The synthesis of a number of 3-alkyl and 3-carboxy substituted pyrroles; their chemical polymerisation onto poly(vinylidene fluoride) membranes, and their use as gas sensitive resistors

A number of synthetic pathways to 1-phenylsulphonyl and 1-tosylsulphonyl py rrole have been reviewed and repeated. Two novel methods of producing this pre-cursor to 3-substituted poly(pyrroles) have been developed utilising cr own ether phase transfer reagents or the aprotic solvent dimethylsulphoxide (DMSO). The most effective method of producing 1-phenylsulphonyl pyrrole w as via the reaction of 1-phenyl or p-toluene sulphonamide and 2,5 diethoxyt etrahydrofuran (the Clauson-Kaas method). The method was facile and yielded 81% of a highly pure product. 1-Phenylsulphonyl and 1-tosylsulphonyl pyrrole were utilised as pre-cursors , in the synthesis of a range of 3-substituted pyrroles via Friedel-Crafts acylation reactions. Subsequent de-protection followed by reduction yielded the 3-alkyl substituted pyrrole monomers, whilst, a thallium transposition via the Willgerdot-Kindler reaction yielded the 3-carboxy derivatives whic h were then deprotected to give the 3-carboxy pyrrole monomers or esterifie d to yield the 3-substituted ester analogues. The 3-substituted pyrrole monomers were then polymerised chemically onto po ly(vinylidene fluoride) membranes to yield conducting polymer films. The re sulting 3-substituted polymer films were tested for their gas sensitivity t owards a number of classes of volatile organic compounds (VOCs). The 3-subs tituted polymers were found to exhibit enhanced sensitivity and differing s electivities to the test vapours when compared to poly(pyrrole) alone. The selectivity of the resulting sensors to certain organic vapours could be co ntrolled by altering the substituents on the pyrrole ring, for instance whe re alkyl chains were added the responses of the resulting sensors to non-po lar vapours such as hexane were enhanced. The addition of longer alkyl chai ns to the pyrrole ring resulted in a progressive enhancement in the sensiti vity to non-polar vapours whilst the sensitivity to polar compounds remaine d constant or was reduced. (C) 2000 Elsevier Science S.A. All rights reserv ed.