Carbonylation of toluene

The carhonylation reaction of toluene with carhon monoxide in the presence of HF/BF3 catalyst produces p-tolualdehyde. A high yield results (96% based on toluene and 98% based on CO). p-Tolualdehyde could be further oxidized to terephthalic acid, an important monomer for polyesters  

Xylenes (dimethylbenzenes) are an aromatic mixture composed of three isomers (0-, m-, and p-xylene). They are normally obtained from catalytic reforming and cracking units with other Ce, C7, and Cg aromatics. Separating the aromatic mixture from the reformate is done by extraction-distillation and isomerization processes (Chapter 2). 

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Continuous-Flow Stirred-Tank Reactors. The synthesis of j )-tolualdehyde from toluene and carbon monoxide has been carried out using CSTR equipment (81). -Tolualdehyde (PTAL) is an intermediate in the manufacture of terephthabc acid. Hydrogen fluoride—boron trifluoride catalyzes the carbonylation of toluene to PTAL. In the industrial process, separate stirred tanks are used for each process step. Toluene and recycle HF and BF ... 

Isomerization of xylenes is always coupled with separation processes. In most cases, p-xylene is removed from the reaction mixture by crystallization or selective adsorption. The recovered o-/m-xylene mixture, in turn, is usually recycled for reequilibration. Because of cost of separation, the highly selective carbonylation of toluene to p-tolualdehyde gained significance. Subsequent reduction gives p-xylene. 

In the manufacture of terephthalic acid by the oxidation of p-xylene, separation of the xylene from its isomeric mixture is necessary (see Section 2.5.2). An alternative process introduced in Japan uses the oxidation of p-tolualdehyde, which is obtained in good regioselectivity by the HF—BF3 catalyzed carbonylation of toluene without the necessity of separation of the isomers. 

Also under development is use of the alternative feedstock, toluene, for PTA and/or DMT production. Carbonylation of toluene to produce p-tolualdehyde was shown to proceed in 90-95% yield when catalyzed by HF BF3 [31], or by higher perfluoroalkyl sulfonic acids [32], or in greater than 99% yield when catalyzed by trifloromethanesulfonic acid [33]. The p-tolualdehyde, which is regularly an intermediate in both the Witten DMT and Amoco TPA processes (see Schemes 2 and 3, respectively), can then be readily oxidized with minimal changes to the oxidation process. 

Carbon monoxide carbonylates methane at 573-673 K in the presence of nitrous oxide on a rhodium-doped iron phosphate catalyst to produce methyl acetate [88a]. Vapor-phase carbonylation of toluene yields p-tolualdehyde, which can be easily oxidized to terephthalic acid [88b]. 

Wasserscheid et al. found that aluminum chloride dissolves in triflimide ionic liquids to form biphasic solutions. These solutions can be used to promote the Friedel-Crafts acylation reaction, and an interesting variant is the carbonylation of toluene with carbon monoxide (Scheme 5.2-28) [72]. The ionic liquid can be recycled, but the aluminum chloride is lost when the reaction is worked up. 

Scheme 5.2-28 The carbonylation of toluene in [cation] Tf2N]-AICl3 [72].

Aromatic carbonylation (Scheim 63) represents another inportant type of Friedel-Crafts reaction. In 1985, Texaco patented the reaction of toluene with carbon monoxide to 4-tolualdehyde in a Lewis acidic ionic liquid [29]. Brausch et al. used a new type of highly acidic ionic liquid with the formula [cation] [NTf2]—AlCl3 for the carbonylation of toluene,... 

Brausch, N., Metlen, A. and Wasserscheid, P., New, highly acidic ionic liquid systems and their application in the carbonylation of toluene, Chem. Commun. 1552-1553 (2004). 

The direct carbonylation of toluene into p-tolualdehyde has received much attention. Good results have been obtained using HF/BF3 catalysts under low pressure [139]. 

A similar selectivity in the carbonylation of toluene, although with lower yields, was obtained with NTf2 pyridinium salts in combination vdth AICI3 [105]. A maximum molar ratio of 2 mol AICI3 per mole of chloride IL is possible, until 5 mol AICI3 per NTf2 IL can be solubilized, yielding a much more acidic medium. 

