Dry ozonation

All classes of primary amine (including primary, secondary, and tertiary alkyl as well as aryl) are oxidized to nitro compounds in high yields with dimethyl dioxirane." Other reagents that oxidize various types of primary amines to nitro compounds are dry ozone, various peroxyacids," MeRe03/H202,"" Oxone ," ° tcrt-butyl hydroperoxide in the presence of certain molybdenum and vanadium compounds, and sodium perborate." ... 

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

A diagram of a typical gas-phase (ozone-ethylene) chemiluminescent ozone analyzer is shown in Figure 6-10. The detector responds linearly to ozone concentrations between 0.003 and 30 ppm no interferences were initially observed. More recently, however, it has been established that, as the relative humidity goes from 0 to 60% and the temperature from 20° to 25° C, water vapor produces a small positive signal that results in an increase of about 8% in the ozone concentration measurement. This potential source of error can be minimized by using humidified, rather than dry, ozone in air streams when calibrating. 

Hydroxylation of t-carbon atoms. Detailed directions including necessary precautions for dry ozonation have been published. Seven examples for preparation of tertiary alcohols arc included (yields 72-90%). 

A severe limitation of the effective use of ozone in organic synthesis is its low solubility in organic solvents. The so-called dry ozonation technique of Mazur solves this problem.102 Dry silica gel with the preadsorbed organic substrate is saturated with ozone at —78°C. After warming up to room temperature, the products are eluted in the usual way. Under these conditions ozone exhibits an enhanced reactivity presumably due to the slightly acidic nature of silica gel 103... 

The results of dry ozonation, namely, regioselectivities and stereoselectivities, are very similar to those in superacidic liquid-phase ozonation. Tertiary C—H bonds in strained systems such as norbomane are inert to dry ozonation.93 Such compounds are oxidized at the secondary carbon to yield a mixture of alcohols and ketones.93 104 Similarly, substituted cyclopropanes exhibit a general preference for the oxidation of the secondary C—H bond in the a-position to the ring 104... 

In electrophilic oxygenation with ozone in superacidic media or in dry ozonation over silica gel, protonated ozone, namely, +C>3H, was suggested to be the de facto electrophile. These reactions are fundamentally different from conventional ozonations with O3, which is a highly dipolar molecule. In 03H+ the dipole is removed by protonation. Cacace and Sporenza were able to directly identify +C>3H in the gas phase and also measure the proton affinity of ozone.107... 

Photon Chain. In the ultraviolet region quantum yields of over two (14) and as high as six (44) have been reported. Although the evidence seems to be sufficient to this author, Benson (11,13) does not believe that quantum yields of greater than two in dry ozone have been unequivocally demonstrated. He has pointed out that traces of water could greatly accelerate the rate of ozone decomposition. Nevertheless, Benson has postulated that a photon chain could yield a chain decomposition and account for quantum yields of over two, a proposal which was first made by Noyes and Leighton (64). 

Precise determinations of quantum yields in dry ozone photolysis would be of considerable value in clarifying the possible mechanisms. If an energy or photon chain exists, there is no reason why the quantum yield should be limited to about 6. It should be possible to use experimental conditions where it would be much higher. If an energy or photon chain does not exist, the quantum yield should not exceed 4 or, perhaps, 6. It should be emphasized that the most precise work in the ultraviolet yields a maximum quantum yield of 6 and that an error of 2 in this value would be possible. 

Lee and coworkers reported in 2004 the preparation of a key l- 3-methylcarba-penem intermediate (III, Fig. 15) by condensation of 4-acetoxy-(3-lactam with a titanium enolate of 2 -hydroxypropiophenone [279]. The resulting ketone was converted into the corresponding carboxylic acid (IV, Fig. 15) by a dry ozonation method. 

C. (S)-(+)-4-Methyl-3-heptanone f(S>-A]. A 100-mL Schlenk tube, fitted with a gas inlet and Teflon stopcocks, is charged with 4.3 g (18 mmol) of crude (ZSS)-3 dissolved in 50 mL of dichloromethane (Note 11), and cooled to -78°C (acetone/dry ice bath) under nitrogen. Dry ozone (Note 12) is passed through the yellow solution until a green-blue color appears (ca. 4 hr). The... 

