Problem Set 8
Chapter 9, Alkynes
Due: November 9, 2009
Friedrich Wöhler (1800-1884)
Connections Aluminum was once a precious metal although it was plentiful. The problem was how to remove it from its ore. Friedrich Wöhler, of urea synthesis fame, was able to accomplish this feat but by an impractical method. He was to meet a young chemist, Frank Jewett, recently arrived in Göttingen from Yale. Aware of the difficulty Wöhler had had and probably encouraged by Wöhler, Jewett, as a professor at Oberlin College, passed the problem onto Charles Martin Hall, a young student at the college. Hall solved the problem in his family garage. Thus was born Alcoa. At the same time in Spray, North Carolina, Thomas Willson, a Canadian, and American James Moorhead were unsuccessfully trying to refine aluminum using an electric arc. Unsuccessful in purifying aluminum, they sought calcium metal. Heating coal tar and lime in an electric furnace they obtained a brittle material that produced a combustible gas upon exposure to water. The material was not calcium nor was the gas hydrogen. The pair was calcium carbide and acetylene, the basis for Union Carbide (RIP).
Charles Martin Hall (1863-1914)
1. Determine the structures A-K.
Explain your reasoning. 2. Provide reagents for the following
reactions. Explain your reasoning. 3. Design a synthesis of muscalure
[(Z)-tricos-9-ene], the sex attractant of the common
housefly, Musca domestica. As a source of carbon you
have available 1-butyne, 1-pentyne and acetylene. You may
use 1-pentyne and acetylene only once, i.e, only seven of
the carbons may be provided by these two alkynes. All
reagents are available. 4. Estimate the heat
of formation of 1-,2-,3- and
4-octyne. Equilibration of any one of these isomers with KOH
at 200oC produces about as much 2-octyne as
3-octyne both of which individually exceed the amount of
1-octyne. However, the amount of 4-octyne is less than the
amount of 2- or 3-octyne. Explain. [Hint: 2- and
3-octyne have an entropic advantage over 4-octyne.]
5. Two bottles are found on a laboratory
shelf labeled "alkyne A" and "alkyne B".
Hydrogenation of A or B over a platinum
catalyst gives the same alkane C. Compound A
reacts with H2 in the presence of Lindlar's
catalyst to form D. Compound D reacts with
O3 to form a single compound E,
C3H6O. On the other hand, compound
B reacts with aq. H2SO4 in the
presence of HgSO4 to give two ketones J
and K. Under the same conditions, A gives
only J.
Compound B also reacts
with Na/NH3 to give F, which itself reacts
with Br2/H2O to give a pair of
constitutional isomers, G and H.. Treatment of
either G or H with aqueous NaOH gives the same
compound I, C6H12O, that is
also formed by the reaction of F with peracid. What
are the structures of A-K? Explain and illustrate.
[Note: G and H are not distinguished from
one another. Pay attention to stereochemistry.] 6. The reaction on the right, which was
conducted on three different cycloalkynes, was reported in
1985 by Suzanne Abrams and Angela Shaw of the National
Research Council of Canada. Rather than use NaNH2
as your text suggests, they used the lithium salt of
tetradeutero-1,3-diaminopropane in
tetradeutero-1,3-diaminopropane as a solvent at room
temperature. a) Name the alkynes used in these
experiments. [Note: Not surprisingly, cyclooctyne was
found to be unstable to the reaction conditions.]
b) The base in this experiment is
formed by adding n-butyllithium to the solvent,
tetradeutero-1,3-diaminopropane. Use the pKa
table to explain why this is a sound way to prepare this
base.
c) Provide an explanation (mechanism) as to how each
methylene group becomes deuterated. [Hint: Such
reactions are often called "zipper" reactions.
Why?]