Hydroformylation
The hydroformylation (also: oxo, rare Roelen synthesis or Roelen reaction ) is an industrially important homogeneously catalyzed reaction of olefins with synthesis gas for the production of aliphatic aldehydes and is considered one of the most important developments in industrial chemistry of the 20th century. As hydroformylation catalysts, the chemical industry uses organometallic cobalt or rhodium. The process is carried out at pressures of about 10 bar to 100 bar and temperatures between 40 and 200 ° C.
The initially formed aldehydes are usually hydrogenated to alcohols that are used as plasticizers for PVC, Tensidrohstoff for washing and cleaning agent and as solvent or be further processed into polymers. The total capacity of Hydroformylierungsanlagen was approximately 10.8 million tonnes per year in 2002.
The use of new, more active catalytic systems with ligands that control the regio-and stereoselectivity, the hydroformylation was an important tool in organic synthesis of fine chemicals.
- 7.1 reactions of olefins
- 7.2 Reactions of the aldehydes
- 7.3 Reactions of the catalyst complex
History
In the work of Ruhr Chemie in Oberhausen Otto Roelen discovered the hydroformylation in 1938 by accident while trying the (FT ) process occurring due ethene in the process in the Fischer- Tropsch synthesis. In experiments in which ethene and ammonia was fed to the FT process, Roelen found deposits of Propionaldimin, a condensation product of ammonia and propionaldehyde. In contrast to other researchers, he interpreted the formation of propionaldehyde as an independent reaction, which he attributed to the addition of ethene and not looking at her as a side reaction of the Fischer- Tropsch synthesis.
After initial attempts to optimize the reaction towards the formation of aldehyde, which he began in July 1938, Roelen enough already one end of the same year a patent for the oxo synthesis. The name " oxo " is based on the false assumption that it was a general synthesis for the preparation of aldehydes and ketones, as in the hydroformylation of ethene was incurred the by-product of diethyl ketone in large quantities.
The Ruhr Chemie, Otto Roelens employers who chose as the solvent for the hydroformylation of toluene, since it was easily separated from the products formed. At a reaction temperature of 115 ° C, the process achieved a yield of 70 to 80% propionaldehyde, 15 % organic by-products and 5 % loss at full conversion of ethene.
Catalyst and a catalyst used Roelen cobalt, thorium and magnesium oxide -containing, which was normally used for the Fischer- Tropsch synthesis. He found, however, that many other salts of cobalt were suitable as a catalyst precursor and suspected Cobaltcarbonylhydrid was the active catalyst species.
IG Farben used a process model with a fixed on pumice catalyst in an aqueous system. The feedstocks used IG Farben an equimolar mixture of ethene, carbon monoxide and hydrogen at reaction temperatures of 150 to 200 ° C and a reaction pressure of 15 to 30 MPa. In this process variant, about 20 to 25 % of ethene was hydrogenated to ethane, the selectivity to propionaldehyde was only 65%. The loss of catalyst was offset by the addition of cobalt salts of fatty acids.
Roelen worked early at the hydroformylation of Fischer-Tropsch olefins having a chain length of 11 to 17 carbon atoms for the production of fatty alcohols. In 1940, the Ruhr Chemie began construction of a plant whose capacity should be 7000 years tons of fatty alcohols. The Ruhr Chemie took over the plant in the war no longer in operation.
Developed alongside the original method of Ruhr chemical companies such as Union Carbide, BASF and Shell process variants that operate at pressures of about 5 MPa and temperatures of about 100 ° C. The processes are based on cobalt and rhodium complexes phosphanmodifizierten. Lauri Vaska reported in 1963 on the representation of the complex Rhodiumtetracarbonylhydrid. This complex and its Triphenylphosphananaloga sat Geoffrey Wilkinson in 1968 for the hydroformylation one. Phospanmodifizierte Rhodiumcarbonylhydride are considered second generation of hydroformylation catalysts. They were used from 1976 by Union Carbide industrial scale, allowing a reduction of the operating pressures compared to the original oxo. Shell used a tributylphosphanmodifiziertes Cobaltcarbonylhydrid for the hydroformylation of long-chain olefins, which were further hydrogenated directly to the alcohol.
Problems with the deactivation of the catalyst and its discharge improved in the 1980s by the introduction of water-soluble catalysts crucial in the Ruhr Chemie / Rhône -Poulenc process. Based on the model developed by Wilkinson Rhodiumtristriphenylphospahncarbonylhydrid and the work of Kuntz Rhône Poulenc developed the Ruhr Chemie within 24 months and with a scale-up factor of 1: 24000 the technical process. The water-soluble rhodium catalysts are considered third generation of the hydroformylation catalysts.
