Patent Application
20170283352
The present invention relates to a method of preparing a compound of the formula (IV)
wherein R1 is alkyl of 1 to 4 carbon atoms, and where an intermediate stage, the compound of formula (I)
is prepared from cyclohexene by use of hydrogen peroxide and of a catalyst comprising a zeolite of framework structure MWW, wherein the framework of the zeolite as per (ii) comprises silicon, titanium, boron, oxygen and hydrogen. The present invention more particularly relates to a method of preparing vanillin via guaiacol as intermediate stage.
Vanillin (3-methoxy-4-hydroxybenzaldehyde) or ethylvanillin, but also isopropylvanillin, as examples of a compound of formula (IV) are some of the most important aroma chemicals in the world. Vanillin is the number two food additive, behind aspartame. The main field of use for vanillin is in the food industry, although the artificial flavoring substance ethylvanillin is increasingly being used as a substitute for vanillin. Vanillin also finds use as a fragrance in the perfume industry and as an intermediate in the pharmaceutical industry. Vanillin is derivable from natural sources such as, for instance, lignin or ferulic acid, although a significant proportion is obtained synthetically. The majority of these syntheses proceed via the intermediate known as guaiacol (2-methoxyphenol).
There is accordingly a constant need for economically advantageous methods of synthesis to prepare compounds of formula (IV) such as, for example, vanillin or ethylvanillin, particularly via the compound of formula (I), for example 2-methoxyphenol or 2-ethoxyphenol, as an intermediate stage.
GB 2 252 556 A discloses a method of preparing 2-methoxy- and 2-ethoxycyclohexanols by reacting cyclohexene with hydrogen peroxide, methanol or, respectively, ethanol and optionally sulfuric acid in the presence of a catalyst composition prepared by drying and calcining a mixture of titanium tetraethoxide and silica gel in hexane or ethanol. Only when employed to prepare 2-methoxycyclohexanol does this method achieve a target product selectivity, for 2-methoxycyclohexanol, of 95%, albeit with the disadvantage that the admixture of sulfuric acid to the reaction mixture is required to achieve this high selectivity.
A. Corma et al., “Activity of Ti-Beta Catalyst for the Selective Oxidation of Alkenes and Alkanes”, Journal of Catalysis (1994), volume 145, pages 151-158 discloses a method of preparing 2-alkoxycyclohexanol by reacting cyclohexene with hydrogen peroxide and an alkyl alcohol selected from the group consisting of methanol, ethanol and tert-butanol in the presence of a catalyst in the form of a Ti—Al-Beta zeolite. This method has the disadvantage that high excesses based on hydrogen peroxide are employed of cyclohexene and alkyl alcohol.
Y. Goa et al., “Catalytic Performance of [Ti, Al]-Beta in the Alkene Epoxidation Controlled by the Postsynthetic ion Exchange”, Journal of Physical Chemistry B 2004, volume 108, pages 8401-8411 discloses a method of preparing 2-methoxycyclohexanol by reacting cyclohexene with hydrogen peroxide and methanol in the presence of a catalyst in the form of a Ti—Al-Beta zeolite. The ostensibly high selectivities reported for this method are based not on the target product, 2-methoxycyclohexanol, but on a mixture consisting of 1,2-cyclohexanediol and 2-methoxycyclohexanol.
E. G. Derouane et al., “Titanium-substituted zeolite beta: an efficient catalyst in the oxy-functionalisation of cyclic alkenes using hydrogen peroxide in organic solvents”, New. J. Chem., 1998, pages 797-799 discloses a method of preparing 2-alkoxycyclohexanol by reacting cyclohexene with hydrogen peroxide and an alkyl alcohol selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol and tert-butanol in the presence of a catalyst in the form of a Ti—Al-Beta zeolite.
WO 2014/016146 A1 describes a method of preparing vanillin from 1,2-dihydroxybenzene.
CN 103 709 018 A describes the preparation of guaiacol from cyclohexene oxide by reaction with methanol and subsequent dehydrogenation.
It is an object of the present invention to provide a novel method of preparing compounds of general formula (IV)
wherein R1 is alkyl of 1 to 4 carbon atoms.
It is more particularly an object of the present invention to provide a novel method of preparing compounds of general formula (IV)
wherein R1 is alkyl of 1 to 4 carbon atoms, via the intermediate stage of formula (I)
We have found that, surprisingly, this object is achieved when the intermediate stage, the compound of formula (I)
is prepared by employing a specific zeolitic material of framework structure MWW as a catalyst having a high selectivity for the target product, the compound of formula (I).
The present invention accordingly provides a method of preparing a compound of formula (IV)
wherein R1 is alkyl of 1 to 4 carbon atoms, comprising
R1 in the compound of formula (I) and the alcohol R1OH is alkyl of 1 to 4 carbon atoms, i.e., of 1, 2, 3 or 4 carbon atoms. Step (i) permits the use of a mixture of two or more alcohols R1OH that differ in alkyl R1. R1 may in principle be suitably substituted, in which case R1 may have one or more substituents, which may each be, for example, hydroxyl, chloro, fluoro, bromo, iodo, nitro or amino. Alkyl R1 is preferably unsubstituted alkyl, preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl, more preferably from the group consisting of methyl, ethyl, n-propyl, and isopropyl, more preferably from the group consisting of methyl and ethyl. R1 is more preferably methyl.
The composition of the liquid mixture as per (i) is in principle not subject to any special restriction.
In principle, the liquid mixture provided as per (i) may have a molar ratio prior to the reaction as per (ii) of cyclohexene:R1OH less than, equal to or greater than 1:1. Preferably, the liquid mixture provided as per (i) has a molar ratio prior to the reaction as per (ii) of cyclohexene:R1OH not more than 1:1. Further preferably the liquid mixture provided as per (i) has a molar ratio prior to the reaction as per (ii) of cyclohexene:R1OH in the range from 1:1 to 1:50, more preferably from 1:3 to 1:30 and more preferably from 1:5 to 1:10.
