In-situ ATR FT-IR spectroscopy has been used to investigate the reaction between CO 2 and piperidine, as well as commercially available functionalised piperdine derivatives, e.g., those with methyl-, hydroxyl-, and hydroxyalkyl-substituents. The effect of the substituent's on CO 2 absorption has been assessed in relation to the prevalent IR identifiable ionic reaction products, along with CO 2 absorption capacity and initial absorption rate. The results obtained highlight the enhanced

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... of cyclic 2°amines compared to conventional 1°and 2°amines, MEA and DEA respectively. Formation of the COOderivatives of the 3-and 4-hydroxyl and hydroxyalkyl substituted piperidines were found to be kinetically less favourable than that of piperidine and the 3 and 4 -methyl substituted piperdines. As the CO 2 loading of piperidine and the 3-and 4-substituted piperidines exceeded 0.5 mol CO 2 / mol amine, hydrolysis of their COOderivative was observable in the IR spectral profiles. From the subset of amines analysed the 2-alkyl and 2-hydroxyalkyl substituted piperidines were found to favour HCO 3 formation. Despite forming predominantly HCO 3 these amines also exhibited initial absorption rates comparable to that of MEA and DEA, 2-MP in particular was found to exhibit a significantly higher initial absorption rate. Computational calculations at the B3LYP/6-31+G** and MP2/6-31+G** level of theory revealed that for the 2alkyl and hydroxyalkyl substituted piperidines a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area on the nitrogen atom will play a role in destabilising the COOderivative and increasing its susceptibility to hydrolysis.