Patent Application
20130072722
The present invention relates to supported metal catalysts, wherein the catalysts are modified by at least one amine, a method for the preparation thereof and hydrogenation processes utilising the supported metal catalysts.
WO2008098830 (to Evonik Degussa GmbH) relates to supported and unsupported transition metal catalysts which surfaces have been modified with sulfur-containing modifiers. Example 2 describes the preparation of modified Pt catalysts wherein H2PtCl6.6H2O is reduced onto to Al2O3. The Pt/Al2O3 catalyst is then suspended in methanol and modified by the addition of a modifier.
In one aspect the present invention provides a supported metal catalyst, wherein the catalyst is modified by at least one amine,
provided that when the metal is Pt and the support is Al2O3, the amine is not:
Another aspect of the invention provides a process for the preparation of a supported metal catalyst as defined herein, wherein the process comprises the steps of:
Yet another aspect of the invention provides a process for the preparation of an optionally substituted amine, comprising the step of hydrogenating an optionally substituted benzyl-amine in the presence of hydrogen and a supported metal catalyst as described herein.
Another aspect of the invention provides a process for the preparation of an optionally substituted arylamine, comprising the step of hydrogenating an optionally substituted aryl compound comprising one or more nitro groups in the presence of hydrogen and a supported metal catalyst as defined herein.
Yet another aspect of the invention provides a process for the preparation of an optionally substituted alkene, comprising the step of hydrogenating an optionally substituted alkyne in the presence of hydrogen and a supported metal catalyst as defined herein.
The point of attachment of a moiety or substituent is represented by “—”. For example, —OH is attached through the oxygen atom.
“Alkyl” refers to a straight-chain, branched or cyclic saturated hydrocarbon group. In certain to embodiments, the alkyl group may have from 1-20 carbon atoms, in certain embodiments from 1-15 carbon atoms, in certain embodiments, 1-8 carbon atoms. The alkyl group may be unsubstituted or substituted. Unless otherwise specified, the alkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Typical alkyl groups include but are not limited to methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl and the like.
“Alkenyl” refers to a straight-chain, branched or cyclic unsaturated hydrocarbon group having at least one carbon-carbon double bond. The group may be in either the cis- or trans-configuration around each double bond. In certain embodiments, the alkenyl group can have from 2-20 carbon atoms, in certain embodiments from 2-15 carbon atoms, in certain embodiments, 2-8 carbon atoms. The alkenyl group may be unsubstituted or substituted. Unless otherwise specified, the alkenyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Examples of alkenyl groups include but are not limited to ethenyl (vinyl), 2-propenyl (allyl), 1-methylethenyl, 2-butenyl, 3-butenyl, cyclobut-1,3-dienyl and the like.
“Alkynyl” refers to a straight-chain, branched or cyclic unsaturated hydrocarbon group having at least one carbon-carbon triple bond. In certain embodiments, the alkynyl group can have from 2-20 carbon atoms, in certain embodiments from 2-15 carbon atoms, in certain embodiments, 2-8 carbon atoms. The alkynyl group may be unsubstituted or substituted. Unless otherwise specified, the alkynyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Examples of alkynyl groups include but are not limited to ethynyl, prop-1-ynyl, prop-2-ynyl, 1-methylprop-2-ynyl, but-1-ynyl, but-2-ynyl, but-3-ynyl and the like.
“Aryl” refers to an aromatic carbocyclic group. The aryl group may have a single ring or multiple condensed rings. In certain embodiments, the aryl group can have from 6-20 carbon atoms, in certain embodiments from 6-15 carbon atoms, in certain embodiments, 6-12 carbon atoms. The aryl group may be unsubstituted or substituted. Unless otherwise specified, the aryl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl and the like.
“Arylalkyl” refers to an optionally substituted group of the formula aryl-alkyl-, where aryl and alkyl are as defined above.
“Halo” refers to —F, —Cl, —Br and —I.
“Heteroalkyl” refers to a straight-chain or branched saturated hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). The heteroalkyl group may be unsubstituted or substituted. Unless otherwise specified, the heteroalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom.
“Heterocycloalkyl” refers to a saturated cyclic hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). The heterocycloalkyl group may be unsubstituted or substituted. Unless otherwise specified, the heterocycloalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heterocycloalkyl group include but are not limited to epoxide, morpholinyl, piperadinyl, piperazinyl, thirranyl and the like.
“Heteroaryl” refers to an aromatic carbocyclic group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). Unless otherwise specified, the heteroaryl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heteroaryl groups include but are not limited to furanyl, indolyl, oxazolyl, pyridinyl, pyrimidinyl, thiazolyl, thiphenyl and the like.
“Substituted” refers to a group in which one or more (e.g. 1, 2, 3, 4 or 5) hydrogen atoms are each independently replaced with substituents which may be the same or different. Examples of substituents include but are not limited to -halo, —C(halo)3, —Ra, ═O, ═S, —O—Ra, —S—Ra, —NRaRb, ═NRa, ═N—ORa, —CN, —SCN, —NCS, —NO2, —C(O)—Ra, —COORa, —C(S)—Ra, —C(S)ORa, —S(O)2OH, —S(O)2—Ra, —S(O)2NRaRb, —O—S(O)—Ra and —CONaNb; wherein Ra and Rb are independently selected from the groups consisting of H, alkyl, aryl, arylalkyl, heteroalkyl, heteroaryl, heteroaryl-alkyl-, or Ra and Rb together with the atom to which they are attached form a heterocycloalkyl group, and wherein Ra and Rb may be unsubstituted or further substituted as defined herein.