In principle, the liquid mixture provided as per (i) may comprise a solvent. Any solvent is preferably selected from the group consisting of C1-C6-alkyl nitriles, i.e., C1-, C2-, C3-, C4-, C5- or C6-alkyl nitriles, dialkyl ketones of the formula R2—CO—R3, where R2 and R3 are each independently selected from the group consisting of C1-C6-alkyl, i.e., C1-, C2-, C3-, C4-, C5- or C6-alkyl, and a mixture of two or more thereof, more preferably selected from the group consisting of C1-C3-alkyl nitriles, i.e., C1-, C2- or C3-alkyl nitriles, dialkyl ketones of the formula R2—CO—R3, where R2 and R3 are each independently selected from the group consisting of C1-C3-alkyl, i.e., C1-, C2- or C3-alkyl, and a mixture of two or more thereof, more preferably selected from the group consisting of acetonitrile, acetone and a mixture thereof.
When a solvent is included, the molar ratio of solvent:cyclohexene in the liquid mixture provided as per (i) may in principle be less than, equal to or greater than 1:1 prior to the reaction of (ii). Preferably, the molar ratio of solvent:cyclohexene in the liquid mixture provided as per (i) is not less than 1:1 before the reaction of (ii). More preferably, the molar ratio of solvent:cyclohexene in the liquid mixture provided as per (i) is in the range from 20:1 to 1:1, more preferably from 15:1 to 1:1, more preferably from 10:1 to 1:1, before the reaction of (ii). When the solvent in the mixture comprises a mixture of two or more solvents, the molar ratio of solvent:cyclohexene is based on the mixture of solvents.
The mixture provided as per (i) preferably comprises no solvent. In this case, the liquid mixture provided as per (i) is preferably not less than 90 wt %, more preferably not less than 95 wt %, more preferably not less than 98 wt %, more preferably not less than 99 wt %, more preferably not less than 99.5 wt %, more preferably not less than 99.9 wt % comprised of cyclohexene, R1OH, methanol, hydrogen peroxide and any water from hydrogen peroxide being employed, as described below, in the form of an aqueous solution.
The temperature at which the liquid mixture is provided as per (i) is in principle not subject to any restriction. The liquid mixture as per (i) is preferably provided at a temperature in the range from 5 to 50° C., more preferably at a temperature in the range from 10 to 40° C., more preferably at a temperature in the range from 15 to 30° C.
The step of providing the liquid mixture as per (i) is in principle not subject to any special restriction. For instance, the liquid mixture as per (i) is providable by mixing the cyclohexene, the alcohol R1OH, the hydrogen peroxide and optionally the solvent in any order. The liquid mixture as per (i) is preferably provided by admixing the hydrogen peroxide to a mixture comprising the cyclohexene, the alcohol R1OH and optionally the solvent. It is preferable in this case for the mixture comprising the cyclohexene, the alcohol R1OH and the optional solvent to be presented as the initial charge at a temperature in the range from 5 to 50° C., more preferably from 10 to 40° C., more preferably from 15 to 30° C., and for the temperature of the mixture resulting from admixing the hydrogen peroxide to be suitably maintained within the aforementioned temperature ranges.
The hydrogen peroxide is preferably admixed in the form of a solution in one or more suitable solvents. Possible solvents include, for example, water or organic solvents such as, for example, organic solvents selected from the group consisting of C1-C6-alcohols, C1-C6-alkyl nitriles, dialkyl ketones of the formula R2—CO—R3, where R2 and R3 are each independently selected from the group consisting of C1-C6-alkyl, and a mixture of two or more thereof, preferably from the group consisting of C1-C3-alcohols, C1-C3-alkyl nitriles, dialkyl ketones of the formula R2—CO—R3, where R2 and R3 are each independently selected from the group consisting of C1-C3-alkyl, and a mixture of two or more thereof, more preferably from the group consisting of methanol, acetonitrile, acetone and a mixture thereof. The hydrogen peroxide is preferably admixed in the form of a methanolic or aqueous, preferably aqueous, solution. The hydrogen peroxide content of the preferably aqueous solution is not subject to any special restrictions and preferably ranges from 25 to 75 wt %, more preferably from 40 to 70 wt %, based on the overall weight of the aqueous solution.
In principle, the molar ratio of cyclohexene:hydrogen peroxide in the liquid mixture provided as per (i) may be less than, equal to or greater than 1:1 before the reaction of (ii). Preferably, the molar ratio of cyclohexene:hydrogen peroxide in the liquid mixture provided as per (i) is not less than 1:1 before the reaction of (ii). More preferably, the molar ratio of cyclohexene:hydrogen peroxide in the liquid mixture provided as per (i) is in the range from 1:1 to 5:1, more preferably from 1.5:1 to 4.5:1, more preferably from 2:1 to 4:1, before the reaction of (ii).
The mixture provided as per (i) preferably comprises no strong nonnucleophilic inorganic acid, preferably no sulfuric acid.
The inventors found that, surprisingly, the catalyst employed in (ii) has a high level of selectivity for the target product 2-alkoxycyclohexanol. The catalyst employed as per (ii) is not subject to any special restrictions. Preferably, however, the zeolitic material of framework structure MWW evinces one or more of the following features as per the itemized embodiments, including the combinations of embodiments as per the stated dependencies:
As far as the amount of catalyst is concerned, the mass ratio of hydrogen peroxide:zeolitic material of framework structure MWW is preferably in the range from 10:1 to 0.1:1, preferably from 1:1 to 0.2:1, more preferably from 0.75:1 to 0.25:1, at the start of the reaction as per (ii).
The reaction as per (ii) may generally be carried out as per any suitable procedure. Options thus include, for example, a discontinuous process in one or more batch reactors or a continuous process in one or more reactors operated in a continuous manner and optionally interconnected in series and/or in parallel.
The procedure for performing the reaction as per (ii) in a discontinuous process is not subject to any special restriction. A suitable reactor for the reaction as per (ii) is, for example, a reactor fitted with suitable heating means, a suitable stirrer and a reflux condenser. The reaction as per (ii) is preferably carried out in an open system. The reaction as per (ii) is preferably carried out under suitable agitation of the reaction mixture, for example stirring, in which case the energy input due to agitation may be varied or kept substantially constant during the reaction. The energy input may be suitably chosen according to, for example, the volume of the reaction mixture, the form of the catalyst or the reaction temperature. When the reaction as per (ii) is carried out in batch mode, the catalyst used as per (ii) is preferably an MWW framework structure zeolitic material as described above in Embodiments 1 to 15 and 18 to 33.
