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Scalable and Selective Preparation of 3,3’,5,5’-Tetramethyl-2,2’-biphenol Thomas Quell, Nadine Hecken, Katrin M. Dyballa, Robert Franke, and Siegfried R. R Waldvogel Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.6b00356 • Publication Date (Web): 08 Dec 2016 Downloaded from http://pubs.acs.org on December 13, 2016

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Organic Process Research & Development

Scalable and Selective Preparation of 3,3’,5,5’Tetramethyl-2,2’-biphenol Thomas Quell†, Nadine Hecken†, Katrin M. Dyballa‡, Robert Franke‡,§, Siegfried R. Waldvogel†*

†

Institut für Organische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14,

D-55128 Mainz, Germany; Email: [email protected]; ‡Evonik Industries AG, PaulBaumann-Straße 1, D-45772 Marl, Germany; §Lehrstuhl für Theoretische Chemie, RuhrUniversität Bochum, D-44780 Bochum, Germany.

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Table of Contents Graphic


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KEYWORDS: Biphenol, scalable, selenium dioxide, C,H activation, phenol-phenol coupling, oxidation.

ABSTRACT: Biphenols are indispensable building blocks in ligand systems for organic catalysis. 3,3’5,5’-tetramethyl-2,2’-biphenol is a particular versatile motif in different catalytic systems. We developed an easy to perform and scalable process to give access to large quantities of this important building block by the use of selenium dioxide, a common and readily available oxidizer.

INTRODUCTION The structural motif of biphenol is present in numerous molecules like natural products,1,2 drugs,3,4 or in material science.5,6 Their outstanding significance as ligands for catalytic systems classifies them as so-called “privileged ligands”.7–10 This issue underlines their importance for scientific, and technical applications the steady high interest in an efficient scalable synthesis. In particular, 3,3’,5,5’-tetramethyl-2,2-biphenol (2) has widespread capability to act as backbone in phosphorous-based ligand systems: With this biphenol the rhodium-catalyzed hydroformylation reaction was promoted,11,12 nickel-catalyzed hydrocyanation,13 rhodium-catalyzed asymmetric hydrogenation of prochiral olefins,14 or the enantioselective, copper-catalyzed generation of stereogenic centers is reported.15–17 This ligand is also appropriate for enantioselective addition of arylboronic acids 18,19 as well as iso- and syndioselective ROMP of norbonene.20 Additionally, 3,3’,5,5’-tetramethyl-2,2-biphenol can be transformed into sodium[bis(3,3´,5,5´-tetramethyl2,2´-biphenoxy)borate].21 This product is extraordinarily stable at electrochemical conditions and


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applicable in electrochemical double-layer capacitor electrolytes for capacitive energy storage.22,23 The conversion of 2,4-dimethylphenol (1) to the desired 3,3’,5,5’-tetramethyl-2,2’-biphenol turned out to be challenging.24,25 The direct C-H activation led to polycyclic by-products with a high structural diversity.26–28 Nevertheless, a broad spectrum of oxidative methods was studied. One approach is based on metal catalysts at aerobic conditions using cobalt,29 vanadium,30 ruthenium,31 or copper salts.32,33 Furthermore, iron(III)-chloride,34 sodium hypochlorite,35 and sodium persulfate12 claim to act as oxidizer in stoichiometric amounts. A more sophisticated option deals with the anodic oxidation for direct C-H activation,36–38 or template-supported oxidation approach.39 However, none of these methods can give access to large quantities of 3,3’,5,5’-tetramethyl-2,2’-biphenol. Therefore, we have developed an easy to perform and scalable protocol to synthesize and isolate the desired product 2.40 Our method is based on a selenium dioxide-mediated, direct C-H activation of 2,4-dimethylphenol (1). Selenium dioxide is an easy to handle, versatile, and readily available oxidizer. This material is a co-product within the roasting process of copper, lead, zinc, or iron ores and can be isolated from the fly ashes.41 In the course of the 2,4-dimethylphenol oxidation process, elemental selenium is co-formed. This by-product can be easily separated by percolation and reoxidized by heating at aerobic conditions.42 Therefore, selenium dioxide is an excellent reagent for academic and technical applications.43,44 RESULTS AND DISCUSSION We tried to elucidate the optimal reaction conditions to conduct the oxidation displayed in Scheme 1, in order to be as selective as possible to facilitate the subsequent isolation and purification steps.


