The continuous-flow synthesis of carbazate hydrazones using a simplified computer-vision controlled liquid–liquid extraction system

Abstract

Please cite this article as: O'Brien, M., Cooper, D.A., Mhembere, P., The continuous-flow synthesis of carbazate hydrazones using a simplified computer-vision controlled liquid-liquid extraction system, Tetrahedron Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet. 2016.10.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Tetrahedron LettersThe continuous-flow synthesis of carbazate hydrazones using a simplified computervision controlled liquid-liquid extraction system. --- Corresponding author. e-mail: m.obrien@keele.ac.ukIn recent years, the emergence of continuous flow methodology has created new opportunities for chemical synthesis. 1 Compared with traditional batch processes, flow methods can often offer significant safety benefits, particularly for transformations involving hazardous conditions or reagents.2 Additionally, the small dimensional scales involved lead to the efficient and scaleinvariant interfacial transfer of energy and matter.3 A particularly attractive aspect of flow chemistry is the ability to incorporate inline purification stages. Solid-supported scavengers 4 and phaseswitching protocols have been extremely successful in this regard. 5 However, solid-supported chemicals can often be much more expensive than their solution phase counterparts. 6 In addition, they often give rise to significant and scale-dependent dispersion effects 7 and become depleted over time, thus requiring replacement or regeneration. This can be a time consuming operation which usually necessitates halting of the flow process. As liquids can be continuously pumped through the system, inline liquid-liquid phase separation does not suffer from this problem and, whilst dispersion cannot be eliminated, it can be controlled and rendered scale invariant.One general method of inline liquid-liquid separation used in continuous flow makes use of the selective wetting of certain materials, particularly expanded porous PTFE membranes, to separate aqueous and organic solutions. 8 We have been interested, however, in gravity-based separations of immiscible liquids based on their densities.9 This is essentially a continuous flow adaptation of the classical separating funnel. The basic concept is shown in Figure 1. A biphasic stream of immiscible liquids with differing densities will, when passed into a suitable vessel, separate vertically. The dense phase will exit the vessel through a lower exit and the light phase will exit the vessel through an upper exit. In Figure 1 the organic phase is the dense phase and the aqueous extractant is the light phase, although these roles could be switched if less dense o...

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