In one aspect, the present invention provides a supported metal catalyst, wherein the catalyst is modified by at least one amine,
provided that when the metal is Pt and the support is Al2O3, the amine is not:
A supported metal catalyst typically comprises an inert support material and a catalytically active material. The support may be selected from the group consisting of carbon, alumina, calcium carbonate, titania, silica, zirconia, ceria and a combination thereof. When the support is alumina, the alumina may be in the form of alpha-Al2O3, beta-Al2O3, gamma-Al2O3, delta-Al2O3, theta-Al2O3 or a combination thereof. When the support is carbon, the carbon may be in the form of activated carbon (e.g. neutral, basic or acidic activated carbon), carbon black or graphite (e.g. natural or synthetic graphite). Examples of suitable carbon supports are Norit Carbon GSX, Ceca L4S, Ceca 2S, Ceca CPL, Timcal T44 Graphite or a combination thereof.
Preferably, the catalyst comprises at least one metal is selected from Group VIII or IB of the Periodic Table. More preferably, the metal is selected from the group consisting of at least one of the platinum group metals (i.e. Pd, Pt, Ru, Rh, Ir and Os), the coinage metals (i.e. Cu, Ag and Au), iron, cobalt and nickel. Most preferably, the metal is palladium, platinum and/or gold.
In one embodiment, the supported metal catalyst comprises a single metal e.g. Pt, Pd or Au.
In another embodiment, the supported metal catalyst comprises two metals e.g. Au—Pd, Au—Pt or Pd—Au. The ratio of each metal may be any suitable ratio. In one embodiment, the ratio is from about 0.01:1 wt % to about 20:1 wt % with respect to each metal, more preferably from about 0.1:1 to about 10:1 wt % e.g. 0.5:1, 1:1, 2:1, 4:1 or 9:1 wt %.
Whether the supported metal catalysts comprises a single metal or two or more metals, the metal loading of the supported metal catalyst may be any suitable loading, such as from about 0.01 wt % to about 20 wt % per metal.
The at least one amine is preferably selected from the group consisting of natural amino acids, non-natural amino acids, peptides, substituted or unsubstituted alkylamines, substituted or unsubstituted alkyldiamines, substituted or unsubstituted alkylpolyamines and combinations thereof. In one embodiment, the substituted or unsubstituted alkylamine, alkyldiamine or alkylpolyamines have from 1-20 carbon atoms and in certain embodiments, 1-15 carbon atoms.
Natural amino acids and their nomenclature are well-known in the art, for example, see to Biochem. J., 1984, 219, 345 which is incorporated herein by reference in its entirety for all purposes. By “non-natural amino acids” we mean a compound comprising an amino and a carboxylic acid group but which is not a natural amino acid. Examples, of non-natural amino acids are hydroxylysine, hydroxyproline, alloleucine, allotheonine, aminovaleric acid, aminohexanoic acid, homoserine, homoarginine, homophenylalanine, aminopropanoic acid, aminopropanoic acid, aminobutyric acid, aminopentanoic acid, aminohexanoic acid, aminohexandioic acid, aminoheptandioic acid, diaminopropanoic acid, diaminobutanoic acid, diaminopentanoic acid, diaminoheptandioic acid, carboxyglutamic acid, butylglycine, chlorophenylalanine dichlorophenylalanine, cyclohexylalanine, citrulline, dehydrophenylalanine, fluorophenylalanine, indolecarboxylic acid, iodophenylalanine, naphthylalanine, phenylglycine, O-acetylphenylserine, pyridylalanine, sarcosine, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, O-methyltyrosine, caproic acid and isomers thereof.
The amino acid (whether natural or non-natural) may have the D-, L- or DL-configuration.
In one embodiment, it is preferred that the natural amino acid or non-natural amino acid does not comprise a sulfur-containing functionality as the sulfur-containing functionality may poison the catalyst.
When the at least one amine is a peptide, it is preferred that the peptide consists of 2, 3, 4, 5 or more amino acids. The amino acids may be natural and/or non-natural as described above. Examples of peptides are GlyGly and GlyGlyGly.
Preferably, the at least one amine is selected from the group consisting of lysine, glycine, proline, alanine, serine, phenylalanine, asparginine, aspartic acid, valine, butylamine, 6-aminocaproic acid, 1,6-diaminohexane, hexylamine and combinations thereof.
The ratio of amine:metal may be any suitable ratio. In one preferred embodiment, however, the ratio is from about 0.05:1 to about 5:1.
Preferably, the supported metal catalyst is selected from the group consisting of:
The catalyst may comprise crystallites. In this instance, the crystallites may vary in size from about 1 nm to about 50 nm. In one embodiment, the crystallites may be ≧about 4 nm. In another embodiment, the crystallites may be ≦about 40 nm.
In another embodiment, the catalyst comprises facetted particles. Without wishing to be bound by theory, it is believed that the large planes and lack of corner sites in the facetted particles may contribute to the selective nature of the supported metal catalysts in hydrogenation reactions. In certain embodiments, the facetted particules may display clear to grain boundaries. Without wishing to be bound by theory, this may indicate that the particles grew together from two different nucleation points.
