Volume 1, Issue 2

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Green initiatives worldwide should unite into a global network for sharing technology and best practices. This network is needed to informally share technology outside any system of financial incentives. When the global network works effectively toward global metrics, measurable improvement for all, regardless of nation or local government, can be made. Knowledge from accumulated research on organizational dynamics, knowledge management and communication should be applied to developing the structure for this network.

In this review, case studies focused on syntheses of active pharmaceutical ingredients, intermediates and lead compounds are reported employing micro reactors and continuous flow technology in areas such as medicinal chemistry, chemical development and manufacturing. The advantages of flow technology are currently very clear as opposed to conventional batch methods. Most strikingly and relevant for pharmaceutical’s time-to-market needs, flow processing has the important advantage of the ease with which reaction conditions can be scaled. As this technology is new and has major full-process scale implications, we also wanted to point out that this cannot be applied and released to all chemistries yet, thereby also critically mirroring disadvantages and advantages of the step-change technology. However, the positive impact has been dominating and thus pharmaceutical and fine-chemical industries have increased their awareness and interest in flow chemistry applications. Beyond pharmaceutical syntheses, this review aims to conclude with the special needs of pharmacy on flow and micro reactor chemistry, which is not the same as for the fine-chemical industry. Here, the needs of Brazil are considered, as the mirroring of micro reactor and flow chemistry was done from a European – academic and business – perspective. The hope is to stimulate and promote flow developments in emerging developing nations.

This paper describes the preparation of a ZSM-5 zeolite layer onto conventional Si wafers and Si micromonoliths, by using microwave-assisted seeded hydrothermal synthesis. A homogeneous ZSM-5 zeolite layer up to 680 nm was obtained over the external surface of a Si micromonolith (surface to volume ratio >300,000 m -1 ) after only 4 min of hydrothermal synthesis at 453 K. As a proof of concept, the catalytic activity of the prepared ZSM-5 coated micromonoliths, after a conventional Pt ion-exchange process, was demonstrated in the combustion of traces of n-hexane (200 ppmV) in air.

Continuous flow synthesis of many β-amino α, β-unsaturated esters has been demonstrated, through the reaction of a β-ketoester compound with ammonia and primary amines. Several combinations have been studied in detail in batch mode and a few have been taken for continuous flow synthesis based on their suitability. Upon studying the feasibility of continuous flow synthesis of different β-amino crotonates, the synthesis of methyl amino crotonate in the presence of a recyclable and reusable homogeneous acid catalyst has been studied in detail. Tubular reactors were seen to overcome the heat and mass transfer limitations, thereby providing a simple device for even a pilot scale production. A similar approach can be used for the synthesis of other β-amino crotonates. The continuous flow synthesis approach for producing methyl amino crotonate, in the absence of any external solvent, makes it a green process technology.

Transesterification of vegetable oil with methanol, promoted by alkaline catalysts has been tested in many different reactors and surprisingly the reaction time, in some of these reactors, resulted very short, in the range of few seconds. In particular, by using static mixers, micro-reactors, oscillatory flow reactors, cavitational reactors, microwave reactors or centrifugal contactors, it is possible to obtain high biodiesel yields in a much shorter time than in stirred tank reactors. As the reaction occurs between two immiscible phases, a general conclusion could be that the higher the interface area the shorter the reaction time. In this paper, we will confirm this assumption because, by using a very efficient micro-mixer, followed by a void tube, very high conversions have been obtained in a few seconds of residence time. Another important observation is that passing from 1% to 2% b.w. of KOH catalyst concentration, a very high increase in the conversion is obtained. This means that the final conversion is not due to the chemical equilibrium but to the catalyst deactivation. For describing all the observed phenomena a new biphasic kinetic model based on a reliable mechanism has recently been developed and used here for quantitatively describing the performed runs.

An efficient, green and simple solvent-free method is described for the synthesis of α-aminophosphonates based on one-pot three-component condensation of trimethylphosphite, aldehydes and amines in the presence of zinc iodide. This method offers some advantages such as shorter reaction times, simple work-up and excellent yield at room temperature.

N-methylol dimethylphosphonopropionamide flame retardant agent (FR) combined with a melamine resin crosslinking agent (CL) and a catalyst (phosphoric acid, PA) is used for enhancing the flame-retardant property of cotton fabrics. Titanium dioxide (TiO 2 )/nano-TiO 2 co-catalyst is added to the FR formulation in order to enhance the crosslinking of the FR-CL-PA components. Atmospheric pressure plasma jet is used as a pre-treatment, to enhance the fabric properties by a sputtering or etching effect. The Kawabata Evaluation System for Fabrics (KES-F) was used to determine the tensile, shearing, bending, compressional and surface properties. In comparison, with the control fabric the specimens after FR treatment had worse tensile, bending, compression, surface friction and variation properties; an improvement was observed only in the shearing properties. With the aid of plasma pre-treatment, tensile and compressional properties of the FR-treated specimens were improved, while the shearing and bending, as well as the surface friction and variation properties, were affected negatively. A neutralization process could neutralize excessive acids and remove both the unfixed chemicals on the treated fabric surfaces, and the unattached metal oxide particles as well. The process improved the fabric handle in some aspects, such as tensile energy, extensibility, shear stiffness, bending rigidity, bending moment, compressional linearity, compressional energy and coefficient of friction.

The treatment of commercially available polymethyl methacrylate (PMMA) microspheres with palladium (Pd)Cl 2 and formaldehyde, generated supported Pd(0)-PMMA with 0.79 (wt)% catalyst loading. The catalyst has been used for copper- and ligand-free Sonogashira reactions in aqueous media. It is highly reactive for the reactions of iodobenzenes with aryl acetylenes or alkyl acetylenes. The performance of the recovered catalyst had no significant difference in five cycles. The Pd leaching was detected at a very low level (2.1–9.8 ppm) for each cycle. PMMA-supported PdCl 2 , Pd(OAc) 2 , PdCO 3 , and PdCl 2 (MeCN) 2 have also been tested for Sonogashira reactions.

To ensure a sufficient reaction control, including fast mixing and heat removal, microstructured devices were chosen to conduct anionic polymerisations. To decrease the experimental effort and the resulting costs, a numerical approach was followed to apply decision support during experimental planning. Semi-quantitative CFD calculations were used to determine the best suited micromixer out of a collection of different devices. Using the numerical investigated micromixers for experimental investigations, the general order gained from CFD calculations was confirmed. It could be shown that CFD calculations can beneficially be used to rank micromixing devices for specific process conditions and synthesis tasks.

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