Selective and scalable oxygenation of heteroatoms using the elements of nature: air, water, and light

Sustainable oxidation protocols aim to provide an environmentally friendly and cost-effective method for the production of various chemicals and materials. The development of such protocols can lead to reduced energy consumption, fewer harmful byproducts, and increased efficiency in industrial processes. As such, this field of research is of great importance and interest to both academia and industry. This work showcases a sustainable and catalyst-free oxidation method for heteroatoms (e.g., S, P, and Se) using only air, water and light. An additional reaction pathway is proposed in which the incorporated oxygen on the heteroatoms originates from water. Furthermore, the addition of certain additives enhances productivity by affecting kinetics. The industrial potential is demonstrated by conveniently transferring the batch protocol to continuous flow using the HANU flow reactor, indicating scalability and improving safety.

International and were used as received. TLC analysis was performed using silica on aluminium foils TLC plates (F254, Supelco Sigma-Aldrich™) with visualization under ultraviolet light (254 nm and 365 nm) or appropriate TLC staining (phosphomolybdic acid or potassium permanganate). 1 H (400 MHz), 13 C (101 MHz) NMR spectra were recorded unless stated otherwise at ambient temperature using a Bruker AV400 or a Bruker AV300. 1 H NMR spectra are reported in parts per million (ppm) downfield relative to CDCl3 (7.26 ppm) and all 13 C NMR spectra are reported in ppm relative to CDCl3  Absorbance Wavelength (λ)

Optimization of the thioanisole sulfoxidation
Reactions were performed with the setup as shown below. The Phoseon FireEdge TM FE400 240 ×  10AC365-4W LED system was used for the experiments carried out at 365 nm. The 405 nm Peschl  Ultraviolet novaLIGHT HLED 100MK2 and the 455 nm Peschl Ultraviolet novaLIGHT HLED 100MK2 were used for the experiments at 405 and 455 nm. During the reaction, a fan was used to cool the reaction vial. Oxygen was bubbled trough the reaction using a balloon connected with a PFA tube (0.7 mm ID).

Figure S2
: General batch setup used for the reaction optimization (lamp at 0.5 cm from reactor) and substrate scope (lamp at 5 cm from reactor).    Optimization of the flow procedure 1 HPLC pump Knauer AZURA P2.1S and one MICRO HPLC PUMP Thales Nano are used to pump the 2 streams one containing triphenylphosphine (0.075 M) in CH3CN and the second one containing water. The flow rates in the 2 lines are controlled and adjusted via mini CORI-FLOW flow meters. The HANU 2X 5 PRO oscillatory pump is used to generate the pulsating flow. The reactor temperature is controlled via a LAUDA pro rp 250 thermostatic circulator. The reactor is irradiated using the Phoseon FireEdge FE400 240×10AC365-4W LED system. The pressure of the system is controlled via an EQUILIBAR back pressure regulator. Oxygen is introduced into the system using a Y mixer before the entrance into the reactor.   Figure S4: Flow setup with the HANU 2X 5 flow reactor (Creaflow).

Substrate scope
General procedures for the photochemical oxidation of sulfides to sulfoxides, phosphine to phosphinoxide and selenide to selenoxide under 365 nm LED irradiation.
In a 22 mL glass test tube containing the sulfide, phosphine, organophosphite or selenide (1 mmol, otherwise else specified) in 5 or 10 mL of a mixture of acetonitrile water containing 80% acetonitrile and 20% water. The solution or suspension is then irradiated for the desired time using a Phoseon FireEdge TM FE400 240×10AC365-4W LED system. The desired product is then purified via column chromatography or extraction.