Hydrogenation of biphenyl

Examining Table XVII, one can see that it is true that, for dibenzothiophene, the direct desulfurization route (/cDo) suffers the greatest inhibition by H2S only 7.5% of the original activity remained in the inhibited case. However, the hydrogenative route (kHs,) was also severely inhibited by H2S only 25% of the original activity remained. The largest inhibition was, in fact, in the hydrogenation of biphenyl (A f,P ). 

The catalysts were tested in the dehydrogenation of tetrahydrothiophene (DHN of THT), the hydrodesulphurization of thiophene (HDS of thiophene) and the hydrogenation of biphenyl (HN of BP). The reactions were carried out in the vapor phase using dynamic flow microreactors equipped with an automatic online analysis. Reaction conditions are given in Table 1. 

TABLE 11.4 Selective Hydrogenation of Biphenyl and Diphenylmethane over Platinum Metals"... 

The hydrogenation of biphenyls over Raney nickel proceeds in a marmer similar to that observed for the hydrogenation of naphthalenes. The hydrogenation of p-phenylphenol (25) takes place over a Pd/C catalyst at 125°C... 

Hydrogenation of Biphenyls (2a-d) with the Activated Hydrogenated Alloy... 

Hydrogenation of biphenyl (2a) over the hydrogen storage alloy (1-H4) ... 

Hydrogenation of biphenyl was found to proceed at 160°C over the hydrogen storage alloy, and either phenylcyclohexane or biphenyl could be selectively prepared by changing the ratio of the substrate to the alloy... 

Cyclohexylbenzene has been prepared by the hydrogenation of biphenyl and of cyclohexenylbenzene over nickel, by the reaction of cyclohexyl chloride or bromide with benzene in the presence of aluminum chloride, and by the addition of benzene to cyclohexene in the presence of aluminum chloride, sulfuric acid, or boron halides. ... 

Biphenyl, CeHs-CeHs has a conjugation energy of 71 kcal/mole. (a) Draw an atomic orbital picture of biphenyl, (b) What are its most important resonance contributing structures (c) Estimate the heat of hydrogenation of biphenyl. 

Figure 6.6 presents data for gaseous, noncatalyzed reactions (pyrolysis, thermal cracking, oxidation, 10 species and 21 data) with typical heats of reaction of 120-150 MJ/kmol. In general, noncatalyzed reactions take about 1000 times longer than the same catalyzed reaction at the same reaction temperature. Data lying outside the factor-of-ten bands are benzene (-r) via hydrodealkylation and benzene (+) via hydrogenation of biphenyl (-r). 

The hydrogenation of biphenyl over a Pt-Pd/Al203 catalyst was carried out in a three-phase plug-flow microreactor [156]. The reactor consisted ofsix parallel reactor tubes with an itmer diameter of 2.2 mm and a catalyst-bed of maximum 200 mm long. 

Pyrolysis. Benzene undergoes thermal dehydrocondensation at high temperatures to produce small amounts of biphenyls and terphenyls (see Biphenyl AND terphenyls). Before the 1970s most commercial biphenyl was produced from benzene pyrolysis. In a typical procedure benzene vapors are passed through a reactor, usually at temperatures above 650°C. The decomposition of benzene iato carbon and hydrogen is a competing reaction at temperatures of about 750°C. Biphenyls are also formed when benzene and ethylene are heated to 130—160°C ia the presence of alkaH metals on activated AI2O3 (33). 

As in the case of biphenyl, current worldwide production figures for terphenyls are not readily obtainable, but the volume is probably around 6.8—8.2 million kg/yr. Currently, most of the terphenyl produced is converted to a partially hydrogenated form. U.S. production of terphenyls has remained steady at several thousand metric tons per year over the past decade. The 1991 small lot price for mixed terphenyls was about 3.89/kg whereas the specially fractionated heat-transfer-grade terphenyl—quaterphenyl mixture sold as Therminol 75 heat-transfer fluid was priced around 6.93/kg. Partially hydrogenated mixed terphenyls were priced in the 6.05—7.48/kg range depending on quantity and grade. 

Bromo-5-imino-5//-dibenz[c,c]azepinium hydrobromide (35) is thought to be the product formed by the action of hydrogen bromide on a solution of biphenyl-2,2 -dicarbonitrilc (34) in benzene.41... 

Catalytic hydrogenation of 5//-dibenzo[r/,/][l, 2,3]triazepine gives biphenyl-2-amine (2).331... 

Brick et al. have studied this bromination in more detail and showed that the extent of the bromination can be controlled by changing the ratio of the reagents. The first substitution was found to be in the para position but subsequent intramolecular rearrangements allowed the formation of 2-5-dibrominated species. Brick et al. also reported the functionalization of such species using Pd-catalyzed reactions such as Heck and Suzuki couplings to give fully substituted p-stilbenes, p-biphenyls, diarylamines, and methylcinnamates. Hydrogenation of... 

Benzyne reacts with benzene to give a mixture of products in low yield. The original experiments 38> showed that the 1,4-cyclo-adduct (benzo-barrelene) (19), the valence-bond isomerised 1,2-cyclo-adduct (benzo-cyclo-octatetraene) (20), and the product of insertion into a carbon-hydrogen bond (biphenyl) (21), were obtained in 2,8, and 6% yields respectively. 

Table 3 Enantioselective hydrogenation of N-(l-phenylethylidene)aniline (8) to (Biphenyl-(1-phenylethyl) amine (9) in IL/CO2 systems ...

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