Process for the production of aldehydes by hydroformylation

In an oxo process wherein an olefin is caused to react with carbon monoxide and hydrogen, a rhodium catalyst is provided by carrying out the hydroformylation in the presence of a rhodium source and free mixed ligands comprising a tertiary organo phosphorus and tertiary organo arsenic in excess of the quantity required for coordination to the rhodium atom. For example, HRh(CO)(PPh.sub.3).sub.3 with excess AsPh.sub.3 /PPh.sub.3 may be used to give a high reaction rate and good selectivity to n-aldehyde.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for the production of aldehydes by the 
hydroformylation of olefins and, more particularly, it is concerned with 
an improved process for producing aldehydes by reacting olefins, carbon 
monoxide and hydrogen in the presence of rhodium-containing complex 
compound catalysts and free ligands. 
2. Description of the Prior Art 
Rhodium-phosphine type or rhodium-phosphite type complexes are known as 
catalysts for the hydroformylation of olefins and a number of studies have 
been made thereon, see for example Chem. Comm., 305 (1967) Apr. 12, 1967. 
The stability of a rhodium catalyst is increased by modification with 
phosphine, arsine or stibine, which permits practicing the oxo reaction at 
a rather low pressure. According to Japanese Pat. No. 903326, straight 
chain-rich aldehydes are prepared at a low total pressure with a low 
partial pressure of carbon monoxide and a high partial pressure of 
hydrogen in the presence of a rhodium triaryl phosphine catalyst and a 
triaryl phosphine ligand in a large excess to the rhodium. However, this 
method has the disadvantage that the hydroformylation reaction rate of an 
olefin is markedly decreased because of using a ligand in a large excess 
to rhodium, and a considerable quantity of a paraffin is formed by the 
hydrogenation of the olefin ["Hydrocarbon Processing" (4) 112) (1970)] due 
to the reaction at a low total pressure with a low partial pressure of 
carbon monoxide and a high partial pressure of hydrogen. 
Rhodium catalysts in combination with arsines or stibines instead of 
phosphines have been proposed, but the studies thereof have not been made 
so intensively because of their lower activity compared with tertiary 
phosphine-rhodium catalysts. 
Applicants have proposed in their U.S. Ser. No. 073,664 filed on even date 
herewith based on Japanese Patent Applications No. 121456/78 and 
121457/78, hydroformylation of an olefin using a rhodium complex 
containing both a tertiary organo phosphorus ligand and tertiary 
organo-arsenic ligand [H Rh(CO)(ligand).sub.3 ] which is an active species 
for the hydroformylation in the presence of excess mixed ligands of a 
tertiary organo phosphorus compound and tertiary organo arsenic compound. 
That is to say, in the hydrogormylation of an olefin, the reaction rate is 
remarkably improved, the quantity of paraffin formed by the hydrogenation 
of the olefin is decreased and, in addition, the selectivity to normal 
chain aldehyde is kept similar or improved in comparison with carrying out 
the reaction in the presence of a tertiary organo phosphorus rhodium 
catalyst and excess tertiary organo phosphorus ligand. The said process is 
superior to the prior art from the viewpoint of efficiency of 
hydroformylation. 
However, the present method has advantages with regard to the ease of 
preparing or providing the rhodium-mixed ligands catalyst of this 
invention. 
SUMMARY OF THE INVENTION 
The inventors have made studies of a catalyst system consisting of an 
easily synthesizable or available rhodium source, for example, an 
inorganic rhodium compound such as rhodium metal or rhodium oxide, a 
rhodium organic salt such as rhodium acetate, or a rhodium complex such as 
rhodium carbonyl, Rh (CO) (PPh.sub.3).sub.2 Cl or HRh (CO) 
(PPh.sub.3).sub.3 and excess mixed ligands of a tertiary organo phosphorus 
and tertiary organo arsenic and have found that when hydroformylation is 
carried out with this catalyst system, the effect of hydroformylation is 
equal to that of applicants' above-mentioned application. That is to say, 
the present invention relates to a process for producing aldehydes by 
reacting an olefin with carbon monoxide and hydrogen, the aldehydes having 
one more carbon atom than the olefin, which comprises carrying out the 
reaction in the presence of a rhodium source and free mixed ligands 
comprising a tertiary organo phosphorus and tertiary organo arsenic 
represented by the general formula XR.sub.3 [wherein X represents 
phosphorus or arsenic and R represents an organo group, which may be same 
or different] in excess of the quantity required for coordination to the 
rhodium atom. 