The form of the metal in the supported catalyst may comprise the elemental metal and/or a metal oxide and/or metal hydride. For clarity, however, the elemental metal, metal oxide and/or metal hydride will be referred to by the metal name. For example, a supported palladium catalyst may comprise elemental (metallic) palladium, palladium oxide and/or metal hydride. Regardless of the actual form(s) of palladium present, however, the catalyst will be referred to as a “supported palladium catalyst”.
In another aspect, the present invention provides a process for the preparation of a supported metal catalyst as described above, wherein the process comprises the steps of:
The at least one water soluble metal salt may be selected from the group consisting of:
Preferably, the at least one water soluble metal salt is selected from the group consisting of H2PtCl6, H2PdCl6, HAuCl4, Na2PdCl4 and a combination thereof.
Preferably, the aqueous solvent is deionised water. Optionally, the water may further comprise one or more water miscible solvents. Typical water miscible solvents include but are not limited to alcohols (such as methanol, ethanol, n-propanol and/or iso-propanol), acetone, acetonitrile, dioxane, tetrahydrofuran, dimethylformamide and dimethylsulfoxide.
In one embodiment, the at least one amine is soluble in the aqueous solvent. If it is found, however, that the at least one amine is not soluble, the at least one amine may be further treated in order to solubilise it. For example, when the at least one amine is an amino acid which is not soluble in water, the amino acid may be solubilised by the addition of a base (such as an alkali hydroxide), an acid (e.g. hydrochloric acid) or a solvent (such as acetone).
The support, the at least one water-soluble metal salt and the at least one amine may be combined in the aqueous solvent in any suitable order. In one preferred process of the invention, however, the support, the at least one metal salt and the at least one amine are each mixed in a portion of aqueous solvent (e.g. water). The mixture of the at least one metal salt, followed by the mixture of the at least one amine, is then added to the mixture of the support. If desired, each aqueous mixture may be allowed to stand before stirring and, if desired, allowed to stand and re-stirred before combining them together optionally with further stirring.
In one embodiment, the mixture of the support is stirred and boiled before the mixtures of the at least one metal salt and at least one amine are added.
In one embodiment, the mixture of the at least one amine is added slowly (e.g. dropwise) to the mixture of the at least one metal salt and support.
In one embodiment, the mixture of the at least one metal salt is added rapidly to the mixture of the support.
In one embodiment, the mixture of the at least one amine is added rapidly to the mixture of the at least one metal salt and support.
In another preferred process of the invention, the at least one water-soluble metal salt and the at least one amine are reacted to form an amino acid metal complex which may be optionally recovered and purified. The amino acid metal complex may then be combined with the at least one support and the reaction mixture optionally heated.
Preferably, the reducing agent is (i) a combination of a base and formaldehyde, (ii) a formate, (iii) a borohydride, (iv) a hypophosphite, (v) hydrazine, or (vi) hydrogen.
When the reducing agent is a combination of a base and formaldehyde, the base can be an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali metal carbonate, an alkaline earth metal carbonate or an alkali metal hydrogen carbonate. Preferably, the base is to sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, sodium hydrogen carbonate or potassium hydrogen carbonate, especially sodium hydroxide or sodium hydrogen carbonate.
The combination of a base and formaldehyde can be added to the reaction mixture to form a formate in situ. Alternatively, the formate may be prepared prior to its addition to the support, at least one water soluble metal salt and at least one amine. In this instance, when the reducing agent is a formate, the formate may be an alkali metal formate or alkaline earth metal formate. Examples of formates are sodium formate, potassium formate, magnesium formate and calcium formate.
When the reducing agent is a borohydride, the borohydride may be an alkali metal borohydride, such as sodium borohydride or potassium borohydride. Preferably, the alkali metal borohydride is sodium borohydride.
When the reducing agent is a hypophosphite, the hypophosphite can be an alkali metal hypophosphite. Examples of alkali metal hypophosphites are sodium hypophosphite and potassium hypophosphite. Sodium hypophosphite is preferred.
When the reducing agent is hydrazine, the hydrazine can be anhydrous or a solution in a solvent, such as tetrahydrofuran or water.
The reducing agents described above may be added to the aqueous mixture of the support, the at least one water soluble metal salt and the at least one amine alone or as a solution in further aqueous solvent.
When the reducing agent is hydrogen, the supported metal catalysts may be reduced prior to or during a hydrogenation reaction.
Step (a) and step (b) may be carried out at one or more temperatures between about 15° C. and 100° C. In one embodiment, step (a) is carried out at a temperature between about 15° C. and about 25° C., most preferably room temperature. In another embodiment, step (a) is carried out at the boiling temperature of the aqueous solvent.
In one embodiment, step (b) is carried out at one or more temperatures between about 25° C. and about 100° C. In a preferred embodiment, after the addition of the reducing agent, the reaction mixture is heated and stirred to about 90° C. When the reaction mixture reaches this temperature, the reaction mixture is allowed to cool, for example by removing the heat source or adding further aqueous solvent, to about 60° C. or below, whereupon the stirring may be stopped if desired. In another preferred embodiment, after the addition of the reducing agent, to the reaction mixture is boiled for a period of time and then cooled to about 60° C. or below e.g. by the addition of further solvent or removing the heat source.
