Compatibility with aqueous media

A potentially more sensitive and selective approach involves reaction of formic acid with a reagent to form a chromophore or fluorophore, followed by chromatographic analysis. A wide variety of alkylating and silylating reagents have been used for this purpose. Two serious drawbacks to this approach are that inorganic salts and/or water interfere with the derivatisation reaction, and these reactions are generally not specific for formic acid or other carboxylic acids. These techniques are prone to errors from adsorption losses, contamination, and decomposition of the components of interest. Enzymic techniques, in contrast, are ideal for the analysis of non-saline water samples, since they are compatible with aqueous media and involve little or no chemical or physical alterations of the sample (e.g., pH, temperature). 

There are a number of chemical transformations which are not only compatible with aqueous media but actually benefit strongly from the unique characteristics of water. These are demonstrated in Tables 1-311. 

As described previously, NaBHsCN has found wide usage in the biochemical arena where mildness and compatibility with aqueous media are essential, and reductive amination has been utilized especially... 

At last, it should also be noted that activated charcoal is a support compatible with aqueous media. Wettability of charcoal is accounted for by residual carboxylic groups present at its surface. So, Pd/C makes a good recyclable phosphine-free catalyst applicable to aqueous chemistry. 

In a second attempt to extend the scope of Lewis-acid catalysis of Diels-Alder reactions in water, we have used the Mannich reaction to convert a ketone-activated monodentate dienophile into a potentially chelating p-amino ketone. The Mannich reaction seemed ideally suited for the purpose of introducing a second coordination site on a temporary basis. This reaction adds a strongly Lewis-basic amino functionality on a position p to the ketone. Moreover, the Mannich reaction is usually a reversible process, which should allow removal of the auxiliary after the reaction. Furthermore, the reaction is compatible with the use of an aqueous medium. Some Mannich reactions have even been reported to benefit from the use of water ". Finally, Lewis-acid catalysis of Mannich-type reactions in mixtures of organic solvents and water has been reported ". Hence, if both addition of the auxiliary and the subsequent Diels-Alder reaction benefit from Lewis-acid catalysis, the possibility arises of merging these steps into a one-pot procedure. 

Hydrophilic/hydrophobic properties. In water-based systems, the filler should be compatible with water because filler dispersion occurs in an aqueous medium before a polymer emulsion is added. In general, most fillers are hydropho-... 

By varying all the parameters of the process the authors prepared a set of copolyesters containing units and blocks with a tertiary amino group, which, in turn, could be transformed into a hydrophilic hydrochloride salt thus imparting water-compatibility to the initially organosoluble macromolecules. The principle involved was the formation of a block-type structure of chains in order to facilitate their further protein-like folding in an aqueous medium. It was shown that the main factors responsible for the blockiness were the relative reactivities of the (B) and (C) components (NMDEA and bisphenol) and the order of their addition to the reaction. 

The catalyst choice was based on several unique properties of the rare-earth Lewis acids (1) ready availability, (2) a large number of triflates with varied Lewis acidity, (3) compatibility with amine nucleophiles and (4) potential for reactions in aqueous medium. 

The application of A-type GIC materials in rechargeable batteries has frequently been investigated, namely in metal/graphite cells in concentrated sulfuric acid by Fujii (Me = Pd) [153,154] and in acids of medium concentration by Beck and Krohn (Me = Pb or Zn) [155-157]. The latter electrolytes have an improved compatibility with the negative metal electrode. Metal-free accumulators with GIC as a positive electrode were built with anthraquinone in aqueous acids [80] and with polypyrrole in aprotic electrolytes [58,158,159]. General discussions of the potentialities of graphite-type active materials in rechargeable batteries have been published by Besenhard and Fritz [160] and Beck et al. [5-10]. At the end of this review (Section 9) the discussion relevant to batteries will be summarized. 

Nucleophilic Opening at C(l). The latent reactivity at C(l) can be activated via the Payne rearrangemenf by treatment of 2,3-epoxy alcohol A with aqueous NaOH in the presence of a cosolvent. This results in equilibration of A with the isomeric 1,2-epoxy 3-ol B. Even if epoxide A is preferred at equilibrium, C(l) in isomer B is steri-cally less hindered and hence should react faster with the nucleophile in an 8 2 manner. Once B is formed, it will react selectively and irreversibly with the nucleophile to furnish product C. The success of epoxide opening (B C) by nucleophiles depends on whether the reagent is compatible with the alkaline aqueous medium required for the Payne reaiTangement. 

Polyanilines have been shown to be compatible with biomolecules in neutral and near neutral aqueous solutions - a medium of preference for most biomolecules [97, 105],... 

The cell medium must favour electrochemical reaction. The mobile phase must be conducting but not necessarily aqueous nonpolar solvents and hence adsorption chromatography are not compatible with electrochemical detection. The mobile phase must not contain any chlorides or hydroxycarboxylic acids. The electrochemical yield is not higher than between 1 and 10% so that most of the sample leaves the cell unchanged. A conversion level of 100% is known as coulometric detection", but the equipment is not more sensitive than amperometric systems. 

A major improvement was realized with the use of indium, a metal with a very low first ionization potential (5.8 eV) which works without ultrasonic radiation even at room temperature [87]. As the zero-valent indium species is regenerated by either zinc, aluminum, or tin, a catalytic amount of indium trichloride together with zinc, aluminum [88], or tin [89] could be utilized in the allylation of carbonyl compounds in aqueous medium. The regeneration of indium after its use in an allylation process could be readily carried out by electrodeposition of the metal on an aluminum cathode [90], Compared with tin-mediated allylation in ethanol-water mixtures, the indium procedure is superior in terms of reactivity and selectivity. Indium-mediated allylation of pentoses and hexoses, which were however facilitated in dilute hydrochloric acid, produced fewer by-products and were more dia-stereoselective. The reactivity and the diastereoselectivity are compatible with a chelation-controlled reaction [84, 91]. Indeed, the methodology was used to prepare 3-deoxy-D-galacto-nonulosonic acid (KDN) [92, 93], N-acetylneuraminic acid [93, 94], and analogs [95],... 

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