Isobutane chlorination

Propylene oxide [75-56-9] is manufactured by either the chlorohydrin process or the peroxidation (coproduct) process. In the chlorohydrin process, chlorine, propylene, and water are combined to make propylene chlorohydrin, which then reacts with inorganic base to yield the oxide. The peroxidation process converts either isobutane or ethylbenzene direcdy to an alkyl hydroperoxide which then reacts with propylene to make propylene oxide, and /-butyl alcohol or methylbenzyl alcohol, respectively. Table 1 Hsts producers of propylene glycols in the United States. 

It was shown that no rearrangement of isobutyl radical to tert-butyl radical (which would involve the formation of a more stable radical by a hydrogen shift) took place during the chlorination of isobutane. 

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

It is also clear that during periods of low surface ozone, chlorine atoms are a major reactant for hydrocarbons (e.g., Jobson et al., 1994 Solberg et al., 1996 Ariya et al., 1998). Figure 6.39, for example, shows the measured ratios of isobutane, n-butane, and propane during an ozone depletion event (Jobson et al., 1994). These particular pairs of hydrocarbons were chosen to differentiate chlorine atom chemistry from OH reactions. Thus isobutane and propane have similar rate constants for reaction with Cl but different rate constants for reaction with OH. If chlorine atoms are responsible for the loss of these organics, their ratio should remain relatively constant in the air mass, as indicated by the line marked Cl. Similarly, isobutane and n-butane have similar rate constants for removal by OH but different rate constants for reactions with... 

Only two alkanes have the molecular formula C4H10 butane and isobutane (2-methylpropane)— both of which give two monochlorides on free-radical chlorination. However, dehydrochlorination of one of the monochlorides derived from butane yields a mixture of alkenes. 

Russell, G. A. Solvent effects in the reactions of free radicals and atoms. II. Effects of solvents on the position of attack of chlorine atoms upon 2,3-dimethylbutane, isobutane and 2-deuterio-2-methyl-propane. J. Amer. chem. Soc. 80, 4987 (1958). 

Another factor that limits the usefulness of the chlorination reaction in the laboratory is the lack of selectivity exhibited by the chlorine atom when more than one type of hydrogen is available to be abstracted. As an example, the reaction of isobutane with chlorine produces l-chloro-2-methylpropane and 2-chloro-2-methylpropane in a 2 1 ra-... 

Let s carefully analyze the reasons why these products are formed in this ratio. When a chlorine atom encounters an isobutane molecule, it may abstract a primary hydrogen, leading ultimately to the formation of l-chloro-2-methylpropane ... 

Other catalytic reactions carried out in fluidized-bed reactors are the oxidation of naphthalene to phthalic anhydride [2, 6, 80] the ammoxidation of isobutane to mcthacrylonitrilc [2] the synthesis of maleic anhydride from the naphtha cracker C4 fraction (Mitsubishi process [81, 82]) or from n-butane (ALMA process [83], [84]) the reaction of acetylene with acetic acid to vinyl acetate [2] the oxychlorination of ethylene to 1,2-di-chloroethane [2, 6, 85, 86] the chlorination of methane [2], the reaction of phenol with methanol to cresol and 2,6-xylenol [2, 87] the reaction of methanol to gasoline... 

Tertiary hydrogen atoms react with Cl about 5.5 times as fast as primary ones. Predict the product ratios for chlorination of isobutane. 

Use the bond-dissociation enthalpies in Table 4-2 (page 143) to calculate the heats of reaction for the two possible first propagation steps in the chlorination of isobutane. Use this information to draw a reaction-energy diagram like Figure 4-8, comparing the activation energies for formation of the two radicals. 

Using a similar technique Priola and coworkers (S) studied the reaction between t-butyl chloride and EtjAl, Et2AlCl, EtAlClj and AICI3 using methylene chloride and methyl chloride solvents at —78° C, for 2 h. The results of this study can be summarized as follows 1. The major reaction products are isobutane and 2,2-dimethylbutane in reactions where EtsAl is used. 2. Other products such as 23-dimethyl-butane, isooctane and l-chloro-33 -dimethylbutane are also formed in amounts strictly dependent on the molar ratios of t-BuCl/alkylaluminum or the chlorine content of the alkylaluminum. 3. When EtjAlO or EtAlCl2 react with f-BuCl, the product consists of branched Q, Cg, Cg hydrocarbons and a higher alkyl chloride. 4. Interestingly, AlClj/does not react with t-BuCl, however, it yields a crystalline complex at —78° in the absence of an added olefln. 

Depending upon which nydrogen atom is replaced, any of a number of isomeric products can be formed from a single alkane. Ethane can yield only one halo-ethane propane, /2-butane, and isobutane can yield two isomers each /i-pentane can yield three isomers, and isopentane, four isomers. Experiment has shown that on halogenation an alkane yields a mixture of all possible isomeric products, indicating that all hydrogen atoms are susceptible to replacement. For example, for chlorination ... 

Chlorination of isobutane presents a similar problem. In this case, abstraction of one of the nine primary hydrogen leads to the formation of isobutyl chloride, whereas abstraction of the single tertiary hydrogen leads to the formation of rer/-butyl chloride. We would estimate, then, that the probability factor favors... 

H. C. Brown (of Purdue University) and Glen Russell (now of Iowa State University) decided to test the possibility that free radicals, like carbonium ions, might rearrange, and chose the chlorination of isobutane as a good test case, because of the large dilVerence in stability between rm-butyl and isobutyl radicals. If rearrangement of alkyl radicals can indeed take place, it should certainly happen here. 

Abstraction of the secondary hydrogen atom is more exothermic than abstraction of the primary hydrogen atom, for the related reasons that (1) secondary C-H bonds are weaker than primary ones and (2) secondary radicals are more stable than primary ones. So, we get more 2-chloropropane than 1-chloropropane. But in this case, that isn t the only factor involved remember that there are six primary hydrogen atoms and only two secondary ones, so the relative reactivity of the primary and secondary positions is even more different than the simple ratio of products from the reaction suggests. This statistical factor is more evident in the second example we gave above, the chlorination of isobutane. Now the choice is between formation of a tertiary radical and formation of a primary one. 

Oxidation of all the saturated paraffin hydrocarbons up to isobutane in the presence of chlorine was found to result in the preferential reaction of the oxygen with the carbon to give carbon dioxide and of the chlorine with hydrogen to give hydrochloric acid gas.1- ... 

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