Reactions combined hydrogenation

SCHEME 9.72 Tandem reaction combining hydrogen-bonding donor and Au catalysis. 

Reactions of Hydrogen and Other Elements. Hydrogen forms compounds with almost every other element. Direct reaction of the elements is possible in many cases. Hydrogen combines direcdy with the halogens, X2, to form the corresponding hydrogen halide. 

Hydrogen sulfide has been produced in commercial quantities by the direct combination of the elements. The reaction of hydrogen and sulfur vapor proceeds at ca 500°C in the presence of a catalyst, eg, bauxite, an aluminosihcate, or cobalt molybdate. This process yields hydrogen sulfide that is of good purity and is suitable for preparation of sodium sulfide and sodium hydrosulfide (see Sodium compounds). Most hydrogen sulfide used commercially is either a by-product or is obtained from sour natural gas. 

Reaction with Hydrogen and Metals. Bromine combines directiy with hydrogen at elevated temperatures and this is the basis for the commercial production of hydrogen bromide [10036-10-6]. Heated charcoal and finely divided platinum metals are catalysts for the reaction (17). 

Oxychlorination. This is an important process for the production of 1,2-dichloroethane which is mainly produced as an intermediate for the production of vinyl chloride. The reaction consists of combining hydrogen chloride, ethylene, and oxygen (air) in the presence of a cupric chloride catalyst to produce 1,2-dichloroethane (eq. 24). The hydrogen chloride produced from thermal dehydrochlorination of 1,2-dichloroethane to produce vinyl chloride (eq. 25) is usually recycled back to the oxychlorination reactor. The oxychlorination process has been reviewed (31). 

The equivalent of a substance is that amount of it which, in a specified reaction, combines with, releases or replaces that amount of hydrogen which is combined with 3 grams of carbon-12 in methane l2CH4. ... 

The scope of reactions involving hydrogen peroxide and PTC is large, and some idea of the versatility can be found from Table 4.2. A relatively new combined oxidation/phase transfer catalyst for alkene epoxidation is based on MeRe03 in conjunction with 4-substituted pyridines (e.g. 4-methoxy pyridine), the resulting complex accomplishing both catalytic roles. 

Write balanced chemical equations for the following reactions (a) Hydrogen fluoride is produced by the reaction of hydrochloric acid and sodium fluoride. (b) Hydrochloric acid combines with sodium fluoride to yield hydrogen fluoride, (c) Sodium fluoride reacts with hydrochloric acid to give hydrofluoric acid. 

To improve the efficiency of combined hydrogen production and C02 capture, several technologies are in development that combine catalytic reactions and the separation of either hydrogen or C02. Major targeted areas of application are the production of bulk hydrogen as a transport fuel and electricity production with pre-combustion C02 capture. 

Give examples of simple radical and biradical reactions - combination, disproportionation, hydrogen abstraction and fragmentation. 

In the discussion of the Daniell cell we indicated that this cell produces 1.10 volts. This voltage is really the difference in potential between the two half-cells. There are half-cell potentials associated with all half-cells A list of all possible combinations of half-cells would be tremendously long. Therefore, a way of combining desired half-cells has been developed. The cell potential (really the half-cell potentials) depends on concentration and temperature, but initially we ll simply look at the half-cell potentials at the standard temperature of 298 K (25°C) and all components in their standard states (1 M concentration of all solutions, 1 atmosphere pressure for any gases, and pure solid electrodes). All the half-cell potentials are tabulated as the reduction potentials, that is, the potentials associated with the reduction reaction. The hydrogen half-reaction has been defined as the standard and has been given a value of exactly 0.00 V. All the other half-reactions have been measured relative to it, some positive and some negative. The table of standard reduction potentials provided on the AP exam is shown in Table 16.1 and in the back of this book. 

By far the most important chemical reaction of hydrogen is undoubtedly that which it enters into with oxygen. When hydrogen is mixed with oxygen and the temperature of the mixed gases raised, they combine with explosive violence, producing steam. This reaction may be expressed by the following equation —... 

This reaction between hydrogen and bromine is in many espects comparable with the combination of hydrogen with chlorine, but unlike the latter, the reaction cannot be brought about by sunlight However, if the two gases are heated, they will combine, but their combination is attended with the evolution of less heat than... 

As shown in Figure 1-1, the fuel cell combines hydrogen produced from the fuel and oxygen from the air to produce dc power, water, and heat. In cases where CO and CH4 are reacted in the cell to produce hydrogen, CO2 is also a product. These reactions must be carried out at a suitable temperature and pressure for fuel cell operation. A system must be built around the fuel cells to supply air and clean fuel, convert the power to a more usable form such as grid quality ac power, and remove the depleted reactants and heat that are produced by the reactions in the cells. 

Most CFCs are manufactured by combining hydrogen fluoride and either carbon tetrachloride or chloroform. The hydrogen fluoride comes from fluorspar, CaF2, reacting with sulfuric acid. The chlorinated methanes are manufactured from methane. Important reactions in the manufacture of CFC-11 and -12 and HCFC-22 are given in Fig. 12.2. 

---