A-hydroxycarboxylic add

A concerted mechanism is also possible in the oxidation of a -hydroxycarboxylic adds, and these compounds readily undergo oxidative decarboxylation ... 

Solutions of a-hydroxycarboxylic and aminopolycarboxylic adds are commonly used to elute americium from cation-exchange resins. When these reagents are used in a displacement elution system, they provide excellent separation of americium from trivalent lanthanides and other trivalent actinides. Separation factors, acS, for americium from curium range from 1.2 to 1.4 for a-hydroxycarboxylic adds and from 1.2 to 2 for the separation of americium from curium with aminocarboxylic adds [16]. 

Examination of Table 8.9 reveals that aminopolycarboxylic adds complex Am(iii) more strongly than do either hydroxycarboxylic or aminoalkylpolyphos-phoric adds (e.g. ethyIenediaminebis(methyIene)phosphonic add). Keller [3] observes that in the series of a-hydroxycarboxylic adds (e.g. glycolic and lactic) the stability of the ameridum complex decreases with increasing number of carbon atoms. The logarithm of the stability constant of the complexes of Am with aminopolycarboxylic adds increases linearly (Fig. 8.9) with the number of bound donor atoms of the ligand. 

M. and Fu, G.C. (2009) Catalytic asymmetric cydoaddition of ketenes and nitroso compounds enantioselective synthesis of a-hydroxycarboxylic add derivatives. Angew. Chem. Int. Ed., 48, 2391-2393. 

Carbon dioxide itself can accept e. during radiolysis of water, giving rise to the carbon dioxide anion-radical. This anion-radical can add to carboradicals. Thus, aliphatic alcohols react with the radiolytically generated hydroxyl radicals, rupturing their C—H bonds RCHjOH + OH HjO + RCH OH. These radicals accept the radiolytically generated COj" forming a-hydroxycarboxylic acids RCHjOH + CO2 RCH(OH)COO (Morkovnik and Okhlobystin 1979). 

Cornell, R.M. Schindler, P.W. (1980) Infrared study of the adsorption of hydroxycarboxylic adds on a-FeOOH and amorphous Fe (III)-hydroxide. Colloid Polymer Sd. 258 1171-1175... 

Figure 3.42 shows an addition of a carboxylic acid to isobutene, which takes place via the ferf-butyl cation. This reaction is a method for forming fert-butyl esters. Because the acid shown in Figure 3.42 is a /3-hydroxycarboxylic add whose alcohol group adds to an additional isobutene molecule, this also shows an addition of a primary alcohol to isobutene, which takes place via the ferf-butyl cation. Because neither an ordinary carboxylic acid nor, of course, an alcohol is sufficiently addic to protonate the olefin to give a carbenium ion, catalytic amounts of a mineral or sulfonic acid are also required here. 

For work on a 1-mole scale one would thus have to use a 1000-liter flask to activate and then lactonize the entire w-hydroxycarboxylic add at once. Of course, it is much more practical to work in a smaller reaction vessel. However, there one must also not exceed the mentioned concentration limit of <1 /xmol/L. Therefore, one can introduce only as much of the carboxylic add in this smaller reaction vessel at a time so that its concentration does not exceed 1 /xmol/L. Subsequently, one would have to activate this amount of acid and would then have to wait until it is lactonized. After that additional acid would have to be added and then activated, and so on. A more practical alternative is shown in Side Note 6.1. 

Formation constants for the species [M(OAc) ] " (M = Zn or Cd n = 1-3) have been determined in addition, zinc forms a tetraacetato complex. Stability constants for complexatipn of Zn " and Cd " by other carboxylic and hydroxycarboxylic adds have been reported. 

The rate of ceric oxidation of substituted benzilic (2,2-diphenyi-2-hydroxyacetic) acid in sulfuric add, aqueous perchloric/acetic add and acetonitrile is the subject of two reports from Hanna and Sarac (1977a, b). The reaction proceeds like the other a-hydroxycarboxylic acids by oxidative decarboxylation, producing substituted benzo-phenones and COj. The primary interest in the first of these two reports (Hanna and Sarac 1977a) is in the organic chemical aspects of the reactions. However, it is observed that the relative rates vary with the media in the order H2SO4 > HC104/acetic acid > acetonitrile. Although little mechanistic information exists, it is apparent that the oxidation proceeds via an inner-sphere, electron transfer process. 

