Halides from 1,1-dihalide

II. Halides from Alcohols and Phenols by Triphenylphosphine Dihalide... 

Problem 16.9 Prepare the following acids from alkyl halides or dihalides of fewer C s. (a) C H CHjCOOH,... 

Ionic liquids have been a popular topic of interest in 2002 and a review of the applications of these solvents in organic synthesis has been published (02ACA75>. New, densely functionalized fluoroalkyl-substituted imidazolium ionic liquids have been reported <02TL9497>. An ultrasound-assisted preparation of a series of ambient-temperature ionic liquids, l-alkyl-3-methylimidazolium halides, which proceeds via efficient reactions of 1-methyl imidazole with alkyl halides/terminal dihalides under solvent-free conditions, has been described <02OL3161>. New hydrophilic poly(ethyleneglycol)-ionic liquids have been synthesized from... 

The possibility of preparing aryl tellurium halides from equimolar amounts of diaryl ditellurium compounds and aryl tellurium trihalides has hardly been explored. Only phenyl tellurium iodide and 2-biphenylyl tellurium bromide could be obtained by this route. The other aryl tellurium halides (including 3,4-dimethoxyphenyl tellurium chloride) decomposed under the reaction conditions to give diaryl tellurium dihalides and tellurium5. 

Ring-bridged vanadocene halide and dihalide, (28) and (29) are obtained from bis(cyclopentadienyl)-substituted dianion (27) as shown in Scheme 16. Furthermore,... 

Acid amide-triphenylphosphine dihalide adducts (4) have found wide application in organic synthesis. - Synthetic equivalents are adducts (5) from acid amides and triphenylphosphine/CCU, which are prepared in situ from the educts. - With these reagents the following transformations have been performed dehydration of amides or aldoximes to nitriles, preparation of isonitriles from secondary form-amides, preparation of imidoyl halides from amides or acylhydrazines and preparation of ketene imines from amides. Using polymer-supported triphenylphosphine the work-up procedure is much easier to achieve. Triphenylphosphine can be replaced by tris(dialkylamino)phosphines. - Instead of CCI4 hexa-chloroethane, hexabromoethane or l,l,2,2-tetrabromo-l,2-dichloroethane can be used " the adducts thus formed are assumed to be more effective than those from the triphenylphosphine/CCU system. 

Values in boldface type are from Darwent and represent his estimates of the best value and uncertainties for the energies required to break the bonds at 0 K. Where values are not available from Darwent. they arc taken from Brewer and coworkers for metal halides and dihalides (boldface italics) or from Feber for transition metal, lanthanide, and actinide halides (italics). The.se values represent enthalpies of atomization at 298 K. The remaining values are from Cottrell (Arabic numerals) and other sources (Arabic numerals with superscripts keyed to references at end of table). 

Diphenyl-1,3-butadiene is easily prepared by removal of hydrogen halide from a dihalide it suffices to heat 2,3-dibromo-l,4-diphenylbutane with quinoline for 0.5 hour at 160°.110... 

This reaction was initially reported by Finkelstein in 1910. It is a preparation of alkyl iodide from alkyl bromide or chloride with potassium or sodium iodide in acetone. Therefore, this reaction is generally known as the Finkelstein reaction. Occasionally, it is also referred to as the Finkelstein halide exchange, Finkelstein displacement, or Conant-Finkelstein reaction. Mechanistically, this reaction is a simple nucleophilic substitution (often via Sn2), as iodide is a stronger nucleophile than bromide or chloride. The yield of this reaction is very high and can be quantitative if occurs in DMF. It was found that the trifluoromethyl group retards the displacement of bromide when it presents as an a- or /3-substituent but accelerates the reaction as a substituent in an allylic chloride. Under normal conditions, this type of halide displacement does not occur for aryl halides. For dihalides, unsaturated or cyclic compounds may form via carbocation intermediates, which form transient covalent iodides or are reduced directly by iodide to free radicals. However, the aromatic halide exchange reacts smoothly when 10% Cul is present in the reaction... 

Conjugated dienes can be prepared from allylic halides or from dihalides. 

For the conversion of olefins to dihalides see section 368 (Halide-Halide) For allylic halogenation see section 146 (Halides from Hydrides)... 

The acyclic imidoselenium(II) dihalides ClSe[N( Bu)Se]nCl (8.23, n =1 8.24, n = 2) are obtained from the reaction SeCla with tert-butylamine in a 2 3 molar ratio in THF. There are no sulfur or tellurium analogues of this class of chalcogen-nitrogen halide. 

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