The reaction may be continued for a period of from about 30 minutes to several hours, but is normally complete within about four hours. On completion, the supported metal catalyst may be collected and separated from the reaction mixture by any conventional separation technique such as filtration, decantation or centrifugation, then subjected to further purification or processing steps such as washing and/or drying if so desired. The separated reaction mixture may be further treated to recover additional supported metal catalyst.
Steps (a) and (b) may be carried out as a one-pot reaction. If desired, however, the product obtained after mixing the support, the at least one water soluble metal salt and the at least one amine may be collected, separated and, if necessary, subjected to further purification or processing steps as described above, before the addition of the reducing agent. The isolation of the product of step (a) may be suitable when the reducing agent is hydrogen and the support metal catalyst is prepared in situ during a hydrogenation reaction.
The supported metal catalyst may be prepared on any desired scale. For example, it has been found that the above mentioned process may be reliably scaled up to prepare about 3 kg of supported metal catalyst.
The supported metal catalysts of the present invention may be used in hydrogenation reactions. For example, it has been found that the catalysts are chemoselective in the hydrogenation of substrates containing one or more halogen atoms i.e. the desired hydrogenation reaction proceeds with a reduced propensity for concurrent dehalogenation. Without wishing to be bound by theory, it is believed that the at least one amine binds to the surface of the catalyst and that the presence of the at least one amine controls the size and shape of the catalyst which subtly influences the surface of the catalyst electronically.
Another aspect of the invention therefore provides a process for the preparation of an optionally substituted amine, comprising the step of hydrogenating an optionally substituted benzyl-amine in the presence of hydrogen and a supported metal catalyst as described herein.
In one embodiment, the benzyl-amine is a compound of formula A, which on hydrogenation forms a compound of formula B and C:
wherein,
R1, R2, R3, R4, R5, R6, R7, R8, R9, R10 and R11 are independently selected from the group consisting of H, alkyl, aryl, alkenyl, alkynyl, arylalkyl-, —O-alkyl, —O-aryl, —O-alkylaryl, heterocycle, halo, —NO2, —CN, —SCN, —NCS, —OH, —C(halo)3, —NR′R″R′″, —COR′, —COON, —COOR′, —OCOR′, —OC(O)—OR′, —CONR′R″, —C═N—O—R′, —S-alkyl, —S-aryl, —S-alkylaryl, —SO2R′, —S(O)2NR′R″, —O—S(O)—R′, —C(S)R′, —C(S)OH, —C(S)OR′, —OC(S)—OR′, —C(S)NR′R″, wherein the alkyl, aryl, alkenyl, alkynyl, arylalkyl- and heterocyclic groups may be optionally further substituted; and
R′, R″ and R′″ are independently selected from the group consisting of H, alkyl, aryl, arylalkyl- and heterocycle, wherein the alkyl, aryl, arylalkyl- and heterocyclic groups may be optionally further substituted.
In one embodiment, R1, R2, R3, R4 and R5 are each H.
In one embodiment, at least one of R7, R8, R9, R10 or R11 is a halo group, especially —Cl.
In one embodiment, at least one of R9, R10 or R11 is a halo group.
In one embodiment, the process further comprises an acid, for example, a mineral acid such as hydrochloric acid, hydrobromic acid or hydroiodic acid. The addition of an acid may be useful when the compound of formula A contains one or more halogen atoms. This is because the presence of the acid has been found to further reduce the undesirable dehalogenation reaction.
The molar ratio of acid to substrate may be any suitable molar ratio. Conveniently, the molar ratio may be about 1:1.
In yet another aspect, the present invention provides a process for the preparation of an optionally substituted arylamine, comprising the step of hydrogenating an optionally substituted aryl compound comprising one or more nitro groups in the presence of hydrogen and a supported metal catalyst as defined herein.
In one embodiment, the aryl compound further comprises one or more halo groups.
Preferably, the process further comprises an acid, for example, a mineral acid such as hydrochloric acid, hydrobromic acid or hydroiodic acid. The addition of the acid is useful for the same reason as given above i.e. the presence of the acid further reduces the undesirable dehalogenation reaction. The molar ratio of acid to substrate may also be as described above.
In yet another aspect, the present invention provides a process for the preparation of an optionally substituted alkene, comprising the step of hydrogenating an optionally substituted alkyne in the presence of hydrogen and a supported metal catalyst as defined herein.
Preferably, wherein the alkyne is a compound of formula D:
wherein,
R12 and R13 are independently selected from the group consisting of H, alkyl, aryl, alkenyl, alkynyl, arylalkyl-, —O-alkyl, —O-aryl, —O-alkylaryl, heterocycle, halo, —NO2, —CN, —SCN, —NCS, —OH, —C(halo)3, —NR′R″R′″, —COR′, —COON, —COOR′, —OCOR′, —OC(O)—OR′, —CONR′R″, —C═N—O—R′, —S-alkyl, —S-aryl, —S-alkylaryl, —SO2R′, —S(O)2NR′R″, —O—S(O)—R′, —C(S)R′, —C(S)OH, —C(S)OR′, —OC(S)—OR′, —C(S)NR′R″, wherein the alkyl, aryl, alkenyl, alkynyl, arylalkyl- and heterocyclic groups may be optionally further substituted; and
R′, R″ and R′″ are independently selected from the group consisting of H, alkyl, aryl, arylalkyl- and heterocycle, wherein the alkyl, aryl, arylalkyl- and heterocyclic groups may be optionally further substituted.
