Kinetics and mechanism study on the preparation of 4,4′-diaminostilbene-2,2′-disulfonic acid by reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid with zero-valent iron

Add time:09/28/2019    Source:infona.pl

This research is aimed at improving the understanding of the reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS) by zero-valent iron for the manufacture of 4,4′-diaminostilbene-2,2′-disulfonic acid (DSD). The formation of 5-amino-2-formylbenzene sulfonic acid (ABAS) during the process indicates that oxidation with the cleavage of CC double bond does occur besides the principle nitro-group reduction processes. The kinetics of the reduction of DNS and the formation of DSD are pseudo-first order. Typical k obs and kobs′ for the reduction of DNS and formation of DSD are 0.10898±0.01841min −1 and 0.07167±0.00213min −1 , respectively (with 20g/L, 60–80mesh and the BET surface area of 0.815m 2 g −1 zero-valent iron, at 40rpm mixing rate, 24°C, neutral unbuffered conditions). Surface-area normalized rate constant (k SA ) for the reduction of DNS is 0.4012Lm 2 h −1 . The effects of Fe 0 concentration, rate of mixing and temperature on the k SA were investigated, and the results indicate that the rates of reaction were controlled by mass transfer.

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