An alcohol conversion process

Abstract

The present invention relates to an alcohol conversion process wherein a homogenous transition metal catalyst is used. In the process, the hydrogen partial pressure is maintained in a pressure range, and the hydrogen partial pressure can be increased or hydrogen removed from the system. Hydrogen can also be used as an external additive.

Description

[0001] An alcohol conversion process

[0002] The present invention relates to an alcohol conversion process.

[0003] A commonly used industrial production of alcohols is mainly based on an oxo process. Said process comprises the reaction of an alkene with oxo gas, which is a mixture of hydrogen and carbon monoxide in a 1 :1 molar ratio. The reaction is followed by hydrogenation of the aldehyde into the desired alcohol.

[0004] An alternative process for the synthesis of alcohols is based on the Guerbet reaction which is known for many decades (M. Guerbet, C. R. Hebd. Seances Acad. Sci. 1899, 128, p. 511-513). It is generally accepted that the mechanism leading to Guerbet alcohols comprises the following three steps: (i) dehydrogenation of a primary alcohol to the respective aldehyde; (ii) aldol condensation of two aldehyde molecules to an a,p-unsaturated aldehyde with elimination of water; and (iii) hydrogenation of the unsaturated aldehyde to the dimer alcohol. An alkaline catalyst, e.g. sodium or potassium hydroxide or sodium or potassium alkoxides, is required for the Guerbet reaction. Often homogeneous or hetereogeneous metal catalysts are added to accelerate the dehydrogenation and hydrogenation steps. However, the Guerbet reaction generally suffers from harsh conditions, poor selectivity, separation issues and low yield.

[0005] In the chemical industry, butanol is an important intermediate product and solvent for a broad variety of products, including paints and various plastics. Up to now, butanol is produced from a petro-based feedstock, leading to a significant product carbon footprint for butanol and the resulting products. Therefore, it is important for the chemical industry to find and open an economical and sustainable process route to butanol with a lower product carbon footprint.

[0006] Ethanol may be a sustainable feedstock to produce chemicals. Using ethanol in the Guerbet reaction may be a profitable and sustainable approach to produce butanol. Whereas the Guerbet reaction is used up to date to produce higher alcohols from higher boiling alcohol feedstocks than ethanol, there is so far no industrial usage for the Guerbet reaction for ethanol as the feedstock to produce butanol. While the Guerbet reaction itself may seem a simple chemical reaction, employing ethanol as the feedstock causes inherent problems particularly concerning selectivity. Because the product, n-butanol, can itself also undergo dehydrogenation, higher alcohols often result as side products in the process, making the reaction so far not profitable on an industrial scale.

[0007] Y.Xie et aL, “Highly efficient Process for Production of Biofuel from ethanol Catalyzed by Ruthenium Pincer Complexes”, Journal of the American Society, vol. 138, no. 29, 2016-07-18, pages 9077 to 9080, relates to a ruthenium pincer-catalyzed Guerbet-type process for the production of biofuel from ethanol.

[0008] WO 2012 / 119928 A1 relates to a method for producing alkanol amines which comprise a primary amino group and a hydroxyl group by alcohol amination of diols comprising two hydroxyl groups, using ammonia, and elimination of water. The reaction is homogeneously catalyzed in the presence of at least one complex catalyst, which contains at least one element selected from groups 8, 9 and 10 of the periodic table and at least one donor ligand.

[0009] WO 2013 / 156399 A1 relates to a method for producing branched alcohols using at least one alcohol of formula R1-CH2-CH2-OH, the groups R1being different or the same and being selected from C2-C3 alkyl, linear or branched, in a homogeneous phase in the presence of at least one base, characterized in that at least one complex compound containing Ru(ll) is used, in which the Ru(ll) has at least one ligand L1, which is at least bidentate, at least one coordination site of L1being a nitrogen atom.

[0010] Therefore, it was an object of the present invention to provide an alcohol conversion process allowing a profitable and sustainable approach to produce alcohols such as butanol with increased productivities.

[0011] The present invention thus relates to an alcohol conversion process based on the Guerbet reaction, wherein a homogenous transition metal catalyst is used. The process is economically feasible due to maintenance of the hydrogen partial pressure in a pressure range, said partial pressure influencing the reactivity. Increasing the hydrogen partial pressure may slow the reactivity but may increase the product alcohol selectivity simultaneously. Similarly, when hydrogen is removed from the system, for example via the gas phase, increased rates are observed. Moreover, hydrogen can be used as an external additive to reduce the formation of undesired side products, such as alcohols with higher boiling points, in the Guerbet process. This results in increased productivities.

[0012] The present invention in particular relates to an alcohol conversion process, comprising

[0013] (i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor;

[0014] (ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, and the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor provided according to (i), R being selected from the group consisting of H and Ci-C4-alkyl;

[0015] (iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SR and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the reaction space comprises the reaction mixture MG and a gas phase, wherein said alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SR in the range of from 1 x 105to 4 x 106Pa, wherein said gas phase comprises H2 and the alcohol conversion conditions further comprise maintaining the H2 partial pressure of the gas phase in the range of from 2 x 104to 1.1 x 106Pa;

[0016] (iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CHR-CH2)X-OH and a mixture Me comprising the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor; wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; wherein the catalyst comprises a compound of formula (A) wherein

[0017] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0018] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures:

[0019] L3is selected from the group consisting of CO, PRaRbRc, AsRaRbRc, SbRaRbRc, SRaRb, RdCN, RdNC, N2, PF3, pyridine, and thiophene;

[0020] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;

[0021] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, OH, OR, NRd2, NH3, NRd3, and Rd2NSO2Rd;

[0022] Ra, Rb, Rc, Rd, R5, R6and R7are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2 and Ci-C - alkyl; and

[0023] X is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-Cw-alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cw-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H)

[0024] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0025] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures:

[0026] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;

[0027] Ra, Rb, Rc, Rd, R5, R6and R7, are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-C -cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2and C1-C10- alkyl;

[0028] X is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-C -alkyl.

[0029] Figure 1 illustrates higher conversions being obtained in the experiment with an overpressure of 10 bar than in the experiment under intrinsic pressure (Example 5 vs. Example 6 vs. Comparative Example 1 ).

[0030] Figure 2 is a conversion-time diagram for different pressures.

[0031] Figure 3 is an overpressure versus time diagram for Example 5, Example 6, and Comparative Example 1 .

[0032] The process in accordance with the present invention is preferably a continuous process. Alternatively, the process is preferably a semi-batch process or a batch process.

