Dimethyl ether and propane

Aerosols containing dimethyl ether and propane (DMEP) for freezing warts and verrucas are available over the counter. They are licensed not as medicines but as medical devices. 

Sommerville, M.L., Johnson, C.S., Cain, J.B., Rypacek, F. and Hickey, A.J. (2002) Lecithin microemulsions in dimethyl ether and propane for the generation of pharmaceutical aerosols containing polar solutes. Pharm. Dev. Tech., 7, 273-288. 

In fact, the boiling point of dimethyl ether is almost as low as the boiling point of propane. Both dimethyl ether and propane lack the ability to form hydrogen bonds. The slightly higher boiling point of dimethyl ether can be explained by considering the net dipole moment. 

The rate constants for the reactions between OH and a range of ethers and hydroxy ethers have been reported at 298 K233 as well as those for reactions between dimethyl ether and methyl f-butyl ether over the range 295-750 K.234 Data from the former study show deviations from simple structure-activity relationships which were postulated to arise due to H-bonding in the reaction transition states.233 The atmospheric lifetime of methyl ethyl ether has been determined to be approximately 2 days.235 Theoretical studies on the H-abstraction from propan-2-ol (a model for deoxyribose) by OH have been reported using ab initio methods (MP2/6-31G ).236 The temperature dependence (233-272 K) of the rate coefficients for the reaction of OH with methyl, ethyl, n-propyl, n-butyl, and f-butyl formate has been measured and structure-activity... 

Bobbo, S.,Fedele, L., Camporese, R., Stryjek, R. (2000c) Isothermal vapor-liquid equilibrium for the three binary systems 1,1,1,2,3,3-hexafluoropropane with dimethyl ether or propane, and 1,1,1,3,3,3-hexafluoropropane with dimethyl ether. Fluid Phase Equilibria 174, 3-12. 

As expected, the height of the potential energy barrier decreases with increasing bond length, but otherwise equal structure. This is seen with comparison of ethane with methyl silane and disilane (Table 4-3). The potential barrier increases with increasing steric hindrance, as can be seen in the series ethane-propane-isobutane-neopentane, methanol-dimethyl ether, and acetaldehyde-propylene-isobutylene. 

Horstmann, S. Birke, G. Fischer, K. Vapor-hquid equilibrium and excess enthalpy data for the binary systems propane + dimethyl ether and propene + dimethyl ether at temperatures from (298 to 323) K J. Chem. Eng. Data 2004,49,38-42... 

Entries 11 and 13 in Table 3.4 present data relating the efiect of methyl substitution on methanol and methylamine. The data show an increased response to methyl substitution. While the propane barrier is 3.4 kcal/mol (compared to 2.88 in ethane), the dimethylamine barrier is 3.6kcal/mol (compared to 1.98 in methylamine) and in dimethyl ether it is 2.7 kcal/mol (compared to 1.07 in methanol). Thus, while methyl-hydrogen eclipsing raised the propane barrier by 0.5 kcal/mol, the increase for both dimethylamine and dimethyl ether is 1.6 kcal/mol. This increase in the barrier is attributed to greater van der Waals repulsions resulting from the shorter C—N and C—O bonds, relative to the C—C bond. 

Thermodynamic information can also be obtained from simulations. Currently we are measuring the differences in chemical potential of various small molecules in dimethylimidazolium chloride. This involves gradually transforming one molecule into another and is a computationally intensive process. One preliminary result is that the difference in chemical potential of propane and dimethyl ether is about 17.5 kj/mol. These molecules are similar in size, but differ in their polarity. Not surprisingly, the polar ether is stabilized relative to the non-polar propane in the presence of the ionic liquid. One can also investigate the local arrangement of the ions around the solute and the contribution of different parts of the interaction to the energy. Thus, while both molecules have a favorable Lennard-Jones interaction with the cation, the main electrostatic interaction is that between the chloride ion and the ether molecule. 

Early studies in this field [35, 36] indicated that a high surface-to-volume ratio, which represents a hurdle for gas-phase combustion, is instead an advantage for catalytic combustion. In fact the small scale enhances considerably the rate of gas-solid mass transfer, which favors the kinetics of the combustion process and compensates for the short residence time. Also, as is well established for large-scale systems, the presence of a catalytic phase allows for stable combustion at significantly lower temperature than traditional homogeneous burners [55, 56]. This makes the design and operation of microcombustors more fiexible. Several recent studies have explored the potential of catalytic microcombustors using H2 [37, 38, 50], methane [37], propane [52,53,57] and mixtures of H2 with propane [57], butane [38,47,52] and dimethyl ether [52]. 

Commonly used solvents inclnde liqnid carbon dioxide, propane, bntane, light oil, triethy-lamine, acetone, methanol, hexane, dimethyl ether, cmde oil, benzene, isopropyl ether, toluene, tricresyl phosphate, methyl isobutyl ketone, methyl chloride, and bntyl acetate. In addition to remediation uses, solvent extraction has been applied in a variety of indnstries, including food processing, pharmaceuticals, fine chemicals, and mining and minerals processing. 

Problem 13.4 Explain why (a) propanol boils at a higher temperature than the corresponding hydrocarbon b) propanol, unlike propane or butane, is soluble in H O (c) n-hexanol is not soluble in H O (dimethyl ether (CH,OCH,) and ethyl alcohol (CH,CH,OH) have the same molecular weight, yet dimethyl ether has a lower boiling point (-24°C) than ethyl alcohol (78°C). M... 

General procedure for deprotection of mono- and polymethyl-aryl ethers with boron tribromide.41 To a 10-ml flask fitted with a septum and magnetic stirrer bar are added reactant (3.6 mmol) and 5 ml of dichloromethane. An inert atmosphere is established and maintained. This mixture is cooled in a dry ice/propan-2-ol bath and boron tribromide [0.13 ml, 1.32 mmol (for monomethyl ethers), or 0.38 ml, 4 mmol (for dimethyl ethers)] is added through the septum by use of a syringe. The cold bath is removed and the mixture stirred for 30 minutes, poured into ice water, stirred for 30 minutes, saturated with salt and extracted with dichloromethane. The extract is dried and concentrated. The purity of the product is established by h.p.l.c. analysis on a Waters Associates 6000A model using both refractive index and u.v. absorbance detectors with a Waters 3.9mm i.d. x 30cm p-Bondapack Ci8 reverse phase column. 

At first the calculations were performed on eleven simple molecules ethane, propane, isobutane, neopenthane, ethene, 2-butene, methanol, dimethyl ether, dimethoxymethane, trimethoxymethane, and tetramethoxymethane. The correlation between calculated and experimental principal values is shown in Figure 1. The correlation coefficient is R2 = 0.97 and the root mean square deviation of the calculated from the experimental values is 13 ppm. 

In some cases, strange approximations were applied in order to circumvent the problems connected with large systems. The interaction energy of the antibiotic tetranactin with an ammonium ion was calculated by replacing the tetranactin by four formaldehyde and four water molecules 158). In an improved study the tetranactin was approximated by using formic acid, ethane, propane and methanol molecules 159>. In an other study [18] crown-6 was simulated by three dimethyl ether molecules 160). 

Because we often deal with liquid alcohols, we forget how surprising it should be that the lower-molecular-weight alcohols are liquids. For example, ethyl alcohol and propane have similar molecular weights, yet their boiling points differ by about 120 °C. Dimethyl ether has an intermediate boiling point. 

Demyanov PI, Gschwind RM (2006) Formation of hydrogen bonds in complexes between dimethylcuprate(I) anion and methane, propane, or dimethyl ether. A theoretical study. Organometallics 25 5709-5723... 

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