Patent Application
20080045737
The invention thus provides a process for the continuous preparation of silanes of the general formula (I)
R6R5CH—R4CH—SiR1R2R3 (I),
in which a silane of the general formula (II)
HSiR1R2R3 (II),
is reacted with an alkene of the general formula (III)
R6R5CH═CHR4 (III),
where
The continuous process gives the silane of the general formula (I) in high yields and excellent purity. Contrary to the prior art, for example as disclosed in: REACTIVE DISTILLATION, STATUS AND FUTURE DIRECTIONS, Kai Sundmacher and Achim Kienle, Wiley-VHC, 2002, ISBN 3527305793, page 187, section 7.5, the process of the invention displays significant advantages over heterogeneous catalysis, in which it is hardly possible to meet the contradictory demands on catalyst residence time, pressure drops and good vapor-liquid contact. In the process of the invention, it is possible, as a result of the use of homogeneous catalysis, to vary both the amount and point of addition of the catalyst. The process is therefore significantly easier to control and monitor and can be carried out significantly more reliably. The yields can also be increased significantly by recirculation of the alkene of the general formula (III). Industrial apparatuses for carrying out the process include any distillation columns suitable for a continuous reaction.
C1-C18-Hydrocarbon radicals R1, R2, R3 are preferably alkyl, alkenyl, cycloalkyl or aryl radicals. R1, R2, R3 preferably have not more than 10, in particular not more than 6, carbon atoms. R1, R2, R3 are preferably straight-chain or branched C1-C6-alkyl radicals or C1-C6-alkoxy radicals. Preferred halogen substituents are fluorine and chlorine. Particularly preferred radicals R1, R2, R3 are the radicals methyl, ethyl, methoxy, ethoxy, chlorine, phenyl and vinyl.
R4, R5, R6 are each a hydrogen atom, a monovalent unsubstituted or F—, Cl—, OR—, NR2—, CN— or NCO-substituted C1-C18-hydrocarbon radical, chlorine radical, fluorine radical or C1-C18-alkoxy radical, where 2 radicals from among R4, R5, or R6, together with the carbon atoms to which they are bound, may form a cyclic radical. R5 and R6 preferably have not more than 10, in particular not more than 6 carbon atoms. R5 and R6 preferably have not more than 10, in particular not more than 6 carbon atoms. R5 and R6 are preferably straight-chain or branched C1-C6-alkyl radicals or C1-C6-alkoxy radicals. Particularly preferred radicals R5 and R6 are the radicals hydrogen, methyl, ethyl, chloromethyl, chlorine and phenyl.
Hydrocarbon radical R4 preferably has not more than 6, in particular not more than 2 carbon atoms. Particularly preferred radicals R4 are the radicals hydrogen, methyl, ethyl. Hydrocarbon radical R also preferably has not more than 6, in particular not more than 2 carbon atoms.
As alkene(s) of the general formula (III), preference is given to using allyl chloride.
The alkene of the general formula (III) can be used either in a superstoichiometric amount or in a substoichiometric amount relative to the silane component (II). The molar ratio of the alkene (III) to silane (II) is preferably in the range from 0.1 to 20, more preferably from 0.8 to 1.5.
The process of the invention can be carried out using any homogeneous catalyst useful for the addition of Si-bonded hydrogen onto aliphatically unsaturated compounds. Examples of such catalysts are compounds or complexes of the group of noble metals consisting of platinum, ruthenium, iridium, rhodium and palladium, for example platinum halides, platinum-olefin complexes, platinum-alcohol complexes, platinum-alkoxide complexes, platinum-ether complexes, platinum-aldehyde complexes, platinum-ketone complexes, including reaction products of H2PtCl6.6H2O and cyclohexanone, platinum-vinylsiloxane complexes, in particular platinum-divinyltetramethyldisiloxane complexes with or without a content of detectable inorganically bound halogen, bis(γ-picoline)platinum dichloride, trimethylenedipyridineplatinum dichloride, dicyclopentadieneplatinum dichloride, (dimethyl sulfoxide)ethyleneplatinum(II) dichloride and reaction products of platinum tetrachloride with olefin and a primary amine or secondary amine or both primary and secondary amine, for example the reaction product of platinum tetrachloride dissolved in 1-octene with sec-butylamine. In a further preferred embodiment of the process of the invention, complexes of iridium with cyclooctadienes, for example μ-dichlorobis(cyclooctadiene)diiridium(I), may be used.
