Method for producing terpene aldehydes and terpene ketones

Abstract

The invention relates to a method for producing terpene aldehydes and terpene ketones by oxidatively dehydrogenating the corresponding terpene alcohols, comprising or consisting of the following steps: (a) providing terpene alcohols or terpene-alcohol-containing reactants; (b) bringing the starting substances from step (a) in contact with a heterogeneous ruthenium catalyst; (c) heating the mixture from step (b) to at least 150° C. in the presence of oxygen; optionally (d) separating the terpene aldehydes or terpene ketones from the obtained reaction mixture.

Claims

1. A method for producing terpene ketones by oxidative dehydrogenation of the corresponding terpene alcohols, the method comprising: bringing starting materials comprising terpene alcohols or terpene alcohol-containing reactants into contact with a heterogeneous ruthenium catalyst to form a mixture; heating the mixture at a temperature of about 180 to about 320° in the presence of oxygen to form a reaction mixture; and optionally separating the terpene ketones from the resulting reaction mixture, wherein a reaction to form the reaction mixture is carried out in a reactor through which a gas stream flows continuously, said gas stream comprising at least one terpene alcohol and an oxygen-containing gas and optionally an inert gas when entering the reactor.

2. The method as claimed in claim 1, wherein the starting materials comprise menthol.

3. The method as claimed in claim 1, wherein the heterogeneous ruthenium catalyst comprises one or more metal oxides.

4. The method as claimed in claim 3, wherein the one or more metal oxides are selected from the group comprising cerium oxides, copper oxides, iron oxides, manganese oxides, cobalt oxides, molybdenum oxides, silver oxides, and mixtures thereof.

5. The method as claimed in claim 3 wherein the one or more metal oxides are selected from the group comprising CeO.sub.2, CuO, Cu.sub.2O, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, MnO, MnO.sub.2, Mn.sub.2O.sub.3, Mn.sub.3O.sub.4, Co.sub.3O.sub.4, CoO, MoO.sub.3, AgO, Ag.sub.2O, and mixtures thereof.

6. The method as claimed in claim 1, wherein the heterogeneous ruthenium catalyst comprises catalytically active species that are applied to a support material.

7. The method as claimed in claim 6 wherein the support material is also catalytically active.

8. The method as claimed in claim 6, wherein the support material is an oxidic support material.

9. The method as claimed in claim 6, wherein the support material is selected from the group comprising cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, silica, iron oxide, manganese oxide, niobium oxide, aluminosilicate, hydrotalcite, hydroxyapatite, and mixtures thereof.

10. The method as claimed in claim 6, wherein the support material comprises activated carbon.

11. The method as claimed in claim 6, wherein a concentration of ruthenium on the support material is between approximately 0.1 and approximately 10% by weight.

12. The method as claimed in claim 1, wherein the oxygen-containing gas comprises at least 0.1% by volume oxygen, based on the total volume of the oxygen-containing gas, determined at 20° C. and 1013.25 hPa.

13. The method as claimed in claim 1, wherein (i) the flow rate of the gas stream based on the volume of the heterogeneous catalyst (gas hourly space velocity GHSV) is about 100 h-1 to about 5000 h-1, and/or (ii) the concentration of terpene alcohol in the gas stream entering the reactor is about 1 mol % to about 15 mol %.

14. The method as claimed in claim 13, wherein (i) the flow rate of the gas stream based on the volume of the heterogeneous catalyst (gas hourly space velocity GHSV) is about 200 h-1 to about 1000 h-1, and/or (ii) the concentration of terpene alcohol in the gas stream entering the reactor is about 3 mol % to about 10 mol %.

15. The method as claimed in claim 6, wherein a concentration of ruthenium on the support material is between approximately 0.5 and approximately 5% by weight.

16. The method as claimed in claim 1, wherein a reaction to form the reaction mixture is carried out at a temperature in the range of approximately 250 to approximately 300° C.

17. A method for producing terpene aldehydes and terpene ketones by oxidative dehydrogenation of the corresponding terpene alcohols, the method comprising: bringing starting materials comprising terpene alcohols or terpene alcohol-containing reactants into contact with a heterogeneous ruthenium catalyst of type RuMnCe/CeO.sub.2; heating the mixture to at least 150° C. in the presence of oxygen to form a reaction mixture; and optionally separating the terpene aldehydes or terpene ketones from the resulting reaction mixture.

18. A method for producing terpene aldehydes and terpene ketones by oxidative dehydrogenation of the corresponding terpene alcohols, the method comprising: bringing starting materials comprising menthol or a menthol-containing reactant into contact with a heterogeneous ruthenium catalyst to form a mixture; heating the mixture to at least 150° C. in the presence of oxygen to form a reaction mixture; and optionally separating the menthone from the resulting reaction mixture.

Description

DESCRIPTION OF THE INVENTION

(1) The invention provides a method for producing terpene aldehydes and terpene ketones by oxidative dehydrogenation of the corresponding terpene alcohols, comprising or consisting of the following steps:

(2) (a) providing terpene alcohols or terpene alcohol-containing reactants;

(3) (b) bringing the starting materials of step (a) into contact with a heterogeneous ruthenium catalyst;

(4) (c) heating the mixture of step (b) to at least 150° C. in the presence of oxygen; and optionally

(5) (d) separating the terpene aldehyde or terpene ketone from the resulting reaction mixture.