[0033] Preferably, the alcohol conversion conditions according to (iii) comprise the presence of at least one inert gas in the reaction space SR, wherein the at least one inert gas is preferably selected from the group consisting of nitrogen, argon, and a mixture thereof. Also preferred is that the alcohol conversion conditions according to (iii) comprise a pressure in the reaction space SR in the range of from 1 x 105to 3.5 x 106Pa, preferably in the range of from 1 x 105to 3.1 x 106Pa, more preferably in the range in the range of from 1 x 105to 2 x 106Pa, more preferably in the range in the range from 1 x 105to 1.5 x 106Pa. In a further embodiment, it is preferred that the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 200 °C, preferably in the range of from 120 to 180 °C, more preferably in the range of from 130 to 170 °C.

[0034] Preferably, the alcohol conversion conditions according to (iii) comprise an amount of the base in the reaction mixture MG in the range of from 0.1 to 10 weight-%, preferably in the range of from 0.5 to 8 weight-%, more preferably in the range of from 1 to 5 weight-%, based on the total weight of the reaction mixture MG. Also, the alcohol conversion conditions according to (iii) preferably comprise an amount of the catalyst in the reaction mixture MG in the range of from 0.001 to 2 weight-%, preferably in the range of from 0.001 to 1 weight-%, more preferably in the range of from 0.001 to 0.5 weight-%, based on the total weight of the reaction mixture MG.

[0035] It is preferred that according to (ii), the H2partial pressure of the gas phase in the reaction space SR is maintained in the range of from 2 x 104to 1 .0 x 106Pa, more preferably in the range of from 2 x 104to 6 x 105Pa, even more preferably in the range of from 5 x 104to 6 x 105Pa, even more preferably in the range of from 7 x 104to 6 x 105Pa.

[0036] The H2 partial pressure of the gas phase is preferably maintained by introducing H2 into the gas phase. Also, the H2 partial pressure of the gas phase is preferably maintained by relaxation of the gas phase.

[0037] “Maintaining” the H2 partial pressure of the gas phase in the sense of the present invention includes ensuring that the H2 partial pressure is within the desired range during the reaction. In case the H2 partial pressure is within the desired range, no active steps have to be carried out mandatorily, but the pressure may still be adjusted to a different part of the range if desired. However, in order to ensure that the H2 partial pressure is neither too high nor too low, the H2 partial pressure may preferably be adjusted, or must be adjusted in case of ensuring that the H2 partial pressure is maintained within the desired range, for example by relaxation of the gas phase, in which case the H2 partial pressure may be reduced, or, alternatively, by introducing H2 into the gas phase, in which case the H2 partial pressure may be increased. Depending upon the H2 partial pressure during the reaction, one or even both of said alternatives may be carried out if desired to adjust the H2 partial pressure and to maintain the H2 partial pressure within the desired pressure range at all times during the reaction.

[0038] The pressure during the reaction can be monitored by, for example, determination of the overall pressure and comparison to the starting pressure. As hydrogen tends to build up during the reaction, the H2 partial pressure changes, e.g. increases, resulting in the pressure to increase over time. For example, by actively measuring and controlling the overall pressure during the reaction, it may be ensured that the H2 partial pressure is within the claimed range. If the overall pressure built up is too high, this tends to be at least in part the result of the H2 partial pressure increasing. By relaxation of the gas phase, hydrogen can be removed from the gas phase and the H2 partial pressure can be maintained in the desired range. Thus, in one preferred embodiment, the H2 partial pressure of the gas phase is preferably maintained in the respective range by monitoring the overall pressure of the reaction and adjusting the overall pressure if required, preferably by relaxation of the gas phase, in which case the H2 partial pressure may be reduced, or, alternatively, by introducing H2 into the gas phase, in which case the H2 partial pressure may be increased.

[0039] Alternatively, the hydrogen partial pressure can be determined by other means, such as taking samples of the gas phase during the reaction and analyzing same. As another alternative, the pressure may be monitored via online measurement, and adjusted accordingly as outlined above.

[0040] The process preferably further comprises recycling at least a part of the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor comprised in the mixture Me obtained according to (iv) to (ii) or (iii). It is also that the liquid mixture ME prepared according to (ii) further comprises a solvent. The solvent preferably has a boiling point of 110 °C or more, more preferably a boiling point of 140 °C or more, more preferably a boiling point of 160 °C or more, more preferably a boiling point of 180 °C or more, more preferably a boiling point of 190 °C or more.

[0041] The solvent preferably has a solubility in water at 25 °C of from 0 to 0.5 weight-%, preferably of from 0 to 0.1 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.05 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.01 weight-%, based on 100 weight- % water. Also, preferred is that a distribution coefficient of the catalyst in a system of the solvent and water is from 0 to 0.01 , more preferably from 0 to 0.005, more preferably from 0 to 0.005, based on 1 kg catalyst.

[0042] Preferably, the solvent is a mixture of at least two aromatic hydrocarbons with a boiling point of 180 °C or more. The solvent is preferably selected from the group consisting of biphenyl, diphenyl ether, 1-tert-butyl-3,5-dimethyl-benzene, ethylbenzene, cyclododecane, cyclononane, cyclooctane, cycloheptane, decaline, n-butylbutyrate, n-hexylhexyrate, n-octyloctyrate, texanole, di-n-butylether, di-iso-butylether, di-sec-butylether, and a mixture of two or more thereof, preferably from the group consisting of biphenyl, diphenyl ether, and a mixture thereof, wherein more preferably, the solvent is a mixture of biphenyl and diphenyl ether.

[0043] In a preferred embodiment, the solvent does not include any one of benzene, toluene, xylene or mesitylene.

[0044] Preferably, the solvent does not form an azeotrope with water. An azeotrope or a constant heating point mixture is a mixture of two or more components in fluidic states whose proportions cannot be altered or changed by simple distillation. This happens because when an azeotrope is boiled, the vapor has the same proportions of constituents as the unboiled mixture. Each azeotrope has a characteristic boiling point. It is not possible to separate the components by fractional distillation.

[0045] Furthermore, it is preferred that the solvent is a mixture of biphenyl and diphenyl ether, preferably wherein the solvent is a mixture of biphenyl and diphenyl ether at a molar ratio of biphenyl relative to diphenyl ether in the range of from 1 :2 to 1 :6, preferably in the range of from 1 :2.5 to 1 :4.

[0046] The alcohol conversion conditions according to (iii) preferably comprise an amount of the solvent in the reaction mixture MG in the range of from 5 to 50 weight-%, preferably in the range of from 5 to 30 weight-%, more preferably in the range of from 5 to 10 weight-%, based on the total weight of the reaction mixture MG.

