Methanol dehydrohalogenation

Nickel catalysts have been used for many dehydrohalogenations (30), but these catalysts are much more suspectible to poisoning by halide ion than are noble metals. As a result, the catalyst-to-substrate ratio must be much higher when using nickel, and reduction times are apt to be lengthy (36). Reductive deiodination of 6 to 7 was achieved over Raney nickel in methanol containing triethylamine. Despite massive loadings, the reduction was slow (20). 

Dicarboxanilide-acetylene Di(N-phenyl-carboxamide) acetylene or Bis(carboxanilide)- cetylene, CgHjHNOC.CsC.CONHCeHj mw 264.27, N 10.60% pinkish-white crysts (from MeOH-water), mp 194-96° was prepd from acetylenedicacboxylic acid by a series of reactions to give bromofumaranilide which was dehydrohalogenated by a dil soln of methanolic KOH. 

Fluoro-l-haloalka-l,3-dienes are prepared in a similar manner by treatment of substituted 2,2-(dihalocyclopropyl)methanols with a hydrogen fluoride/pyridine/diisopropylamine/ sodium fluoride system to give compound 2, followed by dehydrohalogenation with potassium /< r/-butoxide.80... 

Treatment of PVC, suspended in chlorobenzene, with Et2AlCl followed by the addition of methanol greatly improved the thermal stability (6). This will be the subject of a separate publication. However, the nature of the improvement was different—i.e., film pressed in air at 200°C was yellow not colorless, but processing stability as determined by the torque rheometer test in the Brabender Plasticorder at 195°C was far superior and was measured in hours rather than minutes. The removal of labile chlorine atoms by Et2AlCl undoubtedly contributed to heat resistance. However, in the absence of a further reaction, such dehalo-genation probably became dehydrohalogenation, contributing to color development. 

Dehydrohalogenation of this compound can be accomplished under E2 conditions by treatment with base. Sodium methoxide in methanol would be appropriate, for example, although almost any alkoxide could be employed to dehydrohalogenate this tertiary bromide. 

A cortisone synthesis using remote functionalization at an unactivated carbon centre has been achieved.97 Cortexolone (224) was converted into the 5a-H,3j3-OH derivative (formation of the bismethylenedioxy-compound followed by lithium-ammonia-ethanol reduction). Inversion98 of 3)8- to 3 -OH followed by esterification with m-iodobenzoic acid produced (225), which on irradiation in methylene chloride containing phenyl iodide dichloride gave the 9 a -chloro-derivative (not isolated). This was dehydrohalogenated and saponified by methanolic potash to yield (226) (75%) and thence, by further known steps, cortisone acetate. 

The dehydrohalogenation of a yQ-chloroalkylbenzene is readily accomplished by refluxing with excess aqueous methanolic potassium hydroxide. Substituted a-alkylstyrenes which are difficult to obtain by other methods are prepared in this way by a two-step process involving catalytic condensation of aromatic compounds with aliphatic chlorohydrins followed by removal of hydrogen halide from the resulting haloalkylated derivatives. ... 

Quaternary ammonium hydroxides are strong bases comparable to NaOH and KOH. Recently one of them, benzyltrimethylammonium hydroxide (Triton B), has proved to be a very efficient dehydrohalogenation agent. Thus a 40% methanolic solution of Triton B in benzene affords higher yields of acetylenes than acloholic KOH or NaNHi (e.g. equations 66 and 67) . In a continuation of this work it has been found that the method is not only applicable to acetylenic hydrocarbons, but... 

In order to determine the structure of the photochemical rearrangement product of carvone camphor in methanol, and to prove its structure, the research team of T. Gibson subjected the bicyclic carboxylic acid product to a degradation sequence, which commenced with the HVZ reaction, followed by dehydrohalogenation, dihydroxylation and glycol cleavage. 

Dehydrohalogenation Benzyltrimethylammonium mcsitoate. r-Butylamine. Calcium carbonate. j Uidine. Diazabicyclo[3.4.0]nonene-5. N.N-Dimethylaniline (see also Ethoxy-acetylene, preparation). N,N-Dimelhylformamide. Dimethyl sulfoxide-Potassium r-but-oxide. Dimethyl sulfoxide-Sodium bicarbonate. 2,4-Dinitrophenylhydrazine. Ethoxy-carbonylhydrazine. Ethyldicyclohexylamine. Ethyidiisopropylamine. Ion-exchange resins. Lithium. Lithium carbonate. Lithium carbonate-Lithium bromide. Lithium chloride. Methanolic KOH (see DimethylTormamide). N-PhenylmorphoKne. Potassium amide. Potassium r-butoxide. Pyridine. Quinoline. Rhodium-Alumina. Silver oxide. Sodium acetate-Acetonitrile (see Tetrachlorocyclopentadienone, preparation). Sodium amide. Sodium 2-butylcyclohexoxide. Sodium ethoxide (see l-Ethoxybutene-l-yne-3, preparation). Sodium hydride. Sodium iodide in 1,2-dimethoxyethane (see Tetrachlorocyclopentadienone, alternative preparation) Tetraethylammonium chloride. Tri-n-butylamine. Triethylamine. Tri-methyiamine (see Boron trichloride). Trimethyl phosphite. 

Dehydrohalogenation. Kuhn et dissolved 2,4-dibromo-l, 1,5,5-tetraphenyl-pentadiene-1,4 in DMF, flushed the system with nitrogen, and slowly added methanolic... 

Preparation. The precursor, l-chloro-4- o-nitrophenyl)-2-butene (3), is prepared by the Meerwein reaction of diazotized o-nitroaniline (2) with butadiene in acetone in the presence of cupric chloride and sodium acetate. - Dehydrohalogenation with methanolic potassium hydroxide then gives the diene (4). ... 

Isoprene epoxidized on the vinyl group (l,2-epoxy-3-methyl-3-butene, 14) would also be an attractive synthon for monoterpenoids if it were more readily accessible. Among the possible preparative methods (Scheme 2), acid-catalyzed isomerization of 2,3-epoxy-l-halo-3-methylbutanes (epoxidized prenyl halides) and dehydrohalogenation of the resulting isomers seemed the best route until chlorination of prenyl acetate (15, R = OAc) with hypochlorous acid was published. Dehydration of the mixture of products gave a maximum of the chloroacetate 16, which yielded the epoxide 14 with sodium hydroxide in methanol. ... 

Dehydrohaloge nation. Zaugg et al.3 report dehydrohalogenation of the bromo-amide (1) to the imidate (2) by the reagent in methanol or DMF. Hassner and Fpwler4... 

Dehydrohalogenation. f-Alkylamines react with epichlorohydrin in methanol at 20-25° to give l-r-alkylamino-3-chloro-2-propanols. On dehydrohalogenation... 

Part V is devoted to the study of H transfers in organic and organometallic reactions and systems. In Ch. 18 Koch describes kinetic studies of proton abstraction from CH groups by methoxide anion, of the reverse proton transfer from methanol to hydrogen bonded carbanion intermediates, and of proton transfer associated with methoxide promoted dehydrohalogenation reactions. Substitutent effects, kinetic isotope effects and ah initio calculations are treated. Of great importance is the extent of charge delocalization in the carbanions formed which determine the kinetic and thermodynamic acidities. 

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