Dimethyl ether, vapor pressure

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. 

On July 28,1948, a rail car containing liquefied dimethyl ether ruptured and released its entire contents. The rupture was due to the generation of excessive pressures created by long solar exposure following initial overfilling. The gas was ignited after 10 to 25 seconds. The ensuing vapor cloud explosion caused the death of 207 people and injured 3818. 

Example Based on intermolecular forces, predict which will have the higher vapor pressure and higher boiling point, water or dimethyl ether, CH3-O-CH3. 

Answer Dimethyl ether will have the higher vapor pressure and the lower boiling point. 

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

A continuous-flow reactor with a fixed catalyst bed was employed at pressurized conditions. Gaseous dimethyl ether was supplied to the reactor at its vapor pressure with carbon monoxide while liquid reactants such as methyl acetate, methyl iodide, and water were fed with microfeeders. Methyl acetate used in this experiment was dehydrated by Molecular Sieve 5A before use. A part of the reaction mixture was sampled with a heated syringe and was analyzed by gas chromatography. 

Solvatochromic Approach Solvatochromic relationships are multivariate correlations between a property, usually solubility or partitioning property (see Sections 11.4 and 13.3), and solvatochromic parameters, parameters that account for the solutes interaction with the solvent. In the case of vapor pressure, the solvatochromic parameters only have to account for intermolecular interaction such as selfassociation between the solute (i.e., pure compound) molecules themselves. The following model has been reported for liquid and solid compounds, including hydrocarbons, halogenated hydrocarbons, alkanols, dialkyl ethers, and compounds such as dimethyl formamide, dimethylacetamide, pyridine, and dimethyl sulfoxide... 

FIGURE 10.1.1.1.1 Logarithm of vapor pressure versus reciprocal temperature for dimethyl ether. 

Kennedy, R.M., Sagenkahn, M., Aston, J.G. (1941) The heat capacity and entropy, heats of fusion and vaporization, and the vapor pressure of dimethyl ether. The density of gaseous dimethyl ether. J. Am. Chem. Soc. 64, 2267-2272. 

The methylphosphine prepared by this procedure has a vapor pressure at —78.5° (Dry Ice slush) of 29 mm. The principal impurity is dimethyl ether, estimated by mass spectrometry and infrared spectrometry to amount to less than 1%. 

The catalytic dehydration of methanol (ME) to form dimethyl ether (DME) and water was earried out over an ion exehange eatalyst [K. Klusacek, Collection Czech. Chem. Commun.,49, 170(1984)]. The packed bed was initially filled with nitrogen and at r = 0 a feed of pure methanol vapor entered the reactor at 413 K, 100 kPa, and 0.2 cmVs. The following partial pressures were recorded at the exit to the differentialreaetor containing 1.0 g of catalyst in 4.5 cm of reactor volume. 

Dimethyl ether may be used as an aerosol propellant for topical aerosol formulations in combination with hydrocarbons and other propellants. Generally, it cannot be used alone as a propellant owing to its high vapor pressure. Dimethyl ether is a good solvent and has the unique property of high water solubility, compared to other propellants. It has frequently been used with aqueous aerosols. A coarse, wet, spray is formed when dimethyl ether is used as a propellant. 

Dimethyl ether is a liquefied gas and exists as a liquid at room temperature when contained under its own vapor pressure, or as a gas when exposed to room temperature and pressure. 

Chemical and Physical Properties Trichlorfon is an organophosphate compound, which has an empirical formula of C4HgCl304P and a molecular weight of 257.44. It is a racemic mixture of two isomers. Trichlorfon is a pale clear, white or yellow crystalline powder, melting point 75-84°C, boiling point 100°C, vapor pressure 7.8mmHg at 20°C, and is stable at normal temperatures and pressure. At higher temperatures and pH less than 5.5, trichlorfon decomposes to form dichlorvos (0,0-dimethyl-0-(2,2-dichlorovinyl) phosphate, DDVP). It is readily soluble in chloroform and methylene chloride, and less soluble in water, benzene, and diethyl ether. 

Physical Properties. Tabun is a colorless compound, which is said to have a somewhat fmity odor. The odor changes with decomposition so that with lesser amounts of decomposition the odor of cyanide (like bitter almonds) is apparent, whereas with greater amounts the odor of dimethyl-amine (like fish) is apparent. Tabun s vapor pressure is the lowest of all the G agents (approximately 0.04 mm Hg at 20°C). This suggests that tabun could be a relatively persistent threat at lower temperatures. Tabun has a vapor density of 5.6 relative to air and a liquid density of 1.08 g/mL (25°C). Its mp is —50°C, and its bp is approximately 240°C. It is three times as water soluble (approximately 10% at 20°C) as is VX, and also soluble in typical organic solvents (e.g., ethanol, diethyl ether, and chloroform). As with other nerve agents, dissolution in inert solvents (e.g., diethyl ether) enhances tabun s stability. 

Properties Wh. cryst. solid odorless very sol. in alcohol, water, ether, dimethyl sulfoxide sol. in acetone, ethyl acetate mod. sol. in chloroform si. sol. in benzene m.w. 71.08 sp.gr. 1.12 (30 C) vapor pressure 0.007 mm Hg m.p. 83-86 C b.p. 87 C Toxicology TLV-TWA 0.03 mg/m (skin) LD50 (oral, rat) 124 mg/kg poisonous material harmful if inhaled, absorbed thru skin, or ingested suspected human carcinogen possible reproductive hazard mutagen TSCA listed... 

Properties Wli. cryst. solid unpleasant sweet taste discolors to pink in light and air very sol. in alcohol, ether, glycerol, CCI acetic acid, pyridine, amyl alcohol, liq. ammonia sol. in water, acetone, dimethyl sulfoxide, oxygenated soivs. si. sol. in chloroform, benzene m.w. 110.12 dens. 1.285 (15 C) vapor pressure 1 mm (108.4 C) m.p. HOC b.p. 280.5 C flash pt. (CC) 127 C... 

Properties Colorless clear liq. fumes in air and gradually turns yel. ammonia-like fishy odor sol. in DMSO, 95% ethanol, acetone misc. with dimethyl formamide, hydrocarbons, petrol, ether, ether dec. in water evolves heat on contact with water m.w. 60.10 sp.gr. 0.791 (22/4 C) vapor pressure 157 mm Hg (25 C) m.p. -58 C b.p. 63 C flash pt. 1 C ref. index 1.4075 (20 C) strongly alkaline surf. tens. 28 dynes/cm... 

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