Biphasic workup

Gladysz and Rocaboy have reported the application of fluorous (diacetoxyiodo)arenes 123-126 (Figure 5.6) in oxidations of hydroquinones to quinones in this procedure the fluorous reagents can be conveniently recovered by simple liquid/liquid biphasic workups [107]. 

Likewise, the series of fluorous (dichloroiodo)arenes 127-129 and alkyl iodine(III) dichlorides 130-132 (Figure 5.7) have been prepared in 71-98% yields by reactions of the corresponding fluorous iodides with chlorine [69]. These compounds are effective reagents for the chlorination of alkenes (e.g., cyclooctene) and aromatic compounds (e.g., anisole, 4-rcrt-butylphenol and acetophenone). The organic chlorinated products and fluorous iodide co-products are easily separated by organic/fluorous liquid/liquid biphasic workups. The fluorous iodides can be recovered in 90-97% yields and reoxidized with chlorine [69]. 

Typically, the reaction is performed in a liquid-liquid biphasic system where the substrates and products (upper phase) are not miscible with the catalyst/ionic liquid solution (lower phase). The SiH-functional polydimethylsiloxane and the olefin are placed in the reaction vessel and heated up to 90 °C. Then the precious metal catalyst (20 ppm) and the ionic liquid (1 %) are added. After complete SiH conversion, the reaction mixture is cooled to room temperature and the products are removed from the reaction mixture by either simple decantation or filtration (in case of non-room-temperature ionic liquids). The recovered catalyst/ionic liquid solution can be reused several times without any significant change in catalytic activity. A treatment or workup of the ionic liquid-catalyst solution after each reaction cycle is not necessary. The metal content of the products was analyzed by ICP-OES (Inductively coupled plasma optical emission spectroscopy) and the chemical identity of the organomodified polydimethylsiloxane was verified by NMR spectroscopy. 

Often the starting point in these analyses is how to automate existing processes. This may not be practical and may involve a great deal of time and resources, ft is often better to rethink a traditional process from an automation point of view. A classic example of this is the effort that many companies have invested in the automation of a traditional aqueous workup. Mixing of biphasic mixtures has led to many problems. A better solution, in this case developed by rethinking the problem, is to use solid phase extraction (SPE) technology. 

Palladium-catalyzed amidocarbonylation of aldehyde amide mixtures was performed in ionic liquids to obtain N-acyl-a-amino acids [36]. It was found that strongly acidic ionic liquids such as [Rmim]HS04 (R= —(CH2)3S03H) act as powerful cocatalysts giving higher yields compared to traditionally added sulfuric acid. A subsequent biphasic approach was applied to the workup of catalytic batches and the catalyst-containing IL phase reused without further addition of palladium, phosphine, or cocatalyst. 

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