Conversion of an allylic ether to its corresponding acetal

A process for converting an allylic ether to its corresponding acetal is disclosed. In this process an allylic ether is contacted with an organic hydroxy compound and a catalytically effective amount of a cobalt compound to produce the corresponding acetal.

BACKGROUND OF THE DISCLOSURE 
1. Field of the Invention 
The present invention is directed to the conversion of an allylic ether to 
its corresponding acetal. More specifically, the present invention is 
directed to the conversion of the ether group of an allylic ether to the 
corresponding acetal group by contacting the ether with an organic hydroxy 
compound in the presence of a cobalt catalyst. 
2. Background of the Prior Art 
The conversion of an allylic ether to its corresponding acetal is of 
significant commercial potential. Such a step, for instance, can be 
utilized in a synthesis route to the formation of the commercially 
important compound azelaic acid from readily available butadiene. Other 
commercial applications have also been identified or proposed. 
The only prior art disclosing a process for converting an allylic ether to 
its corresponding acetal is Yamahara et al., Japanese Patent Publication 
No. 53-37,325. The Yamahara et al yield of acetal formation is low. 
Furthermore, the catalyst utilized in the Yamahara et al. disclosure is a 
ruthenium compound, a noble metal which is not only expensive but the 
halides thereof are also highly corrosive necessitating processing 
utilizing expensive, highly corrosive resistant materials such as 
titanium. 
The above remarks establish the need in the art for a new process for 
converting allylic ethers to their corresponding acetal in commercial 
yield and selectivity. Moreover, a process is desired which can employ 
relatively low priced non-corrosive catalysts. 
SUMMARY OF THE INVENTION 
A new process has now been discovered which permits conversion of an 
allylic ether to its corresponding acetal in commercially exploitable 
yield and selectivity. Moreover, this process permits utilization of cheap 
non-corrosive catalysts. 
In accordance with the present invention a process for converting the ether 
group of an allylic ether to its corresponding acetal is provided. In this 
process an allylic ether is contacted with an organic hydroxy compound and 
a catalytically effective amount of a cobalt compound which results in the 
formation of the corresponding acetal. 
DETAILED DESCRIPTION 
The present invention relates to a method for converting the ether group of 
an allylic ether to the corresponding acetal. An allylic ether has the 
formula 
##STR1## 
where R.sup.1 is a cyclic or acyclic hydrocarbon group having from 1 to 
about 12, especially from 1 to about 10, carbon atoms R.sup.1 preferably 
is an alkyl, alkenyl, aryl or alkaryl group or an alkyl, alkenyl, aryl or 
alkaryl group having ester, ether, acetal, formyl, ketone, carboxy or 
other functional groups. The radical R.sup.2 also is a cyclic or acyclic 
hydrocarbon group having from 1 to about 12, especially from 1 to about 8, 
carbon atoms. Preferably, R.sup.2 is an alkyl or aralkyl group. In the 
preferred embodiment wherein R.sup.1 and R.sup.2 are alkyl groups, 
structural isomers thereof are also intended to be included in the 
foregoing definition. 
In a preferred embodiment the allylic ether of the present invention is 
provided with acetal or carboxylate functionality. That is, the allylic 
ether includes an acetal or carboxylate group. In Formula I, an allylic 
ether provided with acetal or carboxylate group is defined by the above 
definition of R.sup.1 such that R.sup.1 is a cyclic or acyclic hydrocarbon 
group having 1 to about 12, especially 1 to about 10, carbon atoms 
substituted with an acetal or carboxylate group, respectively. 
A preferred class of allylic ethers, possessed of carboxylate 
functionality, that is reacted to form an acetal in accordance with the 
present invention are alkyl n-alkoxy-(n-2)-alkenoate compounds. These 
compounds are characterized by the limitation that n is an integer equal 
to the number of carbon atoms in the main chain of the alkenoate group. It 
is emphasized that the alkenoate main chain may be substituted with 1 or 
more alkyl groups. The alkoxy group is usually a lower alkoxy having from 
1 to about 6 carbon atoms, preferably, from 1 to about 4 carbon atoms. The 
alkyl group also usually contains 1 to about 6 carbon atoms, preferably, 1 
to about 4 carbon atoms. Finally, the alkenoate group usually contains 3 
to about 12 carbon atoms, preferably, 3 to about 10 carbon atoms. 
