rystals if you add a little extra solvent after it dissolves completely. lask fr
ID: 556559 • Letter: R
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rystals if you add a little extra solvent after it dissolves completely. lask from the hot plate and allow the solution to cool slowly. As the solutionu seved it with a solid product that forms on a spatula after the solution. The solution may become Remove the the spatula is dipped into supersaturated unless this is done, and crys- on will occur too rapidly. Yellow crystals are formed. Cool the mixture in an e bth to complete the crystallization. Collect the product on a Hirsch funnel un- vacuum. Rinse the flask with small amounts (about 1 mL total) of ice-cold % to complete the transfer of product to the Hirsch funnel. Continue drawing ethanol air through the crystals on the Hirsch funnel by suction for about 5 minutes. Then remove the crystals and air-dry them. Yield Caleulation and Melting-Point Determination The melting point of pure benzil is 95 C.Submit the benzil to the instructor un Weigh the dry benzil and calculate the percentage yield. Determine the melting point less it is to be used to prepare benzilic acid (Experiment 32C. Obtain the infrared spectrum of benzil using the dry film method. Compare the spectrum to the one shown. Also compare the spectrum with that of benzoin. What differences do you notice? 32C EXPERIMENT 32C Preparation of Benzilic Acid In this experiment, benzilic acid will be prepared by causing the rearrangement of the a-diketone benzil. Preparation of benzil is described in Experiment 32B. The rearrangement of benzil proceeds in the following way: K+ Ph Ph (23 Ph-c-OH Ph Ph Benzilic acid The driving force for the reaction is provided by the formation of a stable carboxy- late salt (potassium benzilate). Once this salt is produced, acidification yields ben- zilic acid. The reaction can generally be used to convert aromatic a-diketones to aromatic -hydroxyacids. Other compounds, however, also will undergo benzilic acid-type of rearrangement (see questions). SPECIAL INSTRUCTIONS This experiment works best with pure benzil. The benzil prepared in Experi- ment 32B is usually of sufficient purity after it has been crystallized. ©2013Congage Learning An ts Reserved May not be scarred. copied or duplicated, or posted toaputoy acost towetole.« whole QEnpartExplanation / Answer
Benzil molecular weight = 210.8
Benzilic acid molecular weight = 228.2
Therefore 210.8 g of benzil will produce 228.2 g benzilic acid
Is 100 % yield
For 0.100 g of benzil 100 % yield is achieved by cross multiplying
210.8 = 228.2
0.100 = ?
228.2 x 0.100 / 210.8 = 0.108 g
Therefore 0.100 g will produce 0.108 g of benzilic acid.
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