Bromine as oxidant

The action of chlorine or bromine as oxidizing agents on alkaline polyfluoro phenoxides gives halogenatcd cyclohexadienone compounds such as 8.170 A similar result is obtained in the reaction of naphthoxides (vide infra).110... 

This procedure uses readily available reagents and provides a simple and efficient method for nitrile synthesis. The entire sequence of four steps can be performed in a single day. Although product formation in the second step is presumably thermodynamically controlled, the cyanohydrazine is favored in all cases studied except with aryl ketones. A water-methanol solution of ammonium chloride and potassium cyanide can also be employed for the cyanohydrazine formation, but lower yields (ca. 60%) are obtained. The third step, a conveniently performed titration procedure with bromine as oxidant, can be effected with other oxidizing reagents such as 4-phenyl-4H-l,2,4-triazole-3,5-dione, ferl-butyl hypochlorite, and Jones reagent.12 The final diazene-... 

Brominated Diphenyl Oxides. Brominated diphenyl oxides are prepared by the bromination of diphenyl oxide. They are often referred to as diphenyl ethers. Taken together, the class constitutes the largest volume of brominated flame retardants. They range ia properties from high melting sohds to hquids. They are used, as additives, ia virtually every polymer system. 

Most nonmetallic elements (except nitrogen, oxygen, chlorine, and bromine) are oxidized to their highest state as acids. Heated with concentrated acid, sometimes ia the presence of a catalyst, sulfur, phosphoms, arsenic, and iodine form sulfuric, orthophosphoric, orthoarsenic, and iodic acid, respectively. SiHcon and carbon react to produce their dioxides. 

Another problem arises from brominated aromatic species derived from inorganic bromides used as oxidation cocatalysts. As a result, the cmde NDA is converted to its dimethyl ester, DMNDA [840-65-3] and solvent recrystalHzed to give a high purity diester (36—38). A process for purifying NDA directly by hydrogenation (pure TA process) has also been described (39). 

Halogen-substituted succinimides are a class of products with important appHcations. /V-Bromosuccinimide [128-08-5] mp 176—177°C, is the most important product ia this group, and is prepared by addition of bromine to a cold aqueous solution of succinimide (110,111) or by reaction of succinimide with NaBr02 iu the presence of HBr (112). It is used as a bromination and oxidation agent ia the synthesis of cortisone and other hormones. By its use it is possible to obtain selective bromine substitution at methylene groups adjacent to double bonds without addition reactions to the double bond (113). 

The time-weighted, 8-h average limit for exposure to bromine pentafluoride is 0.1 ppm (67). Materials of constmction suitable for use with the bromine fluorides include nickel. Monel metal, or Teflon. For shipping, bromine trifluoride and pentafluoride are classified as oxidizers under DOT regulations. The trifluoride also requires a poison label. 

By similar procedures diazirines were prepared not only from simple aliphatic ketones but also from hydroxyketones and )3-aminoketones (B-67MI50800), and so were a large number of diazirines from steroidal ketones (65JA2665). Permanganate, bromine, chlorine and hypochlorite were used as oxidants. A one-step preparation of diazirines from ketones like 3-nonanone, ammonia and chlorine has been claimed in a patent (66USP3290289). 3,3-Diazirinedicarboxylic acid derivatives like (286) were obtained directly from oxime tosylates by the action of two moles of O-ethoxyamine (81AG(E)200). 

The [SaN]" cation was first obtained in low yield in 1978 by the oxidation of S7NH with SbCls. The reaction of in situ generated [SN]" salts with sulfur (Scheme 5.3) or the reduction of the [ClSNSCl] cation with anhydrous tin(II) chloride in SO2 or CH2CI2 can be used to prepare [S2N] salts. The best large scale synthesis involves the reaction of AsFs with a mixture of S4N4 and sulfur in the presence of a trace amount of bromine (as a catalyst) (Eq. 5.10). ... 

Oxidative decomplexation of iron acyl complexes in the presence of alcohols provides the corresponding carboxylates 7. Usual conditions employ ca. 7% alcohol in dichloromethane or dichloromethane/carbon disulfide as the solvent with bromine as the oxidant. 

