1,2-Propylene glycol formation

Table 1 kinetic model of propylene glycol formation. 

The primary and secondary alcohol functionahties have different reactivities, as exemplified by the slower reaction rate for secondary hydroxyls in the formation of esters from acids and alcohols (8). 1,2-Propylene glycol undergoes most of the typical alcohol reactions, such as reaction with a free acid, acyl hahde, or acid anhydride to form an ester reaction with alkaU metal hydroxide to form metal salts and reaction with aldehydes or ketones to form acetals and ketals (9,10). The most important commercial appHcation of propylene glycol is in the manufacture of polyesters by reaction with a dibasic or polybasic acid. 

Polyethers are also products of commercial importance. Ethers can be formed by thermal dehydration, as shown for the formation of dipropylene glycol from propylene glycol. CycHc ethers can form by elimination of water from di- or tripropylene glycol. 

By-products include propylene dibromide, bis-(bromopropyl) ether, propylene glycol, and propionic acid. Bromide losses are to the brominated organics and bromate formation. Current efficiency is a function of ceU design and losses to bromate. Energy consumption decreases with an increase in electrolyte concentration and a decrease in current density. Space—time yield increases with current density. See Table 5 for performance data (see... 

Vanillin, being an aldehyde, is able to form acetals and hemiacetals. Therefore, in flavor formulations using high concentrations of vanillin in conjunction with carriers such as propylene glycol, a glc analysis often shows a reduced vanillin peak after storage of the compounded flavor, and the presence of new peaks indicating acetal formation. Addition of about 0.5% of water to the formula reverses the reaction, ie, there is a reduction of acetal, and the reappearance of vanillin peaks. 

C. K. Deem, D. D. Schmidt, and R. A. Molner. Use of MMH (mixed metal hydroxide)/propylene glycol mud for minimization of formation damage in a horizontal well. In Proceedings Volume, number 91-29.4th CADE/CAODC Spring Drilling Conf (Calgary, Canada, 4/10-4/12) Proc, 1991. 

Wyman, J.F., B.H.Gray, L.H.Hill, J.Coleman, C.Flemming, and D.E.Uddin. 1985. Interspecies variability in propylene glycol dinitrate-induced methemoglobin formation. Toxicol. Appl. Pharmacol. 81 203-212. 

Toxieology. Propylene glycol dinitrate (PGDN) is a vasodilator, and at extremely high concentrations it causes methemoglobin formation. 

Moreover, flexible foams are characterized by utilization of special emulsifiers in their synthesis yielding an open-cell architecture, whereas for rigid foams emulsifiers are chosen that create more closed-cell structures. As diisocyanate for both types, the commercially available mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate is especially suitable. If foam formation is to take place at room temperature, and especially when hydroxy compounds with secondary hydroxy groups are used [poly(propylene glycol)s], the presence of a catalyst is generally required (see Sect. 4.2.1). 

Fig. 5. Plot of log(rates) vs. log(pressure) for rhodium-catalyzed CO hydrogenation. Reaction conditions 75 ml sulfolane, 3 mmol Rh, 1.25 mmol pyridine, H2/CO = 1, 240 C, 4 hr (96). Total rate includes rates to methanol, methyl formate, ethanol, ethylene glycol monoformate, and propylene glycol ( ) total ( ) methanol ( ) ethylene glycol. Open figures are for an experiment with H2/CO = 0.67.

The second thickening mechanism involves the use of a hydroxyl donor in addition to the polymer. The combination of a carboxyl donor and one or more hydroxyl donors will result in thickening because of the formation of hydrogen bonds. Some commonly used hydroxyl donors are polyols (such as glycerin, propylene glycol and PEG), sugar alcohols such as mannitol, nonionic surfactants with five... 

The appreciably lower micellar solubilities of oleic acid, oleyl alcohol, and propylene glycol monooleate are consistent with the view that the formation of a liquid crystalline aggregate—lamellar, cylindrical, or... 

Two parallel routes for the elimination of glycol formate are suggested, involving either reaction with H2 or with cocatalyst water. The detection of formic acid in the reaction products suggests another mechanism, with initial production of formic acid from H2 and C02, followed by reaction with the oxirane. This mechanism is not favored however since the yields of glycol formates varied substantially when various substituted oxiranes were reacted. This would not have been expected in a mechanism with formic acid as an intermediate. A third mechanism, not considered by the authors, could proceed through initial production of propylene carbonate, followed by reduction to the mono- or di-formate. 

Unsaturated sterols such as cholesterol, campesterol, sitosterol and bile alcohols with unsaturated side chains can be transfer hydrogenated efficiently and with high yields under microwave irradiation, using ammonium formate and a Pd/C catalyst in methylene chloride/propylene glycol solvents (Scheme 4.3)17. 

In a subsequent reaction with the solvent, PO produces small amounts of propylene glycol or glycol monoethers. The rate of formation of PO from propylene, H202, and TS-1 in methanol at 313 K is shown in Fig. 22. The selectivity to PO is 85%, but it can be improved by silanization of the catalyst, which reduces the hydrolytic activity, or by addition of small amounts of sodium acetate to the reaction mixture. With these modifications, at 97%... 

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