Stearate salts

Water-Repellent. Three techniques used for water repeUency are modification of cement by the addition of waterproofers, use of repellent additives to the concrete mix, and surface treatment of concrete stmctures with repellents. The modification of portland cement by intergrinding with stearate salts or other water-repellent material can reduce the water permeabiUty of mortar. Considerable controversy exists, however, as to whether these cements produce concrete that is superior to carefully mixed concrete without such additives (79). 

The U. S. Dispensatory26 reports maximum serum levels of 0.2 ijg./ml. 1 hour after administration of a 250 mg. dose, 0.6 (ig./ml. 2 hours after a 500 mg. dose, and 1.2 ug./ml. 2 hours after a 1 g. dose. Higher blood levels are achieved on a multiple dosage schedule. Since it is acid labile, a resistant coating is used in tablet formulations to overcome the deleterious effect of gastric fluid on erythromycin base or the stearate salt is prepared which does not dissolve readily in the stomach. 

Other studies on the influence of tablet excipients on dmg decomposition have identified problems with stearate salts and it has been suggested that these salts should be avoided as tablet lubricants if the active component is subject to hydroxide-ion-catalysed degradation. The degradative effect of the alkali stearates is inhibited in the presence of malic, hexamic or maleic acids owing, it is thought, to competition for the lubricant cation between the dmg and the additive acid. 

The dissolution of solid particles of salts can be inhibited if the parent acid or base precipitates at the surface of the particles undergoing dissolution. For example, stearate salts show reduced dissolution if stearic acid layer precipitates on the surface in an acidic pH environment. 

The possibility of producing slowly dissolving salbutamol salts for delivery to the lung was investigated by preparing its adipic and stearic acid salts (Jashnani et al. 1996). The aqueous solubilities of the adipate and stearate salts were 353 and 0.6 mg/mL, respectively, compared to the free base and sulphate, which had solubilities of 15.7 and 250 mg mL, respectively. In terms of the IDR, the stearate dissolved much more slowly than the other salts and the free base. This was explained as due to the deposition of a stearate-rich layer on the dissolving surface of the compacted salt surface. 

As noted by Jashnani and Byron (1996), in formulation terms, it is always worth optimising the salt form. In this study, the performance comparisons of dry powder aerosol generation in different environments were determined for the sulphate, adipate (diethanolate) and stearate salts of albuterol. Overall, the stearate emptied and aerosolized best from the inhaler and showed the least sensitivity to environmental factors such as temperature and humidity. Another use of low solubility salts is to mask the taste of those compounds with unpleasant taste when delivered by DPI (or pMDI for that matter). By lowering the solubility, and hence dissolution rate, the taste can often be effectively eliminated. 

Figure 112. Relationship between degradation rate and melting point of aspirin in the presence of various stearate salts. (0) No additive (1) 3% Zn salt (2) A1 salt (3) Na salt (4) Ca salt (5) and (8) Mg salt (6) 1% Mg salt (7) 2% Mg salt (9) 5% Mg salt. The values of k were calculated according to the equation [1 - (l-x) ]2 = kt. (Reproduced from Ref. 471 with permission.)...

Another highly water-insoluble moiety which protects erythromycin from acidic decomposition is its acid-addition salt with a highly Upophilic acid. As an example, the stearate salt is a commonly prescribed form of erythromycin [53],... 

Combinations of a 2 -ester and a lipophilic acid-addition salt have also been extensively employed. Erythromycin estolate (2 -propionate, lauryl sulphate salt) has been widely used due to its better oral absorption than other forms of erythromycin [62, 67, 68]. Similar results have been found with erythromycin acistrate (2 -acetate, stearate salt) [69, 70], which is reported to be less hepatotoxic in animals than other forms of erythromycin [71], Two salts of 2 -propionylerythromycin,A-acetyIcysteinate (erythromycin stinoprate) and mercaptosuccinate, are being investigated as combinations of an antimicrobial and mucolytic agent [72-74],... 

Detailed analyses of the temperature dependence of X-ray diffraction patterns of alkali stearate salts in water have allowed rather complex phase diagrams to be constructed [63]. An example involving potassium stearate (KS), based on samples cooled from 373 K but not annealed at subambient temperatures, is shown in Figure 1.7. The lowest temperature dotted line represents the separation between the coagel phase (solid soap particles (C) dispersed in water (E)) and tempera-tures/compositions at which various gel phases (G) can exist or coexist with a solid. Between 303 and c. 316K and at 30 wt% of KS, a stable transparent gel (G) is observed. The L (neat) phase consists of bilayer sheets (lamellae) of KS molecules whose alkyl chains are melted and separated by aqueous layers whose average thickness depends upon the phase composition. The M (middle) phase is composed of... 

Cholestyramine resin in the form of glycocholate or taurocholate salts did not inhibit cholesterol rise in plasma in cholesterol-fed cockerels (22), presumably because these forms of resin were already saturated with bile acids and could not take up more. The stearate salts of cholestyramine resins, however, were fully active. The therapeutic effectiveness of the resin depends on the selectivity between the bile salt anions and the chloride anion as well as the capacity for the organic ion. Studies have therefore been made (18, 19) to determine the separation factors for these ions on various resins in order to investigate some of the properties of the resin that are responsible for the high affinity of the large organic ions for the ion-exchange resins. Since the number of equivalents of cholate anion bound were equal to the number of equivalents of chloride ion released by the resin, within the limits... 

The most widely used surface modification is treatment with stearic acid. This is believed to result in a stearate salt coating on most fillers and metal stearates are also used. Stearic acid will react with basic minerals to give a surface that is covered with strongly bonded long organic ions (this is discussed in more detail in Chapter 4). Stearic acid-modified silicates are commercially available but in these cases the stearic acid is almost... 

Methanol Ethylene Ethylene / vinylacetate Amide slip agent, stearate salts Sodium acetate residue... 

More polar additives antioxidants, stabilizers Polar additives amide slip agents, surfactants, carboxylates (stearate salts)... 

Stearic acid reacts to form stearate as shown above, and such coatings can also be applied as stearate salts. The use of salts has been shown to have favourable effects on compound properties. For example, when magnesium stearate is used as an alternative to stearic acid for coating magnesium hydroxide, tensile and impact properties (measured using an instrumented drop weight impact tester) are both improved as shown in Table 1. 

Catalysts used in commercial PO products include complexes of unsaturated fatty acids and stearate salts of a transition metal such as iron or manganese. In the presence of light or at elevated temperatures transition metal fatty acid complexes generate free radicals that carry out chain scission of PO. 

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