Methylene reaction with methane

As aheady mentioned, it was observed that one mole of hydrogen is liberated when methane is reacted with the tantalum hydride with the formation of tantalum methyl. The reaction with methane above 150°C leads to the formation of the Ta-methyl, Ta-methylene, and Ta-methylidyne species plus H2 (M=Ta) [40-42, 54]. These observations are a proof that the first step of alkane metathesis is the formation of metal alkyl intermediate via cleavage of the C-H bond of the alkane likely by sigma bond metathesis. Further, detailed mechanistic [22, 55] and experimental kinetic studies revealed that the alkenes and hydrogen are the primary products [56]. Initially, it was believed that the active site was a bis-siloxy tanta-lum-monohydride, but progressively, evidence came in favor of an equilibrium between bis-siloxy tantalum-monohydride d and bis-siloxy-tantalum-tris-hydride d° [57], and the mechanism would fit much better with a bis-siloxy-tantalum-tris-hydride [58]. 

Chloroform can be manufactured from a number of starting materials. Methane, methyl chloride, or methylene chloride can be further chlorinated to chloroform, or carbon tetrachloride can be reduced, ie, hydrodechlorinated, to chloroform. Methane can be oxychlorinated with HCl and oxygen to form a mixture of chlorinated methanes. Many compounds containing either the acetyl (CH CO) or CH2CH(OH) group yield chloroform on reaction with chlorine and alkali or hypochlorite. Methyl chloride chlorination is now the most common commercial method of producing chloroform. Many years ago chloroform was almost exclusively produced from acetone or ethyl alcohol by reaction with chlorine and alkali. 

Scheme 2.12 shows some representative Mannich reactions. Entries 1 and 2 show the preparation of typical Mannich bases from a ketone, formaldehyde, and a dialkylamine following the classical procedure. Alternatively, formaldehyde equivalents may be used, such as l>is-(di methyl ami no)methane in Entry 3. On treatment with trifluoroacetic acid, this aminal generates the iminium trifluoroacetate as a reactive electrophile. lV,A-(Dimethyl)methylene ammonium iodide is commercially available and is known as Eschenmoser s salt.192 This compound is sufficiently electrophilic to react directly with silyl enol ethers in neutral solution.183 The reagent can be added to a solution of an enolate or enolate precursor, which permits the reaction to be carried out under nonacidic conditions. Entries 4 and 5 illustrate the preparation of Mannich bases using Eschenmoser s salt in reactions with preformed enolates. 

The problem of relative orientation of two reacting fragments in the course of the reaction leads to the discussion of competing mechanisms, as, for instance, in the reaction of methylene with methane (18) ... 

Whereas alkylation of activated methylene systems by classical methods produces a mixture of mono- and dialkylated products, with the latter frequently predominating, phase-transfer catalytic procedures permit better control and it is possible to obtain only the monoalkylated derivatives. Extended reaction times or more vigorous conditions with an excess of the alkylating agent lead to dialkylated products or, with dihaloalkanes, carbocyclic compounds as the technique mimics dilute concentration conditions, e.g. the resonance stabilized cyclopentadienyl anion, generated under solidiliquid two-phase conditions, or under liquiddiquid conditions, reacts with 1,2-dihaloethanes to form spiro[2,4]hepta-4,6-diene (70-85%) [1-3]. Reaction with dichloromethane produces bis(cyclopenta-2,4-dien-l-yl)methane (60%) [4],... 

The mechanism proposed for carbene-abstraction and carbene-insertion reactions is based on the calculations of Dewar (MINDO/2) and Hoffmann (extended Hiickel) Hoffmann dealt only with the concerted reactions of singlet carbenes, whereas Dewar discussed both singlet and triplet carbene reactions. The calculations of Dewar s ) for the reaction of triplet methylene with methane gave the following results ... 

Condensation of ester (44e) with the anion of malononitrile gave the alkene (44g) <91JPR35>. Oxadiazole (43e) and triethyl phosphite gave a methane phosphate which underwent a Wittig reation with aldehydes ArCHO to form alkenes (43f). When the alkyl side chain contained an active methylene group, as in (43g), reaction with arenediazonium salts ArN2X yielded arylhydrazones (43h) <88LA909>. 

