Ethylbenzene from acetophenone

For the replacement of oxygen by hydrogen in ketones and aldehydes the method of Kishner and Wolff is used as often as is that of Clemmensen. In the former method the hydrazone or semicarbazone of the carbonyl compound is heated for several hours—preferably in the presence of hydrazine hydrate—in a sealed tube or autoclave with sodium ethoxide at about 160°. The explanation of the reaction is that, under the catalytic influence of the ethoxide, the hydrazone is transformed into a diimine which then decomposes in the same way as does phenyldiimine (p. 286)  

The reverse process, conversion of CH2 into CO succeeds in the case of ketones with selenium dioxide. Thus acetone may be directly oxidised to methylglyoxal. This oxidising agent has been used very frequently recently because of the great variety of ways in which it can be applied. 

Carry out the ozonisation in a thin-walled gas wash-bottle (capacity 400 c.c.) with an inlet tube widened out to a bell shaped opening or twisted to a spiral. Connect the bottle to the ozoniser by bending the inlet tube of the former at a right angle so that it can be inserted into the delivery tube of the ozoniser, which is fitted with a mercury seal. 

Dissolve 16 g. of cyclohexene in 200 c.c. of pure, dry ethyl acetate,2 cool the solution in the bottle with an efficient ice-salt mixture to - 20° (or, better, with solid carbon dioxide in acetone to - 50° to - 70°) and then connect to the ozoniser. 

During the ozonisation keep the freezing mixture in an insulated jar (see p. 2) in order to maintain the best possible cooling effect. If an ozoniser with at least five discharge tubes is used a very vigorous current of ozonised oxygen can be employed and the operation completed in from four to seven hours. For example, if twenty litres 

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The reaction is illustrated by the preparation of ethylbenzene from acetophenone the resulting hydrocarbon is quite pure and free from unsaturated compounds ... 

An alternative milder procedure is the reduction of the corresponding toluene-p-sulphonylhydrazones with catecholborane, followed by decomposition of the intermediate with sodium acetate in the presence of dimethyl sulphoxide, or with tetrabutylammonium acetate.1 These methods, which do not have the disadvantages of the Clemmensen reduction, are illustrated by the preparation of ethylbenzene from acetophenone (Expt 6.4, Methods A and B). Outline mechanisms for these reactions are given below. 

Therefore, we could synthesize ethylbenzene from acetophenone as follows ... 

Kinetics of oxidation of toluene and cumene to the corresponding a-hydroxy compounds by stoich. trani-[Ru(0)(bpy)(tpy)] VCH3CN were reported a two-electron hydride-ion transfer step may be involved [672]. Electro-oxidation of side-chains in alkylaromatics by [Ru(0)(bpy)(tpy)] (generated electrochemicaUy in situ from [Ru(OH)(bpy)(tpy)] V BuOH/water pH 6.8/Pt electrodes/50°C) was effected toluene gave benzoic acid and ethylbenzene gave acetophenone (Table 4.1) [673]. 

Problem 12.1 How might you prepare ethylbenzene from (a) benzene and ethyl alcohol (b) acetophenone, C6H5COCH3 (c) styrene, C5H5CH=CH2 ... 

We turned our attention next to the autoxidation of ethylbenzene (EB) to the corresponding hydroperoxide (EBHP) which constitutes the first step in the SMPO (styrene monomer propene oxide) process for the co-production of styrene and propene oxide from ethylbenzene and propene (Scheme 7). The overall selectivity to propene oxide obviously depends on the selectivity to EBHP in the first step, which is believed to be 80-85% in the commercial process. This is lower than for cumene as a result of secondary (in the case of EB) versus tertiary (in the case of cumene) C-H bond oxidation. The main byproduct in the autoxidation of ethylbenzene is acetophenone (16). From an economic viewpoint die production of acetophenone should be kept as low as possible. 

In problem (a)/ ethylbenzene is synthesized from acetophenone by a process called the Clemmensen reduction, which reduces the ketone to its corresponding hydrocarbon. The carbonyl is reduced to a hydrocarbon by the action of amalgamated zinc (Zn(Hg)] and concentrated hydrochloric acid. The general equation for the reaction is ... 

