What is meant by Acetophenone?
Acetophenone is defined as an organic compound that is used as an ingredient in perfumes and also as a chemical intermediate in the manufacture of resins, pharmaceuticals, flavoring agents, and also as a fo2wrm of tear gas. It has been used as a drug in sleep induction. The acetophenone formula or structural formula of acetophenone is given as \[C_{6}H_{5}COCH_{3}\].
This compound can be made from acetyl chloride and benzene, but it is most commonly made by oxidizing the ethylbenzene compound in the air.
Properties of Acetophenone
Pure acetophenone is defined as a colorless liquid. Acetophenone melting point is about 20.2 °C (68.4 °F) and acetophenone boiling point is about 202.4 °C (396.3 °F). It is slightly soluble only in water, but it is freely soluble in ethanol (otherwise in the ethyl alcohol), chloroform, and diethyl ether. Acetophenone molecular weight is 120.15 g/mol.
Natural Occurrence
Acetophenone takes place naturally in several foods, including cheese, apple, banana, apricot, cauliflower, and beef. Also, it is a castoreum component, which is the exudate from the castor sacs of the mature beaver.
Pharmacology
In the late 19th century and early 20th centuries, acetophenone was used for various medicinal uses. It was also marketed as an anticonvulsant and hypnotic under the brand name Hypnose. The typical dosage of this compound was 0.12 to 0.3 milliliters, and it was considered to contain superior sedative effects to both chloral and paraldehyde hydrate. Acetophenone, in humans, can be metabolized to carbonic acid, acetone, and benzoic acid. Hippuric acid is an indirect metabolite of acetophenone, and its presence in urine can be used to confirm acetophenone exposure, while other substances, such as toluene, can also cause hippuric acid in urine.
Production
Acetophenone is a by-product of the oxidation of ethylbenzene to ethylbenzene hydroperoxide, which can be recovered. Also, ethylbenzene hydroperoxide is given as an intermediate in the propylene oxide’s commercial production via the propylene process of oxide-styrene co-product. Primarily, ethylbenzene hydroperoxide can be converted to 1-phenyl ethanol (which is the α-methyl benzyl alcohol) in the process of having a small amount of acetophenone by-product. Acetophenone can be hydrogenated or recovered to 1-phenyl ethanol and then dehydrated to produce styrene.
Acetophenone Uses
Precursor to Resins
Commercially significant resins can be produced from the treatment of acetophenone with a base and formaldehyde. The resulting copolymers are traditionally represented using the formula \[\left ( (C_{6}H_{5}COCH)_{x}(CH_{2})_{x} \right )^{n}\], which is derived from the condensation of aldol. These substances are given as the components of inks and coatings. The hydrogenation of the aforementioned ketone-containing resins will result in modified acetophenone-formaldehyde resins. And, the resulting polyol can further be crosslinked with diisocyanates. Modified resins are found in inks, coatings, and adhesives.
Niche Uses
Acetophenone is used to produce fragrances that smell like plum, almond, jasmine, honeysuckle, and strawberry. It can also be used in chewing gums and listed as an approved excipient by the U.S. FDA.
Laboratory Reagent
In the instructional laboratories, acetophenone can be converted to styrene in a two-step method, which illustrates the reduction of carbonyls with the aid of hydride and the dehydration of alcohols, where the chemical reaction is provided below:
\[4C_{6}H_{5}C(O)CH_{3} NaBH_{4} + 4H_{2}O \rightarrow 4C_{6}H_{5}CH(OH) CH_{3} + NaOH + B(OH)_{3} \rightarrow C_{6}H_{5}CH = CH_{2}\]
A similar two-step process can be used industrially, but the reduction step is performed using hydrogenation over a copper catalyst. The chemical reaction for this is given below.
\[C_{6}H_{5}C(O)CH_{3} + H_{2} \rightarrow C_{6}H_{5}CH(OH) CH_{3}\]
The acetophenone compound is a common test substrate for asymmetric hydrogenation experiments because it is prochiral.
Drugs
Acetophenone is also used for the synthesis of several pharmaceuticals.
Dimethyl-amino-propiophenone is generated by a Mannich reaction between formaldehyde and dimethylamine. Usage of diethylamine instead gives the diethylamino analog.
Natural Occurrence
Acetophenone naturally takes place in several foods, including cheese, apple, banana, apricot, beef, and also cauliflower. It's also a member of the castoreum, which is the exudate from mature beaver castor sacs.