DETAILED DESCRIPTION 
The easily obtainable or easily prepared rhodium source of the invention 
includes various rhodium compounds. 
Examples are a rhodium metal such as rhodium black or supported rhodium, an 
inorganic rhodium compound such as rhodium oxide, rhodium nitrate, rhodium 
sulfate, rhodium chloride, rhodium bromide or rhodium iodide, a rhodium 
organic acid salt such as rhodium acetate or rhodium octoate, or a rhodium 
complex such as rhodium carbonyl, Rh(CO).sub.2 (acac), 
Rh(CO)(acac)(PPh.sub.3), Rh(CO)(PPh.sub.3).sub.2 Cl, [Rh(CO).sub.2 
Cl].sub.2, HRh(CO)(PPh.sub.3).sub.3, HRh(CO)(AsPh.sub.3).sub.3, 
HRh(CO)[P(OPh).sub.3 ].sub.3, Rh(acac).sub.3, RhCl(PPh.sub.3).sub.3, 
[RhCl(C.sub.2 H.sub.4).sub.2 ].sub.2, [RhCl(1,5-COD)].sub.2, 
Rh(CO)(AsPh.sub.3).sub.2 Cl, Rh(NO)(PPh.sub.3).sub.3, 
[(1,5-COD)Rh(PPh.sub.3).sub.2 ] ClO.sub.4 or 
[(1,5-COD)Rh(AsPh.sub.3).sub.2 ] ClO.sub.4 
(wherein acac=acetylacetonate, Ph=phenyl and COD=cyclo octadienyl). 
Preferred examples from the viewpoint of commercial availability and ease 
of preparation are complex compounds such as HRh(CO)(PPh.sub.3).sub.3, 
HRh(CO)(AsPh.sub.3).sub.3, Rh(CO).sub.2 (acac), [Rh(PPh.sub.3).sub.3 
].sub.2, HRh(Ph.sub.2 PCH.sub.2 CH.sub.2 PPh.sub.2).sub.2 and HRh(CO) 
[P(OPh).sub.3 ].sub.3. 
The ligands (XR.sub.3) used in the present invention are represented by the 
general formula PR.sup.1 R.sup.2 R.sup.3 and As R.sup.4 R.sup.5 R.sup.6 in 
which R.sup.1 to R.sup.6 represent alkyl, cycloalkyl, aryl, aralkyl, 
alkoxy, cycloalkoxy, aryloxy, and aralkyloxy groups and may be the same or 
different. Preferably, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and 
R.sup.6 are aryl groups and aryloxy groups and more preferably the same 
aryl group. In view of the reactivity and commercial availability, it is 
most preferably that they are all phenyl groups, that is, triphenyl 
phosphine and triphenyl arsine. The mixed ligands used in excess may be 
the same as or different from those contained in the rhodium complex, but 
the same ligands are advantageous commercially. 
The sum of the amounts of mixed ligands may be chosen within a wide range. 
In general, the sum of the amounts of free mixed ligands is 3 mols or more 
per rhodium atom in the rhodium source. Since addition of free mixed 
ligands in too large an excess is disadvantageous with respect to the 
reaction and cost, the excess amount is preferably 5 to 1000 mols, most 
preferably 50 to 500 mols per rhodium atom. 
The proportion of tertiary organo-phosphorus to tertiary organo arsenic 
used as mixed ligands in excess may be chosen within a wide range. This 
proportion is generally 5:1 to 1:5, preferably 2:1 to 1:3, in order to 
maintain the stability of the catalyst and show the effect of a mixed 
ligands system sufficiently. 
