In methylene

Properties. The DPXs are all crystalline soHds melting points and densities are given in Table 1. Their solubiUty in aromatic hydrocarbons is Limited. At 140°C, the solubiUty of DPXN in xylene is only about 10%. DPXC is more readily soluble in chlorinated solvents, eg, in methylene chloride at 25°C its solubihty is 10%. In contrast, the corresponding figure for DPXN is 1.5%. 

Decomposition of diphenoylperoxide [6109-04-2] (40) in the presence of a fluorescer such as perylene in methylene chloride at 24°C produces chemiluminescence matching the fluorescence spectmm of the fluorescer with perylene was reported to be 10 5% (135). The reaction follows pseudo-first-order kinetics with the observed rate constant increasing with fluorescer concentration according to = k [flr]. Thus the fluorescer acts as a catalyst for peroxide decomposition, with catalytic decomposition competing with spontaneous thermal decomposition. An electron-transfer mechanism has been proposed (135). 

Alkah manganate(VI) salts are used as oxidants in synthetic organic reactions (100) and their reactions have been observed to be similar to permanganate, except that manganate(VI) exhibits lower reactivity. Additionally, sohd BaVInO in methylene chloride has been reported to achieve high yields for the oxidation of diols to dialdehydes (101). 

Typical cosolvents include methanol [67-56-17, ethanol [64-17-5] isopropyl alcohol [67-65-OJ, or toluene. The selection of cosolvents depends on the requirement of the formula and their interaction with other ingredients. Methanol is a common cosolvent in methylene chloride formulas since it has good solvency and is needed to swell ceUulose-type thickening agents. A typical methylene chloride formula used to strip wood is as follows (7). 

Solubility and Solvent Resistance. The majority of polycarbonates are prepared in methylene chloride solution. Chloroform, i7j -l,2-dichloroethylene, yy -tetrachloroethane, and methylene chloride are the preferred solvents for polycarbonates. The polymer is soluble in chlorobenzene or o-dichlorobenzene when warm, but crystallization may occur at lower temperatures. Methylene chloride is most commonly used because of the high solubiUty of the polymer (350 g/L at 25°C), and because this solvent has low flammabiUty and toxicity. Nonhalogenated solvents include tetrahydrofuran, dioxane, pyridine, and cresols. Hydrocarbons (qv) and aUphatic alcohols, esters (see Esters, organic), or ketones (qv) do not dissolve polycarbonates. Acetone (qv) promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. 

Other, removable cation-stabilizing auxiliaries have been investigated for polyene cyclizations. For example, a sdyl-assisted carbocation cyclization has been used in an efficient total synthesis of lanosterol. The key step, treatment of (257) with methyl aluminum chloride in methylene chloride at —78° C, followed by acylation and chromatographic separation, affords (258) in 55% yield (two steps). When this cyclization was attempted on similar compounds that did not contain the C7P-silicon substituent, no tetracycHc products were observed. Steroid (258) is converted to lanosterol (77) in three additional chemical steps (225). 

There are a variety of reaction systems that allow the formation of cellulose trinitrate [9046-47-3]. HNO in methylene chloride, CH2CI2, yields a trinitrate with essentially no degradation of the cellulose chain (53). The HNO /acetic acid/acetic anhydride system is also used to obtain the trinitrate product with the fiber stmcture largely intact (51,52). Another polymer analogous reaction utilises a 1 1 mixture of HNO and H PO with 2.5% P2O5 to achieve an almost completely nitrated product (54). 

Pyrrole and alkylpyrroles can be acylated by heating with acid anhydrides at temperatures above 100 °C. Pyrrole itself gives a mixture of 2-acetyl- and 2,5-diacetyl-pyrrole on heating with acetic anhydride at 150-200 °C. iV-Acylpyrroles are obtained by reaction of the alkali-metal salts of pyrrole with an acyl halide. AC-Acetylimidazole efficiently acetylates pyrrole on nitrogen (65CI(L)1426). Pyrrole-2-carbaldehyde is acetylated on nitrogen in 80% yield by reaction with acetic anhydride in methylene chloride and in the presence of triethylamine and 4-dimethylaminopyridine (80CB2036). 

In the alternative approach.the 1,3-dipolar system can be constructed in several ways. Treatment of a-chloroacylhydrazones of diaryl ketones and certain aralkyl and dialkyl ketones (382) with NaH in anhydrous THF gives l-(disubstituted methylene)-3-oxo-l,2-diazetidinium inner salts (383). Reaction of (383) with DMAD in methylene chloride gave (384), a 2 1 adduct with loss of CO. Double bond migration in (384) occurred on heating to give (385). The intermediate in the cycloaddition was found to be (386), which on heating lost CO to form a new ylide system which in turn underwent reaction with more DMAD <81JA7743). 

