&#160;We are grateful for the financial support provided by the National University of Singapore (R-143-000-645-112, R-143-000-665-114) and GSK-EDB (R-143-000-687-592).

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
<ol>
	<li>Preparation of acetylene tank 
	Set gas regulator of acetylene tank to 20 psi (137895 Pa), above the desired back-pressure of 5 psi (34474 Pa) used in the system. 
	Note: Refer to Figure 1 on more details of the gas regulator set up. 
	Note: Back-pressure regulator (BPR) is set at the end of the tubing, refer to Figure 2 and 3 for more details on the SFMT set-up.</li>
	<li>Preparation of 4-iodoanisole solution
	<ol>
		<li>Add a 10 mm magnetic stir bar into a 10 mL round-bottom flask.</li>
		<li>Measure 58.5 mg 4-iodoanisole with a weighing balance and transfer to the round-bottom flask. 
		Caution: Aryl halides are irritants and can be harmful. Consult the relevant MSDSs before proceeding.</li>
		<li>Add 8.5 mg Pd(PPh3)2Cl2, 1.0mg copper(I) iodide, 21.0 mg 1, 3, 5-trimethoxybenzene (internal standard) and 80 &#181;L N,N-Diisopropylethylamine (DIPEA) into the same round-bottom flask. Add approximately 2.5 mL of dimethyl sulfoxide (DMSO) to the round-bottom flask. 
		Caution: Pd(PPh3)2Cl2, copper(I) iodide, DIPEA are irritants and can be harmful. Consult the relevant MSDSs before proceeding. 
		Caution: 1, 3, 5-trimethoxybenzene are flammable and volatile. Keep away from ignition sources. 
		Caution: DMSO is a toxic chemical. Consult the relevant MSDSs before proceeding.</li>
		<li>Seal the round bottom flask with a rubber septum and mixture was stir on a heat plate at room temperature and pressure until all the solid have dissolved. 
		Note: Further sonication can be done to ensure a homogenous solution.</li>
		<li>Degas the reaction mixture with argon-filled balloon for approximately 15 min while maintaining a constant stirring on heat plate. Remove both needles after 15 min to ensure an inert environment within the round-bottom flask. 
		Note: Refer to Figure 4 for details on degas procedure.</li>
	</ol>
	</li>
	<li>Mixing of liquid-gas layer in SFMT reactor
	<ol>
		<li>Extract all the reaction mixture from the round bottom flask with a 8 mL stainless steel syringe connected to a long needle via a needle connector through the rubber septum. Remove the needle and attach the stainless steel syringe to the syringe pump. Connect the syringe to High purity Perfluoroalkoxy alkanes (HPFA) tubing (O.D. 1/16&#34;, I.D. 0.03&#34;, 300 cm, volume = 1.37 mL) via a T-connector. 
		Note: Use a needle connector to connect both the stainless steel and long needle, refer to Figure 5 for more details on using the needle connector. 
		Note: All air bubbles should be remove from the stainless steel syringe before attaching to the syringe pump. 
		Note: Ensure that all the tubing are tighten before connecting the reaction mixture to the set-up to reduce exposure of air, refer to Figure 2 and 3 on the connections for the tubing.</li>
		<li>Set flow rate of the syringe pump to 300 &#181;L/min for the reaction mixture to be pumped into the HPFA tubing. Adjust the flow rate of acetylene with the needle valve to about 1:1 liquid:gas ratio along the plugs. Equilibrated ratio was maintained until the HPFA tubing is filled with gas/liquid slug reagents. 
		Caution: Acetylene is highly flammable. Keep away from ignition sources. 
		Note: BPR is placed in acetone vial before purging the tubing with acetylene gas. 
		Note: Purge the tubing with acetylene gas first until bubble is observed in the acetone vial for the BPR to ensure that the pressure is built up within the SFMT reactor before pumping the reaction mixture into the SFMT reactor. Refer to Figure 6 for better illustration of the liquid:gas ratio.</li>
		<li>Close the valve at the end when all the liquid had been injected into the HPFA tubing or when liquid start to leak from the BPR. Pump in more acetylene until the liquid stops moving in the tubing in order to maintain the pressure within the tubing. Close the valve at the start point and close the needle valve once complete. Transfer the whole set-up into the oil bath and incubate for 2 hours. 
		Note: The valves are kept above the oil bath to prevent contamination from the silicon oil. 
		Note: Pre-heat the oil bath to the desired temperature before transferring the SFMT reactor to it.</li>
		<li>After 1 hour, pump the reaction mixture into a 10 mL vial using a 8 mL stainless steel syringe. Fill an 8 mL stainless steel syringe with diethyl ether (approximately 4.0 mL) to wash out any residue in the tubing. 
