The reaction of ozone with olefins was apparently first studied in 1855 by Schonbein,1 who reported that ozone and ethylene react to give carbonic acid, formaldehyde, and formic acid. The first ozonide was isolated by Houzeau in 18732 3as a white, amorphous, explosive product from the reaction of ozone with benzene. From these beginnings interest in this reaction and its products has grown so that ozonolysis is now recognized as perhaps the most versatile method for oxidative cleavage of the double bond.Several reviews have appeared which are pertinent to the subject of this account, and the reader is referred to them for background information. Long8 and, more recently, Bailey4 have written extensive reviews on organic ozone chemistry. More specialized reviews have been given by Bischoff and Rieche,5 Criegee,6 and Menyailo and Pospelov.7 The term ozonolysis is used here to describe that reaction of ozone with a double bond which leads to cleavage of that bond. The terms ozonization and ozonozation are more general and include all the reactions of ozone with other materials. Interest in the ozonolysis reaction falls conveniently into three general areas: use of ozone to locate unsaturation in structure determinations, use of the reaction synthetically, that is, to convert unsaturation into ketones, aldehydes, alcohols, or acids, and, finally, study of the mechanism of the reaction. This last area is the subject of this account.Considered formally, the over-all reaction is an unusual one in that the three oxygen atoms of ozone are somehow inserted into a carbon-carbon double bond to give a cyclic compound, an ozonide, with one ether and one peroxy bridge between the two carbon atoms origi-
> =C^+ 03Xc/0^c/ A0-0Adinger8 in 1925 that ozone first adds to the double bond to give an unstable adduct or molozoriide, as he called it. This unstable adduct then somehow goes on to give the normal ozonide. A number of points relative to the over-all mechanism require attention. These include (a) the nature of the initial attack of ozone on the double bond, (b) the nature and structure of the initial adduct, (c) the process or processes by which the initial adduct is converted to ozonides and other products, and (d) the influence of olefin geometry and substituents, solvent, temperature, concentration, and other reaction variables on points a-c.I. The Nature of the Initial Attack and the Structure of the Initial AdductThe questions whether the ozonolysis reaction is free radical or ionic in nature are answered by the observation of Criegee6 that ozonolysis of styrene gave no polystyrene. All mechanistic proposals which have been made have been ionic in nature.Wibaut and coworkers first suggested9'10 that the initial attack of ozone on the double bond was electrophilic in character, and evidence has accumulated that this is probably the case.9-17 Huisgen considers the formation of the initial adduct to be an example of a 1,3-dipolar cycloaddition reaction.18 This kind of a reaction would lead to a five-membered 1,2,3-triox...