Methyl chloride hydrolysis

Methanol, a side product of methyl chloride hydrolysis, can be recovered and reused. In addition, recovered water is recycled. The products are formulated on site as solutions and are shipped in 1 to 30 gallon containers. 

The methyl chloride hydrolysis [Equation (12)] is a type II SN2 reaction. The attacking species is a water molecule, which loses a proton to a solvent water molecule with the hydroxide ion formally substituting the chloride ion in methyl chloride. Thus, during hydrolysis, bond breaking and bond formation involving both solute and solvent molecules take place. It is essential, therefore, to consider the solvent molecules explicitly in modeling the methyl chloride hydrolysis. This is in contrast to type I SN2 reactions, such as the reaction in Equation (11), in which bond breaking and bond formation occur only in the solute molecules and the solvent molecules do not participate actively in the reaction except as a medium. 

Ab initio molecular-dynamics simulations have been carried out for a prototype of methyl chloride hydrolysis, with explicit consideration of three water molecules, i.e. one as solute (reactant) and two as solvent. Several complexes and trajectories on the energy surface were identified. 

The ratio of cycHc to linear oligomers, as well as the chain length of the linear sdoxanes, is controlled by the conditions of hydrolysis, such as the ratio of chlorosilane to water, temperature, contact time, and solvents (60,61). Commercially, hydrolysis of dim ethyl dichi oro sil a n e is performed by either batch or a continuous process (62). In the typical industrial operation, the dimethyl dichi orosilane is mixed with 22% a2eotropic aqueous hydrochloric acid in a continuous reactor. The mixture of hydrolysate and 32% concentrated acid is separated in a decanter. After separation, the anhydrous hydrogen chloride is converted to methyl chloride, which is then reused in the direct process. The hydrolysate is washed for removal of residual acid, neutralized, dried, and filtered (63). The typical yield of cycHc oligomers is between 35 and 50%. The mixture of cycHc oligomers consists mainly of tetramer and pentamer. Only a small amount of cycHc trimer is formed. 

In contrast to the hydrolysis technology, the methanolysis process allows for the one-step synthesis of organosdoxane oligomers and methyl chloride without formation of hydrochloric acid (64,65). The continuous methanolysis can also yield quantitatively linear sdanol-stopped oligomers by recycle of the cycHc fraction into the hydrolysis loop. 

Thermal chlorination of methane was first put on an industrial scale by Hoechst in Germany in 1923. At that time, high pressure methanol synthesis from hydrogen and carbon monoxide provided a new source of methanol for production of methyl chloride by reaction with hydrogen chloride. Prior to 1914 attempts were made to estabHsh an industrial process for methanol by hydrolysis of methyl chloride obtained by chlorinating methane. 

LiquidPha.se. The methyl chloride process with the widest use in the United States is the Hquid-phase methanol hydrochlorination process. SHicone producers use methyl chloride in its manufacture and produce an aqueous hydrochloric acid stream as a by-product. This by-product HCl is converted back to methyl chloride by hydrochlorination. In fact, it is possible to produce methyl chloride directiy from the chioromethylsilane hydrolysis step in the siHcone process (18,19) (see Silicon compounds, silicones). 

Methylation of the 6,7-dimethyl derivative of 133 with methyl iodide in sodium hydroxide or sodium ethoxide gave two S,N-dimethyl derivatives, whereas in sodamide or ammonia, only the 5-methyl derivative was obtained. Methylation with diazomethane gave four methyl derivatives and with methyl chloride two di-jV-methyl and one 5,/V-dimethy] derivative were obtained (80H1139). Methylation of 153, obtained from 152, gave 4-methyl-3-methylthio-triazinoindole 155, whose hydrolysis or oxidation gave 154 (76T1735). On the other hand, methylation of 156 gave methiodide... 

Of the factors associated with the high reactivity of cyanuric chloride (high exother-micity, rapid hydrolysis in presence of water-containing solvents, acid catalysed reactions, liberation of up to 3 mol hydrogen chloride/mol of chloride, formation of methyl chloride gas with methanol, formation of carbon dioxide from bicarbonates), several were involved in many of the incidents recorded [1] (and given below). The acid catalysed self acceleration and high exothermicity are rated highest [2]. It is also a mildly endothermic compound (AH°f (s) +91.6 kJ/mol, 0.49 kJ/g). 

