What are Aldehydes, Ketones, and Carboxylic Acids?
Aldehydes, Ketones, and Carboxylic Acids are carbonyl compounds containing a double carbon-oxygen bond. These organic compounds are extremely important in organic chemistry and have numerous industrial applications.
You can Read More Chemistry Articles.
Due to the presence of the carbonyl group in both classes of compounds, their chemical properties are similar. As a result of the presence of a free hydrogen atom, aldehydes are more reactive than ketones.
The carboxyl group, one of the most important functional groups in organic chemistry, is found in organic compounds containing a carbon-oxygen double bond. The Carbonyl group is one of the most important groups present in organic compounds.
What are Aldehydes?
Aldehydes are organic substances with the functional group -CHO.
These carbonyl compounds have a central carbonyl carbon that is double-bonded to an oxygen atom and single-bonded to the R group (any alkyl group) and a hydrogen atom.
Where R represents an alkyl or an aryl group.
Preparation of Aldehydes
Hydrogen reduces acid chlorides to aldehydes in the presence of palladium catalyst spread on barium sulfate.
This reaction is referred to as the Rosenmund reduction and is primarily used to prepare aromatic aldehydes. This reaction cannot be utilized to produce ketones and formaldehyde.
Properties of Aldehydes
- Aldehyde molecules contain a central carbon that is sp2 hybridized, double-bonded to oxygen, and single-bonded to hydrogen.
- Small aldehydes are quite water-soluble.
- Formaldehyde and acetaldehyde are excellent examples. These two aldehydes have considerable industrial significance.
- Aldehydes have a propensity for oligomerization and polymerization.
- The carbonyl center of an aldehyde is electron-attracting. The aldehyde group can therefore be considered somewhat polar.
Nomenclature of Aldehydes
- Acyclic and Aliphatic Aldehydes are designated by their longest carbon chain and the suffix “-al.” For instance, CH3CH3CH2CHO is called butanal due to its four carbon atoms.
- When adding an aldehyde functional group to a ring, the “-carbaldehyde” suffix is required. C6H11CHO, for instance, is known as cyclohexanecarbaldehyde.
- In the case of natural compounds or carboxylic acids, “-oxo” is used as a prefix to emphasize the aldehyde carbon. Specifically, (CHO)-CH2COOH is known as 3-oxopropanoic acid.
Below is a list of common and IUPAC names for some aldehydes.
| Formula | Common name | IUPAC name |
| HCHO | Formaldehyde | Methanal |
| CH3CHO | Acetaldehyde | Ethanal |
| CH3-CH(CH3)-CHO | Isobutyraldehyde | 2-Methylpropanal |
| CH3-CH=CH-CHO | Crotonaldehyde | 2-Butenal |
Uses of Aldehydes
- Formaldehyde is a preservative and disinfectant for biological specimens.
- Aldehyde is used for silvering mirrors.
- Formaldehyde is utilized in the manufacturing of numerous plastics and resins.
- Benzaldehyde is utilized in the perfume and dye industries.
What are Ketones?
Ketones are organic compounds with the structure R-(C=O)-R’ and the functional group C=O.
Carbon-containing substituents are present on both sides of the carbon-oxygen double bond in these carbonyl compounds. The carbonyl carbon of the ketone group is hybridized with sp2 electrons. Ketones have a trigonal planar structure centered on the carbonyl carbon.
This structure’s bond angles are approximately 1200 degrees. Ketones tend to be nucleophilic at the oxygen atom and electrophilic at the carbon atom because the carbon-oxygen bond makes the carbonyl group polar (oxygen is more electron-withdrawing than carbon).
Ketones are mass-produced by industry for use as solvents, pharmaceuticals, and polymer precursors. Important ketones include acetone, cyclohexanone, and methyl ethyl ketone (also known as butanone).
Preparation of Ketones
In reaction with dialkyl cadmium, acid chlorides produce ketones. Grignard reagents are utilized to synthesize dialkyl cadmium.
2R-Mg-X + CdCl2 → R2Cd + 2 Mg(X)Cl
2RCOCl + R2Cd → 2R-CO-R + CdCl2
The method facilitates the preparation of mixed ketones in a convenient manner.
Properties of Ketones
- Due to the presence of a polar carbonyl group, ketones are inherently polar. Therefore, their boiling points are greater than those of nonpolar compounds.
- It cannot form alcohols with intermolecular hydrogen bonds because no hydrogen is attached to an oxygen atom.
- As a result of the shifting of pi electrons, ketones have greater dipole moments than alcohols or ethers.
- The reaction between ketones and hydrogen cyanide yields cyanohydrins. Normally, the reaction occurs in the presence of a base, which acts as a catalyst; in its absence, the reaction proceeds slowly.
- When added to sodium bisulfite, the majority of ketones produce bisulfite addition products.