The above mentioned rhodium source and mixed ligands are provided in a 
hydroformylation reactor in order to carry out the hydroformylation but 
the rhodium source may be contacted with a mixed gas of carbon monoxide 
and hydrogen in the presence of the mixed ligands in excess at an elevated 
pressure before the hydroformylation. In particular, a rhodium source 
containing halogen or rhodium nitrate is preferably treated with an 
alkaline reactant, e.g., aqueous sodium hydroxide, outside the reaction 
system under the above mentioned conditions. 
It is known that the hydroformylation rate decreases with increasing mol 
ratio of a tertiary organo phosphorus to rhodium when carrying out the 
hydroformylation in the presence of a tertiary organo phosphorus-rhodium 
complex and a tertiary organo phosphorus in excess, see Journal of the 
Chemical Society (A) 1970, pp. 2753-2764. 
On the other hand, in a hydroformylation in the presence of a tertiary 
organo phosphorus-rhodium complex and a tertiary organo arsenic in excess, 
decrease of the reaction rate is observed too, with increasing mol ratio 
of a tertiary organo arsenic to rhodium, and moreover, the rate is 
extremely slow and the selectivity to normal aldehyde is low compared with 
that in the tertiary organo phosphorus in excess. 
The present invention shows the unique and commercially valuable result, 
which comprises not slowing down the rate of hydroformylation and not 
lowering the selectivity to n-butylaldehyde caused by the presence of a 
tertiary organo arsenic in excess, but maintaining the selectivity to 
normalbutylaldehyde and improving the reaction rate to 1.5 to 2 times that 
of the known process using tertiary phosphorus ligands. 
Accordingly, a reactor can be reduced in size with the same output. 
Furthermore, it is possible to decrease the quantity of rhodium catalyst 
to olefin and the concentration of rhodium in a catalyst bed. 
The quantity of a rhodium catalyst used in a hydroformylation, depending on 
the procedure and the variety of olefin used as a starting material, may 
be chosen--considering these conditions--within a wide range. In a 
catalyst recycling process wherein an olefin, synthesis gas and rhodium 
catalyst are fed to a reaction tower, the reaction mixture is withdrawn 
from the head of the tower, cooled and subjected to reduced pressure to 
separate a gaseous component, and the liquid product is passed through a 
distillation column to distill off the product and to give a still residue 
containing the rhodium catalyst which is then withdrawn from the bottom of 
the column and recirculated to the reaction tower, for example, the 
quantity of the rhodium catalyst is 10 ppm to 5% by weight, preferably 50 
ppm to 1% by weight as rhodium atom based on olefin feed. 
In a liquid fixed bed process wherein an olefin and synthesis gas are fed 
to a catalyst layer charged previously to a reaction tower and only the 
reaction product in the form of a mixture of gases and vapors is withdrawn 
from the top of the tower, the concentration of rhodium in the catalyst 
layer is generally 10 ppm to 5% by weight, preferably 50 ppm to 1% by 
weight. 
The catalyst system of the present invention may be used batchwise in 
addition to the continuous procedures described above. The reaction 
conditions may be the same as those in the case of using the 
rhodium-tertiary organo phosphorus type catalysts. That is to say, the 
reaction temperature is ordinarily room temperature to 150.degree. C., 
preferably 60.degree. to 120.degree. C., and the total pressure is 
ordinarily normal pressure to 100 atmospheres, preferably normal pressure 
to 50 atmospheres, most preferably normal pressure to 30 atmospheres. In 
addition, the hydrogen to carbon monoxide mol ratio in the reaction zone 
is 10/1 to 1/10, preferably 10/1 to 1/1. A solvent is not always 
indispensable, but in order to maintain stable operation, it is desirable 
to use a solvent. 
The solvent may be chosen from a wide range among those having no 
detrimental influence on hydroformylation, for example, saturated 
hydrocarbons such as hexane, decane and dodecane; aromatic hydrocarbons 
such as benzene, toluene, xylene, cumene and diisopropylbenzene; and 
oxygen-containing compounds such as alcohols, ketones, esters, and 
preferably products and high boiling point by-products of 
hydroformylation. 
