Subscriber access provided by ALBRIGHT COLLEGE
Article
Approaching Bulk Chemical Nitriles from Alkenes: A Hydrogen CyanideFree Approach through Combination of Hydroformylation and Biocatalysis Carmen Plass, Alessa Hinzmann, Michael Terhorst, Waldemar Brauer, Keiko Oike, Hilmi Yavuzer, Yasuhisa Asano, Andreas Vorholt, Tobias Betke, and Harald Gröger ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b05062 • Publication Date (Web): 29 Mar 2019 Downloaded from http://pubs.acs.org on March 29, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Approaching Bulk Chemical Nitriles from Alkenes: A Hydrogen Cyanide-Free Approach through Combination of Hydroformylation and Biocatalysis Carmen Plass†, Alessa Hinzmann†, Michael Terhorst||, Waldemar Brauer†, Keiko Oike†, Hilmi Yavuzer†, Yasuhisa Asano§, Andreas J. Vorholt‡, Tobias Betke†, Harald Gröger*,†
† Chair
of Industrial Organic Chemistry and Biotechnology, Faculty of Chemistry, Bielefeld
University, Universitätsstraße 25, 33615 Bielefeld, Germany.
§ Biotechnology
Research Center, Toyama Prefectural University, 5180 Kurokawa, Imizu,
Toyama 939-0398, Japan.
|| Chair
of Technical Chemistry, Faculty of Bio- and Chemistry Engineering, Technical
University Dortmund, Emil-Figge-Straße 66, 44227 Dortmund, Germany.
‡
Department of Molecular Catalysis, Group Multiphase Catalysis, MPI for Chemical Energy
Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 27
ABSTRACT
A current challenge in catalysis is the development of methodologies for the production of bulk chemicals needed on multi-ten/hundred-thousands of tons per year with the requirement to be produced at very low costs often being in the single-digit US-$ range. At the same time such methodologies should address challenges raised by current manufacturing processes. Within this research area, a cyanide-free approach towards aliphatic nitriles used as industrial bulk chemicals was developed starting from readily accessible n-alkenes as starting materials available in bulk quantities. This chemoenzymatic process concept is exemplified for the synthesis of nonanenitrile (as an n-/iso-mixture) and runs in water at low to moderate temperatures without the need for any types of cyanide sources. The process is based on a combination of a metal-catalyzed hydroformylation as the world-leading production technology for alkyl aldehydes with an emerging enzyme technology, namely the recently developed transformation of aldoximes into nitriles through dehydration by means of aldoxime dehydratases. As a missing link an efficient aldoxime formation with subsequent removal of a slight excess of hydroxylamine as enzyme-deactivating component was found, which enabled to merge these three steps hydroformylation, aldoxime formation and enzymatic dehydration towards a nitrile synthesis without the need for purification of intermediates. ACS Paragon Plus Environment
Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Keywords: Aldoxime dehydratases, Aldehydes, Biocatalysis, Hydroformylation, Nitriles
ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 27
INTRODUCTION
Nitriles belong to the most important product classes within the product tree of industrial chemicals.[1] Besides structurally complex stereoisomers of nitriles in the field of pharmaceuticals,[2] linear or branched alkyl nitriles play an important role in the field of specialty and bulk chemicals, which are needed on multi-ten/hundred-thousands of tons per year with the requirement to be produced at very low costs often being in the single-digit US-$ range.[1,3] Prominent examples of bulk nitrile chemicals include n-hexanenitrile, n-nonanenitrile or higher homologues thereof. Such long-chain alkyl nitriles find, e.g., utilizations as solvents and serve as intermediates for amines in the surfactant area.[4] More recently, the application as a jet fuel was reported as a further future option for utilization of representatives of this product class.[5] Today, three major synthetic approaches are known which, however, all raise challenges for improvement.[1-7] As for an organic chemist introducing a nitrile moiety into an organic framework is often carried out through substitution or addition reactions with hydrogen cyanide or cyanides, this popular method has been widely used also for alkyl nitrile synthesis, in particular on lab scale.[5] A severe drawback, however, is the need for stoichiometric amounts of highly toxic cyanide although established processes on large scale exist. Further matured technologies on ACS Paragon Plus Environment
Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
industrial scale are the ammoxidation,[6] as well as amide hydrogenation.[4] Although applied successfully since decades, limitations are the high required temperatures, which causes a high energy demand and raises selectivity concerns (Scheme 1).