		Caution: Diethyl ether is highly flammable. Keep away from all ignition sources. 
		Note: Hexane could be used to wash away the silicon oil before proceeding to avoid contamination for subsequent steps.</li>
		<li>Saturated NH4Cl aqueous solution (4.0 mL) was added to the combined organic layer, followed by a liquid-liquid extraction with 1.5 mL diethyl ether, with the aid of a separatory funnel. 
		Caution: NH4Cl may be harmful. Consult the relevant MSDSs before proceeding.</li>
		<li>Conduct a gas chromatography mass spectrum (GC-MS) analysis with the organic layer to determine the yield. 
		Note: 1, 3, 5-trimethoxybenzene was added in step 1.2.3 as an internal standard. 
		Note: An internal standard calibration curve was plot with different mass of the product to derive a linear regression curve. The yield of the product is interpolated from the linear regression curve. Refer to Ref. 2 for more details on the calibration curve.</li>
	</ol>
	</li>
</ol>
2. Photo-mediated Reaction5
<ol>
	<li>Add 30.8 mg benzylidenemalonitrile, 4.1 mg 9-mesityl-10-methylacridinium perchlorate, 67.3 mg tetramethylethylene and 2.0 mL dichloroethane into a 10 mL silicon septa vial. 
	Caution: Benzylidenemalonitrile, 9-mesityl-10-methylacridinium perchlorate, tetramethylethylene and dichloroethane are highly flammable. Keep away from all ignition sources.</li>
	<li>Degas for about 15 minutes with argon-filled balloon. Remove both needles after 15 min to ensure an inert environment within the vial. 
	Note: Refer to Figure 4 for details on degas procedure.</li>
	<li>Purge the HPFA tubing (O.D. 1/16&#34;, I.D. 0.03&#34;, 340 cm, volume = 1.5 mL) with argon gas for approximately 5 min by direct connection of the SFMT reactor to the argon gas cylinder with an Union body PEEK. Close both valves to entrap the argon gas within the HPFA tubing after reaching the indicating time of 5 min. 
	Note: Refer to Figure 5 for more details on using the Union body PEEK.</li>
	<li>With a 3 mL disposable syringe attached with a long needle, extract the reaction mixture from 10 mL silicon septa vial. Remove the needle and connect the disposable syringe to the HPFA tubing via a syringe connector. Open both valves to pump in the reaction mixture manually. Close both valves again once the HPFA tubing has been filled with the reaction mixture. 
	Note: Refer to Figure 5 for more details on using the syringe connector. 
	Note: Mix the reaction mixture well with the syringe to ensure a homogenous solution before pumping into the HPFA tubing. 
	Note: There may be excess solvent that will exceed the tubing volume. Place the tubing end on a waste can to collect any overflowed reaction mixture.</li>
	<li>Place the SFMT reactor in the middle of the blue LED (&#955;max = 425 nm, 2 m, 20 W) stripe to ensure equal exposure of the HPFA tubing. The HPFA was exposed for irradiation for approximately 5-48 hours. 
	Note: The length of the blue LED stripe is set to 2 meters to provide enough energy for the reaction to proceed.</li>
	<li>Pump out the reaction mixture with 3 mL disposable syringe into a clean round-bottom flask with a syringe connector piece. Wash out any residue with excess diethyl ether using a 3 mL disposable syringe into the same round-bottom flask. 
	Note: Refer to Figure 5 for more details on using the syringe connector.</li>
	<li>Measure 0.06 mmol of 1, 3, 5-trimethoxybenzene (internal standard) and add to combined organic mixture. Remove excess solvent under reduced pressure with a rotavap machine.</li>
	<li>Measure 0.6 mL of deuterated chloroform with 1 mL disposable syringe attached with long needle and add to the concentrated crude product. Transfer the deuterated mixture into a clean NMR tube for crude 1H NMR analysis. 
	Note: The integral (x) for internal standard at 6.10 ppm is used to calculate the conversion rate by comparing the integral (y) of product formed at 3.38 ppm. 
	<img alt="Equation 1" src="/files/ftp_upload/56897/56897eq1v2.jpg" /></li>
</ol>
3. Photo-mediated Gas-involved Reaction2
<ol>
	<li>Preparation of acetylene tank 
	Set the gas regulator of the acetylene tank to about 20 psi (137895 Pa) which is above the desired back-pressure of 5 psi (34474 Pa) in the system. 
	Note: Refer to Figure 1 on more details of the gas regulator set up. 
	Note: Back-pressure regulator (BPR) is set at the end of the tubing, refer to Figure 2 and 3 for more details on the SFMT set-up.</li>
