Aliphatic Chemical stability

Crucial to this class of inhibitors was the discovery of (1 J ,25)-l-amino-2-vinylcyclopropane carboxylic acid (vinyl-ACC A) as a PI residue [99]. Initially, several reports appeared describing chemically stable replacements for the cysteine residue at the PI position of all tra i-cleaved substrates. An aliphatic side chain with two (aminobutanoic acid) or three (nor-valine) carbon atoms seemed to be an acceptable replacement, with only a moderate loss in potency and improved chemical stability [96, 100]. An improved PI... 

The last group of aliphatic amides to be discussed are the tertiary amides, which, by definition, carry two alkyl substituents on the N-atom. Investigations of their chemical stability have disclosed a surprising difference between tertiary and secondary amides, since the rate of acid-catalyzed hydrolysis of N,N-dimethyl amides is higher than that of A-methyl amides. If steric fac-... 

A coordination polymer such as (65) proves to have exemplary thermal and chemical stability and it has been used as the solid phase for separating a variety of aliphatic and heterocyclic bases. Retention volumes remained constant after many hours use at 100 °C.98... 

Despite the well-known chemical stability of perfluorinated aliphatic compounds, pcr-fluorinated Decalin can be reacted w ith alkane- or arenethiols under very mild conditions yielding octakis(alkylsulfanyl)- or octakis(arylsulfanyl)naphthalenes 2.6 The reaction starts at the tertiary carbon atoms where the C — F bond is the weakest, since perfluorocyclohexane does not react under similar conditions, but perfluorocyclohexene does.6... 

Musikas and co-workers studied extensively the extraction behavior of inorganic acids and U/Pu extraction chemistry with A/,A-dialkyl amides (202-205). Based on the extraction data, they proposed certain dialkyl amides suitable for the reprocessing of irradiated nuclear fuels in nitric acid media. Most of the work reported earlier on amides referred to either aromatic or substituted aliphatic hydrocarbons employed as diluents. However, these diluents are not suitable for commercial-scale reprocessing due to their poor radiation and chemical stability in the presence of nitric acid, as well as their tendency to form a three-phase system. 

The large miscibility gap observed for an ionic liquid mixed with an aliphatic compound (without the addition of water as in the case of NMP) can be directly used for the separation of aromatic from aliphatic hydrocarbons by liquid-liquid extraction. Besides the miscibility gap, there are other requirements necessary for a successful extractant, such as high selectivity, high capacity, a low solubility of the extractant in the raffinate phase, a simple separation of the extract and the raffinate phase, low viscosity, high chemical and thermal stability and a sufficient density difference. Nearly all these requirements are met by the ionic liquids that have so far been investigated. However, our present knowledge of the thermal and chemical stability of ionic liquids is limited. For example, for some ionic liquids (largely dependent on the anion), hydrolysis does occur. 

Carbon dioxide, water, ethane, ethylene, propane, ammonia, xenon, nitrous oxide, and fluoroform have been considered useful solvents for SEE. Carbon dioxide has so far been the most widely used as a supercritical solvent because of its convenient critical temperature, 304°K, low cost, chemical stability, nonflammability, and nontoxicity. Its polar character as a solvent is intermediate between a truly nonpolar solvent such as hexane and a weakly polar solvent. Moreover, COj also has a large molecular quadrupole. Therefore, it has some limited affinity with polar solutes. To improve its affinity, additional species are often introduced into the solvent as modifiers. For instance, methanol increases C02 s polarity, aliphatic hydrocarbons decrease it, toluene imparts aromaticity, R-2-butanol adds chirality, and tributyl phosphate enhances the solvation of metal complexes. 

Organofluorine compounds have achieved enormous industrial significance in view of their generally great chemical stability (e.g., polytetrafluoro-ethylene) or their volatility (e.g., fluoroalkanes used as refrigerants), while some of them are valuable pharmaceutical products. Indeed, there has been increasing interest in perfluorinated aliphatic compounds as surfactants... 

A. Liquid Mixtures.— Aliphatic and alicyclic perfluorocarbons first became available in commercial quantities just over three decades ago. The impetus towards their large-scale production came from the war-time Manhattan Project when it was realized that the chemical stability and inertness of these materials, combined with their unexpectedly low solubility in most other common organic solvents, might prove useful in uranium isotopic separation processes based on... 

Aramids have been developed from the need to enhance the chemical stability of polyamides. Because of the stability of aromatic rings, aramids also have higher tensile strength and thermal resistance than aliphatic polyamides. These qualities make aramids popular for use in impact resistance applications. However, aramids - along with PA - have low UV resistance. If used in outdoor applications, they must be heavily coated to protect against UV radiation. 

Another class of membrane polymers are the polyamides. These polymers are characterised by the amide group (—CO — hlH —). Although aliphatic polyamides comprise a very largeelass of polymers, the aromatic polyamides are to be preferred as membrane materials because of their outstanding mechanical, thermal, chemical and hydrolytic stability, as well as their permselective properties, particularly in reverse osmosis. However, the aliphatic polyamides also show good chemical stability and may be used in microfiltration/ultrafildation applications. 

Aliphatic and aromatic polyesters and copolyesters containing cyclohexanedimethanol units are reviewed covering from the synthesis of monomers up to their polymerization by the different known synthetic routes. Thermal and mechanical properties as well as thermal and chemical stability are discussed with reference to the polyester structure. Compounding, processing, recycling and applications of these polyesters and copolyesters are also reviewed. Finally, an account on the recent developments in blends and composites is provided. 

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