Process for preparing aldehydes

A process for selectively producing aldehydes, particularly acetaldehyde, which comprises introducing into a reaction zone (1) methanol, (2) carbon monoxide, (3) hydrogen, (4) cobalt, (5) iodine and (6) a ligand containing atoms from Group VB of the Periodic Table separated by a sterically constrained carbon-carbon bond and then subjecting the contents of said reaction zone to an elevated temperature and an elevated pressure for a time sufficient to convert methanol to said aldehydes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is directed to a process for selectively producing 
aldehydes, particularly acetaldehyde, which comprises introducing into a 
reaction zone (1) methanol, (2) carbon monoxide, (3) hydrogen, (4) cobalt, 
(5) iodine and (6) a ligand containing atoms from Group VB of the Periodic 
Table separated by a sterically constrained carbon-carbon bond and then 
subjecting the contents of said reaction zone to an elevated temperature 
and an elevated pressure for a time sufficient to convert methanol to said 
aldehydes. 
2. Description of the Invention 
In European Patent Application No. 79302053.8, filed in the names of B. R. 
Gane and D. G. Stewart and published on Apr. 30, 1980, it is disclosed 
that when methanol is reacted with synthesis gas in the presence of a 
catalyst comprising (a) cobalt, (b) an iodide or a bromide and (c) a 
polydentate ligand, wherein the donor atoms are exclusively phosphorus, 
the product obtained will contain a substantial proportion of ethanol. 
When the polydentate ligand used is one wherein at least one of the donor 
atoms is phosphorus and another is arsenic, it is alleged by Gane et al 
that the product will contain a mixture of ethanol and acetaldehyde. 
SUMMARY OF THE INVENTION 
We have found that if we introduce into a reaction zone (1) methanol, (2) 
carbon monoxide, (3) hydrogen, (4) cobalt, (5) iodine and (6) a ligand 
containing atoms from Group VB of the Periodic Table separated by a 
sterically constrained carbon-carbon bond, while controlling the 
proportion of the reaction components and the reaction parameters, we can 
obtain a reaction product predominating in aldehydes, including compounds 
convertible thereto, particularly acetaldehyde. By "compounds convertible 
thereto" we mean to include acetals, such as dimethyl acetal. In general 
the reaction product will contain at least about 30 weight percent, 
especially from about 35 to about 85 weight percent, of aldehydes and 
compounds convertible thereto. The acetaldehyde content of the reaction 
product will be at least about 25 weight percent, especially about 27 to 
about 75 weight percent. At the same time, the alcohol content of the 
reaction product, including compounds convertible thereto, will be very 
small. By "compounds convertible thereto", in the latter instance, we mean 
to include acetates, such as ethyl acetate. In general the reaction 
product will contain less than about 23 weight percent of alcohols and 
compounds convertible thereto, but more often from about two to about ten 
weight percent of alcohols and compounds convertible thereto. As to the 
ethanol content of the reaction product it will be less than about 18 
weight percent, but more often in the range of about 0 to about seven 
weight percent. The compounds referred to above that can be converted to 
aldehydes or alcohols can be converted thereto by any known or suitable 
process, for example, by hydrolysis, that is, contacting a precursor 
thereof with water, with or without an acid (sulfuric) or a basic (sodium 
hydroxide) catalyst. 
As noted, the ligand used herein contains atoms from Group VB of the 
Periodic Table. By "Group VB atoms" we mean to include nitrogen, 
phosphorus and arsenic. By a "sterically constrained carbon-carbon bond" 
we mean to include a carbon-carbon bond of an organic divalent radiacal in 
which the radical centers are located on adjacent carbon atoms and in 
which the bond axis of these adjacent carbon atoms is inhibited from 
rotating by either bond unsaturation or by their incorporation into an 
alicyclic ring system. By bond unsaturation we mean to include an alkylene 
bond, such as 
##STR1## 
and an arylene bond, such as 
##STR2## 
or an acetylenic bond such as --C.tbd.C-- wherein any of the above-defined 
R substituents can be hydrogen, a hydrocarbyl, such as defined 
hereinafter, a halogen, such as chlorine or bromine, a sulfur-containing 
substituent, such as a sulfonato group, a nitrogen-containing substituent, 
such as a nitro group or an amino group, an oxygen-containing substituent, 
such as a hydroxyl group, etc. By "alicyclic ring system", we mean to 
include an aliphatic ring system comprising a three- to eight-membered 
ring, such as 
##STR3## 
wherein n=1, 2, 3, 4, 5, or 6 and any of the above-defined R groups can be 
similar to R' and R". 
