TBPA

TetrabromophthalicAnhydride. Tetrabromophthalic anhydride [632-79-1] (TBPA) is widely used as a reactive flame retardant in unsaturated polyesters as weU as the precursor to a number of other fine retardants. Polyesters prepared from this compound have relatively poor photochemical stabiUty and tend to discolor upon exposure to light. This tendency to discolor can be reduced, but not eliminated, by the use of uv stabilizers. 

TBPA is prepared in high yield by the bromination of phthalic anhydride in 60% oleum (51). The use of oleum as the bromination solvent results in some sulfonation of the aromatic ring (52). Sulfonated material is removed by hydrolyzing the anhydride with dilute NaOH, filtering and acidifying with dilute HCl. The precipitated acid is washed several times with hot water and reconverted to the anhydride by heating at 150°C for several hours. 

Diester/Ether Diol of Tetrabromophthalic Anhydride. This material [77098-07-8] is prepared from TBPA in a two-step reaction. First TBPA reacts with diethylene glycol to produce an acid ester. The acid ester and propylene oxide then react to give a diester. The final product, a triol having two primary and one secondary hydroxyl group, is used exclusively as a flame retardant for rigid polyurethane foam (53,54). 

Halogenated intermediates, dibromoneopentyl glycol [3296-90-0] (DBNPG), and alkoxylated derivatives of tetrabromobisphenol A are used extensively in flame-retardant apphcations. Similar properties can be derived from halogenated dibasic acids, chlorendic anhydride [115-27-5] (CAN), and tetrabromophthahc anhydride [632-79-1] (TBPA). Processes can be used to produce brominated products by the in situ bromination of polymers derived from tetrahydrophthahc anhydride. 

Flame-Retardant Resins. Flame-retardant resins are formulated to conform to fire safety specifications developed for constmction as well as marine and electrical appHcations. Resins produced from halogenated intermediates (Table 5) are usually processed at lower temperatures (180°C) to prevent excessive discoloration. Dibromoneopentyl glycol [3296-90-0] (DBNPG) also requires glass-lined equipment due to its corrosive nature. Tetrabromophthahc anhydride (TBPA) and chlorendic anhydride (8) are formulated with ethylene glycols to maximize fiame-retardant properties reaction cycle times are about 12 h. Resins are also produced commercially by the in situ bromination of polyester resins derived from tetrahydrophthahc anhydride... 

Using any of the carrier proteins available in highly purified form, eg, TBG or TBPA, a convenient and accurate quantitative determination of and is possible by displacement of radioiodinated or T. This procedure enables their quick determination at low concentrations even in the presence of coundess other substances that occur in body duids (31). In a similar fashion, intact cell nuclei or solubilized proteins from rat fiver cell nuclei, which display high affinities for thyroid hormones, especially T, have been used to establish relative binding affinities of many thyromimetic compounds (7). 

The level of circulating hormones is lowered indirecdy by -butyl 3,5-diiodo-4-hydroxyben2oate which displaces them from their carriers (TBG and TBPA) and thus accelerates their metaboHsm and excretion (6). 

Tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA) differs from the other promoters in that its cation is a radical, and as such produces radical cationic sulfonium ions as glycosylating species from thioglycosides.85 The use of this promoter arose from earlier work on the electrochemical generation of 5-glycosyl radical cations as glycosylating species. 

Luche and coworkers [34] investigated the mechanistic aspects of Diels-Alder reactions of anthracene with either 1,4-benzoquinone or maleic anhydride. The cycloaddition of anthracene with maleic anhydride in DCM is slow under US irradiation in the presence or absence of 5% tris (p-bromophenyl) aminium hexachloroantimonate (the classical Bauld monoelectronic oxidant, TBPA), whereas the Diels Alder reaction of 1,4-benzoquinone with anthracene in DCM under US irradiation at 80 °C is slow in the absence of 5 % TBPA but proceeds very quickly and with high yield at 25 °C in the presence of TBPA. This last cycloaddition is also strongly accelerated when carried out under stirring solely at 0°C with 1% FeCh. The US-promoted Diels Alder reaction in the presence of TBPA has been justified by hypothesizing a mechanism via radical-cation of diene, which is operative if the electronic affinity of dienophile is not too weak. 

Infrared measurement of additive concentrations is a more complex analysis than initially expected, as some additives may undergo a variety of chemical reactions during processing, as shown by Reeder et al. [128] for the FTIR analysis of phosphites in polyolefins. Some further examples of IR work refer to PVC/metal stearates [129], and PE/Santonox R [68,130]. Klingbeil [131] has examined the decomposition of various organic peroxyesters (TBPB, TBPP, TBPA and TBPO) and a peroxidicarbonate (BOPD) as a function of pressure, temperature and solvent by means of quantitative FTIR using an optical high p, T reaction cell. 

TBPA f-Butylperoxy acetate TPhT-Ac Triphenyltin acetate... 

Neisseria spp. TbpA, TbpB FbpA FbpB FbpC Iron(III) also from Schryvers and... 

Thioglycosides can also be activated by a one-electron transfer reaction from sulfur to the activating reagent tris-(4-bromophenyl)ammoniumyl hexachloroanti-monate (TBPA+) [102,103]. The use of this promoter was inspired by an earlier report where activation was achieved under electrochemical conditions to give an intermediate S-glycosyl radical cation intermediate [104], and the reactivity and mechanism have also been explored [105,106]. 