	<li>Preparation of bromopentafluorobenzene solution
	<ol>
		<li>Under inert atmosphere, add 74.1 mg bromopentafluorobenzene , 2.8 mg Ir(ppy)2(dtbbpy)PF6 and 46.8 mg 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) into a 10 mL silicon septa. Add 3.0 mL of acetonitrile into the same 10 mL glass vial to dissolve all the reagents. 
		Caution: Bromopentafluorobenzene and acetonitrile are highly flammable and volatile. Keep away from all ignition sources. 
		Caution: Ir(ppy)2(dtbbpy)PF6 and TEMPO may be harmful. Consult the relevant MSDSs before proceeding.</li>
		<li>Degas the reaction mixture with argon-filled balloon carefully for 10 minutes in an ice bath. Remove both needles from the septa to ensure an inert atmosphere in the vial. 
		Note: Refer to Figure 4 for details on degas procedure.</li>
		<li>Add 56.0 &#181;L of DIPEA into the mixture with a 1 mL syringe and degas for another 5 minutes in an ice bath similar to step 3.2.2.</li>
	</ol>
	</li>
	<li>Mixing of liquid-gas layer in SFMT reactor
	<ol>
		<li>With a 8 mL stainless steel syringe attached with long needle via a needle connector, extract the reaction mixture from the silicon septa vial. Remove the needle and attach the syringe to the syringe pump. Connect the outlet to T-connector. 
		Note: Use a needle connector to connect both the stainless steel and long needle, refer to Figure 5 for more details on using the needle connector. 
		Note: All gas should be remove from the stainless steel syringe before attaching to the syringe pump. 
		Note: Ensure that all the tubing are tighten before connecting the reaction mixture to the set-up to reduce exposure of gas, refer to Figure 2 and 3 on the connections for the tubing.</li>
		<li>Set the flow apparatus&#39; flow rate to 100 &#181;L/min and pump the reaction mixture into the HPFA tubing (O.D. 1/16&#34;, I.D. 0.03&#34;, 300 cm, volume = 1.37 mL). Adjust the flow rate of acetylene with the needle valve until 2:1 gas/liquid ratio is observed in the plug. The ratio plugs was determine via estimation in the clear tubing. 
		Note: BPR is placed in acetone vial before purging the tubing with acetylene gas. 
		Note: Purge the tubing with acetylene gas first until bubble is observed in the acetone vial for the BPR to ensure that the pressure is built up within the SFMT reactor before pumping reaction mixture into the SFMT reactor. 
		Note: Refer to Figure 6 for better illustration of the liquid:gas ratio but take note that the volume of the gas should be double the volume of the liquid in the plug by visual estimation.</li>
		<li>Close the valve at the end when all the liquid had been injected into the SFMT reactor (total volume 0.65 ml, 0.065 mmol) or when liquid started to leak from the BPR. Pump in more acetylene until the liquid stop moving in the tubing. Close the valve at the start point and close the needle valve once done. Transfer the whole set-up to a water bath pre-heated to 60&#176;C, and allowed to react for 3 h under blue LED light (&#955;max = 425 nm, 3 m, 30 W). 
		Note: The valves are left above the water bath to prevent any contamination. 
		Note: The length of the blue LED stripe is set to 3 meters to provide enough energy for the reaction to proceed.</li>
		<li>Pump the reaction mixture from the HPFA tubing with a 8 mL stainless syringe into a round-bottom flask. Wash out the residues from the tubing reactor with excess diethyl ether into the same round-bottom flask. Concentrate the mixture under reduced pressure with a rotavap machine. 
		Note: Carefully reduce the pressure as the starting material and products are highly volatile.</li>
		<li>Add 0.6 mL of deuterated chloroform via a 1 mL disposable syringe into the round-bottom flask to dissolve the concentrated crude mixture. Transfer the deuterated mixture into an NMR tubing for 19F NMR analysis. 
		Note: The 19F NMR spectrums of the starting material (bromopentafluorobenzene) and the 2 products (2, 3, 4, 5, 6-Pentafluorostyrene and pentafluorobenzene) were analysed to find a significant peak for each chemical. The crude 19F NMR spectrum is used to compare the integral of these 3 significant peaks in order to determine the ratio of product formed. Refer to Ref. 2 for more details on the calculation of the product conversion and product ratio.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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-tubing2,10,11. These valves aid in the trapping of desired amount of reagents in the HPFA or stainless steel tubing while...

