The key difference between ester and thioester is that ester compounds contain carbon, hydrogen and oxygen atoms whereas thioester compounds contain carbon, hydrogen, oxygen and sulfur atoms.
Ester and thioester compounds are related to each other as their name implies; thioester differs from ester due to the presence of a sulfur atom, which replaces one oxygen atom present in an ester compound. The properties and other differences between ester and thioester are discussed below in this article.
CONTENTS
1. Overview and Key Difference
2. What is an Ester
3. What is a Thioester
4. Side by Side Comparison – Ester vs Thioester in Tabular Form
5. Summary
What is an Ester?
Esters are organic compounds having the general chemical formula R-C(=O)-OR’. These chemical compounds are derived from either organic or inorganic acid compounds in which at least one hydroxyl group is replaced by an alkoxy group. Typically, esters originate from the substitution reaction of carboxylic acids and alcohols.
Figure 01: General Structure of an Ester
There is a carbonyl centre in an ester, which gives the ester its geometry – the trigonal planar around the carbonyl carbon. Structurally, esters are flexible functional groups (unlike amides) because the barrier or rotation around this carbonyl group is low. Moreover, these compounds have low polarity. Therefore, the esters tend to be less rigid and more volatile than the corresponding amides.
When considering the reactions of esters, these chemical compounds tend to react with nucleophiles at the carbonyl carbon. The carbonyl group is weakly electrophilic, but it can undergo attacks by strong nucleophiles such as amines and alkoxides.
There are many different applications of esters; using them as components in perfumes for their fragrant odours, as components in essential oils, food flavourings, cosmetics, etc. Furthermore, esters are important as organic solvents, as natural pheromones, as naturally occurring fats and oils (fatty acid esters of glycerol), etc.
What is Thioester?
Thioesters are organic compounds having the general chemical formula R-C(=O)-SR’. These compounds are analogous to carboxylate esters and differ from them due to the presence of a sulfur atom where the linking oxygen atom occurs in carboxylate ester. A thioester forms when a thiol reacts with a carboxylic acid. In the field of biochemistry, coenzyme-A derivatives such as acetyl-CoA are well-known thioesters.
Figure 02: General Chemical Structure of a Thioester
When considering the preparation of thioesters, the most typical route is the reaction between an acid chloride and an alkali metal salt of a thiol. Another common route is the displacement of halides by the alkali metal salt of a thiocarboxylic acid.
There is a carbonyl centre in a thioester that is reactive towards the nucleophiles, including water. Therefore, these chemical compounds are common intermediates of the conversion of alkyl halides into alkyl thiols. Moreover, a thioester can combine with an amine to give an amide.
There are different applications of thioesters including the synthesis of all esters, participating in the synthesis of a number of other cellular components including peptides, fatty acids, sterols, terpenes, etc.
What is the Difference Between Ester and Thioester?
Ester and thioester are two related compounds. The key difference between ester and thioester is that ester compounds contain carbon, hydrogen and oxygen atoms whereas thioester compounds contain carbon, hydrogen, oxygen and sulfur atoms. Moreover, esters occur naturally and can be produced using different routes such as esterification of carboxylic acids with alcohols while the most typical route for thioesters is the reaction between an acid chloride and an alkali metal salt of a thiol.
Below infographic tabulates more differences between ester and thioester.
Summary – Ester vs Thioester
A thioester differs from an ester due to the presence of a sulfur atom replacing an oxygen atom in an ester. The key difference between ester and thioester is that ester compounds contain carbon, hydrogen and oxygen atoms whereas thioester compounds contain carbon, hydrogen, oxygen and sulfur atoms.
Reference:
1. “Ester.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.
Image Courtesy:
1. “Ester-general” By Sakurambo~commonswiki assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims). (Public Domain) via Commons Wikimedia
2. “Thioester-2D-A” By Thioester-2D-A.png: Ben Millsderivative work: Vladsinger (talk) – Thioester-2D-A.png (Public Domain) via Commons Wikimedia