Process for preparing oxoisophorone using additives

Details Process for preparing oxoisophorone using additives Process for preparing oxoisophorone using additives

2000-06-21

2001-10-02

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S344000, C568S377000, C568S378000

Reexamination Certificate

active

06297404

ABSTRACT:

The present invention relates to a process for preparing 3,5,5-trimethylcyclohex-2-ene-1,4-dione (oxoisophorone; OIP) by oxidation of 3,5,5-trimethylcyclohex-3-en-1-one ((&bgr;-isophorone, &bgr;-IP) with molecular oxygen in the presence of a solvent, of a base and of a transition metal salen derivative as catalyst.
Oxoisophorone (OIP) can be used as flavoring or fragrance in foodstuffs or in cosmetic formulations. OIP is moreover an intermediate for the preparation of vitamins and carotenoids.
It is known to prepare OIP by oxidation of &bgr;-isophorone (&bgr;-IP) with molecular oxygen in the presence of an inert solvent, of a base and of an Mn or Co salen derivative. DE Patent 2610254 C2 describes the use of a large number of cobalt(II) and manganese(II) salen derivatives as catalysts, it being possible to prepare the salen-like chelate ligands from a number of diamines and hydroxy carbonyl compounds. The list of hydroxy carbonyl compounds mentions, besides many others, also halogenated 2-hydroxybenzaldehydes with a widely variable substitution pattern. The conversions, yields and selectivities achieved in this process are often only low, especially on use of unsubstituted aromatic Mn and Co salens (ligands prepared from various diamines and 2-hydroxybenzaldehyde). Substitution on the aromatic system with electron-attracting radicals, such as introduction of a nitro group, leads, as shown in Example 5 loc. cit., to a lower yield.
JP 01090150 describes aromatic mangangese(III) salen derivatives with a wide variability in the substitution pattern, the substituents, the counter ion and the number of C atoms in the amine bridge as catalysts in an analogous process. The best result is achieved on use of a chlorinated Mn(III) salen with X=acetate as counter ion and with low precursor concentrations, the yields being up to 90.7%. However, the low precursor concentrations mean that the space-time yield is likewise low.
EP 0808816 A1 describes an improved process with addition of catalytic additives such as organic acids, aliphatic alcohols, compounds able to form an enol structure, and lithium sulfate. This is said to achieve good selectivities and thus higher space-time yields even with higher precursor concentrations. Starting from precursor concentrations of 1.4 mol/l, selectivities of up to 92% (acetylacetone) with 80% conversion are achieved by the additions. Acetic acid as additive results in the highest reaction rate (5.3×10
−2
1/min). The process has the disadvantage that the space-time yields achieved are possible only on the laboratory scale because on the industrial scale it is not possible in exothermic reactions with molecular oxygen to have large precursor tonnages present initially; on the contrary, they must be introduced slowly (up to 4 hours) into the reaction mixture in order to avoid the risk of explosion. In addition, only 80% conversion means that elaborate removal of the unreacted precursors is necessary.
In all the prior art processes there is formation not only of high boilers, which interfere little with the purification, but also of the following identified byproducts IV (&agr;-isophorone), V, VI and VII, which impede purification or a further chemical reaction of OIP:
&agr;-Isophorone (IV) is formed in the prior art processes in a yield of up to 3.2%, and compound V is formed in a yield of up to 4.4%. Compound VI particularly interferes with subsequent syntheses because it shows a similar chemical behavior to the product OIP.
Besides the low yields with increasing precursor concentration, another disadvantage common to all the prior art processes is that even under simulated industrial conditions in relation to temperature and oxygen consumption the progress of the reaction is irregular so that large variations during the reaction must be monitored and compensated.
