Synthesis And Reactions Of Carboxylic Acids

Carboxylic acids are compounds with the functional group COOH.

Carboxylic acids are polar, and have much higher boiling point than alcohols and aldehydes of similar mass. They are capable of hydrogen bonding and are very soluble in water.


SYNTHESIS/PREPARATION OF CARBOXYLIC ACIDS


Carboxylation of Grignard reagents

Grignard reagent together with CO2 followed by HCl with H2O (or H3O+) in the second step produces a carboxylic acid. One important thing to note is that this reactions adds an extra carbon to the R group from the Gignard reagent. The carbon comes from the carbon dioxide.


Starting Material: RMgX


Reagent: 1.CO2 2.HCl, H2O (or H3O+)


Product: Get rid of MgX and attach the carbon that had MgX to COOH.

Preparation of Carboxylic Acid From Grignard Reagent
Preparation of Carboxylic Acid From Grignard Reagent

Mechanism for Carboxylation of Grignard reagent
Mechanism for Carboxylation of Grignard reagent

In the mechanism, first Grignard reagent attacks carbon dioxide, pushing electrons to the oxygen. Then, O- is protonated using the acid in the second step.


Conversion of Nitriles into Carboxylic Acids

Nitrile R-CN can be converted to carboxylic acid using H2O, H+. In this reaction we turn CN into COOH.


We can make a nitrile by starting with an alkyl halide and doing SN2 reaction on it using CN-, like in the example shown above.



REACTIONS OF CARBOXYLIC ACIDS


Reduction

LiAlH4 turns carboxylic acid into an alcohol


Reagent: 1.LiAlH4 2. H3O+ (or H2O)


Product: Turn COOH into CH2OH

 Reduction Of Carboxylic Acid
 Reduction Of Carboxylic Acid


Fischer Esterification

Carboxylic Acid can be converted into an ester ( COOR group) with the use of ROH and acid.

Product: Turn OH on the COOH into OR

Fischer esterification
Fischer esterification

Fischer esterification mechanism
Fischer esterification mechanism


Esterification Using Diazomethane


Another way to turn carboxylic acid into an ester is with the use of CH2N2.


In this reaction the reagent is CH2N2 and for the product we have to turn OH into OCH3.


esterification of carboxylic acid using diazomethane mechanism
esterification of carboxylic acid using diazomethane mechanism


Decarboxylation

Decarboxylation takes place when there is a COOH group one carbon away from the carbonyl group (C=O) (beta keto acid). In this reaction COOH group is lost from the molecule and becomes CO2.


All we need to do is to locate carboxylic acid one carbon away from the carbonyl group (C=O). Then we just cut that COOH group off. This reaction usually occurs under heat.


decarboxylation reaction and mechanism
decarboxylation reaction and mechanism

Conversion to Acid Chlorides

In this reaction reaction, carboxylic acid gets converted to an acid chloride with the help of SOCl2 (thionyl chloride) reagent. Acid chloride can react further and has many different reaction it can undergo as we will learn in the next chapter.


Reagent: SOCl2

All you need to do is simply, turn OH from the carboxylic acid into Cl.

conversion of carboxylic acids to acid chlorides
conversion of carboxylic acids to acid chlorides

Alkylation Of Carboxylic Acids To Form Ketones


Carboxylic acids can react with two equivalents ( please note that its important to use two equivalents) of organolithium reagent followed by water in the second step to give ketones.


Reagent: 1. 2 R-Li (organolithium reagent) 2. H2O


Product: Get rid of OH and add R group from R-Li to the carbon with =O.

Alkylation Of Carboxylic Acids To Form Ketones
Alkylation Of Carboxylic Acids To Form Ketones

Mechanism For Alkylation Of Carboxylic Acids Using Organolithium
Mechanism For Alkylation Of Carboxylic Acids Using Organolithium

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