Substituted carboxylic acids


Substituted carboxylic acids are organic compounds that contain a carboxyl group (-COOH) attached to a carbon atom which is also attached to one or more substituent groups. These substituent groups can be alkyl, aryl, or any other functional group. The presence of these substituents can significantly affect the chemical and physical properties of the carboxylic acid, including its acidity, solubility, and reactivity. Some common examples of substituted carboxylic acids include acetic acid (with a methyl substituent), benzoic acid (with a phenyl substituent), and amino acids (with amino substituents).

The systematic names of substituted aliphatic carboxylic acids are derived by:

(i) First identifying the parent chain that contains most, if not all, the carboxyl groups.

(ii) Number the parent chain from the carbon of the carboxyl group i.e the carboxyl carbon is C-1.

(iii) Identify the substituents and assign each substituent a locator/address number (2,3,4…etc.) consistent with the numbering in the parent chain.

(iv) Arrange the names of the substituents in alphabetical order in the systematic name of the poly-substituted carboxylic acid.

IUPAC Nomenclature of Substituted Aromatic Carboxylic Acids

 Substituted aromatic acids with one carboxyl group are named as derivatives of benzoic acid, with the position of substituents being cited using the locators (2,3 etc) according to their position on the benzene ring relative to the carboxyl group. The carbon on which the carboxyl group is attached is by convention C-1

Nucleophilic acyl substitution reaction

Nucleophilic acyl substitution reaction is a type of organic reaction in which a nucleophile (an electron-rich atom or molecule) attacks the carbonyl carbon of a carboxylic acid derivative (such as an acid chloride, an ester, or an anhydride) resulting in the substitution of the acyl group with a nucleophile.

A.    Conversion of Carboxylic Acids into Acid Chlorides:   RCO2H ---->RCOCl
    A1.     RCO2H + SOCl2 in CHCl3 --->RCOCl + HCl + SO2
                        Thionyl chloride
    A2.     3 RCO2H + PCl3 ---> 3 RCOCl + H3PO3
                        Phosphorus trichloride is the acid chloride of phosphorus acid.
    A3.     RCO2H + PCl5 --->RCOCl + POCl3 + HCl
                            Phosphorus pentachloride is the acid chloride of phosphoric acid.
B.    Conversion of Carboxylic Acids into Acid Anhydrides:  RCO2H ----> RCO2COR
        Acyclic anhydrides are difficult to prepare directly from the corresponding acids.
        Acetic anhydride is commonly used.       Acetic acid + CH2=C=O (ketene) ----> CH3CO2COCH3
C.    Conversion of Carboxylic Acids into Esters:  RCO2H ----> RCO2R
    C1.     SN2 reaction between carboxylate anion and a primary alkyl halide.
               Sodium butanoate + Methyl iodide --> Methyl butanoate
    C2.     Nucleophilic Acyl Substitution By Alcohol.
               Fischer esterification reaction. Methyl, ethyl, and propyl ester esters are most commonly synthesized.
               Salicylic acid + methanol ----> methyl salicylate + water
D.    Conversion of Carboxylic Acids into Amides:  RCO2H ----> RCONH2
Amides are difficult to prepare by direct reaction of carboxylic acids with amines because amines are bases that convert acidic carboxyl groups into their corresponding anions.
        RCO2H + NH3 ----> RCO21- + NH41+