Nomenclature of Ketones
Ketones are named with the suffix “-anone” after their parent alkanes. The position of the carbonyl group in the ketone is indicated by a number when naming the ketone. For instance, CH3(CO)CH3 is known as 2 propanone. However, this substance is commonly known as acetone.
Commonly, ketones are named by writing the name of each alkyl group attached to the carbonyl carbon, followed by “ketone” as the final word. Butanone, for instance, can be written as methyl ethyl ketone.
| Formula | Common name | IUPAC name |
| CH3-C(O)-CH3 | Acetone | Propanone |
| CH3-C(O)-CH2-CH3 | Ethylmethylketone | Butanone |
| CH3-CH2-C(O)-CH2-CH3 | Diethyl ketone | Pentan-3-one |
| CH3-CH(CH3)-C(O)-CH3 | Isopropyl methyl ketone | 3-Methylbutan-2-on |
Uses of Ketones
- Propanone is utilized in the production of polymers such as perspex.
- Ketones are used as solvents and as precursors in the synthesis of numerous organic compounds.
- Typically, acetone and ethyl methyl ketone are used as industrial solvents.
What is Carboxylic Acid?
Carboxylic acids are organic compounds with a (C=O)OH group linked to a R group (where R refers to the remaining part of the molecule).
Commonly, the COOH group is referred to as a carboxyl group. Typically, carboxylic acids can be represented by the formula R-COOH. Carboxylic acids have a polar nature. Due to the hydrogen bond accepting nature of the C=O group and the hydrogen bond donating nature of the O-H bond, they can also participate in hydrogen bonding. In general, their boiling points are higher than water’s, and they tend to form stable dimers.
In the manufacture of pharmaceuticals, food additives, solvents, and polymers, carboxylic acids play an essential role. The carboxylic acids acetic acid, adipic acid, and citric acid are extremely valuable industrially.
Preparation of Carboxylic Acids
Common oxidizing agents such as potassium permanganate in neutral acidic or alkaline media or potassium dichromate and chromium trioxide in acidic media readily convert primary alcohols to carboxylic acids.
RCH2OH → RCOOH
CH3(CH2)8CH2OH → CH3(CH2)8COOH
Properties of Carboxylic Acids
- Carboxylic acids are polar compounds that can form numerous hydrogen bonds.
- In cold water, aromatic carboxylic acids are practically insoluble. Every carboxylic acid is soluble in organic solvents such as ether, alcohol, and benzene.
- The most acidic organic acids are carboxylic acids, but they are less acidic than mineral acids such as nitric acid and sulfuric acid.
Nomenclature of Carboxylic Acids
- Carboxylic acids are denoted by the addition of the suffix “-oic acid” to their parent chain. For instance, C3H7COOH is known as butanoic acid.
- Even if other substituents are present, the carboxylic acid is considered to be in the first position of the parent chain, as evidenced by the name 3-Chloropropanoic acid.
- The COOH group can also be referred to as “carboxy” and used as a substitute in the parent structure’s name. For instance, 2-furoic acid is also known as 2-carboxy furan.
| Formula | Common name | IUPAC name |
| HCOOH | Formic acid | Ethanoic acid |
| CH3COOH | Acetic acid | Ethanoic acid |
| CH3CH2COOH | Propionic acid | Propanoic acid |
| C6H5COOH | Benzoic acid | Benzenecarboxylic acid |
Frequently Asked Questions – FAQs
Q.1 Do carboxylic acids and aldehydes react?
Carbonyl groups in aldehydes and ketones can be oxidized to form carboxylic acid, the next “oxidation level” compound. Adding water to an aldehyde or ketone yields a compound known as a hydrate or gemdiol (two OH groups on one carbon). Acids and bases facilitate the reaction.
Q.2 Are ketones and aldehydes carboxylic acid derivatives?
In contrast to aldehydes and ketones, carboxylic acid derivatives contain a group containing a negatively charged heteroatom (typically oxygen, nitrogen, or sulfur) that is directly connected to the carbonyl carbon atom. Consider carboxylic acid derivatives to be bilateral.
Q.3 Which is more acidic aldehyde or ketone?
Due to the lower electron-donating effect of protons, aldehydes are more acidic (lower pKa) than ketones, which contain alkyl groups.
Q.4 What does Schiff’s test for?
The Schiff test is a chemical test used to detect aldehydes in a particular analyte by reacting the analyte with a small quantity of Schiff reagent.
Q.5 How do you purify aldehydes?
As previously described, solid aldehyde can be dissolved in ether and purified in this manner. They can also be steam-distilled, sublimated, and crystallized from toluene or petroleum ether as an alternative.
In conclusion – Aldehydes, Ketones, and Carboxylic Acids are extremely important industrial and laboratory carbonyl compounds. Their nomenclature can be determined by adhering to IUPAC guidelines or common practices.
