The key difference between isocyanate and diisocyanate is that isocyanate is a functional group having a nitrogen atom, carbon atom and an oxygen atom bonded to each other respectively via double bonds whereas diisocyanate is a compound having two isocyanate anions or functional groups.
Isocyanate and diisocyanate are similar to each other because a diisocyanate compound forms from the combination of two isocyanate groups. That is how the name diisocyanate forms: “di-” prefix is used to express the meaning “two.”
CONTENTS
1. Overview and Key Difference
2. What is Isocyanate
3. What is Diisocyanate
4. Side by Side Comparison – Isocyanate vs Diisocyanate in Tabular Form
5. Summary
What is Isocyanate?
Isocyanate is a functional group having the chemical formula N=C=O. Therefore, we can give the chemical formula of an isocyanate compound as R-N=C=O. Generally, organic compounds containing an isocyanate group is generally named as an isocyanate. Similarly, if there are two isocyanate groups in an organic compound, we can call it a diisocyanate. Moreover, it is important to know the difference between cyanate esters and isocyanides because they have a close resemblance. Here, the cyanate ester functional group has a different arrangement from that of isocyanate group; cyanate group has O-C≡N structure while isocyanate has O=C=N structure.
Figure 01: Structure of an Isocyanate-containing Compound
The structure of isocyanate is closely similar to the structure of a carbon dioxide molecule. This is because both isocyanate and carbon dioxide have three atoms in a linear geometry (carbon atom being the middle atom) and there are double bonds between these three atoms.
We can produce isocyanate compounds using amines via phosgenation. For example, we can treat amines with phosgene to get isocyanate and hydrochloric acid as products. This reaction, however, proceeds via an intermediate (an organic carbonyl chloride compound). Moreover, the use of phosgene is hazardous, so we need to take precautions when preparing isocyanate in this method.
When considering the reactivity of isocyanates, these compounds can act as electrophiles. Therefore, they are reactive toward a variety of nucleophiles, including alcohols, amines and water. For example, the reaction between an isocyanate and an alcohol produces a urethane linkage. However, if we need to get polyurethane, there should be two isocyanate groups per molecule to get a polymerized structure; diisocyanate is used in that case.
What is Diisocyanate?
Diisocyanate is a term used to name chemical compounds having two isocyanate groups per molecule. This means these compounds have two N=C=O groups. In these compounds, the two isocyanate groups can occur as anions or as functional groups. Diisocyanates are useful in the production of polyurethanes because there are two isocyanate groups that can form two urethane linkages per molecule to form a polymerized structure.
Figure 02: Formation of Polyurethane using a Diol and Diisocyanate
In this polymerization process of producing polyurethane, diisocyanate compound needs to be treated with an organic compound containing two or more hydroxyl groups. E.g. diols, polyols, etc. The general equation for polyurethane formation is as follows:
What is the Difference Between Isocyanate and Diisocyanate?
Isocyanate and diisocyanate are closely similar to each other because a diisocyanate compound forms from the combination of two isocyanate groups. Therefore, the key difference between isocyanate and diisocyanate is that isocyanate is a functional group having a nitrogen atom, carbon atom and an oxygen atom bonded to each other respectively via double bonds whereas diisocyanate is a compound having two isocyanate anions or functional groups.
Below infographic tabulates the differences between isocyanate and diisocyanate.
Summary – Isocyanate vs Diisocyanate
The terms isocyanate and diisocyante are used in discussing the preparation of polyurethane. This is because diisocyante is important as a functional group that is used in polyurethane production. The key difference between isocyanate and diisocyanate is that isocyanate is a functional group having a nitrogen atom, carbon atom and an oxygen atom bonded to each other respectively via double bonds whereas diisocyanate is a compound having two isocyanate anions or functional groups.
Reference:
1. Isocyanate. (2020, August 13). Retrieved August 31, 2020, Available here.
Image Courtesy:
1. “Isocyanate group” By Fvasconcellos (talk · contribs) – Vector version of Image:Isocyanate-group.png by Ben Mills. (Public Domain) via Commons Wikimedia
2. “Polyurethane synthesis” By RLM0518 – Own work (CC BY-SA 3.0) via Commons Wikimedia