Recyclable reagents

Oxidation and reduction reactions can be carried out usiag reformer hydrogen and oxygen from the air. To decide when electroorganic synthesis is likely to be a viable option for a desired product, some opportunity factors are use of cheaper feedstock elimination of process step(s) or a difficult reaction avoidance of waste disposal, toxic materials, and/or abiUty to recycle reagent and abiUty to obtain products from anode and cathode. 

Process Schematic. The final installation in our main production sequence will be the recycle of reagent salts. There are quite a number of options involved in recycling reagents from nearly every operation. Figure 12 shows the process schematic where the three major salt recycle steps are highlighted by heavy lines. 

The methanesulfonates (481) of a-hydroxy esters can be converted to the deoxygenated esters (482) in 70 88% yields by indirect electrolysis with PhSeSePh as a recyclable reagent in a divided cell (Scheme 166). The procedure involves the formation of a-phenylselenoester by substitution of the a-methylsulfonyloxyl group with the PhSe followed by displacement of the CK-phenylseleno group with PhSe . The electrolysis is performed in a DMF-NaCl04-(Pt/C) system in the presence of PhSeSePh and ethyl malonate at 50 °C [567]. 

The electrochemical transformation of 2-methoxy- and 2-methylphenols to give orthoquinoid cyclohexadienone synthons with the aid of iodanes has been reported [173]. Iodanes (or hyperva-lent iodine [174, 175]) are a large family of reagents [176, 177] and often beneficial as clean and recyclable reagents [178]. The two most often utilized reagents are 2-Iodoxybenzoic (IBX) acid and l,l,l-triacetoxy-l,l-dihydro-l,2-benziodoxol-3(lH)-one (Dess-Martin pe-riodinane, DMP) (see Scheme 7). These... 

In the case of catalytic systems, the tedious and expensive synthesis of a concave catalyst is compensated by its (theoretically) unlimited recyclability. Reagents, in contrast, are used up in a reaction. Therefore, concave reagents will only be attractive when, after the reaction, the used functional groups can be returned into the active original functionality. They must be rechargeable . This is trivial for acids and bases but in principle should also be realizable for redox reagents. 

R = I(OAc)2, I(02C-CF3)2, and I(OH)OTs, respectively]. In addition to being useful for general oxidations (alcohol to ketone, hydroquinone to quinone, etc.), the recyclable reagents catalyse a-tosyloxylation of methyl alkyl ketones on the more hindered side, an ostensibly unexpected result for such a bulky reagent. 

Reagents that are not converted in the reactor can be recovered and recycled. Reagents that become converted to byproducts usually cannot be recovered, and the byproducts must be purified for sale or else disposed as waste (see Section 6.4.8). 

Qureshi ZS, Deshmttkh KM, Tambade PI et al (2010) Amberlyst-15 in ionic liquid an efficient and recyclable reagent for the benzylation and hydroalkylation of P-dicarbonyl com-potmds. Tetrahedron Lett 51 724-729... 

He X, Chan TH (2006) New non-volatile and odorless organosulfur compounds anchored on ionic liquids. Recyclable reagents for Swem oxidation. Tetrahedron 62 3389-3394... 

When our company planned to enter the market of vitamin E from natural sources, two major issues had to be addressed. First of all, large amounts of SDDs had to be made available as the starting material for the process. This was realized by a collaboration with Cargill Inc. [30]. Secondly, the permethylation procedures known at that time (that is in the early 1990s) had several serious drawbacks. After intensive research and development work we now perform such processes on an industrial scale in high yield and selectivity and with recyclable reagents [31-33]. 

Iodosylarenes other than iodosylbenzene have also been used in the transition metal catalyzed oxidation reactions. The soluble o-(tert-butylsulfonyl)iodosylbenzene (Section 2.1.4) can serve as an alternative to iodosylbenzene in (porphyrin)manganese(III)-catalyzed alkene epoxidation reactions [718]. A convenient recyclable reagent, w-iodosylbenzoic acid, can selectively oxidize primary and secondary alcohols to the... 

Recyclable reagent 2 is a convenient chlorinating reagent with a reactivity pattern similar to that of (dichloroiodo)benzene. Scheme 5.2 shows several representative chlorinations of organic substrates [10]. The final products are conveniently separated from the polymeric by-product by simple filtration and isolated in... 

Charette and coworkers have developed tetraarylphosphonium (TAP)-supported (diacetoxyiodo)benzene 109 (Figure 5.5), which can be used as a recyclable reagent or a catalyst for the a-acetoxylation of ketones [101]. Similarly to the imidazolium-supported [bis(acyloxy)iodo]arene 99, the reduced form of the TAP-supported reagent 109 can be recovered from the reaction mixture by simple filtration after treatment with ether. 

Bis(trifluoroacetoxy)iodo]perfluoroalkanes are effective recyclable reagents for the oxidation of aliphatic and benzylic secondary alcohols 119 to ketones 120 in the presence of KBr in aqueous solution (Scheme 5.38) [103]. The reduced form of the reagent, the respective iodoperfluoroalkanes 118, can be efficiently isolated from the reaction mixture in 96-98% yield by adding three to five volumes of methanol and separating the resulting fluorous/methanolic liquid/liquid biphasic system. The recovered iodoperfluoroalkanes 118 can be reoxidized to reagents 116 and reused [103]. 

Iodyl-3-propoxypyridine (136) has moderate solubility in organic solvents (e.g., 1.1 mg mr in acetonitrile) and it can be used as a recyclable reagent for the oxidation of sulfides to sulfoxides and alcohols to the respective carbonyl compounds (Scheme 5.41) [109]. The reduced form of this reagent, 2-iodo-3-propoxypyridine (135), can be effectively separated from the reaction mixture by treatment with diluted sulfuric acid and recovered from the acidic aqueous solution by adding aqueous sodium hydroxide. 

Design procedures that make recycling reagents and solvents easy. 

Yadav, J.S., Reddy, B.V.S., Eshwaraiah, B., Anuradha, K. 2002. Amberlyst-15 A novel and recyclable reagent for the synthesis of 1,5-benzodiazepines in ionic hquids. Green Chemistry 6 592-594. 

Niknam, K., Kiasat, A. R., Karami, B. and Heydari, N. 2007. Basic AljOj as a recyclable reagent for the protection of carbonyl groups with phenylhydrazine derivatives and semicarbazides. TurkJ. Chem. 31(2) 135-139. 

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