The procedure for performing the reaction as per (ii) in a continuous process is not subject to any special restriction. The continuous process is preferably carried out using, for example, a fixed bed catalyst, in which case the catalyst used as per (ii) is preferably a molding as described above in Embodiments 16, 17 and 34 to 36, comprising the zeolitic material of framework structure MWW and preferably one or more than one binder material, preferably silicon dioxide. Catalyst velocity in the continuous process is preferably in the range from 0.05 to 5 mol/kg/h, more preferably from 0.1 to 4 mol/kg/h, more preferably from 0.2 to 3 mol/kg/h, catalyst velocity being defined as mol (of hydrogen peroxide)/kg (of MWW framework structure zeolitic material)/h. For a continuous process, the mixture as per (i) is preferably provided as a liquid stream which is routed into the one or more reactors and subjected therein to reaction conditions as per (ii). For the continuous process, it is also possible to route the individual components of the mixture as per (i) in the form of two or more streams, which may comprise the individual components or a mixture thereof, into the one or more reactors where the individual streams are combined after reactor entry to form the mixture as per (i). Two or more reactors operated in a continuous manner may be interconnected two or more at a time in parallel and/or two or more at a time in series. Between two reactors interconnected in series there may be provided one or more interstages, for example to intermediately recover product of value. Between two reactors interconnected in series there may further be supplied one or more of the starting materials cyclohexene, R1OH alcohol, hydrogen peroxide and optional solvent.
Irrespective of the type of processing mode chosen, the reaction as per (ii) is performable using one or more, mutually different catalysts comprising a zeolitic material of framework structure MWVW and comprising B and Ti in the framework. The catalysts may differ, for example, with regard to the chemical composition or the manner of making the zeolitic material of framework structure MWW. When moldings are used, the catalysts may further differ for example with regard to the properties of the molding, e.g., in the geometry of the molding, the porosity of the molding, the binder content of the molding, the binder material or the percentage content of MWW framework structure zeolitic material. The reaction as per (ii) is preferably carried out in the presence of a single catalyst of the present invention.
Following the reaction as per (ii), the catalyst used is separated off from the mixture comprising the compound of formula (I). When the reaction is carried out in a continuous manner, for example in a fixed bed reactor, there is no need for a step to separate off the catalyst, since the reaction mixture leaves the reactor and the catalyst remains behind in the fixed bed reactor. When the reaction is carried out in discontinuous mode, for example in a batch reactor, the catalyst, which is preferably employed in the form of a powder, is removable using a suitable method of separation, examples being filtration, ultrafiltration, diafiltration, centrifugation and/or decanting.
Following removal, the removed catalyst may be subjected to one or more washing steps with one or more suitable washing liquids. Useful washing liquids include, for example, water, ethers such as dioxane, for example 1,4-dioxane, alcohols such as, for example, methanol, ethanol, propanol or a mixture of two or more thereof. Dioxanes are preferred for use as washing liquid. The washing step is preferably carried out at a temperature in the range from 10 to 50° C., more preferably at a temperature in the range from 15 to 40° C., more preferably at a temperature in the range from 20 to 30° C.
When the conversion rate, the selectivity or both the conversion rate and the selectivity offered by the catalyst according to the present invention decrease to below certain values, the catalyst can be regenerated in a suitable manner, for example by washing with one or more suitable washing media, or by drying in one or more suitable atmospheres, at one or more suitable temperatures and at one or more suitable pressures, or by calcination in one or more suitable atmospheres, at one or more suitable temperatures and at one or more suitable pressures, or by a combination of two or more of these measures, which may each be carried out one or more times for within one or more suitable time periods.
The reaction as per (ii) is preferably carried out at a reaction mixture temperature in the range from 40 to 150° C., more preferably at a reaction mixture temperature in the range from 50 to 125° C., more preferably at a reaction mixture temperature in the range from 70 to 100° C. When the reaction as per (ii) is carried out in a discontinuous manner, for example as a batch reaction, it is preferably carried out at the boiling point of the liquid mixture, more preferably under reflux.
When the reaction as per (ii) is carried out in a discontinuous manner, for example as a batch reaction, the duration of the reaction is preferably in the range from 1 to 12 h, more preferably in the range from 1.5 to 10 h, more preferably in the range from 2 to 8 h.
When the reaction as per (ii) is carried out in a discontinuous manner, the term “at the start of the reaction” relates generally to the point in time at which all the starting materials, including the catalyst, are simultaneously present in the reaction mixture and, depending on the temperature, the reaction of the cyclohexene starts. When the reaction as per (ii) is carried out in a continuous manner, the term “at the start of the reaction” relates generally to the point in time at which the mixture provided as per (i) comes into contact with the catalyst.
Preferably, the mole percentage for the compound of formula (I) in the mixture obtained from the reaction as per (ii), based on the sum total of mole percentages for the compounds of formulae (I), (Ib), (Ic), (Id) and (Ie)
in the mixture obtained from the reaction as per (ii) is not less than 85%, preferably not less than 90%. It is not a mandatory requirement here that every one of compounds (Ib), (Ic), (Id) and (Ie) be present in the mixture obtained as per (ii); on the contrary, the mixture obtained as per (ii) may comprise just one, just two, just three or all four of the compounds (Ib), (Ic), (Id) and (Ie) in addition to the compound (I).
The mixture obtained as per (ii), comprising the compound of formula (I), is preferably worked up to recover the compound of formula (I). When the conversion of hydrogen peroxide during the reaction is incomplete, it is preferable to precede the workup by removing the unconverted hydrogen peroxide present in the mixture, for example by decomposing it through admixture of suitable substances, for example via quenching. Examples of substances suitable for decomposing the excess hydrogen peroxide include, for example, tertiary amines, polyamines, salts of heavy metals such as iron, manganese, cobalt and vanadium, sulfinic acids, mercaptans, dithionites, sulfites and strong acids and bases. The decomposition of the excess hydrogen peroxide is preferably carried out using an alkali or alkaline earth metal sulfite, more preferably alkali metal sulfite, more preferably sodium sulfite. For the purposes of the present invention it is preferably not less than 95%, more preferably not less than 97%, more preferably not less than 99%, more preferably not less than 99.5%, more preferably not less than 99.9% of the unconverted hydrogen peroxide which is removed from the mixture obtained from the reaction as per (ii).
