Bromination derivatizing

Com and rice starches have been oxidized and subsequently cyanoethylated (97). As molecular size decreases due to degradation during oxidation, the degree of cyanoethylation increases. The derivatized starch shows pseudoplastic flow in water dispersion at higher levels of cyanoethylation the flow is thixotropic. Com and rice starches have been oxidized and subsequently carboxymethylated (98). Such derivatives are superior in the production of textile sizes. Potato starch has been oxidized with neutral aqueous bromine and fully chemically (99) and physically (100) characterized. Amylose is more sensitive to bromine oxidation than amylopectin and oxidation causes a decrease in both gelatinization temperature range and gelatinization enthalpy. 

Cholestanol, cholesterol Apply sample solution, treat with a 2 to 3-fold excess of 0.1% bromine in chloroform. Only cholesterol is derivatized. [45]... 

J ,3J ,4J ,5J )-2,5-bis(benzyloxy)-3,4-dihydroxy-Nd -bis (lS)-2-methyl-l-[(methylamino)carbonyl]propyl hexanediamide is a C2-symmetric HIV-1 protease inhibitor [29]. Derivatization in the para positions of the benzyl-oxy groups via microwave-assisted Stille reaction on the corresponding di-brominated inhibitor smoothly yielded the desired heteroarylated derivatives (Scheme 10). Interestingly, the 1,3-thiazole derivative showed a higher antiviral activity on the wild type virus than the lead compound. The activity remained at the same level in the presence of seriun. Unfortimately, a low activity was observed on mutants. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Figure 1.53 The purine bases are subject to bromination reactions at the C-8 position, forming an important reactive intermediate for derivatization purposes.

Figure 1 Schematic structures of micelle and liposome, their formation and loading with a contrast agent, (a) A micelle is formed spontaneously in aqueous media from an amphiphilic compound (1) that consists of distinct hydrophilic (2) and hydrophobic (3) moieties. Hydrophobic moieties form the micelle core (4). Contrast agent (asterisk gamma- or MR-active metal-loaded chelating group, or heavy element, such as iodine or bromine) can be directly coupled to the hydrophobic moiety within the micelle core (5), or incorporated into the micelle as an individual monomeric (6) or polymeric (7) amphiphilic unit, (b) A liposome can be prepared from individual phospholipid molecules (1) that consists of a bilayered membrane (2) and internal aqueous compartment (3). Contrast agent (asterisk) can be entrapped in the inner water space of the liposome as a soluble entity (4) or incorporated into the liposome membrane as a part of monomeric (5) or polymeric (6) amphiphilic unit (similar to that in case of micelle). Additionally, liposomes can be sterically protected by amphiphilic derivatization with PEG or PEG-like polymer (7) [1].

Marchand and co-workers ° synthesis of 5,5,9,9-tetranitropentacyclo[5.3.0.0 .0 °.0 ] decane (52) reqnired the dioxime of pentacyclo[5.3.0.0 .0 °.0 ]decane-5,9-dione (49) for the incorporation of the four nitro groups. Synthesis of the diketone precursor (48) was achieved in only five steps from cyclopentanone. Thus, acetal protection of cyclopentanone with ethylene glycol, followed by a-bromination, and dehydrobromination with sodium in methanol, yielded the reactive intermediate (45), which underwent a spontaneous Diels-Alder cycloaddition to give (46). Selective acetal deprotection of (46) was followed by a photo-initiated intramolecular cyclization and final acetal deprotection with aqueous mineral acid to give the diketone (48). Derivatization of the diketone (48) to the corresponding dioxime (49) was followed by conversion of the oxime groups to gem-dinitro functionality using standard literature procedures. 

Fullerenes can be derivatized by various means. For example, reaction with fluorine gas proceeds stepwise to the formation of colorless CeoFeo, which, according to the 19F nuclear magnetic resonance (NMR) spectrum, contains just one type of F site and so evidently retains a high degree of symmetry.9 In view of the low adhesion typical of fluorocarbons, this spherical molecule is expected to have extraordinary lubricant properties. Curiously, bromination of Ceo is reversible on heating otherwise, the reactions of fullerenes resemble those of alkenes or arenes (aromatic hydrocarbons). 

