Introduction of carboxylic

Examples are the introduction of carboxyl or hydroxy groups to increase hy-drophilicity, crosslinking (vulcanization) of polydienes with sulfur, or conversions that proceed only at the terminal groups under retention of the molecular backbone (chain-analogous conversion). 

Water-soluble poly(p-phenylene) 24, shown in Scheme 29, was prepared by the introduction of carboxylic acid pendant substituents along the p-phenylene chains [102]. In initial work in this area, a dicarboxy-substituted dibromobiphe-nyl was polymerized with 4,4f-biphenyl bis-boronic acid via Suzuki coupling... 

Hyperbranched polymers of polybenzene type can be rendered water-soluble like the above-mentioned monodisperse species by introduction of carboxyl groups [62]. Starting from 3,5-dibromophenylboronic acid 1 as AB2 monomeric building block (Fig. 4.34), the polycondensate 2 was assembled in an aryl-aryl coupling analogous to Suzuki coupling in the presence of Pd(0), and subsequently reacted with carbon dioxide to form the hyperbranched compounds 3 with terminal carboxylate groups ... 

The oxidative introduction of carboxylic functions to nanotubes provides a large number of CNT-functional exploitations and permits covalent functionalization by the formation of amide and ester linkages and other carboxyl derivatives [24]. Bifunctional molecules (diamines, diols, etc.) are often utilized as linkers. More illustrative examples are nanotubes decorated with amino-functionalized dendrimers, nucleic acids, enzymes, etc., and the formation of bioconjugates of CNTs [96]. 

In the present synthesis, the preparation of two cyclic ethers (31) and (41) and their transformations to pisiferic acid (1) are described. In this synthesis, the introduction of carboxylic acid at angular position has been accomplished by transannular oxidation. 

The synthesis is lengthy. We believe that the transannular reaction for the introduction of carboxylic acid at annular position is more convenient than the method adopted by Pal and Mukerjee [14]. 

The present work reports an excellent method for the introduction of carboxylic acid on the angular position. In addition Tian et al. [37] have developed a very interesting procedure for the construction of the fundamental skeleton of camosic acid. 

Carboxylation. The introduction of carboxyl groups into the structures of phenols and naph-thols produces some important dye intermediates, including salicylic acid and (3-oxynaphthoic acid (BON acid). This process is conducted under pressure at elevated temperatures using the sodium salts of phenols/naphthols and in the case of (3-naphthol, the carboxyl group enters... 

The reaction appears to be well suited for selective conversion of biomass carbohydrates into their corresponding oxidized derivatives. This system serves to oxidize several polymeric carbohydrates including starches and pullulan.445 49 More recent work has described the TEMPO-catalyzed introduction of carboxyl groups in native cellulose and its different morphological forms,45(M52 cellulose derivatives,453 and the surface of cellulose nanocrystals.454 The related biopolymer, chitin, also is oxidized under these conditions.455... 

Introduction of carboxylic acid groups enhances surface active properties (17) of lignins as well as their reactivity with propylene oxide (50). (A more highly propoxylated lignin has superior solubility and reactivity with diisocyanates.) Carboxylated lignins have, however, not been the target of network-forming reactions. 

Introduction of carboxyl groups (Kdbe-Schmidt synthesis)... 

A method of preventing aggregation of nanotubes is described. The procedure entails the ambient temperature introduction of carboxylic acids onto the nanotube substrate using a mixture of ammonium persulfate and sulfuric acid. By this method up to 0.76meq/g carboxylic acid was introduced onto a nanotube surface after two days. 

A further enhancement of the stability of the cation complexes was obtained by the introduction of carboxylate moieties. However, a bis(syn-distally)-0-functiona-... 

Wurtz Synthesis.—The introduction of carboxyl in place of a halogen in the ring may also be effected by the action of an ester of chlor formic acid and sodium. 

Reductive carbonylation of 1,1-dibromocyclopropanes with tetracarbonylnickel in dimethyl-formamide in the presence of a nucleophile is a powerful method for direct introduction of carboxylic acid functions to cyclopropanes. Nucleophiles, such as alcohols, amines, and silylamines, are particularly reactive and give cyclopropyl esters and amides, respectively, in reasonable to good yields, e.g. formation of 5 and... 

Flemion is quite different from prior membranes in that it is based on specific perfluorinated copolymers with pendant carboxylic acid as a functional group. The introduction of carboxylic functions in the polymer has realized high permselectivity in cation transport with high conductivity, which is indispensable to electrochemical application of ion exchange membranes. 

To the best of our knowledge, only a few studies have attempted to prevent the calcification of HEMA-based hydrogels. It has been reported that introduction of carboxylate anions can either prevent or enhance calcification. Cemy et al. (21) found that copolymers of HEMA with 4 wt% methaciylic acid (MAAc) did not calcify under subcutaneous implantation in a rat for 14 months. A similar result was also observed after the implantation of HEMA/MAAc copolymers in the animal urinary tract (22). Other studies carried out in vitro showed that the presence of carboxylate anions significantly reduced the deposition of calcium phosphate (23) and calcium oxalate (24) on acrylic polymers and certain biopolymers. These findings obviously suggest an inhibitory effect of carboxylate anions on calcification. However, by contrast,... 

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