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Scheme 1. Selenium dioxide mediated coupling of 2,4-dimethylphenol. Simultaneously, yield and conversion should be high without the use of expensive or less available ingredients. In addition, the application of potentially explosive reagents such as peroxides should be avoided as well. The effect of different solvents is described in earlier publications.40,45 These studies were conducted on a scale up to two grams with purification by column chromatography. To simplify the optimization work for elucidation the parameters such as reaction temperature, reaction time, and the amounts of selenium dioxide, we introduced an internal reaction standard. It turned out, that 1,3-dinitrobenzene is suitable for a quick and reliable determination of data. The internal standard proved to be inert in the presence selenium dioxide in boiling acetic acid. Even upon 16 hours no reaction was observed and 1,3dinitrobenzene was quantitatively recovered. With this in hand, we performed gas chromatographic analysis (GC) with different ratios of 2,4-dimethylphenol, 3,3’,5,5’tetramethyl-2,2’-biphenol, and 1,3-dinitrobenzene to obtain calibration data. The determination of conversion and yield was performed by GC. Figure 1 displays the amounts of 1 and 2 over the reaction time. As anticipated, the fraction of 2,4-dimethylphenol decreases over time. On the other hand, 3,3’,5,5’-tetramethyl-2,2’-biphenol is exponentially generated at the beginning, but reached a maximum after approx. 180 minutes. Interestingly, the amount of 2 decreases thereafter. Only little remains of 2,4-dimethylphenol are left and 2 seems to undergo further conversion. Such over-oxidations led to high-molecular weight by-products. This observation is


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provided by the high viscosity of the reaction mixture upon prolonged reaction times. Therefore, it is important to optimize the reaction time to avoid oligomerization processes. In addition, excessive consumption of starting material should be avoided and therefore, the conversion should be stopped in time.

Figure 1. Amount of 2,4-dimethylphenol and 3,3’,5,5’-tetramethyl-2,2’-biphenol determined by GC-analysis during the reaction. Reaction conditions: acetic acid (45 mL), 2,4-dimethylphenol (4.0 g, 32.6 mmol, 1.0 eq.), 1,3-dinitrobenzene (1.0 g, 5.9 mmol, 0.2 eq.), selenium dioxide (2.5 g, 22.9 mmol, 0.7 eq.), 85 °C. After the reaction time, we investigated the eminently suitable equivalents of selenium dioxide. Table 1 exhibits the results of this screening. The reaction times are comparable, but the yield increases with larger amounts of selenium dioxide. We decided to perform further reactions with 0.7 equivalents. More of the oxidizer produces comparable yields but with higher efforts of selenium dioxide, therefore 0.7 equivalents are the most economic compromise.


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Table 1. Optimization of the selenium dioxide equivalents. Entry

SeO2/ eq.

yield/ %a

Time/ min

1

0.50

43

180

2

0.55

45

180

3

0.60

64

150

4

0.70

69

180

5

0.80

70

200

6

1.00

70

180

Reaction conditions: acetic acid (45 mL), 2,4-dimethylphenol (4.0 g, 32.6 mmol,1.0 eq.), 1,3dinitrobenzene (2.0 g, 5.9 mmol, 0.2 eq.), 85 °C. a Yields were determined by GC-analysis with internal standard. The quantity of acetic acid is also an important point for the latter technical application. We were able to increase the concentration of 2,4-dimethylphenol up to 0.18 g/mL without depression of yield. Additionally, the optimal reaction time decreases then to 120 min. Further increase of the concentration of starting material promotes the formation of high molecular by-products. Table 2 shows a series of experiments with different reaction conditions to confirm our internal standard method by isolating the desired product. First, we performed the reaction in presence of 1,3dinitrobenzene to elucidate the optimal reaction time. Then we repeated the same experiment for the previously appointed reaction time, but without 1,3-dinitrobenzene. The more or less identical results underline the value of the internal standard approach. Table 2. Comparison of GC-determined yields and isolated yields.

Entry

Temperature /°C

SeO2 /eq.

Concentration of 1 / g/mL

GC yield/%a

Isolated yield /%

1

90

0.55

0.09

47

43


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2

85

0.70

0.09

69

72

3

85

0.70

0.18

72

73

Reaction conditions: 2,4-dimethylphenol (32.6 mmol,) in acetic acid. a Yields were determined by GC-analysis with 1,3-dinitrobenzene as internal standard. For a technically applicable synthesis, the work-up strategy should be as efficient as possible. We developed two different protocols to work-up the reaction mixture. The first strategy (Figure 2) starts by quenching of the reaction by the addition of water (1 mL/g 2,4-dimethylphenol). The reaction mixture is filtered to remove elemental selenium, followed by an extraction by ethyl acetate (8 mL/g 2,4-dimethylphenol). Further washings with water (three times with 5 mL/g 2,4dimethylphenol) transfers the acetic acid into the aqueous layer. After drying over anhydrous sodium sulfate, the ethyl acetate is distilled off at reduced pressure (300 to 12 mbar) at 60 °C water bath temperature. Alternatively, residual water can by removed by azeotropic distillation instead of using sodium sulfate. The residue still contains non-converted starting material. This can be removed by vacuum distillation at 60 °C (10-3 mbar). The remaining solid is extracted by boiling n-heptane (three times with 7 mL/g 2,4-dimethylphenol). Within this step, only low molecular weight products are dissolved. The heptane distilled off at reduced pressure (200 to 12 mbar) at 60 °C water bath temperature. In the last step, crude 2 is re-crystallized from cyclohexane: The residue is dissolved in boiling cyclohexane (2 mL/g residue) and chilled to 7 °C for 16 hours. The crystals are collected and washed with cold cyclohexane (7 °C).

reaction mixture

distillation

extraction

percolation

extraction

crystallization 2

high molecular by-products acetic acid

non-converted 1

Se

Figure 2. Work-up scheme for protocol A.


