Hydrogenation over platinum catalyst

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. 

The best reagents for reduction of olefinic aldehydes to olefinic alcohols are lithium aluminum hydride and sodium borohydride. Crotyl alcohol, CHjCH = CHCHjOH, and cinnamyl alcohol, CjH,CH =CHCHjOH, have been prepared in excellent yields. Cinnamyl alcohol is further reduced at higher temperatures to hydrocinnamyl alcohol. Citral, (CHj)jC =CHCHjCHjC(CH3)=CHCHO, may be selectively reduced to the ctOTesponding dienol by catalytic hydrogenation over platinum catalyst. A new method for the preparation of enediol esters of the type... 

Olefinic acids have been reduced to saturated acids in excellent yields by a variety of methods. Catalytic hydrogenation at room temperature over platinum oxide catalyst is described for 4-phenyl-3-pentenoic acid (98%). Behenic and undecanoic acids are prepared from the naturally occurring erucic and undecylenic acids with this catalyst. New and "aged platinum oxide catalysts have been compared, Reduction by nickel-aluminum alloy has been preferred to catalytic hydrogenation over platinum catalyst in the preparation of y-isopropylvaleric acid. ... 

The formation of a methiodide indicated the tertiary character of the amine, and lack of any oxidation with periodic acid showed that a 1, 2-glycol grouping of two of the oxygens had to be excluded (43). Attempted condensation with nitromethane did not proceed and no reduction product was obtained by the use of sodium amalgam or hydrogen over platinum catalyst. Richardson and Warren also suggested that rosmarinecine was... 

When 1-hexene is subjected to hydrogenation over platinum catalysts, if hydrogenation is stopped at about 95% completion, most of the unreacted alkene is a mixture of cis- and trans-2-hexene. Account for this observation. 

A hydrocarbon, compound A (CgHio), burned with a yellow, almost nonsmoky flame. On catalytic hydrogenation over platinum catalyst it absorbed 1 mol of hydrogen to form compound B. It also decolorized a Br2- H2Cl2 solution to yield a dibromo derivative, compound C. Ozonolysis of the hydrocarbon gave only one compoimd, D. Compoimd D gave a positive iodoform test when treated with iodine-sodium hydroxide solution. On treatment of compoimd D with an alcoholic solution of silver ammonium hydroxide, a silver mirror was formed within a few minutes. 

Although reduction of L-sorbose appears to yield equimolar amounts of the two hexitols, reduction of penta-O-acetyl-feto-L-sorbose appears to favor the formation of L-iditol. A 60 % yield of L-iditol hexaacetate was obtained when penta-0-acetyl-fc6absolute ether at 4 atmospheres pressure. The hydrogenated product was further acetylated to the hexaacetate and fractionally crystallized 56). A 90% yield is claimed when the reduction is carried out in alcohol using Raney nickel and atmospheric pressure at room temperature (57). 

Hydroxylamine sulfate is produced by direct hydrogen reduction of nitric oxide over platinum catalyst in the presence of sulfuric acid. Only 0.9 kg ammonium sulfate is produced per kilogram of caprolactam, but at the expense of hydrogen consumption (11). A concentrated nitric oxide stream is obtained by catalytic oxidation of ammonia with oxygen. Steam is used as a diluent in order to avoid operating within the explosive limits for the system. The oxidation is followed by condensation of the steam. The net reaction is... 

Because of the presence of alkali in Raney nickel, ketones are hydrogenated over this catalyst to yield the more stable, equatorial alcohol e.g. 59) as the predominant product, Similar results can be expected with platinum in basic media or with platinum oxide in an alcoholic solvent since this catalyst also contains basic impurities. 

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). 

The literature on the hydrogenation of aniline and substituted anilines suggests that the amine functionality can act as a poison [3, 4, 12 and 13] especially over platinum catalysts. The more basic the nitrogen the more... 

Torok B, Karoly F, Gerda S, Mihaly B (1997) Sonochemical enantioselective hydrogenation of ethyl pyruvate over platinum catalysts. Ultrason Sonochem 4(4) 301-304... 

Gyorgy S, Istvan K, Bela T, Mihaly B (2000) Ultrasonics in chemoselective heterogeneous metal catalysis. Sonochemical hydrogenation of unsaturated carhonyl compounds over platinum catalysts. Ultrason Sonochem 7(4) 173-176... 

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. 

Si-H bonds add across olefins over platinum catalysts. This reaction (hydrosi-lation) is used in silicone polymer manufacture, when the silane is a hydrogen bearing oligo(alkylsiloxane). With some types of olefin there have been reports of runaways to explosion because of unexpectedly fast reaction. Dangerous substrates recorded are 2-allylphenols and ethenylsiloxanes. Very low levels of catalyst (ppm) and good cooling are recommended. 

Trimm, D. L. and B. J. Cooper. 1973. Propylene hydrogenation over platinum/carbon molecular sieve catalysts. J. Cat. 31 287-92. 

Acidity or alkalinity of the medium plays a very important role. Hydrogenation of aromatic rings over platinum catalysts requires acid medium. Best results are obtained when acetic acid is used as the solvent. Addition of... 

Depending on the catalysts, catalytic hydrogenation converts naphthalene to tetrahydronaphthalene (tetralin), or cis- or trons-decalin (decahydro-naphthalene) [S, 405, 406, 407]. Tetrahydronaphthalene was converted to ciy-decalin by hydrogenation over platinum oxide [S]. 

Unsaturated amines are hydrogenated at the multiple bonds by catalytic hydrogenation over any catalyst. The double bond in indole was saturated in catalytic hydrogenation over platinum dioxide in ethanol containing fluoro-boric acid and indoline was obtained in greater than 85% yield [456. AUylic amines such as allylpiperidine are also reduced by sodium in liquid ammonia in the presence of methanol (yield 75%) [709. ... 

L-Mannitol has been prepared by the reduction of L-mannosaccharo-dilactone or L-mannose. By far the most convenient procedure is that used by Baer and Fischer for their preparation of L-glyceraldehyde by the oxidative cleavage of l,2 5,6-diisopropylidene-L-mannitol with lead tetraacetate. L-Arabinose was converted to L-mannonolactone by the cyanohydrin synthesis and this was hydrogenated over platinum oxide to the desired L-mannitol. High hydrogen pressures, rather than low as usually employed with this catalyst, were used. 

---