existing approaches - ammoxidation - amide hydrogenation - cyanide chemistry (addition/substitution)
long-chain n-alkyl nitriles N H 3C n
n>1
selected applications - solvents - surfactants (as amine derivatives) - jet fuel
Scheme 1. Production method for long-chain n-alkyl nitriles and applications thereof.
In the following, we report an alternative, chemoenzymatic approach towards such bulk alkyl nitriles, which starts from simple and readily available alkenes and proceeds in water at low to moderate temperatures and without the need for any types of cyanide sources (Scheme 2). In detail, this approach combines a world-leading production technology for aldehydes, namely homogeneous metal-catalyzed hydroformylation[7] (being applied at a >12 million tons scale) with an emerging enzyme technology, namely the recently developed transformation of aldoximes into nitriles through dehydration catalyzed by aldoxime dehydratases.[8,9] The link between these two reactions is the formation of the aldoximes from the aldehydes. This step is a simple and spontaneous condensation of the aldehyde with hydroxylamine as a further bulk ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 27
chemical applied in ε-caprolactam production. Such a chemoenzymatic process concept is shown in Scheme 2, exemplified for nonanenitrile (as an n-/iso-mixture).
Rh-cat. hydroformylation
Oxime formation
+ CO, H2
+ NH2OH
O
- H 2O
H + iso-isomer 1
2, not isolated
biocatalytic dehydration N
OH
H
aldoxime dehydratase - H 2O
N
+ iso-isomer
+ iso-isomer
3, not isolated
4
Scheme 2. Reaction sequence for the synthesis of long-chain alkyl nitriles starting from nalkenes exemplified for nonanenitrile (as an n-/iso-mixture).
RESULTS AND DISCUSSION
A particular challenge was to identify suitable biocatalysts for this specific nitrile target product synthesis as well as to identify process conditions (process windows) under which these three steps can be combined without a need for intermediate isolation. Such a combination would give a perspective towards a three-step, one-pot-like process mode. ACS Paragon Plus Environment
Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
First, we focused on a hydroformylation process for 1-octene as a model substrate, which is scalable and allows a simple separation of the linear/branched nonanal products. A previously developed protocol for the hydroformylation used a very suitable setup for the envisaged combination with a subsequent biocatalytic step.[10] An aqueous/organic phase system with only substrate/product as the organic phase was applied to enable an intrinsic separation from catalyst and products after the reaction, thus securing a very low contamination of the aldehydes from the precious metal. As catalyst system, a rhodium-salt and TPPTS (tris(3sulfophenyl)phosphine trisodium salt) as a cheap ligand, which is also used in the Ruhrchemie/Rhône Poulenc process, were used. The activity of the two-phase system is highly dependent on the interfacial area which is created between the water and the octene phase, which was shown by a kinetic term that implement the interfacial area. [10a] This specific system was scaled up into a liter reactor. The reactivity is sensitive to the water to octene ratio (ϕ) and the stirrer type.[10b] With a 10% water and 90% octene phase and a Rushton turbine as a stirrer and pressure of 80 bar an octene conversion of 80% with an overall yield of the two nonanal isomers of 58% was achieved (Scheme 3). The catalyst concentration was extremely low with 0.00025 mol/L-1 and a high substrate loading of 429 g/L-1 at a 540 g scale was used in our experiment. The resulting n/iso-ratio of the regioisomers 2a and 2b was 2:1 over the whole ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 27
reaction time. This value is characteristic for this catalyst system in the hydroformylation of long alkenes.[10c] The main side reaction was the formation of octene isomers, which lead to lower selectivities during the reaction process due to the accumulation of internal double-bonds. As the Rh-TPPTS catalyst gave a mixture of isomers with an n/iso-ratio of 2:1 (2a:2b), in our subsequent biocatalytic studies we then investigated if the enzymes are capable for transforming both types of regioisomers. By means of the utilization of only water/octene twophase mixture and due to the high difference in density and polarity, the leaching of the catalyst was below 1 ppm.