Since the mid- 1990s, an attempt is made to optimize through use of solvents such as supercritical carbon dioxide, perfluorocarbons systems or ionic liquids, the reaction continues. Furthermore, were tested in addition to the Ruhr Chemie / Rhône -Poulenc process other ways and methods of heterogeneity. It usually does not solve the problem of Katalysatoraustrags.
On August 24, 2013, the 75th anniversary of the patent filing, the Ruhrchemie was taken by the German Chemical Society in the Historic Sites of the chemistry program.
Basics
Many olefins (alkenes and cycloalkenes ) are the hydroformylation accessible. It is formally an addition of hydrogen and a formyl group to the double bond of an olefin, the combination olefin / catalyst plays an important role in the achievable yields and selectivities. Short-chain olefins tend to react more quickly than longer-chain olefins and cyclo-olefins, linear olefins react faster than branched. Almost all the olefins can be hydroformylate, wherein the reaction of tetrasubstituted olefins with alkyl groups, which would lead to a quaternary carbon atom, rarely succeed. Styrene can hardly hydroformylate by cobalt catalysts with rhodium catalysts, however, high conversions are achieved. Conjugated dienes can hydroformylate to dialdehyde with rhodium -phosphine catalysts, cobalt catalysts deliver by hydrogenation of a double bond predominantly monoaldehydes. Non-conjugated dienes can be hydroformylate to dialdehydes when the double bonds are separated in the chain by at least two carbon- carbon single bonds. Allyl alcohol, allyl esters and allyl ethers preferably hydroformylate with isomerisierungsfreien catalysts. α, β -unsaturated keto compounds often react under hydrogenation of the double bond. Unsaturated carboxylic acids and carboxylic acid esters can be hydroformylate well as unsaturated aldehydes and ketones with non-conjugated double bonds.
The primary products of the hydroformylation are aldehydes, which are further processed by aldol condensation, hydrogenation, oxidation, amination and other methods to a wide variety of secondary products. About 70 % of the total industrial production attributable to the production of n -butanal, about 20 % in the production of C5- C13 aldehydes, the rest is accounted for by higher molecular weight aldehydes and propanal.
The hydroformylation Metallcarbonylhydride and their derivatives. You can by the general formula
Are described. The catalysts used have a clearly defined structure and can accurately characterize and synthesize consistent quality or generate in situ. The catalytic process all the metal atoms are available as active centers for the synthesis of the product. The chemical industry uses cobalt and rhodium complexes with various carbon monoxide, phosphine and phosphite ligands. A complex with iron group metals such as iridium, iron, ruthenium, and osmium, as well as poly- systems, such as platinum / tin were tested, but did not exhibit the same activity as Rhodium and cobalt catalysts. Rhodium complexes are the most active hydroformylation catalysts and about 1000 times more active than cobalt complexes. The hydroformylation activity of the organometallic complex catalyst is lowered from the cobalt complex to the iridium, ruthenium, osmium, manganese and iron complexes each approximately by a factor of 10
The ligand design has a big impact on the n-/iso-Verhältnis of the resulting products, mainly by steric effects. Further, the ratio of metal to ligand has an effect on the n-/iso-Selektivität and the side reactions. Small additions of tertiary amines can accelerate the reaction; higher concentrations, however, can lead to the complete suppression of the reaction. The use of rhodium as the catalyst metal, the catalytically active species is a trigonal bipyramidal Rhodiumcarbonylhydrido complex which is present in two isomeric forms. The two phosphine ligands occupy either an equatorial- equatorial (ee ) or the equatorial- apical ( ea) position. The use of bidentate diphosphine good selectivities were found for the linear aldehyde. The influence of the so-called bite angle of the diphosphine ligands was studied in detail.
In addition to the steric effects of the electronic effects of the ligand affect the catalyst activity. Good π - acceptors such as phosphites decrease in rhodium by a strong back-bonding electron density on the metal and weaken accordingly, the rhodium - carbon monoxide - binding. Insertierung of carbon monoxide which in the metal-alkyl compound is facilitated. Organometallic Rhodiumphosphitkomplexe are very good hydroformylation catalysts.
