t-Butyl Hydroperoxide1-3

t-Bu-O-OH

[75-91-2]  · C4H10O2  · t-Butyl Hydroperoxide  · (MW 90.12)

(oxidizing agent used for the oxidation of alcohols and alkenes to allylic oxygenated compounds and epoxides1,2)

Alternate Name: TBHP.

Physical Data: the following data are for a 90% aqueous solution: flash point 35 °C; d 0.901 g cm-3; n20D 1.3960. The density of a 70% aqueous solution is 0.937 g cm-3.

Solubility: sol alcohol, ether, chloroform; slightly sol H2O, DMSO.

Form Supplied in: clear colorless liquid; widely available as 70-90% aqueous solutions, and anhydrous in hydrocarbon solvents. Aqueous solutions may be dried by a phase separation procedure, followed by azeotropic distillation to remove the last vestiges of water if necessary.1

Handling, Storage, and Precautions: eye protection and rubber gloves should be worn when handling this material; avoid skin contact; this reagent should be handled only in a fume hood. Eye and skin irritant; immediately flush with water if contact is made with the eyes. Flammable liquid; oxidizer; sensitive to shocks and sparks. May react explosively with reducing agents. Store in an explosion-proof container, and keep away from reducing materials and strong acids and bases. Avoid using high strength solutions; do not distill. The use of molecular sieves for drying is not recommended.

General Considerations.

The title reagent is used in oxidations of various substrates to give epoxides, ketones, aldehydes, carboxylic acid esters, and nitro or azoxy compounds. The reagent and its metal complexes have been extensively reviewed.1-3 This article describes representative applications to problems in organic synthesis.

Oxidations of Alkenes.

Hydroxylation.

Under basic conditions (tetraethylammonium hydroxide, Et4NOH), in the presence of catalytic amounts of Osmium Tetroxide, TBHP vicinally hydroxylates alkenes (eq 1).4 This method is preferable over the use of osmium tetroxide stoichiometrically due to the expense and toxicity of the latter (see also Osmium Tetroxide-t-Butyl Hydroperoxide). This method is also preferable to the use of osmium tetroxide catalytically with Hydrogen Peroxide5 or metal chlorates,6 both of which give lower yields for tri- and tetrasubstituted alkenes, and can lead to over-oxidation. Et4NOH can be replaced with Et4NOAc, which allows this reaction to be carried out on alkenes containing base-sensitive functional groups, and often gives better yields than the use of Et4NOH (eq 2).7

Chlorohydroxylation of nonfunctionalized alkenes can be accomplished (eq 3) through the reaction of TBHP with Titanium(IV) Chloride.8 Chlorohydroxylation can also be done asymmetrically to the alkenes of allylic alcohols using TBHP with Dichlorotitanium Diisopropoxide and an asymmetric tartrate catalyst, and the stereochemistry can be controlled by the ratio of titanium to tartrate (eq 4) varying (see below).

Oxidation of Allylic, Benzylic, and Propargylic Carbons.1,2

Alkenes with an allylic hydrogen can be selectively oxidized to the allylic alcohol by TBHP in the presence of Selenium(IV) Oxide (eq 5).9 This is preferable to the oxidation using stoichiometric SeO2 by itself, which leads to reduced forms of selenium and can make isolation and purification of the product difficult. Less substituted alkenes require 0.5 equivalents of SeO2 while for more substituted alkenes it may be present in catalytic amounts. The regioselectivity of this reaction favors the more substituted site being oxidized. The addition of small amounts of carboxylic acids also aids this reaction with certain alkenes (eq 5). See also Selenium(IV) Oxide-t-Butyl Hydroperoxide.

Alkenes can also be oxidized to give rearranged allylic alcohols using TBHP with phenylselenenic acid and Diphenyl Diselenide (eq 6).10 The reaction proceeds through a b-hydroxyl phenylselenide adduct of the alkene, which then eliminates the selenide to give the allylic alcohol and a phenylselenenic acid byproduct. This method is preferable to the use of phenylselenenic acid with hydrogen peroxide, since the latter can lead to epoxidation of the alkene of the product to give the epoxy alcohol. This method also does not oxidatively remove the selenium from the phenylselenenic acid byproduct, as the H2O2 method does, allowing the phenylselenenic acid to be recovered and easily reduced back to diphenyl diselenide.

