Methylene Chloride

Methylene chloride, a volatile chlorinated hydrocarbon, is used as a paint remover, metal degreaser, and aerosol propellant. The odor threshold for methylene chloride in the air is 100 ppm. According to Shelton (1989), it has been shown to induce tumors in mice. 

Methylene chloride is a clear, colorless, heavy, nonflammable liquid with a pleasant ethereal odor. It is the least toxic of the chloromethanes and is not phoiochemically reactive. As one of the most powerful solvents in the 270 

Degreasing, Special artd Decaffei nation grades. The Technical and Decaflieination grades meet the requirements of the American Chemical Society Reagent Chemical 2i0 

3rd Edition, the National formulary XVI and Military Specification MIL-D-6996D. 

The slow combustion of methylene chloride is a degenerately branched chain reaction it proceeds by a mechanism similar to that involved in the pyrolysis of the same compound which takes place at a slightly higher temperature [153]. The primary chains are the same and several of the chlorinated hydrocarbon minor products are identical. Oxygen is only involved in the conversion of the intermediate dichloroethylene to the final products hydrogen chloride and carbon monoxide. 

At 533 °C in a vessel whose internal diameter was 34 mm, the maximum rate of reaction was given by 

The initial stages of the reaction showed an exponential acceleration, according to the usual equation for degenerately branched chain reaction 

The secondary oxidation chain involves radical attack and oxidation of the dichloroethylene, viz. 

TABLE 21.5. Improvement of Cancer Dose-Response Assessment for Dichloromethane Using PBPK Models to Compute Relevant Dose Metrics 

Exposure (ppm) CYP Dose Metrics (mg metabolized/volume liver/day) GST Dose Metrics (mg metabolized/volume liver/day) Tumor Prevalence 

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CH OfiSj, H2C(S03H)2- a colourless, crystalline solid which readily absorbs water vapour decomposes on distillation. The potassium salt is prepared by heating methylene chloride with an aqueous solution of potassium sulphite under pressure at 150-I60" C. The free acid is obtained by decomposing the sparingly soluble barium salt with sulphuric acid. The aryl esters are very stable, but the alkyl esters decompose on heating to give ethers. Resembles malonic acid in some of its reactions. 

Selection of solvents. The choice of solvent will naturally depend in the first place upon the solubility relations of the substance. If this is already in solution, for example, as an extract, it is usually evaporated to dryness under reduced pressure and then dissolved in a suitable medium the solution must be dilute since crystallisation in the column must be avoided. The solvents generally employed possess boiling points between 40° and 85°. The most widely used medium is light petroleum (b.p. not above 80°) others are cycZohexane, carbon disulphide, benzene, chloroform, carbon tetrachloride, methylene chloride, ethyl acetate, ethyl alcohol, acetone, ether and acetic acid. 

Methylene chloride. The commercial substance is purified by washing with 5 per cent, sodium carbonate solution, followed by water, dried over anhydrous calcium chloride, and then fractionated. The fraction, b.p. 40-41°, is collected. 

Methylene chloride is a useful substitute for diethyl ether when it is desired to employ a solvent which is heavier than water. 

Methylene chloride. Dichloroethylene (trans) Ethylideiie chloride Dichloroethylene (ci ) Chloroform 2 2 Dichloropropane Methyl chloroform. ... 

Methylene chloride CHjCl, b.p. 41°, is obtained as a by product in the com mercial preparation of chloroform by the reduction of carbon tetrachloride with moist iron and also as one of the products in the chlorination of methane it is a useful extraction solvent completely immiscible with water. 

It is marketed as a 35-40 per cent, solution in water (formalin). The rpactions of formaldehyde are partly typical of aldehydes and partly peculiar to itself. By evaporating an aqueous solution paraformaldehyde or paraform (CHjO), an amorphous white solid is produced it is insoluble in most solvents. When formaldehyde is distilled from a 60 per cent, solution containing 2 per cent, of sulphuric acid, it pol5unerises to a crystalline trimeride, trioxane, which can be extracted with methylene chloride this is crystalline (m.p. 62°, b.p. 115°), readily soluble in water, alcohol and ether, and devoid of aldehydic properties ... 

Place a mixture of 1 0 g. of the hydrocarbon, 10 ml. of dry methylene chloride or ethylene dichloride or syw.-tetrachloroethane, 2 5 g. of powdered anhydrous aluminium chloride and 1-2 g. of pure phthalic anhydride in a 50 ml. round-bottomed flask fitted with a short reflux condenser. Heat on a water bath for 30 minutes (or until no more hydrogen chloride fumes are evolved), and then cool in ice. Add 10 ml. of concentrated hydrochloric acid cautiously and shake the flask gently for 5 min utes. Filter oflf the solid at the pump and wash it with 10-15 ml. of cold water. Boil the resulting crude aroylbenzoic acid with 10 ml. of 2 -5N sodium carbonate solution and 0 2 g. of decolourising carbon for 5 minutes, and filter the hot solution. Cool, add about 10 g. of crushed ice and acidify... 

Direct Borohydride Reduction of Alcohols to Alkanes with Phosphonium Anhydride Activation N-Proovlbenzene. To a solution of 5.56 g (20 mmol) of triphenylphosphine oxide in 30mL of dry methylene chloride at CfC was added dropwise a solution of 1.57 mL (10 mmol) of triflic anhydride in 30mL of dry methylene chloride. After 15 min when the precipitate appeared, a solution of 1.36g (10 mmol) of 3-phenyl-1-propanol in 10 mL of dry methylene chloride was added and the precipitate vanished in 5 min. An amount of 1.5g (40 mmol) of sodium borohydride was added as a solid all at once and the slurry was stirred at room temperature for... 

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. 

The protecting groups are also used to solubilize synthetic intermediates in organic solvents, e.g. methylene chloride. Chromatography is then possible on a larger scale, since silica gel can be used as adsorbent. Six synthetic strategies have been developed (H. Kdster, 1979) ... 

Dichloromethane trichloromethane and tetra chloromethane are widely known by their common names methylene chloride chloroform and carbon tetrachloride respectively... 

Trialkylammonium salts, such as lidocaine hydrochloride, are titrated in an aqueous solution containing a surfactant. The presence of the surfactant increases the trialkylammonium salt s K , giving a titration curve with a more pronounced break. The effect of adding an immiscible organic solvent, such as methylene chloride or toluene, also is demonstrated. 

Volatile analytes can be separated from a nonvolatile matrix using any of the extraction techniques described in Ghapter 7. Fiquid-liquid extractions, in which analytes are extracted from an aqueous matrix into methylene chloride or other organic solvent, are commonly used. Solid-phase extractions also are used to remove unwanted matrix constituents. 

When an analyte is too concentrated, it is easy to overload the column, thereby seriously degrading the separation. In addition, the analyte may be present at a concentration level that exceeds the detector s linear response. Dissolving the sample in a volatile solvent, such as methylene chloride, makes its analysis feasible. 

In liquid-solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett s original work the stationary phase was finely divided CaCOa, but modern columns employ porous 3-10-)J,m particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is... 

For most samples liquid-solid chromatography does not offer any special advantages over liquid-liquid chromatography (LLC). One exception is for the analysis of isomers, where LLC excels. Figure 12.32 shows a typical LSC separation of two amphetamines on a silica column using an 80 20 mixture of methylene chloride and methanol containing 1% NH4OH as a mobile phase. Nonpolar stationary phases, such as charcoal-based absorbents, also may be used. 

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