Epoxide

What is Epoxide?

A cyclic ether with a three-atom ring is known as an epoxide. This ring forms an equilateral triangle- a structure that makes it strained.

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An Overview of Epoxide

The three-atom ring of the epoxide is highly reactive. It is even stronger than the other ethers. Epoxide rings are produced on a large scale for many applications. With low molecular weight, these compounds, exist as colourless, non-polar and volatile entities most of the time. The epoxides which find wide applications in the industry are ethylene oxide and propylene oxide. These are produced on a scale of 15 and 3 million tonnes per year, respectively.

What is The Basic Structure of Epoxide?

The basic structure of an epoxide consists of an oxygen atom which is attached to two adjacent carbon atoms that belong to a hydrocarbon. Further, a more complex form of epoxide is made up of epoxidation of alkenes. In this process, peroxy acid (RCO3H) is used in order to transfer an atom of oxygen. However, the general ethers can be regarded as the class of chemical compounds which contain an ether group. This group is the combination of oxygen, an atom that is connected to two alkyl or aryl groups. The formula for this is ROR in general terms which state that R and R represent the aryl or the alkyl groups. So, it can be concluded that the fundamental structure of it contains two carbons atoms of a hydrocarbon that is attached to an oxygen atom. 

An epoxide is regarded as the cyclic ether with a three-atom ring. Now, this ring which estimates an equilateral triangle makes it strained and therefore becomes highly reactive in compare to the other form of ethers.  It is made up of the oxidation of ethylene over a silver catalyst. 

Applications of Epoxide

It is used as a fumigant and in order to make antifreeze, ethylene glycol and various other useful compounds. As we know that more complicated epoxides are generally made up by the epoxidation of alkenes. This takes place by the common usage of peroxy acid in order to transfer an atom of oxygen. 

Further, another common industrial method of getting epoxide involves a two-step process. In the first step, the alkene is converted into a chlorohydrin. In the second step, the chlorohydrin is treated with a base to eliminate hydrochloric acid which gives birth to the epoxide. This is the process to make propylene oxide. Further, it can be used for assembling polymers which are known as epoxies. These are an excellent form of adhesives and are also greatly helpful in surface coatings. One of the most common forms of epoxy resin is formed from the reaction of epichlorohydrin with a bisphenol-A.

How is Epoxide Synthesised?

Epoxide can be synthesized in numerous ways. Propylene oxide and ethylene oxide are the two different forms of epoxides that are made in a large amount with 15 to 3 tonnes each year. However, there are certain things to consider when talking about the oxidation of alkenes. So, when the alkenes are oxidised it is heterogeneously catalysed. In this case, when ethylene reacts with oxygen under a silver catalyst, it leads to the formation of an epoxide. Now as per the stoichiometry, it can be expressed chemically as 

7H2C= CH2+6O2- 6C2H4O+ 2CO2+2H2O

What Happens When Epoxide is Homogenously Catalysed for Asymmetric Epoxidation?

The chiral epoxides are produced from prochiral alkenes. Numerous metal complexes act as active catalysts. The most essential among them are vanadium, molybdenum and titanium. 

What is Nucleophilic Epoxidation?

By the usage of compounds such as peroxides, electron-deficient olefins can be epoxidized. Now, this form of reaction has two steps. In the first step, the nucleophilic conjugate is added to the oxygen atom in order to give a stabilized carbanion. However, in the case of biosynthesis, epoxides are not common in nature. They are made by oxygenation of alkenes. 

What Are The Uses of Epoxide?

The uses of epoxide are as follows:

  • There are numerous uses of ethylene epoxide. This includes generation of surfactants and detergents.

  • It is also used as a stabilizer in various forms of materials like PVC. Moreover, they are also used in the production of Epoxy resist that have low viscosity and which does not comprise strength and physical properties.

  • Epoxides reaction with amines results in epoxy glues and structural materials. They are also useful in a few things for instance in aerosols, resins and also in chemical intermediates.

Why Are Certain Epoxides Toxic?

