The synthesis of ferrocenyl esters has been achieved using the DCC/DMAP protocol in the ambient temperature ionic liquids 1-butyl-3-methylimidazonium tetrafluoroborate ([bmim][BF 4 ]) and 1-butyl-3-methylimidazonium hexafluorophosphate ([bmim] [PF 6 ]). Yields are very high and efficient recycling of solvent was achieved. IntroductionThe synthesis of the ester functional group using the DCC/ DMAP methodology is widely popular in organic synthesis. 1 It allows for the introduction of the ester functional group under mild conditions and without the use of air-sensitive acid chlorides. The protocol has found widespread use in our group in the synthesis of liquid crystal molecules. 2 The usual solvent for carrying out this type of reaction is anhydrous dichloromethane. With the current desire to avoid the use of chlorinated molecular solvents in chemistry, we decided to investigate the use of potentially cleaner solvents, namely 1-butyl-3-methylimidazonium tetrafluoroborate [bmim][BF 4 ] 1 and 1-butyl-3-methylimidazonium hexafluorophosphate [bmim][PF 6 ] 2 for DCC/DMAP promoted esterifications.Ionic liquids, especially imidazonium salts, are currently receiving a lot of attention in chemistry and have already proved to be useful solvents in organic synthesis. Some of the reactions already successfully carried out in imidazonium salts include Diels-Alder, 3 Wittig, 4 the Suzuki cross-coupling, 5 Heck, 6 oxidations, 7 reductions, 8 and hydrogenations. 9 Results and discussionThe results of the reactions of ferrocenemonocarboxylic acid with a range of substituted phenols in the presence of DCC/ DMAP and ionic liquid ([bmim] [BF 4 ] or [bmim][PF 6 ]) are provided in Table 1. The isolated yields of the ester products are in all cases very good. Small quantities of unreacted ferrocenemonocarboxylic acid were also isolated. One of the primary aims of our study was to investigate the recycling of the ionic liquid and this is clearly important in the context of economic feasibility and sustainable development.The reaction of ferrocenemonocarboxylic acid and 4-methoxyphenol in [bmim] [BF 4 ] in the presence of DCC/DMAP was repeated in the same batch of ionic liquid over five runs and the results are provided in Table 2. The yield of the ester product is consistently high. In each reaction, N,NA-dicyclohexylurea (DCU) formed as a by-product. This remained in the ionic liquid after ether extraction and did not interfere with subsequent reactions. No reaction was observed between ferrocenemonocarboxylic acid and 4-methoxyphenol in [bmim] [BF 4 ] in the absence of DCC. The results presented in Table 1 apart from those in entries 3 and 4 are based on reaction times of 24 h. The 24 h reaction period is normally used for DCC/DMAP promoted esterifications in CH 2 Cl 2 . To investigate the potential effect of the ionic liquid on reaction rate, the reaction of ferrocenemonocarboxylic acid and 4-methoxyphenol was carried out for 3 and 6 h. After 3 h (Table 1, entry 3), the yield of the ester was very low and it was difficult to purif...

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