M. Malik, J.A. Joens / Spectrochimica Acta Part A 56 (2000) 2653–2658
2657
RꢀCHO+nH2O RCH(OH)2+(n−1)H2O
(7)
and that DS$ −n (25 J (mole K)−1) for reac-
tion. Assuming this is correct then four water
molecules are involved in the hydration of each
carbonyl group in gluteraldehyde. The enthalpy
change for gluteraldehyde hydration is 8–10 kJ
(mole)−1 larger in magnitude than that observed
for the aliphatic aldehydes listed above. The dif-
ference may be due to the presence of a second
carbonyl group in gluteraldehyde, which makes
the R group attached to the aldehyde less electron
donating than the corresponding R group in the
aliphatic aldehydes, thereby favoring hydration.
Fig. 3. Plot of In K versus 1/T for gluteraldehyde. K is found
using Eq. (6), with I0 and I(T) determined as discussed in the
text.
The above analysis is based on the assumption
that hydration occurs independently at the two
carbonyl groups in gluteraldehyde. Three argu-
ments supporting this assumption can be given
based on the results of the data analysis. First, the
error in the slope in the van’t Hoff plot for the
gluteraldehyde data is approximately the same as
observed previously in the analysis of data for
aliphatic aldehydes, where only one carbonyl
group is present. Second, there is no systematic
curvature in the van’t Hoff plot as would be
expected if hydration of one carbonyl group af-
fected the hydration of the second carbonyl
group. Finally, the value for I0 found for the
gluteraldehyde data is about twice that found for
aliphatic aldehydes, where I0 fall in the range
3.0–3.6. This is as expected if the concentration of
independent carbonyl groups in gluteraldehyde is
twice the concentration of gluteraldehyde
molecules.
The thermodynamic data for hydration of
gluteraldehyde can be compared with that previ-
ously obtained for hydration of aliphatic alde-
hydes [8,9]. The entropy change for hydration of
gluteraldehyde is approximately the same as that
found for the larger aldehydes such as n-
butryaldehyde (−9698 J (mole K)−1), isobu-
tyraldehyde (−9597 J (mole K)−1), n-pentanal
(−8797 J (mole K)−1) and n-hexanal (−9198
J mole K)−1). Buschmann and coworkers [26]
have suggested that the aldehyde hydration reac-
tion should be written as:
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