Propylbenzenes, reaction

Prepare a solution of benzyl magnesium chloride in a 2-litre three-necked flask from 24-3 g. of magnesium turnings, 600 ml. of sodium-dried ether and 126-5 g. (115 ml.) of redistilled benzyl chloride follow the experimental details given under n-Propylbenzene (Section IV,7). Cool the flask in running water or in ice water. Place a solution of 456 g. of n-butyl-p-toluenesulphonate (Section IV,198) in about twice its volume of anhydrous ether in the dropping funnel, and add it slowly with stirring, at such a rate that the ether just boils a white solid soon forms. The addition is complete after about 2 hours. Pour the reaction product... 

Side-chain bromination at the benzylic position occurs when an alkylbenzene is treated with /V-bromosuccinimide (NBS). For example, propylbenzene gives (l-bromopropyl)benzene in 97% yield on reaction tvith NBS in the presence of benzoyl peroxide, (PhC02)2f as a radical initiator. Bromination occurs exclusively in the benzylic position and does not give a mixture of products. 

Solution "What is an immediate precursor of the target " The final step will involve introduction of one of three groups—chlorine, propyl, or sulfonic acid—so we have to consider three possibilities. Of the three, the chlorination of o-propylbenzene-sulfonic acid can t be used because the reaction would occur at the wrong position. Similarly, a Friedel-Crafts reaction can t be used as the final step because this reaction doesn t work on sulfonic acid-substituted (strongly deactivated) benzenes. Thus, the immediate precursor of the desired product is probably m-chloropropyl-benzene, which can be sulfonated to give a mixture of product isomers that must then be separated. 

Finally, rates of mercuration have been measured using mercuric trifluoro-acetate in trifluoroacetic acid at 25 °C450. The kinetics were pure second-order, with no reaction of the salt with the solvent and no isomerisation of the reaction products rate coefficients (10 k2) are as follows benzene, 2.85 toluene, 28.2 ethylbenzene, 24.4 i-propylbenzene, 21.1 t-butylbenzene, 17.2 fluorobenzene, 0.818 chlorobenzene, 0.134 bromobenzene, 0.113. The results follow the pattern noted above in that the reaction rates are much higher (e.g. for benzene, 690,000 times faster than for mercuration with mercuric acetate in acetic acid) yet the p factor is larger (-5.7) if the pattern is followed fully, one could expect a larger... 

Figure 1. HDN reaction network of quinohne-type compounds. Q=quinoline, THQ5=5,6,7,8-tetrahydroquinoline, DHQ=decahydroq unohne, THQl=l,2,3,4-tetrahydroquiniline OPA=ortho-propylaniline, PCHA=2-propylcyclohexylamine, PCHE=propylcyclohexene, PCH=propylcyclohexane, PB=propylbenzene.

The regiochemistry of Al-H addition to unsymmetrically substituted alkynes can be significantly altered by the presence of a catalyst. This was first shown by Eisch and Foxton in the nickel-catalyzed hydroalumination of several disubstituted acetylenes [26, 32]. For example, the product of the uncatalyzed reaction of 1-phenyl-propyne (75) with BujAlH was exclusively ds-[3-methylstyrene (76). Quenching the intermediate organoaluminum compounds with DjO revealed a regioselectivity of 82 18. In the nickel-catalyzed reaction, cis-P-methylstyrene was also the major product (66%), but it was accompanied by 22% of n-propylbenzene (78) and 6% of (E,E)-2,3-dimethyl-l,4-diphenyl-l,3-butadiene (77). The selectivity of Al-H addition was again studied by deuterolytic workup a ratio of 76a 76b = 56 44 was found in this case. Hydroalumination of other unsymmetrical alkynes also showed a decrease in the regioselectivity in the presence of a nickel catalyst (Scheme 2-22). 

There is some increase in selectivity with functionally substituted carbenes, but it 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 i-propylbenzene, ethylbenzene, and toluene.212 For cycloalkanes, tertiary positions are about 15 times more reactive than secondary positions toward phenylchlorocarbene.213 Carbethoxycarbene inserts at tertiary C—H bonds about three times as fast as at primary C—H bonds in simple alkanes.214 Owing to low selectivity, intermolecular insertion reactions are seldom useful in syntheses. Intramolecular insertion reactions are of considerably more value. Intramolecular insertion reactions usually occur at the C—H bond that is closest to the carbene and good yields can frequently be achieved. Intramolecular insertion reactions can provide routes to highly strained structures that would be difficult to obtain in other ways. 

Fig. 25. Ion image of photoffagment (a) m/e = 91, (b) m/e = 29, from photodissociation of ro-propylbenzene at 193 nm. The delay times between pump and probe laser pulses are 28 fas and 8 fas, respectively, (c) The translational momentum distributions of m/e = 29 (thin solid line) and 91 (thick solid line), (d) The fragment translational energy distribution for the reaction C6H5C3H7 —> C6H5CH2 + C2H5.

Fig. 29. The So and Ti energy diagrams of reactions of C6H5C2H5 —> C6H5CH2+CH3 and C6H5C3H7 —> C6HbCH2 +C2CB obtained by an ab initio calculation. The numbers are the zero point energies for the So and Ti states, the transition states, and the products. The numbers in the parentheses are the energies of propylbenzene.