The catalyst preferably comprises compounds or complexes of platinum or iridium, more preferably platinum, yet more preferably platinum chlorides and platinum complexes, in particular platinum-olefin complexes, and with particular preference, platinum-divinyltetramethyldisiloxane complexes. In a further embodiment, cocatalysts can aid the reaction.
In the process of the invention, the catalyst is used in amounts of from 1 to 1000 ppm by weight, calculated as elemental noble metal and based on the total weight of the components (II) and (III) present in reaction mixtures. Preference is given to using from 2 to 150 ppm by weight, more preferably from 5 to 50 ppm by weight.
In the process of the invention the amount of active catalyst is kept at the desired level by continuous addition of fresh catalyst and simultaneous removal of exhausted catalyst. This prevents a decrease in activity in the reaction and thus downtime of the plant for replacement of catalyst.
The critical advantage of the process of the invention is the continuous introduction of the catalyst into the reactive distillation column. In the process of the invention, a broadened influence on reaction and operating conditions can be exerted by means of the additional regulating parameter of catalyst addition. The process can be controlled better by means of the type, point of addition and amount of catalyst. This leads, for example, to separation effectiveness of the column, avoidance of hotspots (secondary reactions, thermal catalyst decomposition), fluctuations in catalyst activity between different batches are avoided, and the reaction can be stopped quickly by switching off the addition of catalyst (emergency shutdown). Furthermore, the process of the invention allows a simplified start up of the reactive distillation since the catalyst is added only after the necessary column profile has been reached. Product changes are also simplified in a column since flushing of the plant is sufficient for the change of catalyst and disassembly of the plant is no longer necessary. By “continuous” is also meant a discontinuous but oft-repeated addition which simulates continuous addition.
The process can be carried out in the presence or absence of aprotic solvents. If aprotic solvents are used, solvents or solvent mixtures having a boiling point or boiling range up to 120° C. at 0.1 MPa are preferred. Examples of such solvents are ethers such as dioxane, tetrahydrofuran, diethyl ether, diisopropyl ether, diethylene glycol dimethyl ether; chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, 1,2-dichloroethane, trichloroethylene; hydrocarbons such as pentane, n-hexane, hexane isomer mixtures, heptane, octane, naphtha, petroleum ether, benzene, toluene, xylenes; ketones such as acetone, methyl ethyl ketone, diisopropyl ketone, methyl isobutyl ketone (MIBK); esters such as ethyl acetate, butyl acetate, propyl propionate, ethyl butyrate, ethyl isobutyrate; carbon disulfide and nitrobenzene, or mixtures of these solvents. The target product of the general formula (I) can also be used as aprotic solvent in the process. This process variant is preferred.
The noble metal catalysts are preferably dissolved in solvents, most preferably in ionic liquids. This makes it possible for part or even all of the catalyst to be added in feed streams. When ionic liquids are used, the particularly preferred solvent is an ionic liquid of the general formula (IV).
