This is carried out via an SN2 reaction because the use of an alkyl-halide, Primary in the presence of a strong nucleophile, electrophile as well as substrate, with the reagents chosen this reaction as well as substrate, with the reagents chosen this reaction mechanism is the most favorable. The bromide ion from hydrobromic acid acts as the nucleophile.
Being a Primary alkyl-halide a one step mechanism backside attack occurs as expected in this reaction.This is enabled by the lack of hindrance at the negative end of the dipole substrate.
The use of H2SO4 in excess in an ice bath very slowly added allows for an increased yield. The addition must be slow and in an ice bath as it helps to prevent side reactions such as an Elimination Reaction to occur.
The reactions conditions are controlled using this acid also by using distillation to purify compounds which have repetitively high boiling points.These practices are used to control the conditions by taking advantage of the chemical properties which the Chemist can.
This is practice for what one might do after the knowledge of Organic Chemistry is fully taught. The H2SO4 acts as a protonating agent which transforms the 1-Butanol into a very favorable leaving group.
This is through the prioritization of the 1-Butanol creating an hydroxyl group to be a strong leaving group.Although this side reaction occurs, HBr is highly soluble in cold H2O as a gas it is not soluble in hot water. Any HBr which form should theoretically leave in gas form *(safety note incase this occurs remember that HBr is a strong acid and could damage ones lungs or any other exposure tissue. Be sure the fume hood is fully functional with the glass pulled down low enough to allow room for arms to work yet covers and blocks your airways from exposure.
A primary Alklyl Bromide is then prepared by heating the corresponding alcohol at its boiling point determined by the other solvents such as acid.100 mL round bottom flask, tar scale,, 10 mL min. raduated Cylinder, Large Beaker to make an ice bath, Electric Flask Heater, Clamp for flask, ring stand, short refluxing condenser for reflux condensation, tubing for water, drain for water, water valve, temperature fitted so it’s hoovering just above the liquid in the flask, stop watch, still-head, bent adapter attached to condenser for simple distillation, 50 mL Erlenmeyer Flask, small test tube to test the distillate for complete distillation, separator funnel, clean flask, 2nd Ice bath for cooling sulfuric acid, clean flask for separation of the next layer, 3rd clean collecting flask, 1 gram anhydrous calcium chloride pellets, 25 mL clean flask, boiling stone, collect final product in temperature between 99-103 degrees C, narrow mouth bottle of appropriate size, neatly made label with your name/ your partners name/ formula of final product and the name of the final product making sure that the label is neat and easy to read and place it securely to the container of final product.Using a 100 mL round bottom flask and an ice bath big enough to submerge the flask in it.
Add 13. 3 g of NaBr, 15 mL of water and 10 mL of 1-Butanol in the flask then very slowly under a vented hood with the glass pilled down to cover exposed airways. Slowly while swirling the flask then add the sulfuric acid (11. 5 mL).
Add it while the flask is only in the bath. After the solution is fully mixed then prepare a mixture which has been pre listed in the experiment set up.Use the electric flask heater with a ring stand, using a flask clamp, place the flask in the heater and attach a short condenser for reflux condensation. Heat to the boiling point and note the time.
Adjust the heat then and for a steady and brisk reflux. Reflux for 45 minutes , remove from heat and let condenser drain for a few minutes. Then remove the condenser , mount a still head in the flask and a thermometer just above the liquid in the flask. Set up the condenser for a simple distillation through a bent adapter into a 50 mL flask.
Distill mixture and take frequent reading continue to distill until no more water insoluble droplets come over to the flask. This should happen around 115 degrees centigrade. Check the distillate in the test tube with water. (Stopping point for part 1) Pour the solution into a separator funnel shake with about 10 mL of water and note that the 1-Bromobutane creates a new layer.
If there is a pink discoloration add a pinch of sodium bisulfate and shake again to remove any discharged bromine lower layer is 1-Bromobutane, drain into a clean flask. Clean and dry separator funnel.Return the 1-Bromobutane and then insure it is sufficiently cooled in an ice bath and slowly to prevent a non-controlled exothermic reaction while 10 mL of sulfuric acid is added. Shake the separatory funnel briskly and well after 1st ensuring that the stopper and the stopcock are closed properly and make sure while swirling the solution that you take breaks and vent the solution to ensure any gas forming can be released.
