Propylene oxide isomerization

Propylene oxide isomerized over silica-magnesia and other oxides to give propionaldehyde and acetone on acidic and basic sites, respectively, and allyl alcohol on acid-base bifunctional catalysts. Methylvinyl ketone was formed selectively in the reaction of acetone and methanol with oxygen over silica-magnesia. Tanabe and co-workers have studied the alkylation of phenol... 

FIGURE 6.6 Comparison between the calculated [52] and experimental [50,51] rate constants of propylene oxide isomerizations. 

Ethylene oxide and propylene oxide isomerization Metal ortho phosphates... 

Fig. 3.85 Propylene oxide isomerization conversion ox. basicity of catalyst.

Polyester resins can also be rapidly formed by the reaction of propylene oxide (5) with phthaUc and maleic anhydride. The reaction is initiated with a small fraction of glycol initiator containing a basic catalyst such as lithium carbonate. Molecular weight development is controlled by the concentration of initiator, and the highly exothermic reaction proceeds without the evolution of any condensate water. Although this technique provides many process benefits, the low extent of maleate isomerization achieved during the rapid formation of the polymer limits the reactivity and ultimate performance of these resins. 

The temperature of esterification has a significant influence on isomerization rate, which does not proceed above 50% at reaction temperatures below 150°C. In resins produced rapidly by using propylene oxide and mixed phthaUc and maleic anhydrides at 150°C, the polyester polymers, which can be formed almost exclusively in the maleate conformation, show low cross-linking reaction rates with styrene. 

At present, neither of these two processes are being used industriahy. Another process is isomerization of propylene oxide [75-56-9]. 

Isomerization and Hydrogenolysis. lsomeri2ation of propylene oxide to propionaldehyde and acetone occurs over a variety of catalysts, eg, pumice, siUca gel, sodium or potassium alum, and 2eohtes (80,81). Stronger acid catalysts favor acetone over propionaldehyde (81). AHyl alcohol yields of 90% are obtained from use of a supported lithium phosphate catalyst (82). 

Allyl alcohol is produced by the catalytic isomerization of propylene oxide at approximately 280°C. The reaction is catalyzed with lithium phosphate. A selectivity around 98% could be obtained at a propylene oxide conversion around 25% ... 

Excluding polymerizations with anionic coordination initiators, the polymer molecular weights are low for anionic polymerizations of propylene oxide (<6000) [Clinton and Matlock, 1986 Boileau, 1989 Gagnon, 1986 Ishii and Sakai, 1969 Sepulchre et al., 1979]. Polymerization is severely limited by chain transfer to monomer. This involves proton abstraction from the methyl group attached to the epoxide ring followed by rapid ring cleavage to form the allyl alkoxide anion VII, which isomerizes partially to the enolate anion VIII. Species VII and VIII reinitiate polymerization of propylene oxide as evidenced... 

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

When the commodity chemical propylene oxide is heated to high temperature in the gas phase in a shock tube, unimolecular rearrangement reactions occur that generate the CsHgO isomers allyl alcohol, methyl vinyl edier, propanal, and acetone (Figure 15.9). Dubnikova and Lifshitz carried out a series of calculations to determine the mechanistic pathway(s) for each isomerization, with comparison of activation parameters to those determined from Arrhenius fits to experimental rate data to validate the theoretical protocol. 

Figure 15.9 Isomerizations of propylene oxide. What plausible geometries might be proposed as starting guesses for TS structures Once a TS structure is found, will it be obvious for which process it is the TS What features of the TS may have an impact on the level of theory used to determine its energy ...

In an older version of the synthesis, propylene and chlorine react in an aqueous solution to form propylene chlorohydrin.192-194 The slightly exothermic reaction maintains the 30-40°C reaction temperature to yield isomeric propylene chlorohy-drins (l-chloro-2-propanol/2-chloro-1-propanol = 9 1). The main byproduct is 1,2-dichloropropane formed in amounts up to 10%. The product propylene chlorohydrin then undergoes saponification to propylene oxide with calcium hydroxide or sodium hydroxide. 

The detection of 1,2-propylene oxide in the products from methyl ethyl ketone combustion is particularly interesting. It parallels the formation of ethylene oxide in acetone combustion (8) and of 1,2-butylene oxide in the combustion of diethyl ketone. Thus, there is apparently a group of isomerization reactions in which carbon monoxide is ejected from the transition state with subsequent closing of the C—C bond. Examination of scale molecular models shows that reactions of this type are, at any rate, plausible geometrically. 

A recent oommtiruo tion by Gritter and Wallace discloses initiation of a study of the free-radical chemistry of epoxides Under the influence of U t-butoxy radicals, formed by thermal decomposition of di-lerf-butyl peroxide, propylene oxide is believed to yield an epoxy radical as shown in Eq. (3). The latter undergoes Isomerization to CHsCOCH - and further reaction with unreaoted propylene oxide or other available substrates, such as 1-octene, toluene, oyolohexene, and ethanol,fl7a as shown in Eq. (3). 

Propylene oxide was found to react at each of its terminals, yielding a mixture of isomeric chlorohydrina on methanolyais of the boron containing adducts/ On the other hand, epichlorohydrin gave otilv 1,3-diohloro-2-propanol on similar treatment, indicating exclusive attack on the terminal epoxide carbon atom (Eq, 060). 

Attention may now be directed to the reactions of aromatic thiols with epoxides. Mu tz,IH for example, haa investigated the course of addition of thiophenol to propylene oxide, both in alkaline and in acidic solutions. Significantly lower yields obtained in acid tended to confirm the premise that thiophenoxide ion rather than undissociated thiophenol is the attacking nucleophile. Likewise predictable was the isolation of two isomeric phenylthioprcpanois under add conditions, hut of only one in base (Eq. 663). 

There are four processes for industrial production of allyl alcohol. One is alkaline hydrolysis of allyl chloride. A second process has two steps. The first step is oxidation of propylene to acrolein and the second step is reduction of acrolein to allyl alcohol by a hydrogen transfer reaction, using isopropyl alcohol. At present, neither of these two processes is being used industrially. Another process is isomerization of propylene oxide. Until 1984. all allyl alcohol manufacturers were using this process. Since 1985 Showa Denko K.K. has produced allyl alcohol industrially by a new process which they developed- This process, which was developed partly for the purpose of producing epichlorohydrin via allyl alcohol as the intermediate, has the potential to be the main process for production of allyl alcohol. The reaction scheme is as follows ... 

In hydrocarbons a variety of by-products was formed. Propylene oxide gave some j8-hydroxyisobutyraldehyde as well as the normal product, also acetone, isobutyraldehyde, methacrolein, n-butyraldehyde, isobutanol, crotonaldehyde, and n-butanol. Presumably these by-products were formed by dehydration and hydrogenation of the hydroxyaldehydes, except for acetone which was formed by isomerization. The side reactions can be kept to a minimum by operating below 95° C (160). Fewer by-products appear to be formed using alcohols as solvents. Using methanol, Eisenmann (24) noted that carbon monoxide had an inhibitory effect at high pressures. 

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