Halides hydrohalogenation

Special reagents introduced more recently allow significant improvements in hydrohalogenation of alkenes. HC1, HBr, and HI in aqueous-organic two-phase systems under phase-transfer conditions readily add to alkenes affording halides in nearly quantitative yields.123 Appropriately prepared silica and alumina have been found to mediate the addition of HC1, HBr, and HI to alkenes.124 The method is very convenient since it uses hydrogen halides prepared in situ 124 125... 

The addition of hydrogen halides to unsaturated organic compounds is called here hydrohalogenation in order to stress that it is the reverse reaction to dehydrohalogenation. Two types of the hydrohalogenation reaction have to be considered, the addition to a carbon carbon triple bond... 

Optical rotation, enantiomers, 281 Organic catalysts, 323, 347 crystal morphology, 348 hydrohalogenation, 347 Michael reactions, 350 photochemistry, 348 solid-state reactions, 349 see also specific reactions Organic halides, Grignard reagents, 187, 354 Organocopper chemistry, 199, 208, 292,... 

All of die halides except tile hexafluoride and the triiodide may be prepared by the hydrohalogenation of rhe dioxide or of the oxalate of plutonium(lll) at a temperature of about 700°C. With hydrogen fluoride the reaction product is PUF4, unless hydrogen is added to the gas stream, in which case the trifluoride is produced. With hydrogen iodide the reaction product is PuOi, and the other oxyhalides may be formed by the addition of appropriate quantities of water vapor to the hydrogen halide gas. Plutonium triiodide is produced by the reaction of the metal with hydrogen iodide at about 400°C. The hexafluoride is produced by direct combination of the... 

Hydrohalogenation of alkenes and alkynes. In the presence of A1203 or Si02, hydrogen halides or their precursors add to alkenes or alkynes at useful rates and often in quantitative yield.1... 

This general reaction allows the conversion of a halogen group to an ester group without the evolution of hydrohalogen acid and therefore without the corrosion problem that would attend such evolution. The reaction is particularly useful for changing organosilicon halides to esters in order to separate them more easily. 

The hydrohalogenated compounds M5C(CO)i5HX, which have also been obtained from the reactions of M5C(CO),5 with halides followed by protonation, have been shown to lose CO upon heating to give the species M5C(C0),4HX. 

Hydrohalogenation is the addition of hydrogen halides HX (X = Cl, Br, and 1) to aikenes to form alkyl halides. 

Hydrohalogenation of an alkene to form an alkyl halide is the reverse of the dehydrohalogenation of an alkyl halide to form an alkene, a reaction discussed in detail in Sections 8.4 and 8.5. 

Many hydrohalogenation reactions begin with an achiral reactant and form an achiral product. For example, the addition of HBr to cyclohexene, an achiral alkene. forms bromocyclohexane. an achiral alkyl halide. 

Hydrohalogenation (Section 10.9) An electrophilic addition of hydrogen halide (HX) to an alkene or alkyne. 

Alkenes are prepared from alcohols either by direct dehydration or by de-hydrohalogenation of intermediate alkyl halides to avoid rearrangement we often select dehydrohalogenation of halides even though this route involves an extra step. (Or, sometimes better, we use elimination from alkyl sulfonates.)... 

A hydrogen halide (HBr, HCl, or HI) also can be added to an aikene. The product of this reaction, called hydrohalogenation, is an alkyl halide ... 

Hydrohalogenation s. Halides from ethylene derivs. Hydrolysis (s. a. Cleavage,... 

ABSTRACT The gas-solid halogenation and hydrohalogenation using micro-crystalline cyclodextrin complexes are found to be efficient for production of the optical active halides of ethyl trans-cinnamate in moderate optical yields On exposure to HBr at 2QOC for 15-20 hr, the cinnamate in solid a- and S-cyclodextrin complexes yields ethyl R-(+)-3-bromo-3-phenylpropanoate in 46% e.e., and S-(-)-enantiomer in 31% e.e., respectively. No addition nor substitution products are obtained with HCl vapor at 0-50°C for 15-65 hr. Bromination of the B-cyclodextrin complex results in the formation of optical active ethyl erz/t/zrc>-2,3-dibromo-3-phenylpropanoate, while chlorination gives the optical active mixture of trans and cis addition products, ethyl erythro- and threo-2,3-di-chloro-3-phenylpropanoates in 60-80% yields. Mechanism of chiral induction in the present gas-solid reaction has been proposed on the basis of the crystal structure of the complex. 

In 1869 Vladimir Vasil evich Markovnikoff (1838-1904), a pupil of Butlerov, proposed the rule subsequently named after him concerning the addition of hydrogen halides to unsaturated hydrocarbons. In his words If an unsymmetrically constituted hydrocarbon unites with a hydrohalogen acid, the halogen adds to the less hydrogenated carbon atom. .. . This rule provided the first prediction of the course of a reaction in terms of the structure of one of the reactants. 

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