The structural differences between the four isomers n- butanol, isobutanol, secondary and tertiary butanol are reflected in the intermolecular interactions and the special arrangements. Although there are certain differences, these are but of secondary importance when the various butanols are used as solvents or co-solvents in organic paints. Butanol is normally used in the form of n-butanol, isobutanol or blends of the two.
Both alcohols form azeotropic mixtures with water of which the n-butanol mixture (water content 42 %) will boil at 92,7 °C and isobutanol one (water content 33 %) at 89,8 °C. The azeotropic mixture of secondary butanol and water contains 32 % water and boils at 88,5 °C. The evaporation indices of butanols are less than half as much as those of water. n-butanol and isobutanol show only limited miscibility with water at room temperature and the miscibility limits are notwso very different. At 20 °C the maximum percentage of n-butanol that is water soluble is 7,7 %, that of isobutanol 8,5 %. n-butanol will dissolve a maximum of 20,l % of water, isobutanol l5 % max.
The figures for heat of evaporation are 590,3 and 578,8 kl/kg and 35 °C and 28 °C respectively. There is but little difference in the viscosities of the pure alcohols and the viscosity reducing effect due to the addition of the two isomers to certain paint resin solutions is likewise almost the same. Whether preference is given to one type of butanol rather than to another will usually depend on circumstances.