On the other hand, selenium, tellurium, arsenic, antimony, and carbon disulphide appear to bum readily in dry oxygen.11 Dry ozone is decomposed on warming, but may be prepared in the usual way from dry oxygen.12 Iron yields its characteristic tempering colours when heated in dry air or oxygen.13 Both lead nitrate and potassium chlorate decompose when dry. 

Dry ozonization of alkraes and alkynes has also been explraed. Sometimes these results resemble those of the homogeneous ozonization in an i rotic solvent ... 

Dry ozonization is also an efficient proc ure for oxidation of aliphatic primary amines into nitro groups, with yields of about 70%. Arylamines are also oxidized to nitro aronutics, albeit witii low yields. Ozone on silica gel has also been shown to oxidize arenes in some cases. ... 

Dry ozonization of 3/3,28-diacetoxylupane afforded 19/S-hydroxy-3/3,28-diacetoxylupane (123). During the course of this work the lactone (124) was prepared. The physical properties of this lactone differ from these reported for a compound from Dillenia indica which was assigned the structure (124). This... 

Reaction of cholestan-3a-yl xanthate with Fe(C104)2-H0Ac-02 containing a trace of Fe " gave cholestan-la,3 -diyl diacetate (180) in reasonable yield (45%). Further studies on dry ozonization led to a series of 25-hy-droxycholestanes. ° Lead tetra-acetate oxidation of the bromohydrin (181) gave a mixture of the 6/8,19-epoxide (182) and the hemiacetal acetates (183) and (184). 

Chlorination of tertiary carbon atoms (8, 161). Radical chlorination of the trifluoroacetate 1 with N,N-dichlorourethane gives as one product the 25-chloro derivative 2, which can be converted into the 25-hydroxy derivative 3 by refluxing aqueous ethanol. The corresponding 25-hydroxy-8-ketone has been converted into 25-hydroxyvitamin This method for hydroxylation of C25 is somewhat more selective than dry ozonation or peracetic acid oxidation, both of which hydroxylate all four tertiary carbons, but the yield of 3 is about the same as that obtained directly by dry ozonation. 

Hydroxylatiott. Tertiary C—H bonds of alicyclic hydrocarbons are oxidized to the corresponding alcohols by p-nitroperbenzoic acid. Unlike the oxidation with trifluoroperacetic acid (7, 281-282), the reaction occurs regioselectively and with practically complete retention of configuration, and thus is comparable to dry ozonation (6,440). 

Preparative Methods the title reagent can be prepared from commercially available (1,2-benzenedithiol and 1,3-dichloroacetone. After condensation of these reagents in the presence of DMAP, the resulting l,5-benzodithepan-3-one is enantioselectively oxidized to the (/f)-monosulfoxide by modified Sharpless oxidation [cumene hydroperoxide, Ti(0-t-Pr)4] in the presence of (-F)-diethyl tartrate as a chiral ligand. - Subsequent dry ozonation" of the (/f)-monosulfoxide affords (lf ,5f )-bis-sulfoxide 1, having >98% optical purity. Alternative use of (—)-diethyl tartrate in the modified Shaipless oxidation makes possible convenient access to enantiomeric (15,5S)-1. ... 

Ozobenzlne (Fr) (Ozobenzene). CsHgOg, white amorph product. Prepd by A. Renard by passing a current of dried ozone at a temp below 10° thru... 

For the success of rapid sterilization with ozone, the bottles should contain no water in the bottom. The inside wall of the bottle is covered with only a thin film of water, which is sufficient to ensure instantaneous humidification of the dry ozonated air the moment it enters the bottle. Because sterilization with ozonated water would be slower, it is necessary to have the bottom of the bottle dry. The formation of a thin mist in the bottle indicates an adequate humidification of the ozonated air. 

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