Wash Powder High Performance

It is extremely important that the solvents be very dry to achieve high yields of products. We have found that the sodium benzophenone ketyl is best for this purpose. In addition, the benzophenone (Fischer) is ground to a fine powder, dried in vacuo for at least 48 h, and stored in a dry box for use. Ru3(CO)12 is prepared by a published procedure.4 Os3(CO) 2 is used as received. Metallic potassium (Mallinckrodt) in mineral oil is washed with hexane and stored in a controlled atmosphere box. All manipulations are performed either in an atmosphere of prepurified nitrogen or under a vacuum using standard techniques.4... 

Polyterpene resins are related to the oldest reported polymerization, as they were first observed in 1789 by Bishop Watson by treatment of turpentine with sulfuric acid [92]. Commercial polyterpene resins are synthesized by cationic polymerization of /3- and a-pinenes extracted from turpentine, of rf,/-limonene (dipentene) derived from kraft-paper manufacture, and of d-limonene extracted from citrus peels as a by-product of juice industry [1,80,82,93]. The batch or continuous processes are similar for the three monomers. The solution polymerization is generally performed in mixed xylenes or high boiling aromatic solvent, at 30-55° C, with AlCl3-adventi-tious water initiation. The purified feedstream (72-95% purity, depending on monomer) is mixed in the reactor with solvent and powdered A1C13 (2—4 wt% with respect to monomer), and then stirred for 30-60 min. After completion of the reaction, the catalyst is deactivated by hydrolysis, and evolved HC1 is eliminated by alkaline aqueous washes. The organic solution is then dried, and the solvent is separated from the resin by distillation. 

A much more environmentally sound procedure was advocated by Paul et al. [164], who used Zn powder as a catalyst for Friedel-Crafts acylation of aromatic compounds. Zinc is a nontoxic, safe, and inexpensive metal which can be used in solvent-free conditions. It was shown to have a remarkably high activity in the acylation of a series of aromatic compounds with acetyl and benzoyl chlorides when performed under microwave irradiation. Yields were much more better than when using conventional thermal heating (Eq. (80), Table 4.28). The Zn powder could also be re-used up to six times after simple washing with diethyl ether and dilute HCl. 

Conversion of chitin into chitosan involves the deacetylation process, which is a harsh treatment usually performed with concentrated sodium hydroxide solution. Chitin flakes are treated in suspension with aqueous 40-50% caustic solution at 80-120°C with constant stirring for 4-6 h and this treatment is repeated once or more than once for obtaining high-amino-content product. To avoid depolymerization due to oxidation, sodium borohydrate is added. Excess alkali is drained off and the mixture is washed with water several times until it is free from alkali. Most of the alkali is then used either in deproteinization or in deacetylation. Excess water is removed in screw press and the wet chitosan cake is either sun dries or in drier at 60°C. Chitosan thus obtained is in the form of flakes and can be pulverized to powder. The flowchart for the manufacture of chitosan from the starting material (crustacean shells) is shown in Fig. 19.5. 

The procedure of grinding and sieving is cumbersome, and it causes a substantial loss of useful polymer, that can be estimated between 50% and 75 % of the initial amount of bulk material. Most of the lost polymer is very fine sub-micrometric powder, which could adhere to the bigger particles and cause excessively high back pressures in the column during and after the packing procedure if multiple washings and careful sedimentation of the polymer are not performed. 

---