Dichloromethanes

Dichloromethane is a widely used industrial and academic laboratory solvent. New natural sources are recognized subsequent to the previous review, although the amounts are small compared to industrial emissions (Table 3.2). These include estimates of biomass combustion (256, 283, 286), oceanic sources (250, 253, 256, 275, 302), wetlands (275), and volcanoes (216, 217). Macroalgae (Desmarestia 

Methylene chloride is a clear, water-while liquid at ordinary temperatures, with a pleasant, ethereal odor. It is 

Flash Point (Tag open cup) none Azeotropic Water  

Specific Gravity of Vapor Specification for standard grade  

Heat of vaporiaation Kauri-butanol value Solubility in water Spaeifie gravity QZ0 C Spacifie heat Surface tanaion Q2S C Viecoaity C2S C Water aseotrope Q80-97 C Water content Weight par gallon 

Refractive index n2 Side chain chlorine Specific gravity 25/25 C Surface tenaion, DuNouy 25 C Vapor preaaure 130 C 

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Without going into details of the chromatographic method, a SAR separation (asphaltenes having been eliminated) can be performed in a mixed column of silica followed by alumina. The saturated hydrocarbons are eluted by heptane, the aromatics by a 2 1 volume mixture of heptane and toluene, and the resins by a 1 1 1 mixture of dichloromethane, toluene and methanol. 

Unfortunately, the number of mechanistic studies in this field stands in no proportion to its versatility" . Thermodynamic analysis revealed that the beneficial effect of Lewis-acids on the rate of the Diels-Alder reaction can be primarily ascribed to a reduction of the enthalpy of activation ( AAH = 30-50 kJ/mole) leaving the activation entropy essentially unchanged (TAAS = 0-10 kJ/mol)" . Solvent effects on Lewis-acid catalysed Diels-Alder reactions have received very little attention. A change in solvent affects mainly the coordination step rather than the actual Diels-Alder reaction. Donating solvents severely impede catalysis . This observation justifies the widespread use of inert solvents such as dichloromethane and chloroform for synthetic applications of Lewis-acid catalysed Diels-Alder reactions. 

In a Lewis-acid catalysed Diels-Alder reaction, the first step is coordination of the catalyst to a Lewis-basic site of the reactant. In a typical catalysed Diels-Alder reaction, the carbonyl oxygen of the dienophile coordinates to the Lewis acid. The most common solvents for these processes are inert apolar liquids such as dichloromethane or benzene. Protic solvents, and water in particular, are avoided because of their strong interactions wifti the catalyst and the reacting system. Interestingly, for other catalysed reactions such as hydroformylations the same solvents do not give problems. This paradox is a result of the difference in hardness of the reactants and the catalyst involved... 

Recently Desimoni et used the same bis(oxazoline) ligand in the magnesium(II) catalysed Diels-Alder reaction of the N-acyloxazolidinone depicted in Scheme 3.4. In dichloromethane a modest preference was observed for the formation of the S-enantiomer. Interestingly, upon addition of two equivalents of water, the R-enantiomer was obtained in excess. This remarkable observation was interpreted in terms of a change from tetrahedral to octahedral coordination upon the introduction of the strongly coordinating water molecules. 

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. 

DCM - Dichloromethane 100ml pour into the reaction flask with the DMSO. 

To a mixture of 100 ml of dry dichloromethane, 0.10 mol of propargyl alcohol and 0.11 mol of triethylamine was added a solution of 0.05 mol of Ph2PCl in 75 ml of dichloromethane in 3 min between -80 and -90°C. The cooling bath was removed, and when the temperature had reached 10°C, the reaction mixture was poured into a solution of 2.5 ml of 362 HCl in 100 ml of water. After vigorous shaking the lower layer was separated and the aqueous layer was extracted twice with 25-ml portions of dichloromethane. The combined solutions were washed twice with water, dried over magnesium sulfate and then concentrated in a water-pump vacuum, giving almost pure allenyl phosphine oxide as a white solid, m.p. 98-100 5, in almost 1002 yield. 