O 0.00025 mol•Laq-1 [Rh(cod)Cl]2 0.005 mol•Laq-1 TPPTS
1 429 g/L (referring to total reaction volume)
100 °C, 17 h, 80 bar CO/H2 1 liter reactor water :octene 1:9 Rushton turbine 1600 min-1
H
2a +
2b
H
O
n/iso 2:1 80% conversion, 58% yield
540 g scale
Scheme 3. Hydroformylation of n-octene to n-/iso-nonanal.
The subsequent step consists of the condensation of the aldehyde with hydroxylamine under formation of the aldoxime. This reaction was again carried out in water. Our specific interest ACS Paragon Plus Environment
Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
focused on the optimization of this reaction by minimizing the excess of hydroxylamine, since we expected an enzyme deactivation by hydroxylamine, which has been reported by Oinuma et al.[11] We found in initial experiments with E/Z-phenylacetaldehyde oxime (which serves as the standard substrate for this enzyme class) that spontaneous formation of the aldoxime through condensation of the aldehyde with hydroxylamine also occurs with up to >99% conversion in an aqueous buffer solution at room temperature (see Supporting Information). The same desired reaction type was found to proceed well when using the substrate nonanal (as the product being formed in the hydroformylation step). When starting from a sample of nonanal isomers 2a and 2b (with an n/iso-ratio of 2:1 and at a substrate concentration of 10 mM), full conversion was achieved even without an excess of hydroxylamine. In detail, an equimolar amount of hydroxylamine led to a quantitative formation of the corresponding aldoximes within a reaction time of five hours at 35 °C (according to 1H-NMR spectroscopy; Scheme 4). The increase in temperature was needed to achieve full conversion since the iso-isomer is converted slower than n-nonanal. Such an opportunity to form the aldoximes in aqueous media with excellent conversion now also enabled a perspective for combining this aldoxime formation and the enzymatic dehydration step within a one-pot process without the need to isolate and purify the aldoxime as an intermediate prior to a subsequent biotransformation. ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 27
1.0 eq. NH2OH N
O H 2, n/iso 2:1 10 mM
phosphate buffer (pH 6 or pH 7), i-PrOH (10%(v/v)), 35 °C, 5h
OH
H 3, n/iso 2:1 >99% conversion (according to 1H-NMR spectroscopy)
Scheme 4. Optimized spontaneous aldoxime formation requiring only equimolar amount of hydroxylamine.
With this efficient method for an aldoxime preparation in aqueous medium in hand, we next focused on the identification of a suitable aldoxime dehydratase for the desired dehydration step. Toward this end we assessed five aldoxime dehydratases (Oxd; the origin of enzymes is described in Table S2) which are available in recombinant form and can be produced efficiently (Table 1). It is noteworthy that all five aldoxime dehydratases turned out to accept isolated nnonanaldoxime, 3a, as a substrate, which was utilized at a substrate concentration of 10 mM in this initial study in combination with 10%(v/v) of i-PrOH for improving the substrate solubility (Table 1, entries 1-6). In addition, with exception of OxdFG all Oxd enzymes led to the formation of the desired n-nonanenitrile with excellent conversion of >99%. However, utilizing an n/isoACS Paragon Plus Environment
Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
nonanaldoxime mixture (with an n/iso-ratio of 2:1 for 3a and 3b) revealed that the isoregiosiomer 3b is accepted to a less extent (entries 7-12). Nevertheless, also for this less reactive substrate 3b even a short reaction time of 60 min led to full conversion when using the enzymes OxdA and OxdRE (entries 7 and 11).