A particularly preferred class of alkenoates within the class of alkyl 
n-alkoxy-(n-2)-alkenoates of the present invention is the class of 
compounds where the alkenoate main chain contains 9 carbon atoms, i.e., n 
is 9. Such is the case where the alkyl n-alkoxy-(n-2)-alkenoate is alkyl 
9-alkoxy-7-nonenoate. Among the nonenoates within this preferred class are 
methyl 9-methoxy-7-nonenoate, ethyl 9-ethoxy-7-nonenoate, methyl 
9-ethoxy-7-nonenoate, methyl 9-propoxy-7-nonenoate, methyl 
9-butoxy-7-nonenoate, ethyl 9-methoxy-7-nonenoate, ethyl 
9-propoxy-7-nonenoate, propyl 9-methoxy-7-nonenoate, propyl 
9-ethoxy-7-nonenoate and the like. 
Another preferred class of allylic ethers that are converted to their 
corresponding acetals are those allylic ethers having acetal functionality 
and generically defined as 1,1,n-trialkoxy-(n-2)-alkene compounds. This 
preferred class of allylic ethers is characterized by an alkoxy usually 
having 1 to about 6 carbon atoms, preferably, 1 to about 4 carbon atoms 
and an alkene group usually having 3 to about 12 carbon atoms, preferably, 
3 to about 10 carbon atoms. The alkene group can be substituted with one 
or more alkyl groups. The meaning of n in this preferred class of allylic 
ethers is an integer equal to the number of carbon atoms in the main chain 
of the alkene group. 
A particularly preferred class of 1,1,n-trialkoxy-(n-2)-alkenes is the case 
where the alkene chain contains 9 carbon atoms, i.e., where n is 9. Some 
examples of compounds within this broad class of 1,1,9-trialkoxy-7-nonenes 
are 1,1,9-trimethoxy-7-nonene, 1,1,9-triethoxy-7-nonene, 
1,1,9-tripropoxy-7-nonene, 1,1,9-tributoxy-7-nonene and the like. 
The organic hydroxy compound of the present invention comprises any 
saturated or unsaturated organic compound having at least one hydroxy 
group. It may be a straight chain, branched chain, cyclic or heterocyclic 
compound and usually has from 1 to about 10 carbon atoms. Preferably, the 
organic hydroxy compound is an alkanol having from 1 to about 10 carbon 
atoms. More preferably, the alkanol is a lower alkanol having from 1 to 
about 6 carbon atoms. Still more preferably, the alkanol contains 1 to 
about 4 carbon atoms. Most preferably, the alkanol is methanol. 
Other hydroxy compounds that may be used in accordance with the present 
invention include glycols such as 1,2-ethylene glycol, 1,2-propylene 
glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol and the like. 
Additionally, various mixtures of any of the foregoing organic hydroxy 
compounds may also be employed according to one embodiment of the present 
invention. 
The process of the present invention involves reacting one of the aforesaid 
ethers with an organic hydroxy compound of the type discussed above in the 
presence of a catalytically effective amount of a cobalt catalyst. The 
cobalt catalyst of the present invention is preferably a cobalt 
coordination compound or a cobalt salt. 
In the preferred embodiment wherein a cobalt coordination compound is 
employed the compound is preferably dicobalt octacarbonyl or a cobalt 
carbonyl with a ligand. The ligand may be a phosphine, a phosphite or a 
nitrogen-containing compound. Among the nitrogen-containing compounds 
preferred for use as the ligand are aliphatic amines such as triethylamine 
and heterocyclic aromatics such as pyridine. Of these, pyridine is 
particularly preferred. 