(6) Surprisingly, it has been found that the requirement profile described at the outset is met in full by the method according to the invention: the terpene aldehydes or terpene ketones are obtained in high yields and with high selectivities which are significantly above those which were previously achievable according to the prior art. Neither did solvent have to be used, nor was there a need to remove the catalyst in a complex manner; the method also does not require reduced pressure. The temperature range to be maintained is so low that there is no appreciable by-product formation, meaning that qualities are obtained which meet the stringent requirements in the perfume industry.

Terpene Alcohols

(7) In principle, the method according to the invention can be applied to all terpene alcohols. Examples of suitable terpene alcohols include borneols and fenchols, and in particular carveol, citronellol, cuminic alcohol, dihydrocarveol, farnesol, geraniol, nerol, perillyl alcohol, phytol and rhodinol and mixtures thereof. Menthol is preferably used in the context of the method according to the invention, which is converted to menthone or a mixture of menthone and isomenthone.

(8) It is possible to use the terpene alcohols as individual substances. Mixtures of various terpene alcohols can also be converted, or natural product extracts having a content of these terpene alcohols in addition to other components.

Catalysts

(9) In accordance with the present invention, heterogeneous ruthenium catalysts are used, which preferably have an oxidation state greater than zero. These catalysts can also have other catalytically active species, in particular other metal oxides. These can be selected from the group comprising cerium oxides, copper oxides, iron oxides, manganese oxides, cobalt oxides, molybdenum oxides, silver oxides and mixtures thereof. The following oxides are particularly preferred examples: CeO.sub.2, CuO, Cu.sub.2O, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, MnO, MnO.sub.2, Mn.sub.2O.sub.3, Mn.sub.3O.sub.4, Co.sub.3O.sub.4, CoO, MoO.sub.3, AgO, Ag.sub.2O and mixtures thereof. Doping, for example in amounts of about 10 to about 50% by weight, based on the amount of ruthenium, results in a significant increase in the catalyst activity.

(10) In the context of the present invention, catalysts used are especially those in which the catalytically active species are applied to a support material. In this case, it is advantageous to apply these oxidized metal species—based both on ruthenium and on the other metals—to the support in a very finely divided form. Particular preference is given to carrying out the invention when the catalyst support itself consists of a material which is catalytically active for oxidations. The active catalyst is produced using wet chemical methods such as impregnation, impregnation to the onset of moisture, precipitation or co-precipitation. The metals to be introduced in the catalyst synthesis are used in the form of suitable precursors, for example as metal chlorides, metal nitrates or metal acetates. In order to be able to be used according to the invention in a continuous reactor, the crude catalyst mass is then subjected to shaping such as extrusion or pelletization and thermal treatment. The supports are preferably oxidic materials which are selected from the group comprising cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, silica, iron oxide, manganese oxide, niobium oxide, aluminosilicate, hydrotalcite, hydroxyapatite and mixtures thereof. Alternatively, activated carbon can also serve as a support.

(11) The concentration of ruthenium or the mixture of ruthenium and other metals in their respective oxidic form on the support material can be between approximately 0.1 and approximately 10% by weight and preferably between approximately 0.5 and approximately 5% by weight.

Method

(12) In accordance with the invention, continuous tubular reactors are used for the oxidative dehydrogenation of menthol. In this case, the catalyst can come into contact with the reactant in a fixed bed or fluidized bed. The design of the reaction plant according to the invention also includes tube bundle reactors.

(13) Gaseous reactants flow through the catalyst introduced into the reactor. These reactants consist of gaseous menthol and an oxygen-containing gas. The oxygen-containing gas is supplied at suitable concentrations by mass flow controllers. The concentration of oxygen in the oxygen-containing gas is at least 0.1%. The terpene alcohol is supplied by a pump and conversion into the gas phase is carried out by conventional evaporator designs.

(14) The method according to the invention requires a minimum temperature of 150° C. to ensure that the reaction proceeds in the gas phase, since this is critical for conversions and selectivity. Otherwise, the preferred temperature range is 150 to approximately 350° C., preferably approximately 180 to approximately 320° C. and especially 250 to approximately 300° C.

(15) By setting the optimum temperature and residence time or GHSV (gas hourly space velocity), the yield and selectivity of, for example, the desired menthone/isomenthone mixture can be maximized. This can be seen as an advantage of this continuous process according to the invention.

(16) It is further preferred to carry out the reaction in a reactor through which a gas stream flows continuously, said gas stream comprising the terpene alcohol, preferably menthol, and an oxygen-containing gas and optionally an inert gas when entering the reactor. In this case, the oxygen-containing gas preferably comprises at least 0.1% by volume oxygen, based on the total volume of the oxygen-containing gas, determined at 20° C. and 1013.25 hPa.