Especially preferred ligands for use herein can be defined by the following 
formula: 
##STR4## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are either alike or 
different members selected from the group consisting of alkyl radicals 
having from one to 24 carbon atoms, preferably from two to 10 carbon 
atoms; aryl radicals having from six to 20 carbon atoms, preferably from 
six to 10 carbon atoms; alkenyl radicals having from two to 30 carbon 
atoms, preferably from two to 20 carbon atoms; cycloalkyl radicals having 
from three to 40 carbon atoms, preferably from three to 30 carbon atoms; 
and aralkyl and alkaryl radicals having from six to 40 carbon atoms, 
preferably from six to 30 carbon atoms; preferably aryl or alkyl; R.sub.5, 
R.sub.6, R.sub.7 and R.sub.8 are either alike or different members 
selected from R.sub.1, R.sub.2, R.sub.3 and R.sub.4, defined above, and 
hydrogen, preferably hydrogen or alkyl; E.sub.1 and E.sub.2 the same or 
different, can be phosphorus or arsenic, preferably with E.sub.1 being 
phosphorus and E.sub.2 being arsenic, most preferably with each of E.sub.1 
and E.sub.2 being phosphorus; and m and n being integers ranging from 0 to 
2, preferably from 0 to 1, provided that m+n=0-4, preferably 0-2; and A 
can be an organic divalent radical in which the radical centers are 
located on adjacent carbon atoms and in which the bond axis of these 
adjacent carbon atoms is inhibited from rotating by bond unsaturation, 
e.g., aromatic, heterocyclic, olefinic, or acetylenic, or by their 
incorporation into an alicyclic ring system comprising a three- to 
eight-membered ring. When A is an alicyclic group or includes an alkylene 
linkage, the bidentate ligand includes cis-type and trans-type steric 
isomers. In the present invention, both isomers can be used. Included 
among the ligands that can be employed herein, some of which are believed 
to be novel, are those defined below in Table I, referring to the 
structural formula hereinabove defined. 
TABLE I 
__________________________________________________________________________ 
R.sub.1 
R.sub.2 
R.sub.3 
R.sub.4 
R.sub.5 
R.sub.6 
R.sub.7 
R.sub.8 
E.sub.1 
E.sub.2 
A m n 
__________________________________________________________________________ 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR5## 
0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR6## 
0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
H H H H P P " 1 1 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
CH.sub.3 
H H H P P " 1 1 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
CH.sub.3 
H CH.sub.3 
H P P " 2 2 
Phenyl 
Phenyl 
Ethyl 
Ethyl 
-- -- -- -- 
P P " 0 0 
Phenyl 
Phenyl 
Ethyl 
Ethyl 
H CH.sub.3 
H H P As 
" 1 1 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR7## 
0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR8## 
0 0 
10. 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR9## 
0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P 
##STR10## 
0 0 
Phenyl 
Phenyl 
Ethyl 
Ethyl 
H H H H P P 
##STR11## 
1 1 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
H H H H P P 
##STR12## 
0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
-- -- -- -- 
P P CC 0 0 
Phenyl 
Phenyl 
Phenyl 
Phenyl 
H H H H P P 
##STR13## 
1 1 
__________________________________________________________________________ 
Any source of iodine which is capable of dissociating, that is, ionizing to 
form free iodide ions in the reaction medium can be used in the present 
invention. Illustrative examples of iodine compounds especially suitable 
for use herein include iodine, potassium iodide, calcium iodide, sodium 
iodide, lithium iodide, aluminum iodide, bismuth iodide, hydrogen iodide, 
methyl iodide, ethyl iodide, etc., and mixtures thereof. 