Allow 5 minutes for a full separation of the layers . When using funnel for separation of the organic and inorganic layers. Use the ring stand and a beaker.Close the stopcock, pour in solution to be separated and rinse and swirl with a small amount of solvent.
Then add the solvent being used for separation and place the stopper on top invert it and vent by releasing the stopcock and swirl it to mix the layers very well. Lastly return it to the ring stand and remove the stopper quickly to allow venting of gas. When removing the top layer make sure to decant the top layer from the top opening. Make sure to use care while using the corrosive sulfuric acid.
Make sure to use proper PPE and identify the two layers using densities. 1-Bromobutane 1. 275 compared to sulfuric acid which has a density value of 1. 84 so the 1-Bromobutane should be the top layer.
Separate the layers and wait 5 minutes and separate again. Wash the 1-Bromobutane with 10 mL of 3M sodium Hydroxide. (density 1. 11) solution to remove any trace acids.
Separate and remove the proper layer the 1- Bromobutane should this time be the bottom layer according to densities. Dry the cloudy 1-Bromobutane using by adding 1 g of anhydrous Calcium Chloride until the liquid is clear, after 5 mins decant into a 25 mL flask.Set up one more simple distillation and add a boiling chip and keep at a constant eye on the temperature. Collect distillate between 99-103 degrees centigrade typical student yield is 10-12 grams.
Note the forerun amount the product which distills before reaching the boiling point. Put a label on the final container in which final product will reside in. Make sure the label is neat clear and precise with your name, you lab partners name, the chemical, name, formula, the molecular formula.There are many reasons the yield would be this low.
It is not at all what I would have expected. From the possible side reactions that could happen forming unwanted produced and due to the boiling point recorded when the final distillation was being preformed (85-87 degrees centigrade) compared to what the book listed it expected to be (99-103 degrees centigrade) this is showing that the final product was likely not very pure at all.The competing elimination reaction would cause a much lower yield of the product wanted and the formation of unwanted products such as 1-butene or 2-butene. With these products in the final product this would make the boiling point and yield being off.
Recording issues during the second part of the lab may have taken place or issues with separating the correct layer in completion or even a mix up of one or more of the layers. The boiling point shows impurity.The lab was not very successful as the typical student yield was recorded in the text was 10 grams at the low end (10-12). our yield was just under half of the expected yield.
(4. 3532 grams was recorded in part 2 of the lab by my lab partner) Do to my inability to attend the second half of the lab and my partner having to work alone this may have unfortunately led to such a low yield with her not having a partner. It is possible there were issues with storing the crude product from part one which was left for 1 week until the final product was obtained.It is possible evaporation may have occurred.
I did observe in part one although fully following the directions and very slowly adding the sulfuric acid while the 1-butanol, water and NaBr were in the flask, it did still produce heat. I did this part myself acid after my partner accidentally added the sulfuric acid to the products quickly and produced a fully uncontrolled reaction which was very exothermic. I did this as carefully as I could the second time but still the reaction was a little exothermic.Possibly in the future maybe the H2SO4 should be cooled as well in an ice bath so both the 3 starting products in the flask would be chilled from the ice bath and the H2SO4 itself would also be cooled.
Another way to obtain better results would be to have done the experiment on the micro-scale which I read fully and using that procedure, and it’s amount would have likely led to a higher yield as to be expected when doing a reaction on the micro-scale.I do like that this organic lab uses a book which compares the two scales which is not what the organic lab book was like from the school I transferred from. This experiment is an excellent example of where using a micro instead of macro scale may have helped significantly in improving the % yield which came out to only 29% as the theoretical yield was calculated to 15 grams. It is difficult to pin point why the experiment was not very successful as I was not able to attend the second half of the lab due to unforeseen circumstances.
Without actually being there it is very hard for me to know what actually happened and where exactly the experiment went wrong producing a low yield with a boiling point not representative of the final product we were trying to obtain and purify at the end. Having a boiling point of 85-87 degrees the 1st being the fore run, compared to 99-103 shows strong evidence of impurities.
Cite this The Macroscale Synthesis of 1-Bromobutane from 1-Butanol by an Sn2 Reaction
The Macroscale Synthesis of 1-Bromobutane from 1-Butanol by an Sn2 Reaction. (2018, Feb 23). Retrieved from https://graduateway.com/macroscale-synthesis-1-bromobutane-1-butanol-sn2-reaction/