Non-Catalytic Systems

Chapter 23 Fluid-Fluid Reactions Kinetics /523 Chapter 24 Fluid-Fluid Reactions Design /540 Chapter 25 Fluid-Particle Reactions Kinetics /566 Chapter 26 Fluid-Particle Reactions Design /589 

Heterogeneous fluid-fluid reactions are made to take place for one of three reasons. First, the product of reaction may be a desired material. Such reactions are numerous and can be found in practically all areas of the chemical industry where organic syntheses are employed. An example of liquid-liquid reactions is the nitration of organics with a mixture of nitric and sulfuric acids to form materials such as nitroglycerin. The chlorination of liquid benzene and other hydrocarbons with gaseous chlorine is an example of gas-liquid reactions. In the inorganic field we have the manufacture of sodium amide, a solid, from gaseous ammonia and liquid sodium  

Fluid-fluid reactions may also be made to take place to facilitate the removal of an unwanted component from a fluid. Thus, the absorption of a solute gas by water may be accelerated by adding a suitable material to the water which will react with the solute being absorbed. Table 23.1 shows the reagents used for various solute gases. 

The third reason for using fluid-fluid systems is to obtain a vastly improved product distribution for homogeneous multiple reactions than is possible by using the single phase alone. Let us turn to the first two reasons, both of which concern the reaction of materials originally present in different phases. 

The following factors will determine how we approach this process. 

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CHAIRMAN SEGLIN Could you have a compensating factor if you used catalysts rather than non-catalytic systems ... 

However, if E° [ArNu/(ArNu) ]>>E° [ArX/(ArX) ], the ET reaction is close to the diffusion limit from right to left (non-catalytic system), and the radical anion (ArNu) has to be oxidized by the anode208. A detailed study of the electrochemically induced reaction of /7-bromobenzophenone with CN" ions in liquid ammonia showed that this is a non-catalytic system208. 

Microkinetics as defined by Dumesic, is the examination of catalytic reactions in terms of elementary chemical reactions that occur on the catalytic surface and their relation with each other and with the surface during a catalytic cycle. This definition can easily be expanded into covering non-catalytic systems as well. Microkinetics, for the most part, has focused on analysis or understanding of the reaction mechanism. The approach, however, also holds the promise of being used to aid in the synthesis of new materials. Microkinetic modeling is now an important tool for many of the practicing reaction engineers. This approach enables one to formulate and follow the detailed concentration profile for most if not all of the reaction intermediates. 

Several non-catalytic systems have been reported to give good yields of esters. For example, if an equimolar mixture of a carboxylic acid, an alkyl halide and a tertiary amine (most commonly triethylamine) are heated for a few hours at 140 °C, excellent yields of esters are usually obtained. Under these conditions, methylene chloride was found to give methanediol-Z /5-esters [9]. Examples of esters synthesized by this approach are presented in Table 6.2. 

Non-catalytic system (cold-flame combustion) or catalytic system (Sn02)... 

Negligible HCHO formation under non-catalytic system. 

Let us consider as an example leaching of zinc sulfide (sphalerite) with ferric sulfate (Fe(III)) as a model non-catalytic system. Elementary sulfur and ferrous sulfate (Fe(II)) are obtained as products. The overall reaction is given below ... 

It has been proposed that protonation or complex formation at the 2-nitrogen atom of 14 would enhance the polarization of the r,6 -7i system and facilitate the rearrangement leading to new C-C bond formation. The equilibrium between the arylhydrazone and its ene-hydrazine tautomer is continuously promoted to the right by the irreversible rearomatization in stage II of the process. The indolization of arylhydrazones on heating in the presence of (or absence of) solvent under non-catalytic conditions can be rationalized by the formation of the transient intermediate 14 (R = H). Under these thermal conditions, the equilibrium is continuously pushed to the right in favor of indole formation. Some commonly used catalysts in this process are summarized in Table 3.4.1. 