Chemical/Physical. Under laboratory conditions, methylene chloride hydrolyzed with subsequent oxidation and reduction to produce methyl chloride, methanol, formic acid, and formaldehyde (Smith and Dragun, 1984). The experimental half-life for hydrolysis in water at 25 °C is approximately 18 months (Dilling et al, 1975). 

Hydrolyzes in water forming methyl alcohol and hydriodic acid. The estimated half-life in water at 25 °C and pH 7 is 110 d (Mabey and Mill, 1978). At 70 °C, the hydrolysis rate was determined to be 3.2 X 10 Vsec which is equivalent to a half-life of 6 h. (Glows and Wren, 2003). May react with chlorides in seawater to form methyl chloride (Zafiriou, 1975). 

When comparing the hydrolysis of methyl bromide with its reaction with Cl under the same conditions (i.e., [Cl-] = 100 mM, see Illustrative Example 13.2), we see that from a thermodynamic point of view, the hydrolysis reaction is heavily favored (compare ArG° values). This does not mean that the methyl bromide present is primarily transformed into methanol instead of methyl chloride (which it would be, if the reaction were to be thermodynamically controlled). In fact, in this and all other cases discussed in this chapter, we will assume that the reactions considered will be kinetically controlled that is, the relative importance of the various transformation pathways of a given compound will be determined by the relative reaction rates and not by the respective ArG° values. Thus, in our example, because CE is about a 103 times better nucleophile as compared to water (see Section 13.2) and because its concentration is about 103 times smaller than that of water (0.05 M versus 55.3 M), the two reactions would be of about equal importance under the conditions prevailing in this groundwater. Note that the product methyl chloride would subsequently also hydrolyze to yield methanol, though at a much slower rate. We will come back to this problem in Section 13.2 (Illustrative Example 13.2). 

Depending on the relative nucleophilicities, [Nu]50% ranges from micromolar to molar concentrations (Table 13.5). Although these values represent only order-of-magnitude estimates, they allow some important conclusions. First, in uncontaminated freshwa-ters (where bicarbonate typically occurs at about 10"3 M, chloride and sulfate occur at about 10 4 M, and hydroxide is micromolar or less, Stumm and Morgan, 1996), the concentrations of nucleophiles are usually too small to compete successfully with water in SN2 reactions involving aliphatic halides. Hence the major reaction will be the displacement of the halide by water molecules. In salty or contaminated waters, however, nucleophilic substitution reactions other than hydrolysis may occur Zafiriou (1975), for example, has demonstrated that in seawater ([CL] 0.5 M) an important sink for methyl iodide is transformation to methyl chloride ... 

Exercise 26-42 From appropriate p values (Table 26-7) and a- values (Table 26-6), calculate the rates of hydrolysis of 4-CH3-, 4-CH30, 4-N02-phenyl methyl chlorides relative to phenylmethyl chloride (a) in water at 30° in the presence of base, and (b) in 48% ethanol at 30°. Explain why there is a greater spread in the relative rates in (b) than in (a). 

However, in the case of 32f, the elements of diethoxy methyl chloride are lost to give 4-methoxyarsabenzene 33 36). Alternatively, if 32f is reduced to secondary arsine 34, methanol is eliminated to give 35 37>. On hydrolysis, 35 affords 4-arsabenzaldehyde 36. Similarly 32g has been converted to 24g which on hydrolysis gave 4-arsabenzoic acid 37 38 39). 

The transition structures for the hydrolysis reactions of methyl, /-butyl, and ada-mantyl chlorides in the gas phase and in water were calculated using the B3LYP/6-31-G(d) level of theory and the PCM solvation model.82 In the gas phase, backside attack is strongly favoured for the methyl chloride reaction and slightly favoured for the t -butyl chloride reaction. Frontside attack is favoured for the adamantyl chloride... 

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