Process for the preparation of 1,4-butanediol

A process for preparation of 1,4-butanediol comprises reaction of allyl alcohol with carbon monoxide and hydrogen in the presence of a soluble rhodium catalyst, certain phosphine promoters and certain carbonitriles as solvent.

BACKGROUND OF THE INVENTION 
The invention relates to a process for the preparation of 1,4-butanediol by 
reaction of allyl alcohol with carbon monoxide and hydrogen in the 
presence of a soluble rhodium catalyst, a phosphine promoter and a 
solvent. 
1,4-Butanediol is a valuable commercial product which finds application on 
a large scale, in particular as intermediate in the preparation of 
polyesters, polyurethanes, butyrolactone and tetrahydrofuran. 
The commercial production of 1,4-butanediol relies virtually exclusively on 
the Reppe process, in which acetylene and formaldehyde are converted into 
2-butyn-1,4-diol, which is hydrogenated to form 1,4-butanediol. In order 
to avoid the drawbacks involved in the use of acetylene in the Reppe 
process, a number of other pocesses have been proposed of which, according 
to Chemical Economy and Engineering Review, September 1980, 12 (No. 9), 
pp. 32-35, the one based on hydroformylation of allyl alcohol is the most 
attractive process for use on an industrial scale. 
In this process--as described for instance in U.K. Patent Specification No. 
1493154--allyl alcohol is first converted into hydroxybutyraldehyde by 
hydroformylation using a rhodiumcarbonyl complex as catalyst, an excess of 
a phosphine ligand and an organic solvent which is immiscible with water. 
Then the hydrobutyraldehyde formed is extracted from the organic solvent 
with water and subsequently hydrogenated to form 1,4-butanediol. 
In the U.K. Patent Specification No. 1565719 a process is described in 
which allyl alcohol is converted direct into 1,4-butanediol in yields of 
up to 50%, by reacting the allyl alcohol with carbon monoxide and hydrogen 
in the presence of a rhodium catalyst and a tertiary phosphine containing 
at least one aliphatic hydrocarbyl group. In this process a solvent can 
advantageously be used which optionally may be immiscible with water and 
from which the 1,4-butanediol can be recovered by extraction with water. 
It has now surprisingly been found that allyl alcohol can be converted 
direct into 1,4-butanediol in higher yields than mentioned in U.K. Patent 
Specification No. 1565719, when the reaction of allyl alcohol with carbon 
monoxide and hydrogen is carried out in the presence of a rhodium catalyst 
in combination with a trialkyl phosphine as ligand and certain 
carbonitriles--which will be defined hereinafter--as solvents. 
SUMMARY OF THE INVENTION 
The invention therefore relates to a process for the preparation of 
1,4-butanediol by reaction of allyl alcohol with carbon monoxide and 
hydrogen in the presence of a soluble rhodium catalyst, a tertiary 
phosphine and a solvent, characterized in that the tertiary phosphine is a 
phosphine of the general formula 
EQU P[(CH.sub.2)nR.sup.1 ][(CH.sub.2).sub.n R.sup.2 ][(CH.sub.2).sub.n R.sup.3 
], 
wherein R.sup.1, R.sup.2 and R.sup.3 each represent hydrogen and n is 1 or 
2, or wherein R.sup.1, R.sup.2 and R.sup.3 each represent a substituted or 
unsubstituted alkyl group and n is 2 and the solvent is a carbonitrile of 
the general formula 
EQU R.sup.4 CH.sub.2 CH.sub.2 CH.sub.2 C.ident.N, 
wherein R.sup.4 represents hydrogen or a substituted or unsubstituted 
hydrocarbyl group.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The soluble rhodium catalyst which can be used according to the invention 
comprises one or more rhodium compounds which are soluble in the reaction 
mixture or which in situ form soluble compounds therein. Examples of such 
rhodium compounds are rhodium oxide rhodium nitrate, rhodium sulphate, 
rhodium acetate, rhodium butyrate rhodium naphthenate, rhodium carbonyl 
complexes, such as dirhodiumoctacarbonyl tetrarhodiumdodecacarbonyl and 
hexarhodiumhexadecacarbonyl, rhodiumdicarbonyl acetylacetonate and 
bis(rhodiumcarbonyl chloride) and rhodiumcarbonylphosphine complexes, such 
as hydridorhodiumtri-(tri-n-butylphosphine)carbonyl and rhodium 
di(tri-n-hexyl-phosphine)carbonyl chloride. 
