Isomerization of allenes to alkynes with an alkaline-earth metal hydride containing catalyst

Providing an isomerization process which can isomerize allenes to alkynes less expensively and stably is an assignment to be solved by the present invention and given thereto. The present invention is an isomerization process including the step of reacting an allene-lype hydrocarbon compound (R.sub.1 R.sub.2 C.dbd.C.dbd.CR.sub.3 R.sub.4) in the presence of alkaline-earth metal hydride working as an isomerization catalyst, thereby isomerizing the allene-type hydrocarbon compound to an alkyne-type hydrocarbon compound (R.sub.1 C.ident.C--CR.sub.2 R.sub.3 R.sub.4).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for isomerizing allenes to 
alkynes. 
2. Description of the Related Arts 
As for a conventional process for isomerizing an acetylene-type compound to 
an allene-type compoun, there has been a disclosure, for example, Japanese 
Unexamined Patent Publication (KOKAI) No. 47-38,593, on a conventional 
isomerization process which is processed by using metallic ruthenium as a 
catalyst at room temperature in order to alternately isomerize the 
acetylene-type compound and the allene-type compound. Moreover, there has 
been another disclosure, for example, Japanese Unexamined Patent 
Publication (KOKAI) No. 4-225,987, on another conventional isoinerization 
process in which an allene-type hydrocarbon compound is isomerized to 
produce metallized 1-alkyne by using a mixture of alkylamine and alkali 
metal hydride as an isomerization catalyst in the presence of alkali 
metal. 
It has been revealed recently that mixtures of allenes, such as CH.sub.2 
.dbd.C.dbd.CH.sub.2, and alkynes, such as HC.ident.C--CH.sub.3, give 
copolymers (or reactive elastomers) by organometallic catalysts 
represented by Ni complexes. In the laboratory level synthesis, it is 
possible to obtain both allene and propyne in their pure forms, and to 
control the compositional ratios of the resultant copolymers by mixing 
them in arbitrary ratios. However, it is quite difficult to separate them 
in a large scale because their physical properties, such as a boiling 
point, are very close (see allene (bp. -32.degree. C.), propyne (bp. 
-23.degree. C.).). 
The MAPP gas has been known, and is commercially available as a material 
supply source of allene/propyne. The MAPP gas contains allene in an amount 
of from 18 to 28% by weight, propyne in an amount of from 23 to 36% by 
weight, and propylene and butane in an amount of from 1 to 8% by weight. 
However, it is difficult to adjust the composition of the MAPP gas at a 
desired compositional ratio. Therefore, the conventional technique, in 
which the metallic ruthenium is used as a catalyst, is not proper 
industrially, because the isomerization reaction is carried out by 
utilizing the thermodynamic equilibrium. Accordingly, the isomerization 
reaction develops slow. Further, the publication does not set forth on how 
to control the isomerization reaction. Consequently, there arises a 
drawback in that the composition ratio cannot be selected. Furthermore, 
there is another problem in that the expensive metallic ruthenium is used 
as a catalyst. 
When the allenes and alkynes are used as monomers for polymerization, it is 
essential to employ a step of drying the monomers. This is because the 
organometallic compounds, which are prepared from transition metals, are 
used as a catalyst. However, it is impossible to isomerize and dry the 
allenes and alkynes at the same time. 
In the latter process, drying is not effective during the isomerization 
reaction. Moreover, when carrying out the allene/alkyne polymerization by 
using the resulting isomerized product, there arises a drawback in that 
the alkylamine contained in the isomerization catalyst poisons the 
polymerization catalysts. 
It is an assignment to be solved by the present invention and given thereto 
to provide a process which can isomerize allenes to alkynes less 
expensively and stably. 
SUMMARY OF THE INVENTION 
As measures to solve the assignment, the inventors of the present invention 
devised the following aspects of the present invention as hereinafter 
described. 
In an aspect of the present invention, an isomerization process according 
to the present invention comprises the step of: 
reacting an allene-type hydrocarbon compound (R.sub.1 R.sub.2 
C.dbd.C.dbd.CR.sub.3 R.sub.4) in the presence of alkaline-earth metal 
hydride working as an isomerization catalyst, thereby isomerizing the 
allene-type hydrocarbon compound to an alkyne-type hydrocarbon compound 
(R.sub.1 C.ident.C--CR.sub.2 R.sub.3 R.sub.4). 
In this aspect of the present invention, the allene-type hydrocarbon 
compound can be expressed by a general formula R.sub.1 R.sub.2 
C.dbd.C.dbd.CR.sub.3 R.sub.4, and the alkyne-type hydrocarbon compound cam 
be expressed by a general formula R.sub.1 C.ident.C--CR.sub.2 R.sub.3 
R.sub.4. Here, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 can be at least one 
member selected from the group consisting of hydrogen, an alkyl group, 
halogen and an acyl group. The allene-type hydrocarbon compound can be 
allene, methylallene, ethylallene, dimethylallene, etc. In particular, it 
is preferred to use allene (i.e., R.sub.1 .dbd.R.sub.2 .dbd.R.sub.3 
.dbd.R.sub.4 .dbd.H). On the other hand, as expressed by the general 
formula, the alkyne-type hydrocarbon compound is isomerized from the 
allene-type hydrocarbon compound by isomerizing the double bonds of the 
allene-type hydrocarbon compound into the triple bond (i.e., an 
acetylene-based compound). The positions of the substituent groups are the 
same as those of the allene-type hydrocarbon compound. Hence, both of the 
compounds exhibit similar properties with each other. 
