potassium permanganate eros rp244

POTASSIUM PERMANGANATE

Potassium Permanganate

1−4

KMnO

[7722-64-7]

KMnO

(MW 158.04)

InChI = 1/K.Mn.4O/q+1;;;;;-1/rK.MnO4/c;2-1(3,4)5/q+1;-1
InChIKey = VZJVWSHVAAUDKD-QPPHZJHPAS

(oxidant; conversion of arenes into carboxylic acids,

10,11

-ketones,

12−15

or α-alcohols;

degradation of aromatic rings;

preparation of diols,

17,18

ketols,

5,19,20,22

and α-diketones

22−24

from nonterminal alkenes; preparation of carboxylic acids,

aldehydes

and 1,2-diols

from terminal alkenes; oxidation of

alkynes to α-diones;

29,30

oxidation of enones to 1,4-diones;

conversion of 1,5-dienes into substituted tetrahydrofurans

32,33

lactones;

conversion of primary and secondary alcohols into

carboxylic acids

1,2,37

and ketones,

1−4,9,35

respectively; oxida-

tion of allylic alcohols to α,β-unsaturated ketones

and other

unsaturated alcohols and α,ω-diols to lactones;

36,37

oxidation of

aliphatic thiols to disulfides and aromatic thiols to sulfonic acids;

oxidation of sulfides and sulfoxides to sulfones,

4,38−40

sulfinic

acids to sulfonic acids,

sulfites to sulfates,

and thiones to

ketones;

preparation of tertiary nitroalkanes from the corres-

ponding amines;

oxidation of tertiary amines to amides or

lactams;

48−50

allylic oxidations when used in conjunction with

-butyl hydroperoxide;

preparation of iodoaromatic compounds

when used with I

and sulfuric acid;

oxidation of nucleic acids

to the corresponding diols and ketols;

oxidation of guaiol and

related compounds to rearranged ketols;

oxidation of poly(vinyl

alcohol) to poly(vinyl ketone);

oxidation of nitroalkanes to

aldehydes or ketones; oxidation of imines to nitrones)

Alternate Name:

potassium manganate(VII).

Physical Data: d

2.70 g cm

−

; decomposition 237

◦

Solubility:

water (at 20

◦

C) 63.8 g L

−

; sol acetone, methanol.

Form Supplied in:

purple solid; commercially available.

Handling, Storage, and Precautions:

stable at or below rt.

Because it is a strong oxidant it should be stored in glass, steel,
or polyethylene vessels. Sulfuric acid should never be added to
permanganate or vice versa. Permanganate acid, an explosive
compound, is formed under highly acidic conditions.

Original Commentary

Donald G. Lee
University of Regina, Regina, Saskatchewan, Canada

Introduction.

Permanganate is an inexpensive oxidant that

has been widely used in organic syntheses. Its most common salt,
KMnO

, is soluble in water and as a consequence oxidations have

traditionally been carried out in aqueous solutions or in mixtures
of water and miscible organic solvents such as acetone, acetic acid,
acetonitrile, benzonitrile, tributyl phosphate, or pyridine. The dis-
covery that KMnO

can, with the aid of phase-transfer agents,

be readily dissolved in nonpolar solvents such as CH

, and

the recent observation that is adsorption onto a solid support pro-

duces an effective heterogeneous oxidant, has further expanded
its usefulness.

The general features of the reactions of permanganate dissolved

in aqueous solutions, or in organic solvents with the aid of a phase-
transfer agent, and as a heterogeneous oxidant will be briefly de-
scribed, followed by specific examples.

Aqueous Permanganate Oxidations.

Potassium permanga-

nate is a general, but relatively nonselective, oxidant when used
in aqueous solutions. When an organic compound contains only
one site at which oxidation can readily occur, this reagent is a
highly efficient and effective oxidant. For example, oleic acid is
converted into dihydroxystearic acid in quantitative yield when
oxidized in a dilute aqueous solution of KMnO

at 0–10

◦

If the aqueous solution is made acidic by addition of mineral

acid, the rate of reaction increases, most probably because of for-
mation of permanganic acid

which is known to be a very strong

oxidant.

The rate of the reaction is also accelerated by addition

of sodium or potassium hydroxide. It has been proposed that this
acceleration may be due to ionization of the organic reductant; for
example, conversion of an alcohol into an alkoxide ion.

How-

ever, similar observations for the oxidation of compounds such as
sulfides, which lack acidic hydrogens, suggests that other factors
may be involved.