Flow chemistry is well poised towards the movement of green and sustainable processes1,2. 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 due to the enhanced and uniform light illumination across the micro-tubing3.
Despite success in continuous-flow technology, there are still limitations in reaction screening for parameters that involve catalysts, solvents and reagents2. Changes made to the pressure in the flow system will drastically affect the flow equilibrium. Moreover, a classic continuous flow system generally is limited to one reaction screening at a time, making it time consuming for efficient parallel reaction screening. The reaction time in continuous flow synthesis is also limited by its micro-tubing reactor size. Furthermore, continuous flow screening is prone to cross-contamination at higher temperature, even though carrier medium is employed between different reactions4.
Hence, to address the difficulty of screening discrete parameters in continuous-flow systems, we developed a stop-flow micro-tubing (SFMT) reactor system for reaction screening that involves gaseous reagents and/or photo-mediated reactions2. SFMT reactors comprise elements of both batch reactors and continuous flow reactors. The introduction of shut-off valves entraps the reagents within the micro-tubing, a concept that is similar to a batch reactor, and when the system is pressurized, the SFMT behaves as a miniature high-pressure reactor. The SFMT can then be submerged into a water or oil bath, introducing heat to the reactor system. Visible lights can also be shone on the micro-tubing during the reaction period to facilitate photo-mediated reactions.
In SFMT, flammable or toxic gases, such as ethylene, acetylene, and carbon monoxide, can be utilized to generate valuable chemicals in a safer way compared to batch reactors1,2,4. It is an asset to use such reactive gases as they are inexpensive chemical feedstocks and can be readily removed after reactions are completed, providing a cleaner procedure2. On the contrary, most reaction development carried out in batch reactors tends to exclude the use of reactive gases due to its inconvenience and risk of explosion at elevated pressure and temperature. If gaseous reagents are employed, they are usually introduced into batch reactors via bubbling or balloons. This generally gave lower reproducibility or reactivity due to the low mixing efficiency at the interface. Although high-pressure vessels are commonly applied to enhance reactivity and solubility of gases, they are laborious with a risk of explosion, especially with flammable gases. In addition, the opaque surface of those commonly used high-pressure reactors made it unsuitable for photo-mediated reactions. Hence, reactions that consist of gaseous reagents and photo-mediated reactions are generally left unexplored. In this context, SFMT reactors provide an ideal platform because the gaseous reagents can be utilized within the micro-tubing with the assistance of a back pressure regulator (BPR) to regulate the internal pressure in a safe and convenient manner2. Apart from reactions that involve gaseous reagents, visible-light promoted synthesis also displays great promises for organic synthesis5,6. However, one of the greatest downfall of visible-light mediated reactions is the scalability in conventional batch reactors due to the attenuation effect of photon transport in large vessels7. If high-power light sources are used, over-irradiation may result in by-product formation. Moreover, gaseous reagents have seldom been applied in photo-chemical reactions mainly due to the complex apparatus system when using gas-phase reactants at high pressure2. Through the introduction of a narrow channel, like SFMT, a high-pressure gas environment can be easily achieved under light irradiation.
Hence, this detailed video aims to help more scientists understand the advantages and the procedure of using SFMT for condition screening of gas-involved transformations and light-mediated reactions.