Amides are produced if iron - acyl complexes are oxidized in the presence of a secondary or primary amine25 52 59 60. This reaction, usually conducted at low temperatures, employs /Y-bromosucciniinide or bromine as the oxidant (see Table 6). 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Treatment of methano-dimer 28 with elemental bromine revealed a remarkable reactivity at low temperatures it proceeded quantitatively to the furano-spiro dimer 29, by analogy with the ethano-dimer 12 giving spiro dimer 9 upon oxidation. With increasing temperatures, the reaction mechanism changed, however, now affording a mixture of 5-bromo-y-tocopherol (30) and spiro dimer 9 (Fig. 6.24). Thus, the methano-dimer 28 fragmented into an a-tocopherol part, in the form of o-QM 3 that dimerized into 9, and a /-tocopherol part, which was present as the 5-bromo derivative 30 after the reaction. Thus, the overall reaction can be regarded as oxidative dealkylation. 

The 2-keto acids such as 2-keto-D-galactonic acid (XXIV) can be derived from the corresponding osone (XXIII) by oxidation with bromine.10 Oxidation of L-gulosone by the same method has provided 2-keto-L-gulonic acid. The success of this oxidation depends to a large extent upon the purity of the osone subjected to oxidation and this, as previously stated, is controlled by the purity of the osazone. 

For the decabromodiphenyl oxide (DBDPO) pyrolysis reactions, two different procedures were used to synthesize the series of brominated diphenyl oxides and dibenozofurans employed as the relative retention time standards AlBr3/Br2 in ethylene dibromide and Fe° (metal)/Br2 in tetrachloroethylene. The rate of the initial bromination steps in the former reaction was so rapid that only the higher degree of bromination adducts could be isolated. The rate of the Fe°/Br2 reaction was found to be much slower, especially during the initial stages, and these reactions yielded a broader range of relative retention time reference peaks. 

In order to confirm the relative retention times established for DBDPO using only CGC, additional sets of partially brominated diphenyl oxides and dibenzofurans were synthesized using the Fe°/ Br2 procedure. The course of these reactions was followed by both CGC and CGC/MS. As a result, it was possible to simultaneously confirm the previous relative retention time peak assignments as well as to correlate the retention times between the two instruments. Some of the pertinent comparative retention time data obtained from these experiments is summarized in Table I. Upon completion of the individual reactions, a cocktail containing both partially brominated furans and diphenyl oxides was mixed. A typical CGC chromatogram and a CGC/MS total ion chromatogram for this cocktail are shown in Figures 1 and 2, respectively. 

Chapter 18 by C. Chiappe focuses on the mechanism of bromination of alkenes, exploring the role of solvent on the formation of cyclic bromonium ion versus P-bromocarbemium ion, as key intermediates. In Chapter 19, H. P. A. Mercier et al. discuss the utility of a novel class of noble-gas onium salts as oxidants for generation and isolation of various trihalomethyl cation salts. 

Elemental composition H 9.15%, N 42.41%, O 48.44%. Hydroxylamine may be measured by coulometric titration to a potentiometric end point using a coulometric titration cell. A standard solution of bromine may be used as oxidizer in the redox reaction. (Skoog, D. A., D. M. West, and F. J. HoUer. 1992. Fundamentals of Analytical Chemistry, 6th ed. pp. 467, Orlando Saunders College Publishing)... 

In 2003, Kulkarni and coworkers presented a method for the -selective oxybromi-nation of a variety of substituted phenols employing a novel heterogeneous catalytic system, the CrZSM-5 as catalyst, H2O2 as oxidant and KBr as bromine source ". Next to CrZSM-5 also other zeolites have been tested as catalysts, but although MoZSM-5 showed the highest conversion after 5 hours (89%), para-selectivity was lower (para 36% ortho 31% dibromination 22%) than observed with the CrZSM-5 material (83%... 

SCHEME 184. Mechanism for the CrZSM-5(30)-catalyzed para-bromination of various phenols with H2O2 as oxidant... 

---