Butylbenzene

A solution of 156 g. (2.0 moles) of benzene and 37 g. (0.5 mole) of n-butyl alcohol is stirred and cooled in a cold water bath while boron trifluoride is passed in until 34 g. (0.5 mole) has been absorbed. (Hood.) Phosphorus pentoxide (17.7 g., 0.125 mole) is added quickly, and the mixture is wanned slowly with stirring to reflux temperature. The solution becomes turbid and separates into two layers, after which stirring is stopped heating, however, is continued for 3 hours. The upper layer is separated, washed with dilute aqueous alkali, and fractionally distilled to give 50 g. (75%) of sec-butylbenzene. This compound boils at 170-172°/744 mm. 

A suspension of 66.5 g. (0.5 mole) of aluminum chloride in 390 g. (5.0 moles) of benzene is stirred rapidly and held at 20-30° while 74 grams (1.0 mole) of ferf-butyl alcohol is added dropwise. The mixture is allowed to stand overnight and then is poured into a mixture of crushed ice and hydrochloric acid. The benzene layer is separated, and the aqueous portion is extracted with ether. The combined ether and benzene solutions are evaporated, and the residue is fractionally distilled through a 30-cm. column, giving a 65-70% yield of iert-butylbenzene boiling at 168-170°/740 mm. 

Submitted by R. R. Read, L. S. Foster, Alfred Russell, and V. L. Simjul. Checked by C. F. H. Allen and James Van Allan. 

three-necked, round-bottomed flask (Notes 1 and 2) is fitted with an efficient reflux condenser (Note 3) protected by a drying tube, a dropping funnel, and a thermometer which extends well into the reaction mixture (Note 4) the flask is arranged so that it can be cooled externally (Note 5). In the flask is placed 161 g. (7 gram atoms) of sodium cut into shavings 1-2 mm. in thickness (Notes 6 and 7) the sodium is just covered with dry ether (about 300 ml.) (Note 8). A mixture of 411 g. (321 ml., 3 moles) of w-butyl bromide and 471 g. (315 ml., 3 moles) of bromobenzene (Note 9) is added slowly from the dropping funnel over a period of about 2.5 hours, the temperature being kept as near 20° as possible the mass acquires a bluish color. 

After the flask and contents have been allowed to stand at room temperature for 2 days with occasional shaking, the liquid is decanted (Note 10). Three hundred milliliters of methanol is then added carefully, and the mixture is refluxed on a steam bath 

The size of the pieces of sodium, the control of temperature, and the use of an electrically heated, jacketed fractionating column are important factors in the successful preparation of the compound. 

A copper flask and copper condenser reduce the hazard from breakage but are not essential and are less convenient with the quantities indicated. 

PROPERTIES RESEARCH GRADE PURE GRADE TECHNICAL GRADE 

Normal Butylbeniene is sometimes stablized with tertiary-butylcatechol (T8C) which can be removed by distillation. 

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The fact that n-butylbenzene can be prepared in reasonable yield by the action of sodium upon a mixture of bromohenzene and n-butyl bromide can be partly explained on the assumption that n-butyl bromide reacts with phenyl-sodium more rapidly than does bromobenzene. It is interesting to note that n-butylbenzene can be prepared either from benzylsodium and n-propyl bromide or from phenylsodium and n-butyl bromide (Section VI,29). 

The n-butylbenzene contains some unsaturated hydrocarbons these can be removed by repeated shaking with small quantities of concentrated sulphuric acid (see Section III,7,No[Pg.512]

The formation of alkylbenzenes, largely free from unaaturated compounds, provides another interesting application of organosodium compounds. Thus pure M-butylbenzene is readily obtained in good yield from benzyl sodium and n-propyl bromide. Benzyl-sodium is conveniently prepared by first forming phenyl-sodium by reaction between sodium and chlorobenzene in a toluene medium, followed by heating the toluene suspension of the phenyl-sodium at 105° for about 35 minutes ... 

Ethylbenzene. Prepare a suspension of phenyl-sodium from 23 g. of sodium wire, 200 ml. of light petroleum (b.p. 40-60°) and 56 3 g. (50 9 ml.) of chlorobenzene as described above for p-Toluic acid. Add 43 -5 g. (30 ml.) of ethyl bromide during 30-45 minutes at 30° and stir the mixture for a further hour. Add water slowly to decompose the excess of sodium and work up the product as detailed for n-Butylbenzene. The yield of ethylbenzene, b.p. 135-136°, is 23 g. 

Ratio toluene- /-f-butylbenzene. The partial rate factors are based on the relative rates for toluene benzene of ref. i. 

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just... 

Figure 12 7 illustrates attack on the benzene ring by tert butyl cation (step 1) and subsequent formation of tert butylbenzene by loss of a proton from the cyclohexadienyl cation intermediate (step 2)... 

One drawback to Fnedel-Crafts alkylation is that rearrangements can occur espe cially when primary alkyl halides are used For example Friedel-Crafts alkylation of benzene with isobutyl chloride (a primary alkyl halide) yields only tert butylbenzene... 

Step 2 Loss of a proton from the cyclohexadienyl cation intermediate yields tert butylbenzene C(CH3)3... 

The synthesis of butylbenzene illustrates the acylation-reduction sequence... 

Direct alkylation of benzene using 1 chlorobutane and aluminum chloride would yield sec butylbenzene by rearrangement and so could not be used... 

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