Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations

Summary

A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

Abstract

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

Introduction

Flow chemistry is well poised towards the movement of green and sustainable processes^1,2. In contrast to batch reactors, continuous flow reactors possess significant advantages, such as improved thermal management, enhanced mixing control, and internal pressure regulation. These advantages greatly reduce the formation of by-products in the continuous flow system. Furthermore, continuous-flow enhances the biphasic gas-liquid reactions within the micro-tubing due to the excellent interfacial surface area of the reagents in different states. Continuous flow reactors also provide a good platform for photosynthesis....

Protocol

Refer to all relevant material safety data sheets (MSDS) before handling any possible toxic and carcinogenic chemicals. Conduct appropriate risk assessments before starting any reactions, including the use of engineering controls, such as fume hoods and gas cylinders, as well as wearing sufficient personal protective equipment. Proper training should be conducted before using any highly flammable gas to avoid any accidents caused by mishandling of the gas cylinders.

1. Gas-involved Reaction²

1. Preparation of acetylene tank
   Set gas regulator of acetylene tank to 20 psi (137895 Pa), abov....

Results

In this study, SFMT is used to carry out transformations that include gaseous reagents ( Table 1), light-mediated reactions (Table 2), and reactions that involves both gaseous reagents and photo-catalysis (Table 3).

Figure 1 displays a typical set-up for the gas regulator to be connected to the gas cylinder so as to regulate the pressure of the gas being pumped into the SFMT system.

Figure 2 represents the .......

Discussion

The newly developed SFMT reactor is a modification of the continuous-flow system by adding shut-off valves to the micro-tubing². In this system, the flow rate of a desired volume of reagents can be halted at will, simulating a batch reactor but in micro-tubing^2,10,11. These valves aid in the trapping of desired amount of reagents in the HPFA or stainless steel tubing while.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetylene Cylinder	Chem Gas PTE LTD (Singapore)
Logato 200 series Syringe pumps	KD Scientific Inc	788200
Blue LED Strips	Inwares Pte Ltd (Singapore)	3528 FlexiGlow LED Strips
PFA Tubing High Purity 1/16" OD x .030" ID x 50ft	IDEX Health&Science	1632-L	Depending on diameter of tubings needed
KDS Stainless Steel Syringe	KD Scientific Inc	780802
Shut-Off Valve Tefzel (ETFE) with 1/16" Fittings	IDEX Health&Science	P-782
BPR Assembly 20 psi	IDEX Health&Science	P-791
Luer Adapter Female Luer - Female Union	IDEX Health&Science	P-628	Known as syringe connector in this paper
1/4-28 Female to Male Luer Assy	IDEX Health&Science	P-675	Known as needle connector in this paper
Union Body PEEK .020 thru hole, for 1/16" OD"	IDEX Health&Science	P-702-01
Super Flangeless Ferrule w/SST Ring, 1/4-28 Flat-Bottom, for 1/16" OD	IDEX Health&Science	P-250X
PEEK Low Pressure Tee Assembly 1/16" PEEK .020 thru hole	IDEX Health&Science	P-712	Known as T-connector in this paper
Super Flangeless Nut PEEK 1/4-28 Flat-Bottom, for 1/16" & 1/32" OD	IDEX Health&Science	P-255X
Micro Metering Valve Assembly, 1/4-28 Flat-Bottom, for 1/16" OD	IDEX Health&Science	P-445NF	Known as Needle valve in this paper
Shut Off Valve Assembly PEEK .020	IDEX Health&Science	P-732
Terumo Syringe without needle	Terumo medical		1 mL and 3 mL depending on the volume needed
Terumo needle	Terumo medical		22G X 1½” (0.70 X 38 mm)
Sterican needle	B | Braun Sharing Enterprise		21G X 4¾” (0.80 X 120 mm)
Bruker ACF300 (300 MHz)			For 300 MHz NMR scanning
AV-III400 (400 MHZ)			For 400 MHz NMR scanning
AMX500 (500 MHz)			For 500 MHz NMR scanning
Merck 60 (0.040-0.063 mm) mesh silica gel	Merck
4-Iodoanisole	Sigma Aldrich	I7608-100G
412740 ALDRICH Bis(triphenylphosphine) palladium(II) dichloride ≥99% trace metals basis	Sigma Aldrich	412740-5G
Copper(I) iodide purum, ≥99.5%	Sigma Aldrich	03140-100G
N,N-Diisopropylethylamine	Tokyo Chemical Industry Co., Ltd	D1599
1, 3, 5-trimethoxybenzene	Tokyo Chemical Industry Co., Ltd	P0250
2,3-Dimethyl-2-butene ≥99%	Sigma Aldrich	220159-25ML
Bromopentafluorobenzene 99%	Sigma Aldrich	B75158-10G
TEMPO Green Alternative 98%	Sigma Aldrich	214000-25G
Acetonitrile	Sigma Aldrich	271004-1L
Diethylether	Sigma Aldrich	346136-1L
Dimethyl sulfoxide	VWR chemical	23500.322- 25L
1,2-Dichloroethane	Sigma Aldrich	284505-1L
9-mesityl-10-methylacridinium perchlorate			Refer to Ref. 8 for synthesis
Ir(ppy)2(dtbbpy)PF6			Refer to Ref. 9 for synthesis