Chloromethane, formation

Write equations for the initiation and propagation steps for the formation of dichloromethane by free radical chlorination of chloromethane... 

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... 

If the alkyl halide contains more than one, equally reactive C-halogen centers, these will generally react each with one aromatic substrate molecule. For example dichloromethane reacts with benzene to give diphenylmethane, and chloroform will give triphenylmethane. The reaction of tetrachloromethane with benzene however stops with the formation of triphenyl chloromethane 7 (trityl chloride), because further reaction is sterically hindered ... 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

Heating aluminium powder with carbon tetrachloride, chloromethane or carbon tetrachloride-chloroform mixtures in closed systems to 152°C may cause an explosion, particularly if traces of aluminium chloride are present [1], A mixture of carbon tetrachloride and aluminium powder exploded dining ball-milling [2], and it was later shown that heavy impact would detonate the mixture [3], Mixtures with fluorotrichloroethane and with trichlorotrifluoroethane will flash or spark on heavy impact [4], A virtually unvented aluminium tank containing a 4 1 2 mixture of o-dichlorobenzene, 1,2-dichloroethane and 1,2-dichloropropane exploded violently 7 days after filling. This was attributed to formation of aluminium chloride which catalysed further accelerating attack on the aluminium tank [5], An analysis of the likely course of the Friedel-Crafts reaction and calculation of the likely heat release (29.1 kJ/mol) has been published [26],... 

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). 

An unusual reaction of methoxythiocarbonyl chloride with tetra-n-butylammo-nium iodide in the presence of sodium thiosulphate leads to the formation of 0,5-dimethyl dithiocarbonate [49], The reaction appears to involve a reduction step, with the iodide anion being regenerated from the released iodine by the thiosulphate ions (Scheme 4.7). In the absence of the thiosulphate ions, the thiocarbonyl chloride decomposes to yield chloromethane and carbonyl sulphide. 

Electrochemical oxidation of cadmium in a solution of ](4-methylphenyl)sulfonyl]-2-pyridylamine] (HL) in acetonitrile/di chloromethane mixtures resulted in CdL2 complex formation [149]. The electrochemical oxidation of cadmium amalgam in nonaqueous solvents CH2CI2, 1,2-C2H4CI2, and PC was also used for the preparation of cadmium complexes with 18-membered macromonocyclic ligands, 18-06, 18-S6, I8-N2O4, and 18-N6 [150]. The stoichiometry and stability of resulted complexes were determined. The same method was used to examine the complexation of Cd(II) cation with 12-crown-4 ether, azacrown ether 1,4,8,11-tetra-azacyclotetradecane, and thiaazacrown... 

To maximize the formation of monohalogenated product, a radical substitution reaction must be carried out in the presence of excess alkane. For example, when a large excess of methane is used, the product is almost completely methyl chloride (chloromethane). 

An early paper reported that reaction of PtCll- and 1 obeyed the rate law (30) expressed in Eq. (1) through the formation of a methylplatinum intermediate that decomposed in the presence of excess chloride to form chloromethane. Fanchiangef al. made a more detailed study of this reaction and proposed the reaction mechanism shown in Fig. 2, from which... 

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. 

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... 

The chlorination of methane does not have to stop with the formation of chloromethane (methyl chloride). It is usual when chlorinating methane to obtain some of the higher chlorination products dichloromethane (methylene chloride), trichloromethane (chloroform), and tetrachloromethane (carbon tetrachloride) ... 

We can use the overall reaction order to distinguish between the two possible mechanisms, A and B. Experimentally, the rate of formation of methanol is found to be proportional to the concentrations both of chloromethane and of hydroxide ion. Therefore the reaction rate is second order overall and is expressed correctly by Equation 8-2. This means that the mechanism of the reaction is the single-step process B. Such reactions generally are classified as bimolecular nucleophilic substitutions, often designated SN2, S for substitution, N for nucleophilic, and 2 for bimolecular, because there are two reactant molecules in the transition state. To summarize For an SN2 reaction,... 

We have included in this chapter stability constants for these systems in di-chloromethane, although this is a low permittivity medium and therefore the reliability of these data may be reduced by the formation of ion pairs. However, these data may be useful in solvent extraction processes due to the immiscibility of this solvent with water which allows the direct partition of electrolytes in the dichloromethane solvent system [59,60],... 

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 ... 

Show all of the steps in the mechanism for the formation of dichloromethane from chloromethane ... 

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