What is the major reason for the 1-butanol starting material having a higher boiling point than the isolated 1-bromobutane product even though the molar mass of 1-butanol is only about half that of the 1-bromobutane? Explain, with reference to the relevant intermolecular forces for each of the samples. Your explanation should include a diagram to illustrate the most important intermolecular force for each liquid. B.P. Molar mass 1-butanol 118 degree C 74.12 g 1-bromobutane 102 degree C 137.03 g In addition to the major product (1-bromobutane) there are a number of side products which can be formed in this reaction. Assuming that the substitution reaction (S_N2) is in competition with elimination (via the E2 mechanism), deduce the structure of the resulting alkene. The alkene formed in part a) can be protonated resulting in the formation of a carbocation. Draw the carbocation. The carbocation in part b) can then react via S_N1 or E1 to yield a number of substitution and elimination products. Deduce the products formed under the following conditions. Some of the reactions may produce stereoisomers. The reaction of the carbocation with bromide ion (SN1 conditions). Include stereoisomers and name them using the R/S system. The reaction of the carbocation with water (SN1 conditions). Include stereoisomers and name them using the R/S system. - draw only the final structures produced after deprotonation of the reaction intermediate. The reaction of the carbocation with any weak base to yield an alkene (via E1 mechanism). There are three potential alkenes formed, if we consider structural isomers and geometric isomers (cis-trans). Deduce the structures of all three alkenes and name them. If we assume that the most important side reaction is the elimination reaction shown in part e), what is the major side product for this reaction? (i.e. Which of the alkenes is the major side product?)
A. Assume the above synthesis of 1-bromobutane is known to proceed in 75% yield and you would like to prepare 7.5 g of material. Back calculate how many mLs of 1-butanol you will need for the reaction to synthesize the 7.5 g of product, assuming that the 1-butanol is the limiting reagent. Place this number in the table. Also, calculate all the remaining missing data to fill the table.
Experimental Procedure:The NaBr, 1-butanol, and water are combined in a round-bottomed flask containing a stir bar and cooled to 0 oC. Concentrated sulfuric acid is slowly added with stirring. The reaction flask is then prepared for a 50-minute âbriskâ reflux using a heating mantle. After reflux, two layers will be present. The condenser is removed and replaced with a distillation apparatus. Distill the mixture, recording the temperature range, until no more water- insoluble droplets are collected and the temperatures reaches around 115 oC. (The boiling point is elevated due to azeotropic distillation of the water with the 1-bromobutane and increasing amounts of sulfuric acid).
B. Propose a way that you could test if the droplets coming over are âwater-insolubleâ.
Be specific with the manipulations, glassware, and what observation you would see.
The collected liquid is transferred to a separatory funnel and 10 mL of water is added. Two layers form, the bottom being the 1-bromobutane layer. The layers are separated, one through the bottom and one through the top, and the separatory funnel is cleaned and dried. The bromobutane layer is returned to the separatory funnel and washed with ice-cold sulfuric acid to remove traces of the starting material, butene and ethereal by-products.
C. Will the top or bottom layer be the bromobutane layer when washing with concentrated sulfuric acid? Why?
The sulfuric acid layer is removed and the 1-bromobutane is washed with 10 mL 3 M NaOH followed by 10 mL aqueous sodium chloride (brine).
D. What is the purpose of each of these washes?
NaOH â
Brine -
Care should be taken to save the correct layer. The 1-bromobutane is then dried over anhydrous CaCl2.
E. How will you decide how much drying agent to use? How will you know that the 1-bromobutane is dry.
The product is distilled to obtain a clear, colorless liquid.
F. TLC âSuppose you wanted to follow the above reaction by TLC.
a. Describe how you would go about finding a good solvent or solvent pair to use.
b. Suggest a specific solvent system you would try.
c. Draw below what you would want the TLC plate to look like and show the expected relative Rf values for the 1-butanol and 1-bromobutane. Label the spots, baseline, and solvent front.