The role of titanium salt is to activate the carbonyl compounds as Lewis acid. As described above, bis(iodozincio)methane (3) is nucleophilic enough to attack the carbonyl group of aldehydes or ce-alkoxyketones. In the reaction with simple ketones or esters, however, the addition of titanium salt is necessary to facilitate the nucleophilic attack. Instead of this Lewis acid activator, simple heating may induce the nucleophilic attack. Treatment of 2-dodecanone with 3 without titanium salt at higher temperature, however, does not improve the yield of alkene (Scheme 13). The reason for the low reactivity of 3 at higher temperature comes from the structural change of 3 into the polymeric methylene zinc 4 through the Schlenk equilibrium shown in equation 740. 

Treatment of 2,3-epoxyalkanol with bis(iodozincio)methane (3) gave homoallylic alcohol derivatives (equation 49). The formation can be explained via a pinacolone rearrangement followed by methylenation reaction (equation 50)74. The rearrangement is induced by the presence of bis(iodozincio)methane (3). 

Vanpee and Grard133 made a quantitative study of the formation of saturates (mainly ethane) in the photolysis of CH2CO with added methane (ratios CH4/CH2CO = 1 to 7) at 28 to 250 °C. and found that the results could be explained by a mechanism involving competition between CH4 and CH2CO for methylene by reactions of the first order in methylene. The rate of reaction of CH2 with CH4 was found to be 0.183 that of the reaction with ketene. Decomposition of excited ethane by the reaction... 

An important question regarding the reaction of methylene with methane and with hydrogen is whether the reactions proceed by direct addition... 

The chief discrepancy between the experimental results of Chanmugan and Burton and of Bell and Kistiakowsky (see Secs. IV-A and B) is that the latter workers found evidence for the presence of methyl in the reaction of methylene with hydrogen and with methane (or their deuterated isomers), whereas the results of Chanmugan and Burton were more consistent with the direct addition mechanism, at least at low temperatures. 

Condensation of Q—C4 alkanes to produce highly branched oligomeric and polymeric hydrocarbons41 was also achieved by their condensation in FSO3H—SbF5. Block methylene units in the polymeric chain were observed even when methane was brought into reaction with alkenes under similar conditions.42... 

PROBLEM 8.13 The industrial degreasing solvent methylene chloride, CH2C12, is prepared from methane by reaction with chlorine ... 

No trace of any ring expanded products due to C—C insertion was seen in the reactions of methylene with strained spirobicyclic molecules (46) and (47).59 Ab initio calculations on the reaction between quartet methylidyne (CH) with methane predicted a barrier of 3.5 kcal mol-1.60... 

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... 

The reaction of methane with chlorine in the presence of ultraviolet light gives a mixture of methyl chloride, methylene chloride, chloroform and carbon tetrachloride. When excess of chlorine is used and the time of the reaction is prolonged, the final product is predominantly carbon tetrachloride. 

The production of aniline is a major international business, carried on in the US, Europe and Asia, mainly for the conversion, by reaction with formaldehyde under acid-catalyzed conditions, into diaminodiphenylmethanes 9a, 9b and 9c, and then into isocyanates, mainly 4,4/-methylenebis(phenylisocyanate) (MDI, also known as 4,4 -methylene-di-paraphenylene isocyanate, 4,4 -diphenylmethane diisocyanate, methylene diphenylene diisocyanate and diisocyanato diphenyl methane) (9d), from which polyurethanes are produced. This accounts for well over 60% of total demand (Figure 1). Aniline is also used in bulk for the production of antioxidants and vulcanization accelerators for rubber. Some 15.5 million lbs. of cyclohexylamine are made each year mainly by catalytic hydrogenation of aniline. Half the demand is for use as a boiler water additive. Other major uses include in the manufacture of herbicides, plasticizers, emulsifying agents, dyes, dry-cleaning soaps, acid gas absorbents and, in Asia, cyclamate sweeteners. Apart from India, the use of aniline for dyestuff manufacture represents about 10% of demand. 

A,7V-polyazolylmethanes can be prepared by reaction of azoles with methylene chloride in an autoclave at 150 °C (Scheme ll).20 At 200 °C this reaction leads to 4,4 -dipyrazolylmethane, which upon reaction with boranes gives a pyrazaboles polymer. Some derivatives have been prepared from the reaction of potassium salts of the azole and methylene iodide. The ligand (tetrakis-(l-pyrazolyl)methane was prepared analogously. In selected cases a basic medium was employed.21... 

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