7 alkyl halides are treated with sodium iodide in acetone and with ethanolic solution of silver nitrate

1. Sn1 and Sn2 lab-Orgo 1 lab
• 7 alkyl halides are treated with sodium iodide
in acetone and with ethanolic solution of
silver nitrate
• Author: Dr. Robert D. Craig, Ph.D

2. The procedure for today!!
• In the experiments that follow, 7 alkyl halides
are treated with sodium iodide in acetone and
with ethanolic solution of silver nitrate.
•
• 1. Sodium Iodide in Acetone
• 2. ethanolic silver nitrate solution

3. 7 alkyl halides
• The seven alkyl halides are 1-chlorobutane, 1-
butane, 2-chlorobutane, 2-chlorobutane, 2-
chloro-2-mehtylpropane, 2-brombutane, 1-
chloro-2-methylpropane and bromo benzene.
•
•
• You can just follow pg 338 to 340 exactly! Th
Microscale Run. Low level Stress!!!
•

4. 1. Sodium Iodide in Acetone
favors the Sn2 reaction
• Acetone with a dielectric constant of 21 is a
relatively nonpolar solvent that will readily
dissolve sodium iodide. The iodide ion is an
excellent nucleophile, and the nonpolar
solvent (acetone) favors the Sn2 reaction; it
does not favor ionization of the alkyl halide.

5. Sodium Iodide in Acetone
favors the Sn2 reaction
nucleophile
Electrophile Rate = k[ROTs][OAc]
Leaving Group

6. favors the Sn2 reaction
• The extent of reaction can be observed
because sodium bromide and sodium chloride
are not soluble is acetone and precipitate
from solution if a reaction occurs.

7. A precipitation reaction!!
Na+ I- + R-Cl  R-I + NaCl (s)
Na+I- + R-Br  R-I + NaBr (s)

8. 2. ethanolic silver nitrate solution
Favors an Sn1
• When an alkyl halide is treated with an
ethanolic solution of silver nitrate, the silver
ion coordinates with an electron pair of the
halogen. This weakens the carbon-halogen
bond because a molecule of insoluble silver
halide is formed, the promoting an Sn1
reaction of the alkyl halide. The solvent,
ethanol, favors ionization of the halide, and
nitrate ion is a very poor nucleophile, so alkyl
nitrates do not form by an Sn2 reaction.

10. Rate-determining step is formation of
carbocation
rate = k[RX]

11. SN1 in Reality

12. Carbocation is wants to do it own
thing!
• Carbocation is more likely to react on side
opposite leaving group
• Suggests reaction occurs with carbocation
loosely associated with leaving group during
nucleophilic addition (Ion Pair)

13. lets make it happen!
R-X Ag+-> R-X -> R+ + AgX (s)
•
On the basis of the foregoing discussion,
• Let’s “make it happen!”
•
• The Microscale run!

14. The Microscale run
• Label 7 small containers (reaction tubes, 3 mL,
centrifuge tubes, 10 x 75 mm test tubes, or 1
mL vials), and place 0.1 mL of 100 mg of each
of the following halides in the tubes.
•

15. The Microscale run
• Youre alkyl halides!
• 1-chlorobutane, 1-butane, 2-chlorobutane, 2-
chlorobutane, 2-chloro-2-mehtylpropane, 2-
brombutane, 1-chloro-2-methylpropane and
bromo benzene

16. The Magic !
• To each tube then rapidly add 1 ml of 18%
solution of sodium iodide in acetone, stopper
each tube, mix the contents thoroughly, and
note the time.

17. The precipitate!!!
• Note the time of the first appearance of any
precipitate. If no reaction occurs within about
5 min, place those tube in a 50 oC water bath
and watch for any reaction over the next 5 to
6 min.

18. The precipitate!!!
• Empty the tubes, rinse them with ethanol,
place the same amount of each of the alkyl
halides in each tube as in the first part of the
experiment, add 1 ml of 1% ethanolic silver
nitrate to each tube,
• And note the time of addition of as well as the
time of appearance of the first traces of any
precipitate.
•

19. unreactive halides
• If a precipitate does not occur in 5 min, heat
the tubes containing these unreactive halides
in a 50 oC water bath for 5 to 6 min and
watch for any reaction

20. effect of the solvent
• To test the effect of the solvent on the rate of
Sn1 reactivity. Compare the time needed for a
precipitate to appear when 2-chlorobutane is
treated with 1% ethanolic silver nitrate
solution and when treated with 1% silver
nitrate in a mixture of 50% ethanol and 50%
water .

21. Tertiary alkyl halides react rapidly in
protic solvents in Sn1

22. your analysis
• In your analysis of these experiments consider
the :
• Nature of the leaving group
• Effect of the structure of the alkyl halide
• Effect of the solvent
• Effect of the temperature

23. Lets go to the Video tape!!!
• http://www.youtube.com/watch?v=g5_GEzr9
1BQ
•
• http://www.youtube.com/watch?v=hXIQUChlJ
q0&feature=related