A mixture comprising an aqueous phase and an organic phase is preferably obtained from the reaction as per (ii), preferably after removal of unconverted hydrogen peroxide. It is preferable here to precede (iii) by separating the aqueous phase from the organic phase. In principle, any batch or continuous methods known to a person skilled in the art are employable here. The organic phase separated off in this way is then employed in (iii) as the mixture obtained as per (ii).
It is possible in principle for the mixture obtained as per (ii), for example the organic phase separated off as described above, to comprise the compound of formula (Ib)
in addition to the compound of formula (I). It is conceivable in this case to precede (iii) by separating the compound of formula (Ib) in a suitable manner from the mixture obtained from the reaction as per (ii), preferably after removal of unconverted hydrogen peroxide and preferably after a step of separating off the aqueous phase.
Step (iii)
In (iii) the compound of formula (I) is suitably separated off from the mixture obtained as per (ii) to obtain a mixture concentrated in respect of the compound of formula (I). Any suitable methods of separation are employable for this step of separating off the compound of formula (Ib), although a distillative form of separation is preferable. The distillation preferably yields a mixture which is concentrated in respect of the compound of formula (I) in that it is not less than 95% by weight, preferably more than 95% by weight, for example not less than 96% by weight or not less than 97% by weight or not less than 98% by weight or not less than 99% by weight, comprised of the compound of formula (I). Optionally, this distillative step of separating off may also be used to separate off the compound of formula (Ib) and to separate off the aqueous phase in a single step.
The distillation conditions to be employed with preference are readily adaptable by a person skilled in the art to the separation problem in each case, i.e., for example to the boiling points of the compounds of formulae (I) and (Ib). Examples of preferred distillation conditions for methyl R1 are a pot temperature in the range from 85 to 95° C. and an overhead pressure in the range from 15 to 25 mbar.
The mixture obtained by the step of separating off, concentrated with respect to the compound of formula (I), is preferably mixed with water before (iv). This aqueous mixture thus obtained is then sent into (iv) for dehydrogenation. Preference is given to aqueous mixtures comprising the compound of formula (I) at from 5% to 50% by weight, preferably at from 10% to 40% by weight, more preferably at from 15% to 35% by weight, more preferably at from 20% to 30% by weight, all based on the overall weight of the aqueous mixture.
Depending on its exact configuration, the dehydrogenation as per (iv) is in principle performable in the mixture obtained as per (iii), preferably in the aqueous mixture obtained as per (iii).
Preferably, the mixture obtained as per (iii), preferably the aqueous mixture obtained as per (iii), is suitably brought into the gas phase prior to dehydrogenation and a gas phase hydrogenation is carried out as per (iv). Preferably, therefore, the mixture which is obtained as per (iii) and which is concentrated in respect of the compound of formula (I), preferably the aqueous mixture prior to dehydrogenation as per (iv), is vaporized. Preferred temperatures for this vaporization range from 175 to 375° C., preferably from 225 to 325° C., more preferably from 250 to 300° C. Useful vaporizing apparatus includes in principle any vaporizer/evaporator known to a skilled person as suitable for this purpose.
The mixture thus preferably vaporized is then fed to the dehydrogenation as per (iv), this feeding preferably being effected using a carrier gas. Carrier gases are preferred which behave inertly or substantially inertly during the dehydrogenation as per (iv). The carrier gas is preferably selected from the group consisting of hydrogen, nitrogen, argon, carbon monoxide, water vapor and a mixture of two or more thereof, more preferably from the group consisting of hydrogen, nitrogen, argon, carbon monoxide and a mixture of two or more thereof, more preferably from the group consisting of hydrogen, nitrogen, argon and a mixture of two or more thereof. More preferable is a carrier gas comprising hydrogen and nitrogen and more preferably being not less than 95% by volume, more preferably not less than 98% by volume, more preferably not less than 99% by volume comprised of hydrogen and nitrogen. The nitrogen:hydrogen volume ratio is more preferably in the range from 2:1 to 20:1, more preferably in the range from 5:1 to 10:1.
Both the vaporizing step and the dehydrogenating step are preferably carried out in a continuous manner in the present invention.
The dehydrogenation is preferably carried out in the presence of a heterogeneous catalyst wherewith the mixture to be dehydrogenated is brought into contact. In principle, the arrangement of the catalyst in the reactor used for the dehydrogenation is not subject to any special restrictions. The heterogeneous catalyst is preferably arranged as a catalyst bed, more preferably as a fixed catalyst bed.
The chemical nature of the heterogeneous catalyst is not subject to any special restrictions beyond ensuring that the dehydrogenation of the present invention can be carried out. The dehydrogenatingly active component of the catalyst is preferably a dehydrogenatingly active noble metal, more preferably selected from the group consisting of Pd, Rh, Pt and a combination of two or more thereof.
The dehydrogenatingly active component of the catalyst, preferably the dehydrogenatingly active noble metal, is preferably supported in a suitable manner on a carrier. The carrier material is not subject to any special restrictions beyond ensuring that the carrier material behavior during the dehydrogenation is substantially inert or promotive of the dehydrogenation. The carrier material is preferably selected from the group consisting of activated carbon, aluminum oxide, silicon oxide and a combination of two or more thereof.
One preferred catalyst for the purposes of the present invention comprises Pd as dehydrogenatingly active component and activated carbon as carrier material, the palladium content of the catalyst preferably being in the range from 1% to 10% by weight, more preferably in the range from 2% to 8% by weight, more preferably in the range from 3% to 7% by weight, all based on the overall mass of the catalyst.
In another catalyst preferred for the purposes of the present invention and comprising Pd as dehydrogenatingly active component and activated carbon as carrier material, the palladium content of the catalyst is preferably in the range from 0.1% to 5% by weight, more preferably in the range from 0.2% to 3% by weight, more preferably in the range from 0.5% to 2% by weight, all based on the overall mass of the catalyst.