Scheme 5.1 Mechanism of thioglycoside activation (a) by thiophiles X1 such as /V-bromosuccinimicle (NBS), 11,12 methyl triflate,13 dimethyl(methylthio)sulfonium triflate (DMTST),14 phenylselenyl triflate (PhSeOTf),17,18 iV-iodosuccinimide/triflic acid (MS/TfOH),19 20 and iodonium di-sym-collidine perchlorate (IDCP)21 (b) by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA,+)25 and (c) via anomeric sulfoxides.26 The stereochemical outcome of these glycosylations follows the same general trends as with many other glycosyl donor/promoter combinations (m-CPBA = mcta-chloroperbenzoic acid).

Oxidation of PBN by tris(4-bromophenyl)aminium ion (TBPA +) in the presence of nucleophiles 110... 

OXIDATION OF PBN BY TRIS(4-BROMOPHENYL)AMINIUM ION (TBPA +) ([10P) IN THE PRESENCE OF NUCLEOPHILES... 

TBPA + is a commonly used ET oxidant. It also possesses electrophilic reactivity, reacting with bond formation to acetate, cyanide and chloride ion, all of which have high E° values (Table 5), to give 2-substituted derivatives of [10] (Eberson and Larsson, 1986,1987). Nucleophiles with lower E° (Br-, I, ... 

Indeed, carboxylates and a host of other nucleophiles gave spin adducts when oxidized in dichloromethane by TBPA + together with PBN (Eberson, 1992). These results are shown in Table 8, with the nucleophiles listed in order of decreasing °(Nu7Nu ) (Table 5). Fluoride ion gave rise to both [6] and [7],... 

Table 8 Spin adducts formed in the oxidation of PBN-Nu by TBPA + in dichloromethane, unless otherwise stated.0...

DMPO is more difficult to oxidize than PBN by about 0.2 V (Table 1) and is therefore expected to engage in spin trapping via its radical cation with greater difficulty, as found for the 0sCl6-4-N02-PBN reaction. Only acetate ion, tetramethylsuccinimide ion and triethyl phosphite gave the corresponding adducts upon oxidation with TBPA + in dichloromethane in the presence of DMPO, whereas fluoride ion gave the hydroxyl adduct. The latter was probably formed from water available from the unavoidable hydration shell around fluoride ion in its tetrabutylammonium salt. 

Table 9 Rate constants for the reaction between TBPA + and Nu (as Bu4N+ salts in the appropriate cases) in HFP at 20°C, compared to acetonitrile.11...

Table 10 Inhibitory effect of HFP on the formation of spin adducts from the reaction of PBN, Nu and TBPA + in dichloromethane. ...

The oxidation of mixtures of PBN and Nu- by TBPA + in HFP gave no spin adducts from the commonly used nucleophiles (Table 10), except in the case of triethyl phosphite and related phosphorus compounds (Eberson et al., 1996a). Thus any PBN + formed must react so slowly with Nu that the spin adduct concentration is too low to be detectable. Titration of the percentage HFP in dichloromethane which just barely allowed for the formation of the... 

Recently, the radical cation of PBN has been characterized by matrix spectroscopy and its reactivity has been studied by fast spectroscopic methods (Zubarev and Brede, 1994), and found to conform to the behaviour deduced from the OsCU and TBPA + studies. y-Radiolysis of PBN in a glassy matrix of isobutyl chloride or Freon-113 (CF2C1CFC12) at 77 K produced an intensely green glass containing PBN +, the epr spectrum of which had an anisotropic nitrogen coupling constant Ay = 2.75 mT and gy = 2.0037. Tlie mechanism of the radiolysis reaction is well established (Neta, 1976) and involves the formation of solvated electrons (e ), which add to the matrix species and produce chloride ion, and positive holes (h+) which eventually come to rest at the matrix component of lowest Ip (Symons, 1997), in this case PBN (see reactions (30) and (31)). 

An advantage of these enzymes is that they are stereocomplementary, in that they can synthesize the four possible diastereoisomers of vicinal diols from achiral aldehyde acceptors and DHAP (Scheme 4.2). Although this statement is generally used and accepted, it is not completely true since tagatose-l,6-bisphosphate aldolase (TBPA) from Escherichia coli-the only TBPA that has been investigated in terms of its use in synthesis-does not seems to control the stereochemistry of the aldol reaction when aldehydes different from the natural substrate were used as acceptors [7]. However, this situation could be modified soon since it has been demonstrated that the stereochemical course of TBPA-catalyzed C—C bond formation may be modified by enzyme-directed evolution [8]. 

Thyroxine binding prealbumin (TBPA) carries about 30% T but no Tj. Its affinity is only of the order of 10 M, but it is much more abundant in semm than is TBG. The amino acid sequence and the structure of this protein are known. Four identical subunits (127 amino acids each) form a prolate ellipsoid. Noncovalent interactions between the subunits form a channel of I nm diameter along the long axis, which has a funnel-shaped opening of 2.5 nm. The T molecule is held in one arm of this channel, binding... 

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