Dimethyl solvents

CH3.O-CH2.CH2-O.CH2-CHj-O.CH3. Dimethyl ether of diethylene glycol. A colour-less liquid b.p. 160 C. Typical ether, useful as a high-temperature solvent. 

Dimeihylamine, C2H7N, (CH3)2NH. Colourless, inflammable liquid with an ammoniacal odour, mp -96" C, b.p. 7°C. Occurs naturally in herring brine. Prepared in the laboratory by treating nitrosodimetbyl-aniline with a hot solution of sodium hydroxide. Dimethylamine is largely used in the manufacture of other chemicals. These include the solvents dimethylacetamide and dimethyl-formamide, the rocket propellant unsym-metrical dimethylhydrazine, surface-active agents, herbicides, fungicides and rubber accelerators. 

HC0N(CH3)2, also possess exceptional solvent properties. The alkyl-glycols, dioxan and dimethyl-formamide should be used with caution, however, as their hot vapours are poisonous. 

Di-alkyl ethers of ethylene glycol, ROCHjCHjOR. The dimethyl ether, b.p. 85°/760 mm., is miscible with water, is a good solvent for organic compounds, and is an excellent inert reaction medium. The diethyl ether (diethyl cdloaolve), b.p. 121-57760 mm., is partially miscible with water (21 per cent, at 20°). 

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

An interesting case are the a,/i-unsaturated ketones, which form carbanions, in which the negative charge is delocalized in a 5-centre-6-electron system. Alkylation, however, only occurs at the central, most nucleophilic position. This regioselectivity has been utilized by Woodward (R.B. Woodward, 1957 B.F. Mundy, 1972) in the synthesis of 4-dialkylated steroids. This reaction has been carried out at high temperature in a protic solvent. Therefore it yields the product, which is formed from the most stable anion (thermodynamic control). In conjugated enones a proton adjacent to the carbonyl group, however, is removed much faster than a y-proton. If the same alkylation, therefore, is carried out in an aprotic solvent, which does not catalyze tautomerizations, and if the temperature is kept low, the steroid is mono- or dimethylated at C-2 in comparable yield (L. Nedelec, 1974). 

Dimethyl sulfoxide has the structure (CH3)2 —0 and is commonly referred to as DMSO It IS a relatively inexpensive solvent ob tamed as a byproduct in paper manufacture... 

Similarly sodium methoxide (NaOCHj) is a suitable base and is used m methyl alco hoi Potassium hydroxide m ethyl alcohol is another base-solvent combination often employed m the dehydrohalogenation of alkyl halides Potassium tert butoxide [K0C(CH3)3] is the preferred base when the alkyl halide is primary it is used m either tert butyl alcohol or dimethyl sulfoxide as solvent... 

Diglyme shown above the arrow in the equation is the solvent in this example Diglyme is an acronym for d/ethylene g/ycol dimethyl ether and its structure is CH3OCH2CH2OCH2CH2OCH3... 

When the reaction was earned out m aqueous methanol as the solvent hexyl bromide was converted to hexyl cyanide m 71% yield by heating with sodium cyanide Although this IS a perfectly acceptable synthetic reaction a peiiod of ovei 20 hours was lequued Changing the solvent to dimethyl sulfoxide brought about an increase m the reaction rate... 

Wittig reactions may be carried out m a number of different solvents normally tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) is used... 

Suitable strong bases include the sodium salt of dimethyl sulfoxide (m dimethyl sulfox ide as the solvent) and organohthmm reagents (m diethyl ether or tetrahydrofuran)... 

The reaction is of the 8 2 type and works best with primary and secondary alkyl halides Elimination is the only reaction observed with tertiary alkyl halides Aryl and vinyl halides do not react Dimethyl sulfoxide is the preferred solvent for this reaction but alcohols and water-alcohol mixtures have also been used... 

The nature of the solvent is as important as the polymer in determining , as is apparent from the wide range of values for poly (dimethyl siloxane) in different solvents. 

Poly(7-benzyl-L-glutamate) is known to possess a helical structure in certain solvents. As part of an investigationf of this molecule, a fractionated sample was examined in chloroform (CHCI3) and chloroform saturated ( 0.5%) with dimethyl formamide (DMF). The following results were obtained ... 

Other Propellants. Dimethyl ether (DME) [115-10-6] is finding use as an aerosol propeUant. DME is soluble in water, as shown in Table 5. Although this solubiHty reduces DME s vapor pressure in aqueous systems, the total aerosol solvent content may be lowered by using DME as a propeUant. The chief disadvantage is that DME is flammable and must be handled with caution. 

Institut Eransais du Pntrole dimethyl sulfoxide (DMSO) solvent contains up to 2% water to improve selectivity reflux con-sist of aromatics and paraffins ambient rotating-blade extractor, typically 10—12 stages low corrosion allows use of carbon steel equipment solvent has alow freezing point and is non-toxic two-stage ex-traction has dis-placement solvent in the second stage... 

Dimethylformamide [68-12-2] (DME) and dimethyl sulfoxide [67-68-5] (DMSO) are the most commonly used commercial organic solvents, although polymerizations ia y-butyrolactoae, ethyleae carboaate, and dimethyl acetamide [127-19-5] (DMAC) are reported ia the hterature. Examples of suitable inorganic salts are aqueous solutioas of ziac chloride and aqueous sodium thiocyanate solutions. The homogeneous solution polymerization of acrylonitrile foUows the conventional kinetic scheme developed for vinyl monomers (12) (see Polymers). 

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

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