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Halogen promoter

Despite these restrictions, the acceptor-bound succinoyl MPEG28 was found to permit glycosylations with glycosyl trichloroacetimidates promoted by boron trifluoride, triflic anhydride, and trimethylsilyl or triethylsilyl triflates, with glycosyl halogenates promoted by silver triflate, and with thioglycosides promoted by the iodonium ion. It is compatible with long-term ester protection, with allylic,... [Pg.183]

CSIR [39] Incorporation of halogen promoters in the catalyst Pd(5%) on alumina... [Pg.266]

If only the monocarboxybc acid is required, the ester after hydrolysis with potash may be strongly acidified with sulphuric acid and the mixture heated under reflux the mineral acid promotes decarboxylation at a temperature just above 100°. The net result is the replacement of the halogen atom of the alkyl halide by —CH COOH thus in the above example ... [Pg.484]

Halogenation (e.g., bromination) takes place in chloroform for the 2,4-dialkylthiazoles, and the majority of studies have been of 2,4-dimethylthiazole (227, 228). In other cases and in acetic or stronger acids, substitution occurs at the 5-position and is promoted by electronreleasing groups in the 2-position. When the releasing group is in the 4-(or 5-)-position, steric hindrance may decrease the yield of substitution at the 5- (or 4-) position. Nevertheless, the thiazole nucleus is not very reactive since 4-methylthiazole and 2.5-dimethylthiazole are inert in dilute sulfuric acid with bromine (229-231). [Pg.380]

DMF can also be manufactured from carbon dioxide, hydrogen, and dimethylamine ia the presence of halogen-containing transition-metal compounds (18). The reaction has also been performed with metal oxides and salts of alkaU metals as promoters (19). [Pg.513]

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). [Pg.392]

Ethylene oxide is produced in large, multitubular reactors cooled by pressurized boiling Hquids, eg, kerosene and water. Up to 100 metric tons of catalyst may be used in a plant. Typical feed stream contains about 30% ethylene, 7—9% oxygen, 5—7% carbon dioxide the balance is diluent plus 2—5 ppmw of a halogenated moderator. Typical reactor temperatures are in the range 230—300°C. Most producers use newer versions of the Shell cesium-promoted silver on alumina catalyst developed in the mid-1970s. [Pg.202]

Halogenation and dehalogenation are catalyzed by substances that exist in more than one valence state and are able to donate and accept halogens freely. Silver and copper hahdes are used for gas-phase reactions, and ferric chloride commonly for hquid phase. Hydrochlorination (the absoration of HCl) is promoted by BiCb or SbCl3 and hydrofluorination by sodium fluoride or chromia catalysts that form fluorides under reaction conditions. Mercuric chloride promotes addition of HCl to acetylene to make vinyl chloride. Oxychlori-nation in the Stauffer process for vinyl chloride from ethylene is catalyzed by CuCL with some KCl to retard its vaporization. [Pg.2094]

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. [Pg.2190]

Generally, isolated olefinic bonds will not escape attack by these reagents. However, in certain cases where the rate of hydroxyl oxidation is relatively fast, as with allylic alcohols, an isolated double bond will survive. Thepresence of other nucleophilic centers in the molecule, such as primary and secondary amines, sulfides, enol ethers and activated aromatic systems, will generate undesirable side reactions, but aldehydes, esters, ethers, ketals and acetals are generally stable under neutral or basic conditions. Halogenation of the product ketone can become but is not always a problem when base is not included in the reaction mixture. The generated acid can promote formation of an enol which in turn may compete favorably with the alcohol for the oxidant. [Pg.233]

Bromination with A-bromosuccinimide generally gives the same result as bromination with free bromine or hypobromous acid. The reaction is considered to proceed with a small concentration of free bromine and does not generate an appreciable concentration of acid. Conditions are therefore mild. In addition, A-bromosuccinimide has been used to brominate the allylic position of a, -unsaturated ketones in the presence of free-radical promoters or with irradiation, and thus gives access to dienones by dehydro-halogenation, for exaraple " ... [Pg.280]

By the same token, in base-promoted E2 dehydrohalogenations, the rate of elimination of the halogen as a halide ion is expected to be I > Br > Cl F This element effect has indeed been documented in many instances, a few examples of which are listed in Table I... [Pg.895]

Table 1. Relative Rates of Base-Promoted Dehydrohalogenations of Halogenated Compounds... Table 1. Relative Rates of Base-Promoted Dehydrohalogenations of Halogenated Compounds...
Reactivity is enhanced in conditions which promote the generation of halogen atoms, though this does not imply that all reactions proceed via the intermediacy of X atoms. The reversible thermal dissociation of gaseous I2 v 21 was... [Pg.805]

Nearly every substitution of the aromatic ring has been tolerated for the cyclization step using thermal conditions, while acid-promoted conditions limited the functionality utilized. Substituents included halogens, esters, nitriles, nitro, thio-ethers, tertiary amines, alkyl, ethers, acetates, ketals, and amides. Primary and secondary amines are not well tolerated and poor yield resulted in the cyclization containing a free phenol. The Gould-Jacobs reaction has been applied to heterocycles attached and fused to the aniline. [Pg.430]


See other pages where Halogen promoter is mentioned: [Pg.227]    [Pg.266]    [Pg.39]    [Pg.547]    [Pg.784]    [Pg.337]    [Pg.799]    [Pg.259]    [Pg.421]    [Pg.3]    [Pg.281]    [Pg.288]    [Pg.252]    [Pg.280]    [Pg.227]    [Pg.266]    [Pg.39]    [Pg.547]    [Pg.784]    [Pg.337]    [Pg.799]    [Pg.259]    [Pg.421]    [Pg.3]    [Pg.281]    [Pg.288]    [Pg.252]    [Pg.280]    [Pg.100]    [Pg.457]    [Pg.466]    [Pg.467]    [Pg.3]    [Pg.36]    [Pg.63]    [Pg.100]    [Pg.3]    [Pg.274]    [Pg.322]    [Pg.259]    [Pg.222]    [Pg.514]    [Pg.66]    [Pg.273]    [Pg.452]    [Pg.119]    [Pg.561]    [Pg.838]    [Pg.5]   
See also in sourсe #XX -- [ Pg.228 ]




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Aldehydes base-promoted halogenation

Base-promoted halogenation of ketones

Base-promoted halogenation, of aldehydes

Base-promoted halogenation, of aldehydes and ketones

Halogenation base-promoted

Ketones base-promoted halogenation

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