Table of Contents
What are Carboxylic Acids?
- A carboxylic acid is a molecule with a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group. The simplest carboxylic acid is formic acid, HCOOH.
- Carboxylic acids are prepared by the oxidation of an alcohol. The alcohol is converted to an aldehyde, which is then oxidized to the carboxylic acid.
- Carboxylic acids undergo a variety of reactions. The most important reaction is the acid-catalyzed dehydration of a alcohol to form an alkene. Carboxylic acids can also react with ammonia to form amides.
Structure of Carboxylic Acid
A carboxylic acid contains a carbon atom bonded to an oxygen atom that is double-bonded to an oxygen atom, forming a carbonyl group. Attached to the carbonyl group is a hydrogen atom and a carboxyl group.
1. Using Primary Alcohols for Preparation of Carboxylic Acid
The first step in preparing a carboxylic acid ester is to react a primary alcohol with an acid chloride in the presence of a base. The acid chloride is an electrophile that attacks the carbon atom in the alcohol that is bonded to the hydroxyl group. This reaction forms an acyl chloride, which is a reactive intermediate.
The acyl chloride then reacts with an alcohol molecule to form the carboxylic acid ester. This reaction is catalyzed by a base, which helps to stabilize the acyl chloride intermediate. The base also helps to prevent the formation of an unwanted by-product, an aldehyde.
2. Preparation from Aldehydes
Aldehydes can be converted to ketones by treatment with a strong base, such as sodium hydride. The base abstracts a proton from the aldehyde, resulting in the formation of an enolate ion. The enolate ion can then be attacked by a ketone, resulting in the formation of a ketone and an alcohol.
3. Preparation from Alkylbenzenesulfonates
The preparation of alkylbenzenesulfonates is illustrated by the following example.
Example
To a mixture of benzene (100 ml) and sulfuric acid (10 ml) at room temperature is added sodium methylbenzenesulfonate (5.0 g, 27.0 mmol). The reaction mixture is then heated to reflux for 16 hours. The reaction mixture is then cooled to room temperature and the sodium methylbenzenesulfonate is filtered off. The filtrate is then concentrated in vacuo and the residue is chromatographed on silica gel using hexane/ethyl acetate (9:1) as the eluent to give methylbenzenesulfonate (2.5 g, 26% yield) as a colorless oil.
1H NMR (CDCl 3 ): δ 1.20 (t, 3H, J = 7.2 Hz), 1.40-1.60 (m, 4H), 2.20 (s, 3H), 3.10 (q, 2H, J = 7.2 Hz), 6.80 (d, 1H, J = 8.4 Hz), 7.20-7.40 (m, 5H).
4. Preparation from Nitriles
Nitriles can be reduced to aldehydes with sodium borohydride in aqueous solution.
The aldehyde can then be oxidized to the carboxylic acid with permanganate or chromic acid.
5. Preparation from Carbonyl Compounds
Aldehydes and ketones can be converted to carboxylic acids by reaction with anhydrous or concentrated sulfuric acid.
6. Preparation of Amides
- There are a variety of methods for preparing amides, the most common of which is the reaction of an amine with a carboxylic acid.
- This reaction is often catalyzed by a base, such as sodium hydroxide, and usually takes place in an aqueous solvent, such as water or ethanol. The amine and carboxylic acid react to form an amide and water.
- Other methods for preparing amides include the reaction of an amine with an acyl chloride or an ester, and the reaction of an imine with a carboxylic acid.
7. Preparation of Grignard Reagents
1-Methyl-3-phenylpropane can be converted to the Grignard reagent methylmagnesium bromide by treatment with magnesium and bromoethane in an ether solvent.
The Grignard reagent is then added to a solution of ketone in an ether solvent, such as diethyl ether, to form the corresponding ketal.
8. From Acid Chlorides to Alcohols
The conversion of an acid chloride to an alcohol can be accomplished by treating the acid chloride with aqueous sodium hydroxide. The reaction produces an alcohol and sodium chloride.
RCOCl + NaOH → ROH + NaCl
Physical Properties of Carboxylic Acid
The carboxylic acid is a colorless liquid with a pungent odor. It is soluble in water and miscible with alcohols and ethers.
1. Reaction with Metals
The most common reaction of nitric acid is with metals. In this type of reaction, nitric acid reacts with the metal to produce a salt and nitrogen dioxide gas. The salt that is produced can be a variety of different compounds, depending on the metal that was reacted with the nitric acid. Some common compounds that are produced include sodium nitrate, potassium nitrate, and ammonium nitrate.
