Oxides carbonyl dibromide

However, at 70-80 C, carbonyl dibromide does not react with sulfur(IV) oxide (although it does dissolve in it) [918a]. 

Carbonyl dibromide is not commercially available, and therefore must be prepared when required. It is conveniently prepared by the oxidation of tetrabromomethane with sulfuric acid ... 

Another direct route to polycarbonate was reported by Okuyama et al. [36]. The process consists of an oxidative carbonylation procedure. It is catalyzed with a Pd complex system. l,l -Di-tert-butyl-3,3 -methylenediiimidazolin-2,2, dylidene [palladium dibromide and produces a highest molecular weight polymer, (M = 9,600, Mw = 24,000) in 80% yields. 

If, however, PEG-400 is employed as the solvent and phase transfer catalyst, under a nitrogen atmosphere, then the monoacid is obtained in good yield. Since vinylic dibromides are easily synthesized from carbonyl compounds, this constitutes a valuable method for oxidative homologation(19). 

The oxidation of a-hydroxy acids by benzyltrimethylammonium tribromide (BTMAB) to the corresponding carbonyl compounds shows a substantial solvent isotope effect, A (H20)/A (D20) = 3.57, but no KIE for a-deuteromandelic acid.133 The oxidation of glucose by hypobromous acid is first order in glucose and the acid.134 [l,l-2H2]Ethanol shows a substantial kinetic isotope effect when oxidized by hexamethylenetetramine-bromine (HABR) in acetic acid to aldehyde.135 Kinetics of the oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine have been studied by the same group.136 Dioxoane dibromide oxidizes y-tocopherol to 5-bromomethyl-y-tocopherylquinone, which spontaneously cyclizes to 5-formyl-y-tocopherol.137... 

In reaction with benzaldehyde or its dimethyl acetal, or benzylidene dibromide, sucrose undergoes conversion into its 4,6-acetal in moderate yield (28-35%).160,161 The transacetalation reaction of dialkyl acetals prepared from unsaturated or aromatic aldehydes can take place under very mild acidic conditions. For example, sucrose-derived monomers or surfactants (variously substituted 4,6-(9-methylidenesucroses) have been prepared146,162 and 4,6-monoacetals incorporating masked aromas or fragrances derived from p-citral or a- or p-ionone were prepared directly from sucrose in high yields.163,164 These latter molecules, whose unsaturated carbonyl system is very susceptible to oxidation, are thus temporarily protected and are readily released under very mild conditions (Scheme 13). 

In all of these reactions, the diaryl tellurium oxide is reduced to the diaryl tellurium. To make the conversion of thiocarbonyl to carbonyl groups catalytic with respect to the diaryl tellurium oxide, the diaryl tellurium must be converted back to the diaryl tellurium oxide. A catalytic cycle was developed with 1,2-dibromotetrachloroethane as the agent oxidizing the diaryl tellurium to the diaryl tellurium dibromide and 20% aqueous potassium carbonate as the base hydrolyzing the tellurium dibromide to the tellurium oxide1. 

Benzoyl peroxide (dibenzoyl peroxide), (CjHjCOO>2 (mp 104-106 °C dec), and /r-nitrobenzoyl peroxide (p-02NCgH4COO)2 (mp 156 °C dec), which is synthesized from p-nitrobenzoyl chloride and sodium peroxide [229], are rarely used as oxidants, and if so, they do not offer appreciable advantages over other organic oxidation agents. The anti addition of benzoyl groups to double bonds and the benzoxylation of aromatic rings are achieved in the presence of iodine [230], and alcohols are oxidized to carbonyl compounds in the presence of nickel dibromide [231],... 

The copolymer 174 was prepared from diaUcyl thienylated benzodithiophene (173) and perfluororalkyl-carbonyl substituted thieno[3,4-h]thiophene (172) monomers (Scheme 41). Thus, reaction of thieno[3,4-6]thiophene-2-carbaldehyde (150) with heptadecafluorooctyl iodide in the presence of methyllithium to form 170 was followed by oxidation with Mn02 giving ketone 171. Bromination with two equivalents of NBS furnished dibromide 172, and this was Stille cross-coupled with 173 in the presence of Pd2(dba)3 to obtain the copolymer 174 [63]. 

MacrocycHzation for the synthesis of macrolactones was also achieved by C-C bond formation using a variety of techniques (Scheme 6.5). Oxidative acetylene coupling for exaltolide 12, as reported by Bergelson et al. [61], nickel-carbonyl-mediated coupling of allyhc dibromides by Corey and Kirst [62], palladium-catalyzed... 

Nair et al. (2001) describe the bromination of alkenes using a mixture of ammonium hexanitratocerate(IV) and potassium bromide in a two-phase system consisting of water and dichloromethane. For instance, styrene is transformed by this reaction system in excellent yield at room temperature into 1,2-dibromo-phenyl ethane (scheme 28). It is assumed that the bromide ion is first oxidized by CAN to the bromine radical, which subsequently undergoes addition to the double bond to produce a benzylic radical. Trapping of another bromine radical results in the formation of the 1,2-dibromide. The method is not only applicable to substituted styrenes, but also to alkenes and o, 5-unsubstituted carbonyl compounds. However, the choice of the solvent is of prime importance the reaction only occurs in the water/dichloromethane two-phase system. In other solvents, like aqueous solutions of methanol or acetonitrile, a variety of products such as phenacyl bromides and nitratobromides are formed (scheme 29). The nitrato bromides are formed exclusively when the reaction is carried out in a deoxygenated atmosphere. In the two-phase system water/dichloromethane, side reactions are avoided be-... 

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