Moreover all the known processes use, from the large number of possible combinations of bases and solvents, triethylamine as base, often combined with diglyme (dimethyldiglycol) as solvent. Since this mixture has an ignition point of 0° C., the known processes can be carried out on the industrial scale only with great safety precautions for this reason too.
Moreover the reaction in the known processes is slow to start so that initially the concentration of the continuously introduced precursor (&bgr;-IP) rises. This results in the disadvantage, especially on the industrial scale, that for safety reasons initially a smaller amount of precursor can be introduced, resulting in a lower space-time yield. In addition, an increased proportion of &bgr;-isophorone leads to an increased isomerization back to &agr;-isophorone, resulting in a lower selectivity for &bgr;-isophorone.
It is an object of the present invention to remedy the disadvantages described and to develop a process which provides good yields, selectivities and space-time yields even with high precursor concentrations also on the industrial scale. It is further intended to reduce the formation of the byproducts IV, V, VI and VII and the rise in the &bgr;-IP concentration before the start of the reaction.
We have found that this object is achieved by a process in which 3,5,5-trimethylcyclohex-2-ene-1,4-dione is prepared by oxidation of 3,5,5-trimethylcyclohex-3-en-1-one with molecular oxygen in the presence of a solvent, of a base and of a catalyst of the formula I
where
R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
are, independently of one another, hydrogen, halogen, NO
2
, COR
9
, OCOR
9
, COOR
9
, SO
2
R
9
or SO
3
R
9
, where
R
9
is hydrogen or a C
1
-C
4
-alkyl radical,
M is Mn(II), Mn(III)
(+)
X
(−)
, Co(II), Co(III)
(+)X(−
), Fe(II), Fe(III)
(+)
X
(−)
, Cu(II) or Ru(II), where
X
(−)
is a negatively charged counter ion for metals in oxidation state III,
which process is carried out in the presence of one or more acetate salts of the general formula II
(R
10
R
11
R
12
C—COO
(−))
m
Y
(m+)
  (II)
as additive, where
R
10
, R
11
and R
12
are, independently of one another, hydrogen, F, Cl, Br, I or a C
1
-C
4
-alkyl radical,
Y is NH
4
+
or a singly to quadruply charged metal cation and
m is 1, 2, 3 or 4.
The starting compound for the process is 3,5,5-trimethylcyclohex-3-en-1-one (&bgr;-isophorone; &bgr;-IP). Conversion to 3,5,5-trimethyl-cyclohex-2-ene-1,4-dione (oxoisophorone; OIP) takes place in a solvent by oxidation with molecular oxygen in the presence of a base, the aforementioned catalyst of the formula I and acetate salts of the general formula II as additives.
The catalysts of the formula I are metal salen complexes or metal salen derivatives derived therefrom, which consist of a central metal atom and a tetradentate chelate ligand (salen ligand). The salen ligand can be prepared in a manner known per se from ethylenediamine and the appropriate salicylaldehydes which are optionally substituted by R
1
to R
8
.
M means the metals Mn, Co, Fe, Cu or Ru in oxidation state II or III. For equalization of charges, the metals in oxidation state III carry a negatively charged counter ion X
(−)
in the complex. Examples of negatively charged counter ions X
(−)
which may be mentioned are halides such as Cl
(−)
, Br
(−)
, I
(−)
, C
1
-C
5
alkanoates such as acetate, propionate or other anions such as N
3
(−)
, thiocyanate, cyanate, isothiocyanate, BF
4
(−)
, PF
6
(−)
, SO
4
2(−)
, PO
4
3(−)
or NO
3
(−)
. Preferred metals or metals with counter ion are Co(II), Mn(II), or Mn(III)Cl
(−)
.
The aromatic radical in the salen ligand may have no substituents (R
1
=R
2
=R
3
=R
4
=R
5
=R
6
=R
7
=R
8
=hydrogen) or be substituted by the radicals R
1
to R
8
independently of one another by halogen such as F, Cl, Br or I or NO
2
, COR
9
, OCOR
9
, COOR
9
, SO
2
R
9
or SO
3
R
9
. R
9
can be hydrogen or a C
1
-C
4
-alkyl radical such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl or t-butyl.
R
1
, R
3
, R
6
and R
8
in prefe

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