JA173) illustrates this possibility (Scheme 34). Thus 3,3,5-trimethyl-3//-pyrazole (371 R = H) on irradiation in pentane solution gives 1,3,3-trimethylcyclopropene (372 R = H) the intermediate diazoalkene (373) has been characterized. The tetramethyl derivative (371 R" = Me) when irradiated at -50 °C in methylene chloride leads to a species believed to be a l,2-dlazablcyclo[2.1.0]pent-2-ene (374). This isomerization is thermally reversible, the 3H- pyrazole being regenerated at room temperature. 

BBr3, CH2CI2, -10°, 1 h -> 25°, 2 h, 80-100% yield. Benzyl carbamates of larger peptides can be cleaved by boron tribromide in trifluoro-acetic acid, since the peptides are more soluble in acid than in methylene chloride. ... 

The resulting product is purified by thin layer chromatography on silica gel in methylene dichloride yielding 8)S-di-5a-cholestane-3,6-dione (162) 13 mg, overall yield 26% mp 160-164°, which consists of 83% of dj-species. 

In contrast to the wide application that nitrosyi chloride has found in terpene chemistry, nitrosyi fluoride has only recently been discovered. Its first use in steroid chemistry was reported by Boswell who treated cholesterol acetate with nitrosyi fluoride at 0° in methylene dichloride and obtained the 5a-fluoro-6-nitrimine (31) already mentioned in section VI (page 461) in connection with the synthesis of 6,6-difluoro steroids. This... 

A solution of 17-cyanoandrosta-5,16-dien-3jS-ol acetate (46 g) and anhydrous potassium acetate (0.46 g) in methylene dichloride (310 ml) is treated with a mixture of 40% peracetic acid (37 ml) and anhydrous potassium acetate (1.84 g) in methylene dichloride (46 ml), the temperature of the solution being maintained below 25°. The mixture is stored at room temperature for 4 hr and then washed successively with water, 5% sodium bicarbonate solution (aqueous sodium bisulfite, 10g/150g water, has been used to decompose excess reagent before workup) and water until neutral. Evaporation of the dried solution and addition of ether gives 24.1 g of 5oc,6a-epoxy-17-cyanoandrost-16-en-3 -ol acetate mp 187-190°. One recrystallization from methanol gives 20.4 g of oxirane melting at 191-194°. 

Selective hydroxylation with osmium tetroxide (one equivalent in ether-pyridine at 0 ) converts (27) to a solid mixture of stereoisomeric diols (28a) which can be converted to the corresponding secondary monotoluene-sulfonate (28b) by treatment with /7-toluenesulfonyl chloride in methylene dichloride-pyridine and then by pinacol rearrangement in tetrahydrofuran-lithium perchlorate -calcium carbonate into the unconjugated cyclohepte-none (29) in 41-48 % over-all yield from (27). Mild acid-catalyzed hydrolysis of the ketal-ketone (29) removes the ketal more drastic conditions by heating at 100° in 2 hydrochloric acid for 24 hr gives the conjugated diketone (30). 

A-Homo-cholest-4a-en-3-one (16a) A total of 200 ml of a cold 0.232 M solution of diazomethane in methylene dichloride is added dropwise to a stirred solution of cholestenone (15a 5.6 g) in anhydrous methylene dichloride (25 ml) containing freshly prepared fiuoroboric acid catalyst. Nitrogen evolution begins immediately, and after 5 min the colorless solution turns cloudy due to precipitated polymethylene. After the addition is complete, the mixture is stirred for 1 hr and filtered. The filtrate is diluted with ether, washed with saturated sodium bicarbonate solution followed by... 

A stream of ozone is passed into a solution of 17j5-hydroxyestr-5(10)-ene-3-one acetate (123a, 4.2 g) in methylene dichloride (17 ml) and methanol (20 ml)... 

The synthesis of fluoroalkyl and chloroalkyl fluoromethyl ketones is achieved by oxidation of the corresponding alcohols by sodium dichromate and sulfunc acid in methylene chlonde in the presence of a phase transfer catalyst [49] (equation 45)... 

Table 5. Reactions of Iodine Chloride viith Fluorodienes in Methylene Chloride at -S C under Argon [ll ...

To reduce the danger of an explosion in this reaction, trifluoromethanesuifonyi azide can be generated in methylene chloride in situ and used for subsequent transformations without isolation [775]... 

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