- Title
- An ATR-FTIR study on the effect of molecular structural variations on the CO₂ absorption characteristics of Heterocyclic Amines: part II
- Creator
- Robinson, Kelly; McCluskey, Adam; Attalla, Moetaz I.
- Relation
- Chemphyschem Vol. 13, Issue 9, p. 2331-2341
- Publisher Link
- http://dx.doi.org/10.1002/cphc.201200066
- Publisher
- Wiley Blackwell
- Resource Type
- journal article
- Date
- 2012
- Description
- This paper reports on an ATR-FTIR spectroscopic investigation of the CO₂ absorption characteristics of a series of heterocyclic diamines: hexahydropyrimidine (HHPY), 2-methyl and 2,2-dimethylhexahydropyrimidine (MHHPY and DMHHPY), hexahydropyridazine (HHPZ), piperazine (PZ) and 2,5- and 2,6-dimethylpiperazine (2,6-DMPZ and 2,5-DMPZ). By using in situ ATR-FTIR the structure–activity relationship of the reaction between heterocyclic diamines and CO₂ is probed. PZ forms a hydrolysis-resistant carbamate derivative, while HHPY forms a more labile carbamate species with increased susceptibility to hydrolysis, particularly at higher CO₂ loadings (>0.5 mol CO₂/mol amine). HHPY exhibits similar reactivity toward CO₂ to PZ, but with improved aqueous solubility. The α-methyl-substituted MHHPY favours HCO₃− formation, but MHHPY exhibits comparable CO₂ absorption capacity to conventional amines MEA and DEA. MHHPY show improved reactivity compared to the conventional α-methyl-substituted primary amine 2-amino-2-methyl-1-propanol. DMHHPY is representative of blended amine systems, and its reactivity highlights the advantages of such systems. HHPZ is relatively unreactive towards CO₂. The CO₂ absorption capacity CA (mol CO2/mol amine) and initial rates of absorption RIA (mol CO₂/mol amine min−1) for each reactive diamine are determined: PZ: CA =0.92, RIA=0.045; 2,6-DMPZ: CA =0.86, RIA=0.025; 2,5-DMPZ: CA =0.88, RIA=0.018; HHPY: CA =0.85, RIA=0.032; MHHPY: CA =0.86, RIA=0.018; DMHHPY: CA =1.1, RIA=0.032; and HHPZ: no reaction. Calculations at the B3LYP/6-31+G** and MP2/6-31+G** calculations show that the substitution patterns of the heterocyclic diamines affect carbamate stability, which influences hydrolysis rates.
- Subject
- absorption; amines; carbon dioxide fixation; IR spectroscopy; nitrogen heterocycles
- Identifier
- http://hdl.handle.net/1959.13/1311410
- Identifier
- uon:22205
- Identifier
- ISSN:1439-4235
- Language
- eng
- Full Text
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