Table 1. Investigation of aldoxime dehydratases (Oxd) as biocatalysts for the synthesis of nonanenitrile (4) as an n-/iso-mixture.
N 3a +
H 3b
OH
H
N
10 mM substrate conc., Oxd 50 mg/ml BWW, whole cell catalyst - H 2O KPB 50 mM, pH 7, i-PrOH (10(v/v)), 30 °C, 1 h
OH
4b
n/iso 2:1
n/iso 2:1
entrya
Substrate
Oxd
Conv. [%]
1
n-3
A
>99
2
n-3
B
>99
3
n-3
Bb
>99
ACS Paragon Plus Environment
N
4a +
N
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 12 of 27
4
n-3
FG
42
5
n-3
RE
>99
6
n-3
RG
>99
7
n-/iso-3
A
>99 (n),
>99 (iso)
8
n-/iso-3
B
96 (n),
32 (iso)
9
n-/iso-3
Bb
>99 (n),
43 (iso)
10
n-/iso-3
FG
57 (n),
15 (iso)
11
n-/iso-3
RE
>99 (n),
>99 (iso)
12
n-/iso-3
RG
99 (n),
88 (iso)
aConditions:
50 mg/mL whole cells (which corresponds to 0.12–1.10 U/mg BWW, see Table
S4), 10 mM 2, 30 °C, pH = 7.0, 60 min. Conversion determined by GC-analytics. b OxdB with Cterminal His-tag. BWW = bio wet weight.
With the efficient three individual steps hydroformylation, spontaneous aldoxime formation and enzymatic dehydration in hand, we focused on the combination of these reaction steps (as shown in Scheme 2) in order to avoid intermediate isolations. Accordingly, compatibility of the enzyme with the components from the aldoxime formation step was studied as both (aldehyde and hydroxylamine) could be present in the reaction mixture at least in low amount (if not fully consumed in the aldoxime forming step). When investigating the effect of aldehyde 2 and hydroxylamine on the biocatalyst, n/iso-nonanal showed almost no negative effect on the enzyme in concentrations of up to 1 mM (see Supporting Information). In contrast, the activity ACS Paragon Plus Environment
Page 13 of 27
of the tested enzymes was strongly decreased even in the presence of very low concentrations of hydroxylamine, which turned out to severely harm the Oxd enzymes (Figure 1). In detail, a nearly dramatic loss of activity was observed already at hydroxylamine concentrations of 0.5 mM and 1 mM, and even at 0.05 mM in part a significant drop in activity was observed.
N 3a
OH
H
recombinant whole-cell catalyst with Oxd enzyme (50 mg/ml BWW)
+
H
N
OH
+
N
4b
hydroxylamine additive
n/iso 2:1
N
4a
- H 2O KPB 50 mM, pH 7, i-PrOH (10%(v/v)), 30 °C, 1 h
3b
n/iso 2:1
n-Isomer iso-Isomer
100
X rel. / %
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
50
0
Oxd A
Oxd RE no additive
Oxd A
Oxd RE 0.05 mM
Oxd A
Oxd RE
Oxd A
0.1 mM
Oxd RE 0.5 mM
Oxd A
Oxd RE 1 mM
Figure 1. Inhibition of aldoxime dehydratases by hydroxylamine. BWW: bio wet weight; 50 mg/ml BWW corresponds to 0.12–1.10 U/mg BWW, see Table S4, OxdA: 10 mM substrate
ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 27
concentration; OxdRE: 20 mM substrate concentration. Xrel.: relative conversion referring to additive-free biotransformations.