Feed/catalyst injection. A well-designed injection system provides a rapid and uniform vaporization of the liquid feed. This will lower delta coke by minimizing non-catalytic coke deposition as well as reducing the deposits of heavy material on the catalyst. 

A catalytic oxidation system may cost 150 per car, but the catalyst cost is estimated to be 30, less than 1% of the cost of an automobile (2). In a few years, the gross sale of automotive catalysts in dollars may exceed the combined sale of catalysts to the chemical and petroleum industries (3). On the other hand, if the emission laws are relaxed or if the automotive engineers succeed in developing a more economical and reliable non-catalytic solution to emission control, automotive catalysis may turn out to be a short boom. Automotive catalysis is still in its infancy, with tremendous potential for improvement. The innovations of catalytic scientists and engineers in the future will determine whether catalysis is the long term solution to automotive emissions. 

Finally we mention in this section the non-catalytic selective bromination of aniline by the application of a zeolite pre-loaded with Bt2 as a slow release reagent (ref. 27). Aniline, dissolved in CCI4 was treated with Br2 adsorbed onto various zeolites and zeolite CaA was found to be most selective for monosubstitution (92%). The addition of organic bases improved the performance, probably due to scavenging of HBr. Also the toluidines could be monobrominated with this system with >95% selectivity. 

How relevant are these phenomena First, many oscillating reactions exist and play an important role in living matter. Biochemical oscillations and also the inorganic oscillatory Belousov-Zhabotinsky system are very complex reaction networks. Oscillating surface reactions though are much simpler and so offer convenient model systems to investigate the realm of non-equilibrium reactions on a fundamental level. Secondly, as mentioned above, the conditions under which nonlinear effects such as those caused by autocatalytic steps lead to uncontrollable situations, which should be avoided in practice. Hence, some knowledge about the subject is desired. Finally, the application of forced oscillations in some reactions may lead to better performance in favorable situations for example, when a catalytic system alternates between conditions where the catalyst deactivates due to carbon deposition and conditions where this deposit is reacted away. 

Aregioselective catalytic system for the allylic substitution of non-symmetric allyl carbonates by carbon and nitrogen nucleophiles based on [ Bu N][Fe(NO)(CO)3] and PPhj was developed (Scheme 2.26). The high regioselectivity was ascribed to the slow a-allyl- to Jt-aUyl-isomerisation relative to the rate of substitution. However, the use of high excess of the pro-nucleophile and DMF solvent are drawbacks on the atom efficiency and functional group tolerance of the system. 

Scheme 6.13 Mizoroki-Heck reaction of non-activated aryl chlorides and diazo compounds using Seller s catalytic systems...

The Horner-Wittig reaction of a-phosphoryl sulphoxides 442, which are chemically stable, results in the formation of a, -unsaturated sulphoxides 443 in high yields (equation 264). The reaction has been found to be non-stereoselective, mixtures of E and Z isomers being formed from aldehydes and unsymmetrical ketones . In the case of aromatic aldehydes this reaction can also be advantageously performed in a two-phase catalytic system even without the usual PTC catalysts (Table 24). Intramolecular Horner-Wittig reaction of a-phosphoryl-5-oxosulphoxides 444 leads to a, -unsaturated cyclic sulphoxides 445 (equation 265). Starting from optically active 0,0-... 

There are a host of other, non-catalytic applications of TUD-1 possible, for example in the area of sorption. In fact, the successful application of TUD-1 as a controlled release drag delivery system was recently demonstrated (33). 

A catalytic system consisting of cat. Sml2, Zn/Hg, Lil, and Me3SiOTf induces spirolactonization (Scheme 20) [56]. Me3SiOTf plays a similar role in converting the intermediary alkoxides to the silyl ethers. The efficacy of Lil depends on the formation of Sml3 from Sm OTf, which facilitates reduction by Zn/Hg. The Lewis acidity of Zn(II) is reduced by conversion to a non-Lewis-acidic species such as Li2Znl2(OTf)2. 

Catalytic systems (platinum, palladium and nickel) have been investigated as have been non-metal lie reagents. Our results in these areas are also presented. 

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