<table>
	<tbody>
		<tr>
			<td>Acetylene Cylinder</td>
			<td>Chem Gas PTE LTD (Singapore)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Logato 200 series Syringe pumps</td>
			<td>KD Scientific Inc</td>
			<td>788200</td>
			<td></td>
		</tr>
		<tr>
			<td>Blue LED Strips</td>
			<td>Inwares Pte Ltd (Singapore)</td>
			<td>3528 FlexiGlow LED Strips</td>
			<td></td>
		</tr>
		<tr>
			<td>PFA Tubing High Purity 1/16&#34; OD x .030&#34; ID x 50ft</td>
			<td>IDEX Health&#38;Science</td>
			<td>1632-L</td>
			<td>Depending on diameter of tubings needed</td>
		</tr>
		<tr>
			<td>KDS Stainless Steel Syringe</td>
			<td>KD Scientific Inc</td>
			<td>780802</td>
			<td></td>
		</tr>
		<tr>
			<td>Shut-Off Valve Tefzel (ETFE) with 1/16&#34; Fittings</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-782</td>
			<td></td>
		</tr>
		<tr>
			<td>BPR Assembly 20 psi</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-791</td>
			<td></td>
		</tr>
		<tr>
			<td>Luer Adapter Female Luer - Female Union</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-628</td>
			<td>Known as syringe connector in this paper</td>
		</tr>
		<tr>
			<td>1/4-28 Female to Male Luer Assy</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-675</td>
			<td>Known as needle connector in this paper</td>
		</tr>
		<tr>
			<td>Union Body PEEK .020 thru hole, for 1/16&#34; OD&#34;</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-702-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Super Flangeless Ferrule w/SST Ring, 1/4-28 Flat-Bottom, for 1/16&#34; OD</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-250X</td>
			<td></td>
		</tr>
		<tr>
			<td>PEEK Low Pressure Tee Assembly 1/16&#34; PEEK .020 thru hole</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-712</td>
			<td>Known as T-connector in this paper</td>
		</tr>
		<tr>
			<td>Super Flangeless Nut PEEK 1/4-28 Flat-Bottom, for 1/16&#34; &#38; 1/32&#34; OD</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-255X</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Metering Valve Assembly, 1/4-28 Flat-Bottom, for 1/16&#34; OD</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-445NF</td>
			<td>Known as Needle valve in this paper</td>
		</tr>
		<tr>
			<td>Shut Off Valve Assembly PEEK .020</td>
			<td>IDEX Health&#38;Science</td>
			<td>P-732</td>
			<td></td>
		</tr>
		<tr>
			<td>Terumo Syringe without needle</td>
			<td>Terumo medical</td>
			<td></td>
			<td>1 mL and 3 mL depending on the volume needed</td>
		</tr>
		<tr>
			<td>Terumo needle</td>
			<td>Terumo medical</td>
			<td></td>
			<td>22G X 1&#189;&#8221; 
			(0.70 X 38 mm)</td>
		</tr>
		<tr>
			<td>Sterican needle</td>
			<td>B | Braun Sharing Enterprise</td>
			<td></td>
			<td>21G X 4&#190;&#8221; 
			(0.80 X 120 mm)</td>
		</tr>
		<tr>
			<td>Bruker ACF300 (300 MHz)</td>
			<td></td>
			<td></td>
			<td>For 300 MHz NMR scanning</td>
		</tr>
		<tr>
			<td>AV-III400 (400 MHZ)</td>
			<td></td>
			<td></td>
			<td>For 400 MHz NMR scanning</td>
		</tr>
		<tr>
			<td>AMX500 (500 MHz)</td>
			<td></td>
			<td></td>
			<td>For 500 MHz NMR scanning</td>
		</tr>
		<tr>
			<td>Merck 60 (0.040-0.063 mm) mesh silica gel</td>
			<td>Merck</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>4-Iodoanisole</td>
			<td>Sigma Aldrich</td>
			<td>I7608-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>412740 ALDRICH 
			Bis(triphenylphosphine) 
			palladium(II) dichloride 
			&#8805;99% trace metals basis</td>
			<td>Sigma Aldrich</td>
			<td>412740-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper(I) iodide 
			purum, &#8805;99.5%</td>
			<td>Sigma Aldrich</td>
			<td>03140-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N-Diisopropylethylamine</td>
			<td>Tokyo Chemical Industry Co., Ltd</td>
			<td>D1599</td>
			<td></td>
		</tr>
		<tr>
			<td>1, 3, 5-trimethoxybenzene</td>
			<td>Tokyo Chemical Industry Co., Ltd</td>
			<td>P0250</td>
			<td></td>
		</tr>
		<tr>
			<td>2,3-Dimethyl-2-butene 
			&#8805;99%</td>
			<td>Sigma Aldrich</td>
			<td>220159-25ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromopentafluorobenzene 
			99%</td>
			<td>Sigma Aldrich</td>
			<td>B75158-10G</td>
			<td></td>
		</tr>
		<tr>
			<td>TEMPO Green Alternative 
			98%</td>
			<td>Sigma Aldrich</td>
			<td>214000-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Sigma Aldrich</td>
			<td>271004-1L</td>
			<td></td>
		</tr>
		<tr>
			<td>Diethylether</td>
			<td>Sigma Aldrich</td>
			<td>346136-1L</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>VWR chemical</td>
			<td>23500.322- 25L</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-Dichloroethane</td>
			<td>Sigma Aldrich</td>
			<td>284505-1L</td>
			<td></td>
		</tr>
		<tr>
			<td>9-mesityl-10-methylacridinium perchlorate</td>
			<td></td>
			<td></td>
			<td>Refer to Ref. 8 for synthesis</td>
		</tr>
		<tr>
			<td>Ir(ppy)2(dtbbpy)PF6</td>
			<td></td>
			<td></td>
			<td>Refer to Ref. 9 for synthesis</td>
		</tr>
	</tbody>
</table>

