Catalytic hydrogenations toluene diamine

Isocyanates. The commodity isocyanates TDI and PMDI ate most widely used in the manufacture of urethane polymers (see also Isocyanates, organic). The former is an 80 20 mixture of 2,4- and 2,6-isomers, respectively the latter a polymeric isocyanate obtained by phosgenation of aniline—formaldehyde-derived polyamines. A coproduct in the manufacture of PMDI is 4,4 -methylenebis(phenyHsocyanate) (MDI). A 65 35 mixture of 2,4- and 2,6-TDI, pure 2,4-TDI and MDI enriched in the 2,4 -isomer are also available. The manufacture of TDI involves the dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Separation of the undesired 2,3-isomer is necessary because its presence interferes with polymerization (13). 

The y -phenylenediamines are easily obtained by dinitrating, followed by catalytically hydrogenating, an aromatic hydrocarbon. Thus, the toluenediamines are manufactured by nitrating toluene with a mixture of sulfuric acid, nitric acid, and 23% water at 330 0 which first produces a mixture (60 40) of the ortho and para mononitrotoluenes. Further nitration produces the 80 20 mixture of 2,4- and 2,6-dinitrotoluene. Catalytic hydrogenation produces the commercial mixture of diamines which, when converted to diisocyanates, are widely used in the production of polyurethanes (see Amines, aromatic,... 

Toluene diamine (TDA) is a precursor for toluene diisocyanate (TDI) used to manufacture TDI based polyurethanes. TDA is made by the catalytic hydrogenation of dinitrotoluene. 

Polyurethanes [351]. The production starts from toluene, which is converted by HNO3 in concentrated sulfuric acid to give a mixture of 2,4- and 2,6-dinitrotoluene (DNT). Catalytic hydrogenation with hydrogen gas gives toluene diamines (TDA). The reaction of TDA with phosgene forms toluene diisocyanate (TDI) (see Fig. 93). 

All three possible toluene nitration outcomes are separately carried through the reduction and phosgenation stages to give the corresponding diisocyanate mixtures, or pure 2,4-toluene diisocyanate. Reduction to the diamines with hydrogen (ca. 50 atm) is conducted catalytically using Raney nickel in the liquid phase at about 90°C, to avoid the considerable explosion risk of gas phase operation (Eq. 19.64). 

The direct conversimi of esters into amides is a synthetically useful transformation. However, most of the methodologies developed till now usually require harsh reaction conditions, are poorly compatible with sensitive substrates, and present a low atom economy [136, and references cited therein]. Very recently, MUstein and co-workers demonstrated that esters can be selectively converted into amides generating molecular hydrogen as the only by-product (Scheme 31) [137]. The catalytic reactions were carried out with 2 equiv. of amine per ester in toluene or benzene at reflux in the presence of 0.1 mol% of the dearomatized PNN-pincer ruthenium complex [RuH(CO)(PNN)] (28) (see Scheme 21). Strikingly, both the acyl and the aUcoxo units of the starting ester are involved in the amide production. Hence, to avoid mixtures of products, the process was only applied to symmetrical esters. The catalytic protocol was effective for both primary and secondary cyclic amines. In addition, the coupling of piperazine and butylbutyrate provided compound 46, which results from the bis-acylation of the diamine (Scheme 31). 

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