Halogens, as oxidants

As for halogens as oxidizing reagents, bromine has proved more useful than its homologs chlorine and iodine. It was employed as early as 1879 on di- and tetra-methyl-p-phenylenediamine [27-29] and early in this century, Wieland used it to generate the aminium salts of triarylamines and tetraarylhydrazines [30, 31]. Since bromine adds readily to unsaturated as well as to some strained ring compounds, it is not expected to be very useful in the context of the radical cations discussed here. 

Scheme 8.13 Oxidative halodetelluration with halogens as oxidant...

The use of halogens as oxidizing agents has also been reported,75 resulting in a PPy/X product containing halide (X-) ions as the dopant counterions. These same workers used chemical polymerization to produce PPy-polymethylpyrrole copolymers. 

Already in the 1960s, Hoffmann-La Roche developed a process for the production of canthaxanthin. Selective oxidation of/3-carotene maybe carried out with various reagents. Hoffmann-La Roche used NBS in chloroform/alcohol or chlo-roform/acetic acid. [65] BASF [66] and Rh6ne-Poulenc [67], on the other hand, employed halogenates as oxidants. The BASF procedure uses a biphasic system... 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

Generally these derivatives are rather unstable and behave as oxidizing and halogenating agents. 1-Iodoimidazoles are more stable than other analogs. 

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

The tendency for F2 to give F" ions in solution is also much greater than for the other halogens as indicated by the steady decrease in oxidation potential (E°) for the reaction X2(soln) -I-2e" 2X" (aq) ... 

Numerous chemical reactions have been carried out on ferrocene and its derivatives.317 The molecule behaves as an electron-rich aromatic system, and electrophilic substitution reactions occur readily. Reagents that are relatively strong oxidizing agents, such as the halogens, effect oxidation at iron and destroy the compound. 

Halogens are frequently used as oxidation agents and, under two-phase conditions, they can either be employed as ammonium complex halide salts [3], or in the molecular state with or without an added quaternary ammonium catalyst [4]. Stoichiometric amounts of tetra-n-butylammonium tribromide under pH controlled conditions oxidize primary alcohols and low-molecular-weight alkyl ethers to esters, a,cyclic ethers produce lactones [3], and secondary alcohols yield ketones. Benzoins are oxidized to the corresponding benzils (80-90%) by the tribromide salts in acetonitrile in the presence of benzoyl peroxide [5]. 

Typically, small molecule drugs are produced using reactions such as oxidation-reduction, acid-base, halogenation, alkylation, and substitution. 

Gonsidering the small amount of curium produced, a surprising number of compounds have been formed and identified. For example, there are two common oxides, curium dioxide (GmO ) and curium trioxide (Cm O ). Gurium also combines with other nonmetals such as the halogens as follows curium iodide (Cml ), curium bromide (CmBrp, and curium tetrafluo-ride (CmF ). 

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