Phosphorus Acids as Highly Efficient Promoters for the Palladium‐Phenanthroline Catalyzed Carbonylation of Nitrobenzene to Methyl Phenylcarbamate^†

Abstract

A new family of promoters, based on phosphorus acids, is reported for the catalytic carbonylation of nitrobenzene to methyl phenylcarbamate by palladium-phenanthroline complexes. With the new promoters, unprecedented reaction rates (TOF up to 6000/h) and catalyst stability (TON up to 10 5 ) could be reached. The best promoter is phosphoric acid, which is also very cheap, nontoxic and easily separable from the reaction products.

One-Pot Synthesis of Dialkyl Hexane-1,6-Dicarbamate from 1,6-Hexanediamine, Urea, and Alcohol over Zinc-Incorporated Berlinite (ZnAlPO4) Catalyst

“…The reactivity of the alcohols was highest for MeOH, and decreased with increasing the alkyl chain length (entries [1][2][3][4][5]. This result may be ascribed to stronger inductive effect on the carbonyl of urea with higher polarity of the longer chain alcohol.…”

“…The catalytic performances of different Zn to AlPO 4 molar ratios for ZnAlPO 4 catalysts were investigated. The results are shown in Table 1.…”

“…The reason could be due to the rate of both 3 and 4 production from Reactions (1) and (2) [24,25], being higher with an increase of urea/HDA molar ratio from 2.0 to 3.0 than that of the consumption from Reactions (3), (4), (5) and (6), respectively. On the other hand, for both 1 and 5, the rate of production from Reactions (3), (4) and (7) [20,26], were lower at the urea/HDA molar ratio higher than 2.2 than that of consumption from Reactions (8) and (9) Figure 3 presents the effect of the urea/HDA molar ratio on the conversion of HDA, yield of 2, and selectivities for the four main byproducts (1, 3-5) under the reaction conditions: HDA 0.9 mol, ZnAlPO4 3.0 g, butanol 7.74 mol (708.0 mL), time 6 h, temperature 493 K and pressure 1.2 MPa. With the increase of urea/HDA molar ratio from 2.0:1 to 3.0:1, the conversion of HDA and the yield of 2 increased rapidly from 2.0:1 to 2.6:1 while it increased only slightly from 2.6:1 to 3.0:1, and a maximum value of 92.0% was achieved for the yield of 2 at the urea/HDA molar ratio of 3.0:1.…”

“…The berlinite-structured AlPO 4 and ZnAlPO 4 were hydrothermally synthesized by the same procedure as reported in our previous work [17]. The synthesized specimens were denoted as ZnAlPO 4 (X), where X refers to the Zn/Al molar ratio in the specimen.…”

“…However, a number of drawbacks may occur in the route, including difficult handling of the toxic phosgene and the seriously corrosive side product HCl [2]. Several phosgene-free routes for organic carbamates synthesis have also been reported [4][5][6][7][8][9], among which the synthesis from amines, urea and alcohols by a one-pot reaction [9] has received considerable attention. This route appears to be promising because, on the one hand, ammonia is obtained as a main byproduct and, on the other hand, urea can be prepared on a large scale by the dehydration of ammonia and CO 2 [10].…”