When the residue, obtained on evaporation of an aqueous equilibrium solution of glucose, was derivatized with the standard reagent, two peaks were obtained on gas chromatography, corresponding to the peaks obtained with the two separate a and p anomers the ratio of the peak areas was a p = 39.8 60.2, agreeing well with the ratio 36.2 63.8 determined by the optical method or 37.4 62.6 determined by the bromine oxidation technique (25). 

Fig. 3 Typical chromatogram of aflatoxins B (0.2 ng), B2 (0.04 ng), G (0.2 ng), and G2 (0.04 ng) standard. Mobile phase water methanol acetonitrile 54 29 17. Pump A regulated at 1 ml/min pumpB (postcolumn derivatization with bromine) regulated at 0.4 ml/min.

W Kok, CH van Neer, WA Traag, LGM Tuinstra. Determination of aflatoxins in cattle feed by liquid chromatography and post-column derivatization with electrochemically generated bromine. J Chrom 367 231-236, 1986. 

Mizutani et al. (144) derivatized BHT to 2,6-di- er -butyl-4-methyl-4-methoxy-2,5-cyclo-hexadienone (BMMC) using up the quantitative Coppinger and Campbell reaction of BHT with bromine in methanol. Separation was carried out on a RadialPak /zPorasil column using a hexane-2-propanol mixture as mobile phase. Detection of BMMC was monitored at 236 nm,... 

Reaction of tetra-0-acetyl-/ -D-glucopyranosylbenzene (77) with bromine radicals at room temperature gives a complex set of products at —30°, however, only one is formed, but, because of its instability, it has not been isolated or derivatized. As was speculated,59 these observations are consistent with the product having been that of substitution at C-1, that is, a benzylic, a tertiary, and an a-oxygenated bromide which would be unstable for any one of these reasons, far less for all three. 

Figure 4-5. Reaction mechanism for the derivatization followed by reductive cleavage based on Lu and Ralph (1997). Reaction of the lignin with acetylbromide (AcBr) results in the acetylation of the y-carbon, while the a-carbon is brominated. Zinc (Zn) catalyzes the cleavage of the ether bond between the P-carbon of one residue and the 0-4 position of the adjacent residue. The resulting monomer is acetylated with acetic anhydride (Ac20) and pyridine (Py). R can be a proton or an aryl group. In H-residues R3 and R5 are protons, in G-residues R3 is a methoxyl group and R5 is a proton, whereas in S-residues both R3 and R5 are methoxyl groups. The wavy bonds indicate that both the S- and R- (4.26, 4.27) or E- and Z-stereo-isomers (4.28, 4.29) are present.

Regarding ozonation processes, the treatment with ozone leads to halogen-free oxygenated compounds (except when bromide is present), mostly aldehydes, carboxylic acids, ketoacids, ketones, etc. [189]. The evolution of analytical techniques and their combined use have allowed some researchers to identify new ozone by-products. This is the case of the work of Richardson et al. [189,190] who combined mass spectrometry and infrared spectroscopy together with derivatization methods. These authors found numerous aldehydes, ketones, dicarbonyl compounds, carboxylic acids, aldo and keto acids, and nitriles from the ozonation of Mississippi River water with 2.7-3 mg L 1 of TOC and pH about 7.5. They also identified by-products from ozonated-chlorinated (with chlorine and chloramine) water. In these cases, they found haloalkanes, haloalkenes, halo aldehydes, haloketones, haloacids, brominated compounds due to the presence of bromide ion, etc. They observed a lower formation of halocompounds formed after ozone-chlorine or chloramine oxidations than after single chlorination or chlorami-nation, showing the beneficial effect of preozonation. 

Recently we completed an evaluation of the effectiveness of the Aflatest (Vicam) immunoaffinity column for analysis of corn, peanuts and peanut butter for aflatoxin (11). In this procedure the sample is extracted with Me0H/H20, filtered, and the extract diluted to <30% MeOH with water. An aliquot is then applied to the immunoaffinity column. The column is then washed with water and the aflatoxins eluted with methanol. Total aflatoxins are then determined by solution fluorometry with bromine (SFB), or individual toxins by reverse phase high performance liquid chromatography with post column I2 derivatization (PCD). In the collaborative study corn samples naturally contaminated with aflatoxins and samples of corn, peanuts and peanut butter spiked at 30, 20 and 10 ng/g, were analyzed by 24 collaborators. The results of this study are tabulated in Table V. 

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