Polycarboxylates processes

Cobalt in Catalysis. Over 40% of the cobalt in nonmetaUic appHcations is used in catalysis. About 80% of those catalysts are employed in three areas (/) hydrotreating/desulfurization in combination with molybdenum for the oil and gas industry (see Sulfurremoval and recovery) (2) homogeneous catalysts used in the production of terphthaUc acid or dimethylterphthalate (see Phthalic acid and otherbenzene polycarboxylic acids) and (i) the high pressure oxo process for the production of aldehydes (qv) and alcohols (see Alcohols, higher aliphatic Alcohols, polyhydric). There are also several smaller scale uses of cobalt as oxidation and polymerization catalysts (44—46). 

Polycarboxylates may also be added to increase dispersing power and so reduce the possibility of incrustations. Fine-tuning will again depend on the process details, the machine type and the degree of scouring necessary. 

There is an interesting technique which makes it possible to introduce carboxylic acid groups into a copper phthalocyanine structure by an economical route. Carrying out the phthalic anhydride/urea process in the presence of a small amount of trimellitic acid or another benzene polycarboxylic acid will afford a car-boxylated pigment. 

Polycarboxylic acid synthases. Several enzymes, including citrate synthase, the key enzyme which catalyzes the first step of the citric acid cycle, promote condensations of acetyl-CoA with ketones (Eq. 13-38). An a-oxo acid is most often the second substrate, and a thioester intermediate (Eq. 13-38) undergoes hydrolysis to release coenzyme A.199 Because the substrate acetyl-CoA is a thioester, the reaction is often described as a Claisen condensation. The same enzyme that catalyzes the condensation of acetyl-CoA with a ketone also catalyzes the second step, the hydrolysis of the CoA thioester. These polycarboxylic acid synthases are important in biosynthesis. They carry out the initial steps in a general chain elongation process (Fig. 17-18). While one function of the thioester group in acetyl-CoA is to activate the methyl hydrogens toward the aldol condensation, the subsequent hydrolysis of the thioester linkage provides for overall irreversibility and "drives" the synthetic reaction. 

Addition Polymers. The most commonly referenced reaction of isocyanates involves their addition to polyhydroxyl, polyamine, or polycarboxylic acid compounds to yield addition polymers. Due to the wide diversity of raw material characteristics and the broad range of functionality, polyurethane polymers having a wide range of processing and performance characteristics are available. 

The aromatic polycarboxylates have generally been regarded as difficult to process at best. The sulfonate copolymer is similarly a high melt viscosity material. It can, however, be injection molded and extruded. In the interests of brevity we will not detail our experience in these areas, except to observe that only properly prepared and purified polysulfonates are stable to thermal processing, and predrying the resin prior to molding is preferred. 

Chromium(V) species, the main photoreduction products, are stable only in exceptional cases (as in the polyvinylalcohol matrix 256)). The reduction of chromium(V) to chromium(III) is a far slower process when chromium is in the presence of strong chelating agents such as polycarboxylate derivatives (257), but in general, Cr(V) undergoes a series of redox reactions and, in absence of other redox and coordinating partners, is transformed in part into a Cr(III) species and in part to Cr(VI), for example ... 

Imide-Modified Isocyanurate Foams. The imide linkage is a thermally stable linkage, and therefore, imide-modified isocyanurate foams have higher thermal stability and flame retardance than urethane-modified isocyanurate foams. R. Grieve (114) prepared such foams in a one-shot process by reacting a polycarboxylic acid anhydride with an organic polyisocyanate in the presence of a catalytic amount of a monomeric homocyclic polyepoxide and a tertiary amine. 

Detailed studies of ligand and solvent effects on electrochemical reductions of Cr111 amino-polycarboxylates have been performed.741,742 The observed differences in electrochemical behavior between cis- and trans-N204 Cr111 complexes have been explained by different Jahn-Teller distortions (JTD) of their Cr11 analogs (Section 4.6.6.8).741 Electrochemical reduction of Crm-edta complexes has been used as a model reaction in studies of heterogeneous electron-transfer processes.743... 

Gomez et al. " electrodeposited Co-Mo magnetic alloys from a sulfate-citrate bath on carbon electrodes. Although the focus of their paper was not on elucidating the mechanism of induced codeposition, it was suggested that hydrogen could not be responsible for the deposition of Mo in the Co-Mo system, because its concentration was fairly low and because another mechanism should explain the need for citrate or polycarboxylate anions in solution. The deposition process was foimd to be favored when molybdate was present in solution, even at very low concentrations. Hence, the authors adopted the model of Podlaha and Landolt, according to which a mixed-metal complex of cobalt(II), citrate and molybdenum dioxide is adsorbed on the surface and promotes Mo reduction. 

Colloid. [Rhone-Poulenc/Perf. Resins Coatings] Polycarboxylate salts, acrylics dispersant, vise, stabilizer for paints defoamer latex processing aid. 

Braga et al. have used an approach based on a combination of redox and acid-base processes to obtain partially deprotonated polycarboxylic acids capable of self-assembly in network structures. ... 

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