Homogeneous modification

Bulk materials used as oxidation catalysts not only allow for oxygen transport but also accommodate a wide and homogeneous modification of their electronic... 

The capacity to preconcentrate anions has enabled the use of chitosan and its derivatives in modified electrodes, for application in sensor and biosensor electrochemistry [233]. To facilitate improving water solubility of biologically useful chitosan derivatives, N-methylene phosphonic chitosan has been prepared using a one-step reaction that allowed homogeneous modifications [234]. 

Li, W.Y.J. Liu, A.X. Sun, C.R Zhang, R.C. Kennedy, J.R Homogeneous modification of cellulose with succinic anhydride in ionic liquid using 4-dimethylaminopyridme as acatalyst. Carbohydr. Polym. 

One of the early attempts of in situ activation was the reaction of carboxylic acids with sulphonic acid chlorides that was adopted for the homogeneous modification of cellulose. The exclusion of the base simplified the reaction medium and the isolation procedure [29]. There is an ongoing discussion about the mechanism which initiates esterification of cellulose with the carboxylic acids in the presence of p-toluenesulphonic acid chloride (TosCl). The mixed anhydride of p-toluenesulphonic acid (TosOH) and the carboxylic acid is favoured [30]. However, from H NMR experiments with acetic acid/TosCl, it was concluded that a mixture of acetic anhydride (2.21 ppm) and acetyl chloride (2.73 ppm) was responsible for the high reactivity of this system (Figs 16.2 and 16.3). 

Research of the possibilities of the homogeneous modification of the polymers of other types (e.g., polyamides, polyurethanes, polycarbonates, polyimides, polyesters, etc.) and the examination of their properties and structures... 

Ke, G. 2009. Homogeneous modification of carbon nanotubes with cellulose acetate. Chin. Chem. Lett. 20 1376-1380. 

Mitsui Toatsu Chemical, Inc. disclosed a similar process usiag Raney copper (74) shortiy after the discovery at Dow, and BASF came out with a variation of the copper catalyst ia 1974 (75). Siace 1971 several hundred patents have shown modifications and improvements to this technology, both homogeneous and heterogeneous, and reviews of these processes have been pubHshed (76). Nalco Chemical Company has patented a process based essentially on Raney copper catalyst (77) ia both slurry and fixed-bed reactors and produces acrylamide monomer mainly for internal uses. Other producers ia Europe, besides Dow and American Cyanamid, iaclude AUied CoUoids and Stockhausen, who are beheved to use processes similar to the Raney copper technology of Mitsui Toatsu, and all have captive uses. Acrylamide is also produced ia large quantities ia Japan. Mitsui Toatsu and Mitsubishi are the largest producers, and both are beheved to use Raney copper catalysts ia a fixed bed reactor and to sell iato the merchant market. 

In comparison to heterogeneous catalyzed reactions, homogeneous catalysis offers several important advantages. The catalyst complex is usually well defined and can be rationally optimized by ligand modification. Every metal center can be active in the reaction. The reaction conditions are usually much milder (T usually < 200 °C), and selectivities are often much higher than with heterogeneous catalysts. 

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... 

The maximum principle and, in particular. Theorem 3 in Chapter 1, Section 2 will be quite applicable once we rearrange problem (II) supplied by homogeneous boundary conditions (scheme (16)) with obvious modifications and minor changes. The traditional tool for carrying out this work is connected with... 

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