In the alternate preferred embodiment wherein a cobalt salt is utilized, 
cobalt alkanoates and cobalt halides are particularly preferred. Of the 
halides, the chloride is usually employed. 
In a particularly preferred embodiment of the process of the present 
invention, carbon monoxide is utilized. Although carbon monoxide gas is 
not a reactant, its presence is important to the effectiveness of the 
cobalt catalyst in the catalytic reaction of this invention. 
The reaction of the process of the present invention preferably occurs at a 
temperature in the range of between about 140.degree. C. and about 
250.degree. C. and a pressure in the range of between about 300 and 4,000 
psig. More preferably, process of the present invention occurs under 
anhydrous conditions at a temperature in the range of between about 
150.degree. C. and about 180.degree. C. and a pressure in the range of 
between about 500 and about 1,000 psig. This pressure is provided in whole 
or in part by carbon monoxide. In a preferred embodiment it is desirable 
to include hydrogen gas in the reaction. Although the partial pressure of 
the hydrogen gas is relatively minor, compared to that of carbon monoxide, 
its presence improves the effectiveness of the process of this invention. 
The following examples are given to illustrate the present invention. In 
that these examples are provided solely for illustrative purposes, the 
invention should not be limited thereto.

EXAMPLE 1 
A 71 ml Parr [trademark] bomb was charged with 3 ml. 
1,1,9-trimethoxy-7-nonene; 3 ml methanol and 0.1 g. cobalt chloride. The 
bomb was purged three times with carbon monoxide. Thereafter, the bomb was 
pressurized to 500 psig with carbon monoxide gas. A final pressure of 600 
psig was obtained by further pressurization with hydrogen gas. The 
pressurized bomb was heated to 160.degree. C. and held at these 
thermodynamic conditions for 6 hours. 
The product of this reaction was analyzed by gas chromotographic means. 
This analysis indicated the presence of 0.25 ml of 
1,1,9,9-tetramethoxynonane. This represented a yield of 8%. 
EXAMPLE 2 
A Parr [trademark] bomb was charged with the same ingredients and amounts 
as in Example 1. The bomb was then purged four times with hydrogen gas. 
The bomb was thereafter pressurized to 300 psig with hydrogen gas and 
heated to 160.degree. C. The bomb was maintained at these conditions for 6 
hours. 
The product of this reaction was analyzed by gas chromotographic means. The 
product was found to include 0.2 mol. of 1,1,9,9-tetramethoxynonane 
representative of a yield of 7%. 
EXAMPLE 3 
A glass bottle was charged with 30 g. methyl 9-methoxy-7-nonenoate (MMNE); 
5.3 g. pyridine; 19.2 g. methanol; and 3.5 g. pentamethylbenzene, a gas 
chromotography standard, and the contents mixed. It is noted that the 
methyl 9-methoxy-7-nonenoate was 71.5% pure. Thus, the MMNE contained 
21.45 g. MMNE; 4.06 g. methyl 8-methoxy-2-methyl-6-octenoate (MMMO); 0.14 
g. of the desired product, methyl 9,9-dimethoxynonanoate (MDNA); 0.62 g. 
methyl 8,8dimethoxy-2-methyloctanoate (MDMO); and 3.73 g. of the 
impurities derived from carbomethoxylation of 8-methoxy-1, 6-octadiene. 
The mixture was added to a nitrogen gas-purged 300 ml. autoclave reactor 
along with 1.02 g. cobalt carbonyl having the structural formula Co.sub.2 
(CO).sub.8 which was separately charged from a vial. 
The reactor was sealed, purged three times with carbon monoxide and 
pressurized to 40 psig with hydrogen gas. The total pressure was increased 
to 690 psig by the addition of 650 psig carbon monoxide gas. The reactor 
was heated to 170.degree. C. and carbon monoxide gas added to bring the 
pressure up to 1,000 psig. The reactor was maintained at these conditions 
for 4 hours with samples taken hourly. 