A mixture of 0.10 mol of the acetylenic alcohol, 0.12 mol of triethylamine and 200 ml of dichloromethane (note 1) was cooled to -50°C. Methanesulfinyl chloride (0.12 mol) (for its preparation from CH3SSCH3, (08300)30 and chlorine, see Ref. 73) was added in 10 min at -40 to -50°0. A white precipitate was formed immediately. After the addition the cooling bath was removed and the temperature was allowed to rise to -20°0, then the mixture was vigorously shaken or stirred with 100 ml of water. The lower layer was separated off and the aqueous layer was extracted twice with 10-ml portions of CH2CI2. The combined solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum (note 2). The yields of the products, which are pure enough (usually 96%) for further conversions, are normally almost quantitative. 

To a suspension of 2.0 mol of finely powdered 2-butyne-l,4-d1ol (note 1) in 600 ml of dry dichloromethane were added 50 g of anhydrous p-toluenesulfon1c acid (note 2). Isobutene (6 mol) was introduced with vigorous stirring. The flow was adjusted in such a way that only a small amount escaped from the solution (note 3). The reaction was slightly exothermic, so that no external cooling was applied. 

In each step of the usual C-to-N peptide synthesis the N-protecting group of the newly coupled amino acid must be selectively removed under conditions that leave all side-chain pro-teaing groups of the peptide intact. The most common protecting groups of side-chains (p. 229) are all stable towards 50% trifluoroacetic acid in dichloromethane, and this reagent is most commonly used for N -deprotection. Only /ert-butyl esters and carbamates ( = Boc) are solvolyzed in this mixture. 

The furo- and pyranobenzopyranones 114 and 115 are prepared by the reaction of 0-enolate of i(-keto lactone 113[132], The isoxazolc 117 is obtained by the oxidation of the oxime 116 of a, /3- or, d, 7-unsaturated ketones with PdCh and Na2C03 in dichloromethane[l 33], but the pyridine 118 is formed with PdCl2(Ph3P)2 and sodium phenoxide[134]. 

Fn some cases, r-allylpalladium complex formation by retention syn attack) has been observed. The reaction of the cyclic allyiic chloride 33 with Pd(0) affords the 7r-allylpalladium chlorides 34 and 35 by retention or inversion depending on the solvents and Pd species. For example, retention is observed in benzene, THF, or dichloromethane with Pd2(dba)3. However, the complex formation proceeds by inversion in these solvents with Pd(Ph3P)4, whereas in MeCN and DMSO it is always inversion[33]. The syn attack in this case may be due to coordination of Pd to chlorine in 33, because Pd is halophilic. The definite syn attack in complex formation has been observed using stereoche-mically biased substrates. The reaction of the cxoallylic diphenylphosphino-acetate 36 with phenylzinc proceeds smoothly to give 37. The reaction can be explained by complex formation by a syn mechanism[31]. However, these syn attacks are exceptional, and normally anti attack dominates. 

Carbon tetrachloride with four polar C—Cl bonds and a tetrahedral shape has no net dipole moment because the result of the four bond dipoles as shown m Figure 1 7 is zero Dichloromethane on the other hand has a dipole moment of 1 62 D The C—H bond dipoles reinforce the C—Cl bond dipoles... 

The gas phase chlorination of methane is a reaction of industrial importance and leads to a mixture of chloromethane (CH3CI) dichloromethane (CH2CI2) trichloromethane (CHCI3) and tetrachloromethane (CCI4) by sequential substitution of hydrogens... 

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

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

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

Methane reacts with CI2 to give chloromethane dichloromethane trichloromethane and tetrachloromethane... 

The products of these reactions are called vicinal dihalides Two substituents m this case the halogens are vicinal if they are attached to adjacent carbons The word is derived from the Latin vicinalis which means neighboring The halogen is either chlorine (CI2) or bromine (Br2) and addition takes place rapidly at room temperature and below m a variety of solvents mcludmg acetic acid carbon tetrachloride chloroform and dichloromethane... 

A commonly used peroxy acid is peroxyacetic acid (CH3CO2OH) Peroxyacetic acid is normally used m acetic acid as the solvent but epoxidation reactions tolerate a variety of solvents and are often earned out m dichloromethane or chloroform... 

PCC IS pyridinium chlorochromate PDC is pyridinium dichromate Both are used in dichloromethane ... 

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