Preparation of substituted olefins

Details Preparation of substituted olefins Preparation of substituted olefins

2000-02-17

2003-01-14

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Oxygen containing

C568S478000, C568S480000, C560S004000, C560S012000, C564S037000, C558S435000

Reexamination Certificate

active

06506944

ABSTRACT:

The present invention relates to a process for preparing substituted olefins by self metathesis or cross metathesis.
Olefin metathesis (disproportionation) involves, in its simplest form, a reversible, metal-catalyzed transalkylidenation of olefins by rupture and reformation of carbon-carbon double bonds. In the case of the metathesis of acyclic olefins, a distinction is made, for example, between a self metathesis in which an olefin is transformed into a mixture of two olefins having different molar masses (for example, conversion of propene into ethene and 2-butene) and cross metathesis or co-metathesis which describes a reaction of two different olefins (for example, reaction of propene with 1-butene to give ethene and 2-pentene). Further application areas of olefin metathesis include syntheses of unsaturated polymers by ring-opening metathesis polymerization (ROMP) of cyclic olefins and acyclic diene metathesis polymerization (ADMET) of &agr;,&ohgr;-dienes. Relatively new applications are the selective ring opening of cyclic olefins with acyclic olefins and also ring closure reactions (RCM) by means of which, preferably starting from &agr;,&ohgr;-dienes, unsaturated rings of various ring sizes can be prepared.
Catalysts suitable for metathesis reactions are, in principle, homogeneous and heterogeneous transition metal compounds.
Heterogeneous catalysts, for example molybdenum, tungsten or rhenium oxides on inorganic oxidic supports, display high activity and regenerability in reactions of nonfunctionalized olefins, but must frequently be pretreated with an alkylating agent to increase the activity when functionalized olefins such as methyl oleate are used. Olefins containing protic functional groups (for example hydroxyl groups, carboxyl groups or amino groups) lead to spontaneous deactivation of the heterogeneous catalyst.
The present invention concerns a process for preparing bifunctionalized C
6
-hydrocarbons of the ECH
2
CH═CHCH
2
E type, for example adipic acid and derivatives thereof, with a metathesis reaction of an olefin of the RCH═CHCH
2
E type being carried out as key step for forming the C
6
unit.
C
6
-Hydrocarbons of this type are, after functionalization, industrially important precursors and intermediates: adipic acid serves, for example, as precursor for the production of nylon 6.6 (fiber sector) and has hitherto been prepared mostly by oxidative cleavage of cyclohexane. More recent developments involve formative reactions for adipic acid from butadiene, for example by the Monsanto process by carbonylation of the intermediate 1,4-dimethoxy-2-butene and in the BASF process by two-stage carbonylation of butadiene in the presence of methanol.
The two-stage carbonylation requires drastic reaction conditions and gives, starting from butadiene, only quite moderate yields of adipic acid, namely about 70% over the two stages.
The abovementioned metathesis reaction therefore appears to be a possible alternative route to the desired compounds.
The generally high activity of homogeneous metathesis catalysts in respect of olefins is drastically reduced when using electron-depleted olefins such as acrylic acid or their derivatives. In particular, self metathesis reactions of olefins of the RCH═CH(CH
2
)
n
E type to form RCH═CHR and E(CH
2
)
n
CH═CH(CH
2
)
n
E become problematical in the presence of the known metathesis catalysts when E is an electron-withdrawing substituent, n is zero or 1 and R═H, alkyl or aryl. Use of substituted olefins such as methyl 3-pentenoate, 3-pentenoic acid or 3-pentenonitrile in self metathesis reactions is consequently accorded little mention in the literature because of unsatisfactorily low activity.
J. Chem. Soc., Chem. Commun. 1983, 262-263, J. Chem. Soc., Chem. Commun. 1981, 1081-1082 and J. Organomet. Chem. 1985, 280, 115-122, describe the self metathesis of unsaturated nitrites of the CH