When chloroform was used as the solvent, significantly lower conversions were observed compared to using the substrate as the solvent. This is due to the higher temperatures used under solvent-free conditions, which results in increased activation of the allq lperoxo chromium intermediate at these temperatures and faster transfer of the o)ygen atom. Thus, the conversion of toluene to benzaldehyde increased from 19 to 98% in the absence of chloroform. Similarly, the conversion of ethylbenzene to acetophenone increased from 25 to 98%. The selectivities under either set of conditions were similar for the oxidation of toluene. However, when ethylbenzene was used as the solvent in its oxidation, the selectivity to acetophenone increased from 67 to 89%, showing the beneficial effect of the higher boiling point solvent. 

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). 

Ru(acac)(bpy)3](PFg) is made from RuCl Cbpy), acetylacetone and (NH )PFg. It is dark brown IR and electronic spectra, TGA and cyclic voltammetry were measured. As [Ru(acac)(bpy)2]" /TBHP/CH3Cl2 it oxidised primary alcohols to aldehydes, secondary alcohols to ketones, di-tert-butylcatechol to the o-benzoqui-none and alkanes to ketones, e. g. ethylbenzene was converted to acetophenone and fluorene to fluorenone [787],... 

Method A. Huang-Minlon modification of the Wolff-Kishner reduction. Place 36.0 g (0.3 mol) of redistilled acetophenone, b.p. 201 °C, 300 ml of diethylene glycol, 30ml of 90 per cent hydrazine hydrate (CAUTION) and 40g of potassium hydroxide pellets in a 500-ml two-necked round-bottomed flask fitted with a reflux condenser insert a thermometer supported in a screw-capped adapter in the side-neck so that the bulb dips into the reaction mixture. Warm the mixture on a boiling water bath until most of the potassium hydroxide has dissolved and then heat under reflux for 1 hour either by means of a free flame or by using a heating mantle. Remove the reflux condenser and fit a still-head and condenser for downward distillation. Distil until the temperature of the liquid rises to 175 °C (1). Separate the upper hydrocarbon layer from the distillate and extract the aqueous layer twice with 20 ml portions of ether. Dry the combined upper layer and ethereal extracts with magnesium sulphate, remove the ether on a water bath and distil the residue. Collect ethylbenzene at 135-136 °C the yield is 20 g (62.5%). 

The electro-Fenton method (or EFR) was initially used for synthetic purposes considering the hydroxylation of aromatics in the cathodic compartment of a divided cell. Thus, the production of phenol from benzene (Tomat and Vecchi 1971 Tzedakis et al. 1989), (methyl)benzaldehydes and (methyl)benzyl alcohols from toluene or polymethylbenzenes (Tomat and Rigo 1976,1979,1984,1985) by adding Fe3+ to generate Fe2+ via reaction (19.13), as well as benzaldehyde and cresol isomers from toluene or acetophenone and ethylphenol isomers from ethylbenzene (Matsue et al. 1981) with direct addition of Fe2+, have been described. Further studies have reported the polyhydroxylation of salicylic acid (Oturan et al. 1992)... 

In the circumstances where activated ring systems are used as substrates, nuclear bromination is sometimes a problem. Two substrates worth mentioning which are mildly activated and have been used in the photolytic hydrogen peroxide/hydrogen bromide system are ethylbenzene and 4-t-butyltoluene. The ethylbenzene has been oxidized to acetophenone in 57% yield and 61% selectivity, the remainder being the intermediate product 1-bromoethylbenzene. The preparation of 4-t-butylbenzaldehyde from the toluene affords a yield of 58% (Figure 3.77). 

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. 

The fungus Mortierella isabellina (NRRL 17S7) hydroxylates the ethylbenzenes (92) to the 1-arylelha-nols (93 equation 32) with a degree of enantioselectivity as shown in Table 9. By-products resulting from teiminal carbon hydroxylation and overoxidation (acetophenones) are also obtained. 

The most commonly studied unimolecular initiator for NMRP has been (see Scheme 8.2) I. This initiator was first synthesized by Priddy et al. by abstracting an H-atom from ethylbenzene in the presence of TEMPO [3]. They then studied I as a model of the chain-end in polystyrene made in the presence of TEMPO. They found that I decomposes upon heating under anaerobic conditions to form products resulting from both radical coupling and disproportionation (Scheme 8.2). Georges et al. also studied the thermolysis of I but instead of the formation of diphenylbutane as the minor product, they observed acetophenone [4], Acetophenone is likely formed because of the presence of dissolved oxygen during their experiment. 

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