Ester chemical stability

A complication here, however, is noted with those drugs that exhibit a limited chemical stability in either acidic or alkaline fluids. Since the rate and extent of degradation is directly dependent on the concentration of drug in solution, an attempt is often made to retard dissolution in the fluid where degradation is seen. There are preparations of various salts or esters of drugs (e.g., erythromycin) that do not dissolve in gastric fluid and thus are not degraded there but which dissolve in intestinal fluid prior to absorption. A wide variety of chemical derivatives are used for such purposes. 

Phosphoric and polyphosphoric acid esters Perfluorinated anionics Sulfonic acid salts Strong surface tension reducers Good oil in water emulsifiers Soluble in polar organics Resistant to biodegradation High chemical stability Resistant to acid and alkaline hydrolysis... 

In 1958, Barthel et al. [25] reported dimethrin (15), which was the first substituted benzyl alcohol ester of chrysanthemic acid. This compound was not put into practical use due to its low insecticidal activities. Phenothrin (16), one of the m-phenoxybenzyl alcohol esters developed by Fujimoto et al. [26], was found to have superior chemical stability as well as safety, and has been the sole pyrethroid used as a lice control agent for humans. Further improvement was made by Matsuo et al. [27] who introduced a cyano function at the a position of the benzyl part of phenothrin, leading to a-cyano-m-phenoxybenzyl alcohol esters (17). Thereafter, this alcohol moiety has been used as a component for a number of photostable pyrethroids for agricultural purposes however, the development of cross-resistance can be seen in some pests. 

Yang C, Gao H, Mitra AK (2001) Chemical stability, enzymatic hydrolysis, and nasal uptake of amino acid ester prodrugs of acyclovir. J Pharm Sci. 90 617-624. 

L. K. Wadhwa, P. D. Sharma, Glycolamide Esters of 6-Methoxy-2-naphthylacetic Acid as Potential Prodrugs-Physicochemical Properties, Chemical Stability and Enzymatic Hydrolysis , Int. J. Pharm. 1995, 118, 31-39. 

C. Yang, H. Gao, A. K. Mitra, Chemical Stability, Enzymatic Hydrolysis, and Nasal Uptake of Amino Acid Ester Prodrugs of Acyclovir ,. /. Pharm. Sci. 2001, 90, 617-624. 

Badawy, S.I., Williams, R.C., and Gilbert, D.L., Chemical stability of an ester prodrug of a glycoprotein Ilb/IIIa receptor antagonist in solid dosage forms,. Pharm. Sci., 88, 428,1999. 

The energetic nature of the N-NO2 group means that At-nitro-based explosives are some of the most powerful explosives available and these have largely superseded aromatic C-nitro compounds for military applications. Many nitramines exhibit high brisance and high chemical stability in combination with a favourable low sensitivity to impact and friction compared to nitrate ester explosives of similar power. 

The industrial production of copolymers of trioxane with ethylene oxide or di-oxolane (1-5%) is conducted as a bulk polymerization in special equipment. The incorporation of small amounts of C-C bonds into the C-0 chain has a remarkable effect on the thermal and chemical stability. In homopolymers the thermal decomposition starts at the semiacetal end groups ( unzipping ) and leads to a complete destruction of the polymer chain, whereas this reaction stops in copolymers already at the first C-C bond. A thermally stable OH end group is thus formed which, in addition, contributes to a much better alkali resistance compared to ester group-terminated homopolymers (see Examples 3-40 and 5-13). 

Ethers are saturated hydrocarbons with an oxygen atom in the center and are closely related to acetals. They have high hydrolytic and biological stability relative to esters and acetals, which were frequently used in the past as components of drilling muds. Their chemical stability improves their technical properties, but their low biodegradability leads to poor environmental performance [8]. 

As regards explosive strength, nitramines occupy a position midway between nitro compounds and nitric esters. They also hold a central position regarding other properties, such as chemical stability and sensitiveness to impact and friction. 

All of the unique properties imparted by fluorocarbons can be traced back to a single origin the nature of the C—F bond. These properties include low surface tension, excellent thermal and chemical stability, low coefficient of friction, and low dielectric constant. However, not all of these properties are possessed by the entire inventory of available fluorocarbons. The fluorocarbons can be assigned to two major categories (1) fluoropolymers, which are materials that are comprised mainly of C—F bonds and include such examples as PTFE, and (2) fluorochemicals (FA) based on the perfluoroalkyl group, which are materials that generally have fewer C—F bonds and often exist as derivatives of other classes of molecules (e.g., acrylates, alcohols, esters). In addition, the properties that dictate the uses of fluorocarbons can be classified into (1) bulk properties (e.g., thermal and chemical stability, dielectric constant) and (2) surface properties (e.g., low surface tension, low coefficient of friction). The types of materials available and properties imparted are not exclusive and overlap substantially. From this array of fluorocarbons and attributes, a large variety of unique materials can be constructed. 

T. Urbanski and Magiera [85] have examined the chemical stability and explosive properties of the ester and conclude that neither the substance itself nor a solution of nitrocellulose in it are sufficiently stable for practical application. Its temperature of initiation is 150°C (whereas nitroglycol is initiated at 220°C), and it is considerably more sensitive to impact than nitroglycol. They also found that an impact energy of 0.91 kgm/cm2 is necessary to ensure a 10% probability explosion of nitroglycol, as compared with barely 0.11 kgm/cm2 for the ester. 

Increase in the proportion of sulphuric acid in the mixture tends to reduce the chemical stability of the product, probably in consequence of the formation of unstable sulphuric esters of cellulose. 

In certain brilliantine compositions, vegetable and animal oils are used as substitutes for mineral oil. In these systems, because of their potential for rancidity, antioxidants must be included. Other alternatives to mineral oils that have found utility in brilliantines are the polyethylene glycols which come in a variety of solubilities and spreading properties. Use of these materials offers the advantage of chemical stability to rancidity. Other additives found in brilliantines to improve their aesthetics include colorants, fragrance, medicated additives, lanolin, and fatty acid esters. 

I) Natural liquid fatty esters, such as lard oil. palm oil. sperm oil. etc. These arc good lubricants hut have poor chemical stability. 

Phosphate esters have the desirable qualities of both chemical stability (Flynn and Lamb, 1970) and biological lability (Amidon et al., 1977 Amidon, 1981). There is evidence that the soluble phosphate ester is enzymatically hydrolyzed to the active agent in the body (Melby and St. Cyr, 1961 ... 

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