Under acidic conditions, permanganate is reduced to soluble

manganese(II) or -(III) salts, thus allowing for a relatively easy
workup. However, under basic conditions the reduction product
is a gelatinous solid, consisting primarily of manganese dioxide,
that is difficult to separate from the product. As a consequence, for
laboratory scale preparations the reaction product is not isolated
until after the MnO

has been reduced by addition of HCl and

sodium bisulfite. For large scale (industrial) processes, MnO

removed either by filtration or by centrifugation.

Phase-transfer

Assisted

Permanganate

Oxidations.

KMnO

may be dissolved in nonpolar solvents such as benzene

or CH

by complexing the potassium ion with a crown ether

or by replacing it with a quaternary ammonium or phosphonium
ion. Although most reactions observed are similar to those found
in aqueous solutions, the ability to dissolve permanganate in
nonpolar solvents has greatly increased the range of compounds
that can be oxidized.

The first example of a phase-transfer assisted permanganate

oxidation involved the complexing of the potassium ion by a crown
ether in benzene;

however, it was later found that the use of

quaternary ammonium or phosphonium salts was less expensive
and just as efficient.

Phase transfer into a nonpolar solvent can occur either from

an aqueous solution or from solid KMnO

. Evaluation of vari-

ous phase-transfer agents for these purposes has indicated that
benzyltributylammonium chloride is highly efficient for trans-
fer from aqueous solutions while alkyltriphenylphosphonium
halides, tetrabutylammonium halides, and benzyltriethylammo-
nium halides are all effective for the transfer from solid KMnO

Adogen 464, an inexpensive quaternary ammonium chloride com-
mercially available, is usually satisfactory for both purposes.

Quaternary ammonium and phosphonium permanganates can

also be used as stoichiometric oxidants. For descriptions of their

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

properties, refer to the separate articles on Methyltriphenyl-
phosphonium Permanganate

and Benzyltriethylammonium Per-

manganate

Heterogeneous Permanganate Oxidations.

The use of

permanganate, activated by adsorption on a solid support, as a
heterogenous oxidant has further increased the scope of these re-
actions. CH

or 1,2-dichloroethane (if a high reflux tempera-

ture is required) are the preferred solvents and Alumina, silica, or
hydrated Copper(II) Sulfate are the most commonly used solid
supports. The selectivity of the oxidant is dramatically altered by
use of a solid support. For example, although carbon–carbon dou-
ble bonds are very easily cleaved in homogeneous permanganate
solutions, secondary allylic alcohols can be cleanly oxidized to
the corresponding α,β-unsaturated ketones without disruption of
the double bond under heterogeneous conditions.

In addition to increased selectivity, the use of permanganate

under heterogeneous conditions allows for easy product isolation.
It is necessary only to remove spent oxidant by filtration followed
by flash evaporation or distillation of the solvent. Products iso-
lated in this way are often sufficiently pure to permit direct use in
subsequent synthetic procedures.

Benzylic Oxidations.

Permanganate oxidizes side chains of

aromatic compounds at the benzylic position.

In aqueous solu-

tion, carboxylic acids are usually obtained (eqs 1 and 2).

10,11

MeO

KMnO

O, py

71%

(1)

(2)

-Bu

KMnO

The oxidation of alkylbenzenes proceeds through the corre-

sponding α-ketones, which can occasionally be isolated (eqs 3
and 4).

12,13

(3)

80%

(4)

Under heterogeneous conditions where alumina (acid, Brock-

man, activity 1)

or copper sulfate pentahydrate

is used as the

solid support, α-ketones and alcohols are obtained with little or
no carbon–carbon cleavage (eqs 5–8).

(5)

KMnO

, alumina

ClCH

Cl, ∆

69%

(6)

KMnO

, CuSO

•5H

88%

(7)

KMnO

, alumina

ClCH

Cl, ∆

86%

(8)

KMnO

, alumina

ClCH

Cl, ∆

79%

Oxidation of Aromatic Rings.

Permanganate will oxida-

tively degrade aromatic rings under both acidic and basic
conditions.

The effect of acid and base on the reaction has been

demonstrated by the oxidation of 2-phenylpyridine; under basic
conditions the product is benzoic acid (presumably because the
oxidant attacks the site of greatest electron density) (eq 9), while
under acidic conditions (where the nitrogen would be protonated)
the product is picolinic acid (eq 10).

(9)

KMnO

–

(10)

KMnO

Polycyclic aromatic compounds are also oxidatively degraded

to a single-ring polycarboxylic acid (eq 11).

KMnO

–

(11)

Oxidation of Nonterminal Alkenes.

Nonterminal alkenes

can be converted into 1,2-diols, ketols, or diketones by choice
of appropriate conditions. The reaction, which proceeds by syn
addition of permanganate to the double bond as indicated, gives
the corresponding cis-diol under aqueous alkaline conditions
(eq 12).

