Vanillin Rhodia process

Another example of the substitution of classic routes for chemical synthesis by multistep catalytic processes is the Rhodia vanillin process (Figure 9.10), which involves four steps, all employing a heterogeneous catalyst. 

Figure 2.58 Rhodia vanillin process. Source adapted from Ratton [229].

Several syntheses exist for vanillin. A process recently developed by Rhodia seems to be superior [11]. The process (Scheme 5.2) involves four catalytic steps starting from phenol aromatic ring hydroxylation, O-methylation, hydroxymethyl-ation, and oxidation. The process combines elegance and precision in organic synthesis. 

An elegant example is the Rhodia process for the manufacture of the flavor ingredient, vanillin [30]. The process involves four steps, all performed with a heterogeneous catalyst, starting from phenol (Fig. 1.48). Overall, one equivalent of phenol, H202, CH3OH, H2CO and 02 are converted to one equivalent of vanillin and three equivalents of water. 

Vanillin is a flavoring agent used in syrups, ice cream, and other edible products. Xuebao Fine Chemicals Co. Ltd. (China) used to manufacture vanillin from o-nitro chlorobenzene. The process produced toxic chemicals, three to five different tars, high CODs, high VOCs, high health and safety risks, and unacceptable standards for a flavoring product. The plant dumped untreated effluents into a nearby river, and toxic tars were stockpiled in unmonitored landfills. Rhodia Chemicals purchased Xuebao in 2000. The process was modified so that it is now based on the catechol route (see Fig. 9.29). This process does not produce any waste and uses several heterogeneous catalysts. 

FIGURE 9.29. Catalytic vanillin synthesis Rhodia process. 

Rhodia A commercial process for making vanillin from guaiacol, developed by Rhodia in the 1970s. 

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