QUESTIONS TO ANSWER:

1-What is the role of the silica gel beads in the reactionsetup?
2-What is the byproduct of the reaction if the Grignard reaction ifthese silica beads weren’t there?
3-The sulfuric acid has 2 roles what are they?
4-Why we cant we use hydrochloric acid instead of sulfuric acid?and explain
5. If there was another spot on the TLC plate, what would be thatother spot assuming all starting material was consumed? At whatstage of the workup do we separate this biproduct fromtriphenylmethanol?

RXNS OF GRIGNARD REAGENTS Experiment

BACKGROUND INFO:

Procedure:

1. Set up the apparatus using the dry conical vial and a dryingtube filled with Drierite and plugged at each end with a piece ofcotton. Heating should be done using a stirring hotplate.

1. Transfer 4 mL of anhydrous diethyl ether to larger vial providedin the kit andquickly cap the vial. Use this throughout theexperiment when anhydrous ether is needed and be sure to keep thevial capped whenever it is not in use.

2. Accurately weigh about 0.05 g of magnesium turnings. Do nottouch them. Use the mortal and pestle to remove any oxidation fromthe surface of the metal. Add the magnesium to a clean dry 5 mLconical vial. Add the spin vane to the vial with the magnesium.

3. Prepare a solution of 0.24 mL of bromobenzene in 0.5 mL ofanhydrous diethyl ether in the small vial provided in the kit.Gently swirl the solution so that it becomes homogeneous.

4. Using a clean vial from your drawer, obtain ~1.5 mL of 3 MSulfuric acid and place it in an ice bath for later use.

At this point it is important to follow the steps and keepeverything capped and use the syringe. DO NOT CLOSE THE NEEDLEUNTIL YOU ARE FINISHED USING IT. It cannot be reopened onceclosed.

1. Using the syringe provided in your kit, draw up 1.0 mL of theanhydrous diethyl ether. Add this to the conical vial by insertingthe needle through the septum cap

2. Draw 0.25 mL of the bromobenzene solution into the syringe andrecap the vial. Insert the syringe needle through the septum capand add the solution to the reaction vial and begin gentle heating(very low heat). Hold the plunger of the syringe to control therate of addition.

3. Begin slowly stirring the reaction mixture in the conicalvial.

4. After a few minutes, the solution will start to boil. You willhave to turn off

   the stirrer briefly to determine this.

5. After small bubbles begin to form, immediately lift the vial offthe hot plate and turn off the heat. The stirrer should stillwork.

6. The mixture will start to turn slightly cloudy or chalky oncethe reaction has started, and bubbling will continue withoutfurther heating. You can turn the stirrer off briefly to seeclearly what is happening. If this does NOT happen, see yourinstructor

7. As soon as the reaction begins, add another 0.5 mL of anhydrousdiethyl ether to the reaction vial.

8. Add the remaining bromobenzene solution DROPWISE at a rate thatdoes not cause too vigorous a reaction.
   DO NOT LET THE VOLUME IN THE VIAL GET TOO LOW OR EVAPORATECOMPLETELY – add more anhydrous diethyl ether

9. Add 0.5 mL of anhydrous diethyl ether to the vial that containedthe bromobenzene solution. Add this solution to the vial in oneportion

10. Continue to stir the solution for 15 minutes. DO NOT LET THEVOLUME DROP BELOW 2 MLS. The solution should turn a yellow or browncolor

11. During the time that the solution is stirring, prepare asolution of 0.12 mL of methyl benzoate in 0.5 mL of anhydrousdiethyl ether in the screw-cap vial that originally held thebromobenzene solution. There is no need to clean the vial beforeuse. Quickly cap the vial.

12. When the Grignard reaction has run 15 minutes, draw the methylbenzoate solution into your syringe and add it dropwise to thereaction vial. This reaction is exothermic, so add slowly enoughthat the diethyl ether vapors do not reach the Claisen adapter.(The solution should turn pink or red, even if only briefly.)

13. Add 0.3 mL of anhydrous diethyl ether to the vial that containedthe methyl benzoate to rinse the vial. Add this solution in oneportion to the conical vial

19. Let the reaction mixture continue to stir for 15 minutes. Ifit stops stirring with the spin vane you can take off the top andoccasionally stir with your spatula.

At this point, put away the needle and syringe that came in yourkit and do not use them again!

1. Remove the Claisen adapter and drying tube and place the conicalvial in an ice bath. Be very careful taking off the drying tube.This point is where most of them are broken! Return your kit to thestockroom at this point.

2. Slowly add about 1.5 mL of ice-cold 3 M sulfuric acid dropwiseto the reaction mixture. Add slowly to avoid frothing of thereaction mixture. The contents of the vial may solidify. Use asmall glass stirring rod or spatula to break up the solid duringthe acidification. If needed, close the vial and shake with ventingto induce dissolution of all solid materials. Two distinct layersshould appear when all the material is in solution.

3. If needed, add solvent grade diethyl ether to get the materialinto solution. (You may use anhydrous ether if you have some leftover, but use solvent grade once you run out of anhydrous at thispoint.) You may also need to add more 3 M sulfuric acid. Cap thevial and thoroughly mix the two layers. Be sure to vent the vialoften. (Usually when the entire solid is dissolved there will beapproximately equal ether and aqueous layers and the vial will benearly full.)

