The Macroscale Synthesis of 1-Bromobutane from 1-Butanol by an Sn2 Reaction

Robin A. Powers
Exp 1/Page 1
Organic Chemistry Lab II
September 25th 2017

Title: The Macroscale Synthesis of 1-Bromobutane from 1-Butanol by an SN2 reaction.
Purpose: To convert 1-Butanol into 1-Bromobutane with the highest yield possible by use of an SN2 reaction with H2SO4 to improve the actual yield.
Introduction: 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.

Principal Reaction: [pic 1][pic 2][pic 3][pic 4]

                                                       OH +                  +                                         H                                     [pic 5][pic 6][pic 7][pic 8][pic 9][pic 10][pic 11][pic 12][pic 13][pic 14][pic 15][pic 16]

                        O                                                                                           O                                       Br    [pic 17]

                                                                                                                                                        + H2O          [pic 18][pic 19]

                                                                                                                    H                                 +Na
             HO        S           O          H                                                                                                      +H2SO4 [pic 20][pic 21][pic 22][pic 23][pic 24][pic 25]

                       O

        1-Butanol:                                                                                                           1-Bromobutane:
        B.P.- 118 oC                                                                                                                                                                                       B.P.- 101.6oC
        M.W.- 74.12(g/mol)                                             O                                            M.W.-137.03(g/mol)

        Density- .810(g/cm3)                                                                            Density- 1.275 (g/cm3)[pic 26][pic 27]

Side Reactions: Na+Br- + H2SO4                       H-Br+Na+ - O--O--OH[pic 28][pic 29][pic 30]

                                                                       
                                                                                           O
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.
Competing Reactions:
CH3CH2CH2CH2OH             CH3CH=CHCH3 + CH3CH2CH=CH2 + H2O[pic 31][pic 32]

                       H2SO4  2-Butene/1-Butene
Elimination reaction (possible competing reaction)



Calculations of the Limiting Reagent:
Moles = Moles/Molar Mass   Density = Mass * Volume
1) 1-Butanol –  =.810 g/mL  
Molar Mass = Volume * Density

mL to Grams = 10mL * .810 (g/ mL)

Molar Mass = 8.1 grams / 74.12 (g/ mol)
Molar Mass = .109 = .11 moles (2 sig figs)

2) Sodium Bromide - 13.3 g NaBr

Molar Mass = 13.3 NaBr / 102.86
Molar Mass = .129 moles NaBr (3 sig figs)
3) Sulfuric Acid -

mL to grams = 11.5mL * 1.11 (g/mL)