Structure and Thermal Behavior of Dissolved Water in Saturated and Unsaturated Esters Studied by FT-IR Spectroscopy

Kyo TAKAOKA*, Koichi KOBAYASHI, Masashi TAKAHASHI and Mototaka SONE†

Department of Energy Science and Engineering, Faculty of Engineering, Musashi Institute of Technology; 1-28-1 Tamazutumi, Setagaya-ku, Tokyo 158-8557 Japan
† Department of Electrical and Electronics Engineering, Faculty of Engineering, Musashi Institute ofTechnology; 1-28-1 Tamazutumi, Setagaya-ku, Tokyo 158-8557 Japan

The state of dissolved water in esters such as butyl acetate(BAc), t-butyl acetate(TBAc), ethyl hexanoate(EH), hexyl acetate(HAc), 2-hexenyl acetate(2HEAc), methyl decanoate(MD), methyl 10-undecenoate(MU), methyl linoleate(ML) and dioctyl phthalate(DOP) were studied by FT-IR spectroscopy and examination was also made of thermal stability of these water clusters in such esters.
The water clusters formed by interaction between the ester and water molecule, and consisted of the small ctusters(C1, C2 and C3) and the large clusters(LC1, LC2 and LC3). The C1(dimer and trimer) were formed in the free volume among hydrophobic groups(alkyl and allyl group). The C2 due to the hydrogen bond by interaction between the carbonyl group and water molecule, and the C3 were formed by interaction between the ether group and water molecule.
In TBAc, the magnitude of the size of Cl, as compared with clusters in BAc, was miniaturized but the amount of C2, LC1 and LC2 were increased.
The amount of dissolved water in esters decreased in the following order. 2HEAc>HAc>EH. In 2HEAc, the amount and the magnitude of the size of clusters increased by the interaction of the double bond of acyl group and water molecule.
In MU, ML and DOP, the clusters were changed under the influence of the carbon number of alkyl group, allyl group and double bond. The amount and themagnitude of the size of clusters incresed by the interaction of water molecule and double bond(allyl group).
In the range from 40 to 80 °C, the Cl disappeared by vaporization of the water molecules. The LC2 and the LC3 in the dissolved water were gradually ruptured into smaller cluster with increasing temperature, but a little remaindat 180 °C. The water molecules produced by thermal decomposition of large clusters recombined with anhydrous ester in the process of diffusion and vaporization in the ester.


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