Question

1. what is the purpose of the following in this experiment:

a. concentrated (and not dilute) hydrochloric acid

b. collecting the distillate in ice

c. sodium bicarbonate extraction

d. water extraction

e. anhydrous sodium or magnesium sulfate

chapter Alkyl Halides and Nucleophilic Aliphatic Substitution 13.1 SYNTHESIS OF BUTYL CHLORIDE Alkyl halides can be prepared by reacting an alcohol with concentrated hydrogen halides: R-OH + H-X- R-OH, R-X. HO where X-CI, Br, I. The reaction of hydrochloric acid with 2 and 3 alco hols involves the formation of a carbocation, R. When possible, 2 carbo cations rearrange to form the more stable 3 carbocations. On the other hand, 3 carbocations are relatively stable and seldom yield rearranged products. However, elimination side reactions (EI) in which an alkene is formed can be significant. In this experiment, butyl alcohol is reacted with concentrated hydrochloric acid, and the product (i-butyl chloride) is removed as it is formed via an azeotropic distillation. (CH),C-OH .HCI - t-butyl alcohol (CH),C-Cl + H,O 1-butyl chloride The distillate is washed first with a sodium bicarbonate solution to neu- tralize any remaining traces of acid, and then with water to remove any basic bicarbonate that may regenerate the starting alcohol or form an alkene during the final distillation: (CHỊ) C-Cl + (CH, C=CH2 + H2 + Cl + CO2 suggested References Carey Ownic Chemistry 3rd ed. 137–44. New York: McGraw-Hill, 1936. Ege, Seyhan N., Organic Chemistry: Structure and Reactivity. 3rd ed., 452-56. Lexington, MA:D. C. Heath, 1994. Loudon, G. Marc, Organic Chemistry, 3rd ed., 416-23. Redwood City, CA: Benjamin/Cummings, 1995. March, J., Advanced Organic Chemistry. 4th ed., 298-99. New York: John Wiley, 1992. McMurry, J., Organic Chemistry. 4th ed.. 391-98, Pacific Grove, CA: Brooks/Cole, 1996 Morrison, R. T, and R. N. Boyd, Organic Chemistry. 6th ed., 229-33. Englewood Cliffs, NJ: Prentice Hall, 1992.

Answer 1

1. what is the purpose of the following in this experiment:

a. concentrated (and not dilute) hydrochloric acid

In this reaction we get t-butyl cation as intermediate : (CH₃)₃-C⁺ ; if we add dilute acid than there will not be enough conc. of Cl- ions which acts as nucleophile , and cation intermediate will get get enough time to undergo elimination (E1) giving an alkene . Thus adding dilute HCl will increse side reaction and we will get lesser yield of desired product. So, for having enough conc. of Cl- conc. HCl is used.

b. collecting the distillate in ice :

Neutralization reaction of HCl with bicarbonate is exothermic reaction it will increse temp. of distillate solution ; which can promote elimination reaction or formation of alcohol (as bicarbonate is in excess ), so for preventing this we collect distillate in ice.

c. sodium bicarbonate extraction :

To neutralize HCl which was not neutralized during collection distillate initially.

d. water extraction : It is to remove any basic bicarbonate which may regenerate alcohol or form alkene by elimination.

e. anhydrous sodium or magnesium sulfate :

sodium or magnesium sulfate is hygrosopic ,and absorbs any moisture or water remaining in organic layer after water extraction.