Chlorine to olefins

Zeolites can also function as reservoirs for selective halogenation of hydrocarbons 114) and as convenient media for addition of chlorine to olefins, with subsequent dehydrohalogenation to form reaction mixtures rich in highly halogenated alkenes 108). Similarly, highly chlorinated benzenes have been prepared in low yield by passing cyclohexane over NaY in the presence of NOCl and HCI, NO and CI2, or CI2 alone at 149°-260° 115). 

CC14, CHCI3, and CH2C12 are suitable solvents for addition reactions of chlorine to olefins. Liquid olefins are mostly chlorinated without a solvent. 

The chlorination of the ISB-DMB copolymer indicates a substitutive stoichiometry one chlorine atom is incorporated into the copolymer for every molecule of chlorine in the reaction. Table 1 shows these results chlorine utilization decreases when significantly more than one mole of chlorine is present for each olefin unit in the copolymer. The criticality of the ratio of chlorine to olefin unit has been shown in the chlorination of ISB-isoprene copolymers. Similarly, the decrease of copolymer molecular weight as reflected in My is more drastic when higher levels of chlorine are used (Figure 1). 

Addition Chlorination. Chlorination of olefins such as ethylene, by the addition of chlorine, is a commercially important process and can be carried out either as a catalytic vapor- or Hquid-phase process (16). The reaction is influenced by light, the walls of the reactor vessel, and inhibitors such as oxygen, and proceeds by a radical-chain mechanism. Ionic addition mechanisms can be maximized and accelerated by the use of a Lewis acid such as ferric chloride, aluminum chloride, antimony pentachloride, or cupric chloride. A typical commercial process for the preparation of 1,2-dichloroethane is the chlorination of ethylene at 40—50°C in the presence of ferric chloride (17). The introduction of 5% air to the chlorine feed prevents unwanted substitution chlorination of the 1,2-dichloroethane to generate by-product l,l,2-trichloroethane. The addition of chlorine to tetrachloroethylene using photochemical conditions has been investigated (18). This chlorination, which is strongly inhibited by oxygen, probably proceeds by a radical-chain mechanism as shown in equations 9—13. 

Oxidation. 1,1,1-Trichloroethane is stable to oxidation when compared to olefinic chlorinated solvents like trichloroethylene and tetrachloroethylene. Use of a 48-h accelerated oxidation test gave no hydrogen chloride, whereas trichloroethylene gave 0.4 wt % HCl and tetrachloroethylene gave 0.6 wt % HCl (22). 

Alkyl chlorides. Olefins are chlorinated to alkyl chlorides in a single fluidized bed. HCl reacts with O9 over a copper chloride catalyst to form chlorine. The chlorine reacts with the olefin to form the alkyl chloride. The process developed by the Shell Development Co. uses a recycle of cat yst fines in aqueous HCl to control the temperature [Chem. Proc., 16, 42 (1953)]. 

The most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoprene. These olefins are usually coproduced with ethylene by steam cracking ethane, LPG, liquid petroleum fractions, and residues. Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons. They can easily react with inexpensive reagents such as water, oxygen, hydrochloric acid, and chlorine to form valuable chemicals. Olefins can even add to themselves to produce important polymers such as polyethylene and polypropylene. Ethylene is the most important olefin for producing petrochemicals, and therefore, many sources have been sought for its production. The following discusses briefly, the properties of these olefmic intermediates. 

Higher paraffinic hydrocarbons than methane are not generally used for producing chemicals by direct reaction with chemical reagents due to their lower reactivities relative to olefins and aromatics. Nevertheless, a few derivatives can be obtained from these hydrocarbons through oxidation, nitration, and chlorination reactions. These are noted in Chapter 6. 

A. Synthetic Methods.—Electrophilic addition of P compounds to olefinic compounds is a well-established route to phosphonic acids, although yields are often disappointing. With phosphorus pentachloride it has been found that yields are greatly improved when phosphorus trichloride is added to the reaction mixture. Since the orientation of the addition implies that electrophilic addition to phosphorus rather than chlorine is the initial step, it seems likely that the trihalide participates by decreasing the free concentration of chlorine rather than by a more active role. This... 

Chlorination of olefins has also been achieved with SbCls in chlorinated solvents, which gives with mono-olefins vicinal dichloroalkanes by a syn addition. A concerted mechanism was initially proposed68 to rationalize this stereochemical behavior and the unexpectedly large amount of c -l,4-dichloro-2-butene found in the reaction of butadiene. In this case, however, because of orbital symmetry control it has been suggested that the addition occurs in an antarafacial direction69. 

Linear alkylbenzenes are made from -paraffms (Cio-Cu) by either partial dehydrogenation to olefins and addition to benzene with HF as catalyst (60%) or chlorination of the paraffins and Friedel-Crafts reaction with benzene and an aluminum chloride catalyst (40%). See Chapter 24 for more information. 

Addition of halogens to ketenes 5-27 Addition of HOBr or HOC1 to triple bonds addition of chlorine acetate or other reagents to olefins 5-34 Addition of acyl halides to olefins... 

When chlorine is added to olefinic double bonds in the presence of hydrogen fluoride and aluminum trifluoride as catalyst addition, substitution and isomerization occurs17-25-26. Detailed investigations have been undertaken to elucidate the reaction pathways and the influence of the catalyst system on the prod uct distribution in the case of tetrachloroethene and chlorine.17... 

Although very few studies of free-radical reactions of sulfenyl compounds have as yet been reported, irradiation with ultraviolet light enhances the rate of addition of CI3CSCI to olefins.218 Evidence for free-radical behavior is found in the easy decompositions which are observed for RSC1 under irradiation, e.g., the conversion of methanesulfenyl chloride to chloromethanesulfenyl chloride287 under the influence of sunlight. In the photoinitiated chlorination reaction with trichloro-... 

In contrast to chlorine and bromine atoms, iodine atoms in general do not seem to add readily to olefins. Some early work has been carried out by Forbes and his co-workers (97), but the quantitative information is very incomplete. Inefficient iodination of olefins is largely due to the instability of the diiodides, since the equilibria are in general shifted... 

The most serious limitation of TEMPO-mediated oxidations under Anelli s conditions is posed by the presence of HOC1—generated in situ— as a secondary oxidant, a quite reactive chemical that adds to olefins and produces electrophilic chlorination in many electron-rich substrates. 

Alkyl chlorides have been obtained by the direct chlorination of hydrocarbons 1 and by the addition of hydrogen chloride to olefines.2 However, they have usually been prepared from the corresponding alcohol by the action of a number of reagents, such as dry hydrogen chloride,3 dry hydrogen chloride in the presence of zinc chloride,4 phosphorus trichloride,3 phosphorus oxychloride,6 phosphorus pentachloride,7 phosphorus trichloride... 

Kinetic studies of the reactivity of allyltrialkylsilanes towards the p-methoxy substituted diphenylcarbenium ion revealed an increase of the reaction rate by several orders of magnitude compared to olefins lacking the silyl group383. These studies also indicated that the /i-silylcarbenium ion is generated in the rate-determining step. The reaction rate, however, is dramatically decreased when one or more alkyl groups on silicon are replaced by chlorine atoms383. 

The fluorination of internal F-alkenes and cycloalkenes proceeds at higher temperature the replacement of vinylic fluorine by chlorine in olefin leads to a remarkable acceleration of the reaction (Eq. 82) ... 

Under similar conditions, chlorine and bromine triflates add to olefin 9 ... 

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