The quantity of rhodium compound may vary within wide limits. Generally the 
quantities used are such that per mol allyl alcohol the reaction mixture 
comprises 10.sup.-4 to 10.sup.-1 gram atom rhodium. Preference is given to 
the presence of 10.sup.-3 to 10.sup.-2 gram atom rhodium per mol allyl 
alcohol. 
The tertiary phosphine used in combination with the rhodium catalyst as 
ligands are represented by the general formula 
EQU P[(CH.sub.2).sub.n R.sup.1 ][(CH.sub.2).sub.n R.sup.2 ][(CH.sub.2).sub.4 
R.sup.3 ], 
wherein R.sup.1, R.sup.2 and R.sup.3 are linear terminally bonded alkyl 
groups containing not more than 16, but preferably 2, 3, 4, 5 or 6 carbon 
atoms and n equals 2, or wherein R.sup.1, R.sup.2 and R.sup.3 each 
represent hydrogen and n is 1 or 2. Specific examples of suitable 
phosphines are trimethylphosphine, triethylphosphine, 
tri-n-propylphosphine, tri-n-butylphosphine, tri-n-hexylphosphine, 
tri-n-octylphosphine, dimethylphosphine, di-n-butyloctadecylphosphine, 
di-n-pentylethylphosphine, tri-n-octadecylphosphine, 
tri-n-dodecylphosphine and tri-n-decylphosphine. 
The reaction can be carried out in the presence of as little as about 3 mol 
phosphine per gram atom rhodium, but it is preferred to use at least 5 mol 
phosphine per gram atom rhodium. 
As solvents are used in the process according to the invention 
carbonitriles of the general formula 
EQU R.sup.4 CH.sub.2 CH.sub.2 CH.sub.2 C.ident.N, 
wherein R.sup.4 represents hydrogen or a hydrocarbyl group which may or may 
not be substituted, in particular an alkyl group containing up to about 10 
carbon atoms in particular up to about 8 carbon atoms. Examples of 
suitable carbonitriles are propane carbonitrile, butane carbonitrile, 
heptane carbonitrile, octane carbonitrile, decane carbonitrile, undecane 
carbonitrile, tridecane carbonitrile, 1,5-pentane dicarbonitrile and 
1,8-dicarbonitrile. Preference is given to the use of carbonitriles in 
which R.sup.4 of the general formula is a linear terminally bonded alkyl 
group containing at least 2 carbon atoms. 
The use of the preferred carbonitriles offers an additional advantage--on 
top of the higher yields of 1,4-butanediol--in that the 1,4-butanediol 
formed separates from the reaction mixture and is therefore easy to 
recover. Optionally this separation from the reaction mixture can be 
further enhanced by the addition of other, phase separation promoting, 
solvents such as water, alcohols and aromatic hydrocarbons, such as 
benzene and toluene. 
However, if desired, the reaction can also be carried out in a reaction 
medium which remains homogeneous, by using as solvent besides the 
carbonitrile solvent, for example an ether, such as diethyl ether, dioxane 
or tetrahydrofuran. 
The quantity of carbonitrile solvent present in the reaction mixture may 
vary within wide ranges. Quantities of from about 1/10 mol carbonitrile 
per mol allyl alcohol may be used. Preferably the quantities of 
carbonitrile amount to 1/5 mol and more per mol allyl alcohol. 
The carbon monoxide-hydrogen mixtures used in the process according to the 
invention may be very varied in composition. The carbon monoxide to 
hydrogen molar ratios may vary from 10:1 to 1:10. Preference is given to 
mixtures whose molar ratios lie between 5:1 and 1:5 and in particular to 
mixtures having molar ratios between 1:1 and 1:3. If required, the carbon 
monoxide to hydrogen molar ratio of the mixture used may be so altered 
during the course of the reaction as to range from an excess of carbon 
monoxide to an excess of hydrogen, in relation to the 1:2 carbon monoxide 
to hydrogen molar ratio which is the ratio in which carbon monoxide and 
hydrogen are consumed during the conversion of allyl alcohol into 
1,4-butanediol. 
In the carbon monoxide-hydrogen mixture inert gases, such as nitrogen, 
carbon dioxide, noble gases or methane can be included as diluent. 
