Propylene oxidation, mechanism

Scheme 3. Selective propylene oxidation mechanism (17. From (2/).

The biodegradation of poly(alkylene glycols) is hindered by their lack of water solubiUty, and only the low oligomers of poly(propylene glycol) are biodegradable with any certainty (179—181), as are those of poly(tetramethylene glycol) (182). A similar xo-oxidation mechanism to that reported for poly(ethylene glycol) has been proposed. 

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) nonionic surfactants. 

With strong nucleophiles such as methoxide, ring opening follows an Sn2 mechanism. Examine the next to lowest-unoccupied molecular orbital (LUMO+1) for propylene oxide. On which carbon is it most heavily concentrated Is this also the least crowded carbon (Examine a spacefilling model for propylene oxide.) What should be the product of Sn2 addition ... 

In a reactor provided with a mechanical stirrer, a reflux refrigerant and a thermometer, there is introduced 393 grams 1-[2-phenyl, 2-methoxy] ethyl piperazine and 22 grams 3-phenyl-3-methoxy propylene oxide in 750 ml of absolute ethanol. 

The objective of this study is to investigate the mechanism of propylene oxidation by a transient infrared spectroscopic technique over Rh/Al203. This technique allows simultaneous measurement of the dynamics of adsorbed species by in situ infrared spectroscopy and the product formation profile by mass spectrometry. 

Preparation of propylene oxide. The mechanism suggested involves a hy-pobromination at the anode ... 

The BHP is then used to oxidize propylene to the oxide. This reaction is ionic and its mechanism follows. The yield of propylene oxide from propylene is 90%. 

Table 10.3 summarizes the uses of propylene oxide. Propylene glycol is made by hydrolysis of propylene oxide. The student should develop the mechanism for this reaction, which is similar to the ethylene oxide to ethylene glycol conversion (Chapter 9, Section 8). Propylene glycol is a monomer in the manufacture of unsaturated polyester resins, which are used for boat and automobile bodies, bowling balls, and playground equipment. 

The polymerization of optically pure propylene oxide by FeCl3 -derived initiators yields an optically active polymer. E. J. Vandenberg [J. Polym. Sci., A-l(7), 525 (1969)] attempted to gain insight into the mechanism by polymerizing the 2,3-epoxybutanes. The optically active trans-2,3-epoxybutane was polymerized to an optically inactive crystalline polymer. Evaluate this result and discuss its implications on the propagation mechanism for propylene oxide polymerization. 

Although no direct evidence was available, Ben-Taarit et al. advanced a tentative mechanism for propylene oxidation [2]. As only heterogeneous or mixed oxides catalyze the formation of acrolein, the behavior of Cu+ y zeolite is similar to the heterogeneous case. On the contrary, on Rh +Y, acetone was selectively produced [2]. This is now in line with the behavior of Rh salts in... 

At lower temperatures the Mars-van Krevelen mechanism no longer applies. Sancier et al. (440) studied propylene oxidation in the presence of 1802 over bismuth molybdate and found that the acrolein product contained 180 and not exclusively leO from the oxide lattice in contrast with results obtained by Keulks and co-workers (441, 442) at higher temperatures. This lower-temperature oxidation must involve adsorbed oxygen in some form but the nature is not clear. It is now accepted that not all these oxidation reactions do involve lattice oxygen (442,443). 

Polyethers are prepared by the ring opening polymerization of three, four, five, seven, and higher member cyclic ethers. Polyalkylene oxides from ethylene or propylene oxide and from epichlorohydrin are the most common commercial materials. They seem to be the most reactive alkylene oxides and can be polymerized by cationic, anionic, and coordinated nucleophilic mechanisms. For example, ethylene oxide is polymerized by an alkaline catalyst to generate a living polymer in Figure 1.1. Upon addition of a second alkylene oxide monomer, it is possible to produce a block copolymer (Fig. 1.2). 

Phenyl Cellosolve and Ucon Fluid 50-HB-260, and greater than additive toxicity with propylene oxide. The mechanism for such interactions is not known. 

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