Structure and thermal behavior of dissolved water in saturated and unsaturated esters studied by FT-IR spectroscopy

The state of dissolved water in esters such as butyl acetate (BAc), t-butyl acetate (TBAc), ethyl hexanoate (EH), hexyl acetate(HAc), 2-hexenyl acetat e (2HEAc), methyl decanoate (MD), methyl 10-undecenoate(MU), methyl linolea te(ML) and dioctyl phthalate(DOP) were studied by FT-IR spectroscopy and ex amination was also made of thermal stability of these water clusters in suc h esters. The water clusters formed by interaction between the ester and water molecu le, and consisted of the small clusters (C1, C2 and C3) and the large clust ers (LC1, LC2 and LC3). The C1 (dimer and trimer) were formed in the free v olume among hydrophobic groups(alkyl and allyl group). The C2 due to the hy drogen bond by interaction between the carbonyl group and water molecule, a nd the C3 were formed by interaction between the ether group and water mole cule. In TBAc, the magnitude of the size of C1, as compared with clusters in BAc, was miniaturized but the amount of C2, LC1 and LC2 were increased. The amount of dissolved water in eaters decreased in the following order. 2 HEAc > HAc > EH. In 2HEAc, the amount and the magnitude of the size of clus ters increased by the interaction of the double bond of acyl group and wate r molecule. In MU, ML and DOP, the clusters were changed under the influence of the car bon number of alkyl group, allyl group and double bond. The amount and the magnitude of the size of clusters increased by the interaction of water mol ecule and double bond (allyl group). In the range from 40 to 80 degrees C, the CI disappeared by vaporization of the water molecules. The LC2 and the LC3 in the dissolved water were gradu ally ruptured into smaller cluster with increasing temperature, but a littl e remaindat 180 degrees C. The water molecules produced by thermal decompos ition of large clusters recombined with anhydrous ester in the process of d iffusion and vaporization in the eater.