Sulfonation in continuous-flow microreactors

A continuous-flow process for sulfonating 1,2-diaminobenzene with 100% yield, the continuous-flow process comprising:

• introducing a sulfonation mixture into a microreactor inlet of a continuous-flow microreactor to produce a flow of the sulfonation mixture through the continuous-flow microreactor, the sulfonation mixture comprising 1,2-aminobenzene dissolved in a molar excess of sulfuric acid, the continuous-flow microreactor comprising one individual fluidic module or a plurality of sequentially connected individual fluidic modules, wherein:
• each individual fluidic module comprises a module inlet and a module outlet, the module inlet in fluidic communication with the module outlet;
• each individual fluidic module comprises a continuous channel defined in a reaction volume of the individual fluidic module, the continuous channel defining a tortuous fluidic flowpath from a reaction-volume inlet of the reaction volume to a reaction-volume outlet of the reaction volume, the reaction-volume inlet being in fluidic communication with the module outlet, the reaction-volume outlet being in fluidic communication with the module outlet, the continuous channel having a continuous-channel width of from 0.4 mm to 6 mm;
• one individual fluidic module is an inlet module, such that an inlet-module inlet of the inlet module defines the microreactor inlet;
• one individual fluidic module further is an outlet module, such that an outlet-module outlet of the outlet module defines a microreactor outlet;
• at least one individual fluidic module is a residence module providing fluidic communication between the inlet module and the outlet module;
• and
• the microreactor outlet is in fluidic communication with the microreactor inlet through the continuous channel of each individual fluidic module;
• maintaining a reaction temperature of from 180° C. to about 220° C. in at least the at least one residence module while the sulfonation mixture flows from the microreactor inlet to the microreactor outlet for a total residence time from 25 to 60 minutes;
• receiving the sulfonation mixture from the microreactor outlet;
• and
• precipitating a sulfonated reaction product out of the sulfonation mixture received from the microreactor outlet.