Of ferf.-butylbenzene

Write a mechanism for the formation of ferf-butylbenzene from benzene and fert-butyl alcohol in the presence of phosphoric acid. 

El Slow dissociation of ferf-butylbenzene ions observed with ICR Faulk and Dunbar [32]... 

Addition of ferf-butylbenzene to the strongly acidic solvent HF/SbF followed by aqueous workup gives benzene. Propose a mechanism for this dealkylation reaction. What is the other product of the reaction ... 

Mechanism 12.4 illustrates the reaction of benzene with ferf-butyl cation (step 1) followed by formation of ferf-butylbenzene by abstraction of a proton from the cyclohexa-dienyl cation intermediate (step 2). 

Fig. 6.15. El spectmm of ferf-butylbenzene. Again, molecular ion and primary fragment ion are dominating the spectmm. Spectrum used by permission of NIST. NIST 2002.

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... 

It is proposed that 32 reacts from its nn excited state by the nitro-to-nitrite (33) inversion followed by nitrite homolysis, when the naphthoxy radical must diffuse away from the cages to obtain the dimerization intermediate 35. However, the source of oxidizing agents is not identified. In comparison, o-nitro-ferf-butylbenzenes 37 are excited to undergo intramolecular H-atom transfer and cyclization to give indol-IV-oxides 40 (equation 34)38. The discrepancy may arise from the nature of the excited state, e.g. that of 37 may react from its njr state. 

The alkylation product of benzene (W) and ferf-butylbenzene (S4) with ethylene yields predominantly sec-butyl alkylates. This is the case because the ethylbenzene alkylate formed reacts very rapidly in the normal side-chain alkylation reaction. The sec-butyl aromatic alkylates much less readily. The much greater ease of side-chain alkylation over nuclear alkylation also accounts for the exclusive formation of side-chain alkylates from compounds, such as cumene, that are predominantly metalated on the ring by alkylalkali metal compounds. 

Tables I and II include data for the co-oxidations of styrene and butadiene in chlorobenzene and ferf-butylbenzene solutions, as well as with no added solvent. These solvents were chosen because the rate of oxidation of cyclohexene varies significantly in them at the the same rate of initiation (6). There is a variation in the over-all rate of oxidation under these solvent conditions, but there appears to be no significant difference in the measured ra and rb (Table II). If the solvent does affect the propagation reaction in autoxidation reactions, it affects the competing steps to the same degree.

Materials. Cumene and Tetralin were purified by extraction with concentrated sulfuric acid, until the extracts were colorless, then with 2N caustic soda and distilled water, and finally dried and distilled. Both were stored in darkness under No and percolated through silica gel immediately before use. ferf-Butylbenzene (99.9% by GLC) was used as an inert diluent for cumene and Tetralin where indicated. Squalane (M and B Embaphase) was used as received. AIBN was recrystallized from ether and had a melting point of 102°-103°C. Metal dialkyl dithiophos-phates were prepared as described previously (6) zinc diisopropyl dithio-phosphate was finally recrystallized twice from n-heptane and had a melting point of 146 °C. 

Table I. AIBN-Initiated Oxidation of Organic Phosphorus Compounds in ferf-Butylbenzene at 70°C.

C-H Insertion versus Double-Bond Addition in the Reaction of Carbon with Aromatics. The factors that determine if C atoms react with an aromatic by C—H insertion or DBA are not yet understood. Benzene and substituted benzenes are postulated to react by C—H insertion although detailed labeling studies have only been carried out in benzene, toluene, and ferf-butylbenzene. No C—H insertion is observed in the reaction of carbon with 71, while C—H insertion is a minor pathway when carbon reacts with 76 and 87. 

One cannot help being impressed by the dominant character of the methyl group. It would seem that when the electron release of the methyl groups is balanced across the benzene nucleus the knock resistance is increased this indicates that the velocity of combustion is slowed down. On the other hand, when the electron releases of the methyl groups supplement each other, as in the case of the vicinal derivatives, knock resistance is decreased this indicates that the combustion velocity is increased. An accumulation of methyl groups either upon the side chain, as in ferf-butylbenzene, or upon the nucleus, as in isodurene, seems to increase the knock resistance. 

Even ferf-butylbenzene reacts satisfactorily (86% yield) without de-tert-butylation. Acylation of p-xylene with benzoic acid gave 71% yield with continuous removal of water. Water removal was also the decisive factor in producing anthraquinones with phthalic anhydride in satisfactory yields (52-89%). 

SAMPLE SOLUTION (a) Friedel-Crafts alkylation of benzene with isobutyl chloride is not suitable, because it yields ferf-butylbenzene by rearrangement. 

The sum of these partial rate factors is 147 for toluene, 90 for tert-buty I benzene. Toluene is 147/90, or 1.7, times more reactive than ferf-butylbenzene. 

The ferf-butyl cations liberated from compounds Ar—tert- Bu, upon ipso reaction of a proton, may also react again with the aromatic compound from which they stemmed. If this course is taken, the te/7-butyl groups are ultimately bound to the aromatic nucleus with a regioselectivity that is dictated by thermodynamic control. Figure 5.4 shows how in this way 1,2,4-tri-ferf-butylbenzene is smoothly isomerized to give 1,3,5-tri-fcrt-buty 1-benzene. 

The use of ferrocene-based ligands such as 3 and PPFA (8) result in the formation of catalysts that extended the scope of the arylation reaction to more difficult transformations [37,38,56]. For example, di-n-butylamine could now be effectively coupled with electronically neutral as well as electron-deficient aryl bromides. Reaction of 4-ferf-butylbromobenzene with di-n-butylamine with the ( )-BlNAP/Pd- or DPPF/Pd-based catalysts resulted in significant amounts of terf-butylbenzene formation, however the use of ligands 3 and 8 resulted in formation of the desired product in excellent yield, Eq. (25). 

As was the case with ligand 4,2-biphenyldi-fert-butylphosphine (6) effects the amination of acyclic secondary amines at room temperature [42 a, 48]. The catalyst derived from this commercially available ligand and Pd2(dba)3 promotes the coupling of 4-bromo-ferf-butylbenzene and di- -butylamine or AT-methylaniline in excellent yields at room temperature, Eq. (28). 

Related to the demethylation of gemdisubstituted cycloalkanes is the aromatization of gemdialkylcyclohexanes, which takes place, on platinized carbon, with the elimination of an alkyl group and formation of mono-alkylbenzenes 140, 141). However, l-methyl-l-alkylcyclohexanes (alkyl = Et, Prop, But) yield more alkylbenzene than toluene, while for 1-methyl-l-tert-butylcyclohexane, toluene largely predominates over ferf-butylbenzene (Table Xli) 140-144). 

Other polyalkylbenzenes have also been studied 47 54>. 1,2-Di-tert-butylbenzene in ether solution upon irradiation produces a mixture of 1,3- and l,4-di-fer/-butylbenzene 48>. o-tert-Butyltoluene also gives a mixture of the m- and p-isomers but it is less reactive than the di-tert butylbenzene 48>. o- and m-xylene in ether solution gave no detectable isomerization reaction. When a nitro, acetyl or methoxy substituent was placed in the 4-position of the o-di-ferf-butylbenzene, the isomerization reaction did not occur 48>. Using higher intensity light, however, o- and i-xylene were found to isomerize to the other isomeric xylenes 47>. 

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