These results are consistent with literature data reporting only a 30% activity for OxdA at a 0.01 mM hydroxylamine concentration.[11] When comparing the two prioritized enzymes OxdA and OxdRE with each other, OxdRE showed a somewhat higher stability at elevated hydroxylamine concentrations of 0.5 and 1 mM albeit these concentrations are still in a very low range.
As the stability of the Oxd enzymes is dramatically affected by very low amounts of hydroxylamine, even the encouraging finding (described above) that only equimolar amount of hydroxylamine is needed for aldoxime formations might not be sufficient to avoid an at least slight surplus of hydroxylamine in practical use (due to, e.g., weighing differences leading to a slight excess of hydroxylamine being sufficient to hamper enzyme stability). Thus, we were searching for a method which enables us to directly use the aldoxime in situ but at the same time to ensure that no hydroxylamine is remained when adding the enzyme.
ACS Paragon Plus Environment
Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
We were pleased to find an elegant and easy-to-carry-out solution for this task which consists of heating the reaction mixture for 16 h up to 100 °C, thus leading to a decomposition of hydroxylamine while leaving the formed aldoxime product untouched. The decomposition of hydroxylamine in aqueous solution at elevated temperature is described in literature to proceed under formation of ammonia, nitrites and nitrates.[12] However, it should be added that such a procedure has to be taken with high caution as in general thermal decomposition of hydroxylamine raises safety concerns since hydroxylamine turned out as a chemically instable compound, which also has led to two tragic incidents in industry.[13] Thus, we only utilized this thermal decomposition method to remove trace amounts of hydroxylamine being present in highly diluted concentration in aqueous medium. The suitability of this methodology to remove very low amount of hydroxylamine at low concentration is illustrated in Figure 2, which shows a comparison of a biotransformation starting from various aldoxime / hydroxylamine solutions in original form with the one based on a heat-treatment according to the method described above. As can be seen from Figure 2, biotransformations utilizing the heat-treated substrate solutions with added hydroxylamine as an additive gave significantly higher conversions. These results underline the positive impact of this method for removal of trace amount of hydroxylamine being present in aqueous medium at very low concentration through thermal in situ decomposition. ACS Paragon Plus Environment
ACS Catalysis
100
without heating with heating
80
60
X/%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 16 of 27
40
20
0
iso
n 0.05 mM
iso
n 0.1 mM
iso
n 0.5 mM
iso
n 1 mM
Figure 2. Effect of heating the hydroxylamine solution on the inhibition of the biotransformation. X = conversion. Conditions: 20 mM 3, 50 mg/ml BWW corresponds to 0.80 U/mg BWW (see Table S4), OxdRE, potassium phosphate buffer (KPB, 50 mM, pH = 7), iPrOH (10%(v/v)), 500 µL total volume, 30 °C, 1 h, 0.05–1 mM H2NOH · HCl by addition of 1.2– 25 µL of a 20 mM solution, either used directly or heated for 16 h to reflux.
Thus, this protocol also enabled a perspective towards a coupling of the aldoxime formation step with the biotransformation as a sequential one-pot process (Scheme 5). Accordingly, when starting from the aldehyde isomers as substrate (10 mM) and when carrying out the biotransformation directly with the reaction mixture from the spontaneous aldoxime formation
ACS Paragon Plus Environment
Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
after heat-treatment for removal of hydroxylamine, we were pleased to find that this one-pot process proceeds very efficiently furnishing the desired n/iso-nonanenitrile 4a/4b with a high overall conversion of 81% over two synthetic steps. In contrast, a comparison experiment without heat-treatment of the reaction mixture resulting from aldoxime formation via condensation of n/iso-nonanal 2a/2b and hydroxylamine gave a strongly decreased conversion of only 6% (see Supporting Information).