[0047] In a further preferred embodiment, from 90 to 100 weight-%, more preferably from 95 to 100 weight-%, more preferably from 98 to 100 weight-%, more preferably from 99 to 100 weight-% of the liquid mixture ME prepared according to (ii) consist of the at least one alcohol R-CH2-CH2- OH, the base, the solvent and the at least one of a catalyst, a precursor thereof, or a reduced form of the catalyst or the precursor.

[0048] Preferably, the mixture Me obtained according to (iv) comprises the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor and further comprises the solvent. The process further preferably comprises recycling at least a part of the solvent comprised in the mixture Me obtained according to (iv) to (ii) or (iii).

[0049] The liquid reaction mixture MG obtained according to (iii) further preferably comprises at least one unreacted alcohol R-CH2-CH2-OH, the process further comprising separating at least a part of said unreacted alcohol R-CH2-CH2-OH from the liquid reaction mixture MG. Separating at least a part of the unreacted alcohol R-CH2-CH2-OH from MG is preferably carried out by distillation, extraction, flashing, or by employing a membrane. Preferably, at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii).

[0050] Preparing a liquid mixture ME in step (ii) preferably comprises at least one alcohol R-CH2-CH2- OH, a base, a solvent, and the at least one of a catalyst, or precursor thereof provided according to (i).

[0051] In formula (A) n is preferably 0 if R1, R2, R3and R4are hydrogen.

[0052] Preferably, at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (B) wherein

[0053] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0054] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0055] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0056] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0057] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-Cw-aryl; and C5-C10- heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0058] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH.

[0059] Also preferred is that the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (C) wherein

[0060] M is selected from the group consisting of Ir, Ru, and Mn;

[0061] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0062] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0063] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C - heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0064] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH.

[0065] It is moreover preferred that the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (D) wherein

[0066] M is selected from the group consisting of Ir, Ru, and Mn;

[0067] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0068] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene; Ra, Rb, Rcand Rd, are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and C5-C10- heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0069] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH.

[0070] M is preferably selected from the group consisting of Ir and Ru, and more preferably M is Ru.

[0071] M is preferably Ru, and the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 170 °C, preferably in the range of from 120 to 170 °C, more preferably in the range of from 120 to 160 °C, more preferably in the range of from 130 to 150 °C.

[0072] L3is preferably CO.

[0073] Preferably, L1and L2are each (PRaRb), and Raand Rbare Ci-Cw-alkyl, preferably wherein Raand Rbare each isopropyl or tert-butyl. Alternatively, L1and L2are each preferably (PRaRb), wherein Raand Rbare Ci-Cio-cycloalkyl, preferably wherein Raand Rbare each cyclohexyl. Alternatively, L1and L2are each preferably (PRaRb), and Raand Rbare Cs-C -aryl.

[0074] Y is preferably selected from the group consisting of F, Cl, Br, and I, more preferably Y is selected from the group consisting of Cl or Br, more preferably Y is Cl. It is also preferred that Y is CO.

[0075] Preferably, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E) wherein Cy is cyclohexyl.

[0076] Also preferred is that the reduced form of the catalyst comprises a compound of formula (E’) wherein Cy is cyclohexyl.

[0077] It is furthermore preferred that the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (F) wherein iPr is isopropyl.

[0078] Also preferred is that the reduced form of the catalyst comprises a compound of formula (F’) wherein iPr is isopropyl.

[0079] It is moreover preferred that the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (G) wherein tBu is tert-butyl.

[0080] Preferably, the reduced form of the catalyst comprises a compound of formula (G’) wherein tBu is tert-butyl.

[0081] The at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor preferably comprises a compound comprising a metal M selected from the group consisting of lrCI3x H2O, [lr(COD)CI]2, [lr(COE)2CI]2, [lr(C2H4)2CI]2, [lr(COD)OH]2, [lr(COD)MeO]2, [lrCp*CI2], [IrCp Cl2], lr4(CO)i2, [lr(PPh3)2(CO)CI], [lr(acetylacetonate)3], and [lr(acetylacetonate)(COD)], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, COE is cyclooctenyl, and methylallyl is 2-methylallyL Alternatively, at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of [Ru(p-cymene)CI2]2, [Ru(benzene)CI2]y, [Ru(CO)2CI2]y, where y is in each case in the range from 1 to 1000, [Ru(CO)3CI2]2, [Ru(COD)(allyl)], RuCI3x H2O, [Ru(acetylacetonate)3], [Ru(DMSO)4CI2], [Ru(cyclopentadienyl)(CO)2CI], [Ru(cyclopentadienyl)(CO)2H], [Ru(cyclopentadienyl)(CO)2]2, [Ru(Cp)(CO)2CI], [Ru(Cp*)(CO)2H], [Ru(Cp*)(CO)2]2, [Ru(indenyl)(CO)2CI], [Ru(indenyl)(CO)2H], [Ru(indenyl)(CO)2]2, ruthenocene, [RU(COD)CI2]2, [Ru(Cp*)(COD)CI], [RU3(CO)I2], [Ru(PPh3)4(H)2], [Ru(PPh3)3(CI)2], [Ru(PPh3)3(CO)(CI)2], [Ru(PPh3)3(CO)(CI)(H)J, [Ru(PPh3)3(CO)(H)2], and [Ru(cyclooctadienyl)(methylallyl)2], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, and methylallyl is 2-methylallyL

[0082] Preferably, the reduced form of the precursor comprises a compound of formula (P-l) or (P-ll): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroquinoline unit, a decahydroquinoline unit, a tetrahydroacridine unit, or a tetradecahydroacridine unit; and wherein L1and L2are, independently of each other, as defined above; wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0083] More preferred is that the reduced form of the precursor comprises a compound of formula (P-l): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroacridine unit, or a tetradecahydroacridine unit.

[0084] In another more preferred embodiment, the reduced form of the precursor comprises a compound of formula (P-ll): wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0085] Preferably, integer x is 1 or 2, more preferably x is 1 .

[0086] Preferably, R is selected from the group consisting of H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, preferably from the group consisting of H, methyl, ethyl, propyl, and isopropyl, more preferably from the group consisting of H, ethyl, and propyl, wherein more preferably R is H.

[0087] In a preferred embodiment, the liquid mixture ME prepared according to (ii) preferably further comprises a compound of formula (H’): wherein R1, R2, R3and R4’ L1, L2, and n are identical to R1, R2, R3and R4, L1, L2, and n of the catalyst of formula (A).