The catalyst system of the present invention can be adapted to 
.alpha.-olefins such as ethylene, propylene, butene-1, hexene-1 and 
octene-1, olefins with internal double bonds such as butene-2 and 
octene-2, and vinyl compounds such as styrene, acrylonitrile, acrylic acid 
esters and allyl alcohols. The present catalyst system is most suitable 
for obtaining aldehydes rich in normal chain type isomers from 
.alpha.-olefins. 
The present invention provides a commercially valuable process whereby in 
the hydroformylation of olefins, the reaction rate is increased, the 
quantity of paraffin by-product is decreased and, in addition, the 
selectivity to normal chain aldehyde is kept similar or improved in 
comparison with carrying out the reaction in the presence of a 
rhodium-tertiary organo phosphorus complex and excess tertiary organo 
phosphorus ligand in combination; and the greater ease of obtaining the 
catalyst and the similar effect on reaction rate, by-product and 
selectivity to normal aldehyde are shown in comparison with carrying out 
the reaction in the presence of a rhodium-tertiary organo 
phosphorus+tertiary organo arsenic complex and excess mixed ligands of 
tertiary organo phosphorus+tertiary organo arsenic ligand. 
The following examples are given in order to illustrate the present 
invention in detail without limiting the same.

EXAMPLE 1 
0.109 mmol of tris (triphenyl phosphine) rhodium carbonyl hydride 
[HRh(CO)(PPh.sub.3).sub.3 ], 3.60 mmol of triphenyl phosphine, 3.60 mmol 
of triphenylarsine and 20 ml of n-dodecane were charged to a 300 ml 
stainless steel autoclave equipped with a magnetic stirrer which was 
purged with nitrogen. 5.0 g of propylene was introduced under pressure 
into the autoclave which was then heated to 110.degree. C., an H.sub.2 /CO 
gas with a molar ratio of 1:1 was introduced and the reaction pressure was 
adjusted to 20 Kg/cm.sup.2, followed by stirring. The synthesis gas was 
continuously supplied from a gas holder to keep the reaction pressure 
constant. After the reaction had been continued for 18 minutes, from the 
start until the conversion of propylene reached about 90%, the autoclave 
was cooled and the product was withdrawn and subjected to analysis by gas 
chromatography. The reaction rate measured by the pressure decrease of the 
synthesis gas in the gas holder was 11.1 ml/sec. The conversion of 
propylene was 89.3% and the ratio of normal isomer to branched isomer of 
butylaldehyde was 3.1. The yield of propane was 0.4%. 
EXAMPLES 2 to 9 and COMATIVE EXAMPLES 1 to 6 
Hydroformylations were carried out in a manner analogous to Example 1 
except that the ratio of PPh.sub.3 /rhodium and AsPh.sub.3 /rhodium, 
reaction temperature and the mol ratio of H.sub.2 /CO were varied, thus 
obtaining the results shown in the following Table. 
As can be seen from these results, in the catalyst system containing mixed 
excess PPh.sub.3 and AsPh.sub.3, the reaction rate is increased to about 
1.5 to 2 times that in the catalyst system containing excess PPh.sub.3 
only and the quantity of propane formed is somewhat decreased. 
EXAMPLE 10 and COMATIVE EXAMPLE 7 
RhCl(CO)(AsPh.sub.3).sub.2 which was synthesized from RhCl.sub.3.3H.sub.2 O 
by the known method [L. Vallarince, J. Chem. Soc., (A) 2287 (1966)] was 
reacted in the presence of AsPh.sub.3 in excess, in ethanol solvent, and 
under a nitrogen atmosphere at 65.degree. C. After the reaction, the 
mixture was cooled to about 0.degree. C., and then an ethanol solution of 
NaBH.sub.4 was added dropwise, thereby forming HRh(CO)(AsPh.sub.3).sub.3. 
Hydroformylations were carried out in a manner analogous to Example 1 
except that the above mentioned complex as rhodium source and mixed excess 
ligands of 5.45 mmol PPh.sub.3 and 5.45 mmol AsPh.sub.3 were used. The 
results are shown in the Table with the results of comparative Example 7 
carried out in the presence of AsPh.sub.3 as the only excess ligand. 