1. 1.00 eq.NH2OH • HCl 0.5 eq. Na2CO3 pH = 7.0, 8 h, 35 °C, O i-PrOH (10%(v/v))
H
50 mg/mL OxdRE (whole cell catalyst), pH = 7, 3 h, 30 °C, i-PrOH (10%(v/v))
2. 100 °C, 16 h
N
+ iso-isomer
+ iso-isomer
2, n/iso 2:1
4, n/iso 2:1
10 mM
81% overall conversion
Scheme 5. One-pot synthesis of n/iso-nonanenitrile (4) starting from a mixture of n/iso-nonanal (2; n-/iso-ratio: 2:1), 50 mg/ml BWW corresponds to 0.80 U/mg BWW.
Taking into account that the aldehyde formed in the hydroformylation step does not require a purification but can be directly used after simple phase separation via extraction and solvent evaporation, this results in a straightforward three-step transformation of n-octene into nonanenitrile with overall 65% conversion (Scheme 6). This overall conversion refers to all three
ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 18 of 27
steps starting from 1-octene and has been calculated from the conversion for the first step (80%, see Scheme 3) and the conversion of the second and third step being done in one pot (81%, see Scheme 5). It should be added that in principle also a process running without the phaseseparation step would be conceivable. However, as the metal catalyst for the hydroformylation is the most expensive component in the overall process, the phase-separation appeared to us as an elegant approach to achieve a simple catalyst separation from the aldehyde intermediates which then makes a re-use of the aqueous phase bearing this metal component possible.
Step I
1 6 mL
H
Step II
H
+ iso-isomer O
+ iso-isomer
2, n/iso 2.2:1
3,n/iso 2.2:1
1. phase separation 2. use of 1 mmol for further synthesis
1. addition of biocatalyst
Step I Rh(acac)(CO)2 (0.00025 mol/L) TPPTS (0.005 mol/L) H2O (4 mL) 80 °C, 80 bar CO/H2, 4 h
Step II 1.) NH2OH (1 eq), pH 7.0, 35 °C i-PrOH (10%(v/v), 8 h 2.) 100 °C, 16 h
Step III + iso-isomer
N OH
N
4, n/iso 2.2:1
67 % overall conversion I-III 41% isolated yield II-III
Step III OxdRE whole-cell catalyst (50 mg/mL, 0.80 U/mg BWW) pH 7.0, 30 °C, i-PrOH (10%(v/v), 3 h
Scheme 6. Complete reaction sequence for the synthesis of n/iso-nonanenitrile starting from
n-octene, .
In our three-step one-pot experiment, we conducted our hydroformylation experiment at a reduced lab scale using 6 mL 1-octene and 4 mL aqueous phase, which contains a rhodium salt ACS Paragon Plus Environment
Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
and TPPTS ligand with some slightly changes in the set-up compared to the experiment at elevated lab scale. For the first step (hydroformylation) we obtained 74 % conversion to our
n/iso-aldehyde mixture in a ratio of ~2.2:1 (n:iso). The second step (condensation with hydroxylamine) was conducted using the organic phase from the first step after phase separation without purification in an amount, which contains 1 mmol of aldehyde. After treatment with 1 equivalent of hydroxylamine and heating the reaction mixture for 16 h to 100 °C, OxdRE whole cell catalyst was added (after cooling down) in an amount corresponding to a final concentration of 50 mg/mL, which is related to a standard activity of the catalyst of 0.8 U/mg BBW. The resulting the mixture was stirred for 3 h at 30 °C, thus reaching a conversion of aldoxime mixture into the desired nitrile mixture of 90 %. Subsequently, the nitrile mixture was purified by column chromatography resulting in an isolated yield of 41% calculated from the used aldehyde amount in the second step. Furthermore, an overall conversion of 67 % starting from 1-octene was reached in our three-step-one-pot experiment. In conclusion, a route for aliphatic nitriles which corresponds to a formal hydrocyanation of alkenes without using hydrogen cyanide has been developed. This chemoenzymatic nitrile synthesis is based on a combination of metal-catalyzed hydroformylation with enzymatic aldoxime dehydration. In addition, as a missing link an aldoxime formation with subsequent in ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 27
situ-removal of excess of hydroxylamine as a strongly enzyme-deactivating component was found, which then enabled to merge these three steps hydroformylation, aldoxime formation and enzymatic dehydration towards a nitrile synthesis without the need to purify the intermediates.