–

(12)

MnO

–

45%

Syn

addition can also be achieved in nonaqueous solvents with

the aid of a phase-transfer agent (PTA). Subsequent treatment with
aqueous base gives 1,2-diols in good yields

(eq 13).

Equally

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

good results were reported when the reaction was carried out in
aqueous t-butyl alcohol.

1. KMnO

, PTA, CH

2. 10% NaOH

86%

(13)

Under neutral conditions the product obtained from the oxi-

dation of alkenes is the corresponding ketol.

Good yields are

obtained when aqueous acetone containing a small amount of
acetic acid (2–5%) is used as the solvent. The function of acetic
acid is to neutralize hydroxide ions produced during the reduc-
tion of permanganate. The oxidations of 5-decene and methyl
2-methylcrotonate provide typical examples (eqs 14 and 15).

19,20

KMnO

MeCOMe, H

O, MeCO

74%

(14)

OMe

(15)

KMnO

MeCOMe, H

O, H

80%

Heterogeneous oxidations of alkenes with a small amount of t-

butyl alcohol and water present to provide an ‘omega phase’

results in the formation of α-ketols in modest to good yields
(eqs 16 and 17).

KMnO

, CuSO

•5H

, t-BuOH, H

55%

(16)

KMnO

, CuSO

•5H

, t-BuOH, H

79%

(17)

Under anhydrous conditions, 1,2-diones are formed in good

yields when alkenes are oxidized by permanganate. Appropriate
conditions can be achieved by using acetic anhydride solutions
(eq 18)

or by dissolving permanganate in CH

with the aid

of a phase-transfer agent (eq 19).

KMnO

66%

(18)

KMnO

, PTA

, MeCO

H, H

69%

(19)

Similar yields are obtained under heterogeneous conditions,

where workup procedures are much easier.

The carbon–carbon double bonds of alkenes can also be

oxidatively cleaved to give carboxylic acids in good yield by use

of the Lemieux–von Rudloff reagent (aqueous potassium perio-
date containing catalytic amounts of permanganate).

3,25

Under

heterogeneous conditions, either aldehydes or carboxylic acids
are obtained, depending on the conditions used (eqs 20 and 21).

KMnO

, alumina, H

75%

(20)

KMnO

, silica

74%

(21)

Oxidation of Terminal Alkenes.

Although oxidation of ter-

minal alkenes by permanganate usually results in cleavage of the
carbon–carbon double bond to give either a carboxylic acid

an aldehyde,

1,2-diols can be obtained through use of a phase-

transfer assisted reaction (eqs 22–24).

2,28

KMnO

, PTA

, H

75%

(22)

( )

KMnO

, alumina, H

55%

(23)

CHO

( )

(24)

( )

80%

( )

1. KMnO

, CH

, PTA

2. 3% NaOH

Oxidation of Alkynes.

Oxidation of nonterminal alkynes

results in the formation of α-diones. Good yields are obtained
when aqueous acetone containing NaHCO

and MgSO

containing about 5% acetic acid,

is used as the solvent

(eqs 25–27). A phase-transfer agent to assist in dissolving KMnO

must be used when CH

is the solvent. Terminal alkynes are

oxidatively cleaved, yielding carboxylic acids containing one
carbon less than the parent alkyne.

KMnO

, PTA

, AcOH

61%

(25)

( )

KMnO

, PTA

, AcOH

80%

(26)

(27)

KMnO

, acetone, H

NaHCO

, MgSO

81%

Oxidation of Enones to 1,4-Diones.

Enones react with

nitroalkanes (Michael addition) to form γ-nitro ketones that can
be oxidized in good yield to 1,4-diones under heterogeneous con-
ditions (eq 28).

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

(28)

MeCH

–

MeCN

KMnO

, silica

80%

Oxidation of 1,5-Dienes.

The oxidation of 1,5-dienes results

in the formation of 2,5-bis(hydroxymethyl)tetrahydrofurans with
the indicated stereochemistry (eq 29).

When R

in (eq 29) is

chiral, a nonracemic product is obtained.

Use of heterogeneous

conditions results in the formation of lactones (eq 30).

(29)

KMnO

, CO

MeCOMe, H

–20 °C

60–70%

OAc

(30)

KMnO

, CuSO

•5H

62%

Oxidation of Alcohols and Diols.

Primary and secondary

alcohols are converted to carboxylic acids and ketones, respec-
tively, when oxidized by aqueous permanganate under either
acidic or basic conditions (eq 31).

Similar results are obtained

with phase-transfer assisted oxidations in organic solvents such
as CH

(eq 32).

