2.6- Dimethyl-4-bromophenol

This sequence explains Price s observations adequately and seems to be required in this particular case. The oxidative elimination of halide ion from salts of phenols does not always follow this course, however. In the peroxide-initiated condensation of the sodium salt of 2,6-dichloro-4-bromophenol (Reaction 23) molecular weight continues to increase with reaction time after the maximum polymer yield is obtained (Figure 5) (8). Furthermore, Hamilton and Blanchard (15) have shown that the dimer of 2,6-dimethyl-4-bromophenol (VIII, n = 2) is polymerized rapidly by the same initiators which are effective with the monomer. Obviously, polymer growth does not occur solely by addition of monomer units in either Reaction 22 or 23 some process leading to polymer—polymer coupling must also be possible. Hamilton and Blanchard explained the formation of polymer from dimer by redistribution between polymeric radicals to form monomer radicals, which then coupled with polymer, as in Reaction 11. Redistribution has indeed been shown to occur under... 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

Cresol red Crystal Violet Malachite Green Methanil Yellow Thymol Blue Orange IV -2,4-Dinitrophenol -Erythrosin, Na2 salt -Dimethyl Yellow Cl 11020 Bromophenol Blue Congo Red Cl 22120 Methyl Orange Bromocresol Green Alizarin Red S Cl 42750 Methyl Red Cl 13020 -Bromocresol Purple Chlorophenol Red p-Nitrophenol Alizarin Bromothymol Blue Brillant Yellow Phenol Red Neutral Red Cl 50040 -m-NItrophenol -Cresol Red Metacresol Purple Phenolphthalein -Thymolphthalein -P-Naphthyl Violet Alizarin Yellow R 2,4,6-T rinitrotoluene... 

In a two-phase system similar to that used by Price, Stamatoff (29) obtained from 2,6-dichloro-4-bromophenol a branched polymer having approximately the statistical ratio of ortho and para ether linkages. When the reaction was carried out using the anhydrous salt of the phenol in the presence of highly polar aprotic solvents, such as dimethyl sulfoxide, the product was the linear poly(2,6-dichlorophenylene oxide) (Reaction 23). 

As shown in Scheme 3, 4-bromo-2,6-bis(hydroxymethyl)anisole (16) [11], derived from p-bromophenol (14) by treatment with 37% aq. formaldehyde at room temperature for 12 days, followed by methylation with dimethyl sulfate and... 

Dimethyl sulfate (38.4 g., 0.30 mole) is added slowly [Caution— toxic substance) with stirring to a solution of 44 g. (0.26 mole) of 7B-bromophenol (p. 54) in 107 g. of a 10% aqueous solution of sodium hydroxide. Stirring is continued until the reaction mixture is neutral. The organic layer is separated by ether extraction, and the ethereal solution is dried. Distillation gives a colorless oil, b.p. 209-212°/752 mm. This is redistilled and 35 g. (73%) of m-bromoanisole is collected at 210-211 . 

Sulfate-reducing bacteria couple the reductive dehalogenation of aromatic compounds to growth (DeWeerd et al., 1990 Dolfing and Tiedje, 1987), and both chlorinated benzoates and bromophenols are used as electron acceptors (Boyle et al., 1999 Mohn and Tiedje, 1990). Separate populations of SO4 reducers can be either sources (indirectly) or sinks for acrylate. Acrylate is formed during the breakdown of the marine osmolyte dimethyl-sulfoniopropionate, a process that is catalyzed by SO4 reducers in sediments, and then reduced by other SO -reducing species (van der Maarel et al., 1998, 1996d). 

The Pd-catalyzed AAA reaction of bromophenol 54 and allylic carbonate 72 in the presence of chiral bis-phosphine ligand 73 gave aryl ether 74 in 72% yield with 88% ee (Scheme 15). After protection of the aldehyde function in 74 as a dimethyl... 