[0088] In the liquid mixture ME prepared according to (ii) and subjected to alcohol version conditions according to (iii), the molar ratio of the compound of formula (H) relative to the compound of formula (A) is in a range of from 0.01 :1 to 10:1 , preferably in the range of from 0.05:1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.3:1 to 10:1 , more preferably in the range of from 0.5:1 to 10:1 , more preferably in the range of from 0.7:1 to 10:1 , more preferably in the range of from 0.8:1 to 10:1 , more preferably in the range of from 1 :1 to 10:1 more preferably in the range of from 1.01 :1 to 10:1 , more preferably in the range of from 1.02:1 to 8:1 , more preferably in the range from 1 .03:1 to 7:1 , more preferably in the range from 1 .04:1 to 6:1 , and more preferably in the range from 1 .05: 1 to 5: 1 .

[0089] Preferably, the compound of formula (H) is selected from the group consisting of dicyclohexyl- [[5-(dicyclohexylphosphanylmethyl)acridin-4-yl]methyl]phosphane, diisopropyl-[[5- (diisopropylphosphanylmethyl)acridin-4-yl]methyl]phosphane, dicyclohexyl-[[5- (dicyclohexylphosphanylmethyl)pyridin-4-yl]methyl]phosphane and diisopropyl-[[5- (diisopropylphosphanylmethyl)pyridin-4-yl]methyl]phosphane, preferably wherein the compound of formula (H) is cyclohexyl-[[5-(dicyclohexylphosphanylmethyl)acridin-4-yl]methyl]phosphane or diisopropyl-[[5-(diisopropylphosphanylmethyl)acridin-4-yl]methyl]phosphane.

[0090] Preferably, the base is selected from the group consisting of alkali hydroxides, alkali alkoxides, and a mixture thereof. The alkali hydroxide is preferably selected from the group consisting of NaOH, KOH, and a mixture thereof, preferably wherein the alkali hydroxide is KOH. The alkali alkoxide is preferably selected from the group consisting of sodium alkoxides, potassium alkoxides, and a mixture thereof, preferably from the group consisting of sodium ethoxide, potassium ethoxide, and a mixture thereof.

[0091] The at least one alcohol R-CH2-CH2-OH is preferably a bio-based alcohol, preferably obtainable or obtained from sugar-containing crops, preferably from one or more of sugar cane and corn.

[0092] In the process in accordance with the present invention, the reaction space SR is comprised in a reactor vessel, wherein the reactor vessel is preferably a complete-mixing reactor vessel.

[0093] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0094] 1 . An alcohol conversion process, comprising

[0095] (i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor; (ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, and the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor, R being selected from the group consisting of H and Ci-C4-alkyl;

[0096] (iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SR and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the reaction space comprises the reaction mixture MG and a gas phase, wherein said alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SR in the range of from 1 x 105to 4 x 106Pa, wherein said gas phase comprises H2 and the alcohol conversion conditions further comprise maintaining the H2 partial pressure of the gas phase in the range of from 2 x 104to 1 .1 x 106Pa;

[0097] (iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CH R-CH2)X-OH and a mixture Me comprising the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor; wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; wherein the catalyst comprises a compound of formula (A) wherein

[0098] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0099] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures: L3is selected from the group consisting of CO, PRaRbRc, AsRaRbRc, SbRaRbRc, SRaRb, RdCN, RdNC, N2, PF3, pyridine, and thiophene;

[0100] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;

[0101] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, OH, OR, NRd2, NH3, NRd3, and Rd2NSO2Rd;

[0102] Ra, Rb, Rc, Rd, R5, R6and R7are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2 and Ci-C - alkyl; and

[0103] X is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-C -alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cw-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H)

[0104] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0105] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures:

[0106] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;

[0107] Ra, Rb, Rc, Rd, R5, R6and R7, are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2 and C1-C10- alkyl;

[0108] X is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-C -alkyl.

[0109] 2. The process of embodiment 1 , wherein the process is a continuous process.

[0110] 3. The process of embodiment 1 , wherein the process is a semi-batch process or a batch process.

[0111] 4. The process of any one of embodiments 1 to 3, wherein the alcohol conversion conditions according to (iii) comprise the presence of at least one inert gas in the reaction space SR, wherein the at least one inert gas is preferably selected from the group consisting of nitrogen, argon, and a mixture thereof.

[0112] 5. The process of any one of embodiments 1 to 4, wherein the alcohol conversion conditions according to (iii) comprise a pressure in the reaction space SR in the range of from 1 x 105to 3.5 x 106Pa, preferably in the range of from 1 x 105to 3.1 x 106Pa, more preferably in the range in the range of from 1 x 105to 2 x 106Pa, more preferably in the range in the range from 1 x 105to 1 .5 x 106Pa. The process of any one of embodiments 1 to 5, wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 200 °C, preferably in the range of from 120 to 180 °C, more preferably in the range of from 130 to 160 °C. The process of any one of embodiments 1 to 6, wherein the alcohol conversion conditions according to (iii) comprise an amount of the base in the reaction mixture MG in the range of from 0.1 to 10 weight-%, preferably in the range of from 0.5 to 8 weight-%, more preferably in the range of from 1 to 5 weight-%, based on the total weight of the reaction mixture MG. The process of any one of embodiments 1 to 7, wherein the alcohol conversion conditions according to (iii) comprise an amount of the catalyst in the reaction mixture MG in the range of from 0.001 to 2 weight-%, preferably in the range of from 0.001 to 1 weight-%, more preferably in the range of from 0.001 to 0.5 weight-%, based on the total weight of the reaction mixture MG. The process of any one of embodiments 1 to 8, wherein according to (ii), the H2 partial pressure of the gas phase in the reaction space SR is maintained in the range of from 2 x 104to 3.1 x 106Pa, preferably in the range of from 2 x 104to 1 .1 x 106Pa, more preferably in the range of from 2 x 104to 6 x 105Pa. The process of any one of embodiments 1 to 9, wherein the H2 partial pressure of the gas phase is maintained by introducing H2 into the gas phase. The process of any one of embodiments 1 to 9, wherein the H2 partial pressure of the gas phase is maintained by relaxation of the gas phase. The process of any one of claims 1 to 11 , wherein the H2 partial pressure of the gas phase is maintained by monitoring the overall pressure during the reaction, preferably by monitoring and, if required, adjusting the overall pressure of the gas phase, more preferably by adjusting the overall pressure of the gas phase by relaxation of the gas phase and / or by introducing H2 into the gas phase. The process of any one of claims 1 to 11 , wherein the H2 partial pressure of the gas phase is maintained by taking samples of the gas phase during the reaction and analyzing same, and, if required, by preferably adjusting the overall pressure of the gas phase, more preferably by adjusting the overall pressure of the gas phase by relaxation of the gas phase and / or by introducing H2 into the gas phase. The process of any one of embodiments 1 to 13, further comprising recycling at least a part of the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor comprised in the mixture Me obtained according to (iv) to (ii) or (iii). 15. The process of any one of embodiments 1 to 14, wherein the liquid mixture ME prepared according to (ii) further comprises a solvent.