Majority of the epoxides are regarded as toxic. The reason for their toxicity is high reactivity that makes them mutagenic. The three-member epoxide rings are extremely strained. Thus, it is vulnerable towards ring-opening by nucleophiles. Some of the common nucleophiles are NH2, OH and S. Further there are many of such groups in biological systems. The reactions with OH and S are two of the mechanism which the body uses in order to eradicate epoxides. However, there is negligible proof that epoxides can give birth to cancer but also again, unavoidable is the facts the majority of the epoxides are mutagenic. They also form covalent bonds to guanine. Further, the adduct prevents the proper G-C base pairing. 

Brief Information on The Formation and Utilisation of Epoxides

Epoxides are greatly helpful in functional groups with regards to organic chemistry in order to generate reactive centres. Majority of the drugs are harmful as well as beneficial. They rely on the process of epoxidation in order to become biologically active. There are two processes of epoxidation which are ring-closing and ring opening-reactions. Epoxides contain an oxirane that is a three-membered ring which contains an oxygen atom. To prepare epoxides a double bond is needed across which the oxygen is to be added across the C-C bond in order to form the oxirane ring. 

The ring-closing reactions can be accomplished in three different ways that start with an alkene reactant. MCPBA and Peroxy acids are commonly used peroxides that help in the preparation of an epoxide. Now, the third process needs hydroamination across the double bond in order to form a halohydrin. The intra-molecular SN2 reaction gives birth to epoxide that forms due to the reaction with a strong base. Ring-opening and formation of alcohol via intermolecular SN2 reaction take place due to the reaction of epoxides with any strong nucleophile. Medical equipment sterilization by using ethylene oxide is one of the practical examples of ring-opening reactions where microbes present on the surface of the equipment are exposed to ethylene oxide. 

FAQ (Frequently Asked Questions)

1. Are epoxides polar?

The epoxide unit of a three-membered ring contains a 2 X C and 1 X O atoms. Via S bonds the atoms are bonded with each other. Both the C-O bonds are polar due to the high electronegativity of the O atom.

2. How are epoxides and ethers named?

There are numerous ways of naming epoxides. However, ethers have two types of names. The compound is named as an alkane with an alkoxy alkane. For instance, (CH3)2 CH-O-CH3 is 2-methoxypropane which IS the substitutive name of ether. 

Coming on to, functional class names of ether, R-OR' is named with the names of R and R in alphabetical order which is followed by the class name of ether. For Example, (CH3)2 CH-O-CH3 is ethyl isopropyl ether. 

Epoxides, on the other hand, have four types of names. The compound that is named as an alkene with an epoxy substituent can be regarded as the substitutive names. For instance, 1, 2-epoxybutane. The compound is named as an epoxide of the corresponding alkene which can be regarded as the functional names. For instance, 1-2 epoxybutane is also known as but-1-ene-epoxide. 1, 2-epoxybutane is called ethyloxirane. The O atom is number 1 automatically and so ethyl group is on C-2. This is known as the Hantzsch-Widman name of the epoxide. Lastly, ethylene oxide and propylene oxide are known as oxides of the corresponding alkene. 

3. Are epoxides electrophiles?

The carbons that are present in an epoxide group are highly reactive electrophiles because substantial ring strain is relieved when the ring opens upon nucleophilic attack. In the cell and the laboratory, epoxides are usually formed by the oxidation of an alkene. It can be considered that epoxides are electrophilic by the strained three-membered ring system where nucleophilic attach and carbon releases the ring strain.

4. How do you break epoxides?

Epoxides can be opened by another form of anhydrous acids (HX) in order to form a trans halohydrin. Now when both the epoxide carbons are either primary or secondary, the less substituted carbon and also an SN-2 like reaction will be attacked by the halogen anion. For breaking an epoxide ring it is essential to consider that in an aqueous solution the base catalysed epoxide ring-opening occurs by SN2 attack of a hydroxide ion at the less hindered carbon. It involves protonation of the epoxide oxygen atom which is followed by an SN-1 like carbocation formation at the more substituted carbon.