The alkaline-earth metal hydride can be used as the isomerization catalyst 
in the present invention. The alkaline-earth metal hydride can be 
beryllium hydride, magnesium hydride, calcium hydride, strontium hydride, 
barium hydride, etc. In particular, it is preferred to use calcium 
hydride. 
The isomerization reaction is carried out by bringing a raw material 
containing the allene-type hydrocarbon into contact with the 
alkaline-earth metal hydride working as the isomerization catalyst. As for 
the reaction temperature of the isomerization, the isomerization reaction 
can preferably be carried out, for example, at a temperature of 
-20.degree. C. or more because allene is a gas. It is most preferred to 
carry out the isomerization reaction at around room temperature in view of 
operating the reaction. Moreover, in order to facilitate the isomerization 
reaction of the allene-type hydrocarbon compound having substituent 
groups, it is possible to isomerize it under a heated condition, for 
instance, at 50.degree. C. In addition, when the isomerization reaction is 
carried out by heating, it is preferred to carry out the reaction in a 
pressure resistant container because the alkynes and allenes described 
here are mainly gases. 
In the isomerization reaction, it is possible to control the isomerization 
degree of the allenes by appropriately selecting the reaction temperature 
and the contacting time with the catalyst. The isomerization reaction 
usually develops fast at room temperature. However, even if there exists 
calcium hydride, it is possible to completely suppress the isomerization, 
for example, at -78.degree. C. 
The alkaline-earth metal hydride also works as a dehydration agent to the 
alkynes and allenes. When it is brought into contact with the alkynes and 
allenes at a temperature of -40.degree. C. compound below, it is possible 
to suppress the isomerization reaction, but to exclusively develop the 
drying step. 
When a mixture of the alkynes and allenes is employed for the 
copolymerization catalyzed by organometallic compounds (e.g., Ni 
complexes), it is essential to dry both allenes and alkynes. When the 
drying is carried out insufficiently, the cross-linking reaction occurs 
during the polymerization so that only the insoluble and unmeltable 
products are obtained. However, in accordance with the aforementioned 
processing or isomerization reaction, the isomerization and drying can be 
carried out in a single step, because the dehydration is carried out 
simultaneously when the reactants are brought into contact with the 
present isomerization catalyst. Accordingly, it is possible to develop the 
polymerization without deteriorating the activity of the polymerization 
catalysts (e.g., Ni complexes). As a result, it is possible to readily 
produce copolymers having desired compositional ratios, copolymers which 
include the isomerized alkynes and allenes. In other words, it is possible 
to obtain an allene/alkyne (especially, propyne) mixture gas having an 
arbitrary composition in a fully dried state. 
By applying the present process, it is possible to readily obtain monomers 
which can produce the following useful polymers. 
The alkynes can be also used independently as monomers for producing 
acetylene-based polymers. 
Monomers for Allene/Propyne Copolymers (Reactive Elastomers) 
The allene/propyne copolymers are low-temperature elastomers which have 
structures similar to that of polybutadiene. In accordance with the 
present isomerization process, the monomers can be formed to have desired 
compositional ratios, and copolymers can be prepared to have compositions 
which are based on the isomerization. The resulting copolymers are 
different from polybutadiene, and are characterized in that they have two 
kinds of double bonds whose reactivities differ from each other. It is 
possible to readily prepare copolymers of different compositions by freely 
controlling the isomerization of allene/propyne mixture gases of the 
monomers. 
Monomers for Conductive Polymers 
The present isomerization process can produce propyne which is 
substantially pure. Polypropyne is a polymer which has alternate double 
bonds. The polymer exhibits an intermediate conductivity. However, when it 
is copolymerized with acetylene, it is possible to prepare conductive 
films which have film-forming abilities. 
Monomers for Synthesizing Oxygen-Enrichment Films 
Pure propyne is also an important precursor for a considerable number of 
substituted alkynes. Recently, the polymers of substituted alkynes have 
been expanding the applications. In particular, 
poly(1-trimethylsilyl-1-propyne) is an excellent material which exhibits 
the maximum oxygen permeability in all of polymers. 
