, and use more efficient purification methods like vacuum filtration or column chromatography.

Step-by-step explanation:

There appear to be several potential issues contributing to the low yield and impurity of your Menshutkin reaction product. First, consider the scale of reagent ratios as well as the reaction time and conditions. Your use of a water bath for evaporation may not provide the reduced pressure necessary to completely remove solvent, which could be detrimental to the yield and purity.

Furthermore, using dichloromethane at room temperature could be less effective for washing and may not remove all impurities. The reddish color indicates possible side reactions or incomplete purifications.

Professional suggestions to improve the yield would include ensuring the adequate molar ratios of reactants, verifying the purity of the starting materials, optimizing the reaction conditions (temperature and time), and improving upon the purification method, potentially through the use of vacuum filtration or column chromatography for a more efficient removal of by-products.