Deprotonated carboxylic acid

Although lithium aldolates generally display a rather moderate preference for the u/f/z-isomer4, considerable degrees of diastereoselectivity have been observed in the reversible addition of doubly deprotonated carboxylic acids to aldehydes20. For example, the syn- and uw/z-alkox-ides, which form in a ratio of 1.9 1 in the kinctically controlled aldol addition, equilibrate in tetrahydrofuran at 25 C after several hours to a 1 49 mixture in favor of the anti-product20. 

A completely different dipolar cycloaddition model has been proposed39 in order to rationalize the stereochemical outcome of the addition of doubly deprotonated carboxylic acids to aldehydes, which is known as the Ivanov reaction. In the irreversible reaction of phenylacetic acid with 2,2-dimethylpropanal, metal chelation is completely unfavorable. Thus simple diastereoselectivity in favor of u f/-adducts is extremely low when chelating cations, e.g., Zn2 + or Mg- +, are used. Amazingly, the most naked dianions provide the highest anti/syn ratios as indicated by the results obtained with the potassium salt in the presence of a crown ether. 

Carboxylic acids are more acidic than alcohols and acetylene. Strong aqueous bases can completely deprotonate carboxylic acids, and salts of carboxylic acids are formed. Strong aqueous mineral acids readily convert the salt back to the carboxylic acids. Saits are soluble in water but insoluble in nonpolar solvents, e.g. hexane or dichloromethane. 

Table 19.3 lists common bases that can be used to deprotonate carboxylic acids. It is noteworthy that even a weak base like NaHC03 is strong enough to remove a proton from RCOOH. 

Common Bases Used to Deprotonate Carboxylic Acids... 

Concerning drugs, both cationic and anionic compounds are commonly used (protonated basic side chain, protonated aza heterocycles, deprotonated carboxylic acids, enolic species, and acidic sulfonamides) (Figure 21.1). 

Strongly basic nucleophiles irreversibly deprotonate carboxylic acids, forming carboxylate anions. Addition-elimination reactions on carboxylate anions are hard to do because (1) the addition is hard to do and (2)... 

Besides functional initiators, a wide range of functional terminating agents have been utilized for the preparation of functional poly(2-oxazoline)s, including deprotonated carboxylic acids [184, 185], amines [185, 186], and deprotonated thiols (Scheme 8.27) [187]. The termination with primary amines can be complicated by the formation of secondary amines that can react with a second polymer chain after proton transfer to the unreacted primary amines. 

Divalent ions such as calcium and magnesium form cross-links between deprotonated carboxylic acid groups by which the negative charge is neutralised and the hydrophilisation is counteracted. To prevent this, disodium edetate is added in (aqueous) carbomer gel pH 6.5 NRF (Table 18.16). 

Protein solutions should not be stored at a pH which is equal to their iso-electric point. At the iso-electric point, the amount of deprotonated carboxylic acid groups and protonated amino groups are equal and thus the net charge of the particle is zero. In that situation the zeta-potential is zero and irreversible aggregation can easily occur. For the same reason, the electrolyte concentration in the solution should not be too high. A very low or high pH is not recommended because the hydrolysis of proteins is both acid and base catalysed. The oxidation of many proteins is catalysed by the divalent metal ions, in particular Fe and Cu ". Divalent metal ion catalysed oxidation of proteins can be prevented by the addition of disodium edetate to complex these ions. However, certain divalent metal ions can also act as stabilisers for specific proteins. 

Notice that pyridine is used, once again, to remove the HCl that is formed as a by-product. We can avoid the need for pyridine by using a carboxylate ion (a deprotonated carboxylic acid) instead of a carboxylic acid ... 

Braun and coworkers finally tackled a group of enolates that may be considered the hardest one doubly deprotonated carboxylic acids 54 [33]. It turned out that here again, the standard allylation protocol with the ingredient lithium chloride could be used in an efficient manner and led to the p,y-unsaturated carboxylic... 

Scheme 5.18 Palladium-catalyzed allylic alkylations of doubly deprotonated carboxylic acids.

Benzene-1,4-dicarboxylic acid (H2bdc) is one of the most commonly utilized ligands in MOF chemistry, being the linker ligand for MOF-5. Deprotonated carboxylic acids or carboxylates are hard donors and are... 

Deng reaction 985,1004 3-deoxy sugars 914 deprotonated carboxylic acid 479 deprotonations 43... 

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