The supported metal catalysts of the present invention are useful in the preparation of cis-alkenes, trans-alkenes or a mixture thereof. In one embodiment, the hydrogenation is selective. In a preferred embodiment, the alkene predominantly comprises a cis-alkene.
The hydrogen pressures of the hydrogenation reactions mentioned above are suitably in the range of up to about 100 bar and conveniently in the range of from about 1 to 10 bar.
Preferably, the ratio of catalyst: starting material may vary in the range from about 1:1 to about 1:20,000, more preferably, 1:1 to about 1:3000, even more preferably, about 1:200 to about 1:2500 and most preferably, about 1:250 to about 1:2000.
The hydrogenation reactions preferably further comprise a solvent. Any suitable solvent may be used, for example, aqueous solvents, polar solvents, non-polar solvents, aprotic solvents, protic solvents or a combination thereof. Preferably, the solvent is one or more C1-10 alkanols, more preferably, methanol, ethanol, propanol isomers (i.e. n- or i-propanol), butanol isomers (i.e. n-, i- or t-butanol), pentanol isomers, hexanol isomers, heptanol isomers or combinations thereof. Methanol and ethanol are especially preferred solvents.
The concentration of the starting material in the solvent may be any suitable concentration. Conveniently, the concentration may be about 0.5M.
Reaction temperatures are suitably in the range from 10 to 100° C., preferably in the range from about 15 to about 80° C., most preferably about 20 to about 60° C.
The reactants may be added in any suitable order, but in a preferred process of the invention, the starting material (i.e. substrate to be hydrogenated) and the supported metal catalyst is placed in a hydrogenation vessel, together with a solvent (if used). The vessel is then charged with hydrogen and heated and/or stirred if necessary. The reaction may be continued until the calculated number of moles of hydrogen has been consumed.
The invention will now be described by way of example only and with reference to the following drawings in which:
a-c are TEM analyses of Pd-Lysine on a carbon support.
a-b are the TEM analyses of 0.5% Pd-Gly/Graphite catalyst.
The ligands butylamine, hexylamine, 6-amino caproic acid, 1,6-diaminohexane, lysine, glycine, alanine, arginine, serine, proline, asparagines, aspartic acid, valine and phenylalanine were purchased from Alfa Aesar. The precious metal salts (Na2PdCl4, H2PtCl6, HAuCl4) were purchased from Alfa Aesar. The supports Carbon GSX was purchased from Norit, L4S, 2S and CPL were purchased from Ceca. T44 Graphite was purchased from Timcal and calcium carbonate “Calopake F” was purchased from Ellis & Everard. Pd on alumina and Pd/C (5% Pd/C Type 39, 5% Pd/C 87 L, 5% Pd/Alumina Type 324, 5% PdPb/CaCO3 A305060-5, and 5% Pt/C type 18) were obtained from Johnson Matthey PLC.
The Use of Lysine to Precipitate Palladium onto Carbon
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes. Lysine (0.77 g, 1 equiv, dissolved in 10 ml of water) was then added dropwise to the slurry over 5 minutes. It was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The TEM analysis of the catalyst is illustrated in
The diffraction pattern
The above Example has since been scaled up from 10 g scale to a 100 g and a 3 kg scale.
The reaction as exemplified in Example 1 has also undertaken with different carbon supports -Ceca L4S, Ceca 2S, CPL. Large particles were similarly formed.
The reaction exemplified in Example 1 has been undertaken using different ligands.
a. Butylamine Precipitation
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed. Butylamine (0.34 g, 1 equiv, dissolved in 5 ml of water) was then added to the slurry. It was then stirred for 30 minutes. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (25 ml) and added dropwise to the slurry over 10 minutes. This was stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The XRD diffraction pattern indicates the presence of a major amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size was estimated by Rietveld analysis (LVoI-IB method) to be 7.5 nm.
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes. 6-Amino caproic acid (0.62 g, 1 equiv, dissolved in 10 ml of water) was then added dropwise to the slurry over 5 minutes. It was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The XRD diffraction pattern indicates the presence of a major amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been to estimated by Rietveld analysis (LVoI-IB method) to be ˜8.6 nm.
c. 1,6-diaminohexane
The same synthetic method was used as above with the exception that one equivalent of 1,6-diaminohexane (0.55 g) was used to precipitate the metal onto the carbon support.
The XRD diffraction pattern indicates the presence of a significant amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜11.9 nm.
d. Glycine
The same synthetic method was used as above with the exception that one equivalent of Glycine (0.35 g) was used to precipitate the metal onto the carbon support.
The XRD diffraction pattern indicates the presence of a major amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜16.9 nm.
XPS analysis of the Pd-Gly/GSX catalyst formed is illustrated in
e. Hexylamine
The same synthetic method was used (as above) with the exception that one equivalent of hexylamine (0.47 g) was used to precipitate the metal onto the carbon support.
