Stearic acid, stearate absorption

Infrared evidence for the formation of an acid-soap complex is, of course, most cogent for the species existing in phase 2, where the main absorption band of the C=0 group centers at a frequency different from that of either of the two constituents. Similar absorption at 6.1 microns for the 1 to 1 sodium stearate-stearic acid complex had been observed by one of us (S. G.). Some of the acid-soaps show a complete absence of the 6.4-micron absorption band (Table II). It is therefore likely that this band in the spectra of the other acid-soaps results from the presence of a small amount of unreacted soap which has very strong absorption at this frequency. On the other hand, acid-soaps in the 1 (or 3) phase are seldom completely free of 6.1-micron absorbing material—i.e., phase... 

Erythromycin (XX) is labile at pH values below pH 4, and hence is unstable in the stomach contents. Erythromycin stearate (the salt of the tertiary aliphatic amine and stearic acid), being less soluble, is not as susceptible to degradation. The salt dissociates in the intestine to yield the free base, which is absorbed. There are differences in the absorption behaviour of the erythromycin salts and differences in toxicity, which may be related to their aqueous solubilities. Erythromycin ethylsuccinate was originally developed for paediatric use because its low water solubility and relative tastelessness were suited to paediatric formulations. The soluble lactobionate is used in intravenous infusions. 

Barany E et al. have studied the influence of stearic acid and several stearates, as emulsifiers in eream, on normal as well as on irritated skin [3]. Their results highlighted the possibility of absorption of these emulsifiers into the lipid bilayer, which increased trans-epidermal water loss (TEWL) in normal skin and decreased TEWL in damaged skin. 

Calcium carbonate can be mixed with 0.5 to 1% by weight of stearic acid and subjected to high shear mixing at high temperatures. The stearic acid is converted to calcium stearate in the process. The treatment improves the processability, reduces moisture absorption, and improves the mechanical and electrical properties of the filled polymer. 

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