An important criterion is the hydroformylation regioselectivity for n- or iso- product. Thus, the n- isomer of Propenhydroformylierung is processed on an industrial scale to 2 -ethylhexanol, whereas the iso- isomer is of only secondary importance for the representation of isobutanol, neopentyl glycol or iso- butyric acid. The step of insertion of the olefin into the metal - hydrogen bond to give the alkyl complex helps decide the selectivity of the formation of n- or iso- aldehydes:
With higher molecular weight olefins can result in isomerization of the double bond, which are formed from mixtures of aldehydes. In the metal-carbon bond of the alkyl complex a Kohlenstoffmonoxidligand inserted to form a acyl complex.
Keulemans set 1948 rules for product distribution ( Keulemans rules) Accordingly, from straight-chain olefins always a mixture of n- and 2- alkyl alcohols in a ratio of 40-60 % and 60-40 % 2 - n - alkyl alcohols. An addition of the formyl group to tertiary carbon atoms does not take place; iso -butene, for example, is only the 3- methyl butanol. The addition of carbon atoms in α -position to the tertiary carbon atoms is sterically hindered, but can take place. For attachment to the carbon atoms in α -position to the quaternary carbon atoms, it does not. An isolated tertiary carbon atom impedes the formation of the possible isomers. The hydroformylation is always accompanied by a double bond. In addition to the 2- alkyl branch, there is no tendency to increase the degree of branching. Preferably a linear product is obtained by shifting the double bond.
Kinetic studies provided for the cobalt-catalyzed reaction, the following rate equation:
The reaction is exothermic to about 125 kJ mol -1. For rhodium-catalyzed hydroformylation turnover numbers are achieved by about 6000 molOlefin molKatalysator - 1 h-1.
Reaction mechanism
The catalytic mechanism of the cobalt-catalyzed hydroformylation was investigated in 1960 and informed by the later Nobel prize winner Richard F. Heck and David Breslow. In the rear - Breslow mechanism from a Kohlenstoffmonoxidligand Cobaltcarbonylhydrid is first to form a 16- electron species eliminated (1). This creates a vacant coordination site to which an olefin can be deposited to form a 18- electron species by means of π - bond ( 2). The next step is the formation of a 16-electron alkyl complex ( 3), is taken a Kohlenstoffmonoxidligand in the vacant coordination site (4). These inserted into the metal -carbon bond of the alkyl group to form a 16- acyl complex electron (5). By oxidative addition of hydrogen ( 6) of the aldehyde is released, and the active species is recovered (7). To form the initial complex closes the catalytic cycle. As a side reaction of the 16 - electron complex, in an equilibrium reaction, one molecule of carbon monoxide record (8).
Rhodiumhydridocarbonyle and their phosphanmodifizierte analogues react by a similar mechanism was investigated in 1968 by Geoffrey Wilkinson. In the first step, therefore, dissociates a phosphine ligand from the complex and forms a planar, coordinatively unsaturated 16- electron species. At these coordinates an olefin to form a 18- Elektroenen complex. After insertion of the olefin in the hydrogen - bond with rhodium Alkylkomplexbildung and after addition of a further molecule of carbon monoxide that inserted into the rhodium - alkyl linkage to form the acyl complex. Both of the cobalt as well as the rhodium-catalyzed hydroformylation of the subsequent oxidative addition of hydrogen is considered to be the rate-determining step, and subsequent reductive elimination of the aldehyde. In addition of carbon monoxide closes the catalytic cycle and the starting complex is restored.
The formation of the square-planar intermediate with two bulky phosphine ligands is considered as an explanation for the high n-/iso-Verhältnis the rhodium-catalyzed hydroformylation. The steric constraints in the transient state cause the alkyl ligand is preferably linear coordinates. This explains why the n-/iso-Verhältnis is positively influenced by increasing phosphane and declining carbon monoxide partial pressure.
The mechanism was analyzed by infrared spectroscopic and high pressure NMR methods. The use of deuterium in the reaction ( Deuteroformylierung ) allows the examination of the resulting products by 1 H NMR spectroscopy, and thus conclusions about the mechanism.
Technical Procedures
The technical procedures differ in the chain length of the olefin to be hydroformylated in the manner of the catalyst metal and the separation of the catalyst. The original procedure of the Ruhr Chemie sat ethene by means of Cobaltcarbonylhydrid to propanal. Today processes are used with cobalt-based catalysts mainly for the production of medium-to long-chain olefins, as based catalysts are usually used for the hydroformylation of propene to rhodium. The rhodium catalysts are significantly more expensive than cobalt catalysts. In the hydroformylation of higher molecular weight olefins lossless separation from the catalyst is difficult. The methods differ primarily in the type of catalyst separation and recovery of the catalyst.
