What Is Norbornene?
Norbornene is a cyclic hydrocarbon with the molecular formula C7H10.
Its IUPAC name is bicyclo[2.2.1]hepta-2-ene, and it is also known as norbornylene or norcamphene.
The CAS number used to identify the substance is 498-66-8.
Uses of Norbornene
Norbornene is rarely used in its pure form. It is used as a raw material for other useful compounds, as a pharmaceutical intermediate, as a pesticide ingredient, as an aromatic ingredient, and in synthetic organic research.
A characteristic application is when it is used as a monomer for polymerization due to the presence of vinyl bonds in its ring. Homopolymer, which is polymerized solely from Norbornene, has high heat resistance due to the rigid ring structure in its main chain. It is also highly transparent and has a low birefringence index, making it suitable for use as an optical waveguide for optical communications.
In addition, polymers copolymerized with other vinyl monomers, such as ethylene, propylene, and butadiene, are also used. In particular, the addition of norbornene to ethylene-propylene rubber is useful for controlling the physical properties of the rubber.
At this time, various norbornene derivative monomers have been proposed, in which substituents are added to norbornene in addition to norbornene as a monomer.
Properties of Norbornene
Norbornene is a white solid at room temperature and pressure and has a sour, pungent odor. Its melting point is 44-46°C and boiling point is 96°C, so it melts and vaporizes easily with a little heating. Being a simple hydrocarbon, it is virtually insoluble in water, while it is highly soluble in organic solvents.
Norbornene’s skeleton is strongly distorted because it is constrained by two ring structures. The distortion at the rigid double bond is particularly large and unstable, and the reactivity of this part is very high. Therefore, ring-opening metathesis reactions and addition polymerization reactions are likely to occur.
In terms of safety, since it is a strong eye irritant, protective eyewear should be worn when working with it, and if it should get into the eye, it should be carefully flushed with water continuously. There are also concerns about the effects on unborn children and long-term toxicity to aquatic organisms, so releasing it into the environment should be discouraged. Furthermore, it is highly flammable and is designated as a hazardous material, so handling and storage of more than the designated quantity is subject to regulations.
Other Information on Norbornene
1. How Norbornene Is Produced
The industrial production process for Norbornene is the Diels-Alder reaction of cyclopentadiene and ethylene. In the Diels-Alder reaction, an alkene is added to the conjugated diene to give a six-membered ring structure. Also called [4+2] cycloaddition, this reaction can be used to produce cyclic compounds such as Norbornene.
This reaction is exothermic and can cause a runaway reaction if not reacted with proper cooling. In the past, two people died in an accident at a Norbornene derivative manufacturing plant in which the reaction was in progress, but the stirrer was stopped, resulting in inadequate cooling, a runaway reaction, and the contents spewing out and catching fire. Therefore, it is a compound that must be manufactured with industrial care.
2. Derivatives of Norbornene
One of the most commonly used derivatives with the norbornene structure is 5-ethylidene-2-norbornene. This is a compound in which an ethylidene is added to the 5th position of Norbornene. It is used as a synthetic rubber, raw material, mainly in ethylene-propylene rubber, and is also useful as an odor-adding material for city gas.
In addition, epoxidized derivatives, taking advantage of their rigid backbone, can be used as raw materials for epoxy resins to improve the heat resistance and rigidity of epoxy resins.
However, while these derivatives may be synthesized by obtaining norbornene, one manufacturing method is to derivatize its precursor, such as cyclopentadiene, and then form the norbornene backbone later by the Diels-Alder reaction.