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Hydroformylation, also known as oxo synthesis, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group (CHO) group and a hydrogen atom to a carbon-carbon double bond. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 This process has witnessed continuous growth since its invention in the 1930’s: production capacity reached 6. 6×106 tons in 1995. It is important because the resulting aldehydes are easily converted into many secondary products. For example, the resulting aldehydes are hydrogenated to alcohols which are converted to detergents. In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon A detergent (as a noun is a material intended to assist Cleaning. Hydroformylation is also used in specialty chemicals, relevant to the organic synthesis of fragrances and natural products. Organic synthesis is a special branch of Chemical synthesis and is concerned with the construction of Organic compounds via Organic reactions Organic Perfume is a mixture of fragrant Essential oils and Aroma compounds Fixatives and Solvents used to give the human body animals objects and living The development of hydroformylation, which originated within the German coal-based industry, is considered one of the premier achievements of 20th century industrial chemistry. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties

The process typically is accomplished by treatment of an alkene with high pressures (between 10 to 100 atmospheres) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Transition metal catalysts are required. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst

Contents

Catalysts

The original catalyst was HCo(CO)4, discovered by Otto Roelen. Dicobalt octacarbonyl is the Chemical compound Co2(CO8 This Metal carbonyl is a versatile reagent in organometallic chemistry and Otto Roelen ( March 22, 1897 in Mühlheim, Germany &ndash, 1993, Germany) was a German chemist [1][2] Subsequent work demonstrated that the ligand tributylphosphine (PBu3) improved the selectivity of the cobalt-catalysed process. Tributylphosphine, formula P(CH or PBu is a Tertiary phosphine, most commonly encountered as a Ligand in Transition metal complexes Since the 1970’s, most hydroformylation relies on catalysts based on rhodium. Rh redirects here For other uses see Rh (disambiguation Rhodium (ˈroʊdiəm is a Chemical element with the symbol [3] [4] Subsequent research led to the development of water-soluble catalysts that facilitate the separation of the products from the catalyst. [5]

Mechanism

The overall mechanism resembles that for homogeneous hydrogenation with additional steps. Hydrogenation is the Chemical reaction that results in addition of Hydrogen (H2 The reaction begins with the generation of coordinatively unsaturated metal hydrido carbonyl complex such as HCo(CO)3 and HRh(CO)(PPh3)2. Such species bind alkenes, and the resulting complex undergoes a migatory insertion reaction to form a alkyl complex.

Selectivity

A key consideration of hydroformylation is the "normal" vs. "iso" selectivity. For example, the hydroformylation of propylene can afford two isomeric products, butyraldehyde or isobutyraldehyde:

H2 + CO + CH3CH=CH2 → CH3CH2CH2CHO ("normal")
vs. Propene, also known as propylene, is an unsaturated organic compound having the Chemical formula C 3 H 6 This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. Butyraldehyde, also known as butanal, is an Organic compound that is the Aldehyde analog of Butane as well as an isomer of Butanone Isobutyraldehyde is the Chemical compound with the formula (CH32CHCHO
H2 + CO + CH3CH=CH2 → (CH3)2CHCHO ("iso")

These isomers result from the differing ways of inserting the alkene into the M-H bond. Of course, both products are not equally desirable. Much research was dedicated to the quest for catalyst that favored the normal isomer.

Steric effects

When the hydrogen is transferred to the carbon bearing the most hydrogen atoms (Markovnikov addition) the resulting alkyl group has a larger steric bulk close to the ligands on the cobalt. In Chemistry, Markovnikov's rule or Markownikoff's rule is an Observation based on Zaitsev's rule. If the ligands on the cobalt are bulky (such as tributyl phosphine), then this steric effect is greater. Hence the mixed carbonyl/phosphine complexes offer a greater selectivity towards the straight chain products.

Migatory insertion step for propylene for a cobalt carbonyl bis-tributyl phosphine complex

Electronic effects

In addition the more electron rich the hydride complex is, the less proton like the hydride is, thus as a result the electronic effects which favour the markovnikov addition to an alkene are less able to direct the hydride to the carbon atom bearing the most hydrogens already. Thus as a result as the metal centre becomes more electron rich the catylst becomes more selective for the straight chain compounds.