Oxidations of allylic carbons to carbonyls to give enones may be effected by the reaction of the alkene with TBHP catalyzed by Hexacarbonylchromium (eq 7).11 These reaction conditions are milder than other chromium reagents used for the same purpose, and are selective towards allylic carbons. This system has also been used for the oxidation of benzylic carbons to carbonyls, with much better yields than Chromic Acid oxidations.12 Other chromium(VI) catalysts can also be used along with TBHP to oxidize allylic and benzylic carbons to the corresponding carbonyl.13

Propargylic carbons can also be oxidized, using TBHP and SeO2 (eq 8).14 Unlike allylic systems, propargylic systems show a great tendency towards oxygenation on both sides of the triple bond, and are generally more reactive towards a oxygenation. A mixture of the propargylic alcohol, ketone, diol, and ketol will generally result from this reaction. If there are two sites possible for oxygenation, methine and methylene groups have about the same reactivity towards these conditions, while methyl groups show a lesser preference for oxidation. In symmetrical alkynes the diol is prevalent, and in some cases where the alkyne is in conjugation with other p systems the ketone is an important product, whereas in most other cases the ketone and ketol are minor products. If the alkyne has one methine and one methylene substituent, the enynone can be an important product.

If a chromium(VI) catalyst is used in the presence of TBHP, propargylic carbons will be oxidized to the alkynic ketone (eq 9).15 The more highly substituted alkyl substituent on the alkyne is preferentially oxidized, and symmetrical alkynes give the monoketone accompanied by the diketone.

Oxidation of p-allylpalladium complexes can also occur with TBHP using a molybdenum(IV) catalyst to give the allylic alcohol (eq 10).16 Hydroxyl attack will occur axially, syn to the complexed palladium. This conversion can also be carried out with peroxy acids or singlet oxygen, but these methods are not as selective.

Epoxidation.1,2,17

TBHP is widely used as an epoxidizing agent, both synthetically and industrially.18 TBHP has been used to effect regiospecific, stereospecific, and asymmetric epoxidations. In general, the rates of epoxidations using TBHP are slowed by polar solvents, and increased with higher alkyl substitution of the alkene. TBHP is considered superior to hydrogen peroxide for epoxidations, because it is soluble in hydrocarbon solvents, while hydrogen peroxide can readily transform the epoxide to the vic-glycol.

Epoxidations of simple alkenes can be carried out using TBHP with a vanadium or molybdenum catalyst (eq 11).19

Epoxidations of alkenes in compounds containing other functional groups can also be accomplished using TBHP with a molybdenum catalyst (eq 12).19,20 For nonconjugated dienes, more highly substituted alkenes can be selectively epoxidized over less substituted alkenes. Conjugated dienes are less susceptible to epoxidation than isolated alkenes, but the regioselectivity for the different double bonds of a conjugated system follows the same pattern as that for isolated alkenes (eq 13).

Epoxidations of compounds with functional groups in the allylic position can also be effected using TBHP and a molybdenum or vanadium catalyst, but the yields are not as high as those for isolated double bonds, and longer reaction times are required.21 TBHP epoxidizes the alkenes of allylic and homoallylic alcohols stereoselectively with either molybdenum or vanadium catalysts (eqs 14 and 15).21 With acyclic systems, vanadium-catalyzed epoxidations give predominantly the erythro product, and molybdenum-catalyzed epoxidations give predominantly the threo product.22

For cyclic systems, vanadium- and molybdenum-catalyzed reactions give predominantly the cis product (eq 16).23 There are several factors that can affect the selectivity of this reaction for cyclic allylic alcohols. With increasing ring size, the selectivity decreases slightly for vanadium-catalyzed reactions, and more dramatically for molybdenum-catalyzed reactions. The selectivity was also observed to be better for cyclic allylic alcohols where the hydroxyl is in a quasi-axial position.