The heterogeneous catalyst is preferably activated in a suitable manner prior to dehydrogenation as per (iv). As part of this activation, the catalyst is preferably flushed with a gas, preferably at an elevated temperature as compared with room temperature. The gas employed for flushing is preferably selected from the group consisting of hydrogen, nitrogen, argon and a mixture of two or more thereof, more preferably from the group consisting of hydrogen, nitrogen and a mixture thereof. It is inter alia preferable to flush first with a mixture of hydrogen and nitrogen wherein the volume ratio of nitrogen:hydrogen is preferably in the range from 10:1 to 30:1, more preferably in the range from 15:1 to 25:1, and then with hydrogen. Preferred temperatures for flushing are in the range from 300 to 550° C., more preferably from 350 to 500° C., more preferably from 375 to 450° C. These temperatures are the temperature of the gas, or gas mixture, used for flushing the catalyst. The catalyst may in principle be flushed outside the reactor used for dehydrogenation. The catalyst is preferably flushed inside the reactor used for dehydrogenation.
Before or after this flushing, preferably before this flushing, the catalyst is washable in a suitable manner, preferably with an aqueous solution comprising a base, preferably a hydroxide, more preferably an alkali metal hydroxide, more preferably potassium hydroxide. An example of what is preferable is a wash with an aqueous solution of an alkali metal hydroxide, preferably potassium hydroxide, having an alkali metal hydroxide content in the range from 0.2% to 7% by weight, preferably from 0.5% to 6% by weight, more preferably from 1% to 5% by weight, based on the overall weight of the aqueous solution.
Prior to the actual hydrogenation, the reactor used for the dehydrogenation and comprising the catalyst is preferably suitably purged with a gas which is preferably selected from the group consisting of nitrogen, argon and a mixture thereof, more preferably comprises nitrogen, more preferably is technical-grade nitrogen.
The temperature at which the dehydrogenation as per (iv) is carried out is preferably in the range from 200 to 400° C., more preferably from 250 to 350° C., more preferably from 275 to 325° C. This temperature is to be understood as the temperature of the catalyst employed for the dehydrogenation. When the catalyst is, as is preferable, in the form of a catalyst bed, more preferably in the form of a fixed catalyst bed, this temperature is to be understood as meaning the temperature of the fixed catalyst bed.
Preferably, the formylating step as per (v) is preceded by the compound of formula (II) being separated off from the mixture obtained after dehydrogenation as per (iv) to obtain a mixture concentrated in respect of the compound of formula (II). Any suitable methods of separation are employable for this step of separating off the compound of formula (II), although a distillative form of separation is preferable. The distillation preferably yields a mixture which is concentrated in respect of the compound of formula (II) in that it is not less than 95% by weight, preferably more than 95% by weight, for example not less than 96% by weight or not less than 97% by weight or not less than 98% by weight or not less than 99% by weight, comprised of the compound of formula (II).
The distillation conditions to be employed with preference are readily adaptable by a person skilled in the art to the separation problem in each case. Examples of preferred distillation conditions for methyl R1 are a pot temperature in the range from 55 to 80° C. and an overhead pressure in the range from 0.5 to 5 mbar. It is preferably the mixture concentrated as per the compound of formula (II) which is separated off at the top of the column.
Step (v) comprises formylating the formula (II) compound present in the mixture obtained as per (iv) to obtain a mixture comprising the compound of formula (IV).
This formylation may in general be carried out according to any suitable procedure. The invention preferably comprises reacting the formula (II) compound present in the mixture obtained as per (iv) with glyoxylic acid, to obtain a mixture comprising the compound of formula (III)
The preferred starting material for this is an aqueous solution comprising the glyoxylic acid. Preference is given to aqueous solutions whose glyoxylic acid content is in the range from 30% to 70% by weight, preferably from 40% to 60% by weight. The reaction with glyoxylic acid is accordingly with preference carried out in aqueous phase. The present invention accordingly provides the method as described above and wherein the formylating step as per (v) comprises:
The reaction as per (v-1) more preferably takes place in a basic medium. The preference for this is for the reaction mixture to comprise a Bronstedt base, preferably selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides and a mixture of two or more thereof, more preferably from the group consisting of alkali metal hydroxides and a mixture of two or more thereof. The reaction mixture more preferably comprises sodium hydroxide.
In a preferred embodiment of the method according to the present invention, an initial charge comprises an aqueous solution comprising glyoxylic acid and preferably further comprising a Bronstedt base, preferably selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides and a mixture of two or more thereof, more preferably from the group consisting of alkali metal hydroxides and a mixture of two or more thereof, wherein the Bronstedt base more preferably comprises sodium hydroxide and more preferably is sodium hydroxide. This aqueous solution is then preferably mixed with an aqueous solution comprising the mixture obtained as per (iv) and preferably a Bronstedt base, preferably selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides and a mixture of two or more thereof, more preferably from the group consisting of alkali metal hydroxides and a mixture of two or more thereof, wherein the Bronstedt base more preferably comprises sodium hydroxide and more preferably is sodium hydroxide. More preferably, in the resulting mixture, the molar ratio of Bronstedt base, more preferably sodium hydroxide, to the sum total formed from the compound of formula (II) and from glyoxylic acid is in the range from 0.2:1 to 2:1, preferably from 0.5:1 to 1.5:1, more preferably from 0.75:1 to 1.25:1.
The reaction as per (v-1) is preferably carried out at a reaction mixture temperature in the range from 10 to 40° C., more preferably in the range from 15 to 35° C., more preferably in the range from 20 to 30° C. Suitable stirring is more preferably applied to the reaction mixture during said reaction. The pH of the mixture obtained after the reaction as per (v-1) is preferably in the range from 9.5 to 12.5, more preferably from 10 to 12, more preferably from 10.5 to 11.5.
The mixture obtained as per (v-1) is preferably purified in a further step to obtain a mixture that is concentrated in respect of the compound of formula (III). This purification is preferably carried out such that the mixture obtained, purified in respect of the compound of formula (III), is an aqueous mixture. The present invention accordingly provides the method as described above and wherein the formylating step as per (v) further comprises:
In principle, this purification as per (v-2) is not subject to any special restriction. Preferably, this purification comprises an extraction with one or more suitable organic solvents, more preferably comprising toluene. It is further preferable for the purposes of the present invention to use toluene to extract the mixture obtained as per (v-1). Preferably unconverted compound of formula (II) is extracted from the aqueous phase in the course of this extraction. The formula (II) compound thus separated off is then advantageously recyclable into the method of the present invention for use as starting material for the formylation as per (v). The present invention accordingly provides the method as described above and wherein the purification as per (v-2) comprises an extraction, preferably an extraction with an organic solvent, preferably comprising toluene.