AUTHOR INFORMATION
Corresponding Author
*Harald Gröger: Tel.: +49 521 106 2057,
E-mail:
[email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript Notes The authors declare no competing financial interest.
ASSOCIATED CONTENT
ACS Paragon Plus Environment
Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Supporting Information. A file comprising general experimental information, standard protocols for hydroformylation, activity measurements of cells and kinetic measurements, aldoxime dehydratase (Oxd) sequences, plasmids and expression, and experimental information about the sequential one-pot processes and synthesis of reference compounds is provided.
This information is available free of charge on the ACS
Publications website.
ACKNOWLEDGMENT
C.P., A.H., W.B., K.O., H.Y., T.B. and H.G. gratefully acknowledge generous support from the German Federal Ministry of Education and Research (BMBF) within the funding programme “Biotechnologie 2020+, Nächste Generation biotechnologischer Verfahren” (grant number: 031A184A), the Fachagentur Nachwachsende Rohstoffe (FNR) and the German Federal Ministry of Food and Agriculture (BMEL), respectively, within the funding programme on the utilization of biorenewables (grant number: 22001716) and Umicore AG & Co. KG as well as OXEA GmbH. 21 ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 22 of 27
REFERENCES
[1]
Pollak, P.; Romeder, G.; Hagedorn, F.; Gelbke, H.-P., eds., Nitriles. Ullmann's
Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000.
[2]
Selected examples of recently developed nitrile drugs: a) Vildagliptin: Pellegatti,
L.; Sedelmeier, J. Synthesis of Vildagliptin Utilizing Continuous Flow and Batch Technologies. Org. Process Res. Dev. 2015, 19, 551-554; b) Saxagliptin: Savage, S. A.; Jones, G. S.; Kolotuchin, S.; Ann Ramrattan, S.; Vu, T.; Waltermire, R. E. Preparation of Saxagliptin, a Novel DPP-IV Inhibitor. Org. Process Res. Dev. 2009, 13, 1169-1176.
[3]
Arpe, H.-J. Industrielle Organische Chemie, Wiley-VCH, Weinheim, 2007.
[4]
Reck. R. A. Industrial Uses of Palm, Palm Kernel and Coconut Oils: Nitrogen
Derivatives. J. Am. Oil Chem. Soc. 1985, 62, 355-365.
[5]
Reviews on cyanation reactions: a) Hydrocyanation of C=C bonds: RajanBabu, T.
V.; Casalnuovo A. L. in: Chapter 28: Cyanation of Carbonyl and Imino groups,
Comprehensive Asymmetric Catalysis I-III, vol. 1, (Jacobsen, E.; Pfaltz, A.; Yamamoto, 22 ACS Paragon Plus Environment
Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
H. eds.), Springer, Berlin, 1999, p. 367; b) Chemocatalytic Strecker reaction: Gröger, H. Catalytic Enantioselective Strecker Reactions and Analogous Syntheses. Chem. Rev. 2003, 103, 2795-2827; c) Enzymatic cyanohydrin formation: Gruber-Khadjawi, M.; Fechter, M.; Griengl H. in: Chapter 23: Cleavage and Formation of Cyanohydrins,
Enzyme Catalysis in Organic Synthesis, Vol. 2, (Drauz, K.; Gröger, H.; May, O. eds.), Wiley-VCH, Weinheim, 2012, 947-990.
[6]
Martin, A.; Kalevaru N. V., Ammoxidation of Hetero-aromatic Compounds to the
Corresponding Nitriles, in: Industrial Catalysis and Separations – Innovations for Process
Intensification (Raghavan, K. V.; Reddy, B. M. eds), Apple Academic Press, Toronto, New Jersey, 2015, chapter 7, p. 249.
