Isopropylbenzene, synthesis

The most widely used industrial synthesis of phenol is based on isopropylbenzene (cumene) as the starting material and is shown m the third entry of Table 24 3 The eco nomically attractive features of this process are its use of cheap reagents (oxygen and sulfuric acid) and the fact that it yields two high volume industrial chemicals phenol and acetone The mechanism of this novel synthesis forms the basis of Problem 24 29 at the end of this chapter... 

Phenol was manufactured for many years by the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.S). Now, however, an alternative synthesis from isopropylbenzene, commonly called... 

Propene is used as a starting material for the synthesis of acetone, cumene (isopropylbenzene), and polypropylene (PP). 

There is some increase in selectivity with functionally substituted carbenes, but the selectivity is still not high enough to prevent formation of mixtures. Phenylchlorocarbene gives a relative reactivity ratio of 2.1 1 0.09 in insertion reactions with isopropylbenzene, ethylbenzene, and toluene.132 For cycloalkanes, tertiary positions are about 15 times more reactive than secondary positions toward phenylchlorocarbene.133 Carbethoxycarbene inserts at tertiary C—H bonds about three times as fast as at primary C—H bonds in simple alkanes.134 Because of low selectivity, intermolecular insertion reactions are seldom useful in synthesis. Intramolecular insertion reaction are of considerably more use. Intramolecular insertion reactions usually occur at the C—H bond that is closest to the carbene, and good yields can frequently be obtained. Intramolecular insertion reactions can provide routes to highly strained structures that would be difficult to obtain in other ways. 

The related manufacture of cumene (isopropylbenzene) through the alkylation of benzene with propylene is a further industrially important process, since cumene is used in the synthesis of phenol and acetone. Alkylation with propylene occurs more readily (at lower temperature) with catalysts (but also with hydrogen fluoride and acidic resins) similar to those used with ethylene, as well as with weaker acids, such as supported phosphoric acid (see further discussion in Section 5.5.3). 

The most widely used industrial synthesis of phenol is based on isopropylbenzene can you recall howto pre-... 

Unlike alkylation, acylation is controlled easily to give monosubstitution, because once an acyl group is attached to a benzene ring, it is not possible to introduce a second acyl group into the same ring. Because of this, a convenient synthesis of alkylbenzenes starts with acylation, followed by reduction of the carbonyl group with zinc and hydrochloric acid (Section 16-6). For example, propylbenzene is prepared best by this two-step route because, as we have noted, the direct alkylation of benzene with propyl chloride produces considerable amounts of isopropylbenzene and polysubstitution products ... 

An increasingly important process for the synthesis of phenol starts with cumene, isopropylbenzene. Cumene is converted by air oxidation into cumene hydroperoxide, which is converted by aqueous acid into phenol and acetone. 

For many years, phenol was manufactured b the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.9). Now, however, an alternative synthesis from isopropylbenzene (cumene) is used. Cumene reacts with air at high temperature by a radical mechanism to form cumene hydroperoxide, which is converted into phenol and acetone by treatment with acid. This is a particularly efficient process because two valuable chemicals are prepared at the same time. 

Autoxidation is one of the key steps in the industrial synthesis of phenol and acetone from benzene and propylene. In the second step of this synthesis, cumene (isopropylbenzene) is autoxidized to give cumyl hydroperoxide. 

SAMPLE SOLUTION (a) The last step in the synthesis of o-isopropylaniline, the reduction of the corresponding nitro compound by catalytic hydrogenation, is given as one of the three preceding examples. The necessary nitroarene is obtained by fractional distillation of the ortho-para mixture formed during nitration of isopropylbenzene. 

Synthesis of biaryl compounds is not the only use for oxidative dimerization it can lead to formation of new carbon-carbon bonds also in the aliphatic series. These reactions have been carried out with peroxides, especially diacetyl peroxide, for example, the formation of 2,3-dichlorosuccinic acid from chloro-acetic acid and of 2,3-dimethyl-2,3-diphenylbutane from isopropylbenzene 291 and hydrogen peroxide292 and a mixture of ammonium persulfate and sodium... 

The key stage is the alkylation of cumene. From its reaction in the liquid phase at 300°C in the presence of a silica/alumina catalyst with 3 moles of propene the 1,4-isomer required for hydroquinone is separated by fractionation (ref.30) and the mixture of 1,2- and 1,3-di-isopropylbenzenes together with the tri-isopropyl isomer equilibrated with benzene at 270°C with the same catalyst to enrich the proportion of the 1,3-compound required for the synthesis of resorcinol. The sequence of steps for hydroquinone is shown. By-product 4-isopropylphenol is mostly reoxidised and recycled giving a total yield of 71% based on di-isopropylbenzene (ref.31). 

Synthesis of alkylaromatics. Alkylaromatics are widely used for production of styrene (ethylbenzene), phenol (isopropylbenzene), and long chain alkylated benzene for detergent intermediates. 

As an example, let us consider the problem of synthesizing propylbenzene. If we attempt this synthesis through a Friedel-Crafts alkylation, a rearrangement occurs and the major product is isopropylbenzene (see also Practice Problem 15.4) ... 

Synthesis of Cumene (Isopropylbenzene) from Diisopropylbenzenes in the presence of Benzene using Triflic acid as catalyst at room temperature... 

Acetone ((CH3)2C=0), the simplest ketone, is also produced on a large scale— about 4 billion pounds annually. The most common methods for its commercial synthesis are the oxidation of propene (analogous to eq. 9.2), the oxidation of isopropyl alcohol (eq. 7.35, R = R = CHj), and the oxidation of isopropylbenzene (eq. 9.3). 

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