It is further preferable for the purposes of the present invention for the mixture obtained as per (v-1) to be suitably acidified before said extraction and to perform said extraction on the basis of a mixture having a lower pH. Preferably, the pH of the mixture is adjusted to a value in the range from 0.5 to 1.5 in the course of (v-2). More preferably, the pH adjustment to a value in the range from 0.5 to 1.5 is effected in two or more steps, preferably in two steps. The extraction referred to is preferably carried out after the first step. The pH of the mixture after this first step is preferably in the range from 4.0 to 5.0.
Any suitable acids are in principle usable for adjusting the pH. The use of sulfuric acid is particularly preferable. pH here is to be understood as meaning the pH as determined on using a pH-sensitive glass electrode.
What the present invention accordingly provides as per (v-2) is preferably an aqueous mixture preferably having a pH in the range from 0.5 to 1.5 and comprising the compound of formula (III).
The formula (III) compound present in the mixture obtained as per (v-1), preferably as per (v-2), is preferably, in a further step of the present invention, subjected to an oxidative decarboxylation to obtain a mixture comprising the compound of formula (IV). The present invention accordingly provides the method as described above and wherein the formylating step as per (v) further comprises:
The oxidative decarboxylation is preferably preceded by the aqueous mixture used, obtained as per (v-1), preferably as per (v-2), being mixed with one or more organic solvents, preferably comprising toluene, so the mixture used in (v-3), which comprises the compound of formula (III), is an aqueous-organic mixture.
The step of oxidatively decarboxylating as per (v-3) is preferably carried out in the presence of an oxidizing agent. Any suitable oxidizing agents are usable in principle. The oxidizing agent is preferably selected from the group consisting of CuO, PbO2, MnO2, Co3O4, HgO, Ag2O, Cu(II) salts, Hg(II) salts, Fe(III) salts, Ni(III) salts, Co(III) salts, chlorates and a mixture of two or more thereof, preferably from the group consisting of CuO, MnO2, Cu(II) salts, Fe(III) salts and a mixture of two or more thereof. The oxidative decarboxylation as per (v-3) is more preferably carried out in the presence of FeCl3 as oxidizing agent.
Preferred temperatures at which the oxidative decarboxylation as per (v-3) is carried out range from 60 to 110° C., more preferably from 70 to 100° C., more preferably from 80 to 95° C. This temperature is to be understood as meaning the temperature of the reaction mixture.
Step (v), as described above, provides a mixture, preferably an aqueous mixture, more preferably an aqueous-organic mixture comprising the compound of formula (IV). This mixture is in principle usable as such for further reactions when the formula (IV) compound present in the mixture, for example vanillin, ethylvanillin or isopropylvanillin, serves as intermediate for subsequent steps of synthesis and the aqueous or aqueous-organic mixture is suitable therefor. The present invention accordingly also provides a mixture comprising the compound of formula (IV), obtained or obtainable as per any one above-described method comprising (i) to (v), preferably comprising (i) to (v-3).
It is preferable for the purposes of the present invention for the compound of formula (IV) to be separated off in a suitable manner from the mixture obtained as per (v), preferably (v-3), and preferably be purified thereby. The present invention accordingly also provides the above-described method further comprising
In principle, any procedures known to a person skilled in the art are employable for this step of separating off. It is particularly preferable to take the aqueous-organic phase more preferably obtained as per (v-3) and separate off the organic phase, comprising the compound of formula (IV), in a suitable manner. The present invention accordingly provides the above-described method wherein the mixture obtained as per (v), preferably as per (v-3) comprises water and one or more than one organic solvent, and wherein (vi) comprises:
Any procedure known to a person skilled in the art is employable to separate off the organic phase comprising the compound of formula (IV), preferably further comprising an organic solvent, preferably toluene.
The aqueous phase separated off from the organic phase as per the preferred method recited is preferably extracted with an organic solvent, preferably comprising toluene, to transfer into an organic phase any formula (IV) compound still present in the aqueous phase. Preference here is for the extracting step to be carried out at an elevated temperature as compared with room temperature for the mixture to be extracted, the temperature more preferably being in the range from 50 to 95° C., more preferably from 60 to 95° C., more preferably from 70 to 95° C., more preferably from 80 to 95° C., more preferably from 85 to 95° C. The one or more than one organic solvent used preferably comprises toluene and more preferably is toluene. The present invention accordingly also provides the above-described method wherein (vi) further comprises:
It is generally conceivable for this removed organic phase as per (vi-1) or the removed organic phase as per (vi-1) or the combined organic phases as per (vi-1) and (vi-2), comprising the compound of formula (IV), to be used as such, for instance when the compound of formula (IV) serves as intermediate for subsequent steps of synthesis. It is preferable for the purposes of the present invention for the organic phase as per (vi-1), or the combined organic phases as per (vi-1) and (vi-2), to be washed in a further step wherein the washing medium preferably comprises water, more preferably is water. This washing step is preferably carried out at a washing medium temperature in the range from 10 to 40° C., preferably from 15 to 35° C., more preferably from 20 to 30° C. The present invention accordingly also provides the above-described method wherein (vi) further comprises:
It is generally conceivable for the preferably washed organic phase comprising the compound of the formula (IV) to be used as such, for instance when the compound of formula (IV) serves as intermediate for subsequent steps of synthesis. It is preferred for the purposes of the present invention for the organic phase obtained as per (vi-1), or the organic phases obtained as per (vi-1) and (vi-2), preferably the organic phase washed as per (vi-3), or the organic phases washed as per (vi-3), to be concentrated in respect of the compound of formula (IV) to further preferably obtain the compound of formula (IV). The term “the compound of formula (IV)” as used in this context signifies a mixture or composition preferably not less than 99% by weight, based on the overall weight of the mixture or composition, comprised of the compound of formula (IV). And the procedure used for this concentrating step is not subject to any special restrictions. A concentrating step is preferably carried out under a pressure reduced from ambient pressure to preferably within the range from 1 to 100 mbar, more preferably from 1 to 50 mbar, more preferably from 1 to 10 mbar. The present invention accordingly also provides the above-described method wherein (vi) further comprises:
The present invention is further illustrated by the following embodiments and combinations of embodiments apparent from dependencies and other references:
1. A method of preparing a compound of formula (IV)
The invention is more particularly elucidated in the examples and reference examples which follow.
