Hydrogenation over Platinum

In acetic anhydride, the. /V-oxide 76 is reduced to the acetylpyrazoline 173 (93%), presumably via 172.108 The dioxide 96 is reduced in stages, each of which can be isolated it gives first 83, then 174, and finally 175.119 

---

Hydrogenation of 3 carene is in pnnciple capable of yielding two stereoisomenc products Wnte their structures Only one of them was actually obtained on catalytic hydrogenation over platinum Which one do you think is formed" Explain your reasoning with the aid of a drawing or a molecular model... 

An unknown acetylenic ammo acid obtained from the seed of a tropical fruit has the molec ular formula C7H11NO2 On catalytic hydrogenation over platinum this ammo acid yielded homoleucme (an ammo acid of known structure shown here) as the only product What is the structure of the unknown ammo acid" ... 

Nitro groups are readily reduced to primary amines by a variety of methods Cat alytic hydrogenation over platinum palladium or nickel is often used as is reduction by iron or tin m hydrochloric acid The ease with which nitro groups are reduced is especially useful m the preparation of arylamines where the sequence ArH ArN02 ArNH2 IS the standard route to these compounds... 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

Gaseous hydrogen chloride is bubbled through a solution of 0.8 g of 22,23-dibromoergost-8(14)-en-3/3-yl acetate in 25 ml of chloroform at 0° for 2 hr. The solvent is removed by evaporation and the solid mixture of A8(i4) A -isomers is hydrogenated over platinum oxide (0-2 g) in ether... 

P. N. Rylander, Catalytic Hydrogenation over Platinum Metals , Academic Press, New York, 1967. 

The above generalities apply particularly to palladium. Hydrogenation over platinum or rhodium are far less sensitive to the influence of steric crowding. Reduction of 1-t-butylnaphthalene over platinum, rhodium, and palladium resulted in values of /ci//c2 of 0.42, 0.71, and 0.024, respectively. Also, unlike mononuclear aromatics, palladium reduces substituted naphthalenes at substantially higher rates than does either platinum or rhodium. For example, the rate constants, k x 10 in mol sec" g catalyst", in acetic acid at 50 C and 1 atm, were (for 1,8-diisopropylnaphthalene) Pd (142), Pt(l8.4), and Rh(7.1)(25). 

Arylamines are usually prepared by nitration of an aromatic starting material, followed by reduction of the nitro group (Section 16.2). The reduction step can be carried out in many different ways, depending on the circumstances. Catalytic hydrogenation over platinum works well but is often incompatible with... 

For a discussion, see Rylander, P.N. Catalytic Hydrogenation over Platinum Metals, Ref. Ill, p. 59. Also see Hudlicky, M. Reductions in Organic Chemistry, Ellis Horwood Ltd., Chichester 1984. 

W. H. Hartung and R. Simonoff, Org. React., 7, 263 (1953) P. N. Rylander, Catalytic Hydrogenation over Platinum Metals, Academic Press, New York, 1967, Chap. 25 P. N. Rylander, Catalytic Hydrogenation in Organic Synthesis, Academic Press, New York, 1979, Chap. 15 P. N. Rylander, Hydrogenation Methods, Academic Press, Orlando, FL, 1985, Chap. 13. 

Rylander in Catalytic Hydrogenation Over Platinum Metals (p. 39, Academic Press, New York, 1967). Nitrobenzene in ethanol was hydrogenated at room temperature and 1 atm over various amounts of 5% Pd on carbon. Four loading levels of catalyst were used. At each level, the reduction was carried out in two different types of batch reactor. 

---