POLYMERIC REDUCING AGENT

Poly(4-vinylpyridine) boran has b n used as a reducing agent for carbonyl compounds This polymeric reducing agent was prepared by the reaction of poly(4-vinylpyridinium hydrochloride) with sodium borohydride. 

If the chiral amino alcohol is incorporated into polystyrene, a chiral polymeric reducing agent is obtained. Acetophenone O-methyloxime was reduced by such a polymeric borane complex to give optically active 1-phenylethylamine with 99% ee35 36 With borane-tetrahydrofuran and 1 mol% of the chiral amino alcohol (lS,3S,5S)-(a,a-diphenyl)hydroxymethyl-2-azabicy-clo[3.3.0]octane (7), (7 )-1-phenylethylamine can be synthesized from acetophenone O-methyloxime in 64% yield with 17% ee37. 

An unusual synthetic application of a soluble macromolecular reducing reagent described by Smith is the use of aqueous solutions of hydrazonium polyacrylate or hydrazonium poly[2-(acryl-amido)-2-methylpropanesulfonate] to prepare stable colloidal dispersions of red, amorphous selenium. (34). In these reactions, the solutions were prepared sufficiently dilute so that each macromolecular hydrazonium polyacrylate could react individually. When a solution of H2Se02 was added to this polymeric reducing agent, the selenious acid molecules in the... 

Figure 4 The 17-P-sterol acrylate ester template 6, used by Bystom et al. (Ref. 9) to prepare regio- and stereo-selective polymeric reducing agents for the diketone 7.

Just as the use of a surfactant salt of triethylborohydride introduces both the reducing agent and the stabilizer as a single reagent, [62] polymeric reducing agents can be used which also can function as a polymeric staUlizer. Examples include the use of polyethyleneimine in the preparation of colloidal silver. [70, 71]... 

Tiianium(III) chloride, TiClj. Violet or brown solid (TiCU plus H3 at 700°C TiCU plus AIR3 (brown form)). Forms violet 6 hydrate. Used as a reducing agent. The fibrous brown form is an active agent in the Ziegler-Natta siereoregular polymerization of olefines. 

Benzoyl peroxide Direct sunlight, sparks and open flames, shock and friction, acids, alcohols, amines, ethers, reducing agents, polymerization catalysts, metallic naph-thenates... 

Water-soluble peroxide salts, such as ammonium or sodium persulfate, are the usual initiators. The initiating species is the sulfate radical anion generated from either the thermal or redox cleavage of the persulfate anion. The thermal dissociation of the persulfate anion, which is a first-order process at constant temperature (106), can be greatly accelerated by the addition of certain reducing agents or small amounts of polyvalent metal salts, or both (87). By using redox initiator systems, rapid polymerizations are possible at much lower temperatures (25—60°C) than are practical with a thermally initiated system (75—90°C). 

Hydroperoxides are generally used with reducing agents, eg, iron salts, in redox emulsion polymerization systems. 

Simplified nitrile mbber polymerization recipes are shown in Table 2 for "cold" and "hot" polymerization. Typically, cold polymerization is carried out at 5°C and hot at 30°C. The original technology for emulsion polymerization was similar to the 30°C recipe, and the redox initiator system that allowed polymerization at lower temperature was developed shortiy after World War II. The latter uses a reducing agent to activate the hydroperoxide initiator and soluble iron to reactivate the system by a reduction—oxidation mechanism as the iron cycles between its ferrous and ferric states. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Aluminum, copper, brass, lead, zinc salts, mineral acids, oxidizing or reducing agents all can cause rapid decomposition Stability During Transport Unstable, slowly evolves oxygen Inhibitor of Polymerization Not pertinent.. 

As we have mentioned previously, 1,3-diketone and anilide were very effective reducing agents for vinyl polymerization initiated by ceric ion, respectively. Acetoacet-anilide (AAA), a compound having a 1,3-diketone and an anilide structure as well ... 

---