A-Methylstyrene oxide

The hydrolysis of various para-substituted a-methylstyrene oxides was studied using 10 EHs [184]. The hydrolysis of the isobutyl compound with the enzyme from A. niger WHS the key step in the synthesis of (S)-ibuprofen (Figure 6.65). The (R)-diol was recycled via chemical racemization. 

Epoxidation reactions carried using UHP as the source of hydrogen peroxide require that the anhydride and other reactions conditions are chosen carefully. For particularly nucleophilic alkenes our best procedure uses acetic anhydride and disodium hydrogen phosphate at room temperature. In this way we were able to obtain a-methylstyrene oxide in a 75% yield and the epoxide from a-pinene in 79% yield as shown in equation (13). 

Finally, a chemoenzymatic enantioconvergent procedure led to (S)-ibuprofen in four steps and 47% overall yield (Fig. 11.2-20). The latter compound is a widely used antiinflammatory drug and pain remedy and is one of the top ten drugs sold worldwide l,HH. In the key step, the conditions for the enantioconvergent hydrolysis of para-iso-butyl-a-methylstyrene oxide was optimized (elevated substrate concentration at +4 °C) to afford the non-reacted epoxide in >95 % ee[136l After separation from the epoxide, the formed diol (70% ee) was recycled via a two-step sequence via the corresponding bromohydrin, which was cyclized back to give ( )-epoxide. The latter material was subjected to repeated biocatalytic resolution in order to improve the economy of the process. 

To 1 mL THF solution containing 1 mg IrCl3-xH20 (3.35 x 10 mmol) was added 45 mg (R)-a-methylstyrene oxide (0.335 mmol). The reaction mixture was stirred at 50 C and monitored by GC. After about 2 h, the reaction completed, and the solvent was removed to afford 100% racemic a-methylphenylacetaldehyde. 

Johnson and Katekar have found that when one of the sulphur substituents in a sulphoximine was an alkyl group, treatment with a strong base such as sodium hydride would remove a proton alpha to sulphur to form a sulphoximine ylide. Thus, phenyl methyl sulphoxide with tosyl azide formed the sulphoximine (109). Treatment with sodium hydride apparently formed the ylide (110), as evidenced by its reaction with acetophenone to form a-methylstyrene oxide in 68% yield. By a similar... 

Catalyst Oxidant Temp PC Norbonylene oxide a-Methylstyrene oxide... 

The reaction is remarkably clean for some alkenes, notably cyclooctene, which is transformed to the epoxide with no side products. Other alkenes, however, give a plethora of products, many containing nitrogen, together with some epoxide. Reactive olefins sometimes undergo rapid reactions but no epoxides are isolated. For example a-methylstyrene is cleaved quantitatively to acetophenone. This is also the fate of a-methylstyrene oxide when that substance is exposed to the NO/O2 mixture. The cleavage of the styrene epoxide does not make the substance an... 

One year later, the same authors studied the biohydrolysis of seven differently substituted a-methylstyrene oxide derivatives, including the para-bromo-a-methyl styrene oxide, using ten different EHs [14]. The best results were obtained with the... 

The yield of acetone from the cumene/phenol process is beUeved to average 94%. By-products include significant amounts of a-methylstyrene [98-83-9] and acetophenone [98-86-2] as well as small amounts of hydroxyacetone [116-09-6] and mesityl oxide [141-79-7]. By-product yields vary with the producer. The a-methylstyrene may be hydrogenated to cumene for recycle or recovered for monomer use. Yields of phenol and acetone decline by 3.5—5.5% when the a-methylstyrene is not recycled (21). 

The most widely used process for the production of phenol is the cumene process developed and Hcensed in the United States by AHiedSignal (formerly AHied Chemical Corp.). Benzene is alkylated with propylene to produce cumene (isopropylbenzene), which is oxidized by air over a catalyst to produce cumene hydroperoxide (CHP). With acid catalysis, CHP undergoes controUed decomposition to produce phenol and acetone a-methylstyrene and acetophenone are the by-products (12) (see Cumene Phenol). Other commercial processes for making phenol include the Raschig process, using chlorobenzene as the starting material, and the toluene process, via a benzoic acid intermediate. In the United States, 35-40% of the phenol produced is used for phenoHc resins. 

