Preparation of Ketones by Oxidation Hydration Friedel Crafts Acylation and Other Reactions
Ketones can be understood as an organic compound with a carbonyl group, where one carbon atom is bonded to an oxygen atom, whereas the other bonds are hydrocarbon radicals. The compounds have significant physiological properties and are used for medical purposes. Anti-inflammatory agents have ketone groups. Ketones are the building blocks of paints, solvents, lacquers, and textiles. Several manufacturing explosives are made up of ketones. Ketone is also used in the application of the hydraulic agents and preservation and tanning. In no small measure, the ketone is one of the most significant compounds for the growing industrial sector.
Structure of Ketones
A carbonyl group (C=O) has two R groups attached to it, and the R group needs to have at least one molecule of carbon compound. It is the R group that determines the type of ketone. Furthermore, the molecular formula of the same is represented as RCOR.
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Ketone Reactions
Ketones are considered to be one of the most reactive compounds in chemistry. Still, in comparison to the aldehydes, the ketones are less responsive and reactive. Ketones and aldehydes are similar, considering the carbonyl group forming the base of any chemical activity. The ketones have uneven electronic distribution, which is responsible for its polar nature. The unequal distribution is responsible for the carbon atoms having a positive charge.
In the case of the secondary alcohol, ketone preparation is possible with oxidation, resulting in the formation of ketonic compounds. However, in the case of ketones, they do not go through any further process of oxidation similar to that of the aldehydes.
The oxidation of secondary alcohol results in the forming of several oxidizing agents, including chromic acid, potassium permanganate pyridinium chlorochromate, and manganese dioxide.
Identifying Ketones
It is effortless to locate a ketone merely from the chemical word. In case the name of the chemical term ends with a suffice "one," then the compound has the presence of ketone in it.
To identify the ketone from its physical properties, you need to check the solution's water solubility and the boiling point. If it is a keystone, then the water solubility will be very high, and a boiling point will be high. When a solution has the presence of ketone, it can be marked by the charge of the molecules.
In case the solution has a high polarity that is the characteristic of electron hogging, it is considered to be very attractive relatively.
Preparation of Ketones
Several methods of Preparation of Ketones are widely practised in the chemical laboratories and on an industrial scale. Some of the methods have been listed down below:
Preparation of Ketones From Nitriles
Ketones under this process can be obtained by treating the nitriles with the Grignard reagent. After the solution is prepared, it needs to undergo hydrolysis to form the final product, ketone.
For example: When Magnesium is made to react with nitrile with an aqueous acid, then ketone is formed along with Ammonia and Magnesium salt is the residual. Some bonds are formed while some are broken in this chemical process of preparation of ketone from nitrates.
Preparation of Ketones by Dehydrogenation of Alcohols
In case, two hydrogen molecules are removed from the concerned alcohol molecule, then the dehydrogenation process of alcohol occurs. During the oxidation process, the C-O and the O-H strong bonds are broken down to form merely C=O bonds. Thus, to produce ketones, secondary alcohol must go through the process of dehydrogenation.
However, in the case of the tertiary alcohols after the oxidation process, the dehydrogenation must be altered with dehydration. Thus, when it comes to tertiary alcohol, alkalines are used for manufacturing.
Example: When n-Propyl alcohol undergoes an oxidation reaction under copper solution then Propionaldehyde is formed and hydrogen gas is released.
Preparation of Ketones from Acyl Chlorides
In case, the acyl chlorides are treated with as strong metal halide and then the Grignard reagent is made to react, ketones are formed. For example cadmium chloride when made to react with the reactive reagent, then the dialkyl cadmium is a solution obtained. The result formed then is prepared to act with acyl chlorides to create ketones. However, if you consider using Rosenmund's Reaction for the same, then the ketone will not be formed.
Ketones Preparation From Benzene and Substituted Benzenes to Form Aromatic Ketones
Aromatic ketone formation is a straightforward process with the help of benzenes and substituted benzenes. In chemistry, this is supposed to be the best-suited method to prepare aromatic ketone. In the technique, the benzene is treated with acid chloride to obtain ketone. Such a reaction is only possible in the presence of a catalyst such as an anhydrous aluminium chloride, which is a Lewis acid.