[7]
Börner, A.; Franke R., eds., Hydroformylation: Fundamentals, Processes, and
Applications in Organic Synthesis, Wiley-VCH, Weinheim, 2016.
[8]
Review: Betke, T.; Higuchi, J.; Rommelmann, P.; Oike, K.; Nomura T.; Kato, Y.;
Asano, Y.; Gröger, H. Biocatalytic Synthesis of Nitriles through Dehydration of Aldoximes: The Substrate Scope of Aldoxime Dehydratases. ChemBioChem 2018, 19, 768-779. 23 ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
[9]
Page 24 of 27
Selected recent examples: a) Asano, Y.; Kato, Y. Z‐Phenylacetaldoxime
Degradation by a Novel Aldoxime Dehydratase from Bacillus sp. Strain OxB‐1. FEMS
Microbiol. Lett. 1998, 158, 185-190; b) Xie, S.-X.; Kato, Y.; Asano, Y. High Yield Synthesis of Nitriles by a New Enzyme, Phenylacetaldoxime Dehydratase, from Bacillus sp. Strain OxB-1. Biosci. Biotechnol. Biochem. 2001, 12, 2666-2672; c) Kato, Y.; Asano, Y. Molecular and Enzymatic Analysis of the “Aldoxime–Nitrile Pathway” in the Glutaronitrile Degrader Pseudomonas sp. K-9. Appl. Microbiol. Biotechnol. 2006, 70, 92-101; d) Metzner, R.; Okazaki, S.; Asano, Y.; Gröger, H. Cyanide-free Enantioselective Synthesis of Nitriles: Synthetic Proof of a Biocatalytic Concept and Mechanistic Insights.
ChemCatChem 2014, 6, 3105-3109; e) Betke, T.; Rommelmann, P.; Oike, K.; Asano. Y.; Gröger, H. Cyanide-Free and Broadly Applicable Enantioselective Synthetic Platform for Chiral Nitriles through a Biocatalytic Approach. Angew. Chem. Int. Ed. 2017, 56, 1236112366.
24 ACS Paragon Plus Environment
Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
[10] Warmeling, H.; Hafki, D.; von Söhnen, T.; Vorholt, A. J. Kinetic Investigation of Lean Aqueous Hydroformylation – An Engineer’s View on Homogeneous Catalysis.
Chem. Eng. J. 2017, 326, 298-307.
[11] Oinuma, K.-I.; Hashimoto, Y.; Konishi, K.; Goda, M.; Noguchi, T.; Higashibata, H.; Kobayashi, M. Novel Aldoxime Dehydratase Involved in Carbon-Nitrogen Triple Bond Synthesis of Pseudomonas chlororaphis B23. J. Biol. Chem. 2003, 278, 29600-29608.
[12] Liu, L.; Papadaki, M.; Pontiki, E.; Stathi, P.; Rogers, W. J.; Mannan; M. S. Isothermal Decomposition of Hydroxylamine and Hydroxylamine Nitrate in Aqueous Solutions in the Temperature Range 80–160 °C. J. Hazard. Mat. 2009, 165, 573-578.
[13] a) Wang, Q.; Wei, C.; Pérez, L. M.; Rogers, W. J.; Hall, M. B.; Mannan, M. S. Thermal Decomposition Pathways of Hydroxylamine: Theoretical Investigation on the Initial Steps. J. Phys. Chem. A 2010, 114, 9262-9269; b) Iwata, Y.; Koseki, H. Risk Evaluation
of
Decomposition
of
Hydroxylamine/Water
Solution
at
Various
Concentrations. Process Safety Progress 2002, 21, 136-141.
25 ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 26 of 27
26 ACS Paragon Plus Environment
Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Graphic for Table of Content
27 ACS Paragon Plus Environment