The XRD diffraction pattern indicates the presence of a major amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜7.3 nm.
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes. The relevant amino acid (1 equiv, dissolved in 10 to ml of water) was then added to the slurry. It was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle and DI water was added to the slurry until the temperature had fallen to below 60° C., the stirring was also stopped. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The following amino acids were used:
The use of other amino acids were also tried (namely: asparginine, aspartic acid, valine and phenylalanine). These did not dissolved in water at pH 7, therefore the above preparation could not be used in this instance. However, the addition of base did dissolve the amino acids (due to deprotonation of the carboxylic acid group). The preparation of phenylalanine stabilised Pd/C was attempted using one equivalent of NaOH to solubilise the amino acid.
In order to see if the use of different isomers of amino acids had any effect, the D-(Sample e) and L-(Sample f) isomers of phenylalanine were used.
0.79 g of each of the isomers were combined with 0.19 g of NaOH (1.0 equivalent) and stirred in 10 ml of DI water.
The same preparation as above was used.
The diffraction pattern
The same preparation as above was used.
The diffraction pattern
The same preparation as above was used.
The diffraction pattern
The same preparation as above was used.
The diffraction pattern
The same preparation as above was used.
The diffraction pattern
The same preparation as above was used.
The diffraction pattern
a. Sodium Borohydride Reduction
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes. Lysine, 0.77 g, 1 equiv, dissolved in 10 ml of water) was then added dropwise to the slurry over 5 minutes. It was then stirred for a further 30 minutes.
NaBH4 (0.20 g) was dissolved in DI water (6 ml). This solution was then added to the slurry and stirred for 1 hour. The flask was then allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water. The black solid was collected and dried in the oven at 90° C. for 24 hours.
The XRD pattern indicates the presence of a significant amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜6.6 nm.
b. Sodium Hypophosphite Reduction
The same synthetic method was used as above with the exception that one equivalent of NaH2PO2 (0.50 g) was used as the reductant.
The XRD pattern indicates the presence of a major amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043) supported on carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜5.9 nm.
The use of sodium hypophosphite also results in a poorer monodispersity of metal particles on the surface, in comparison to formaldehyde.
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Lysine (1.54 g, 2 equivs, dissolved in 10 ml of water) was then added dropwise to the slurry over 5 minutes. It was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) to was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The same synthetic method was used as above with the exception that 0.1 equivalents of lysine (0.08 g) was used to precipitate the metal.
Carbon GSX (9.0 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Na2PdCl4 (2.92 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Glycine (0.70 g, 1 equiv, dissolved in 10 ml of water) was then added to the slurry. It was then stirred for a further 30 minutes.
NaOH (0.62 g) was dissolved in DI water (6 ml) and 2.04 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern
Carbon GSX (9.9 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Na2PdCl4 (0.29 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Glycine (0.07 g, 1 equiv, dissolved in 10 ml of water) was then added to the slurry. It was then stirred for a further 30 minutes.
NaOH (0.06 g) was dissolved in DI water (6 ml) and 0.20 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. this was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60 C, the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern
a. Pd Glycine-Precipitated on Alumina (5% Pd-Gly/Alumina)
Alumina (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes. Glycine (0.35 g, 1 equiv, dissolved in 10 ml of water) was then added to the slurry. It was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle and DI water was added to the slurry until the temperature had fallen to below 60° C., the stirring was also stopped. The solution was then filtered and the resulting solid was washed with 500 ml of DI water. The filtrate had a faint tinge of yellow. The dark brown solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern
b. Pd on Alumina—No Precipitant (5% Pd/Alumina) (Comparative)
Alumina (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle and DI water was added to the slurry until the temperature had fallen to below 60° C., the stirring was also stopped. The solution was then filtered and the resulting solid was washed with 500 ml of DI water.
The dark brown solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it. The slurry was then stirred and boiled for 30 minutes.
H2PtCl6 (2.04 g; (25.0% solution) 0.51 g of metal) was dissolved in water (8 ml) and rapidly added to the boiling slurry. This was boiled for a further 30 minutes. Lysine (0.38 g, 2.61 mmol, 1 equiv, dissolved in 10 ml of water) was then added rapidly, which was then boiled for a further 90 minutes.
0.36 ml of formaldehyde solution (40%) was dissolved in 5 ml of water along with one equimolar quantity of NaHCO3 (0.44 g, 5.18 mmol) and added rapidly to the slurry. The boiling slurry was maintained for a further one hour. After this time, the slurry was topped up with water in order to cool it to less than 60° C.
After standing, the supernatant was decanted off and the black solid was collected by filtration. This was then washed with 500 ml of DI water. The black solid was collected and dried in the oven at 90° C.
The diffraction pattern (not shown) indicated the presence of a major amount of crystalline platinum supported on GSX carbon. The Pt crystallite size was estimated by Rietveld analysis (LVoI-IB method) to be ˜9.0 nm.
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Hydrogen tetrachloroaurate (1.20 g; (41.24% solution) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Lysine 0.38 g (1 equiv, dissolved in 10 ml of water) was then added immediately to the slurry, which was then stirred for a further 30 minutes.
