Hygroscopicity characterization

Hygroscopic (moisture) effects arise for polymer materials such as some epoxies that absorb moisture chemically after curing and therefore expand. These effects are directly analogous to thermal effects and are characterized by coefficients of moisture expansion and p2 in principal material coordinates in direct analogy to a.( and 02 for coefficients of thermal expansion. All calculations for thermal effects with the a can be replaced by or supplemented with analogous terms for moisture expansion. 

It is, therefore, required that all initial compounds be dried properly prior to performing the reduction. This procedure is not at all trivial and refers, first of all, to the diluent salts, and especially to potassium fluoride, KF, which is characterized by a strong hygroscopic property and a tendency to form stable crystal hydrates. The problem of contamination due to hydrolytic processes can usually be resolved in two manners. The first is to apply another tantalum-containing complex fluoride compound that does not undergo hydrolysis. The second involves the adjustment of the reduction process parameters and use of some additives that will "collect" the oxygen present, in the form of water, hydroxyl groups or other compounds. 

Complete characterization of arylboronic acids is often difficult because they are readily transformed into stable cyclic anhydrides called boroxines5 and other polymeric species. Arylboronic acids are also known to be hygroscopic. Thus, arylboronic acids are often prepared and used directly as a mixture of different entities. Commercial arylboronic acids will very often contain varying amount of anhydrides. 

The conversion of arylboronic acids to the corresponding neopentyl glycol arylboronic esters has several advantages The esters are readily soluble in organic solvents, shelf stable, non-hygroscopic and easily characterized as a single entity.9 Furthermore, boronic esters can be utilized in many of the transformations where arylboronic acids usually are employed, making them an attractive alternative from a practical point of view. 

The unambiguous characterization of glycosyl esters of nucleoside pyrophosphates is difficult, as no suitable crystalline derivatives are known for them, and the hygroscopic nature of their ammonium and metal salts prevents reliable interpretation of the data of elementary analysis. 

Miles, JCS 1931 2532-42 (Formation and characterization of crysts of LA and some other initiating expls) 5)K.S.Warren, PATR 1152 (1942), "Study of the Action of Lead Azide on Copper 6)J.Fleischer J.B. Burtle, USP 2,421,778 (1947) "Initiating Explosives 7)Wm.H.Rinkenbach A.J. Clear, PATR Rev 1(1950), "Standard Laboratory Procedures for Sensitivity, Brisance and Stability of Explosives 8)U.S.Military Specification MIL-L-3055, Amend 1(1952) (Requirements and tests for dextrinated lead azide) 9)J-Bernstein, GLR 51-HI-2332, Pic Arsn (1952) "Hygroscopicity of Dextrinated Lead Azide 10)J.W.Lavitt, PATR 1957 (1953), "An Improved Microscopic Method for the Determination of the Crystal Size Distribution of 2-Micron RDX" 11)F.P. Bowden K.Singh, Nature 172, 378(1953) (Size effects in the initiation and growth of explosives) 12)J.W.C.Taylor, A.T.Thomas... 

Crystalline paraperiodic acid, H5I06, which is hygroscopic and readily soluble in water, is commercially available. Most of the salts of periodic acid are characterized by their slight solubility in water. For oxidation experiments sodium metaperiodate, NaIC>4, is the most suitable salt because of its solubility in water (9.3% at 20° and 12.6% at 25°).99 Sodium metaperiodate is commercially available and also can be obtained readily from the slightly soluble trisodium paraperiodate, Na3H2I06, by crystallization from nitric acid in the ratio of 150 cc. of water and 45 cc. of concentrated nitric add to 100 g. of salt.9 Trisodium paraperiodate is formed in 90% yield by the reaction of bromine and sodium iodide in aqueous sodium hydroxide solution at 80°.100 It is also produced in 80% yield by the oxidation of sodium iodate with chlorine in aqueous sodium hydroxide solution.99 In connection with this preparation of trisodium paraperiodate from sodium iodate, it should be noted that in the usual periodate oxidation reactions the periodate is converted quantitatively into iodate. Paraperiodic acid has been prepared in about 93% yield from trisodium paraperiodate " 1 it has been prepared also by the electrolytic oxidation 191 >192 of iodic add. 

Unlike the anhydrous metal salts, these mixtures are very sensitive to temperature fluctuations. At ambient temperatures they are extremely hygroscopic and rapidly absorb up to 10 wt% water from the atmosphere. Above 70 °C the liquids lose water and this is characterized by a change in color of the chromium-based liquid from dark green to purple. At about 50 to 60 °C the water concentration in the liquid remains constant and can be used in an open atmosphere without significant alteration in the liquid composition. Thermogravimetry shows that the waters of hydration are released in two steps the first starts at about 85 °C, which equates to approximately 3 waters, and the second at about 180 °C, corresponding to the other 3 water molecules [101]. 

The physical and chemical properties necessary to characterize fully the drug substance, which includes, but is not limited to, identification of impurities, particle size, solubility, bulk density, polymorphism, hygroscopicity, etc. 

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