Halogens reaction with ethylene

Another use of hydrogen fluoride, although not in halogen exchange, is the reaction with ethylenes or acetylenes to form the addition products, 1,1-difluoroethane [75-37-6] and vinyl fluoride [75-02-5]-. 

The halogenation reaction of ethylene has been modeled by many researchers [170, 172-176], For chlorination in apolar solvents (or in the gas phase), the formation of two radical species requires the use of flexible CASSCF and MRCI electronic structure methods, and such calculations have been reported by Kurosaki [172], In aqueous solution, Kurosaki has used a mixed discrete-continuum model to show that the reaction proceeds through an ionic mechanism [174], The bromination reaction has also received attention [169,170], However, only very recently was a reliable theoretical study of the ionic transition state using PCM/MP2 liquid-phase optimization reported by Cammi et al. [176], These authors calculated that the free energy of activation for the ionic bromination of the ethylene in aqueous solution is 8.2 kcalmol-1, in good agreement with the experimental value of 10 kcalmol-1. 

Reaction with ethylenic and acetylenic compounds. Isolated double bonds are. halogenated by the reagent. Internal acetylenes undergo trans halogenation, whereas terminal acetylenes are converted into tribromoolefins. 

Russel [142] developed a method based on the conversion of chlorine, bromine and iodine ions into the corresponding halogenated ethanols by reaction with ethylene oxide. Belcher et al. [143] offer a method for determining trace amounts of chloride ions, based on reaction with mercury phenylnitrate to give phenylmercury chloride, which is chromatographed with flame-ionization detection. 

Many of the features of the generally accepted mechanism for the addition of halogens to alkenes can be introduced by referring to the reaction of ethylene with bromine... 

Although acetonitrile is one of the more stable nitriles, it undergoes typical nitrile reactions and is used to produce many types of nitrogen-containing compounds, eg, amides (15), amines (16,17) higher molecular weight mono- and dinitriles (18,19) halogenated nitriles (20) ketones (21) isocyanates (22) heterocycles, eg, pyridines (23), and imidazolines (24). It can be trimerized to. f-trimethyltriazine (25) and has been telomerized with ethylene (26) and copolymerized with a-epoxides (27). 

Flame-Retardant Resins. Flame-retardant resins are formulated to conform to fire safety specifications developed for constmction as well as marine and electrical appHcations. Resins produced from halogenated intermediates (Table 5) are usually processed at lower temperatures (180°C) to prevent excessive discoloration. Dibromoneopentyl glycol [3296-90-0] (DBNPG) also requires glass-lined equipment due to its corrosive nature. Tetrabromophthahc anhydride (TBPA) and chlorendic anhydride (8) are formulated with ethylene glycols to maximize fiame-retardant properties reaction cycle times are about 12 h. Resins are also produced commercially by the in situ bromination of polyester resins derived from tetrahydrophthahc anhydride... 

During this period of time we, and a number of other research groups, have been investigating the reactions of highly halogenated aiynes and hetarynes with aromatic hydrocarbons, for the reasons outlined in the introduction. In a reaction of pentafluorophenylmagnesium chloride with ethylene oxide in the presence of benzene, it was shown that, as well as 3-pentafluorophenylethanol (23) a by-product of molecular formula C12H6F4 was produced 43>. 

In selective etherification, it is important to distinguish between reversible and irreversible reactions. The former class comprises etherifications with dimethyl sulfate, halogen compounds, oxirane (ethylene oxide), and diazoalkanes, whereas the latter class involves addition reactions of the Michael type of hydroxyl groups to activated alkenes. In this Section, irreversible and reversible reactions are described separately, and a further distinction is made in the former group by placing the rather specialized, diazoalkane-based alkylations in a separate subsection. 

With the aid of density functional theory, the ZnCl2 acceleration of the Simmons-Smith reaction of ethylene and allyl alcohol has been investigated. A pathway involving direct Lewis acid acceleration of the leaving halogen atom (327) was found to be a more facile process than the more popular pathway involving 1,2-chlorine migration (328). 

Howard, C.J. Rate constants for the gas-phase reactions of OH radicals with ethylene and halogenated ethylene compounds, J. Chem. Phys., 65(ll) 4771-4777, 1976. 

Mg+" reacts with alkyl halides in the gas phase via a range of substrate-dependent pathways Not all halides are reactive—examples of unreactive substrates include methyl chloride, vinyl chloride, trichloro and tetrachloro ethylene. Reaction with ethyl chloride proceeds via an elimination reaction (equation 18) followed by a displacement reaction (equation 19). For larger alkyl halides, such as isopropyl chloride, chloride abstraction also occurs (equation 20). For multiply halogenated substrates such as carbon tetrachloride, oxidative reactions occur (equations 21 and 22), although organometallic... 

As already described, with the exception of iodo, all halogens have proved useful DMGs in the pyridine series for the preparation of potential intermediates and final products related to biologically interesting molecules (Schemes 36, 41-47, 57). As specific applications, the reaction of chloro ketones 524 with ethylene diamine and 1,2-phenylenediamine give, respectively, pyrido[4,3-c]-l, 4-diazepines 525 and pyrido[4,3-6]-1,5-benzodiazepines 523 in good yields (Scheme 160) (87AP704). 

Phosphorus pentachlonde too has received some attention as a halogenating agent with such epoxides as ethylene oxide,lM 1,2-epoxy-2-methyibutane,10 and 2,3-epoxy hexane.7A 8 The nature of products formed in these reactions is not known with certainty, however. 

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