0.63 ml of formaldehyde solution (40%, 3.5 molar equivalents) was added to the slurry and stirred for 30 minutes. This was then heated up to reflux and maintained at this temperature for a further 30 minutes. The solution was then allowed to cool to room temperature, filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern (not shown) indicated the presence of a major amount of crystalline Gold supported on GSX carbon. The Au crystallite size was estimated by Rietveld analysis (LVoI-IB method) to be ˜27.5 nm.
a. Gly-Gly, Diglycine
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Diglycine (Gly-Gly) (0.63 g, 4.79 mmol, 1 equiv, dissolved in 10 ml of water) was then added immediately to the slurry, which was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern (not shown) indicated the presence of a major amount of crystalline palladium supported on GSX carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜23.9 nm.
b. Gly-Gly-Gly, Triglycine
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Na2PdCl4 (1.46 g; (34.97% solid) 0.51 g of metal) was dissolved in water (8 ml) and added to the slurry. This was stirred for 30 minutes.
Triglycine (Gly-Gly-Gly) (0.92 g, 4.79 mmol, 1 equiv, dissolved in 10 ml of water) was then added immediately to the slurry, which was then stirred for a further 30 minutes.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern (not shown) indicated the presence of a major amount of crystalline palladium supported on GSX carbon. The Pd crystallite size has been estimated by Rietveld analysis (LVoI-IB method) to be ˜21.3 nm.
A bis(glycinato) palladium(II) complex (Pd(gly)2) was prepared according to the method described by J. S. Coe and J. R. Lyons in J. Chem. Soc. A, 1971, 829-33. This was then used as a precursor in the reaction where the amino acid was already complexed to the metal prior to addition.
Carbon GSX (9.5 g) was weighed out and 60 ml of DI water was added to it and briefly stirred. The slurry was then allowed to stand for 1 hour. After this time, the stirring was resumed.
Pd(gly)2 (1.22 g, 4.79 mmol, 0.51 g of metal) was dissolved in water (20 ml) and added to the slurry. The complex was not that soluble and so had to be heated to get it into solution. Upon addition much of this was observed to precipitate out. This was stirred for 2 hours. After this time, there was no visible sign of any of the palladium precursor either in solution or as a solid. Without wishing to be bound by theory, it is believed that, in the additional solvent, it had dissolved and stuck to the carbon support.
NaOH (0.31 g) was dissolved in DI water (6 ml) and 1.02 ml of formaldehyde solution (40%) was added to the base and stirred. This solution was then added to the slurry. This was then heated up to 90° C. Upon reaching this temperature, the flask was raised from the heating mantle. When the temperature had fallen to below 60° C., the stirring was also stopped. Upon reaching room temperature, the slurry was decanted. The flask was then refilled with DI water, stirred rapidly for 5 minutes and allowed to settle. The solution was then filtered and the resulting black solid was washed with 500 ml of DI water.
The black solid was collected and dried in the oven at 90° C. for 24 hours.
The diffraction pattern (not shown) indicates the presence of a minor amount of poorly crystalline Palladium (Pd, PDF No. 00-046-1043).
9.95 g of Timcal T44 graphite was placed in a round bottomed flask and 60 ml of water added to this. This was stirred for one hour before 0.146 g of Na2PdCl4 (in 10 ml of DI water) was to added to this. Glycine (0.035 g) was then dissolved in 10 ml of water and rapidly added to the slurry, which was stirred for a further 30 minutes. NaOH (0.062 g) and formaldehyde solution (0.204 ml) were combined and subsequently added to the slurry, before it was heated to 90° C. Upon reaching this temperature, excess water was added to bring the temperature down to 60° C. The resulting black solid was then filtered off, washed with water (500 ml) and dried in the oven at 105° C. for 2 days.
ICP Analysis: Pd 0.42%
a and 14b are TEM analyses of the glycine-modified Pd on graphite catalyst. The graphite supported catalysts have very large and facetted particles present, with an average particle size of approximately 40 nm. A number of particles display clear grain boundaries, which without being bound by theory, may indicate that the particles grew together from two different nucleation points. In addition, several of the particles display a strange diffraction effect in the electron beam, which may be a result of their relatively large size.
The above method was also used to prepare 1%, 2.5% and 5% loaded catalysts.
9.5 g of Carbon GSX was suspended in 60 ml of DI water. This was allowed to stand for one hour before stirring was commenced. The metal salts (Na2PdCl4 0.73 g and HAuCl4 0.62 g) were dissolved in 10 ml of water and rapidly added to the slurry. This was stirred for 30 minutes. Lysine monohydrate (0.61 g) was then dissolved in 10 ml of water and rapidly added to the slurry and this was stirred for a further 30 minutes. NaOH (0.34 g) and formaldehyde (0.85 ml) were dissolved in 10 ml of water and this solution was added to the slurry, which was then heated to boiling. This was maintained at this temperature for 30 minutes. After this water was added to the slurry to bring the temperature down to 60° C. This was then allowed to cool to room temperature. The slurry was then filtered and washed with 500 ml of water. The resulting black solid was collected and dried in the oven for 3 days.
