The procedure and questions are pictured.

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Experimental procedure Preparation of Grignard reagent: Part A Note: This reaction requires anhydrous conditions to be maintained throughout the experiment. Make sure all the glassware components needed for this reaction, (100-ml round bottom flask, Claisen adaptor, condenser, 125-ml separatory funnel, 25-ml, or 50-mL Erlenmeyer flask), are dry. This can be done by washing them (rinse with acetone) and storing them in the glassware kit a week before this lab, or dried at 110-120°C in the oven for 15 hour just before use). a 1. Assemble apparatus in a fume hood as shown in the experimental setup using a dry 100-ml round bottom flask (equipped a magnetic stirrer bar), water condenser, Claisen head, and drying tube. You may start circulating water in the condenser. 2. Weigh 0.50 gram of magnesium turnings (sold specifically for Grignard reagent preparation) in a plastic weighing boat. Disconnect the 100-ml. round bottom flask from the apparatus setup and place the magnesium turnings in it. Stopper the flask. 3. Measure approximately 2.1 ml bromobenzene (mw 157.0) in a preweighed 10-ml. graduated cyl- inder. Determine the exact mass of bromobenzene by difference and transfer it via Pasteur pipet to a dry 25-or 50-ml. Erlenmeyer flask. Rinse the graduated cylinder with 10 mL of anhydrous diethyl ether and add it to the Erlenmeyer flask containing the bromobenzene. Transfer approxi- mately half of the bromobenzene solution to the round bottom flask containing magnesium and reconnect it to the Claisen adapter in the original setup. Add the remaining half of the bromoben- zene solution to the separatory funnel. Add an additional 7.0 mL of anhydrous ether to the separa- tory funnel (a second drying tube may be placed on the separatory funnel to insure a dry setup).* After making sure that all connections are firm and secure, let the whole setup stand a few centim- eters above the hot/stir plate and start stirring the reaction mixture slowly. If the pieces of magne- sium rise above the walls of the round bottom flask, gently use repeated "knocks" on the outside of the flask to "goad" them back to the main solution (it is important that magnesium remains constantly in contact with the solution throughout the reaction). You can also stop and restart the stirring and change the stirring speed to help keep the Mg in solution. After several minutes, you should be able to see some bubbles emerging from the reaction mixture. If you don't, gently heat the reaction mixture (use low heat setting; the boiling point of diethyl ether is only 34°C!) till the warm air currents from the heater start boiling the ether. This mild heating should start the reaction (bubbles forming and the solution starting to get cloudy).** If it does, stop the heating *Alternatively, 2.1 ml bromobenzene can be conveniently measured using a dry measuring cylinder and added directly to a preweighed, dry100-mL round flask and weighing it again to determine the mass of bromobenzene. Then, 10.0 mL of anhydrous ether is added to it and approximately half of the resulting solution is transferred to the 125-ml. sep- aratory funnel. To the remaining solution in the round bottom flask, a magnet bar is added followed by 0.50 gram of magnesium. The round bottom flask is quickly re-connected to the Claisen condenser. Finally, 7.0 mL of fresh ether is added to the separatory funnel. **If you do not see the gas-bubbling at all, it means that Grignard formation has not started. Try crushing magnesium pieces with a dry glass rod to jump start the reaction. If this strategy fails, add two small crystals of iodine to the stirred reaction mixture and see if the brown color of iodine disappears after several min of heating.. This will signal that the magnesium is ready to react. If this fails, too, then (time permitting-consult the instructor), perhaps a new experiment can be started and repeated in a new dry round bottom.

ment Mask. y. This fore this ry 100 and let the exothermic reaction sustain the smooth boiling till it subsides. At this point, start sustain the boiling action (perhaps at the rate of two drops a second) while maintaining efficient running in the bromobenzene solution from the separatory funnel dropwise at a rate sufficient to stirring. If the reaction stops at any time, low heating to boil the ether should be resumed. Several heating/cooling cycles may be necessary to keep the reaction in progress. A constant reflux must be maintained throughout the reaction. A good indication of the successful Grignard preparation is to notice a significant grey turbidity appearing in the ether solution and "greying or blackening of the diminishing magnesium with disintegration. After the addition is complete, gently heat the reaction mixture to maintain a smooth reflux for another fifteen minutes. Most of the magne- sium should disappear at this time. The few remaining grey pieces of magnesium may be ignored. The final reaction mixture containing the Grignard reagent will appear grey/brownish and turbid (cloudy). If you think that you have significantly lost the ether during the reflex, add some more anhydrous ether to the round bottom flask. This reaction mixture containing the Grignard reagent can be directly used for the synthesis of triphenylmethanol (Part B), or benzoic acid (Part C) as explained in the procedures given below. If you are asked to follow Part C procedure, remove the Claisen head, and stopper the round bottom flask with a glass stopper. app Synthesis of triphenylmethanol: Part B mob 1. (During the time interval of final fifteen-minute reflux in Part A, it is a good idea to use this time to make a solution of 2.4 g of benzophenone in 9.0 mL of anhydrous ether in a dry 50-ml. Erlenmeyer flask. Stopper the flask with a cork stopper, or cover it with a watch glass, until it is ready for Grignard reaction). entis 2. Start stirring the cooled Grignard reagent in the setup, remove the drying tube, and transfer the benzophenone solution quickly to the separatory funnel. Rinse the Erlenmeyer flask with about 5.0 mL of anhydrous ether, swirl it, and quickly add it to the separatory funnnel. Start adding the benzophenone solution diluted in ether from the separatory funnel dropwise to the Grignard reagent and stirr at a rate that maintains a gentle reflux (the reaction is exothermic). Make note of color changes you see during the addition. 3. When the addition is complete, allow the reaction to cool down to room temperature while con- tinually stirring. The reaction mixture first becomes rose colored and then will start thickening or solidifying. If the thickening hinders stirring, use a glass rod or spatula to stir it manually. At this stage, the reaction mixture is in the form of a precipitate of magnesium alkoxide salt. Isolation of the product 1. Measure about 7.0 mL of 6 M hydrochloric acid. Add it cautiously with a Pasteur pipet to the manually stirred solidified residue above. If the lower aqueous acid layer does not turn a pH-paper strip red, add a bit more 6 M HCl till it does. This will hydrolyze the magnesium ***Since the Grignard reagent is not stable over longer periods of time, it must be used in the same lab period fol- lowing Part-B or Part-C procedures which give details of the reaction between the Grignard reagent and dry ice, or benzophenone, respectively. cad, a ated cur p hyd strup