utilization of stop-flow micro-tubing reactors for the development of organic transformations

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.

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 ...

Watch this Scientific Journal Video about Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations at JoVE.com

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

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

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional ...

utilization-stop-flow-micro-tubing-reactors-for-development-organic

Research

JoVE Journal

Chemistry

39.0K Views.  National University of Singapore. A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

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

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic acids containing three to six carbons), such as malate and citrate, are critical to the proper functioning of many biological systems, where they function in cellular respiration and can serve as indicators of cell health. In foods, organic acid content can have significant impact on taste, with increased SCCA levels resulting in a sour or &#34;acid&#34; taste. Because of this, methods for the rapid analysis of organic acid levels are of particular interest to the food and beverage industries. Unfortunately, however, most methods used for SCCA quantification are dependent on time-consuming protocols requiring the derivatization of samples with hazardous reagents, followed by costly chromatographic and/or mass spectrometric analyses. This method details an alternate method for the detection and quantification of organic acids from plant material and food samples using free zonal capillary electrophoresis (CZE), sometimes simply referred to as capillary electrophoresis (CE). CZE provides a cost-effective method for measuring SCCAs with a low limit of detection (0.005 mg/ml). This article details the extraction and quantification of SCCAs from plant samples. While the method provided focuses on measurement of SCCAs from coffee beans, the method provided can be applied to multiple plant-based food materials.

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

This article presents a method for the detection and quantification of organic acids from plant material using free zonal capillary electrophoresis. An example of the potential application of this method, determining the effects of a secondary fermentation on organic acid levels in coffee seeds, is provided.

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...