In the absence of ultrasonic waves, the reactions usually require two or three hours or heating to 80°. Using our procedure, the cyclopropane ring in cyclopropylbenzene was easily opened to give propylbenzene in >95% yield. 

The most fundamental reaction is the alkylation of benzene with ethene.38,38a-38c Arylation of inactivated alkenes with inactivated arenes proceeds with the aid of a binuclear Ir(m) catalyst, [Ir(/x-acac-0,0,C3)(acac-0,0)(acac-C3)]2, to afford anti-Markovnikov hydroarylation products (Equation (33)). The iridium-catalyzed reaction of benzene with ethene at 180 °G for 3 h gives ethylbenzene (TN = 455, TOF = 0.0421 s 1). The reaction of benzene with propene leads to the formation of /z-propylbenzene and isopropylbenzene in 61% and 39% selectivities (TN = 13, TOF = 0.0110s-1). The catalytic reaction of the dinuclear Ir complex is shown to proceed via the formation of a mononuclear bis-acac-0,0 phenyl-Ir(m) species.388 The interesting aspect is the lack of /3-hydride elimination from the aryliridium intermediates giving the olefinic products. The reaction of substituted arenes with olefins provides a mixture of regioisomers. For example, the reaction of toluene with ethene affords m- and />-isomers in 63% and 37% selectivity, respectively. 

Photolytic. A rate constant of 3.7 x 10 L/molecule-sec was reported for the reaction of propylbenzene with OH radicals in the gas phase (Darnall et al, 1976). Similarly, a room temperature rate constant of 5.7 x lO cm /molecule-sec was reported for the vapor-phase reaction of propylbenzene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 6.58 x 10 cmVmolecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). 

The iridium(III)-complex, [Ir(p-acac-0,0,C )(acac-0,0)(acac-C )]2, mediates the activation of unactivated aromatic C—H bond with unactivated alkenes to form anti-Markovnikov products [57]. The reaction of benzene 131 with propene 132 (0.78 MPa of propylene, 1.96 MPa of N2) leads to the formation of n-propylbenzene 133 in 61% selectivities (turnover number (TON) = 13 turnover frequency (TOE) = 0.0110 s ) (Equation 10.34). The reaction of benzene with ethane at 180 °C for 3h gave ethylbenzene (TON = 455 TOE = 0.0421s ). The anti-Markovnikov selectivity was also proven for the reaction with 1-hexane and isobutene, giving 1-phenyUiexane (69% selectivity) and isobutylbenzene (82% selectivity), respectively. 

The reaction of 1,3-cyclohexadiene with la at a temperature of — 50°C gives a 97 3 mixture of 1,4-allylsilylated product, trara-3-allyl-6-(trimethylsilyl)cyclohexene and 1,2-allylsilylated product, tra 5-3-allyl-4-(trimethylsilyl)cyclohexene, in quantitative yield. At the same temperature, the [3 -I- 2] cycloaddition product is detected only in trace amounts after 1 h. As the reaction mixture is warmed to — 10°C, the allylsilylated compounds are converted to the [3-1-2] cycloaddition product (72%). When purified tra 5-3-allyl-6-(trimethylsilyl)cyclohexene and tra i-3-allyl-4-(tri-methylsilyl)cyclohexene are treated separately under the same reaction conditions, the former compound is converted to the [3 -I- 2] cycloaddition product (major) and 3-(trimethylsilyl)propylbenzene [Eq. (11)], while the latter compound is converted to polymeric materials without giving any [3-1-2] cycloaddition product. The reaction rates of allylsilylation and [3-1-2] annulation are also accelerated by the addition of trimethylchlorosilane to aluminum chloride, as observed in other allylsilylation reactions. 

The reaction of ethylbenzene with five equivalents of Ic under the same alkylation conditions used for toluene, gives pentakis- (25%), tetrakis- (9%), tris- (4%), and bis[2-(dichloromethylsilyl)ethyl]ethylbenzene (1%) as well as a mixture of many transalkylated products (44%). It is of interest that longer alkyl-substituted benzenes exhibited different behavior in peralkylations with Ic. The transalkylation of ethylbenzene is responsible for the significantly low yield (25%) of peralkylation product in comparison with yields obtained from the alkylation of benzene " or toluene. Peralkylation of K-propylbenzene and K-butylbenzene gives similar results to those of ethylbenzene. 

Of the olefins, ethylene has been most extensively studied (19, 21, 23-26, 36) it reacts most readily in base-catalyzed alkylations. In general temperatures of 150-200 are used with relatively low ethylene pressures (0-70 atm.). Benzylic hydrogens are replaced by ethyl groups i.e., toluene yields n-propylbenzene. Additional substitution on the a-carbon may yield 3-phenylpentane and 3-ethyl-3-phenylpentane [Reaction (3)]. 

On the basis of products formed in a number of condensation reactions only confusion results for any step by step mechanism involving specific identifiable species as intermediates. Here are some of the facts. Benzene condenses with cyclopropane to form n-propylbenzene (Simons et al., 44). Normal propyl bromide gives chiefly isopropyl benzene (Simons and Archer, 36) as does propylene (Simons and Archer, 28). Ethyl alcohol gives ethylbenzene, but methyl alcohol does not give... 

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