2. Reaction with Other Acids
Nitric acid can also react with other acids to produce a variety of different compounds. When it reacts with sulfuric acid, for example, it produces sulfurous acid and nitrogen dioxide gas. When it reacts with hydrochloric acid, it produces hydrochloric acid and nitrogen dioxide gas.
3. Reaction with Alkalis
Alkalis react with carbonates to form soluble carbonates and water.
For example, when sodium carbonate is added to a solution of calcium carbonate:
Na 2 CO 3 (aq) + CaCO 3 (s) → 2Na+ (aq) + Ca2+ (aq) + CO 3 2- (aq)
The calcium carbonate dissolves to form calcium ions and carbonate ions.
4. Reaction with Carbonates and Bicarbonates
The reaction of aqueous solutions of carbonates and bicarbonates with aqueous solutions of hydrochloric acid is a double replacement reaction.
Na 2 CO 3 (aq) + 2HCl(aq) → 2NaCl(aq) + H 2 O(l) + CO 2 (g)
KHCO 3 (aq) + HCl(aq) → KCl(aq) + H 2 O(l) + CO 2 (g)
5. Formation of Acyl Chlorides
- In the presence of a strong acid, an alcohol can react with a chlorine atom to form an acyl chloride. This is a very important reaction in industry, because acyl chlorides are often used to produce other organic compounds.
- For example, the acyl chloride produced from ethyl alcohol and chlorine can be used to produce ethyl chloride, which is a common precursor to PVC.
6. Formation of Esters (Esterification)
- In the presence of a strong acid catalyst, alcohols react with carboxylic acids to form esters.
- The reaction is reversible, so care must be taken to ensure that the equilibrium is shifted to the right.
- This can be done by using a large excess of alcohol, or by using a catalyst that favors the formation of esters.
7. Formation of Amides (Amide Formation)
- In the presence of a strong acid catalyst, amines react with carboxylic acids to form amides.
- The reaction is reversible, so care must be taken to ensure that the equilibrium is shifted to the right.
- This can be done by using a large excess of amine, or by using a catalyst that favors the formation of amides.
8. Formation of Amide
The amide I band is formed from the stretching vibration of the amide carbonyl group. The amide I band is located in the region of 1650-1750 cm-1 and is due to the coupling of the carbonyl stretch and the NH stretch. The carbonyl stretch is at 1650 cm-1 and the NH stretch is at 1750 cm-1.
The amide I band is due to the coupling of the C=O stretch and the N-H stretch.
9. Decarboxylation
This is a chemical reaction that removes a carboxyl group (COOH) from a molecule. In the cannabis world, it’s a process that’s used to activate the cannabinoids so that they can be absorbed by the body.
10. Terpenes
Terpenes are a large and diverse class of organic compounds that are found in plants. They are responsible for the unique scents and flavors of different plants. In the cannabis world, terpenes are being studied for their potential therapeutic benefits.
10.Formation of Anhydrides
Anhydrides are formed when a carboxylic acid and an alcohol react to form a ester. The carboxylic acid and alcohol both lose a molecule of water to form the anhydride.
For example, the reaction of acetic acid and ethanol produces ethyl acetate, the anhydride of acetic acid.
11.Hell-Volhard Zelinsky Reaction
The Hell-Volhard Zelinsky Reaction is a type of organic reaction that involves the conversion of an aldehyde to an alcohol. The reaction is named after the chemists Moritz Hell and Eduard Volhard, who first described it in 1902, and Vladimir Zelinsky, who developed it into a practical method in the 1930s.
The reaction proceeds via the formation of an enolate ion, which reacts with the aldehyde to produce the alcohol. The enolate ion is formed by the deprotonation of the aldehyde with a strong base, such as sodium hydride or potassium tert-butoxide.
12. Friedel Crafts Reactions
In organic chemistry, Friedel Crafts reactions are a set of reactions involving the alkylation or acylation of aromatic rings by means of an electrophile. The Friedel Crafts acylation is the most common of these reactions. The alkylation of benzene with chlorine in the presence of aluminum chloride is a classic Friedel Crafts reaction.
13. Isomerization
Isomerization is a process that involves the rearrangement of the atoms in a molecule. The most common type of isomerization is the conversion of a single isomer into another isomer of the same molecule. Isomerization reactions can be either reversible or irreversible.
14. Halogenation
Halogenation is a process that involves the addition of one or more halogens to an organic molecule. The most common type of halogenation reaction is the addition of chlorine to an organic molecule. Chlorination is a very versatile reaction that can be used to produce a wide range of products.
15. Aromatic Substitution
Aromatic substitution is a process that involves the replacement of one or more hydrogen atoms in an aromatic molecule with another atom or group of atoms. The most common type of aromatic substitution reaction is the substitution of a hydrogen atom with a halogen atom.