18 alkoxide salt completely to the desired product triphenylmethanol, leaving MgBr, salt in the lower aqueous phase and the product triphenylmethanol in the upper ether phase. The HCI will also destroy excess magnesium with evolution of a gas. If there are any lumps of solid in the mix. ture, agitate and break them with spatula or glass rod (add more ether or 6 M HCl to dissolve solid lumps). Ignore any stubborn lumps. Retrieve the spin bar with the long magnet bar retriever and transfer the two phases into an Erlenmeyer flask. Stopper the flask with a ground-joint stopper (tightly wrap a piece of Teflon tape around the stopper's ground joint to prevent it from sticking which could happen on storage: alternatively rub a tiny spec of vacuum grease on the stopper's ground joint before stoppering the flask). Secure the stoppered flask in a beaker and place it in your glass kit and store it. You may stop here. → 2. (Next lab session) Transfer this two-phase mixture to the separatory funnel. Rinse the Erlenmeyer flask with a few more mLs of the ether and add the rinse to the separatory funnel. There should be two clear phases present in the separatory funnel. Add more ether to it, if you think it is not enough. Drain off the lower aqueous phase into a beaker and save it for a second extraction. Drain off the upper ether phase into a clean Erlenmeyer flask and save (this contains your desired product, triphenylmethanol). Place the acidic aqueous phase back into the separatory funnel. (Add-5.0 mL of ether to it. Stopper the funnel with a glass stopper and shake well. Release the gas pressure by carefully inverting the separatory funnel and releasing the pressure by opening the stop cock. Wait till the two layers separate. Drain off the lower acidic layer and discard it in the waste container designated for it (in the common hood). Drain off the ether layer and combine it with the first extract. Examine the combined extract carefully. It should not have any globules of water present in it. If it does, carefully siphon off the globule with a glass Pasteur pipet. Add 1.0 g (or more if necessary) of anhydrous sodium sulfate for the final drying of ether layer containing the triphenylmethanol product (remember that the by-product biphenyl should also be present in this layer-both are soluble in ether. →→3. Carefully decant the ether layer from the solid sodium sulfate into a clean Erlenmeyer flask. Clamp the flask while suspending it in a 30-40°C water bath and evaporate off all ether with a slow flow of air. This should leave you with some solid mixed with oil at the end as a residue con- taining triphenylmethanol and biphenyl. 4. Add 10.0 mL of petroleum ether (a mixture of hydrocarbons, bp 30-60°C-not be confused with diethyl ether or ether) and stir with a spatula or glass rod, while heating gently and briefly in a 50-60°C water bath, to "leach" the biphenyl into it leaving behind the triphenylmethanol. Remove the Erlenmeyer flask from the water bath and let it cool to room temperature. Filter off the petroleum ether layer containing the by-product biphenyl on a Büchner funnel and wash the crystals of triphenylmethanol with petroleum ether. Air-dry the crude crystals and determine its crude % yield. *Crystallization: The final purification can be achieved by crystallizing the product triphe- nylmethanol from a minimum quantity of hot isopropyl alcohol (2-propanol). Collect the crystals on a Büchner funnel. Dry the product in air or between two thicknesses of filter paper and determine its % yield and melting point (literature value 162°C) of the purified triphenylmethanol.

1. If you would have measured the 'H NMR of your product, or if you were provided with a ¹H NMR of the product you synthesized, which part of the spectrum would you expect the aromatic and other hydrogen atoms to appear? HRMEINTRITT at AVALE BDSwer WILD e neid OF A CHICHA 3. Benzene may have been one of the by-products of the Grignard reagent preparation. What is the source of this by-product? Support your argument with a chemical equation. 4. The HCl destroys excess magnesium with evolution of a gas. What gas is it? Write a balanced chemical equation to represent this reaction. te Dusic CATTRCT DCIere precipAAAAABAANUW entitled) ESSENTIE Waters 7. Would you expect the final product you synthesized to give you a higher or lower spot on your TLC compared to bromobenzene? Support your argument using principles of molecular polarity. Outline the works moet vecture Yo 9. Describe the preparation of the following compounds using Grignard reagents: u ore OH OH OH OH dk *