Procedure:Calculations1. Calculate the volume required to produce 0.0125 mol of acetone.2. Calculate the volume of 2.2 “equivalents” of benzaldehyde. (In other words, 2.2 times asmany moles of benzaldehyde as of acetone.) Note: the equation involves a simple 2:1stoichiometry.By using an actual 2.2:1 ratio, it ensures that the benzaldehyde is surplus and that theacetone is limiting. This is helpful for several reasons:a. Aldehyde oxidation. Aldehydes are often impure, because oxidation to carboxylicacid is fairly facile. By using 2.2 equivalents of benzaldehyde, then even if 10% ofthe benzaldehyde is corrupt we ensure that we still have enough to fully react with theacetone.b. Reaction Time. By having an excess of benzaldehyde, it makes it easier for thereaction to go to completion. Otherwise late in the reaction there isn’t muchbenzaldehyde left to react, so the reaction slows down a lot. By intentionally puttingin some extra, it maintains at least a minimal concentration of electrophilic till thevery end, such that getting 100% conversion of the ketone isn’t so hard and doesn’ttake so long. Ease of Product Purification: Disubstitution versus monosubstitution. Enablingcomplete conversion greatly simplifies purification. If complete conversion does notoccur, either because benzaldehyde runs out or because insufficient time is used, thedesired “disubstitution” product “dibenzalacetone”, in which two benzaldehydes havebeen incorporated, is contaminated by “benzalacetone”, the “monosubstitution”product in which only one benzaldehyde has been incorporated. Since the mono- anddisubstituted products aren’t that different, it’s not that easy to remove the undesiredside-product from the main desired product. But if you just make sure the reactiongoes all the way to the desired product, then you don’t need to worry about it!Doing the Reaction:1. Use a 125-mL Erlenmeyer flask with a magnetic stirring bar.2. Add 50 mL of the NaOH-Ethanol-Water solution mixture.3. Place the solution on the magnetic stirrers and adjust the stirring dial to get a nice, evenstirring action.4. To this add the calculated amount of benzaldehyde by syringe5. Add the calculated amount of acetone by syringe, last. (The acetone should go in last, afterthe benzaldehyde electrophile is already available. If the acetone goes in first, it could doaldol condensation on itself, in which enolate anions just attacks neutral acetone carbonyls.Ketone carbonyls aren’t competitive with aldehyde carbonyls as electrophiles, but if there areno aldehydes available, ketones are better than nothing!)6. Watch the solution carefully, with a watch, at the beginning of the reaction, so that you cankeep good observational records.How long does it take for the solution to turn yellow? Given that all the reactants arecolorless, what does the yellow color mean?
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