The experimental examples which follow utilized the following starting materials:
1. piperidine (Sigma-Aldrich)
2. boric acid (Bernd Kraft)
3. tetrabutyl orthotitanate (Alfa Aesar)
4. CAB-O-SIL® M7D and CAB-O-SIL® M5 (Cabot) fumed silica
5. Ludox® AS-40 (Sigma-Aldrich) colloidal silica
6. cyclohexene (Sigma Aldrich)
7. methanol (Fluka)
8. hydrogen peroxide (Solvay)
The 11B solid state NMR experiments were carried out using a Bruker Avance III spectrometer operating at 400 MHz 1H Larmor frequency (Bruker Biospin, Germany). The samples were stored at room temperature and 63% relative humidity before being packed into 4 mm ZrO2 rotors. Measurements were performed under 10 kHz magic angle spinning at room temperature. 11B-Spectra were obtained using 11B 15° pulse excitation of 1 microsecond (μs) pulse width, an 11B carrier frequency corresponding to −4 ppm in the referenced spectrum, and a scan recycle delay of 1 s. Signal was acquired for 10 ms and accumulated with 5000 scans. Spectra were processed using a Bruker Topspin with 30 Hz exponential line broadening, phasing and baseline correction across the full width of the spectrum. Spectra were indirectly referenced to 1% TMS in CDCl3 on the unified chemical shift scale according to IUPAC (Pure Appl. Chem., vol. 80, No. 1, p. 59) using glycine with carbonyl peak at 175.67 ppm as secondary standard.
29Si solid state NMR experiments were carried out using a Bruker Advance III spectrometer operating at 400 MHz 1H Larmor frequency (Bruker Biospin, Germany). The samples were stored at room temperature and 63% relative humidity before being packed into 4 mm ZrO2 rotors. Measurements were performed under 10 kHz magic angle spinning at room temperature. 29Si-Spectra were obtained using 29Si 90° pulse excitation of 5 microsecond (μs) pulse width, a 29Si carrier frequency corresponding to −112 ppm in the referenced spectrum, and a scan recycle delay of 120 s. Signal was acquired for 20 milliseconds (ms) at 63 kHz high-power proton decoupling and accumulated for at least 16 hours. Spectra were processed using a Bruker Topspin with 50 Hz exponential line broadening, phasing and baseline correction across the full width of the spectrum. Spectra were indirectly referenced to 1% TMS in CDCl3 on the unified chemical shift scale according to IUPAC (Pure Appl. Chem., vol. 80, No. 1, p. 59) using glycine with carbonyl peak at 175.67 ppm as secondary standard.
Water adsorption/desorption isotherms were performed on a VTI SA instrument from TA instruments following a step-isotherm program. The experiment consisted in one or more runs performed on a sample material placed on the microbalance pan inside the instrument. Before measurement was started, the residual moisture content of the sample was removed by heating the sample to 100° C. (5 K/min heat ramp) and maintaining the sample under a nitrogen stream for 6 h. After the drying program, the temperature in the cell was lowered to 25° C. and kept isothermal during measurement. The microbalance was calibrated, and the weight of the dried sample was balanced (0.01 wt % maximum deviation in mass). Water uptake by the sample was measured as the increased weight over the dry sample. An adsorption curve was measured first by increasing the relative humidity (expressed as wt % of water in the atmosphere of the cell) to which the sample was exposed, and measuring the water uptake of the sample as the equalizing weight. The relative humidity was increased from 5 wt % to 85 wt % in 10 wt % increments, with the system policing the relative humidity for each increment, and monitoring the sample weight until attainment of equilibrium conditions after the sample was exposed to 85 wt % to 5 wt % relative humidity in increments of 10 wt % and the change in the weight of the sample (the water uptake) had been monitored and recorded.
FT-IR (Fourier transform infrared) measurements were performed on a Nicolet 6700 spectrometer. The powdered material was compressed into a self-supporting pellet without the use of any additives. The pellet was introduced into a high vacuum cell (HV) accommodated in the FT-IR instrument. Measurement of the sample was preceded by preheating in high vacuum (10−5 mbar) at 300° C. for 3 h. Spectra were recorded after cooling the cell back down to 50° C. Spectra were recorded in the range from 4000 to 800 cm−1 at a resolution of 2 cm−1. The spectra obtained were depicted in a diagram having the wavelength (cm−1) on the x-axis and the absorption (in arbitrary units “a.u.”). A baseline correction was carried out to quantitatively determine the peak heights and the ratios between these peaks. Changes in the range from 3000 to 3900 cm−1 were analyzed and the band at 1880±5 cm−1 was used as reference to compare two or more samples.
The x-ray diffraction spectrum was recorded using a D8 Advance Series 2 from Bruker/AXS, which was equipped with a multiple sample changer.
