Catalyst-solvent systems

An interesting situation is obtained when the catalyst-solvent system is such that the initiator is essentially 100% dissociated before monomer is added and no termination or transfer reactions occur. In this case all chain initiation occurs rapidly when monomer is added, since no time-dependent initiator breakdown is required. If the initial concentration of catalyst is [AB]o,then chain growth starts simultaneously at [B"]q centers per unit volume. The rate of polymerization is given by the analog of Eq. (6.24) ... 

The use of multiple otherwise incompatible catalysts allows multistep reactions to proceed in one reaction vessel, providing many potential benefits. In this chapter, literature examples of nanoencapsulation for the purpose of process intensification have been discussed comprehensively. Current efforts in the literature are mostly concentrated in the areas of LbL template-based nanoencapsulation and sol-gel immobilization. Other cascade reactions (without the use of nanoencapsulation) that allow the use of incompatible catalysts were also examined and showcased as potential targets for nanoencapsulation approaches. Finally, different methods for nanoencapsulation were investigated, thereby suggesting potential ways forward for cascade reactions that use incompatible catalysts, solvent systems, or simply incompatible reaction conditions. 

Catalyst Solvent System PT Agent Time (min) Conversion (%)... 

Rather unexpectedly, the reaction product of alkenylzirconocene chlorides can be alkylated with primary alkyl bromides under the influence of a catalyst-solvent system consisting of 2.5% Pd(acac)2, 2 equiv. LiBr and 1 1 THF-NMP without any phosphine and NMI used above881 (Scheme 77). 

Cubic BN is usually manufactured at about 5 GPa and 1500°C from a mixture of graphitic hexagonal BN and a catalyst solvent such as lithium or magnesium nitride. Many other catalyst solvent systems have been found and most of them involve a nitride-forming element. As pressure and temperature increase, the catalyst requirements relax as with carbon. 

In the investigation of catalyst-solvent systems it was found that not only tertiary amines but also N N-disubstituted amides such as dimethyl acetamide (3) or hexamethyl phosphortriamide (HPT) yield catalytically active cupric-cuprous complexes. Some results obtained with these catalysts are shown in Table II. 

Description Polymer-grade ethylene is oligomerized in the liquid-phase reactor (1) with a catalyst/solvent system designed for high activity and selectivity. Liquid effluent and spent catalyst are then separated (2) the liquid is distilled (3) for recycling unreacted ethylene to the reactor, then fractionated (4) into high-purity alpha-olefins. Spent catalyst is treated to remove volatile hydrocarbons and recovered. The table below illustrates the superior purities attainable (wt%) with the Alpha-Select process ... 

Under standard Koch-Haaf conditions, 1,5-cyclooctadiene is converted via cation 43 to the thermodynamically favored tertiary system 44 which is captured to deliver carboxylic acid 45.10 71 When a hydrogen fluoride catalyst solvent system is utilized, however, the 2-carboxylic acid is formed instead.72 ... 

Cathodic reduction of organic dihalides using a Co(II)-salen complex in [bmim] [BF4] (bmim = l-benzyl-3-methylimidazolium) was carried out successfully to give the corresponding dehalogenated compounds [8], The catalyst-solvent system was readily recycled with little loss of reactivity. 

The same authors later expanded the concept and additionaly provided an imidazolium-tagged Howeyda-Grubbs ruthenium carbene catalyst for the RCM reaction [260]. The resulting system proved to be highly active for the conversion of di-, tri- and tetrasubstituted diene and enyne substrates. In the catalyst solvent system [BMIM][PF6]-CH2Cl2 (volume ratios 1 1 to 1 9) the catalyst could be recycled 17 times with only very slight loss in activity. Also in this work it was demonstrated that the imidazolium tag is essential to obtain a stable and recycleable catalyst. 

Two distinct approaches have been adopted (a) the chemical attachment or tethering of the original catalytic species to a support material (applied mainly to reactions in the liquid phase), and (b) the physical absorption of the original soluble catalyst/solvent system into an inert porous material (applicable solely to gas-phase reactants and products). 

Parkin B.A., SchiiUer W.H., Catalyst-solvent systems for dimerization of abietic acid and rosin, Ind. Eng. Chem. Prod. Res. Develop., 11(2), 1972, 156-158. 

The Ni(II) complex of the perfluorinated )8-diketone, C7F15COCHCOC7F15 actively catalyzed the oxidation of a variety of aldehydes to the corresponding carboxylic acids (248) with high jdeld vmder mild conditions (Scheme 49). The solvent used was made of perfluorodecalin and toluene, and the catalyst was recycled several times in the fluorous phase vsrith only a negligible loss of activity. The same catalyst/solvent system was also used for the oxidation of sulfides to sulfones and sulfoxides (Scheme 49). Addition of 2-methylpropanal to this reaction system led to the in situ generation of a peracid, which resulted in high product yields. 

A catalyst—solvent system containing a PIL and HCI or two PILs was used for the chlorination of arene compounds to replace conventional Lewis acid catalysts. The PILs trialed were [HMImJNOs and [HMImJCI. The best selectivity was obtained using [HMImJNOs with HCI, with 99% conversion and 96% selectivity toward the monochloro derivative after 48 h. The nitrate anion was determined to be involved in the reaction, with the IL being reformed afterward and being reusable. 

---