The aromas associated widi very fi esh fish are usually mild, delicate and fi esh (53,54), and generally described as green (hexanal), melon-like ((E,Z)-3,6-nonadienal), iodine-like (bromophenols). Fresh fish and seafood aromas are due to volatile carbonyls and derive fi om lipoxygenase catalyzed oxidation of polyunsaturated fatty acids. The oxidation of Eicosapentaenoic acid (C20 5) leads to C5 to C9 alcohols, aldehydes, ketones and hydrocarbons. The formation of methyl mercaptan, dimethyl sulfide and dimethyl disulfide in fi esh fish at the time of harvest has been reported by Shiomi et al. (55). Although these compounds are usually associated with fish deterioration, they contribute to the fi esh aroma ch cter at low concentrations. For instance, dimethyl sulfide is... 

A methylaluminium phenoxide derived from 2,6-di-tert-butyl-4-bromophenol can function as a catalyst in the stereoselective anti-migration of the dimethyl-t-butylsiloxy group in the epoxides illustrated to afford siloxyaldehydes in high yields (ref. 116). 

Highly brominated poly(2,6-dimethyl-l,4-phenylene oxide)s have been prepared by polymerization of bromophenols and by... 

The preparation of bromine-containing polyphenylene oxides by modification of Price s polymerization of bromophenols was described in the preceding paper. An alternate route to these polymers is the direct bromination of polyphenylene oxides. The bromination of poly(2,6-dimethyl-l,4-phenylene oxide) to... 

For example, for a linear sweep of potential, we obtain curves as illustrated in Figure 1.13, which, upon differentiation, provides the corresponding cyclic voltammogram [130]. Of course, the same methodology can be used to study assisted-ion-transfer reactions such as the transfer of copper(II) assisted by 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline [131], acid-base reactions such the transfer of bromophenol blue [132], and to study electron transfer. Ding et al. have in this way confirmed that electron-transfer reactions between ferricyanide-ferrocyanide in water, and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-DCE, were heterogeneous [133,134]. 

A 0.5-M solution of 2-propenylmagnesium bromide in THF (100 mL, 50 mmol) is added drop by drop to a solution of l,l-dimethyl-2-oxa-l-sila-indan (prepared by lithiation of 0-bromophenol THP ether with butyllithium followed by p-toluenesulfonic catalyzed deprotection, 7.5 g, 46 mmol) in THF (50 mL) cooled with ice at 0 °C, and the resulting mixture is stirred at rt for 9 h. The mixture is diluted with diethyl ether and the ethereal solution was carefully washed sequentially with a saturated NH4CI aq., with water, and finally with brine, and then dried over anhydrous MgS04. After removal of the solvents in vacuo, the residue is distilled under vacuum to give the title compound in 89% yield as a colorless oil, bp 75 °C at 0.4 mmHg. ... 

Three notable marine character-impact aroma exceptions are 5,8,11-tetradecatrien-2-one, which exhibits a distinct seafood aroma character described as cooked shrimp-like or minnow bucket (73). A second example is an extremely potent odorant in cooked shellfish, including shrimp and clam, identified by Kubota and coworkers (74) as pyrrolidino[l,2-c]-4//-2,4-dimethyl-1,3,5-dithiazine. This dithiazine contributes a roasted character to boiled shellfish and has the lowest odor threshold recorded to date, 10" ppt in water. 2,4,6-Tribromophenol and other bromophenol isomers have been associated with the ocean-, brine-, and iodine-like fiavor character in seafood such as Australian ocean fish and prawns. The source of the bromophenols is thought to be poly-chaete worms, which form an important part of the diet for many fish and prawn species (75). Finally, dimethyl sulfide is the character aroma of stewed clams and oysters (69). Representative structures for meat and seafood flavor impact compounds are shown in Fig. 6. 

Bromine vapour then 3,5 dibromo -p-quinone in dimethyl/formamide bromophenol blue in acetone... 

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