Of a halogenated carboxylic

The Reforrnatsku reaction of a-halogenated carboxylic esters with silylated cyanohydrins combined with an intramolecular acylation reaction gives fluorinated derivatives of tetronic acid [28] (equation 17) It is noteworthy to mention that this particular reaction sequence only proceeds with ultrasonic irradiation A very... 

The enol content of a carboxylic acid is far less than that of an aldehyde or ketone and introduction of a halogen substituent at the a carbon atom requires a different set... 

With acyl halides, the corresponding acyl phosphonates are obtained. Furthermore allylic and acetylenic halides, as well as a-halogenated carboxylic esters and dihalides, can be used as starting materials. If substituents R and R are different, a mixture of products may be obtained, because the reaction product RX 5 can further react with phosphite 1 that is still present ... 

Differences in solubility of the reactants may for example be utilized as follows. Sodium iodide is much more soluble in acetone than are sodium chloride or sodium bromide. Upon treatment of an alkyl chloride or bromide with sodium iodide in acetone, the newly formed sodium chloride or bromide precipitates from the solution and is thus removed from equilibrium. Alkyl iodides can be conveniently prepared in good yields by this route. Alkyl bromides are more reactive as the corresponding chlorides. Of high reactivity are a-halogen ketones, a-halogen carboxylic acids and their derivatives, as well as allyl and benzyl halides. 

An aqueous solution containing 0.10 mole/liter of chloroacetic acid, ClH2CCOOH, is tested with indicators and the concentration of H (aq) is found to be 1.2 X 10 2 M. Calculate the value of Ka (if necessary, refer back to Section 11-3.2). Compare this value with KA for acetic acid—the change is caused by the substitution of a halogen atom near a carboxylic acid group. 

Anhydro-D-glucose resulted, as mentioned, from the hydrolytic removal of a halogen atom at C6. Similar hydrolytic scission of sugar esters of carboxylic acids takes place without dehydration and with the liberation of the normal sugar. Thus, saponification of 6-benzoyl- or... 

The a-halogenated carboxylic adds, of which the simplest is chloro-acetic acid, are widely used in synthesis. Their conversion into hydroxy-acids (by hydrolytic elimination of the halogen) and into aminoacids (p. 275) may be mentioned here ... 

The Hunsdiecker reaction is a free-radical reaction for the synthesis of an alkyl halide. The starting material comes from the reaction of a silver carboxylate with a solution of a halogen in a solvent such as carbon tetrachloride (see Figure 12-44). The overall free-radical mechanism is shown in Figure 12-45. 

The carbonylation of alcohols to give the next higher carboxylic acid is catalyzed by nickel. Catalytic systems are based on Ni(CO)4, NiX2, or metallic nickel in the presence of a halogen (86,87). In all of these cases, though, the active species can be derived from nickel(O) species, for example... 

The carboxylate anion is a useful oxygen nucleophile for the displacement of a variety of leaving groups. A halophilic silver salt may be used for the displacement of a halogen such as an alkyl halide. 

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. 

Inductive effects fall off rapidly as the number of a bonds between the carboxyl group and the substituent increases. Consequently, the acid-strengthening effect of a halogen decreases as it becomes more remote from the carboxyl group ... 

The Passerini reaction of a-halogenated carbonyl compounds (8 X = Cl, Br) can be used for the protection of the C-terminal carboxyl groups of A -protected a-amino acid derivatives (7). ... 

---