Halogenation catalysis

Reactions I and II occurring together will obviously lead to a catalytic decomposition of hydrogen peroxide similar in principle to the halide-halogen catalysis. The interrelation between the reactions of iodide, iodate, and iodine with peroxide and the conditions for the isolation of each have been discussed by Bray and Liebhafsky (32). 

Transition-Metal Catalyzed Cyclizations. o-Halogenated anilines and anilides can serve as indole precursors in a group of reactions which are typically cataly2ed by transition metals. Several catalysts have been developed which convert o-haloanilines or anilides to indoles by reaction with acetylenes. An early procedure involved coupling to a copper acetyUde with o-iodoaniline. A more versatile procedure involves palladium catalysis of the reaction of an o-bromo- or o-trifluoromethylsulfonyloxyanihde with a triaLkylstaimylalkyne. The reaction is conducted in two stages, first with a Pd(0) and then a Pd(II) catalyst (29). 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

Catalytic Oxidization. A principal technology for control of exhaust gas pollutants is the catalyzed conversion of these substances into innocuous chemical species, such as water and carbon dioxide. This is typically a thermally activated process commonly called catalytic oxidation, and is a proven method for reducing VOC concentrations to the levels mandated by the CAAA (see Catalysis). Catalytic oxidation is also used for treatment of industrial exhausts containing halogenated compounds. 

The acid-catalyzed additions of bromide and chloride ion to thiiranes occurs readily, with halide preferentially but not exclusively attacking the most substituted carbon atom of the thiirane. The reaction of 1-substituted thiiranes with acetyl chloride shows a slight preference for halide attack at the less substituted carbon atom (80MI50601). For further discussion of electrophilic catalysis of halide ion attack see Section 5.06.3.3.2. The reaction of halogens with thiiranes involves electrophilic attack on sulfur (Section 5.06.3.3.6) followed by nucleophilic attack of halide ion on carbon. 

General base catalysis is catalysis by a Br nsted base acting by accepting a proton. The halogenation of ketones, a reaction discussed in Section 5.3, is general base catalyzed. 

In this context, the use of ionic liquids with halogen-free anions may become more and more popular. In 1998, Andersen et al. published a paper describing the use of some phosphonium tosylates (all with melting points >70 °C) in the rhodium-catalyzed hydroformylation of 1-hexene [13]. More recently, in our laboratories, we found that ionic liquids with halogen-free anions and with much lower melting points could be synthesized and used as solvents in transition metal catalysis. [BMIM][n-CgHi7S04] (mp = 35 °C), for example, could be used as catalyst solvent in the rhodium-catalyzed hydroformylation of 1-octene [14]. 

The author anticipates that the further development of transition metal catalysis in ionic liquids will, to a significant extent, be driven by the availability of new ionic liquids with different anion systems. In particular, cheap, halogen-free systems combining weak coordination to electrophilic metal centers and low viscosity with high stability to hydrolysis are highly desirable. 

The reaction capability of PS is weak, but the reaction capability can be improved by anchoring the functional group to the aliphatic chain or aromatic ring of PS using chemical or conversion reactions. Aliphatic chain reactions are halogenation reactions, oxidation reactions, or unsaturated acids to bonded aliphatic chain of PS (in the presence of a radical catalysis). 

In American patents [31,32, the acylation of PS with acryl, methacrylate chloride, and a and jS-halogen pro-penylchloride has been done in the presence of AICI3 catalysis at 60-100 C. This process can be accomplished by using two methods in the presence of nonsolvent either CH2=CHCOCl, ClCHj—CH2—COCl and BF3 catalysis passed from PS as vapor or acylated material... 

Besides radical additions to unsaturated C—C bonds (Section III.B.l) and sulfene reactions (see above), sulfonyl halides are able to furnish sulfones by nucleophilic substitution of halide by appropriate C-nucleophiles. Undesired radical reactions are suppressed by avoiding heat, irradiation, radical initiators, transition-element ion catalysis, and unsuitable halogens. However, a second type of undesired reaction can occur by transfer of halogen instead of sulfonyl groups283-286 (which becomes the main reaction, e.g. with sulfuryl chloride). Normally, both types of undesired side-reaction can be avoided by utilizing sulfonyl fluorides. 

An irreversible reaction of the intermediate of a redox reaction will greatly facilitate redox catalysis by thermodynamic control. A good example is the reduction of the carbon halogen bond where the irreversible reaction is the cleavage of the carbon halogen bond associated, or concerted, with the first electron transfer -pEe... 

It is not the aldehyde or ketone itself that is halogenated, but the corresponding enol or enolate ion. The purpose of the catalyst is to provide a small amount of enol or enolate. The reaction is often done without addition of acid or base, but traces of acid or base are always present, and these are enough to catalyze formation of the enol or enolate. With acid catalysis the mechanism is... 

The reaction of an a-halo sulfone with a base to give an alkene is called the Ramberg-Bdcklund reaction. The reaction is quite general for a-halo sulfones with an (x hydrogen, despite the unreactive nature of a-halo sulfones in normal 8 2 reactions (p. 437). Halogen reactivity is in the order I>Br>Cl. Phase-transfer catalysis has been used. In general, mixtures of cis and trans isomers are obtained, but usually the less stable cis isomer predominates. The mechanism involves formation of an episulfone, and then elimination of SO9. There is much evidence for... 

Some particular features should be mentioned. Instead of Michael additions, a-nitroolefins are reported to yield allyl sulfones under Pd catalysis (equation 21). Halogenated acceptor-olefins can substitute halogen P to the acceptor by ipso-substitution with sulfinate (equation 22 , equation 23 ) or can lose halogen a to the acceptor in the course of a secondary elimination occurring P to the introduced sulfonyl groups (equation 24). On the other hand, the use of hydrated sodium sulfinates can lead to cleavage at the C=C double bond (equation 25). 

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