[0113] 16. The process of embodiment 15, wherein the solvent has a boiling point of 110 °C or more, preferably a boiling point of 140 °C or more, more preferably a boiling point of 160 °C or more, more preferably a boiling point of 180 °C or more, more preferably a boiling point of 190 °C or more.

[0114] 17. The process of embodiment 15 or 16, wherein the solvent has a solubility in water at 25 °C of from 0 to 0.5 weight-%, preferably of from 0 to 0.1 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.05 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.01 weight-%, based on 100 weight-% water.

[0115] 18. The process of any one of embodiments 15 to 17, wherein a distribution coefficient of the catalyst in a system of the solvent and water is from 0 to 0.01 , preferably from 0 to 0.005, more preferably from 0 to 0.005, based on 1 kg catalyst.

[0116] 19. The process of any one of embodiments 15 to 18, wherein the solvent is a mixture of at least two aromatic hydrocarbons with a boiling point of 180 °C or more.

[0117] 20. The process of embodiments 15 to 19, wherein the solvent is selected from the group consisting of biphenyl, diphenyl ether, 1-tert-butyl-3,5-dimethyl-benzene, ethylbenzene, cyclododecane, cyclononane, cyclooctane, cycloheptane, decaline, n-butylbutyrate, n- hexylhexyrate, n-octyloctyrate, texanole, di-n-butylether, di-iso-butylether, di-sec- butylether, and a mixture of two or more thereof, preferably from the group consisting of biphenyl, diphenyl ether, and a mixture thereof, wherein more preferably, the solvent is a mixture of biphenyl and diphenyl ether.

[0118] 21 . The process of any one of embodiments 15 to 20, wherein the solvent is a mixture of biphenyl and diphenyl ether, preferably wherein the solvent is a mixture of biphenyl and diphenyl ether at a molar ratio of biphenyl relative to diphenyl ether in the range of from 1 :2 to 1 :6, preferably in the range of from 1 :2.5 to 1 :4.

[0119] 22. The process of any one of embodiments 15 to 21 , wherein the solvent does not form an azeotrope with water.

[0120] 23. The process of any one of embodiments 15 to 22, wherein the solvent does not include any one of benzene, toluene, xylene or mesitylene.

[0121] 24. The process of any one of embodiments 15 to 23, wherein the alcohol conversion conditions according to (iii) comprise an amount of the solvent in the reaction mixture MG in the range of from 5 to 50 weight-%, preferably in the range of from 5 to 30 weight-%, more preferably in the range of from 5 to 10 weight-%, based on the total weight of the reaction mixture MG. The process of any one of embodiments 15 to 24, wherein from 90 to 100 weight-%, preferably from 95 to 100 weight-%, more preferably from 98 to 100 weight-%, more preferably from 99 to 100 weight-% of the liquid mixture ME prepared according to (ii) consist of the at least one alcohol R-CH2-CH2-OH, the base, the solvent and the at least one of a catalyst, a precursor thereof, or a reduced form of the catalyst or the precursor. The process of any one of embodiments 15 to 25, wherein the mixture Me obtained according to (iv) comprises the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor and further comprises the solvent. The process of embodiment 26, further comprising recycling at least a part of the solvent comprised in the mixture Me obtained according to (iv) to (ii) or (iii). The process of any one of embodiments 1 to 27, wherein the liquid reaction mixture MG obtained according to (iii) further comprises at least one unreacted alcohol R-CH2-CH2- OH, the process further comprising separating at least a part of said unreacted alcohol R- CH2-CH2-OH from the liquid reaction mixture MG. The process of embodiment 28, wherein separating at least a part of the unreacted alcohol R-CH2-CH2-OH from MG is carried out by distillation, extraction, flashing, or by employing a membrane. The process of embodiment 28 or 29, wherein at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii). The process of any one of embodiments 1 to 30, wherein preparing a liquid mixture ME in step (ii) comprises at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, or precursor thereof provided according to (i). The process of any one of embodiments 1 to 31 , wherein in formula (A) n is 0 if R1, R2, R3and R4are hydrogen. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (B) wherein

[0122] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0123] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0124] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0125] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0126] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and C5-C10- heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0127] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (C) wherein

[0128] M is selected from the group consisting of Ir, Ru, and Mn;

[0129] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0130] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0131] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-C -alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C C -alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and C5-C10- heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0132] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula wherein

[0133] M is selected from the group consisting of Ir, Ru, and Mn;

[0134] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0135] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0136] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-C -cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C - heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0137] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH. The process of any one of embodiments 1 to 35, wherein M is selected from the group consisting of Ir and Ru, preferably wherein M is Ru. The process of any one of embodiments 1 to 36, wherein M is Ru, and wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 170 °C, preferably in the range of from 120 to 1700C, more preferably in the range of from 120 to 160 °C, more preferably in the range of from 130 to 150 °C. The process of any one of embodiments 1 to 37, wherein L3is CO. 39. The process of any one of embodiments 1 to 38, wherein L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cio-alkyl, preferably wherein Raand Rbare each isopropyl or tert-butyl.

[0138] 40. The process of any one of embodiments 1 to 38, wherein L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cio-cycloalkyl, preferably wherein Raand Rbare each cyclohexyl.

[0139] 41 . The process of any one of embodiments 1 to 38, wherein L1and L2are each (PRaRb), and wherein Raand Rbare Cs-C -aryl.

[0140] 42. The process of any one of embodiments 1 to 41 , wherein Y is selected from the group consisting of F, Cl, Br, and I, preferably wherein Y is selected from the group consisting of Cl or Br, more preferably wherein Y is Cl.

[0141] 43. The process of any one of embodiments 1 to 41 , wherein Y is CO.

[0142] 44. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E) wherein Cy is cyclohexyl.