FAQs on Ketone Preparation and Its Important Methods in Organic Chemistry
1. What is ketone preparation in organic chemistry?
Ketone preparation refers to the chemical methods used to synthesize compounds containing a carbonyl group (>C=O) bonded to two carbon atoms. Ketones have the general formula R–CO–R′ and are important in laboratory and industrial organic synthesis.
- The carbonyl carbon is bonded to two alkyl or aryl groups.
- They are commonly prepared from secondary alcohols, alkenes, acyl chlorides, or via Friedel–Crafts acylation.
- Example ketone: propanone (CH3COCH3), also known as acetone.
2. How are ketones prepared from secondary alcohols?
Ketones are prepared from secondary alcohols by oxidation using oxidizing agents such as acidified potassium dichromate. In this reaction, the –OH group is converted into a carbonyl group.
- General reaction: R–CHOH–R′ + [O] → R–CO–R′ + H2O
- Example: CH3CHOHCH3 + [O] → CH3COCH3 + H2O
- Common oxidizing agents: K2Cr2O7/H2SO4, KMnO4.
3. How do you prepare ketones from alkenes?
Ketones can be prepared from alkenes by ozonolysis or acid-catalyzed hydration depending on the alkene structure.
- Ozonolysis: Cleavage of double bond using O3 followed by reduction forms ketones or aldehydes.
- Example: CH3CH=CHCH3 + O3 → 2CH3CHO (after workup conditions).
- Acid-catalyzed hydration of certain alkenes can form secondary alcohols, which upon oxidation give ketones.
4. How are ketones prepared by Friedel–Crafts acylation?
Ketones are prepared by Friedel–Crafts acylation through the reaction of an aromatic compound with an acyl chloride in the presence of AlCl3. This reaction introduces an acyl group (–CO–R) onto a benzene ring.
- General reaction: C6H6 + RCOCl → C6H5COR + HCl (AlCl3 catalyst)
- Example: C6H6 + CH3COCl → C6H5COCH3 + HCl
5. What is the preparation of ketones from acyl chlorides?
Ketones are prepared from acyl chlorides by reacting them with dialkylcadmium or organocuprate reagents, which stop the reaction at the ketone stage.
- General reaction: RCOCl + R′2CuLi → R–CO–R′ + R′Cu + LiCl
- This prevents further reaction to tertiary alcohols.
- It is useful for selective synthesis of unsymmetrical ketones.
6. What is the difference between preparation of aldehydes and ketones?
The main difference is that aldehydes are formed by oxidation of primary alcohols, while ketones are formed by oxidation of secondary alcohols.
- Primary alcohol + [O] → Aldehyde
- Secondary alcohol + [O] → Ketone
- Aldehydes have the group –CHO, while ketones have –CO– between two carbon atoms.
7. Can ketones be prepared by hydration of alkynes?
Yes, ketones are prepared by acid-catalyzed hydration of alkynes in the presence of HgSO4, forming an enol that tautomerizes to a ketone.
- General reaction: RC≡CH + H2O → R–CO–CH3 (H2SO4, HgSO4)
- Example: CH3C≡CH + H2O → CH3COCH3
- The intermediate enol rearranges to the more stable ketone form.
8. How do you prepare ketones by oxidation of alkenes?
Ketones are prepared by oxidative cleavage of alkenes using strong oxidizing agents such as hot KMnO4. The double bond is broken, forming ketones or carboxylic acids depending on substitution.
- Example: (CH3)2C=C(CH3)2 + [O] → 2CH3COCH3
- More substituted carbons tend to form ketones.
9. What are the common laboratory methods for ketone preparation?
Common laboratory methods for ketone preparation include oxidation of secondary alcohols, Friedel–Crafts acylation, hydration of alkynes, and reaction of acyl chlorides with organocuprates.
- Oxidation: Secondary alcohol → Ketone
- Friedel–Crafts: Benzene + Acyl chloride
- Hydration of alkynes: Acid + HgSO4
- Organocuprate reaction: Acyl chloride + R2CuLi
10. Why can’t ketones be prepared by oxidation of tertiary alcohols?
Ketones cannot be prepared by oxidation of tertiary alcohols because tertiary alcohols lack a hydrogen atom on the carbon bearing the –OH group. Oxidation to a carbonyl compound requires removal of this hydrogen.
- Tertiary alcohol structure: R3COH
- No α-hydrogen available for oxidation.
- Strong oxidizing conditions may cause carbon–carbon bond cleavage instead of ketone formation.