Deionized water (841.82 g) in a glass beaker was admixed with piperidine (200 g), and the resulting mixture was stirred at room temperature for 5 min. Boric acid (203.8 g) was then admixed to the mixture and dissolved for 20 min, followed by a solution of tetrabutyl orthotitanate (17.75 g) dissolved in piperidine (99.24 g) admixed under agitation at a stirrer speed of 70 rpm, and the resulting mixture was stirred at room temperature for 30 min. The mixture was admixed with fumed silica (Cab-O-Sil® M7D, 147.9 g) under agitation, and the resulting mixture was stirred at room temperature for 1.5 h. The mixture had a pH of 11.3. The mixture was transferred into a 2.5 l autoclave and slowly heated to 170° C. over 10 hours at a heating rate of about 0.2 K/min and then was maintained at 170° C. for 160 h under agitation at a stirrer speed of 100 rpm. The pressure during the reaction was in the range from 8.3 to 9 bar. The suspension obtained had a pH of 11.2. The suspension was filtered and the filtercake was washed with deionized water until the wash liquor had a pH of less than 10. The filtercake was placed in a drying oven and dried at 120° C. for 48 h, heated to a temperature of 650° C. at a heating rate of 2 K/min and calcined at 650° C. in an air atmosphere for 10 h to obtain a colorless powder (101.3 g). The powder had a boron content of 1.3 wt %, reckoned as elemental boron, a titanium content of 1.3% by weight, reckoned as elemental titanium, and a silicon content of 40% by weight, reckoned as elemental silicon. The hydrocarbon content totaled 0.1% by weight. The water uptake determined as per Reference Example 3 was 13.7% by weight. The 11B solid state NMR spectrum of the zeolitic material is shown in
A Pd-containing solution was prepared as follows: 15.80 g of Pd(NOa)2 solution having a Pd content of 11% by weight was made up with completely ion-free water to an overall volume of 136 mL. 172 g of Supersorbon® activated carbon (particle size 0.7-1.0 mm) were saturated in this solution and then dried in a drying cabinet at 80° C. for 16 h. The catalyst was then calcined in a rotary tube oven at 400° C. for 4 h under flowing N2. The 1% by weight Pd/C catalyst was subsequently doped with KOH. To this end, 24.89 g of a 5% by weight KOH solution were made up to 64 mL with completely ion-free water. 80.90 g of the 1% by weight Pd/C catalyst were saturated in this solution. The catalyst was subsequently dried in a drying cabinet at 80° C. for 16 h.
In a reaction vessel, 1.00 g of the zeolitic material obtained as per Example 1 was mixed with 3.92 g of cyclohexene in 20 ml of methanol. The resulting mixture was admixed with 1.00 g of an aqueous hydrogen peroxide solution (50 wt % hydrogen peroxide). The mixture was stirred under reflux for 4 h. After filtering off the catalyst and weighing back the filtrate thus obtained, a sample was taken of the filtrate. The H2O2 content of this sample was determined cerimetrically. The filtrate was quenched with sodium sulfite in order to decompose any H2O2 still present. A sample was then taken in order to use gas chromatography (GC) analysis to determine the molar amounts of compounds (I) to (Id), which potentially form as per the reaction scheme shown below. The molar amounts were used to compute the selectivity of the catalyst as the molar amount of the desired product in the form of 2-methoxycyclohexanol (compound of formula (I)), based on the molar amount of the mixture of compounds of formulae (I) to (Id). The result was a selectivity of 93%. After separating off the organic phase, distillation gave the 2-methoxycyclohexanol in a purity of greater than 95%. 2-Methoxycyclohexanol aside the mixture obtained was essentially comprised of dihydroxycyclohexane. The following conditions were used for the distillation: external temperature: 100 to 102° C.; pot temperature: 90 to 92° C. (column trace heating: 90° C.); overhead temperature: 81 to 82° C.; overhead pressure: 20.0 mbar.
A reaction column was filled with 13 mL (5 g) of catalyst (1% by weight of Pd on activated carbon, prepared as per Example 2 and prewashed with 5% by weight aqueous KOH solution) and packed with quartz rings (30 mL below the catalyst bed, 30 ml above the catalyst bed). The catalyst was activated by flushing with a gas mixture N2/H2 (95:5) at 400° C. for 15 min. This was followed by flushing with H2 for a further 15 min. After purging with N2, the reactor temperature was adjusted to 300° C. (what is referred to as the reactor temperature is the temperature of the fixed catalyst bed; this temperature is measured via a thermocouple arranged radially and longitudinally in the center of the fixed catalyst bed). An additional vaporizer was attached to prevaporize the 2-methoxycyclohexanol feed stream from Example 3 at 275° C. The carrier gas used was N2 (20 L/h) and H2 (2.5 L/h). The 2-methoxycyclohexanol obtained as per Example 3 was then introduced as feed stream (25% by weight aqueous solution) into the reactor system (prevaporizer+reactor) at a flow rate of 6 g/h. Following 100 h of continuous operation, a 2-phase product mixture was obtained. The 2-phase product mixture thus obtained was subjected to a distillation to recover the guaiacol as product (conversion rate: 52%, (based on 2-methoxycyclohexanol used); selectivity: 72% (based on converted 2-methoxycyclohexanol)). The following conditions were used for the distillation: external temperature: 72 to 78° C.; pot temperature: 60 to 72° C.; overhead temperature: 41 to 50° C.; overhead pressure: 1.5 mbar.
Glyoxylic acid (23.74 g, 50% by weight in H2O, 0.16 mol) and 7% by weight NaOH (91.6 g, 0.16 mol) were introduced into a reaction vessel and stirred at room temperature. Following the slight exothermism of the mixing process, a mixture of guaiacol as per Example 4 (46.5 g, 0.2 mol) and 10% by weight aqueous NaOH (80.1 g, 0.2 mol) was added in the course of 45 min. The mixture was subsequently stirred at room temperature for 4.5 h. After this period, the solution obtained was homogeneous. The solution obtained had a pH of about 11 and was then carefully acidified with concentrated H2SO4 (10.9 g, 0.11 mol) until the pH had a value of 4.5. Then, the mixture was extracted with toluene (3×300 mL) in order to remove, and recycle, unconverted guaiacol. The aqueous phase obtained was further acidified with 97% to 99% by weight H2SO4 (15.4 g, 0.15 mol) until the pH had reached a value of about 1.0. An aqueous solution of the mandelic acid derivative of formula (III) was obtained. This crude solution of the mandelic acid derivative was heated together with toluene (160 mL) to a temperature of 90° C. Then, an aqueous 20% by weight FeCl3 solution (282.4 g) was admixed over 30 min, causing the red solution to turn black. The mixture was then further stirred at 90° C. for 2 h. Toluene (90 mL) was then admixed at 90° C. and the batch was cooled down to room temperature. The two phases were separated and the aqueous phase was additionally extracted with toluene (150 mL) five times. The combined organic phases were washed with water (350 mL) and then concentrated under reduced pressure to obtain vanillin of the formula of a compound of formula (IV) as a slightly beige solid (13.6 g, selectivity 64% based on glyoxylic acid).
| Number | Date | Country | Kind |
|---|---|---|---|
| 14184119.7 | Sep 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/070492 | 9/8/2015 | WO | 00 |
