Dichloromethane acidity

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... 

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 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... 

Peroxy acids usually in dichloromethane as the solvent are also reliable reagents for converting sulfides to sulfoxides... 

Oxidation of primary alcohols to aide hydes (Section 15 10) Pyridinium di chromate (PDC) or pyridinium chloro chromate (PCC) in anhydrous media such as dichloromethane oxidizes primary al cohols to aldehydes while avoiding over oxidation to carboxylic acids... 

Aldehydes are more easily oxidized than alcohols which is why special reagents such as PCC and PDC (Section 15 10) have been developed for oxidizing primary alco hols to aldehydes and no further PCC and PDC are effective because they are sources of Cr(VI) but are used m nonaqueous media (dichloromethane) By keeping water out of the reaction mixture the aldehyde is not converted to its hydrate which is the nec essary intermediate that leads to the carboxylic acid... 

Lipids differ from the other classes of naturally occurring biomolecules (carbohy drates proteins and nucleic acids) in that they are more soluble m nonpolar to weakly polar solvents (diethyl ether hexane dichloromethane) than they are m water They include a variety of structural types a collection of which is introduced m this chapter... 

In 1973 the Semiconductor Equipment and Materials Institute (SEMI) held its first standards meeting. SEMI standards are voluntary consensus specifications developed by the producers, users, and general interest groups in the semiconductor (qv) industry. Examples of electronic chemicals are glacial acetic acid [64-19-7] acetone [67-64-17, ammonium fluoride [12125-01 -8] and ammonium hydroxide [1336-21 -6] (see Ammonium compounds), dichloromethane [75-09-2] (see Cm.OROCARBONSANDcm.OROHYDROCARBONs), hydrofluoric acid [7664-39-3] (see Eluorine compounds, inorganic), 30% hydrogen peroxide (qv) [7722-84-1] methanol (qv) [67-56-1] nitric acid (qv) [7697-37-2] 2-propanoI [67-63-0] (see Propyl alcohols), sulfuric acid [7664-93-9] tetrachloroethane [127-18-4] toluene (qv) [108-88-3] and xylenes (qv) (see also Electronic materials). 

Elfamycins aie slightly acidic because of the 4-hychoxy-2-pyiidone oi the caiboxyhc acid moiety. They are soluble in most polar organic solvents and the alkah and ammonium salts ate water-soluble. The extractabihty of the free acids from aqueous solution into solvents such as dichloromethane and ethyl... 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

A. 2-f2-Bmmoetkyl)-l,3-diozane (1), A 2-L, three-necked flask Is equipped with a mechanical stirrer, thermometer, and gas Inlet tube. In the flask are placed 750 ml of dichloromethane, 112 g (2.00 moll of acrolein (Note 1), and 0.10 g of didnnamalacetone Indicator (Note 2) under nitrogen. The yellow solution is cooled to 0-5°C with an Ice bath. Gaseous hydrogen bromide (Note 3) is bubbled Into the solution with stirring until the Indicator becomes deep red (Note 4). The Ice bath is removed and 1.0 g of p-toluene-sulfonic acid monohydrate and 152.2 g (2.00 mol, 144 mL) of 1,3-propanediol (Note 11 are added. The yellow solution is stirred at room temperature for 8... 

The preparations are much simplified if a stoichiometric amount of hydrogen halide is added using an indicator to determine the end point. We have found that 1,9-diphenylnona-1,3,6,8-tetraen-5-one (dicinnamalacetone) is of appropriate basicity to detect excess anhydrous hydrogen halides in organic solvents including chloroform, dichloromethane, benzene, toluene, acetic acid, and acetone (but not in alcohols). The reaction between the... 

Amines can also be purified via their salts, e.g. hydrochlorides. A solution of the amine in dry toluene, diethyl ether, dichloromethane or chloroform is saturated with dry hydrogen chloride (generated by addition of concentrated sulfuric acid to dry sodium chloride, or to concentrated HCl followed by drying the gas through sulfuric acid, or from a hydrogen chloride cylinder) and the insoluble hydrochloride is filte off and dissolved in water. The solution is made alkaline and the amine is extracted, as above. Hydrochlorides can also be prepared by dissolving the amine in ethanolic HCl and adding diethyl ether or petroleum ether. Where... 

Of the alkyl esters, methyl esters are the most useful because of their rapid hydrolysis. The acid is refluxed with one or two equivalents of methanol in excess alcohol-free chloroform (or dichloromethane) containing about O.lg of p-toluenesulfonic acid (as catalyst), using a Dean-Stark apparatus. (The water formed by the... 

Molecular chlorine is believed to be the active electrophile in uncatalyzed chlorination of aromatic compounds. Simple second-order kinetics are observed in acetic acid. The reaction is much slower in nonpolar solvents such as dichloromethane and carbon tetrachloride. Chlorination in nonpolar solvents is catalyzed by added acid. The catalysis by acids is probably the result of assistance by proton transfer during the cleavage of the Cl-Cl bond. ... 

Dichloromethane — methanol — glacial acetic acid — water (50 + 50-1-25-1-10). 

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