Amjad and McAuley (1974) have investigated the oxidation of malic (2-hydroxy-butane-1,4-dicarboxylic) acid in perchloric add. The reaction occurs at stopped-flow lifetimes and is unaffected by either Ce(III) or nitrate. The Michaelis-Menten plot is linear with finite positive intercept indicating precursor complex formation. The resolved values for the formation constants are comparable to those reported for the hydroxy and keto monocarboxylates, suggesting that the second carboxylate group is not bound in the activated complex. The intramolecular electron transfer rate parameters are less than those reported by Hanna and Fenton for the cyclic a-hydroxycarboxylic acids. 

To further understand the synthesis mechanism used in this work, which uses gelatin instead of ethylene glycol, it is necessary to review the traditional polymeric precursor method proposed by Pechini (Pechini, 1967). The Pechini method involves the formation of stable metal-chelate complexes with certain alpha-hydroxycarboxyl adds, such as dtric acid, and polyesterification in the presence of a polyhydroxy alcohol, such as ethylene glycol, to form a polymeric resin. The metal cations are homogeneously distributed in the polymeric resin, which is then calcined to yield the desired oxides. The most common materials used as source of cations are nitrate salts since they can be fully removed at low temperatures (400 - 500 °C). The synthesis mechanism of the modified Pechini method used in this work can be explained in three basic steps, as shown in Fig. 2. It stands out by its simplicity and low cost, using only citric acid, gelatin and metal nitrates as reagents. 

Solution to 18b The addition of cyanide ion adds one carbon to the reactant, so the starting material for the synthesis of this three-carbon a-hydroxycarboxylic acid must be acetaldehyde. Addition of hydrogen cyanide, followed hy hydrolysis of the resulting cyanohydrin, forms the target molecule. 

Fatty adds may also be directly esterified by hydroxycarboxylic adds, the most common of which are lactic acid and (2S,3S)-tartaric (D-tartaric) acid. Lactic acid gives rise to esters called lactylates, at first a monoester (11-75), which reacts with another molecule of lactic add yielding the ester of a dimeric add (11-76), which may arise also by reaction of a fatty acid with lactides. Other reactions can produce emulsifiers in which one molecule of a fatty add accounts for a greater number of molecules of lactic add (11-77). Stearoyl tartrate, also known as stearoylpalmitoyl tartrate (E483), is approved in the EU as an emulsifier. The main components of this product are distearoyl tartrate, dipahnitoyl tartrate and stearoylpalmitoyl tartrate. 

Lithium/naphthalene-diethylamine a,/ -Ethylene-5-hydroxycarboxylic adds from ketones... 

Fermium readily forms complexes with a variety of organic ligands, e.g. j9-diketones [18], hydroxycarboxylic adds [4, 15, 20-22], organophosphorus esters [23-25], and alkylamines [26]. Lactic and a-hydroxyisobutyric adds have long been used as eluants for inner-series separation of trivalent actinides by cation-exchange chromatography. However, more recently, di-2-ethylhexyl-orthophosphoric acid [27] and Alamine 336 (a mixed n-octyl and n-decyl tertiary amine) [28] have been used for similar separations of Fm by solvent extraction chromatography. 

The discontinuous process for preparing macrolactones described in the text is impractical. Instead of this process one uses a continuous method with a syringe pump one adds a solution of the hydroxycarboxylic acid very slowly—that is, in the course of hours or days—into a small flask, which contains >1 equivalent of the activator and, if necessary, just enough triethylamine to neutralize any released HCl.The rate at which the acid is added is regulated such that it is equal to or smaller than the lactonization rate. This procedure is called working under pseudo-high dilution. At the end of the... 

The unequivocal proof is furnished by the crystal inclusion behavior of simple 2-hydroxy-3-naphthalenecarboxylic acid 25a and its 1-chloro derivative 25 since both allow the formation of a crystalline adduct ( clathratocomplex ) with dimethylformamide with the expected 1 1 stoichiometric ratio Thus, the salicylic add function (2-hydroxycarboxylic acid group) is shown to be an excellent sensor, or a good complementary site for the dimethylformamide molecule in solid state inclusion. 

Generally, lactones with five-membered and six-membered rings are not too reactive. They are relatively stable in acidic solutions, where they typically arise by spontaneous dehydration of hydrox-ycarboxylic adds. In aqueous solutions, particularly in alkaline solutions, the lactone ring opens with the formation of a salt of the hydroxycarboxylic acid. The original lactone may result after acidification, especially on heating. Lactones react with alcohols to form esters and, similarly, the lactone ring opens on reaction with amino compounds to form amides. 

---