Propylene acetoxylation

In the first step of the reaction, the acetoxylation of propylene is carried out in the gas phase, using soHd catalyst containing pahadium as the main catalyst at 160—180°C and 0.49—0.98 MPa (70—140 psi). Components from the reactor are separated into Hquid components and gas components. The Hquid components containing the product, ahyl acetate, are sent to the hydrolysis process. The gas components contain unreacted gases and CO2. After removal of CO2, the unreacted gases, are recycled to the reactor. In the second step, the hydrolysis, which is an equhibrium reaction of ahyl acetate, an acid catalyst is used. To simplify the process, a sohd acid catalyst such as ion-exchange resin is used, and the reaction is carried out at the fixed-bed Hquid phase. The reaction takes place under the mild condition of 60—80°C and ahyl alcohol is selectively produced in almost 100% yield. Acetic acid recovered from the... 

Allyl Acetate. Industrial production of aHyl acetate started only rather recendy. Nevertheless, among the aHyl compounds, its production is second to that of aHyl chloride. It is produced mostiy for manufacturing aHyl alcohol and its manufacture by acetoxylation of propylene has been described previously. The aHyl acetate obtained may be separated and purified by distillation. 

The production of 1,4-butanediol (1,4-BDO) from propylene via the carbonylation of allyl acetate is noted in Chapter 8. 1,4-Butanediol from maleic anhydride is discussed later in this chapter. An alternative route for the diol is through the acetoxylation of butadiene with acetic acid followed by hydrogenation and hydrolysis. 

Pd/Cu-zeolites are also catalysts for the oxidative acetoxylation of propylene to allylacetate [32-39]. The best results are obtained on a catalyst which is pretreated with an alkali solution to neutralize the acidic centres and containing Pd and Cu in an atomic ratio of 1.1 [37]. The alkali treatment suppresses the acid catalyzed addition of acetic acid to propylene, resulting in the formation of isopropyl acetate, which is observed over non-neutralized Na- and H-Y, as well as over unreduced and reduced Pd/Cu-NaY. Experiments with... 

The oxidation of 1-alkenes usually gives 2-acetoxy-l-alkenes.571,572 Oxidative acetoxylation of propylene with Pd(OAc)2 may yield allylic or vinylic acetates depending on reaction conditions573 (see Section 9.2.6). 

The in situ regeneration of Pd(II) from Pd(0) should not be counted as being an easy process, and the appropriate solvents, reaction conditions, and oxidants should be selected to carry out smooth catalytic reactions. In many cases, an efficient catalytic cycle is not easy to achieve, and stoichiometric reactions are tolerable only for the synthesis of rather expensive organic compounds in limited quantities. This is a serious limitation of synthetic applications of oxidation reactions involving Pd(II). However it should be pointed out that some Pd(II)-promoted reactions have been developed as commercial processes, in which supported Pd catalysts are used. For example, vinyl acetate, allyl acetate and 1,4-diacetoxy-2-butene are commercially produced by oxidative acetoxylation of ethylene, propylene and butadiene in gas or liquid phases using Pd supported on silica. It is likely that Pd(OAc)2 is generated on the surface of the catalyst by the oxidation of Pd with AcOH and 02, and reacts with alkenes. 

In the first step of the process (Fig. 1), the acetoxylation of propylene is carried out in the gas phase, using solid catalyst containing palladium as the main catalyst at 160 to 180°C and 70 to 140 psi (0.49 to 0.98 MPa). The reactor effluents from the reactor are separated into liquid components and gas components. The liquid components containing allyl acetate are sent to the hydrolysis process. The gas components contain unreacted gases and... 

When Pd compounds (PdfOAc) ", Pd2(OAc)i , or Pd3(OAc)e) are used as starting material, even small additions of water (1-3%) to the NaOAc/AcOH solvent give rise to a great deal of acetaldehyde instead of vinyl acetate [11-13]. In contrast to this, the Pd metal catalysts (e. g., supported Pd or Pd black, prepared by H2 reduction of Pd" complexes in combination with NaOAc) provide vinyl ester from alkene and AcOH with high selectivity, regardless of the water content up to 10% [11, 14, 15]. Further differences in the selectivity of reaction (1) with Pd" and Pd° catalysts were found for the oxidative acetoxylation of higher alkenes, viz., propylene, 1-hexene, and cyclohexene [7]. All these facts apparently implied that the alkene activation came from two different origins one from Pd" and another from Pd metal or, more exactly, low-valent Pd clusters formed upon Pd" reduction with H2. 

The outer-sphere OAc anions can be replaced by other anions. For instance, the and PF anions readily substitute for OAc anions in an aqueous solution containing KPFft, affording the giant cluster with the idealized formula [Pdsei LeoOeoKPFeleo [Ik 16, 17]. The Pd-561 clusters exhibit a high catalytic activity in alkene acetoxylation in an AcOH solution under mild conditions (20-60 °C at 0.1 MPa). Besides reaction (1), the clusters provide the oxidative acetoxylation of propylene to allyl acetate (eq. (6)) or of toluene to benzyl acetate (eq. (7)). 

These pioneering studies formed the basis for the development of commercial processes for the production of allyl acetate by oxidative acetoxylation of propylene (Eq. 1). Processes are operated by Showa Denko and Daicel in Japan and Hoechst and Bayer in Europe [2,11], The reaction is usually performed in the gas phase, e. g. at 140-170 °C over Pd(OAc)2/Cu(OAc)2/KOAc/Si02 or Pd/ KOAC/S1O2 catalysts and allyl acetate is formed with > 95 % selectivity. Allyl acetate is the raw material for the production of epichlorohydrin and glycerol. 

In his pioneering contributions Moiseev has shown that giant cationic palladium clusters , e.g. Pd56iL6o(OAc)i8o (L = phenanthroline, bipyridine), characterized by use of high-resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data, catalyze, under mild conditions (293 363 K, 1 bar), the oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate. The oxidation of primary aliphatic alcohols to esters, and the conversion of aldehydes into acetals were also studied. ... 

A gas-phase process has also been developed for the conversion of propene to allyl acetate. This process involves the reaction of propylene with HO Ac and O2 over heterogeneous Pd (Pd-Cu-K0Ac/Si02) at 100-300"C. The allyl acetate product is then hydrolyzed to afford allyl alcohol (Eqs. (8.2) and (8.3)) [11]. Pd-catalyzed acetoxylation of propylene affords propenyl and isopropenyl acetate as the major products [12]. Showa Denko K. K. had used this route to produce allyl alcohol since 1985 [13]. This process contributes significantly to allyl alcohol production ( 70 000 t/year) and has the potential to be the main route in the future [13]. 

There are also examples of gas-phase oxidation of allyl alcohol using Pd-Cu or Pd-Ag catalysts (Eq. (8.15)) [48]. The protocol was part of a multistep propylene-oxidation process, and the allyl alcohol starting material was produced from Pd-catalyzed acetoxylation of propylene followed by hydrolysis of allyl acetate (cf. Eqs. (8.2) and (8.3)) [48]. The presence of water improves the conversion of alcohol to acrylic products. 

The Showa Denko process is the oxidative acetoxylation of propylene as shown in eq. (20.57). The allylacetate produced is hydrolyzed to yield allylalcohol. The allylalcohol is used as a raw material for epichlorohydrin, glycerol and 1,4-buta-nediol. 

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