I-propylbenzene

The identification of a specific nitrating species can be approached by comparing selectivity with that of nitration under conditions known to involve the nitronium ion. Examination of part B of Table 10.7 shows that the position selectivity exhibited by acetyl nitrate toward toluene and ethylbenzene is not dramatically different from that observed with nitronium ion. The data for i-propylbenzene suggest a lower ortho para ratio for acetyl nitrate nitrations. This could indicate a larger steric factor for nitration by acetyl nitrate. 

Second-order rate coefficients at 20 °C were as follows benzene (0.0133), toluene (1.26), p-xylene (62) o-xylene (70.2), and i-propylbenzene (0.395). It is difficult to evaluable the quantitative significance of this data, however, since there must be a solvent correction factor to each rate, arising from the differing polarities of the media. That this can be significant can be seen from the data in Table 67,... 

The above mechanism for chloromethylation seems to be general for halo-methylation since bromomethylation gives the same ortho para ratio for toluene, ethylbenzene, and i-propylbenzene, which is entirely in accord with the halogen being substituted in a non rate-determining step of the reaction386. 

The greater steric hindrance to acetylation was also shown by a comparison of the rate of (103At2) of acetylation of toluene (0.763), ethylbenzene (0.660), i-propylbenzene (0.606) and f-butylbenzene (0.462) with those (determined by the competition method) for benzoylation both sets of data (Table 112) were obtained with dichloroethane as solvent at 25 °C, all reagent concentrations being 0.1 A/421. Relative rates of acylation other aromatics under the same conditions have also been obtained and are given in Table 113422. The different steric requirements for acetylation and benzoylation are further shown by the following respective relative rates for acylation of naphthalene derivatives in chloroform at 0 °C naphthalene (1 position) 1.00,1.00, (2 position) 0.31,0.04 2,3-dimethylnaphthalene (1 position) 1.59, 172, (5 position) 7.14, 38.2, (6 position) 3.68, 7.7422a. 

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... 

The ratio of ortho- to the meta- and /faru-products of monoalkylbenzenes with 1 decreased as the size of the substituents on benzene ring increased. No ortho-alkylation product was found in the case of i-propylbenzene due to the sterie interaction between /-propyl and the incoming allyl groups. Sterie hindrance arising from the size of the alkyl groups at ortho positions of the substituted benzenes appeared to be the principal cause of the differences in isomer product ratio." " ... 

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. 

Many partial rate factors are available for the substitution reactions of the other alkylbenzenes, ethylbenzene, i-propylbenzene, and t-butyl-benzene, in addition to the 60 reactions of toluene. The data for these compounds are subject to the same limitations and restrictions described for toluene. The minor uncertainties which do exist are related to the experimental problems involved in the analysis for the small concentration of meta isomer. Rate data for the ortho and para positions are precise (Tables 10, 11, and 12). 

Figure 13.14. Nmr spectrum of /i-propylbenzene. Moving downheld, we see the expected sequence of signals a, primary (3H) A, secondary (2H) c, benzylic (2H) and d, aromatic (5H). Signals a and c are each split into a triplet by the two secondary protons Hi,. The hve protons adjacent to the secondary protons—three on one side and two on the other—are, of course, not equivalent but the coupling constants, /ab and Jbo are nearly the same, and signal b appears as a sextet (5+1 peaks). The coupling constants are not exactly the same, however, as shown by the broadening of the six peaks.

Best yields from alkylbenzenes were obtained from toluene and t-butylbenzene with all three bismaleimides. This probably reflects a balance between inductive effects, which would favor both 2 + 2 and 2+4 cycloadditions in the order Jt-butyl> i-propyl> ethyl > methyl, and steric effects which would hinder the reaction in the same order. Additional steric effects a-rising from the ortho methyl groups of N,N -4,4 -(3,3 -dimethyl biphenyl)bismaleimide are evident since no polymer was formed from this monomer with ethylbenzene or i-propylbenzene (Zhubanov and Akkulova reportediz their best yields were obtained with 1,10-decamethylenebismaleimide and i-propylbenzene.)... 

Highly disperse nickel-alumina catalysts containing 10, 20, and 30% nickel possess a very great ability for hydrogenolysis of the side chains of toluene, ethylbenzene, n- and i-propylbenzenes and n-butylbenzene (30% Ni). 

The photocatalytic oxidation of aikylbenzenes leads essentially to the corresponding a-ketones. For example, as can be seen from Table 1, linear aikylbenzenes give only one product (a-ketone) while ramified aikylbenzenes such as i-propylbenzene give two products with a selectivity equal to 84% in ketone and... 

Photocatalytic oxidation of i-propylbenzene over silanated zeolites added TiOa... 

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