Updated: Nov 16, 2023
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.
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
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
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.
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.
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.
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.
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