What is the Difference Between Ketal and Acetal

The key difference between ketal and acetal is that ketal compounds are formed from ketones, whereas acetal compounds are formed from either aldehydes or ketones.

Acetals and ketals are formed from the reaction of the carbonyl with alcohols, including methanol and ethanol, in the presence of anhydrous conditions and an acid catalyst. However, many alcohols are used in generating acetals and ketals, where ethanol and methanol are the most common forms. Moreover, ketals can be categorized as a subset of acetals.

CONTENTS

1. Overview and Key Difference
2. What is Ketal  
3. What is Acetal
4. Ketal vs Acetal in Tabular Form
5. Summary – Ketal vs Acetal 

What is Ketal?

Ketal compounds are functional groups derived from a ketone via the replacement of the carbonyl group by two alkoxy groups. It is a subclass of acetal compounds. Therefore, we can name it an acetal derived from a ketone. Generally, a ketal is generated from the reaction of a hemiketal with an alcohol in an acidic solution. This substance has two -OR groups coming from the alcohol and two -R groups coming from the ketone that is bonded to the original carbonyl carbon. These -R groups represent either alkyl or aryl groups.

When naming a ketal compound, the name of the appropriate aldehyde or ketone should be used, followed by the O-substituent, which is then followed by the word “ketal” (or “acetal” in the case of acetal compounds) with a space in between them.

On the other hand, a cyclic ketal is a ketal compound having a ketal carbon along with one or two oxygen atoms that occur as members of a ring. Generally, these compounds form when the reaction between ketones and diols takes place.

What is Acetal?

Acetal is a functional group having the chemical formula R2C(OR’)2. In this chemical formula, the R groups are either organic fragments or hydrogen, while the R’ groups are only organic fragments but not hydrogen. Moreover, the two R’ groups can be equivalent to each other, giving a symmetrical acetal. If they are not equivalent, then we can get a mixed acetal.

Typically, acetals are convertible to aldehydes or ketones. Therefore, they have the same oxidation state at the central carbon atom. However, the convertible forms have different chemical stability and reactivity when compared to the analogous carbonyl compounds. Moreover, the central carbon atom of an acetal group has a valency of four – meaning four covalent bonds around it, making the carbon centre saturated. In addition, this carbon centre has a tetrahedral geometry.

What is the Difference Between Ketal and Acetal?

Ketal compounds are functional groups derived from a ketone via the replacement of the carbonyl group by two alkoxy groups, while acetal is a functional group having the chemical formula R2C(OR’)2. The key difference between ketal and acetal is that ketal compounds are formed from ketones, whereas acetal compounds are formed from either aldehydes or ketones. Therefore, ketal compounds are more related to ketones, whereas acetal compounds can be related to aldehydes or ketones based on their formation.

The below infographic presents the differences between ketal and acetal in tabular form for side by side comparison.

Summary – Ketal vs Acetal

Ketal compounds are functional groups derived from a ketone via the replacement of the carbonyl group by two alkoxy groups. Acetal is a functional group having the chemical formula R2C(OR’)2. The key difference between ketal and acetal is that ketal compounds are formed from ketones, whereas acetal compounds are formed from either aldehydes or ketones.

Reference:

1. “14.3: Acetal Formation.” Chemistry LibreTexts, Libretexts, 11 Aug. 2020.
2. “Ketal.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Ketal formation” By Ryan Neff – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Carbohydrate – Acetal” By Edk006 – Own work (CC BY-SA 3.0) via Commons Wikimedia