Propylene oxide kinetics

A very different picture of propylene oxidation kinetics over a copper oxide catalyst was presented by Billingsley and Holland 102) who, on the basis of a differential reactor study at 240°, concluded that the reaction was limited by mass transfer of the oxygen, and proposed the following rate equations ... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Carbon dioxide is one of the most abundant carbon resources on earth. It reacts with an epoxide to give either a cyclic carbonate or a polycarbonate depending on the substrates and reaction conditions. Kinetic resolution of racemic propylene oxide is reported in the formation of both cyclic carbonate and polycarbonate. The fe ei value defined as ln[l-(conversion)(l+%ee)]/ln[l-(conversion)(l% ee)] reached 6.4 or 5.6 by using a Co(OTs)-salen complex with tetrabutylammonium chloride under neat propylene oxide or using a combination of a Co-salen complex and a chiral DMAP derivative in dichloromethane, respectively. 

Kinetic resolution of propylene oxide in its alternating copolymerization with CO2 is performed using similar Co-salen complexes. Reaction conditions,... 

Polavatapu, et al. (128) have identified a VCD band near 12(X) cm in phenylcaibinols that correlates with configuration. Wieser and co-workers (129, 130) have recently reported FTIR-VCD spectra of chiral methyloxetan molecules. In the area of theoretical calculations, Lx>we, Stephens, and Segal (131, 132) have implemented the theory of Stephens (118) in calculations on trans-1,2,-dideuteriocyclopropane, tron5-l,2-dideuteriocyclobutane, and propylene oxide. For the latter two molecules, favorable agreement with experiment was found. The first application of VCD to kinetic analysis has also been reported for (1/ , 2R)-dideuteriocyclobutane thermolysis (133). 

Based on the landmark studies of Jacobsen and coworkers, who employed chiral (salen)CoX complexes for the asymmetric ring opening and kinetic resolution of aliphatic epoxides [18-20], Lu and coworkers synthesized highly isotactic copolymer from rac-propylene oxide and carbon dioxide (Scheme 5) [21]. 

Scheme 5 Kinetic resolution of rac-propylene oxide during its copol3anerization with CO2 in the presence of a chiral (salen)CoX complex...

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

Synopsis of Dubnikova and Lifshitz (2000) Isomerization of Propylene Oxide. Quantum Chemical Calculations and Kinetic Modeling . 

The diethylzinc-alcohol (1 2) system was also extensively studied by Tsuruta and his co workers (85,86). Amorphous zinc dialkoxide was concluded to be an active species, because crystalline zinc alkoxide prepared from zinc chloride and lithium alkoxide proved to have only a very small catalytic activity. Based on kinetic studies of the polymerization of propylene oxide with the ZnEt2-CH3OH (1 2) catalyst system, the catalytically active species was concluded to be the complex formed by coordination of one molecule of monomer to the catalyst. In the polymerization of propylene oxide with the catalyst system, it was concluded that the monomer was polymerized by ring opening brought about by cleaving the CH2-0 bond (87). 

Carbocation-oxonium ion equilibria are obvious complicating factors in studies of the kinetics of initiation of polymerisation and useful thermodynamic data for such equilibria involving Ph3C+ and a variety of linear and cyclic ethers have been reported by Slomkowski and Penczek (132). A dramatic increase in rates of initiation of polymerisation of THF induced by Ph3C+ salts is observed on addition of small amounts of epoxides such as propylene oxide (113a,b), which compete favourably with THF in the primary carbocation-oxonium ion equilibria and simplify the initiation reaction ... 

The first example of kinetic resolution catalyzed by an organometallic compound was the partially enantiomer-selective polymerization of racemic propylene oxide induced with a diethylzinc optically active alcohol system (50). 

In the presence of chiral polymerization catalysts, enantiomeric monomers are consumed at different rates (Scheme 75). Enantiomer-selective polymerization of racemic propylene oxide catalyzed by a diethylzinc-(-f)-bomeol system is a classical example of such kinetic resolution H 176). The polymeric product has an [a]D of +7.4°. The mechanism... 

Several simple alkyl-substituted ethylene oxides undergo addition of hydrogen halide to give the corresponding balohydrins. Wiilt attention, for example, has been accorded to propylene oxide, particularly in connexion with kinetic studies.148 1Mi-1490... 

THF copolymerizes readily with other cyclic ethers such as oxides and oxetanes. The comonomers used include ethylene oxide (67), propylene oxide (99,100), epichlorohydrin (ECH) (101,102), phenyl glycidyl ether (102), 3.3-bis(chloromethyl) oxetane (BCMO) (25, 98, 101, 103) and 3-methyl-3-chloromethyl oxetane (103). Just as in THF homo-polymerization, a large variety of catalysts have veen used. In many cases the kinetics of copolymerization have been studied. Table 22 summarizes the monomer reactivity ratios, rx (THF), and r2 (comonomer) which have... 

Polyetherols are formed by reaction of hydroxymethyl derivatives of uric acid and ethylene oxide or propylene oxide. A kinetic study of the simple model reaction134... 

Figure 7.11 presents the mechanism of propylene oxide synthesis by allyl alcohol isomerization. This assumption correlates well with experimental data the kinetic curve shape... 

Describing the reaction in kinetic terms, let us apply to the fact that the intermediate perFTPhPFe3+00H/Al203 formation stage (7.7) is fast, the epoxide formation stage (7.8) is slow and, consequently, limiting. For kinetic simulation of propylene oxidation to epoxide, this gives an opportunity to apply the Michaelis-Menten equation in Linuver-Berk coordinates ... 

Volta, J. C, Desquesnes, W., Moraweck, B., and Coudurier, G., A new method to obtain supported oriented oxides M0O3 graphite catalysts in propylene oxidation to acrolein, React. Kinet. Catal. Lett. 12, 241 (1979). 

---