Styrene from acetophenone

Phenylacetamides were prepared in the MBR from the corresponding styrene or acetophenone derivatives by Willgerodt reactions (Scheme 2.8) [44]. Yields were comparable with those obtained by others with conventional heating. At similar temperatures, the microwave-heated reactions were completed within minutes rather than hours. Optimization was readily accomplished through the capabilities of the MBR for rapid heating and cooling. The substantially shorter reaction times probably re-... 

The effluent from the acid treatment reactor is about 60% phenol, 35% acetone, plus some miscellaneous nits and lice, most of which, are alpha-methyl styrene, and acetophenone. The effluent is passed through a separator where the acid, water, and salts drop out. The balance of the processing is a series of distillation columns that split out the various streams. 

Selective oxidation of styrene to acetophenone by a Pd(II) catalyst in the presence of ionic liquids has been achieved (equation 27). Electronic effects on the site ofPd(II) oxidation of substituted styrenes are indicated in equation (28). Strong pi-donation from the phenyl substituent favors oxidation at the alkene carbon alpha to the aromatic ring. 

Derivation From acetophenone or styrene by Will-gerodt reaction, dehydration of ammonium phenyl acetate. 

Two commercially important by-products, which are generally isolated in a pure form from the preceding process are a-methyl styrene and acetophenone. Overall process yields are shown in Table 3.6. 

Fig. 19 RuNPs stabilized by a mixture of sulfonated diphosphine+Rame-p-cyclodextrin as selective catalyst for hydrogenation of styrene and acetophenone. (Reproduced frran [110] with permission from Wiley)...

Sales demand for acetophenone is largely satisfied through distikative by-product recovery from residues produced in the Hock process for phenol (qv) manufacture. Acetophenone is produced in the Hock process by decomposition of cumene hydroperoxide. A more selective synthesis of acetophenone, by cleavage of cumene hydroperoxide over a cupric catalyst, has been patented (341). Acetophenone can also be produced by oxidizing the methylphenylcarbinol intermediate which is formed in styrene (qv) production processes using ethylbenzene oxidation, such as the ARCO and Halcon process and older technologies (342,343). 

The coproduct 1-phenylethanol from the epoxidation reactor, along with acetophenone from the hydroperoxide reactor, is dehydrated to styrene in a vapor-phase reaction over a catalyst of siUca gel (184) or titanium dioxide (170,185) at 250—280°C and atmospheric pressure. This product is then distilled to recover purified styrene and to separate water and high boiling organics for disposal. Unreacted 1-phenylethanol is recycled to the dehydrator. 

Wacker oxidation of styrene has also been performed in [bmim][BF4] and [bmim][PF6], at 60 °C with H2O2 and PdCF as a catalyst [19]. This system gave yields of acetophenone as high as 92 % after 3 h. Hydrogen peroxide may also be used under phase transfer conditions for alkene bond cleavage, to produce adipic acid (an intermediate in the synthesis of nylon-6) from cyclohexene (Scheme 9.9). 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

By-products in the reactions in Table 3 are mainly cleavage products (carbonyls) An interesting by-product is found in the oxidation of styrene, as phenyl acetate is produced. It has been found that phenyl acetate is formed via oxidation of either styrene oxide or acetophenone. Nearly the same yield and stereochemical mixture of the epoxides, as in Table 3, can be obtained by oxidation with Ag202. It appears from Table 3 that the epoxidation of alkenes catalyzed by discrete silver complexes also takes place without maintaining the stereochemistry of the alkene, as in the silver-surface catalyzed reaction. 

In some cases, oxidation of double bonds does not stop at the epoxide, but proceeds further to oxidative cleavage of the double bond. It was reported that the reaction of a-methyl styrene with H2O2 in the presence of TS-1 or TS-2 produces a-methyl styrene epoxide (15%), a-methyl styrene diol (10-40%) and acetophenone (40-60%) (Reddy, J. S. et al., 1992). However, results similar to those obtained with titanium silicates were obtained for many other catalysts, such as HZSM-5, H-mordenite, HY, A1203, HGa-silicalite-2, and fumed Si02. These materials have much different properties and differ significantly from titanium silicates thus, the results cast some doubt on the role of the catalyst in this reaction. Furthermore, the oxidation of styrene is reported to proceed with C=C cleavage and formation of benzaldehyde, in contrast to previous reports of the formation of phenylacetaldehyde with 85% selectivity (Neri et al., 1986). 

Methyl 4-0-(4-methoxybenzyl)2,3-di-0-methyl-oc-D-glucopyranoside has been prepared [371] by Liptak s procedure (see Sect. 2.6). This lithium aluminium hydride — aluminium trichloride method was also used in the synthesis of 4-hydroxy-3-methoxy-benzyl [372], 4-hydroxy-3,5-dimethoxybenzyl [372], and 1-phenylethyl [373] ethers from the 4,6-acetals derived from vanillin, syringealdehyde, and acetophenone. Various vinylbenzyl ethers were prepared by the reaction of carbohydrates with vinylbenzyl chloride, and copolymerized with styrene [374]. 

The oxidation of styrenes under Wacker conditions is relatively slow and not always regioselective, but useful yields of acetophenones have been obtained, for example the highly substituted 27 from olefin 26 [40]. Acetophenones, on the other hand, have consistently been obtained in yields higher than 75 % by using a Pd-diketonate complex with t-BuOOH as oxidant in a biphasic C8F17Br/C6H6 me-... 

Heterogeneous systems have also been developed for the cleavage of olefins with hydrogen peroxide.174,175 Titanium-containing zeolites can be used to cleave olefins.176 Adam and co-workers have recently shown that acetophenone, an oxidation product from the Ti-zeolite catalysed oxidation of a-methyl-styrene, derives from 2-hydroxyperoxy-2-phenylpropan-l-ol as an intermediate (which they detected and isolated) (Figure 3.34).177... 

HydrogenadoB. The withdrawal stream from vacuum distillation is hydrogenated to remove the residual hydroperoxide and to convert the acetophenone. Fractionation removes the ethylbenzene and then the phenyl-1 ethanol from the hydrogenation effluent The separation of ethylbenzene must be carefiiUy effected to avoid subsequent superffactio-nation in the presence of styrene. 

---