Hydrogenation thiophenes

During the last 5-6- years a new trend has been noticeable. The study of the reactivity of the thiophenic hydrogens and the influence... 

Incorporating an electron-donor alkyl group into position 2 of 2 was shown by foe present authors to facilitate S-oxidation thus, 2-efoyl-thieno[3,2-6]thiophene-l,1-dioxide (214) was prepared at40°-45° from 2-ethylthieno[3,2-6]thiophene, hydrogen peroxide and acetic acid. The thieno[3,2-6]thiophene system undergoes oxidation even if foe second a-position is carboxy-substituted oxidation of 5-efoylthieno[3,2-6]-thiophene-2-carboxylic acid furnished foe 4,4-dioxide (215) subsequently decarboxylated to sulfone (214) [Eq. (70)]. The [2,3-6] isomers, 20 and 55, with foe sulfur atoms bound to foe same carbon atom, do not form sulfones under similar conditions. 

Several papers in this book and in the recent literature (3) discuss use of pyrolysis techniques coupled with gas chromatography and mass spectrometry to determine forms of organically bound sulfur, but these methods introduce an uncertainty due to the possible interconversion of these sulfur forms during the heating step. For example, it has been shown that when benzyl sulfide was heated to 290°C, tetraphenyl thiophene, hydrogen sulfide and stilbene were produced (4). Coupled with heat and mass transport limitation considerations, particularly for viscous liquids and solids, it is not unreasonable to question whether at least some of the thiophenic forms observed by these techniques were produced during the analysis and may not have been present in the original sample. 

Methylbenzene 2-Chloro pyrimidine Thionyl chloride Thiophene Hydrogen Potassium acetate Sodium hydroxide Nickel Raney... 

Fig. 5.9. Effect of catalyst quantity on the rate of thiophene hydrogenation over a modified cobalt catalyst in a hydrocarbon solvent. (Redrawn using data from Ref 24).

Zeolithe-Y-supported W2C shows metallic hydrogenation properties and can also be used as catalyst in the thiophene hydrogenation. 

Hydrogenation ofbenzene catalyzed by [( qCCjH6)4Ru4H4]. The mechanism of thiophene hydrogenation by [Ir(H)An -T)2(PPh3)d PF,. 

Gas Phase Poisons. The effectiveness was examined of four sulphur compounds, thiophene, hydrogen sulphide, sulphur dioxide and carbonyl sulphide, as gas phase poisons. 

This point may be illustrated by some hydrogenation tests carried out by the author on the sensitivity of a platinum catalyst to poisoning by thiophene at 15 and at 50 respectively. The system examined contained in each case 0.025 g. of stock platinum black suspended in 10 cc. of a 1 iV solution of crotonic acid in acetic acid containing various known amounts of thiophene, hydrogenation being carried out in a shaker under standardized conditions. The results are summarized in Table V, from... 

The two steps of the hydrogenation were assumed to take place on two different types of active site a sites and t sites. The rate of thiophene hydrogenation on (x sites is represented by the equation... 

Simulations were performed under the conditions shown in Table 23.3, using the kinetic parameters reported by Van Parijs et al. [45]. Figure 23.6 shows concentration profiles in a pellet for the reactants and products of the thiophene hydrogenation. 

Fatemi et al. [54] also observed reaction rate hysteresis with temperature cycling by experiment. Thiophene hydrogenation was chosen as an example of a hydrotreating reaction and n-heptane was used as a solvent. Experiments were carried out for two Ni-Mo/y-AUOs samples first a narrow pore catalyst with BJH average pore radius of 26.9 A and secondly a wide pore catalyst with BJH average pore radius of 70.3 A. As shown in Figure 23.16, it was found that the narrow pore catalyst exhibits a more pronounced hysteresis loop than the wide pore catalyst. This difference could be explained since a larger volume of gas condenses and hquid evaporates from the catalyst with narrow pores, which are more susceptible to capillary condensation. 

Contaminants present in gas streams in relatively small concentrations, such as carbonyl sulfide, carbon disulfide, mercaptans, thiophene, hydrogen cyanide, ammonia, and sulfur dioxide, are removed by hot potassium carbonate solution to various degrees. Parrish and Neilson (1974) report laboratory and commercial scale data obtained in purifying natural gases and gas from a pressurized Lurgi gasifier. 

The feed to the CSTR consisted of a mixture of thiophene, hydrogen, and hydrogen sulfide. The mole fractions of butene (C4Hg), butane (C4H10), and hydrogen sulfide in the reactor effluent were measured. The mole fractions of hydrogen and thiophene were not measured. 

Calculate —rr (the rale of disappearance of thiophene) and the partial pressures of thiophene, hydrogen, hydrogen sulfide, butenes (total), and butane in the effluent. You may assume that the ideal gas laws are valid. 

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