The epoxidation of a,b-unsaturated ketone and aldehyde compounds is accomplished by TBHP in the presence of catalytic amounts of Triton-B (Benzyltrimethylammonium Hydroxide) (eq 17).24 This method has also been used for the synthesis of mono- and diepoxy-1,4-benzoquinones (eq 18).25

Cyclic allylic alcohols conjugated to a second alkene react with TBHP catalyzed by vanadium to give not the epoxy but a bicyclic ether and new allylic alcohols, with the oxygen bridging the original allylic alcohol to the terminus of the conjugated diene (eq 19).26

Stereoselective epoxidation of unactivated alkenes can be effected by remote chiral auxiliaries in the presence of molybdenum or vanadium catalysts. The configuration of the remote alcohol determines which face of the alkene is epoxidized (eq 20).27

Allylic alcohols can be asymmetrically epoxidized with TBHP and stoichiometric quantities of a titanium-diethyl tartrate complex, generated in situ.28 Either enantiomer can be formed by using either (+)- or (-)-diethyl tartrate, or by varying the ratio of titanium catalyst to (+)-diethyl tartrate (eq 21), because the nature of the titanium catalyst changes as the molar ratio of titanium to tartrate changes. This latter method is generally preferred due to the ready availability and relatively low cost of (+)-diethyl tartrate. In the presence of 3Å or 4Å molecular sieves, the titanium/tartrate complex may be used in catalytic quantities, but with somewhat lower product enantiomeric purities.29 These methods can also be used for the stereospecific epoxidation of homoallylic alcohols, but in lower degrees of enantiomeric purity, because the hydroxyl group is further away from the reacting center, lessening its directing effec ts.30

The use of TBHP and a titanium/tartrate complex in either stoichiometric or catalytic quantities is known as the Sharpless asymmetric epoxidation.1 This method gives better stereo- and enantioselectivity than epoxidations using peroxy acids. Asymmetric epoxidations can be carried out using other transition metal catalysts and chiral ligands, but the enantioselectivities are not as high.31 The Sharpless asymmetric epoxidation can also be used for the kinetic resolution of allylic alcohols.32

Asymmetric epoxidations of simple alkenes can be accomplished by Sharpless epoxidation of alkenylsilanols.33 The alkenylsilanols are prepared from lithium alkenes, and after the Sharpless epoxidation the silyl group is removed by fluoride ion to give the simple epoxide (eq 22). Asymmetric epoxidations can also be done on alkenes without other functional groups using optically active diols as the solvent, but the ee values are generally very low.34

Epoxidation of vinyl allenes by TBHP and Vanadyl Bis(acetylacetonate) catalyst leads to the formation of cyclopentenones (eq 23).35 The intermediate in this reaction is an epoxide of the allene. The stereochemistry of the double bond can be retained. The stereoselectivity is kinetic in nature, and can be lost due to epimerization of the kinetic product if the reaction is continued for long periods of time.

Other Reactions with Alkenes.

Double bonds of silyl enol ethers can be oxidatively cleaved to the corresponding ketones or carboxylic acids using TBHP with MoO2(acac)2 as a catalyst (eq 24).36 The ease with which enols can be generated regiospecifically makes this a very powerful method in organic synthesis. This reaction selectively cleaves the double bond of silyl enol ethers in the presence of other double bonds within the molecule.

The alkenes of allylic alcohols can also be cleaved under these conditions (eq 25).37 In addition to cleaving the double bond of the allylic alcohol, the single bond between the alkene carbon and the allylic carbon bearing the hydroxyl group is also cleaved under these conditions. Vicinal diols are also cleaved to give the corresponding ketones or carboxylic acids (eq 26).38

Oxidation of a,b-unsaturated esters and ketones with palladium-catalyzed TBHP gives b-keto esters or 1,3-diketones (eq 27).39 Hydrogen peroxide can also be used as the oxidant for this reaction.

Under basic conditions, TBHP can add in Michael fashion to a double bond that has an electron withdrawing group attached (eq 28).40

Reactions with Other Functional Groups.

