Presence of Carboxy Groups

Many derivatives of carboxy chloropyrazines have been prepared by the action of phosphoryl chloride on the corresponding hydroxypyrazine. In this way were prepared 2-chloro-3-methoxycarbonylpyrazine (371, 423, 836), 2-chloro-3-methoxycarbonyl-5,6-diphenylpyrazine (but the corresponding hydroxy compound did not react with phosphorus tribromide) (837), and 3-chloro-2-methoxycarbonyl- 

5- methylpyrazine (371) (2-carboxy-3-chloropyrazine could not be prepared by the action of phosphoryl chloride on 2-carboxy-3-hydroxypyrazine) (423). 2-Chloro-5-methoxycarbonylpyrazine was similarly prepared with phosphoryl chloride containing a few drops of concentrated hydrochloric acid (838). 2-Hydroxy- 

6- methoxycarbonylpyrazine with phosphoryl chloride gave 2-chloro-6-methoxy-carbonylpyrazine (744) [cf. NovaCek et al. (839)]. 

2-Carbamoyl-3-hydroxypyrazine and phosphoryl chloride have been shown to give 2 hloro-3-cyanopyrazine (810, 811, 840) likewise 2-carbamoy 1-3-hydroxy- 

6- diphenylpyrazine gave 2-chloro-3-cyano-5,6-diphenylpyrazine (837), and 2-cyano-5-hydroxy-3,6-dimethylpyrazine gave 2 hloro-5-cyano-3,6-dimethyl-pyrazine (288). The sodium salt of hydroxypyrazine, phosphoryl chloride, dimethylformamide, and chlorine gave 2,3-dichloropyrazine (770) and 2-carbamoyl-pyrazine, phosphoryl chloride, and bromine have been claimed to give 5( )-chloro-2-cyanopyrazine (839). 

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Pneumococcal Sill polysaccharide has been treated with a water-soluble carbodi-imide and then reduced with sodium borohydride the i.r. spectrum of the reduced polysaccharide showed negligible absorption attributable to the presence of carboxy-groups. The reduced material furnished 1,4,5-tri-O-acetyl-2,3,6-tri-0-methyl- and 1,3,5-tri-0-acetyl-2,4,6-tri-0-methyl-D-glucitol following methylation, hydrolysis, further reduction, and acetylation, compatible with the presence of equal proportions of (1 3)- and (1 -> 4)-linkages. The reduced... 

Methods have been reported for the ultrastructural localization of complex carbohydrates, including glycoproteins, in rat macrophages and monocytes, by employing the reactivity of vicinal glycols to periodate ions and the presence of carboxy- and sulphate ester-groups. ... 

To say that one polymer is or is not different from another will always require some arbitrary judgment of what is or is not significant in polymer identification. For example, are the two polymers represented by the source-based expressions shown as Figures 3(a) and 3(c) sufficiently different to be worthy of two separate representations In terms of source-based polymer registration, CAS regards them as two separate polymers. Some industrial consumers of PET may find that the presence of carboxy end groups rather than methoxycarbonyl ones makes no difference for their particular application, while others may find that end group composition makes an appreciable difference to product properties thus, the answer may depend upon many factors. 

Even with PPys or polythiophenes the presence of other functional groups on the 3 or 4 position can be used to adjust the chemical properties and the electrochemical switching properties. For example the addition of alkyl groups results in polymers that are more hydrophobic (9) and also more soluble in common organic solvents. We have also shown that the addition of carboxy groups introduces self doping to the polymer and therefore cation exchange properties (10,11). 

Crini et al., 2002 proposed the synthesis of cyclodextrin-carboxy-methyl cellulose gels. Results obtained with these gels showed that effective and efficient extraction of beta-naphtol is achieved. The presence of carboxyl groups in the polymer networks permit to increase significantly the sorption properties. The carboxylic acid groups present in the adsorbents plays an important role in the adsorption of Cu, Pb and Ni [94]. 

HMO calculations have been ultilized in the search for substituted thiepins liable to be good candidates for synthesis due to electronic substituent effects.7 Based on these results, the presence of at least two carboxy groups and one fluorine group give an increased resonance energy per electron to positive values, indicating at least some thermal stability. 

Poly(unsaturated ester)-siloxane segmented copolymers have been prepared by the polycondensation of epoxy-terminated polydimethylsiloxanes and carboxy-terminated poly(ethylene adipate-co-maleate) oligomers 243). Reactions have been conducted in cellosolve solvent, at 140-150 °C, in the presence of 2% by weight potassium hydroxide catalyst. The molecular weights reported were fairly low. The same group has also prepared poly(hexamethylene adipate)-polydimethylsiloxane copolymers con-... 

D. Coenzyme A.—Succinyl phosphate (42) reacts rapidly and non-enzymatically with CoA in the pH range 3—8 to yield succinyl CoA (43). This reaction is dependent on the presence of a suitably situated free carboxy-group as such nucleophilic attack at carbon is not known with other acyl phosphates. Moreover, maleyl phosphate reacts rapidly with CoA while fumaryl phosphate fails to react under the same conditions. Hence the formation of a cyclic intermediate (44) from succinyl phosphate is... 

A number of BODIPY derivatives that contain reactive groups able to couple with amine-containing molecules are commonly available. The derivatives either contain a carboxy-late group, which can be reacted with an amine in the presence of a carbodiimide to create an amide bond, or an NHS ester derivative of the carboxylate, which can react directly with amines to form amide linkages. The three discussed in this section are representative of this amine-reactive BODIPY family. The two NHS ester derivatives react under alkaline conditions with primary amines in molecular targets to form stable, highly fluorescent derivatives. The carboxylate derivative can be coupled to an amine using the EDC/sulfo-NHS reaction discussed in Chapter 3, Section 1.2. 

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