(17) A further preferred embodiment of the method according to the invention also consists in that (ii) the flow rate of the gas stream based on the volume of the heterogeneous catalyst (gas hourly space velocity GHSV) is about 100 h.sup.−1 to about 5000 h.sup.−1, preferably about 200 h.sup.−1 to about 1000 h.sup.−1 and/or (ii) the concentration of terpene alcohol in the gas stream entering the reactor is about 1 mol % to about 15 mol %, preferably about 3 mol % to about 10 mol %.

(18) Suitable residence times are in the range of τ=1-20 s. At the outlet of the reactor, the gaseous product mixture is condensed and subjected to a gas/liquid separation. The liquid product mixture can then be purified by distillation.

(19) The method can be carried out either batchwise or preferably continuously.

EXAMPLES

Examples 1 to 9

(20) General description of the apparatus used and the reaction regime

(21) The continuous tubular reactor apparatus used consisted of a saturator, thermostat, gas lines, gas metering and control with digital MFCs, a tubular reactor with oven, one sample collection vessel temperature-controlled in an oil bath (filled with 6 mL of ο-xylene) for high boilers and one sample collection vessel cooled in a cryostat for low boilers and several heaters with control elements and thermocouples.

(22) To carry out the tests, the stainless steel tubular reactor was first filled with the previously granulated catalyst (3 mL). The saturator filled with menthol was then immersed in the thermostat solution, which was heated to the desired temperature (usually 120° C.). With the exception of the gas line to the saturator, the temperature of all other lines was set to 200° C. by heaters (heating bands) with thermocouples and control devices and kept constant. During the heating phase, the entire test apparatus was purged with N.sub.2 via a gas line passing the saturator. A gas mixture of 5% by volume O.sub.2/Ar (30 mL/min) was then passed into the saturator, which was temperature-controlled at 120° C., after the N.sub.2 purge gas supply had been closed. The reaction was started by opening the gas valve from the saturator to the reactor. In order to prevent the unreacted menthol from crystallizing out (m.p.: 41-45° C.) at the reactor outlet, the gas line from the reactor outlet to the collection vessel was additionally heated to 100° C. In addition, the sample vessel with 6 mL of ο-xylene as a collecting solution was heated to 60° C. with the aid of a temperature-controlled oil bath during the entire reaction time. A cold trap for collecting any more volatile products was located directly downstream of the actual sampling point. After the reaction was complete, the valve from the saturator to the reactor was closed and the system was purged with N.sub.2. Then, all other control elements for gas metering and temperature control were switched off.

(23) To determine the menthol consumption during the reaction, the saturator was removed after each test and weighed. The total reaction time per temperature was always 3 hours, with hourly sampling. The tests were carried out under the following conditions: 3 mL of catalyst, 5 mol % menthol in the gas stream, 30 mL/min 5% by volume O.sub.2/Ar,

(24) Catalysts used: [a]: Ru/C, [b]: 0.2% Ru/CeO.sub.2, [c]: 0.2-1.0/1.2/1.6% RuMnCe/CeO.sub.2,
wherein catalysts [a] and [b] are commercial products and catalyst [c] was obtained according to the following standard procedure:

(25) To a suspension of 4.46 g of CeO.sub.2 in 100 mL of deionized water was added a solution of 23.4 mg of RuCl.sub.3.Math.H.sub.2O, 260.6 mg of Mn(NO.sub.3).sub.2.Math.4H.sub.2O and 225.4 mg of Ce(NO.sub.3).sub.3.Math.6H.sub.2O in 20 mL of water. Then, with the aid of a syringe pump, a solution of 415.2 mg of NaOH and 314.4 mg of Na.sub.2CO.sub.3 in 8 mL of water was continuously added dropwise over a period of 5 h while stirring the suspension. After the addition was complete, the reaction suspension was heated to 65° C. and stirred for 18 h. The solid was removed by centrifugation, washed three times with 20 mL of water each time, and dried overnight at 90° C. in a drying cabinet. The active components Ru, Mn and Ce are present on the support as oxides and/or hydroxides.

(26) Observed conversions and yields are shown in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Conversions and yields Ru T X.sub.OL Y.sub.ON Y.sub.ISO Y.sub.NP S.sub.ON S.sub.ISO Ex. content [° C.] [mol %] [mol %] [mol %] [mol %] [%] [%] 1   5.sup.[a] 300 99 4 2 59 4 2 2 0.2.sup.[b] 300 92 31 22 11 34 24 3 0.2.sup.[b] 350 93 31 23 10 33 25 4 0.2.sup.[c] 300 52 20 17 4 39 32 5 0.2.sup.[c] 350 68 27 23 6 40 34 6 0.5.sup.[c] 300 94 38 26 5 40 28 7 0.5.sup.[c] 350 96 37 27 5 38 28 8 1.0.sup.[c] 300 92 40 28 6 43 31 9 1.0.sup.[c] 350 93 40 29 9 42 32 Key: X.sub.OL = conversion of menthol in mol % Y.sub.ON = yield of menthone in MOL % Y.sub.ISO = yield of isomenthone in mol % S.sub.ON = selectivity for menthone S.sub.ISO = selectivity for isomenthone