The process is carried out at temperatures lying between 20.degree. C. and 
200.degree. C., preferably between about 30.degree. C. and about 
150.degree. C. and in particular between about 50.degree. C. and about 
120.degree. C. The overall pressure lies between about 1 and about 100 bar 
and in particular between about 20 and about 75 bar. High pressures, for 
instance of up to 1000 bar can be used, but generally they are 
unattractive for economic and technical reasons. The duration of the 
reaction is not critical and it is dependent on the temperature and 
pressure used. Generally the reaction time is 0.25 to 20 hours. Shorter or 
longer periods are not impossible, however. 
The process according to the invention may be carried out batch-wise, 
continuously or semi-continuously. The reaction mixture obtained can be 
worked up by known techniques. 
EXAMPLE I 
Into a magnetically stirred Hastelloy C autoclave (Hastelloy is a 
trademark) of 300 ml content were placed 0.5 mol of a rhodium compound 
rhodium dicarbonylacetylacetonate or bis(rhodiumcarbonyl chloride), 10 ml 
allyl alcohol, 40 ml of a carbonitrile solvent and quantities of 
tri-n-alkylphosphines as described in Table A. The autoclave was flushed 
with carbon monoxide and charged with a mixture of carbon monoxide and 
hydrogen. The carbon monoxide and hydrogen partial pressures are 20 and 40 
bar, respectively. The autoclave was heated for 5 hours at the 
temperatures given in Table A and then cooled. The two-phase system 
obtained whose bottom layer consisted of 1,4-butanediol was analyzed by 
gas-liquid chromatography. The total yield of 1,4-butanediol in a 
two-phase system was calculated on the quantity of allyl alcohol used as 
starting material. 
TABLE A 
______________________________________ 
Phosphine 
Exp. Rhodium ligand Carbonitrile Yield 
No. compound (mmol) solvent Temp. % 
______________________________________ 
decane 
1 Rh(acac) (n-octyl).sub.3 P 
carbonitrile 
75.degree. C. 
40 
(CO).sub.2 (2.5) 
heptane 
2 (RhCl(CO)).sub.2 
(n-octyl).sub.3 P 
carbonitrile 
85.degree. C. 
65 
(10) 
nonane 
3 (Rh(acac) (n-butyl).sub.3 P 
carbonitrile 
95.degree. C. 
69 
(CO).sub.2 (15) 
______________________________________ 
EXAMPLE II 
Into a magnetically stirred Hastelloy C autoclave (Hastelloy is a 
trademark) of 300 ml content were placed 0.5 mmol rhodium 
dicarbonylacetylacetonate, 10 ml allyl alcohol, 40 ml of a solvent and 
quantities of phosphines as described in Table B. The autoclave was 
flushed with carbon monoxide charged with a mixture of carbon monoxide and 
hydrogen. The carbon monoxide and hydrogen partial pressures were 20 and 
40 bar, respectively. The autoclave was heated for 5 hours at 75.degree. 
C. and then cooled. The reaction mixture obtained, which depending on the 
solvent used, either did or did not consist of a two-phase system due to 
separation of 1,4-butanediol (vide Table B) was analyzed by gas-liquid 
chromatography. The total yield of 1,4-butanediol present in the reaction 
mixture was calculated on the quantity of allyl alcohol used as starting 
material. 
TABLE B 
______________________________________ 
Two-phase 
Exp. Phosphine system Yield 
No. ligand (mmol) Solvent yes/no % 
______________________________________ 
1 (n-butyl).sub.3 P (5) 
octane carbon- 
yes 55 
itrile 
2 (n-butyl).sub.3 P (5) 
acetonitrile 
no 10 
3 (n-butyl).sub.3 P (5) 
benzene yes 40 
4 (n-butyl).sub.3 P (5) 
n-decane yes 10 
5 (n-butyl).sub.3 P (5) 
N--methyl- no -- 
pyrrolidone 
6 (n-butyl).sub.3 P (5) 
benzyl no reaction 
carbonitrile 
7 (cyclohexyl).sub.3 P (5) 
undecane no 0* 
carbonitrile 
8 (benzyl).sub.3 P (5) 
heptane no 0* 
carbonitrile 
9 (ethyl).sub.2 (phenyl)P (10) 
tridecane yes 20 
carbonitrile 
______________________________________ 
*product substantially hydroxybutyraldehyde 
Experiments 2 to 9 are comparative experiments; they do not comply with the 
process according to the invention. They demonstrate that for achieving 
good yields as well as the 1,4-butanediol separation from the reaction 
mixture, both the carbonitriles and the phosphines of the invention are 
necessary.