BASF process
In the hydroformylation of BASF (BASF - oxo ) higher olefins are usually used. As a catalyst Cobaltcarbonylhydrid serves. The catalyst is oxidized by the liquid product phase with oxygen from the formally negatively charged co- 1 to the water-soluble CO2 and separated by addition of aqueous formic acid or acetic acid. Thus, an aqueous phase is formed, which contains the catalyst metal in the form of its salt. The aqueous phase is removed and the cobalt reduced in the process. Capital losses are compensated by addition of fresh cobalt salts. A reaction at a low temperature results in an increased selectivity to the linear product. The process is carried out at a pressure of about 30 MPa and in a temperature range of 150 to 170 ° C.
Exxon process
The Exxon process or Kuhlmann or PCUK - oxo process, is used for the hydroformylation of C6 to C12 olefins. For catalyst recovery and the organic product phase is treated with aqueous sodium hydroxide or sodium carbonate solution. By extraction with olefin and neutralization by addition of sulfuric acid solution under the Kohlenstoffmonoxiddruck Metallcarbonylhydrid is recovered. This is stripped off with synthesis gas, taken from the olefin and recycled to the reactor. The method is set at a pressure of about 30 MPa and at a temperature of about 160 to 180 ° C in the passage.
Shell process
The Shell process uses cobalt complexes of phosphine ligand for the hydroformylation of C7 to C14 -olefins. The resulting aldehydes are further hydrogenated directly to the fatty alcohol. These are distilled off overhead from the catalyst and the catalyst is obtained as the bottom product and be recycled into the process. The method has a good selectivity to linear products, which are used as surfactant raw materials use. It is carried out at a pressure of about 4-8 MPa and in a temperature range of about 150 to 190 ° C.
UCC process
The UCC method, also known as low pressure oxo process refers to (LPO ) dissolved in high boiling uses a thick oil rhodium catalyst for the hydroformylation of propene. The reaction mixture is separated into a falling film evaporator of volatiles. The liquid phase is distilled n-butanal and isolated via the top of the catalyst phase entstamme thick- oil. In this method a pressure of about 1.8 MPa in a temperature range of about 95-100 ° C is used.
Ruhr Chemie / Rhône -Poulenc process
In the Ruhr Chemie / Rhône -Poulenc process with a Triphenylphosphantrisulfonat ( TPPTS) is complexed rhodium complex used ( Kuntz Cornils catalyst) as a catalyst. By the substitution of the triphenylphosphine ligands with sulfonate groups of the organometallic complex has hydrophilic properties. The catalyst is carried nine times the sulfonation very well soluble in water ( about 1 kg of l-1 ), but not resulting in the product phase. The water-soluble Triarylphosphansulfonat is used in about 50 -fold excess, so that the washing out of the catalyst, the so-called " leaching " is effectively suppressed. The reactants used propene as well as synthesis gas consisting of hydrogen and carbon monoxide in a ratio of 1.1:1, used. Can be obtained from different sources of raw material independent of petroleum. As a product of a mixture of n -and iso -butanal is formed in the ratio 96:4. The selectivity to n- aldehyde is high, by-products, such as alcohols, esters and higher boiling fractions are hardly formed.
The Ruhr Chemie / Rhône -Poulenc process is the first commercially available two-phase system in which the catalyst is present in the aqueous phase. The progress of the reaction is an organic product phase is formed which is separated continuously by means of phase separation, the aqueous phase catalyst remains in the reactor.
In this method, the olefin and synthesis gas can be introduced from below into the reactor and mixed thoroughly, the phases of the reaction mixture intensively in a stirred tank reactor. The resulting crude aldehyde is removed at the top. In the phase separator, the organic phase is separated from the aqueous. The aqueous catalyst-containing solution is preheated via a heat exchanger and then pumped into the reactor. In a stripper, the excess olefin is separated by the synthesis gas in the absence of a catalyst from the organic phase and returned to the reactor. The released heat of reaction is used via heat exchangers for process steam generation.
The process steam generated is used for the subsequent distillation of the organic phase to separate into iso-and n-butanal. The distillation residue is heated on a falling film evaporator and is fed to the distillation again. Potential catalyst poisons that are introduced via the synthesis gas in the reaction are removed with the aldehyde. Wherein there is no enhancement of catalyst poisons, the complicated fine purification of the synthesis gas can thus be dispensed with.