The cobalt entity suitable for use herein an be defined as being a cobalt 
carbonyl, a hydrido cobalt carbonyl or a cobalt-containing compound 
convertible to a cobalt carbonyl or a hydrido cobalt carbonyl. By "cobalt 
carbonyl" we intended to define a compound containing only cobalt and 
carbon monoxide, such as Co.sub.2 (CO).sub.8 or Co.sub.4 (CO).sub.12. By 
"hydrido cobalt carbonyl" we intended to define a compound containing only 
cobalt, carbon monoxide and hydrogen, such as HCo(CO).sub.4. By 
"cobalt-containing material convertible to a cobalt carbonyl or a hydrido 
cobalt carbonyl" we intend to define any material which when mixed with 
hexane and subjected to 4000 pounds per square inch gauge (27.6 MPa) in an 
atmosphere containing hydrogen and carbon monoxide in a molar ratio of 1:1 
at 150.degree. to 200.degree. C. for a period of three hours will result 
in the formation of a cobalt carbonyl, a hydrido cobalt carbonyl or 
mixtures thereof. Specific examples of a cobalt-containing material so 
convertible to a cobalt carbonyl or a hydrido cobalt carbonyl include 
cobalt(II)sulfate, cobalt oxide(Co.sub.3 O.sub.4), 
cobalt(II)tetrafluoroborate, cobalt(II)acetate, cobalt((II)oxalate, 
cobalt(II)propionate, cobalt(II)octoate, cobalt(II)butyrate, 
cobalt(II)benzoate, cobalt(II)valerate, cobalt(II)formate, 
cobalt(II)cyclohexanebutyrate, cobalt(II)2-ethyl-hexaoate, 
cobalt(II)gluconate, cobalt(II)lactate, cobalt(II)naphthenate, 
cobalt(II)oleate, cobalt(II)citrate, cobalt(II)acetylacetonate, etc. 
The relative amounts of carbon monoxide and hydrogen employed can be varied 
over a wide range. However, in general, the molar ratio of carbon monoxide 
to hydrogen is from about 2:1 to about 1:2, preferably about 1.5:1 to 
about 1:1.5, but most preferably about 1.25:1 to about 1:1.25. Compounds 
or reaction mixtures which give rise to the formation of carbon monoxide 
and hydrogen under the reaction conditions defined herein can be used 
instead of mixtures comprising carbon monoxide and hydrogen which are used 
in the preferred embodiments of this invention. 
In order to obtain a product herein that predominates in aldehydes, 
particularly acetaldehyde, the amount of cobalt employed relative to the 
ligand and to iodine is critical. Thus, the molar ratio of cobalt based on 
the element cobalt, to the ligand must be in the range of about 1:2 to 
about 7:1, preferably about 1:1.5 to about 4:1. The molar ratio of cobalt, 
based on the element cobalt, to iodine, based on the element iodine, must 
be in the range of about 1:1.15 to 1:15, preferably about 1:1.25 to about 
1:5. Based on the methanol introduced into the system, the weight percent 
of combined cobalt and iodine, in their elemental form, can range from 
about 0.01 to about 10 percent, preferably from about 0.1 to about five 
percent. 
The process herein can be carried out either in a batch operation or by 
passing the reactants continuously through a reaction zone. In each case 
the reactor is provided with agitation means and the pressure is 
maintained therein by the addition of hydrogen and carbon monoxide, or 
compounds producing hydrogen and carbon monoxide, as required. In order to 
facilitate the introduction of the phosphorus-containing ligand and the 
cobalt and iodine entities into the reaction zone and/or to facilitate 
recovery of the components of the reaction herein, they can be dissolved 
in an inert solvent, such as ethylene glycol, diethylene glycol monomethyl 
ether, acetone, sulfolanes, such as tetramethylene sulfone, lactones, such 
as .gamma.-butyrolactone and .epsilon.-caprolactone, etc. 
In the reaction zone the contents thereof are maintained at an elevated 
temperature and at an elevated critical pressure for a time sufficient to 
convert methanol to the desired aldehydes. The total pressure (based on 
hydrogen, carbon monoxide and any produced gases) must be at least about 
2200 pounds per square inch gauge (15.02 MPa) but need not be in excess of 
about 10,000 pounds per square inch gauge (68.30 MPa). Especially 
desirable are pressures in the range of about 2500 pounds per square inch 
gauge (17.07 MPa) to about 7500 pounds per square inch gauge (51.19 MPa). 
Temperatures which are suitable for use herein are those temperatures 
which initiate a reaction between the reactants herein to selectively 
produce aldehydes, generally from about 150.degree. to about 250.degree. 
C., preferably from about 170.degree. to 220.degree. C. The reaction is 
conducted for a time period sufficient to convert methanol to aldehydes, 
normally from about five minutes to about five hours, preferably from 
about ten minutes to about 2.5 hours. 
Recovery of the desired aldehydes, for example acetaldehyde, from the 
reaction product can be effected in any convenient or conventional manner, 
for example, by distillation, at ambient pressure and about 21.degree. C. 
The components will distill off in the following sequence for the desired 
recovery: acetaldehyde, propionaldehyde, methyl acetate, methanol, 
butyraldehyde, ethyl acetate, ethanol, etc.