The in situ generation and reactive quench of diazonium compounds in the synthesis of azo compounds in microreactors

Abstract

SummaryIn this paper, a micro-fluidic optimized process for the continuous flow synthesis of azo compounds is presented. The continuous flow synthesis of Sudan II azo dye was used as a model reaction for the study. At found optimal azo coupling reaction temperature and pH an investigation of the optimum flow rates of the reactants for the diazotization and azo coupling reactions in Little Things Factory-MS microreactors was performed. A conversion of 98% was achieved in approximately 2.4 minutes and a small library of azo compounds was thus generated under these reaction conditions from couplers with aminated or hydroxylated aromatic systems. The scaled up synthesis of these compounds in PTFE tubing (i.d. 1.5 mm) was also investigated, where good reaction conversions ranging between 66–91% were attained.

Radical Arylation of Triphenyl Phosphite Catalyzed by Salicylic Acid: Mechanistic Investigations and Synthetic Applications

“…Trying to identify the catalytically active species of the process, we put into reacting the diazonium salt of 1h with SA. After careful crystallization, we only isolated the azo compound II-h in a rather low yield (Scheme e) . However, this tan azo compound was unreactive with stoichiometric amounts of TPP, as well as in THF solution, and catalytically inactive in the studied reaction (Scheme f).…”

Telescoped Sequence of Exothermic and Endothermic Reactions in Multistep Flow Synthesis

“…This reaction was carried out at 5 °C in a 4.5 mL coiled reactor, and reaction solution was maintained for a 113 s residence time. In order to estimate the yield of diazonium salt by HPLC, the reaction mixture at the outlet of the reactor was collected in several vials containing 2 to 10 mL of aqueous solution of β-naphthol (0.45 M) and NaOH (1.5 M). , The samples were collected over a period of 15–30 s to maintain the required stoichiometry to give Sudan-I dye, and the completion of reaction was monitored using HPLC.…”

Revisiting aromatic diazotization and aryl diazonium salts in continuous flow: highlighted research during 2001–2021

“…However, due to the low cost of PTFE and the ability to increase the conversion rate by adjusting the parameters, PTFE is still one of the most popular reactor materials for researchers at present. 93…”