[0143] 45. The process of any one of embodiments 1 to 31 , wherein the reduced form of the catalyst comprises a compound of formula (E’) wherein Cy is cyclohexyl. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (F) wherein iPr is isopropyl. The process of any one of embodiments 1 to 31 , wherein the reduced form of the catalyst comprises a compound of formula (F’) wherein iPr is isopropyl. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (G) wherein tBu is tert-butyl. The process of any one of embodiments 1 to 31 , wherein the reduced form of the catalyst comprises a compound of formula (G’) wherein tBu is tert-butyl. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of I rCh x H2O, [lr(COD)CI]2, [lr(COE)2CI]2, [lr(C2H4)2CI]2, [lr(COD)OH]2, [lr(COD)MeO]2, [lrCp*CI2], [IrCp Cl2], lr4(CO)i2, [lr(PPh3)2(CO)CI], [lr(acetylacetonate)3], and [lr(acetylacetonate)(COD)], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, COE is cyclooctenyl, and methylallyl is 2-methylallyl. The process of any one of embodiments 1 to 31 , wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of [Ru(p- cymene)CI2]2, [Ru(benzene)CI2]y, [Ru(CO)2CI2]y, where y is in each case in the range from 1 to 1000, [RU(CO)3CI2]2, [Ru(COD)(allyl)], RuCh x H2O, [Ru(acetylacetonate)3], [Ru(DMSO)4CI2], [Ru(cyclopentadienyl)(CO)2CI], [Ru(cyclopentadienyl)(CO)2H], [Ru(cyclopentadienyl)(CO)2]2, [Ru(Cp)(CO)2CI], [Ru(Cp*)(CO)2H], [Ru(Cp*)(CO)2]2, [Ru(indenyl)(CO)2CI], [Ru(indenyl)(CO)2H], [Ru(indenyl)(CO)2]2, ruthenocene, [RU(COD)CI2]2, [Ru(Cp*)(COD)CI], [RU3(CO)I2], [Ru(PPh3)4(H)2], [Ru(PPh3)3(CI)2], [Ru(PPh3)3(CO)(CI)2], [Ru(PPh3)3(CO)(CI)(H)], [Ru(PPh3)3(CO)(H)2], and [Ru(cyclooctadienyl)(methylallyl)2], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, and methylallyl is 2-methylallyl. The process of any one of embodiments 1 to 51 , wherein the reduced form of the precursor comprises a compound of formula (P-l) or (P-l I): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroquinoline unit, a decahydroquinoline unit, a tetrahydroacridine unit, or a tetradecahydroacridine unit; and wherein L1and L2are, independently of each other, as defined above; -ll) wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above. 53. The process of any one of embodiments 1 to 52, wherein the reduced form of the precursor comprises a compound of formula (P-l): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroacridine unit, or a tetradecahydroacridine unit.

[0144] 54. The process of any one of embodiments 1 to 53, wherein the reduced form of the precursor comprises a compound of formula (P-l I): wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0145] 55. The process of any one of embodiments 1 to 54, wherein integer x is 1 or 2, preferably wherein integer x is 1 .

[0146] 56. The process of any one of embodiments 1 to 55, wherein R is selected from the group consisting of H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, preferably from the group consisting of H, methyl, ethyl, propyl, and isopropyl, more preferably from the group consisting of H, ethyl, and propyl, wherein more preferably R is H.

[0147] 57. The process of any one of embodiments 1 to 56, wherein the liquid mixture ME prepared according to (ii) further comprises a compound of formula (H’): wherein R1, R2, R3and R4, L1, L2, and n are identical to R1, R2, R3and R4’ L1, L2, and n of the catalyst of formula (A).

[0148] 58. The process of embodiment 57, wherein in the liquid mixture ME prepared according to (ii) and subjected to alcohol version conditions according to (iii), the molar ratio of the compound of formula (H) relative to the compound of formula (A) is in a range of from 0.01 :1 to 10:1 , preferably in the range of from 0.05:1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.3:1 to 10:1 , more preferably in the range of from 0.5:1 to 10:1 , more preferably in the range of from 0.7:1 to 10:1 , more preferably in the range of from 0.8:1 to 10:1 , more preferably in the range of from 1 :1 to 10:1 more preferably in the range of from 1.01 :1 to 10:1 , more preferably in the range of from 1.02:1 to 8:1 , more preferably in the range from 1.03:1 to 7:1 , more preferably in the range from 1.04:1 to 6:1 , and more preferably in the range from 1 .05:1 to 5:1 .

[0149] 59. The process of embodiment 57 or 58, wherein the compound of formula (H) is selected from the group consisting of dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)acridin-4- yl]methyl]phosphane, diisopropyl-[[5-(diisopropylphosphanylmethyl)acridin-4- yl]methyl]phosphane, dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)pyridin-4- yl]methyl]phosphane and diisopropyl-[[5-(diisopropylphosphanylmethyl)pyridin-4- yl]methyl]phosphane, preferably wherein the compound of formula (H) is cyclohexyl-[[5- (dicyclohexylphosphanylmethyl)acridin-4-yl]methyl]phosphane or diisopropyl-[[5- (diisopropylphosphanylmethyl)acridin-4-yl]methyl]phosphane.

[0150] 60. The process of any one of embodiments 1 to 59, wherein the base is selected from the group consisting of alkali hydroxides, alkali alkoxides, and a mixture thereof.

[0151] 61 . The process of embodiment 60, wherein the alkali hydroxide is selected from the group consisting of NaOH, KOH, and a mixture thereof, preferably wherein the alkali hydroxide is KOH.

[0152] 62. The process of embodiment 61 , wherein the alkali alkoxide is selected from the group consisting of sodium alkoxides, potassium alkoxides, and a mixture thereof, preferably from the group consisting of sodium ethoxide, potassium ethoxide, and a mixture thereof.

[0153] 63. The process of any one of embodiments 1 to 62, wherein the at least one alcohol R-CH2- CH2-OH is a bio-based alcohol, preferably obtainable or obtained from sugar-containing crops, preferably from one or more of sugar cane and corn.

[0154] 64. The process of any one of embodiments 1 to 63, wherein the reaction space SR is comprised in a reactor vessel, wherein the reactor vessel is preferably a complete-mixing reactor vessel.

[0155] The present invention is further illustrated by the following examples, which are set forth to illustrate certain aspects of the present invention and are not to be construed as limiting thereof.

[0156] Examples The determination of the distribution coefficient of the solvent in water comprises the following steps:

[0157] 1 . combining the two components, e.g. feed and solvent, in a predefined solvent ratio;

[0158] 2. turbulent mixing of the combined components over a longer period of time (> 10 min) at a defined extraction temperature;

[0159] 3. allowing for phase separation;

[0160] 4. taking samples of each phase at the extraction temperature;

[0161] 5. centrifuging the samples and withdrawing clear samples at the extraction temperature;

[0162] 6. analyzing the samples; and

[0163] 7. comparing the results of extract- and raffinate - calculation of the partition equilibrium / partition coefficient at the selected temperature.