1-trimethylsilyl-1-propyne, the monomer of 
poly(1-trimethylsilyl-1-propyne), has been known to be synthesized by 
employing propyne as a raw material. Propyne can be prepared by using the 
catalyst of the present isomerization process. Accordingly, the present 
isomerization process is a very effective way for supplying propyne from 
the allene/propyne mixture gases less expensively and with ease.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Preferred Embodiment 
100 g of a mixture gas including allene in an amount of 60% by weight and 
propyne in an amount of 40% by weight was introduced into a pressure 
resistant bottle, in which calcium hydride was held in an amount of 10 g, 
and was stirred at 30.degree. C. for 1 hour. After the stirring, the 
composition of the mixture gas was determined by the NMR analysis, and was 
found that the mixture gas included allene in an amount of 12% by weight 
and propyne in an amount of 88% by weight. Therefore, allene was 
isomerized to propyne so that the content was decreased from 60% by weight 
to 12% by weight. On the contrary, the content of propyne was increased 
from 40% by weight to 80% by weight. Thus, it was verified that the 
isomerization reaction developed rapidly. 
An allene/propyne copolymer could be made from the resulting mixture gas by 
using an Ni-complex catalyst. In the polymerization reaction, no desired 
copolymer could be produced when the monomers were not fully dried. 
However, the copolymer prepared by the present process was meltable, and 
was soluble to organic solvents, such as toluene, chloroform and 
tetrahydrofuran. 
Second Preferred Embodiment 
100 g of a mixture gas including allene in an amount of 60% by weight and 
propyne in an amount of 40% by weight was introduced into a pressure 
resistant bottle, in which calcium hydride was held in an amount of 10 g, 
and was stirred at -20.degree. C. for 1 hour. After the stirring, the 
composition of the mixture gas was determined by the NMR analysis, and was 
found that the mixture gas included allene in an amount of 45% by weight 
and propyne in an amount of 55% by weight. Therefore, allene was 
isomerized to propyne so that the content was decreased from 60% by weight 
to 45% by weight. On the contrary, the content of propyne was increased 
from 40% by weight to 55% by weight. Thus, it was verified that the 
isomerization reaction developed rapidly. 
An allene/propyne copolymer could be made from the resulting mixture gas by 
using an Ni-complex catalyst. 
Third Preferred Embodiment 
100 g of a mixture gas including allene in an amount of 60% by weight and 
propyne in an amount of 40% by weight was introduced into a pressure 
resistant bottle, in which calcium hydride was held in an amount of 10 g, 
and was stirred at 30.degree. C. for 8 hours. After the stirring, the 
composition of the mixture gas was determined by the NMR analysis, and was 
found that the mixture gas included allene in an amount of 4% by weight 
and propyne in an amount of 96% by weight. Therefore, allene was 
isomerized to propyne so that the content was decreased from 60% by weight 
to 4% by weight. On the contrary, the content of propyne was increased 
from 40% by weight to 96% by weight. Thus, it was verified that the 
isomerization reaction developed rapidly. 
An allene/propyne copolymer could be made from the resulting mixture gas by 
using an Ni-complex catalyst. 
Comparative Example 
100 g of a mixture gas including allene in an amount of 60% by weight and 
propyne in an amount of 40% by weight was introduced into a pressure 
resistant bottle, in which calcium hydride was held in an amount of 10 g, 
and was stirred at -78.degree. C. for 24 hours. After the stirring, the 
composition of the mixture gas was determined by the NMR analysis, and was 
found that the mixture gas included allene in an amount of 60% by weight 
and propyne in an amount of 40% by weight. Thus, it was verified that no 
isomerization reaction developed. 
Fourth Preferred Embodiment 
100 g of a mixture gas including allene in an amount of 60% by weight and 
propyne in an amount of 40% by weight was introduced into a pressure 
resistant bottle, in which calcium hydride was held in an amount of 10 g, 
and was stirred at 45.degree. C. for 15 minutes. After the stirring, the 
composition of the mixture gas was determined by the NMR analysis, and was 
found that the mixture gas included allene in an amount of 7% by weight 
and propyne in an amount of 93% by weight. Therefore, allene was 
isomerized to propyne so that the content was decreased from 60% by weight 
to 7% by weight. On the contrary, the content of propyne was increased 
from 40% by weight to 93% by weight. Thus, it was verified that the 
isomerization reaction developed rapidly. 
An allene/propyne copolymer could be made from the resulting mixture gas by 
using an Ni-complex catalyst. 
Dehydration Effect of the Present Catalyst 
Toluene was refluxed in the presence of metallic sodium and benzophenone to 
dehydrate so that H.sub.2 O&lt;1 ppm. An allene/propyne mixture gas, which 
was dried by the present isomerization process, was introduced into and 
dissolved into the dehydrated toluene. The liquid color (purplish red) of 
the toluene specifying the dryness did not vary at all. Thus, it was found 
that the allene/propyne mixture gas was in an extremely dried state. On 
the other hand, when an allene/propyne mixture gas was introduced into the 
toluene without bringing it into contact with the calcium hydride, the 
toluene changed its color from purplish red to light green. Thus, it was 
found that the allene/propyne mixture gas was dried insufficiently. 
When the solvent, such as toluene, is admixed and refluxed with 
sodium/benzophenone, the mixture usually changes its color as follows as 
the drying proceeds: light green.fwdarw.green.fwdarw.bluish 
green.fwdarw.bluish purple.fwdarw.purplish red. When the mixture is put 
into the bluish purple or purplish red state, it is judged to be in a 
fully dried state (e.g., H.sub.2 O&lt;1 ppm).