2
═CH(CH
2
)
n
CN type in the presence of heterogeneous Re
2
O
7
/Al
2
O
3
catalysts which have been activated with SnMe
4
or SnEt
4
. While 4-pentenonitrile is reacted in a yield of up to about 90%, allyl cyanide does not undergo any productive metathesis reactions with the exception of isomerization to form crotononitrile.
Recl. Trav. Chim. Pays-Bas 1977, 96(11), 86-90, describes metathesis reactions of low molecular weight unsaturated esters using the homogeneous catalyst system WCl
6
/SnMe
4
. Although methyl 3-pentenoate is reacted with a selectivity of 95% to form 2-butene and the dehydroadipic ester in the presence of 2 mol % of WCl
6
/SnMe
4
, a disadvantage is the high sensitivity of the catalyst system toward impurities in the feed. Metathesis reactions using unsaturated acids are not possible when the catalyst system mentioned is employed.
J. Mol. Catal. 1992, 76, 181-187, is concerned with the metathesis of functionalized olefins using the catalyst system WCl
6
(or WOCl
4
) /1,1,3,3-tetramethyl-1,3-disilacyclobutane (DSBC). In the best experiment using WOCl
4
/DSBC, methyl 4-pentenoate is converted with a selectivity of 94% at conversions of 54% into the corresponding C
8
-diester. In the presence of the same catalyst system, allyl cyanide is converted with a selectivity of 82% at a conversion of 53% into dehydroadipodinitrile with elimination of ethene.
Chem. Lett. 1976, 1021-1024, describes the self metathesis of methyl 4-pentenoate in a conversion of 60% when using WCl
6
/Me
2
Al
2
Cl
2
.
It is an object of the present invention to develop an economically attractive synthetic route to bifunctionalized C
6
-hydrocarbons from readily accessible starting materials under moderate reaction conditions using a suitable, generally usable catalyst system.
We have found that this object is achieved by a process for preparing C
6
compounds of the formula (I)
E—CH
2
—CH═CH—CH
2
—E
1
  (I)
by self metathesis or cross metathesis of compounds of the formulae (II) and/or (III)
R—CH═CH—CH
2
—E  (II)
R
1
—CH═CH—CH
2
—E
1
  (III)
where
E, E
1
are independently —CHO, —COOH, —COOR
2
, —C(O)NR
3
R
4
, —CN,
R, R
1
are independently H, C
1-12
-alkyl, C
6-12
-aryl or C
7-13
-alkylaryl and
R
2
, R
3
, R
4
are independently H, C
1-12
-alkyl, C
7-13
-aralkyl,
in the presence of a homogeneous catalyst comprising ruthenium compounds or ruthenium complexes.
Accordingly, the object is achieved according to the present invention by a process sequence in which the key step for forming a C
6
-hydrocarbon of the ECH
2
CH═CHCH
2
E type is a self metathesis reaction of an olefin of the RCH═CHCH
2
E type according to the following equation:
As coproduct, RCH═CHR is formed in stoichiometric amounts and can, if desired, be processed further by subsequent reactions. For example, &agr;-olefins of the CH
2
═CHR type can be obtained by ethenolysis of RCH—CHR.
In the above equation, E is an aldehyde, ester, acid, acid amide or nitrile function. R is hydrogen or an alkyl, aryl or alkylaryl radical. Preferred alkyl radicals R are linear C
1-6
-alkyl radicals, e.g. methyl or ethyl, or branched C
1-6
-alkyl radicals in which the branching point is at least one methylene group away from the double bond.
It is also possible to react substrates having different radicals R, R
1
and E, E
1
with one another in a cross metathesis reaction. In this case, mixed reaction products have to be expected.
Preferably, E═E′ and R═R′. E and E′ are particularly preferably ester or carboxyl groups. R and R′ are preferably methyl or ethyl groups.
The process of the present invention is carried out in the presence of a homogeneous catalyst comprising ruthenium compounds or ruthenium complexes. Preference is given to using ruthenium-alkylidene complexes as catalyst. The ruthenium-alkylidene complexes are preferably selected from among
where
B can be stabilized by a further ligand L
4
and
X is an anion which does not coordinate or coordinates only weakly to the metal center,
Y is a monodentate or polydentate anionic ligand,
R and R′ are each, independently

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