Methylene halides

The p-naphthyl ethers of methylene halides have m.p. 133°, of ethylene halides 217°, and trimethylene halides 148°. 

The reaction itself works by the action of Na or K from NaOH or KOH which form what is called a catechoxide dianion with the two OHs of the catechol species. This makes the two ripe for an attack by a methylene halide which can be either DCM (methylene chloride, or dichloromethane), DBM (methylene bromide, or di-bromomethane) or DIM (methylene iodide, or diiodomethane). DCM is cheap and works pretty well, but DBM and DIM work better yet are more expensive. 

CHX2 group when treated with methylene halides and lithium dicyclohexylamide at low temperamres. " ... 

Often compounds of CH2X2 type are called methylene halides, e.g. methylene chloride (CH2CI2), CHX3 type compounds are called haloforms, e.g. chloroform (CHCI3), and CX4 type compounds are called carbon tetrahalides, e.g. carbon tetrachloride (CCI4). Methylene chloride (dichlor-omethane, DCM), chloroform and carbon tetrachloride are extensively used in organic synthesis as nonpolar solvents. 

Some interesting electron-transfer reactions of sodium naphthalide have recently been reported. Reaction with phenylmercuric chloride or benzylmercuric chloride gives better than 70% yields of the symmetric diphenyl- or dibenzylmercury compounds. Solutions of alkali metals in HMPA lead to the same results (88). Evidence for the reaction of sodium naphthalide with methylene halides to give methylene anion radical, CH2T, has recently appeared (22). 

Bawn and Dunning4 and Bawn and Tipper6 postulated the formation of methylene in the reaction of Na vapor with methylene halides. The chief evidence was the formation of ethylene as the main product. A small amount of methane was also found. 

More VEELS or RAIRS investigations of the decomposition of methylene halides on metal single-crystal surfaces and infrared work on alumina-supported metals would be welcome. 

J. S. Brimacombe, A. B. Foster, B. D. Jones, and J. J. Willard, Reaction of the cyclohexane-1,2-diols and methyl 4,6-0-benzylidene-a-D-gluco- and galactopyranoside with methylene halides, J. Chem. Soc. C. 2404 (1967). 

Selective monohalogenation (chlorination and bromination) can be accomplished with excess methylene halides in the presence of SbF5.535 Adamantane, for example, gives 1-chloroadamantane in 80% yield at ambient temperature in 24 h. 

The 2-naphthyl ethers from methylene halides have m.p. 133 °C, from ethylene halides 217 °C and trimethylene halides 148 °C. 

Carbon disulfide (CS2) is a highly flammable, volatile, and extremely foulsmelling liquid that causes a burning sensation on the skin. It can produce psychic and visual disturbances as well as nausea, vomiting, and convulsions. Typically carbon disulfide is used as a solvent for substances such as sulfur or phosphorus. There are other solvents (the methylene halides or the xylenes, for example) that would be more pleasant to work with and much less hazardous. 

Hine, J. Thomas, C. H. Ehrenson, S. J. The effect of halogen atoms on the reactivity of other halogen atoms in the same molecule. V. The Sn2 reactivity of methylene halides. 

Know the common names of the alkyl groups, cycloalkyl groups, methylene halides, and haloforms. 

Fedurco, M., Sartoretti, C.J. and Augustynski, J. (2001) Reductive cleavage of the carbon-halogen bond in simple methyl and methylene halides. Reactions of the methyl radical and carbene at the polarized electrode/aqueous solution interface. Langmuir 17, 2380-2387. 

Some of the halomethanes have acquired common names that are not clearly related to their structures. A compound of formula CH2X2 (a methylene group with two halogens) is called a methylene halide, a compound of formula CHX3 is called a haloform, and a compound of formula CX4 is called a carbon tetrahalide. 

The effect of substituting fluorine for hydrogen in the methylene halides is to increase the rate of carbanion formation and presumably to stabilize the carbanion and decrease the pK. The effect of fluorine substitution on the acidity of other carbon acids is not so clear. In some cases fluorine substitution leads to a smaller increase in rate than expected from the inductive effect and in other cases results in a decrease in the rate of carbanion formation and an increase in pK values. The results shown in Table 6 were obtained for the rate coefficient (k) for methoxide ion catalysed carbanion formation per hydrogen atom by following the appearance of the MeOH absorbance in the IR spectrum when the esters were allowed to exchange in MeOD [167]. The acidity of the nitro-paraffins in Table 7 is mostly increased by chlorine substitution (p/T... 

Figure 5 Cyclization of a reactive methylene halide. (From Ref. 60.)...

Cyclization reactions under Barbier conditions can also occur with reactive methylene halides [Eq. (24) and Fig. 5 58,59,60]. 

Generally speaking, about stoichiometric quantities of the reactants are employed—that is, about one mole of methylene dihalide and two moles of base per mole of aromatic reactant charged. In some cases, it may be desirable to employ a slight to moderate excess—for example 5-50% excess of the base and/or the methylene halide to insure completion of the reaction. 

Cade, J.A., Methylenediphosphonates and related compounds. Part 1. Synthesis from methylene halides, J. Chem. Soc., 2266, 1959. 

Starting material Metal halide (eq mol) Methylene halide Reaction conditions Temp.(°C) Time (h) Product yields (%) ... 

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