Flow synthesis using gaseous ammonia in a Teflon AF-2400 tube-in-tube reactor: Paal–Knorr pyrrole formation and gas concentration measurement by inline flow titration

The Use of Gases in Flow Synthesis

“…104 The synthesis of thioureas using gaseous ammonia in flow was also reported with excellent yields achieved from the corresponding isothiocyanates. 104 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 70…”

4. Technology overview/Overview of the devices

“…In the presented example (Figure 4.20) the gas flows in the outer tube, but a similar reaction is feasible with the gas in the inner tube instead [22].…”

Development of methodologies for reactions involving gases as reagents: microwave heating and conventionally-heated continuous-flow processing as examples

“…Diffusion through the inner tube membrane allows for the transfer of gas into the reagent stream. This approach has been successful for numerous reactions, including the ozonolysis of alkenes [79], carboxylation of Grignard reagents with CO 2 [80], Heck reactions using ethene [81], pyrrole and thiourea formation using ammonia [82,83], and both homogeneous and heterogeneous hydrogenation reactions [84,85]. This tube-in-tube design, while excellent for ambient reactions, is not amenable to operation at elevated temperatures.…”