XRD: The diffraction pattern
The above method has also been used to prepare Au—Pd-Lys/GSX catalysts with different metal ratios e.g. 0.5:1, 2:1, 4:1 and 9:1 wt % with respect to Au and Pd respectively, as well as different combinations of metals e.g. AuPt and PdPt.
a. N-debenzylation Reactions
One aspect of the catalytic work has focussed on N-debenzylation reactions containing aryl chloride groups and chloronitrobenzene hydrogenation. In both cases, the conversion to chloroaniline proceeded with significantly less reaction of the aryl chloride functionality than standard catalysts. This was further benefited by the addition of hydrochloric acid to the reaction mixture, which further retarded the undesired dehalogenation.
The hydrogenation of N-benzyl protected 2-chloroaniline was studied. A range of conditions were examined, but the conditions of a 0.5M ethanol solution, reacting at 50° C., 1 bar H2, with a 1:250 catalyst to substrate ratio were found to be suitable. The solutions contained 1,4-dioxane as an internal standard for the resulting analysis.
The reactions were performed in a Baskerville 10 Vessel Multicell Reactor using 5 ml of the ethanolic solution. Where the addition of acid was required, 0.5 ml of hydrochloric acid (1 molar equivalent wrt to substrate) was added to the reaction mixture. Analysis of the solutions was made using GCMS. The presence of acid often resulted on the precipitation of salts from the solution. In order to ensure all of the products could be analysed a basic extraction was performed prior to analysis. This involved the addition of 10M NaOH solution (˜5 ml) and dichloromethane (˜10 ml). Vigorous stirring and extraction of the organic layer allowed analysis that gave satisfactory mass balances to be obtained.
Analysis of the lysine-precipitated Pd/C catalyst was examined over different time periods in the N-debenzylation both in the presence (LysH) and absence (Lys) of one equivalent of HCl (see
Analogous reactions were performed using a standard 5% Pd/C catalyst (Type 39), and these were again run in the presence (39H) and absence (39) of one molar equivalent of hydrochloric acid (
Similar results were also shown to occur when using the analogous meta and para isomers.
The reaction has also been examined using catalysts precipitated using different ligands.
b. Chloronitrobenzene Hydrogenation
The supported metal catalysts of the present invention have shown a propensity to retard dehalogenation reactions in chloronitrobenzene hydrogenations.
The reactions were performed in a Baskerville 10 Vessel Multicell Reactor using 5 ml of the ethanolic solution. Where the addition of acid was required, 0.5 ml of hydrochloric acid (1 molar equivalent wrt to substrate) was added to the reaction mixture. Analysis of the solutions was made using GC or GCMS. The presence of acid often resulted on the precipitation of salts from the solution. In order to ensure all of the products could be analysed a basic extraction was performed prior to analysis. This involved the addition of 10M NaOH solution (˜5 ml) and dichloromethane (˜10 ml). Vigorous stirring and extraction of the organic layer allowed analysis that gave satisfactory mass balances to be obtained.
The following data was taken after a 2.5 hour run, in order to ensure complete conversion of the starting materials.
#Note: Significant quantities of cyclohexylamine (8.3%) and dicyclohexylamine (27.8%) and other products (8.9%) were also observed in this transformation
After this time, the standard Pd/C catalyst has resulted in near complete dehalogenation. In contrast, the amino modified catalysts all showed large quantities of the desired 2-chloroaniline—with the glycine modified catalysts appearing the best for this reaction.
Where the standard catalyst was used, the hydrogen uptake is rapid and overshoots the theoretical uptake required to just reduce the nitro group. The rate of reaction then slows, where it is believed that the aryl chloride groups are then reduced. This is confirmed by GCMS analysis after 2 hours which reveals that 80% of the reaction mixture is aniline.
In contrast, the hydrogen uptake of the lysine-modified catalyst slows earlier than the standard catalyst. The rate of reaction then also slows and it is believed that this is due to the slower dehalogenation occurring.
Addition of hydrochloric acid has also proved beneficial to this reaction, by minimising the rate of dehalogenation. The addition of one equivalent of hydrochloric acid to the reaction mixture resulted in an enhancement of the selectivity of the lysine-modified catalyst to over 90% selectivity.
The use of bimetallic gold-palladium nanocatalysts has been shown to be beneficial to the palladium only system. The reduction in the undesirable dehalogenation of the substrate is observed in the hydrogen uptake curves (see
Reactions were undertaken using 60 ml of a 0.5M ethanol solution of the substrate containing octane as an internal standard in a 100 ml Parr autoclave. 60 mg of the 5%, and 120 mg of the 2.5% loaded Pd catalysts were used (1:1,000 catalyst to substrate molar ratio). Conditions used were a temperature of 50° C., a pressure of 3 bar H2 and mechanical stirring at 400 rpm.
c. Hydrogenation of Alkynes
A number of palladium-based catalysts that were modified with amino acids were initially screened in a Baskerville 10 Vessel Multicell Reactor. This showed that a number of the amino acid modified catalysts gave high quantities of the desired cis-alkene product, in comparison with the standard lead-poisoned Lindlar catalyst. In contrast the analogous 5% Pd/C (87L) sample gave rise to near total over reduction to the unsaturated 1-hexanol.
A number of samples were also probed in a Parr single autoclave, using the same reaction conditions. The hydrogen uptake curves for Lindlar catalyst (PdPb/CaCO3), Pd/C (Type 39) and Pd-Gly/T44 are provided in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1002677.1 | Feb 2010 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2011/050321 | 2/17/2011 | WO | 00 | 11/28/2012 |
