Accessing Novel Process Windows in a High‐Temperature/Pressure Capillary Flow Reactor

Razzaq, Tahseen; Glasnov, Toma N.; Kappe, C. Oliver

doi:10.1002/ceat.200900272

Cited by 68 publications

(72 citation statements)

References 84 publications

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“…The photo microflow synthesis avoids the formation of migration of the double bound of the allyl group to give E/Z 2-(prop-1-enyl)phenols which were reported for the corresponding thermal (high-T) microflow synthesis of allyl phenyl ether, especially at temperatures above 300°C [14]. These substances can undergo ring closure to give 3-dihydro-2-methylbenzo[b]furan and 2-methylbenzo[b]furan as further byproducts of the thermal process which we did not observe.…”

Section: Resultsmentioning

confidence: 91%

“…Unexpected was that the allyl bromide had similar strong effect. Under the high temperatures used in the thermal Claisen rearrangement, which are typically set in microflow even higher [13,14], the allyl bromide decomposes to give propene and HBr. The latter acid can lead to the same decomposition rate of the Claisen product as the acid does.…”

Section: Introductionmentioning

confidence: 99%

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Photo-Claisen Rearrangement of Allyl Phenyl Ether in Microflow: Influence of Phenyl Core Substituents and Vision on Orthogonality

2016

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We converted diverse commercial meta-substituted phenols to the allyl-substituted precursors via nucleophilic substitution using batch technology to allow processing these in microflow by means of the photo-Claisen rearrangement. The latter process is researched on its own, as detailed below, and also prepares the ground for a fully continuous two-step microflow synthesis, as outlined above. It is known that batch processing of electronically deactivated phenols (e.g., bearing a cyano or nitro group) has several orders of magnitude lower reactivity than their parental counterparts [1]. Thus, we here explore if the high quantum yield of microflow, yet at very short residence time, is sufficient to activate the deactivated molecules. In addition, the realization of a true orthogonal two-step flow synthesis can open the door to a large synthetic scope of our approach and possibly overcome limitations due to missing orthogonality of our previously reported thermal approach of combined nucleophilic substitution-Claisen rearrangement in microflow. Consequently, we make for our photo microflow approach an orthogonality check, as previously reported for the thermal approach, and compare both. To get a broader picture, we have investigated some major parametric sensitivities such as the irradiation intensity, the choice of solvent, the reactant concentration, and, most notably, the influence of the substitution pattern. The irradiation intensity was varied by increasing distance between a lamp and the microflow capillary. In addition, the normal photoClaisen microflow process (at room temperature) is compared to a high-temperature photo-Claisen microflow process, to check the potential of such novel process window [2]. This is difficult to realize in batch, as the combination of strong ultraviolet (UV) irradiation and high temperature causes a high hazard potential. Yet, under microflow, this can be safely handled.

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Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Photo-Claisen Rearrangement of Allyl Phenyl Ether in Microflow: Influence of Phenyl Core Substituents and Vision on Orthogonality

2016

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“…In contrast, the combination of sealed microreactor technology and back pressure regulators provides opportunities to heat the reaction mixture far above the boiling point of the solvent. Consequently, solvent selection for high temperature novel process windows is not restricted anymore by the solvent's boiling point [64,88].…”

Section: Temperature Effectsmentioning

confidence: 99%

The Claisen Rearrangement – Part 2: Impact Factor Analysis of the Claisen Rearrangement, in Batch and in Flow

et al. 2014

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In Part 2, the factors impacting the Claisen rearrangement both in batch and flow processing are analyzed, including the choice of substituent, catalyst, temperature, pressure, concentration, flow rates, and solvent. Part 1 of this review series discussed the potential of using short‐time spectroscopy and quantum mechanical calculations to elucidate the mechanism and transition state of the Claisen rearrangement. Flow processing offers profound opportunities for studying these factors known to impact the Claisen rearrangement done in batch. It is shown that the same impact factors also rule flow processing, yet now superposed by the very different residence and reaction time settings and by novel process windows which go beyond conventional processing. As a result, massive intensification can be reached and a mechanistic analysis can be done in entirely unpaved processing fields. This links to the analysis given in part 1: it is likely that flow processing can further promote the understanding of the mechanism and transition state of the Claisen rearrangement and, thereby, promote the achievement of better reaction performance.

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“…The high rates of mass and heat transfer, minimum axial dispersion and the high interfacial area allow micro/milli channel reactors to run highly exothermic, toxic or even explosive reactions safely, permitting greener routes for processing [1,2,3,4,5]. Microreactors are very attractive devices for many different applications [6,7,8,9].…”

Section: Introductionmentioning

confidence: 99%

Numbered-up gas–liquid micro/milli channels reactor with modular flow distributor

Al-Rawashdeh

Nijhuis

et al. 2012

Chemical Engineering Journal

105

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Gas-liquid processing in microreactors remains mostly restricted to the laboratory scale due to the complexity and expenditure needed for an adequate numbering-up with a uniform flow distribution. Here, the numbering-up is presented for multiphase (gas-liquid) flow in microreactor suitable for a production capacity of kg/h. Based on the barrier channels concept, the barrier-based micro/milli reactor (BMMR) is designed and fabricated to deliver flow non-uniformity of less than 10%. The BMMR consists of eight parallel channels all operated in the Taylor flow regime and with a liquid flow rate up to 150 mL/min. The quality of the flow distribution is reported by studying two aspects. The first aspect is the influence of different viscosities, surface tensions and flow rates. The second aspect is the influence of modularity by testing three different reaction channels type: (1) square channels fabricated in a stainless steel plate, (2) in a glass plate, and (3) circular channels (capillaries) made of stainless steel.Additionally, the BMMR is compared to that of a single channel regard the slug and bubble lengths and bubble generation frequency. The results pave the ground for bringing multiphase flow in microreactor one step closer for large scale production via numbering-up.

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Accessing Novel Process Windows in a High‐Temperature/Pressure Capillary Flow Reactor

Cited by 68 publications

References 84 publications

Photo-Claisen Rearrangement of Allyl Phenyl Ether in Microflow: Influence of Phenyl Core Substituents and Vision on Orthogonality

Photo-Claisen Rearrangement of Allyl Phenyl Ether in Microflow: Influence of Phenyl Core Substituents and Vision on Orthogonality

The Claisen Rearrangement – Part 2: Impact Factor Analysis of the Claisen Rearrangement, in Batch and in Flow

Numbered-up gas–liquid micro/milli channels reactor with modular flow distributor

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