[0164] Example 1

[0165] 137.5 g ethanol, 251.5 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%), and 10.11 g potassium ethoxide (4 mol%) were weighed in a glovebox and poured into a 300 mL autoclave. The stirrer was switched to 700 rpm. The reaction mixture was afterwards heated to 150°C and stirred for 6 h at autogenous pressure. After cooling down the reaction solution to room temperature, the autoclave was depressurized pre-shift. The autoclave was removed under air. An aliquot of the orange-brownish solution with little dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%), and then analyzed by GC.

[0166] Example 2

[0167] 69 g ethanol, 125.8 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%), and 5.06 g potassium ethoxide (4 mol%) were weighed in a glovebox and poured into a 300 mL autoclave. The stirrer was switched to 700 rpm. The reaction mixture was afterwards heated to 150°C and stirred for 6 h at autogenous pressure. After cooling down the reaction solution to room temperature, the autoclave was depressurized pre-shift. The autoclave was removed under air. An aliquot of the orange-brownish solution with little dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%), and then analyzed by GC.

[0168] Example 3

[0169] 34.4 g ethanol, 62.9 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%), and 2.53 g potassium ethoxide (4 mol%) were weighed in a glovebox and poured into a 300 mL autoclave. The stirrer was switched to 700 rpm. The reaction mixture was afterwards heated to 150°C and stirred for 6 h at autogenous pressure. After cooling down the reaction solution to room temperature, the autoclave was depressurized pre-shift. The autoclave was removed under air. An aliquot of the orange-brownish solution with little dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%), and then analyzed by GC.

[0170] Example 4

[0171] 17.2 g ethanol, 31.5 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%), and 1.27 g potassium ethoxide (4 mol%) were weighed in a glovebox and poured into a 300 mL autoclave. The stirrer was switched to 700 rpm. The reaction mixture was afterwards heated to 150°C and stirred for 6 h at autogenous pressure. After cooling down the reaction solution to room temperature, the autoclave was depressurized pre-shift. The autoclave was removed under air. An aliquot of the orange-brownish solution with little dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%), and then analyzed by GC.

[0172] Table 1

[0173] Influence of the reactor volume I hydrogen partial pressure on the conversion. Conversion determined to the major products up to C8 alcohols. Selectivies are listed as the selectivities between those major products.

[0174] As may be seen from Table 1 , the yield of (side) products quantified by GC increases when the ratio of liquid reaction volume to autoclave volume decreases I the overpressure decreases: 62 % liquid reaction volume results in 16.0 % conversion while 30 % liquid reaction volume results 25.0 % conversion.

[0175] Example 5

[0176] 70.09 g ethanol, 3.80 g potassium ethoxide (3 mol%), 172.6 mg (Cy-Acr-PNP)RuHCI(CO) (0.015 mol%), and 135.2 mg Cy-Acr-PNP (0.015 mol%) were weighed into a screw thread bottle and stirred overnight at room temperature. The reactant suspension was poured into an autoclave using a syringe in the countercurrent flow of nitrogen, and the screw-threaded bottle was rinsed with ethanol. 7.71 g of a mixture of diphenyl and diphenyl ether in a molar ratio of 1 :3 as a solvent was added last. The reaction mixture was heated to 150 °C for about 15 min with the outlet valve closed at 85% heating power with 750 rpm stirring. The overpressure, e.g., the pressure above atmospheric pressure, was maintained at about 10 bar during the reaction by measuring the overpressure and relaxation of the gas phase when necessary.

[0177] After reaching the reaction temperature of 150 °C, a "zero sample" was taken. Filtered through a 2 pm syringe filter, the sample was spiked with the internal standard 1 ,4-dioxane and analyzed by GC. Further samples were taken after 1 , 2, 3, 6 and 24 h and processed / analyzed analogously.

[0178] Example 6

[0179] Example 6 was carried out in accordance with Example 5, but the overpressure was not kept at 10 bar throughout the reaction, instead the reaction was performed under intrinsic pressure.

[0180] Example 7

[0181] Example 7 was carried out in accordance with Example 5, but the overpressure was not kept at 10 bar throughout the reaction, instead the overpressure was maintained at about 12 bar during the reaction.

[0182] Example 8

[0183] Example 8 was carried out in accordance with Example 5, but the overpressure was not kept at 10 bar throughout the reaction, instead the overpressure was maintained at about 14 bar during the reaction.

[0184] Comparative Example 1

[0185] Comparative Example 1 was carried out in accordance with Example 5, but 10 bar H2 was pressed on before heating and the reaction was carried out under inherent pressure.

[0186] As can be seen from the results illustrated in Figure 1 , higher conversions are obtained in the experiment with 10 bar pressurization than in the experiment under intrinsic pressure (Example 5 vs. Example 6). The low hydrogen partial pressure allows higher conversions in Example 5 compared to Example 6.

[0187] When the reaction is carried out under hydrogen pressure, the conversions decrease further (Comparative Example 1 ).

[0188] Figure 2 illustrates the results of the reactions performed under inherent pressure and under different overpressures, in which the pressure was kept constant (overpressure of 10 bar, 12 bar and 14 bar, respectively). When the experiment was performed at isobaric conditions under otherwise identical conditions, an increase in conversion from 37 to 41 to 47% was observed after 6 h, when the overpressure was adjusted from (and maintained at ) 14 to 12 to 10 bar, respectively. Thus, the reduction of hydrogen partial pressure in the isobaric reactions compared to reactions performed under inherent pressure results in increased conversion, illustrating that ideally, the H2 partial pressure should be maintained (and preferably actively controlled) within a certain pressure range for optimal conditions and results.

[0189] Figure 3 illustrates the overpressure versus time for Example 5, Example 6, and Comparative Example 1. As may be taken from Figure 3, for Example 5, the overpressure was actively controlled, as is also slightly evident by the curve at the beginning showing slight ups and downs which are derived from the relaxation of the gas phase. Example 6 was performed under inherent pressure while Comparative Example 1 , 10 bar H2 was initially pressed on. Figure 3 also shows that ideally, the H2 partial pressure should be maintained (and preferably actively controlled) within a certain pressure range for optimal conditions and results.

[0190] Example 9

[0191] 69 g ethanol, 125.8 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%), and 5.06 g potassium ethoxide (4 mol%) were weighed in a glovebox and poured into a 300 mL autoclave. The stirrer was switched to 700 rpm. The reaction mixture was afterwards heated to 150°C and stirred for 12 h at autogenous pressure. After cooling down the reaction solution to room temperature, the autoclave was depressurized pre-shift. The autoclave was removed under air. An aliquot of the orange-brownish solution with little dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%), and then analyzed by GC.

