Fullerene‐Promoted Singlet‐Oxygen Photochemical Oxygenations in Glass‐Polymer Microstructured Reactors

Abstract

In this paper we report the fabrication of thiolene-based microstructured reactors (MRs) that have been specifically designed to include solid-supported reagents within the microchannels network. We propose a convenient solution to realize reversible press-fit, leak-proof interconnects that greatly simplify the MR coupling to the external environment such as capillary tubing, sample reservoirs and pumps. The MRs have been used to carry out the oxidation of alpha-terpinene and methionine using [60]fullerene, covalently linked to Tentage](R) and silica gel matrices, as a singlet oxygen sensitizer. High conversions have been observed for both substrates although, in the case of a-terpinene, a partial photodegradation of the endo-peroxide product was detected. Interestingly, in the case of methionine, a quantitative conversion to the corresponding sulfoxides was achieved in about 40 seconds, using lowpower, white LED illumination. The reaction time is considerably shorter when compared to the batch procedure that requires, for the same process, about one hour illumination and the use of a 300-W tungsten halogen lam

Flow photochemistry: Old light through new windows

“…Returning to the oxidation of α-terpinene, moderate yields of ascaridole were obtained by using a silica-supported fullerene promoter [38]. Similarly, L-methionine was efficiently oxidised to the corresponding sulphoxide in the same reactor [38].…”

Liquid phase oxidation chemistry in continuous-flow microreactors

“…202 Fullerenes were used as photosensitizer for the singlet oxygen oxidation of α-terpinene and methionine. In both cases, quantitative conversions could be obtained within 40-50 seconds of residence time.…”

A flow reactor setup for photochemistry of biphasic gas/liquid reactions

“…The efficiency of chemical reactions can be greatly enhanced over common batch processes and new approaches to the optimization of established reaction protocols and the execution of hitherto unfeasible processes can be enabled due to the inherent properties of micro/flow reactors: high mass-transfer rates [8], spatial separation of reagent addition and mixing, high reagent dispersion, high energy efficiency, improved irradiation [9–11], ease of upscaling, low hazard potential and multidimensional parameter control [7,9,11–12]. Over the past decade, various reactor types and technical specifications have been developed to address the intricate challenges of many chemical reactions, including the handling of hazardous [13–14] or explosive [15–16] reagents, advanced concentration and temperature gradients [17], multiphasic reactions including solid-phase protocols [18], addition of gaseous reagents [19], high-pressure conditions [20], cascade conversions without intermediate work-up operations [21], as well as thin film, falling film [22], micro-channel [23], and tube-in-tube reactors [24–25] for reactions between gaseous and liquid components. The high energy efficiency, low hazard potential, and precise control of reaction parameters have also prompted several adoptions of microflow techniques in technical manufactures of fine chemicals, polymers [26], and pharmaceutical intermediates [27–30].…”

“…Only very few microreactor setups for such “quasi tri-phasic” processes have been reported [33–34]; most of them are film/falling film [22], microchannel [23,35] or simple tube reactors [35–37]. The reactor reported herein differs from most of the known systems in some key characteristics.…”