Acetyl formation

After the alkyl formation a second migatory insertion converts the alkyl into an acetyl ligand (this is when the alkyl carbon forms a bond with the carbon of a carbonyl ligand). The vacant site on the metal is filled by two hydrogens (from the oxidative insertion of a hydrogen molecule. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 One of these hydrides then takes part in a reductive elimination to form the molecule of the aldehyde and the complex [HCo(CO)3]. Hydride is the name given to the negative Ion of Hydrogen, H− Oxidative addition and reductive elimination are two important classes of reactions in Organometallic chemistry. An aldehyde is an organic compound containing a terminal Carbonyl group.

Hydroformylation of ethylene using a cobalt carbonyl

It is important to note that the rate of migatory insertion of the carbonyl into the carbon-metal bond of the alkyl is fast; in systems where the migatory insertion does not occur (such as nickel hydride tristriphenyl phosphite) the reaction of the hydride with the alkene is reversible. In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Triphenyl phosphite is the Chemical compound with the formula P(OC6H53 This results in the isomerisation of the alkene, in this way oct-2-ene could be converted into a mixture of both oct-1-ene and oct-2-ene by a beta hydride elimination from the alkyl. Beta-hydride elimination is a reaction in which an Alkyl group bonded to a metal centre is converted into the corresponding metal-bonded Hydride and an Alkene In the system below the rate of insertion of the carbonyl carbon into the C-M bond is likely to be greater than the rate of beta-hydride elimination. If the converse was true then some n-C8H17CHO would have been formed. [6] Hydroformylation of 2-octene: the rhodium catalyst is coordinated to acac and carbon monoxide and encapsulated in a molecular self-assembly process by zinc tetraphenylporphyrin or Zn-tpp and the pyridine analogue of triphenylphosphine. Rh redirects here For other uses see Rh (disambiguation Rhodium (ˈroʊdiəm is a Chemical element with the symbol Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Acac redirects here For other uses see ACAC. Acetylacetone is an Organic compound with molecular formula C5H8O2 Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Molecular self-assembly is the process by which Molecules adopt a defined arrangement without guidance or management from an outside source A porphyrin is a heterocyclic Macrocycle derived from four Pyrroline subunits interconnected via their α carbon atoms via Methine bridges (=CH- Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. Triphenylphosphine (in Europe triphenylphosphane is a common Organophosphorus compound with the formula P(C6H53 - often abbreviated to In this process very much like the way enzymes work encapsulation of the catalytic site explains the observed regioselectivity:

Hydroformylation of 2-octene

Asymmetric hydroformylation

Hydroformylation of internal alkenes creates new stereocenters. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins In Chemistry, regioselectivity is the preference of one direction of Chemical bond making or breaking over all other possible directions. A stereocenter, or stereogenic centre, is any Atom in a Molecule bearing groups such that an interchanging of any two groups leads to a Stereoisomer Using chiral phosphine ligands, the hydroformylation can be tailored to favor one enantiomer. The term chiral (pronounced /ˈkaɪɹ(əl̩/ is used to describe an object that is non- superimposable on its mirror image In Chemistry, a ligand is either an Atom, Ion, or Molecule (see also Functional group) that bonds to a central metal generally In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable

Other substrates

Cobalt carbonyl and rhodium complexes catalyse the hydroformylation of formaldehyde and ethylene oxide to give 2-hydroxyacetaldehyde and 3-hydroxypropanaldehyde, which can then be hydrogenated to ethylene glycol and 1,3-propanediol, respectively. Formaldehyde is a Chemical compound with the formula H2CO It is the simplest Aldehyde —an organic compound containing a terminal Carbonyl Acetaldehyde, sometimes known as ethanal, is an organic chemical compound with the formula C[[Hydrogen H]]3CH O or MeCHO Ethylene glycol ( monoethylene glycol ( MEG) 12-ethanediol, IUPAC name: ethane-12-diol) is an Alcohol with two -OH The reactions work best when the solvent is basic (such as pyridine). Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. [7][8]

