Question

Determine the theoretical yield and limiting reagent

Running the Reaction Add 0.100 g benzil and 0.30 mL 95% ethanol to a 3-mL conical vial. Place a spin vane in the vial and attach an air condenser. Heat the mixture with an aluminum block (90-100°C) while stirring until the benzil has dissolved (see inset in Tech- nique 6, Figure 6.1A). Using a 9-inch Pasteur pipette, add dropwise 0.25 mL of an aqueous potassium hydroxide solution' downward through the condenser into the vial. Gently boil the mixture (aluminum block about 110°C) while stirring for 15 minutes. The mixture will be blue-black. As the reaction proceeds, the color will turn to brown, and the solid should dissolve completely. Solid potassiunm benzilate may form during the reaction period. At the end of the heating period, remove the assembly from the aluminum block and allow it to cool for a few minutes Crystallization of Potassium Benzilate Detach the air condenser when the apparatus is cool enough to handle. Transfer the reaction mixture, which may contain some solid, with a Pasteur pipette into a 10-mL beaker. Allow the mixture to cool to room temperature and then cool in an ice-water bath for about 15 minutes until crystallization is complete. It may be necessary to scratch the inside of the beaker with a glass stirring rod to induce crys- tallization. Crystallization is complete when virtually the entire mixture has solid- ified. Collect the crystals on a Hirsch funnel by vacuum filtration and wash the crystals thoroughly with three 1-mL portions of ice-cold 95% ethanol. The solvent should remove most of the color from the crystals. Transfer the solid, which is mainly potassium benzilate, to a 10-mL Erlenmeyer flask containing 3 mL of hot (70°C) water. Stir the mixture until all solid has dis solved or until it appears that the remaining solid will not dissolve. Any remaining solid will likely form a fine suspension. If solid does remain in the flask, filter the mixture in the following manner. Place about 0.5 g of Celite (Filter Aid) in a beaker with about 5 mL of water. Stir the mixture vigorously and then pour the contents into a Hirsch funnel (with filter paper) or a small Büchner funnel while applying a gentle vacuum, as in a vacuum filtration (Technique 8, Section 8.3, and Figure 8.5) Be careful not to let the Celite dry completely. This procedure will cause a thin layer of Celite to be deposited on the filter paper. Discard the water that passes through this filter. Pass the mixture containing potassium benzilate through this filter, using gentle suction. The filtrate should be clear. Transfer the filtrate to a 10-mL Erlern meyer flask. If no solid remains in the flask, the filtration step may be omitted. In either case, proceed to the next step EXPERIMENT 32C Preparation of Benzilic Aciá Formation of Benzilic Acid ith swirling of the lask, add dropwise 0.50 mL of 1M hydrochloric acid to the ion of potassium benzilate. As the solution becomes acidic, solid benzilic acid H should be about 2; if it is higher than this, add a will begin to precipitate. The p few more drops of acid and check the pH again. Allow the mixture to cool to room temperature and then complete the cooling in an ice bath. Collect the benzilic acid by vacuum filtration using a Hirsch funnel. Wash the crystals with 3-4 mL of ice- cold water to remove potassium chloride salt that sometimes coprecipitates with benzilic acid during the neutralization with hydrochloric acid. Remove the wash water by drawing air through the filter. Dry the product thoroughly by allowing it to stand until the next laboratory period. Melting Point and Crystallization of Benzilic Acid Weigh the dry benzilic acid and determine the percentage yield. Determine the melt- ing point of the dry product. Pure benzilic acid melts at 150°C. If necessary, crystal- lize the product from hot water using a Craig tube (Technique 11, Section 11.4, and Figure 11.6). If some impurities remain undissolved, filter the mixture using the fol- lowing procedure. It will be necessary to keep the mixture hot during this filtration step. Transfer the hot mixture to a test tube with a Pasteur pipette. Clean the Craig tube and filter the mixture by transferring it back to the Craig tube with a filter-tip pipette. Cool the solution and induce crystallization, if necessary. Allow the mixtur to stand at room temperature until crystallization is complete (about 15 minutes Cool the mixture in an ice bath and collect the crystals by centrifugation. Determin the melting point of the crystallized product after it is thoroughly dry он о 30 C-C-OH 25 20 15

Answer 1

Date olction0R Reacion for Benzilic aid Benzil holAgueous PotasSjum hydroxide Relux Intesmediadte EL OK rochIonc teumediate ac

Theore tial yield 一 -Theoretical yield is the, calculati not amount of the benzilcadd.Produted-dring the radion. As annou ot benz lic acid produced hon·DLactfDn16 hot honded in question. So it is ta naing an cussum phion imale benzil give d mole Genzilic au d ILgn.of ben 2.1 gives一229 gm-of ben리 lic-a44 21 ③ Linitina Reagent Limitin of abore mation is Benzil