Methane chloromethanes from

Describe a method you would use to separate chloromethane from the other possible reaction products when methane reacts with chlorine. 

Consider the chlorination of methane to chloromethane The heats of formation of the reac tants and products appear beneath the equation These heats of formation for the chemical com pounds are taken from published tabulations the heat of formation of chlorine as it is for all elements IS zero... 

Zinc chloride is also a catalyst for a liquid-phase process using concentrated hydrochloric acid at 100-150°C. Hydrochloric acid may be generated in situ by reacting sodium chloride with sulfuric acid. As mentioned earlier, methyl chloride may also be produced directly from methane with other chloromethanes. However, methyl chloride from methanol may be further chlorinated to produce dichloromethane, chloroform, and carbon tetrachloride. 

Oxyhydrochlorination A two-stage process for making gasoline from lower paraffinic hydrocarbons, especially methane. The methane, mixed with oxygen and hydrogen chloride, is passed over a supported copper chloride catalyst, yielding a mixture of chloromethanes ... 

Relatively soon after the discovery that aqueous solutions containing PtCl - and PtClg- can functionalize methane to form chloromethane and methanol, a mechanistic scheme for this conversion was proposed (16,17). As shown in Scheme 4, a methylplatinum(II) intermediate is formed (step I), and this intermediate is oxidized to a methylplatinum(IV) complex (step II). Either reductive elimination involving the Pt(IV) methyl group and coordinated water or chloride or, alternatively, nucleophilic attack at the carbon by an external nucleophile (H20 or Cl-) was proposed to generate the functionalized product and reduce the Pt center back to Pt(II) (step III) (17). This general mechanism has received convincing support over the last two decades (comprehensive reviews can be found in Refs. (2,14,15)). Carbon-heteroatom bond formation from Pt(IV) (step III) has been shown to occur via nucleophilic attack at a Pt-bonded methyl, as discussed in detail below (Section V. A). 

Alkanes appear to react with platinum(IV) in an identical manner to benzene (34, 84) chloromethane and chloroethane can be detected as the reaction products from methane and ethane, respectively. When propane, butane, or hexane is the reactant, the terminal chloro isomers predominate over the internal isomers. This was interpreted to mean that primary C—H bonds are the most reactive (34), but a more detailed study has shown that this conclusion does not necessarily follow from the experimental results (84). When cyclohexane is the reactant, dehydrogenation (or chlorination and then dehydrohalogenation) occurs to give benzene as one of the reaction products (29, 34, 84). 

If the concerted four-center mechanism for formation of chloromethane and hydrogen chloride from chlorine and methane is discarded, all the remaining possibilities are stepwise reaction mechanisms. A slow stepwise reaction is dynamically analogous to the flow of sand through a succession of funnels with different stem diameters. The funnel with the smallest stem will be the most important bottleneck and, if its stem diameter is much smaller than the others, it alone will determine the flow rate. Generally, a multistep chemical reaction will have a slow rate-determining step (analogous to the funnel with the small stem) and other relatively fast steps, which may occur either before or after the slow step. 

The attack of a chlorine atom on a methane hydrogen is not expected to require a precisely oriented collision. Moreover, the interatomic repulsions should be considerably smaller than in the four-center mechanism discussed previously for the reaction of molecular chlorine with methane because only two centers have to come close together (Figure 4-8). The methyl radical resulting from the attack of atomic chlorine on a hydrogen of methane then can remove a chlorine atom from molecular chlorine and form chloromethane and a new chlorine atom ... 

I. e net result of CH4 + Cl- — CH3- + HC1 and CH3- + Cl2 —> CH3CI + Cl- is formation of chloromethane arid hydrogen chloride from methane and chlorine. Notice that the chlorine atom consumed in the first step is replaced by another one in the second step. This kind of sequence of reactions is called a chain reaction because, in principle, one atom can induce the reaction of an infinite number of molecules through operation of a chain or cycle of reactions. In our example, chlorine atoms formed by the action of light on... 

Ozone is a form of oxygen. Ozone is present in the upper atmosphere and it prevents dangerous solar radiation from reaching the Earth s surface. Some of the chemicals that diffuse into the upper atmosphere decompose ozone. Chemicals that have this effect are methane (CH4), chloromethane (CH3C/) and an oxide of nitrogen (N02). 