In Oberhausen, a plant was built in 1984, which was released in 1988 and again in 1998 with a production capacity of 500,000 t / year butanal expanded. Here, 98 % of propene are implemented and achieves a high selectivity. During the process, less than 1 ppb rhodium is lost.
Hydroformylation of functionalized olefins
In addition to pure olefins functionalized olefins such as allyl alcohol can be hydroformylated. The target product is obtained with isomerisierungsfreien catalysts such as rhodium - triphenylphosphine complexes of 1,4-butanediol and its isomer. The use of the cobalt complex is obtained by isomerization of the double bond n- propanal. The hydroformylation of alkenyl and alkenyl esters is usually in the α -position to the ether or ester function. The hydrdoformylierte esters can lead by subsequent cleavage of the carboxylic acid from the hydroformylation product to α, β -unsaturated aldehydes.
The hydroformylation of acrylic acid and methacrylic acid, Jürgen Falbe. After that forms when the rhodium -catalyzed variant in the first step, the Markovnikov product. The choice of the reaction conditions, the reaction can be steered in different directions. A high reaction temperature and low Kohlenstoffmonoxiddrücke favor the isomerization of the Markovnikov product to the thermodynamically more stable β - isomer, which leads to the n- aldehyde. Low temperatures, high Kohlenstoffmonoxiddrücke and an excess of phosphines that can occupy free coordination sites, leading to faster hydroformylation in the α -position to the ester group and suppress the isomerization.
The hydroformylation of conjugated olefins leads with many catalyst systems by hydrogenation of a double bond to the same products as the corresponding mono-olefins. Rhodium -phosphine complex hydroformylation leads to dialdehydes. The hydroformylation of alkynes resulting α, β -unsaturated olefins.
Organic syntheses
Only the product of Markovnikov addition leads to the target product, while the n- aldehyde is achiral. The stereochemistry is determined in step of olefin.
The hydroformylation can be modified to the so-called Silylformylierung by the replacement of hydrogen by Monohydrosilanen (H -Si - R3). Here, a Trialkylsilylguppe and a formyl group is added to the triple bond of an alkyne and form a 3 -silyl -2- alkenal.
The tandem reaction of hydroformylation using, for example, Knoevenagel reactions, Wittig olefination or Allylborierungen allows the construction of complex molecules, which can be carried out in part, for example in combination with a reductive amination as hydroaminomethylation, in a one-pot reaction.
Secondary and subsequent reactions
Reactions of olefins
Secondary reactions of the olefins are the isomerization and hydrogenation of the olefinic double bond. While the products resulting from hydrogenation of the double bond alkanes not participate in the reaction, the isomerization of the double bond with subsequent formation of the N - Alkyl is a desired process. The hydrogenation is usually of minor importance. However Cobaltphosphanmodifizierte catalysts may have an increased hydrogenation activity, whereby are hydrogenated up to 15% of the olefin.
Reactions of aldehydes
A most desirable side reaction is the hydrogenation of aldehydes to alcohols. Higher temperatures and hydrogen partial pressures favor the hydrogenation of the resulting aldehydes to alcohol. The kinetics of formation of alcohol with cobalt complexes can be described by the following equation:
The reaction mechanism, it is assumed that the first π - complex of the aldehyde together with the catalyst. Under rearrangement to give the alkoxide and subsequent oxidative addition of hydrogen to the alcohol and the starting complex are formed:
The aldehydic carbon-oxygen double bond may also be subject to the hydroformylation and lead to formic acid and its esters. In this case, carbon monoxide is inserted into the oxygen -metal bond. The resulting Formylkomplex can oxidative addition of hydrogen release the formic acid ester:
The aldehydes initially formed can also react further and by aldol condensation products such as the target product precursor 2 - ethylhexanol or higher molecular weight condensation products, so-called thick oil form.
Reactions of the catalyst complex
The triphenylphosphine used can release by hydrogenation of benzene under reaction conditions. The insertion of carbon monoxide in an intermediate metal-carbon bond may lead to the formation of benzaldehyde or by hydrogenation subsequent to benzyl alcohol. The ligand can attach propene, with the resulting Diphenylpropylphosphin can inhibit due to its increased basicity of the reaction.
Trace impurities of the starting materials with oxygen or sulfur and their compounds can contribute to the oxidation of phosphorus (III ) - to phosphorus (V ) compounds or lead to catalytically inactive metal oxides and sulfides.