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

In 1991, Ohfune and coworkers reported palladium(O)-catalyzed carbonylation of vinylaziridines 262 with carbon monoxide (1 atm.) in benzene (Scheme 2.65) [31]. Interestingly, 3,4-trans-azetidinone 264 was exclusively obtained from a dia-stereomeric mixture of trans- and cis-vinylaziridines 262 (3 1). Tanner and Somfai synthesized (+)-PS-5 (267) by use of palladium(O)-catalyzed trons-selective (3-lactam formation in the presence of Pd(dba)3 CHC13 (15mol%) and excess PPh3 in toluene. 

Selective transformations Selective styrene ring opening [103] One-pot domino process for regioselective synthesis of a-carbonyl furans [104] Tandem process for synthesis of quinoxalines [105] Atmospheric oxidation of toluene [106] Cyclohexane oxidation [107] Synthesis of imines from alcohols [108] Synthesis of 2-aminodiphenylamine [109] 9H-Fluorene oxidation [110] Dehydrogenation of ethane in the presence of C02 [111] Decomposition of methane [112] Carbon monoxide oxidation [113]... 

Very recently, Bercaw and co-workers have reported a high yield preparation of 33 via the high pressure carbonylation of (Tj-C5Mes)HfH2 in toluene (72). 

As already noted, the carbonylation of bis(pentamethyl-cyclopentadienyl) actinide hydrocarbyls is irreversible in the cases studied thus far. Thus, thermolysis does not result in CO loss, but rather in interesting chemical reactions. Thermolysis of 1 ( 5) in toluene solution results in hydrogen atom migration to yield an enolate (eq.(5)). NMR studies establish that eq.(5) is essentially quantitative, and that the stereochemical course... 

Ding22 has performed an enantioselective carbonyl-ene reaction under quasi-solvent-free conditions. For example, 22 g of 24 was produced using 1 ml of toluene and 100 pi of dichloromethane (Equation (13)). A variety of substrates were examined, and high yields and high ee s were reported. 

Figure 13. Carbonylation of 2-iodobenzyl alcohol catalyzed by PdCljlPfOCjHslsb in scC02 and in toluene. Reaction conditions S/C = 5000, Pd cat 1,0x 10"2 M DMF solution, Pco =...

Irradiation of toluene in the presence of chlorine yielded benzyl hydroperoxide, benzaldehyde, peroxybenzoic acid, carbon monoxide, carbon dioxide, and other unidentified products (Hanst and Gay, 1983). The photooxidation of toluene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and traces of acetaldehyde or other low molecular weight carbonyls (Altshuller et al, 1970). Other photooxidation products not previously mentioned include phenol, phthalaldehydes, and benzoyl alcohol (Altshuller, 1983). A carbon dioxide yield of 8.4% was achieved when toluene adsorbed on silica gel was irradiated with light X >290 nm) for 17 h (Freitag et ah, 1985). 

Carbonylation of bromobenzene (Scheme 5.7) with [Pd(TPPTS)3] required still higher temperatures (150 T). The possible acyl intermediates of such reactions [PdBr(C6H5CO) Ph3)2] and [PdBr(C6H5CO)(TPPTS)2] were synthetized and characterized [26]. Bromobenzene was also carbonylated to benzoic acid in water/toluene using a catalyst prepared from [PdCl2(COD)j and 27 in the presence of NEt3 [21]. 

Very high regioselectivities (> 99.5% iso) were obtained, using PdCl2(PhCN)2 in combination with (+)-neomethyldiphenylphosphine and toluene-j9-sulfonic acid, under mild conditions (70 °C and 10 bar). More recently, the palladium-catalyzed alkoxycarbonylation and amido-carbonylation of aryl bromides and iodides in [bmim][BF4] and [bmim][PF6] has been described. Enhanced reaction rates were observed compared to conventional media and the ionic liquid-catalyst could be recycled. 

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