Each of the hourly samples was analyzed by gas chromotographic means. The 
results of this sampling is tabulated below in Table 1. 
TABLE 1 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
1 95.3 93.1 
2 96.0 88.3 
3 96.9 83.2 
4 97.6 81.4 
______________________________________ 
Footnotes 
MDNA is methyl 9,9dimethoxynonanoate 
MDMO is methyl 8,8dimethoxy-2-methyloctanoate 
MMNE is methyl 9methoxy-7-nonenoate 
MMMO is methyl 8methoxy-2-methyl-6-octenoate 
EXAMPLE 4 
The autoclave reactor of Example 3 was charged with the same components in 
the same amounts as in Example 3. The reactor was pressurized to 500 psig 
(480 psig CO and 20 psig H.sub.2) and heated to 170.degree. C. The reactor 
was maintained at these conditions for 3 hours with samples taken at 30 
minutes, 1 hr., 2 hrs. and 3 hrs. 
The results of this run is tabulated in Table 2. 
TABLE 2* 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
-- 
0.5 90.2 95.9 
1 93.9 93.9 
2 94.6 91.9 
3 95.4 90.2 
______________________________________ 
*Same meanings as defined in footnotes of Table 1 
EXAMPLE 5 
Example 4 was repeated except that the temperature of reaction was changed 
to 150.degree. C. and the time of reaction was increased to 4 hours. 
Samples were taken at 0.5 hr., 1 hr., 2 hrs., 3 hrs. and 4 hrs. 
The results of this example are summarized below in Table 3. 
TABLE 3 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
0.5 62.3 85.9 
1 87.7 82.9 
2 95.4 89.5 
3 97.3 92.6 
4 97.8 86.8 
______________________________________ 
*Same meanings as footnotes of Table 1. 
EXAMPLE 6 
Example 4 was repeated except for the temperature of reaction which was 
maintained at 160.degree. C. 
The results of this example are tabulated in Table 4 below. 
TABLE 4* 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
0.5 85.0 92.1 
1 94.2 90.6 
2 96.4 91.2 
3 96.4 90.6 
______________________________________ 
*Same meanings as footnotes of Table 1 
EXAMPLE 7 
Example 3 was repeated with only minor differences in purity of the 
starting methyl 9-methoxy-7-nonenoate (MMNE) which contained 24.10 g. 
MMNE; 2.04 g. MMMO; 0.21 g. MDNA; and 0.63 g. MDMO. The example differed 
from Example 3 also in that the cobalt catalyst included 0.026 g. Co.sub.2 
(CO).sub.8 but no pyridine. This example was conducted for 3 hours. 
Samples were taken at 0.5 hr., 1 hr., 2 hrs., and 3 hrs. 
The example is summarized below in Table 5. 
TABLE 5* 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
0.5 95.4 97.4 
1 97.2 &gt;99.0 
2 97.4 &gt;99.0 
3 98.3 &gt;99.0 
______________________________________ 
*Same meanings as footnotes of Table 1. 
EXAMPLE 8 
Example 7 was repeated except for that it was run in the absence of 
hydrogen. The cobalt catalyst was 0.10 g. Co.sub.2 (CO).sub.8. 
The results of this example are tabulated in Table 6 below. 
TABLE 6* 
______________________________________ 
OVERALL CONVER- OVERALL SELECT- 
SION OF MMNE IVITY TO MDNA 
Time, hr. 
AND MMMO (%) AND MDMO (%) 
______________________________________ 
0.5 21.8 95.9 
1 41.6 89.4 
2 67.7 91.1 
3 81.9 93.1 
______________________________________ 
*Same meanings as footnotes of Table 1. 
The above preferred embodiments and examples are given to illustrate the 
scope and spirit of the present invention. These embodiments and examples 
will make apparent, to those skilled in the art, other embodiments and 
examples. These other embodiments and examples are within the 
contemplation of the present invention. Therefore, the present invention 
should be limited only by the appended claims.