[0192] Example 10

[0193] An autoclave was filled with 69 g ethanol, 125.8 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%) and 5.06 g potassium ethanol (4 mol%) in a glovebox. The stirrer was set to 700 rpm and the reaction mixture was heated to 150 °C. The reaction mixture was kept under autogenous pressure for 6 h and then cooled to room temperature. The autoclave was carefully depressurized. Then, 10 bar of H2 was injected and the reaction mixture was stirred for 1 h at 100 °C. After the autoclave was carefully depressurized, the reaction mixture was then heated again to 150 °C and stirred for another 6 h under autogenous pressure. The autoclave was cooled to room temperature, and carefully depressurized and removed under air. An aliquot of the orange-brown solution with dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%) and then analyzed by GC.

[0194] Example 11

[0195] An autoclave was filled with 69 g ethanol, 125.8 mg (Cy-Acr-PNP)RuHCI(CO) (0.01 mol%) and 5.06 g potassium ethanol (4 mol%) in a glovebox. The stirrer was set to 700 rpm and the reaction mixture was heated to 150 °C. The reaction mixture was kept under autogenous pressure for 6 h and then cooled to room temperature. The autoclave was carefully depressurized. The reaction mixture was then heated again to 150 °C and stirred for another 6 h under autogenous pressure. After the autoclave cooled to room temperature, the autoclave was carefully depressurized and removed under air. An aliquot of the orange-brown solution with dark brown solid was filtered, mixed with the internal standard 1 ,4-dioxane (20 wt%) and then analyzed by GC.

[0196] Table 3

[0197] Conversion determined to the major products up to C8 alcohols. Selectivies are listed as the selectivities between those major products.

[0198] In the case of Example 2 and Example 9, it was observed that the reaction did not lead to any further conversion after 6 h, however, relaxing the gas phase (Example 10 / 11 ) improved the conversion even after 6 h. This result illustrates that hydrogen accumulates in the gas phase and deactivates the catalyst.

[0199] Cited literature:

[0200] M. Guerbet, C. R. Hebd. Seances Acad. Sci. 1899, 128, p. 511-513

[0201] - Y.Xie et aL, “Highly efficient Process for Production of Biofuel from ethanol Catalyzed by Ruthenium Pincer Complexes”, Journal of the American Society, vol. 138, no. 29, 2016- 07-18, pages 9077 to 9080

[0202] - WO 2012 / 119928 A1

[0203] - WO 2013 / 156399 A1

Claims

Claims1 . An alcohol conversion process, comprising(i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor;(ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, and the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor, R being selected from the group consisting of H and Ci-C4-alkyl;(iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SR and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the reaction space comprises the reaction mixture MG and a gas phase, wherein said alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SR in the range of from 1 x 105to 4 x 106Pa, wherein said gas phase comprises H2 and the alcohol conversion conditions further comprise maintaining the H2 partial pressure of the gas phase in the range of from 2 x 104to 1 .1 x 106Pa;(iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CH R-CH2)X-OH and a mixture Me comprising the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor; wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; wherein the catalyst comprises a compound of formula (A)whereinM is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures:L3is selected from the group consisting of CO, PRaRbRc, AsRaRbRc, SbRaRbRc, SRaRb, RdCN, RdNC, N2, PF3, pyridine, and thiophene;R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, OH, OR, NRd2, NH3, NRd3, and Rd2NSO2Rd;Ra, Rb, Rc, Rd, R5, R6and R7are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2 and Ci-C - alkyl; andX is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-C -alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cw-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H)M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;L1and L2, are, independently of each other, PRaRb, NRaRb, SRa, SH, S(=O)Ra, heteroaryl containing at least one heteroatom selected from nitrogen and sulfur, AsRaRb, SbRaRb, and a N-heterocyclic carbene represented by the structures:R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit, or R1and R2or R3and R4form together with the pyridyl unit of the catalyst of formula (A) a quinolinyl unit; n is 0 or 1 ;Ra, Rb, Rc, Rd, R5, R6and R7are, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cio-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-C -cycloalkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted C5-C10- aryl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; and unsubstituted or substituted Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2 and C1-C10- alkyl;X is selected from the group consisting of one, two, three, four, five, six, and seven substituents positioned at any carbon atom on the acridinyl unit, or one, two, three, four and five substituents positioned at any carbon atom on the quinolinyl unit, or one substituent positioned at the carbon atom on the pyridyl unit, wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-C -alkyl.

2. The process of claim 1 , wherein according to (ii), the H2 partial pressure of the gas phase in the reaction space SR is maintained in the range of from 2 x 104to 6 x 105Pa.

3. The process of claim 1 or 2, wherein the H2 partial pressure of the gas phase is maintained by introducing H2 into the gas phase.

4. The process of claim 1 or 2, wherein the H2 partial pressure of the gas phase is maintained by relaxation of the gas phase.

5. The process of any one of claims 1 to 4, further comprising recycling at least a part of the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor comprised in the mixture Me obtained according to (iv) to (ii) or (iii).

6. The process of any one of claims 1 to 5, wherein the liquid mixture ME prepared according to (ii) further comprises a solvent, wherein the solvent has a boiling point of 110 °C or more.

7. The process of claim 6, further comprising recycling at least a part of the solvent comprised in the mixture Me obtained according to (iv) to (ii) or (iii).

8. The process of any one of claims 1 to 7, wherein the liquid reaction mixture MG obtained according to (iii) further comprises at least one unreacted alcohol R-CH2-CH2-OH, the process further comprising separating at least a part of said unreacted alcohol R-CH2- CH2-OH from the liquid reaction mixture MG, and wherein at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii).

9. The process of any one of claims 1 to 8, wherein M is Ru, and wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 170 °C.

10. The process of any one of claims 1 to 9, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E)wherein Cy is cyclohexyl.11 . The process of any one of claims 1 to 9, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (F)wherein iPr is isopropyl.

12. The process of any one of claims 1 to 9, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (G)wherein tBu is tert-butyl.

13. The process of any one of claims 1 to 12, wherein integer x is 1 .

14. The process of any one of claims 1 to 13, wherein R is selected from the group consisting of H, ethyl, and propyl.

15. The process of any one of claims 1 to 14, wherein the liquid mixture ME prepared according to (ii) further comprises a compound of formula (H’):wherein R1, R2, R3and R4’ L1, L2, and n are identical to R1, R2, R3and R4, L1, L2, and n of the catalyst of formula (A).

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