Page 19 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

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Encyclopedia of Physical Science and Technology EN001F-4 May 7, 2001 16:19

Acetylene 71

E. Ethynylation in Liquid Ammonia Kerb, and for the large-scale production of isoprene. In the
Using Catalytic Amounts of KOH last-named use it is made catalytically in liquid ammonia,
or Sodium Acetylide as described in Section IX.F.

Tedeschi showed that catalytic amounts of either NaOH or
KOH in liquid ammonia–acetylene medium could affect F. Isoprene from Acetylene and Acetone
the ethynylation of aldehydes and ketones in high cat-
Anic (an affiliate of Ente Nazionale Idocarburi) at
◦
alytic efficiency. The reaction was carried out at 20–40 C
Ravenna, Italy, has been operating a large production facil-
at acetylene–ammonia pressures of 150–300 psig. The
ity for the manufacture of isoprene, which is used to make
mole ratio of reactants for methylbutynol formation aver-
cis-polyisoprene. The route developed by Anic involves
ages 6–18 mol acetone, 18–24 mol acetylene, 0.5–1.5 mol
the catalytic formation of methylbutynol (MB), semihy-
KOH,and18–24molammonia.Theconversiontomethyl-
drogenation to methylbutenol (MBe), and dehydration of
butynol based on acetone averages 75–100%, with a cat-
the latter to isoprene:
alytic yield based on KOH averaging 380–900%. Longer
chain aldehydes and ketones react in the ammonia system NH 3
1. (CH 3 ) 2 CO + C 2 H 2 −−−−−→ (CH 3 ) 2 C C CH
with equal ease. The ethynylation of methylheptenone to 50% KOH |
DHL proceeds catalytically in more than 90% conversion. OH
When stoichiometric to excess amounts of acetylene are MB (6)
used in the ammonia system, acetylenic diol formation is
quite low (0.5–1.0%). Pd catalyst
2. MB + H 2 −−−−−→ (CH 3 ) 2 C CH CH 2
The reaction proceeds via the formation of an alkynol– | (7)
KOH complex. the isolated crystalline complex can be OH
substituted for KOH in the ethynylation reaction with MBe
−H 2 O
equal results. However, lithium hydroxide, unlike lithium
3. MBe −−→ H 2 C C(CH 3 ) CH CH 2 (8)
acetylide in liquid ammonia, fails to yield any acetylenic
hydroxy compound. The mechanism of catalytic ethyny-
Methylbutynol is formed continuously in liquid am-
lation in liquid ammonia and aprotic solvents based on
monia under pressure using 50% aqueous KOH as cat-
key intermediates has been published by Tedeschi. Alkali
alyst. The conversions to both MB and MBe are close
metal acetylides can be used as catalytic species in place
to 100%, and the overall yield to isoprene is well over
of KOH. Although acetylenic glycols can be formed in
90%. The process delivers high-purity isoprene, readily
purified for use in the isotactic polymerization of iso-
Carbonyl compound Alkynol Alkynediol
prene to cis-polyisoprene. A process flow diagram of the
Acetone Methylbutynol Dimethylhexynediol Anic methylbutynol–isoprene process (SNAM Progetti)
Methyl ethyl ketone Methylpentynol Dimethyloctynediol (S-82) is shown in Fig. 6. The plant originally had a capacity of
Methyl isobutyl Dimethylhexynol Tetramethyldecynediol 66 million pounds of isoprene per year but is believed to
ketone (S-61) (S-104) have been expanded.
Butyraldehyde Hexynol
2-Ethylhexaldehyde Ethyloctynol
G. Grignard Route
liquid ammonia using KOH, the reaction is not catalytic, The use of Grignard reagents to form acetylenic products
requiring stoichiometric to excess amounts of base. The is a relatively expensive route used primarily in the phar-
catalytic liquid ammonia–KOH process has great poten- maceutical industry to produce drugs or vitamin interme-
tial for economically producing secondary and tertiary diates. The acetylenic Grignard reagent is readily formed
alkynols. Long-chain terpenoid alkynols used as interme- in 100% yield by reacting ethylmagnesium bromide with
diates in the synthesis of vitamins A and E can be made a terminal acetylenic compound in THF media:
in high conversions and catalytic efficiency in the am-
monia system. Secondary alkynols, such as 1-hexyn-3-ol H 5 C 2 MgBr + R C CH → R G C MgBr + C 2 H 6
and 4-ethyl-1-octyn-3-ol used commercially as corrosion The acetylenic Grignard is used in situ and is best em-
inhibitors, are also readily formed. Methylbutynol, made ployed with sensitive aldehydes or ketones, which are af-
from acetone and acetylene, is important commercially as fected adversely by basic reagents. An intermediate step
a starting point for vitamins A and E, as a stabilizer for in the manufacture of vitamin A involves the formation
chlorinated solvents, as an intermediate for the herbicide of the 1,5-acetylenic di-Grignard, which is then reacted