Suspension agents secondary

Polyvinyl alcohols (PVAl) are manufactured by saponification of vinyl acetate polymers (PVAc). Properties of PVC using PVAl as a protective colloid are influenced by the solution viscosity of the PVAl, i.e. the degree of polymerization of the PVAc and the degree of saponification. Polyvinyl alcohols of 75-90% hydrolysis are primary suspension agents for S-PVC, whereas polyvinyl alcohols of 25-40% hydrolysis are secondary suspension agents, which control the agglomeration of the primary particles. Partially hydrolyzed PVAc can be block or random polymers. 

Rate of complex formation between chiral alcohols and DBTA monohydrate in hexane suspension is quite slow (see Figure 1) and numerous separation steps are necessarry for isolation of the alcohol isomers (filtration of the diastereoisomeric complex then concentration of the solution, decomposition of the complex, separation of the resolving agent and the enantiomer, distillation of the product). To avoid these problems, alternative methods have been developed for complex forming resolution of secondary alcohols. In a very first example of solid phase one pot resolution [40] the number of separation steps was decreased radically. Another novel method [41] let us to increase the rate of complex forming reaction in melt. Finally, first examples of the application of supercritical fluids for enantiomer separation from a mixture of diastereoisomeric complexes and free enantiomers [42, 43] are discussed in this subchapter. 

Alkaline reducing agents are usually recommended for reduction of ketones to secondary alcohols since pinacones are formed preferentially in an acid medium. Sodium in alcohol or in moist ether or benzene, sodium amalgam, and zinc dust in sodium hydroxide solution, etc., are often used for this purpose. 2-Heptanol, for example, is formed in good yield on addition of sodium to an aqueous-alcoholic solution of methyl w-pentyl ketone.306 Reduction is also often carried out by adding sodium to an aqueous-ethereal suspension but by this method the double bond of unsaturated ketones is also partially reduced. 

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