Oxidation of Alcohols.1,2

In the presence of catalytic amounts of diphenyl diselenide, TBHP oxidizes benzylic and allylic alcohols to the corresponding ketones (eq 29).41 Saturated alcohols can be oxidized to the corresponding carbonyl compounds as well if bis(2,4,6-trimethylphenyl) diselenide is used as the catalyst and a small amount of a secondary or tertiary amine is present. These conditions do not affect other double bonds present in the substrate. This system can also be used for the oxidation of a-hydroxy selenides and thiols, selectively oxidizing the hydroxy function to the carbonyl.

Saturated alcohol oxidation can also be achieved without oxidizing alkenes by the reaction of the alcohol with TBHP and benzyltrimethylammonium tetrabromooxomolybdate (BTMA-Mo) as a catalyst, and secondary alcohols will be oxidized preferentially over primary ones under these conditions (eq 30).42 If the reaction time is lengthened, primary alcohols will be converted to the appropriate acid derivative depending upon the conditions used. Using VO(acac)2 as the catalyst will oxidize secondary alcohols over primary ones selectively as well.43

Oxidation of alcohols can also be done using TBHP and a chromium(VI) catalyst (eq 31).44 This system works best for allylic, benzylic, and propargylic alcohols, and will selectively oxidize these in the presence of other alcohols.

Oxidation of Sulfur-Containing Compounds.2

Sulfides can be oxidized with TBHP to give sulfoxides.45 If vanadium, molybdenum, or titanium catalysts are used, the addition of one equiv of TBHP will furnish the sulfoxide, while the use of excess TBHP will oxidize the sulfide to the sulfone (eqs 32 and 33). In the absence of metal catalysts the oxidation cannot be carried beyond the sulfoxide.46 If only one equivalent of TBHP is used, sulfides will be preferentially oxidized over any alkenes present; however, excess TBHP will also oxidize alkenes. The oxidation of thiols with TBHP and MoVI or VV catalysts produces sulfonic acids (eq 34).47

Using Sharpless asymmetric epoxidation conditions (see above), modified by the addition of one mol equiv of water, unsymmetrical sulfides could be asymmetrically oxidized to sulfoxides (eq 35).48 Asymmetric oxidations of sulfides to sulfoxides have also been carried out using optically active diols with TBHP and a molybdenum catalyst, but the enantioselectivities were very low (~10%).49

Oxidation of Phosphines.

Alkyl phosphines can be oxidized to the appropriate phosphine oxides by TBHP (eq 36).50

Oxidation of Selenides and Selenoxides.

Alkenes can be produced oxidatively from selenides, through the selenoxides and elimination. This is done by stirring TBHP with basic alumina and the appropriate selenide (eq 37).51 This transformation can also be accomplished by treatment of the selenide with Hydrogen Peroxide, Ozone followed by Triethylamine, periodate, or peroxy acids.

Oxidation of Nitrogen-Containing Compounds.2

Reactions of TBHP with compounds containing nitrogen have been used to effect a variety of oxidations, both of the nitrogen atom itself and of adjacent carbon atoms. Tertiary amines react with TBHP in the presence of vanadium and molybdenum catalysts to give amine oxides (eq 38).52 This transformation can also be done with cumene and pentene hydroperoxides.

Secondary amines are oxidized to imines by TBHP in the presence of ruthenium(II) catalysts (eq 39).53 Tertiary amines are oxidized by TBHP in the presence of ruthenium catalyst to give a-(t-butyldioxy)alkylamines, which decompose to iminium ion intermediates when treated with acid (eq 40).54 N-Methyl groups are selectively oxidized when other N-alkyl or -alkenyl groups are present.