Figure 1.5 provides examples of o for some simple molecules. For molecules which are conical (hydrogen cyanide and chloromethane), cylindrical (carbon dioxide and ethane), or spherical (neon, methane), empirically generated a values of 10, 20, and 100 are assigned. For flexible molecules, the value of o is unity because they cannot be rigidly rotated. Note that the o values for spherical, cylindrical, and conical molecules are different from the values used by crystallographers. 

Radical chlorination is a difficult reaction to control. As the reaction proceeds and the initial product, chloromethane, accumulates, it can also undergo hydrogen abstraction by a chlorine atom, resulting in the formation of dichloromethane. Chloroform is formed from dichloromethane and carbon tetrachloride from chloroform in a similar manner. The reaction of a 1 1 ratio of methane and chlorine at 440°C (at this high temperature. homolytic fission of the chlorine-chlorine bond occurs without light) results in the product mixture shown in the following equation ... 

Kotsinaris et al. 1998), while on Ag and Pt cathodes methane was the main product. Rondinini et al. (2004) observed the preferential formation of methane from poly-chloromethane on silver in ACN, DMF and aquo-organic solvents. Trichloroethene and trichloromethane were hydrodehalogenated in aqueous solution at different pHs by Chen et al. (2003) on platinized and palladized ceramic (ebonex) supports. Main reaction products were ethane, ethene and HC1 for the former substrate, and methane and HC1 for the latter. In a preceding study (Chen et al. 1999) in oxidative conditions, they observed the parallel degradation to carbon-containing products (mainly CO2) and, in neutral or alkaline pH, Cr/CI()3 as the only chloro-containing products. 

The first type of reaction is called the substitution reaction. In this reaction a hydrogen atom from an alkane is replaced by a halogen. For example, when methane reacts with diatomic chlorine gas, the major organic product is chloromethane CH4 + Cl2 — CH3C1 + HCl. 

Using the same reaction procedure described in the direct reaction of elemental silicon with methylene chloride or chloroform, the reaction of elemental silicon with a gaseous mixture of tetrachloromethane and hydrogen chloride afforded no tetrakis(chlorosilyl)methane instead, tris(chlorosilyl)methanes and bis(chlorosilyl)methanes were obtained, which were the same products derived from the reactions of chloroform and methylene chloride, respectively. This result may be rationalized by the decomposition of tetrachloromethane to chloroform and methylene chloride on the silicon-copper contact mass during the reaction, followed by reaction with elemental silicon to afford the products or by the decomposition reaction of partial silylated chloromethane intermediates.16... 

In the fluorine derivatives of methane and chloromethanes the variation of the GF bond is somewhat complex. As is seen in Table LVIII, the bond length varies from 1 42 A to 1 35 A. 

Alkanes and arenes can also be activated to other reactions by platinum complexes in aqueous solution (57,58). For arenes in the presence of H2PtCl5, reduction from Pt(IV) to Pt(II) occurs and the arene undergoes chlorination. The reaction is catalyzed by platinum(II) (59). Similarly, if a platinum(IV) catalyst such as HjPtClg is used, chloroalkanes are formed from alkanes. As an example, chloromethane is formed from methane (Eq. 23) (60-62). Linear alkanes preferentially substitute at the methyl... 

It is not easy to make chloromethane alone from the reaction between methane and chlorine. Explain why. 

Both oxyhydrochlorinatlon of methane and chloromethane oligomerization studies were conducted in essentially the same microreactor system. All the reactants were introduced at pressures slightly above one atmosphere from gas cylinders, and flow rates were controlled by a Brooks four-channel mass-flow controller. The feed stream for the oxyhydrochlorinatlon reaction was sampled before and after an experimental run, while the product stream was continuously sampled on-line during the run to obtain a mass balance. A quadrupole mass spectrometer was used to analyze the feed and product... 

To determine the tolerance of ZSM-5 to the presence of polychlorinated methanes, mixtures of mono- and dichloromethane were reacted over ZSM-5. Feed streams containing a molar ratio of 2.75 1 mono- to dichloromethane reacted over ZSM-5, and coking of the catalyst was no greater than that experienced for either chloromethane alone or methanol. As expected, the product mixture contained a larger aromatic fraction than the product from chloromethane oligomerization. 

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