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The work-up by protocol B (Figure 4) is more efficient, but requires a highly selective reaction process, like the one we established by using selenium dioxide: After a given reaction time, the mixture is poured onto ice (1.3 g per mL acetic acid), whereby the desired product, with small amounts of by-product, precipitate (Figure 3a). The starting material remains in the water/acetic acid solution (Figure 3b). a)

93%

b)

84%

Figure 3. GC-data of work-up protocol B: a) precipitate and b) water/ acetic acid filtrate. Then the solid is collected and re-dissolved in ethyl acetate (3.3 mL/g 1). Insoluble selenium is then filtered off for further use. The organic layer is washed by water (three times with 0,6 mL/g starting material) to remove remaining traces of acetic acid. Then the solvent is, after drying over anhydrous sodium sulfate, distilled off at reduced pressure. The residue is dissolved in boiling cyclohexane (2 mL/g residue) and chilled to 7 °C for 16 hours to complete the crystallization. The product was filtered off and washed with cold cyclohexane (7 °C). Both work-up protocols A and B lead to identical yields of 68%. precipitationa

crystallizationc

triturationb

reaction mixture

2

Se non-converted 1 acetic acid

Figure 4. Work-up scheme for protocol B.


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Since both work-up procedures are potentially scalable, we started to scale-up this reaction. Two characteristics are important for such a process. First, mixing has to be on large scale as good as on small scales. Figure 5a displays the GC data of a reaction involving a 100 g of 1 scale mixed by a magnetic stirring device. Next to the desired product 2 (green), an unexpected byproduct (red) was detected. Mass spectrometric studies indicate that the by-product is the dehydrotrimer 3 of 1, which was previously reported.35 At these process conditions the byproduct became dominant. Insufficient mixing seems to favors the formation of over-oxidation products. Figure 5b displays the same reaction, stirred by a mechanical stirrer. The by-product is almost completely suppressed and 3,3’,5,5’-tetramethyl-2,2’-biphenol occurs as major product. These results underline the importance of sufficient mixing for this particular transformation. a)

31%

21% 24%

28%

55% 98% Analytical data in agreement with those previously reported.37 AUTHOR INFORMATION Corresponding Author * E-Mail: [email protected]. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors highly appreciate the support by BMBF-EPSYLON (FKZ 13XP5016D). S.R.W. in particular appreciates the donation of selenium dioxide by RETORTE GmbH (Arubis), Röthenbach, Germany. References (1) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B. Chem. Rev. 2009, 109, 897–1091. (2) Bringmann, G.; Price Mortimer, A. J.; Keller, P. A.; Gresser, M. J.; Garner, J.; Breuning, M. Angew. Chem., Int. Ed. Engl. 2005, 44, 5384–5427. (3) Bringmann, G.; Gulder, T.; Gulder, T. A. M.; Breuning, M. Chem. Rev. 2011, 111, 563–639. (4) Nussbaum, F. von; Brands, M.; Hinzen, B.; Weigand, S.; Häbich, D. Angew. Chem., Int. Ed. Engl. 2006, 45, 5072–5129. (5) Pavel, D.; Ball, J. M.; Bhattacharya, S. N.; Shanks, R. A.; Hurduc, N. Comput. Theor. Polym. Sci. 1997, 7, 7–11. (6) Finkelmann, H.; Happ, M.; Portugal, M.; Ringsdorf, H. Makromol. Chem. 1978, 179, 2541– 2544. (7) Brunel, J. M. Chem. Rev. 2005, 105, 857–897. (8) Chen, Y.; Yekta, S.; Yudin, A. K. Chem. Rev. 2003, 103, 3155–3212. (9) Franke, R.; Selent, D.; Börner, A. Chem. Rev. 2012, 112, 5675–5732. (10) Parmar, D.; Sugiono, E.; Raja, S.; Rueping, M. Chem. Rev. 2014, 114, 9047–9153. (11) Smith, S. E.; Rosendahl, T.; Hofmann, P. Organometallics 2011, 30, 3643–3651. (12) Mormul, J.; Mulzer, M.; Rosendahl, T.; Rominger, F.; Limbach, M.; Hofmann, P. Organometallics 2015, 34, 4102–4108. (13) Garner, J. M.; Kruetzer, K. A.; Tam, W. WO 9906358, 2008. (14) Monti, C.; Gennari, C.; Piarulli, U.; de Vries, J. G.; de Vries, André H. M.; Lefort, L. Chem. Eur. J. 2005, 11, 6701–6717. (15) d'Augustin, M.; Palais, L.; Alexakis, A. Angew. Chem., Int. Ed. Engl. 2005, 44, 1376–1378.


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