Question

The products of our reaction (1- and 2-heptene) can form peroxides upon standing in air for a prolonged period of time. Why is 1-heptene more likely to form peroxides than heptane?

Answer 1

Dear friend

A number of commonly used organic solvents can undergo autoxidation to produce unstable and dangerous hydroperoxide and peroxides products. "Autoxidation" generally refers to the slow reaction between organic chemicals and elemental oxygen under mild conditions. Although ethers are generally recognized as dangerous peroxide formers, other organic structures (e.g. acetals, certain allylic alkenes, chloro- and fluoroalkenes, dienes, aldehydes, amides, lactams, ureas, some alkylarenes, ketones, vinyl monomers, and some alcohols) are capable of spontaneous autoxidation to form of highly unstable hydroperoxides, and monomer- and polymeric peroxides. Molecular structure is a major factor in determining the rate of autoxidation and shelf life within a class of peroxide forming chemical. The auto-peroxidation potential of a compound is greatly influenced by adjacent and nearby functional groups.

Peroxide-forming compounds invariably contain an autooxidizable hydrogen atom that is activated by adjacent structural components and/or actinic radiation These compounds react with atmospheric oxygen under ambient conditions to initially form a hydroperoxide.

Activated hydrogen atoms are often on a:

1. Methylene group adjacent to an ethereal oxygen atom (-O-CH2-, e.g. diethyl ether, THF, dioxane and diglyme).

2. Methylene group adjacent to a vinyl group or benzene ring (C=C-CH2- or Ph-CH2-, e.g. allyl or benzyl compounds).

3. CH group adjacent to two ethereal oxygen atoms (-O-CH-O-, e.g. acetals or methylenedioxy compounds).

4. CH group adjacent to two methylene groups (-CH2-CH-CH2-, e.g. isopropyl compounds and decahydronaphthalenes).

5. CH group between a benzene ring and a methylene group (-CH2-CH-Ph, e.g. cumene and tetrahydronaphthalenes).

6. A vinyl group (-C=CH2, e.g. vinyl compounds, dienes, styrenes or other monomers).

In the view of above our 1-heptene and 2-heptene have Methylene group adjacent to a vinyl group (C=C-CH2-) Within a class of peroxide-forming chemicals, the peroxidation potential is usually inversely related to the molecular weight of the compound. Compounds with ten or more carbon atoms at a peroxidizable site are considered low-risk systems. Peroxidation is generally peculiar to the liquid state. Minimal hazard is usually associated with solid, vapor or gaseous potential peroxide formers.

Hence Heptane do not have any one of the above property to undergo auto oxidation. Hence Heptane will not form peroxides.

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