Surfactants, alkyl pyrrole

An enantioselective alkylation of pyrrole with enones has been reported <05JA4154>. For example, treatment of V-methylpyrrole 59 with enone 60 in the presence of a catalytic amount (10 mol%) of bis(oxazoline) catalyst 61 provided chiral adduct 62. Different additives including iodine <05T11751> and an aluminum surfactant <05CC789> have been utilized to mediate the Michael addition of pyrroles to p-nitrostyrenes. 

From the same laboratory, another report48 describes the use of this approach to prepare PPy/poly(alkyl methacrylate). In this case, a chloroform solution of poly(alkyl methacrylate) and pyrrole is dispersed in an aqueous surfactant solution whereupon the oxidant is added. The PPy deposits on the host polymer, and again a nonsolvent is used to precipitate the composite. The composites can then be hot-pressed to obtain films or other objects. Compared to cold pressing, hot pressing improves the mechanical properties but decreases the conductivities. In the hot-pressed materials, a distinct PPy phase could not be observed. 

Emulsion polymerization of pyrrole was also used to prepare blends of polypyrrole with a poly(alkyl methacrylate) [95]. A chloroform solution of a poly-(alkyl acrylate) and pyrrole was dispersed in an aqueous surfactant solution generating an emulsion. An aqueous solution of an oxidant was added to the emulsion with stirring, polymerizing pyrrole. The precipitated blend could be hot pressed in the form of films with conductivities of 6-7Scm . The curve for the variation of the conductivity of the blend with the oxidant/pyrrole ratio shows a maximum at a ratio of two with subsequent decrease. However, the yield increases to nearly 100% up to a ratio of four. The percolation threshold is approximately 10 wt% of pyrrole. The type and the concentration of the surfactant also affect the yield and conductivity. The mechanical properties of the blend depends on the number of carbons in the alkyl chain of the insulating polymer host. The strain at break of hot-pressed films increases and the stress at break decreases in the direction methyl, ethyl, butyl (Figure 18.3). This is an example where the mechanical properties of the conductive blend could be tailored according to the alkyl substituent in the poly(alkyl methacrylate) used in its preparation. 

The reaction of 5-alkyl/arylamino-6-chloropyrazine-2,3-carbonitriles 37 with phenylacetylene 18, catalyzed by Pd-Cu, in the presence of sodium lauryl sulfate as a surfactant in water leads to the formation of highly substituted pyrazino-pyrroles 38 in good to high yields (Scheme 12) [43]. This palladium-catalyzed heteroannulation reaction... 

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