It is apparent from these results that in a HRh(CO)(AsPh.sub.3).sub.3 
/AsPh.sub.3 catalyst system, the activity and the selectivity to normal 
chain aldehyde are lower, but in a mixed ligands catalyst system, higher 
activity and higher selectivity are achieved. 
EXAMPLE 11 
(Rh)(CO).sub.2 (CH.sub.3 CO CH.sub.2 CO CH.sub.3) was synthesized from 
[Rh(CO).sub.2 Cl].sub.2 by the known method [B. E. North et al. J. 
Organometal Chem., 21 445 (1970)]. Hydroformylations were carried out in a 
manner analogous to Example 1 except that this complex as rhodium source 
and mixed ligands of 5.45 mmol PPh.sub.3 and 5.45 mmol AsPh.sub.3 were 
used. The results are shown in the Table. 
EXAMPLE 12 
The hydroformylation of Example 1 was repeated except that a catalyst 
consisting of rhodium supported on activated carbon (Rh content: 1.0% by 
weight) and excess mixed ligands, was used. 
COMATIVE EXAMPLE 8 
The hydroformylation of Example 1 was repeated except that a catalyst of 
rhodium-mixed ligands and excess mixed ligands was used. It is apparent 
from the Table that the present invention and comparative Example 8 show a 
similar effect on activity and selectivity to normal chain aldehyde. 
TABLE 
__________________________________________________________________________ 
n/i 
Pro- 
AsPh.sub.3 / 
Reaction Reaction 
Propy- 
Butylal- 
pane 
Rhodium PPh.sub.3 /Rhod- 
AsPh.sub.3 /Rhod- 
PPh.sub.3 
Tempera- 
H.sub.2 /CO 
Rate lene dehyde 
Yield 
Ex. 
Source ium Source 
ium Source 
(mol 
ture (mol 
d(H.sub.2 /CO)/dt 
Conv. (mol (mol 
No. 
(0.109 mmol) 
(mol ratio) 
(mol ratio) 
ratio) 
(.degree.C.) 
ratio) 
(ml/sec) 
(ml/sec) 
Ratio) 
%) 
__________________________________________________________________________ 
1 HRh(CO)(PPh.sub.3).sub.3 
33 33 1.0 110 1/1 11.1 89.3 3.1 0.4 
2 " 33 67 2.0 " " 12.8 90.2 3.3 0.4 
3 " 50 50 1.0 " " 8.4 87.2 3.5 0.3 
4 " " 75 1.5 " " 8.6 89.8 3.6 0.4 
5 " " 150 3.0 " " 6.9 87.2 3.8 0.4 
6 " 100 50 0.5 " " 5.8 87.3 4.3 0.3 
7 " " " " 100 " 3.2 93.9 4.3 0.2 
8 " " " " 110 5/1 7.5 90.4 7.9 1.9 
9 " 67 33 " " 1.0 4.4 82.3 3.6 0.2 
1* HRh(CO)PPh.sub.3).sub.3 
33 -- -- 110 1/1 5.8 89.6 2.7 0.7 
2* " 50 -- -- " " 5.6 90.9 2.9 0.7 
3* " 100 -- -- " " 4.0 90.2 4.0 0.5 
4* " 200 -- -- " " 2.5 88.7 5.2 0.4 
5* " 100 -- -- 100 " 2.3 87.1 4.0 0.5 
6* " 100 -- -- 110 5/1 5.5 90.4 6.6 2.3 
10 HRh(CO)(AsPh.sub.3).sub.3 
50 50 1.0 110 1/1 7.9 90.7 3.3 0.3 
7* " -- " -- " " 1.0 49.8 1.7 0.3 
11 Rh(CO).sub.2 (acac) 
50 " 1.0 " " 7.6 86.5 3.4 0.4 
12 Rh/C(Rh 1.0 wt. %) 
67 33 0.5 110 1/1 6.0 88.2 3.8 0.2 
8* HRh(CO)(PPh.sub.3).sub.2 
50 50 1.0 110 1/1 8.8 87.2 3.7 0.4 
(AsPh.sub.3) 
__________________________________________________________________________ 
* = Comparative Example