Amides are selectively oxidized to imides by TBHP, and other hydroperoxides, in the presence of cobalt or manganese salts as catalysts (eq 41).55 The selectivity of this transformation is demonstrated by the oxidation of 3-ethoxycarbonyl-2-piperidone to the appropriate imide, with no other oxidation products. Peracetic Acid also effects this transformation, in many cases giving better yields and shorter reaction times, but the conditions for oxidation with TBHP are milder. Oxidation of amides with TBHP catalyzed by ruthenium gives the corresponding t-butylperoxy amide (eq 42).56

Nitronate anions, formed by deprotonation of nitro compounds, react with TBHP catalyzed by VO(acac)2 or Hexacarbonylmolybdenum to give 1-hydroxy nitro compounds (eq 43). Analogous to a-hydroxyl carbonyl compounds, these collapse to give the carbonyl derivative and nitrous acid.57

Introduction of Peroxy Groups into Organic Molecules.58

Using catalytic amounts of copper, cobalt, or manganese salts, TBHP reacts with molecules that contain a slightly activated carbon-hydrogen bond, replacing the activated hydrogen with a peroxy group. This transformation can also be accomplished with other hydroperoxides. Carbon-hydrogen bonds a to an alkene (eqs 44 and 45),59,60,61 phenyl groups,60 carbonyls,61 nitriles,62 oxygen,60,61 or nitrogen (eq 46)63 atoms are activated towards this reaction. The primary function of the metal salts in these reactions is to initiate decomposition of the hydroperoxide.

Peroxy groups may also replace alcohols (eq 47),64 ethers,65 or sulfates66 directly, or be added to an alkene (with Markovnikov regioselectivity),9 by reacting the functionalized organic compound with TBHP and concentrated sulfuric acid in acetic acid. Epoxides are transformed into b-hydroxy dialkyl peroxides using TBHP in the presence of base (eq 48).67

Peroxy t-butyl organosilanes can be prepared by reacting TBHP with the appropriate silyl chloride and pyridine, ammonia, or triethylamine (eq 49).68 Peroxides of a number of other heteroatoms in organic compounds, such as germanium,69 boron,70 cadmium,71 tin,72 aluminum,73 and mercury,74 can also be synthesized using TBHP.

2,4,6-Substituted phenols react with TBHP to give 2- or 4-(t-butylperoxy)-2,4,6-trisubstituted quinones if the 4-substituent is not a methyl group, and 3,5,3,5-tetrasubstituted stilbene-4,4-quinones if the 4-substituent is a methyl group (eq 50).75

Reactions with Carbonyl Compounds.

Aldehydes react with TBHP in the presence of catalytic amounts of copper, cobalt, or manganese salts to give the t-butyl ester (eq 51).76 In the absence of a metal catalyst, benzaldehyde will react with TBHP to give a mixture of the meso and racemic forms of benzopinacol dibenzoate.

TBHP reacts with acid chlorides under basic conditions to give the appropriate t-butyl peroxy ester.77 For small acids, 30% KOH is used, but for longer-chain acids, pyridine is substituted as the base (eq 52).78 The use of pyridine as the base in this reaction allows the synthesis of carbamate peroxy esters from isocyanates and carbamic acid chlorides (eq 53).79

TBHP reacts with ketones or aldehydes in the presence of a strong acid catalyst to give products with diperoxy groups in place of the carbonyl (eq 54), or in the absence of the acid catalyst to give an a-hydroxyl t-butyl peroxide (eq 55).80

Conversion of Halides to Alcohols.

Grignard reagents react with TBHP to give the appropriate alcohol or phenol (eq 56).81 This provides an alternative method for the conversion of halides to alcohols or phenols. Because the hydrogen of the peroxide is activated, either two equiv of Grignard reagent must be used or the magnesium salt of the hydroperoxide, prepared from the hydroperoxide and ethylmagnesium bromide.

Conversion of Alcohols to Halides.

In cases where traditional methods fail, alcohols can be converted to halides by a radical chain reaction.82 This is accomplished by transforming the alcohol into a chloroglyoxylate, reacting it with TBHP, and warming this in the presence of a halogen donor such as CCl4 or BrCCl3, to initiate a radical reaction where first a t-butoxyl radical is eliminated, then CO2 is eliminated twice in succession, leaving an alkyl radical which then reacts with the halogen donor to give the halide (eq 57).


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Andrew K. Jones & Timothy E. Wilson

Emory University, Atlanta, GA, USA

Sham S. Nikam

Warner-Lambert Company, Ann Arbor, MI, USA



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