Conversion of ethylene oxide to the hydroxyaldehyde using a rhodium carbonyl phosphine complex

In the case of dicobalt octacarbonyl or Co2(CO)8 as a catalyst, 2-pentanone can arise from ethylene and CO, in the absence of hydrogen. Dicobalt octacarbonyl is the Chemical compound Co2(CO8 This Metal carbonyl is a versatile reagent in organometallic chemistry and A proposed intermediate is the ethylene-propionyl species [CH3C(O)Co(CO)3(ethylene)] which undergoes a migratory insertion to form [CH3COCH2CH2Co(CO)3]. A migratory insertion is a type of reaction in Organometallic chemistry, where a Cisoidal anion and a neutal ligand on a metal complex join together resulting in a coordinated The required hydrogen arises from the water shift reaction. The water gas shift reaction (WGS is a Chemical reaction in which Carbon monoxide reacts with Water to form Carbon dioxide and Hydrogen For details see [9]

Conversion of ethylene to diethyl ketone using a cobalt carbonyl, while the reaction used a cobalt carbonyl diphosphine complex for clarity the reaction has been drawn out assuming that a cobalt carbonyl is responsible for the reaction

If the water shift reaction is not operative, the reaction affords a polymer containing alternating carbon monoxide and ethylene units. Such polymers are more conventionally prepared using palladium catalysts. Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the [10].

References

  1. ^ Boy Cornils, Wolfgang A. Herrmann, Manfred Rasch (1994). "Otto Roelen, Pioneer in Industrial Homogeneous Catalysis". Angewandte Chemie International Edition in English 33 (21): 2144-2163. doi:10.1002/anie.199421441. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  2. ^ [1]
  3. ^ Imyanitov N. S. , Rudkovskij D. M. (1963). "Hydrogenation and hydroformylation in the presense of Co, Rh, and Ir carbonyls". Neftekhimiya (Rus) 3 (2): 198-200.  
  4. ^ Evans D. , Osborn J. A. , Wilkinson G. (1968). "Hydroformylation of Alkenes by Use of Rhodium Complex Catalyst". Journal of the Chemical Society 33 (21): 3133-3142. The Journal of the Chemical Society was a Scientific journal published from 1862 to 1877 and from 1926 to 1965 by the Chemical Society which merged with other doi:10.1039/J19680003133. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  5. ^ Cornils, B. ; Herrmann, W. A. (eds. ) “Aqueous-Phase Organometallic Catalysis” VCH, Weinheim: 1998
  6. ^ High-Precision Catalysts: Regioselective Hydroformylation of Internal Alkenes by Encapsulated Rhodium Complexes Kuil, M. ; Soltner, T. ; van Leeuwen, P. W. N. M. ; Reek, J. N. H. Journal of the American Chemical Society; 2006; 128(35) pp 11344 - 11345; doi:10.1021/ja063294i
  7. ^ Chan A. The Journal of the American Chemical Society (usually abbreviated as J A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. S. C. , Shieh H-S. (1994). "A mechanistic study of the homogeneous catalytic hydroformylation of formaldehyde: synthesis and characterization of model intermediates". Inorganica Chimica Acta 218 (1-2): 89-95. doi:10.1016/0020-1693(94)03800-7. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  8. ^ Spencer A. (1980). "Hydroformylation of formaldehyde catalysed by rhodium complexes". Journal of Organometallic Chemistry 194 (1-2): 113-123. Journal of Organometallic Chemistry is published by Elsevier. doi:10.1016/S0022-328X(00)90343-7. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  9. ^ Murata K. , Matsuda A. , (1981). "Application of Homogeneous Water-Gas Shift Reaction III Further Study of the Hydrocarbonylation - A highly Selective Formation of Diethyl Keton from Ethene, CO and H2O". Bulletin of the Chemical Society Japan 54: 2089-2092.  
  10. ^ J. Liu, B. T. Heaton, J. A. Iggo and R. Whyman, Angew. Chem. Int. Ed. , 2004, 43, 90-94

Further reading

Dictionary

hydroformylation

-noun

  1. (chemistry) the reaction of an olefin with carbon monoxide and hydrogen to form an aldehyde
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