4. Remove the top ether layer and place it into a 10 mL conicaltube from your drawer and cap the tube.

5. Wash the remaining aqueous layer with 0.5 mL of diethyl ether.Remove this ether from the aqueous layer and place it in the tubewith the first ether layer from step 22.

6. Wash the combined ether layers with 0.5 mL portions of saturatedsodium bicarbonate (VENT!!!!). Discard the bottom aqueous layersaving the ether layer.

7. Repeat with another 0.5 mL portions of saturated sodiumbicarbonate (VENT!!!!) Discard the bottom aqueous layer.

8. Wash one 0.5 mL portion of saturated NaCl. Discard the bottomaqueous layer.

9. After removing the last saturated NaCl wash, add anhydroussodium sulfate to the ether solution until there is some rollingsodium sulfate. Allow the solution to dry for a few minutes.

10. Transfer the dried ether solution to a dry screw-cap vial fromyour drawer. You can add fresh diethyl ether to the sodium sulfateto extract more product and combine with the original driedsolution.

30. Place the uncapped vial in a small, labeled beaker and leaveit in the hood until the next lab period.

Second Day:

1. Obtain your vial from the fume hood.

2. Add 1.0 mL of petroleum ether to the vial and scrape the sidesof the vial with a small stirring rod or spatula. The product willnot dissolve. This process is called trituration.

3. Filter the material using vacuum filtration in a Hirsch funneland allow it to dry for a short time. It will be difficult toremove the entire solid from the vial. The solid that does not comeout can be left in the vial and dissolved with hot isopropylalcohol during the next step.

4. Weigh the centrifuge tube that comes with the kit that you checkout.

5. Transfer the crude product from the filter to the centrifugetube.

6. Heat isopropyl alcohol (~20 mL) to near boiling and add it insmall amounts to the crude product until all is in solution (~2-4mL) while heating. The solid that could not be removed from thevial after trituration can be included by dissolving with a portionof the isopropyl alcohol and added to the product of filtration.(Do not filter hot solution.) Add the minimal amount of isopropylalcohol needed to dissolve the product

7. When all the solid is in solution, cool to room temperature andthen place in an ice bath.

8. Add 3-5 mL of water to the cooled solution in the ice bath. Youshould see cloudiness.

9. Centrifuge the tube until the solid is plastered against oneside and the solution is clear. You will need to find a partner tobalance the centrifuge. Your water level should match yourpartners. If they did not match, you can add more water to the samelevel as your partner.

10. Pipet off all the liquid.

11. Dry the solid product using a stream of nitrogen. It will beflaky when dry.

12. Determine the weight of the product.

13. Determine the melting point of the product and analyze usingthin-layer chromatography. Turn in the remainder of your product asdirected.

TLC Plate Preparation

1) Obtain a TLC plate
a. Make sure to handle the plate by the sides or plastic backingonly. Do NOT touch

the absorbent (dull) side of the TLC plate

1. 2) Using a pencil (NOT PEN THIS TIME), draw a line 1 cm up fromthe bottom of the dull

   ide of the TLC plate. Draw VERY lightly as too much pressurewill ruin the plate.

2. 3) In the middle of the line draw an “X”

3. 4) Prepare the chromatography jar (or beaker)

   1. Obtain a chromatography jar

   2. Add half a piece of filter paper to the inside of the jar

   3. Saturate the filter paper with dichloromethane and fill thebottom of the jar with

      the mobile phase (dichloromethane), making sure not to fill ithigher than the line on the TLC plate. Overfilling the chamber willdissolve your sample instead of eluting on the plate.

4. 5) Prepare your sample – You want to make sure you haveeverything you need for the TLC before preparing your sample.

   a. Place a small amount of crystals (1-2 crystals) on a clean,dry 3-dram vial.
   b. Place a small amount of acetone (3-4 drops) to the 3-dram vialto dissolve the

   crystals.

5. 6) Loading the TLC Plate

   a. Obtain a TLC capillary tube - it should be open on bothends.
   b. Place the capillary tube into the ethyl acetate solution. Thesolution will be

   drawn up the tube by capillary action.
   c. Quickly tap the loaded capillary on the middle of the “X” on theTLC plate. This

   can be done by tapping quickly several time on the “X”
   d. You need to check to see if you sample was transferred properlyto the TLC plate

   by viewing the plate under the short wave UV lamp in 344 HH. Youdo not want

   your sample spot to be too big/small or too faint.
   e. If your acetone evaporates, you can add more and continue.

6. 7) The place the TLC plate into the jar (using tweezers) withthe mobile phase making sure that the bottom line is above themobile phase.

7. 8) Place a lid over the jar and allow the mobile phase to moveup the TLC plate

8. 9) When the mobile phase stops moving (should be at least halfway up the plate), remove

   the plate.

9. 10) Immediately mark the solvent line with a pencil.

10. 11) Allow the plate to completely dry.

11. 12) Take the TLC plate to 344 HH and bring a pencil withyou.

12. 13) Place the TLC plate under the UV lamp and turn on the shortwave UV. The plate should

    look green with dark colored spots.

13. 14) Draw circle(s) around any spot(s) that appears along themiddle of the plate.

14. 15) Measure the distance from the bottom line to the top line(in cm).

15. 16) Measure the distance from the bottom line to the middle ofthe spot(s).

16. 17) Record this data on your lab report.

17. 18) Calculate the Rf of the triphenylmethanol. If you have twospots, determine which one is

    the triphenylmethanol.

18. 19) Turn in your TLC plate along with the sample to yourinstructor with your initials on the

    top of the plate.