In a preferred embodiment of the process of the present invention, the ionic liquid used is an ionic liquid of the general formula (IV)
[A]+[Y]− (IV)
where
[NR7R8R9R10]+ (V),
phosphonium cations of the general formula (VI)
[PR7R8R9R10]+ (VI),
imidazolium cations of the general formula (VII)
pyridinium cations of the general formula (VIII)
pyrazolium cations of the general formula (IX)
picolinium cations of the general formula (XI)
and
pyrrolidinium cations of the general formula (XII)
where the radicals R7-12 are, independently of one another, organic radicals having 1-20 carbon atoms, more preferably aliphatic, cycloaliphatic, aromatic, araliphatic or oligoether groups. Suitable aliphatic groups are straight-chain or branched hydrocarbon radicals which have from one to twenty carbon atoms and in which heteroatoms such as oxygen, nitrogen or sulfur atoms can be present in the chain. The radicals R7-12 can be saturated or have one or more double or triple bonds which can be conjugated or be present in isolated positions in the chain.
Examples of aliphatic groups are hydrocarbon groups having from one to 14 carbon atoms, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl or n-decyl.
Examples of cycloaliphatic groups are cyclic hydrocarbon radicals which have from three to twenty carbon atoms and may contain ring heteroatoms, for example oxygen, nitrogen or sulfur atoms. The cycloaliphatic groups can also be saturated or have one or more double or triple bonds which can be conjugated or be present in isolated positions in the ring. Saturated cycloaliphatic groups, in particular saturated aliphatic hydrocarbons, which have from five to eight ring carbons, preferably five or six ring carbons, are preferred.
Aromatic groups, carbocyclic aromatic groups or heterocyclic aromatic groups can have from six to twenty-two carbon atoms. Examples of suitable aromatic groups are phenyl, naphthyl and anthryl.
Oligoether groups are groups of the general formula (XIII)
—[(CH2)x—O]y—R′″ (XIII),
where
x and y are, independently of one another, from 1 to 250 and R′″ is an aliphatic, cycloaliphatic, aromatic or araliphatic group.
The process of the invention in a reaction distillation column is shown schematically in the drawing of
Here, the numbers in
The alkene 13 of the formula (III) and silane 14 of the formula (II) are used as starting materials. To start up the reactive distillation, alkene 13 and product 6 are placed in the column in the first step and the column profile is established with total reflux and without a bottom stream being taken off. In the 2nd step, the catalyst solution 12, the alkene 13 and the silane 14 are metered in. The amount of silane 14 is then slowly increased. The target product 6 and the by-products are formed and are taken off together as high boilers at the bottom. Process control is effected, for example if the catalyst activity becomes too low, by increased addition of catalyst solution 12. In the case of malfunctions, the introduction of catalyst can be stopped immediately and the reaction stopped as a result. An excess of alkene 13 led to an improvement in the selectivity to the target product. The removal of the catalyst can be effected according to two variants. In variant 7, the removal is effected directly at the bottom of the column when the catalyst solution forms a second phase, for example when ionic liquids are used. In variant 8, the removal is effected in a downstream apparatus, for example in a thin film evaporator or a phase separator. The catalyst solution which has been separated off can, if the catalyst activity is sufficient, be recirculated to the reaction column or is passed to another work-up 15. The reuse of catalyst is a further advantage of the process of the invention.
In a particularly preferred process, the noble metal catalyst or its solution is separated off from the silane mixture in an apparatus located downstream of the reactive distillation column or in the column, for example by means of a phase separator, and recirculated to the reactive distillation column or separated off for renewed work-up and preparation of fresh catalyst.
The process is preferably carried out at a reaction temperature of 0-200° C., more preferably from 20 to 120° C., and preferably at a reaction pressure of 0.5-150 bar, more preferably 1-20 bar.
In the following, the abbreviations have the following meanings:
This example was carried out in a manner analogous to example 1. The difference lies in the immobilization of the Pt catalyst in the ionic liquid [EMIM][BTA]. As CAT-SOL, 500 ppm by weight of Pt based on the total feed as PtCl4 were dissolved in the ionic liquid. The ionic liquid forms a second liquid phase at the bottom of the column or in a downstream apparatus. This makes it possible to recirculate the catalyst to the reactive distillation, which represents a significant advantage of this method.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 039 191.8 | Aug 2006 | DE | national |