Gumylphenol. -Cumylphenol (PGP) or 4-(1-methyl-l-phenylethyl)phenol is produced by the alkylation of phenol with a-methylstyrene under acid catalysis. a-Methylstyrene is a by-product from the production of phenol via the cumene oxidation process. The principal by-products from the production of 4-cumylphenol result from the dimerization and intramolecular alkylation of a-methylstyrene to yield substituted indanes. 4-Cumylphenol [599-64-4] is purified by either fractional distillation or crystallization from a suitable solvent. Purification by crystallization results in the easy separation of the substituted indanes from the product and yields a soHd material which is packaged in plastic or paper bags (20 kg net weight). Purification of 4-cumylphenol by fractional distillation yields a product which is almost totally free of any dicumylphenol. The molten product resulting from purification by distillation can be flaked to yield a soHd form however, the soHd form of 4-cumylphenol sinters severely over time. PGP is best stored and transported as a molten material. 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

The acetone supply is strongly influenced by the production of phenol, and so the small difference between total demand and the acetone suppHed by the cumene oxidation process is made up from other sources. The largest use for acetone is in solvents although increasing amounts ate used to make bisphenol A [80-05-7] and methyl methacrylate [80-62-6]. a-Methylstyrene [98-83-9] is produced in controlled quantities from the cleavage of cumene hydroperoxide, or it can be made directly by the dehydrogenation of cumene. About 2% of the cumene produced in 1987 went to a-methylstyrene manufacture for use in poly (a-methylstyrene) and as an ingredient that imparts heat-resistant quaUties to polystyrene plastics. 

Irradiation of DAAN in benzene gives 3AN. This carbene reacts with oxygen very rapidly to give an intermediate believed to be the carbonyl oxide. The triplet carbene reacts with labeled a-methylstyrene to give the cyclopropane with total loss of stereochemistry (Table 6). Direct irradiation in neat isopropyl alcohol gives the ether in low yield (relative to the yields from XA, DMFL, FL, and BFL). The other products are those expected to result from hydrogen-atom abstraction. Triplet-sensitized irradiation of DAAN in the alcohol does not give a detectable amount of the ether. 

The epoxide and aldehyde were identified and quantified by capillary GLC equipped with a Chiraldex G-TA column using 4-bromochloroben-zene as the internal standard (oven temp 110 °C, carrier gas He, flow rate 60-65mL min-1, split ratio 100 1, detector FID at 250 °C, (IS, 2S)-(E)- -methylstyrene oxide Rt = 6.98min (1R, 2R)-( )-(3-methylstyrene oxide Rt = 7.81 min.) The enantiopurity of the //L2R-epoxide = 70% ee, Yield = 90 % (>99 % trans). 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

The efficiency of this new concept has been demonstrated (15) by the facile synthesis, in 90 % yield in 2 hours at 50°C, of he multiblock poly(a methylstyrene-b-ethylene oxide)-- (Mn ca. 70.000), starting from Br CH2)gO cH2-CH2-oJn(CH2)5-Br in water and... 

Methylenebis(oxy) ]bis(2-chloroformaldehyde), see Bis (2-chloroethoxy) methane Methylene chlorobromide, see Bromochloromethane Methylene dichloride, see Methylene chloride Methylene dimethyl ether, see Methylal Methyl 2,2-divinyl ketone, see Mesityl oxide Methylene glycol, see Formaldehyde Methylene glycol dimethyl ether, see Methylal Methylene oxide, see Formaldehyde Methyl ethanoate, see Methyl acetate (1 -Methylethenyl)benzene, see a-Methylstyrene Methyl ethoxol, see Methyl cellosolve 1-Methylethylamine, see Isopropylamine (l-Methylethyl)benzene, see Isopropylbenzene Methylethyl carbinol, see sec-Bntyl alcohol Methyl ethylene oxide, see Propylene oxide ds-Methylethyl ethylene, see cis-2-Pentene frans-Methylethyl ethylene, see frans-2-Pentene Methyl ethyl ketone, see 2-Bntanone Methylethylmethane, see Butane... 

---