Reactivity of Acetophenone and Benzophenone
When we think about reactivity, here comes the picture that which type of reactivity or towards which reaction we are thinking about. Considering the electrophilic attack on the carbonyl group, we have to consider some things such that in the acetophenone compound, the +I effect of the methyl group & three hyper conjugative structures somewhat stabilizes the carbonyl carbon center. On the other side, the +R effect and +I effect of the phenyl group also stabilize the carbon center.
Here, considering the IR spectra of both of them:
Benzophenone: C=O stretching frequency is \[1659 cm^{-1}\].
Acetophenone: C=O stretching frequency is \[1690 cm^{-1}\].
It indicates that the partial single bond character because of the conjugation is greater for the Benzophenone compared to the Acetophenone. As a result, Acetophenone's reactivity is higher than that of Benzophenone.
Toxicity
The LD50 is given as 815 mg/kg (rats, oral). Currently, acetophenone is listed as a Group D carcinogen representing that; it does not produce any carcinogenic effects in humans.
FAQs on Acetophenone
1. What is acetophenone and what is its chemical formula?
Acetophenone is the simplest aromatic ketone. It consists of an acetyl group (CH₃CO-) attached to a phenyl group (C₆H₅-). Its chemical formula is C₆H₅COCH₃. In its pure form, it is a colourless, viscous liquid with a sweet, floral scent similar to jasmine or honeysuckle, which is why it's often used in perfumery.
2. What is the official IUPAC name for acetophenone?
The official IUPAC name for acetophenone is 1-phenylethan-1-one. The name is derived by identifying the main chain as 'ethanone' (a two-carbon ketone) and noting a 'phenyl' group as a substituent on the first carbon atom, which is also the carbonyl carbon.
3. How is acetophenone typically prepared from benzene in a laboratory setting?
Acetophenone is commonly prepared from benzene using the Friedel-Crafts acylation reaction. In this process, benzene (C₆H₆) is treated with an acylating agent like acetyl chloride (CH₃COCl) or acetic anhydride ((CH₃CO)₂O) in the presence of a Lewis acid catalyst, typically anhydrous aluminium chloride (AlCl₃). The electrophile generated, CH₃C⁺=O, attacks the benzene ring to form acetophenone.
4. What are the primary industrial and commercial uses of acetophenone?
Acetophenone has several important applications across different industries. Its main uses include:
- Perfumery: As an ingredient in fragrances to create scents resembling almond, jasmine, cherry, and strawberry. It is also used in soaps and detergents.
- Resin Production: It is a precursor for producing commercially significant resins when treated with formaldehyde and a base.
- Pharmaceutical Synthesis: It serves as a starting material or intermediate in the synthesis of various pharmaceutical drugs.
- Laboratory Reagent: Used in instructional labs to demonstrate reactions like carbonyl reduction and dehydration of alcohols.
5. Why is the carbonyl group in acetophenone less reactive towards nucleophiles compared to aliphatic ketones like acetone?
The carbonyl group in acetophenone is less reactive than in acetone due to the resonance effect of the attached benzene ring. The lone pair of electrons on the oxygen atom delocalises into the benzene ring, which in turn reduces the electrophilicity (positive character) of the carbonyl carbon. This stabilisation makes the carbonyl carbon a less attractive target for nucleophiles, thus decreasing its reactivity compared to acetone, where the carbonyl carbon's positive charge is only influenced by the weak electron-donating effect of two methyl groups.
6. Can acetophenone undergo the haloform reaction, and why is this reaction significant?
Yes, acetophenone gives a positive haloform reaction (specifically, the iodoform test). This is because it is a methyl ketone, containing the required CH₃-C=O group. When reacted with iodine and a base like sodium hydroxide (I₂/NaOH), it gets converted into sodium benzoate and forms a yellow precipitate of iodoform (CHI₃). This reaction is significant as it serves as a reliable chemical test to distinguish methyl ketones from other ketones.
7. How does the chemical reactivity of acetophenone compare to that of benzophenone?
Acetophenone is more reactive than benzophenone (C₆H₅COC₆H₅) towards nucleophilic addition reactions. There are two main reasons for this:
- Electronic Effects: Benzophenone has two phenyl groups attached to the carbonyl carbon. Both rings delocalise and stabilise the carbonyl group through resonance, making it significantly less electrophilic than acetophenone, which has only one phenyl group.
- Steric Hindrance: The two bulky phenyl groups in benzophenone create more steric hindrance around the carbonyl carbon, making it physically harder for a nucleophile to approach and attack, compared to the smaller methyl group in acetophenone.
