Solubility and swelling of alkali soaps in organic solvents

Abstract

1. 1. The ideal solubility curve of sodium palmitate has been calculated from published heat of transition data. The solubility curves of sodium palmitate in hydroxylic solvents were then found to approach the ideal curve fairly closely, whereas the high degree of nonideality of the solution of soda soap in hydrocarbons became quite conspicuous. 2. 2. The swelling of lithium, sodium, and potassium soap crystals in various organic solvents was measured microscopically. It was found that sodium stearate crystals dissolve or disintegrate but do not swell in hydroxylic solvents at temperatures above 80°C., swell slightly in aliphatic hydrocarbons and high-boiling aliphatic esters, and swell considerably in aromatic hydrocarbons. The degree of swelling at a given temperature and in 1,1-diphenylethane (the strongest swelling agent found) increases continuously from sodium laurate to stearate, decreases as double bonds and hydroxyl groups are introduced into the fatty acid radical, and is much smaller for lithium and potassium stearates than for sodium stearate. All of the observed swelling data could be correlated with the sum of the heats of transition up to the temperature at which the swelling is measured: the larger Σ t Δ H i , the greater the extent of swelling. Swelling of soaps in solvents is thus due to the thermal loosening of the crystal lattice.