KMnO

O, H

66%

(31)

( )

KMnO

, Adogen

, AcOH

92%

(32)

Heterogeneous oxidations are very effective with secondary

alcohols (eq 33)

and provide the added advantage that al-

lylic secondary alcohols can be converted to the corresponding
α

,β-unsaturated ketones without disruption of the double bond

(eq 34).

Unsaturated secondary alcohols in which the double

bond is not adjacent to the carbon bearing the hydroxy group are
resistant to oxidation (eq 35) unless an ‘omega phase’

is created

by adding a small amount of water (50 µL per g KMnO

). The

products are lactones under these conditions (eq 36).

KMnO

, CuSO

•5H

100%

(33)

( )

KMnO

, CuSO

•5H

89%

(34)

( )

KMnO

, CuSO

•5H

(35)

no product

KMnO

, CuSO

•5H

, H

56%

(36)

Good yields of carboxylic acids are obtained from primary

alcohols under heterogeneous conditions (KMnO

/CuSO

only when a base such as KOH or Cu(OH)

CuCO

is intermixed

with the solid support.

Under these conditions the reagent has

also been reported to be selective for primary alcohols.

The oxidation of α,ω-diols under heterogenous conditions

results in the formation of lactones. A good example is found
in the preparation of 3-hydroxy-p-menthan-10-oic acid lactone
(eq 37).

KMnO

, CuSO

•5H

83%

(37)

Oxidation of Organic Sulfur Compounds.

Aromatic thiols

are oxidized by permanganate to the corresponding sulfonic acids
while aliphatic thiols usually give disulfides, which are resistant
to further oxidation.

Sulfides and sulfoxides are easily oxidized

in CH

to the corresponding sulfones under both homoge-

neous

38,39

and heterogeneous conditions (eqs 38–42).

–

KMnO

–

, H

91%

(38)

KMnO

, PTA

, H

90%

(39)

KMnO

, PTA

, H

91%

(40)

KMnO

, PTA

, H

86%

(41)

(42)

KMnO

, CuSO

•5H

96%

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

Permanganate oxidizes sulfoxides more readily than sulfides,

as indicated by the products obtained from the oxidation of com-
pounds containing both sulfide and sulfoxide functional groups
(eqs 43 and 44).

41,42

MeS

KMnO

MeCOMe, H

97%

(43)

O O

Q = benzyltriethylammonium ion

(44)

QMnO

The greater ease of oxidation of sulfoxides is also responsible

for the observation that gem-disulfides are oxidized to monosul-
fones.

Monosulfoxides, although not isolated, are likely to be

intermediates in these reactions (eq 45).

MeS

SMe

MeS

(45)

70%

KMnO

MeCOMe

KMnO

Oxidation of sulfinic acids results in the formation of sulfonic

acids,

while sulfites give sulfates (eqs 46 and 47).

(46)

( )

–

( )

KMnO

–

, H

70%

(47)

KMnO

AcOH

45%

Cyclic thiones are readily oxidized to the corresponding

ketones by permanganate (eq 48).

MeO

OMe

MeO

OMe (48)

KMnO

MeCOMe

64%

Oxidation of Amines.

The synthetic usefulness of perman-

ganate as an oxidant for aliphatic amines is decreased by the fact
that a complex mixture of products is often obtained.

4,46

Good

yields of tertiary nitroalkanes can, however, be obtained from the
oxidation of the corresponding amines (eq 49).

KMnO

MeCOMe, H

70–80%

(49)

CNH

CNO

Primary and secondary amines react with permanganate in

buffered, aqueous t-butyl alcohol to give aldehydes and ketones
(eq 50).

(50)

KMnO

-BuOH, H

70%

Amides (or lactams, if the amine is cyclic) are obtained from

the oxidation of tertiary amines (eqs 51 and 52).

48−50

(51)

KMnO

MeCOMe, AcOH

70%

(52)

KMnO

MeCOMe

70%

Miscellaneous Oxidations.

Use of permanganate in conjunc-

tion with tert-Butyl Hydroperoxide results in allylic oxidation
(eq 53).

AcO

(53)

KMnO

, t-BuOOH

, silica

Aromatic compounds are oxidized to aryl iodides when treated

with permanganate, Iodine, and Sulfuric Acid (eq 54).

(54)

KMnO

, I

70%

Chemical modification of nucleic acids by treatment with

permanganate results in oxidation of the

double bond to give

either diols or ketols (eq 55).

KMnO

pH 8.6

36%

KMnO

pH 4.3

40%

(55)

Guaiol and related compounds can be oxidized to rearranged

ketols using aqueous glyme as the solvent (eq 56).

(56)

KMnO

, pH 8

glyme, H

70%

cis

-2,5-Dihydro-2,5-dimethoxyfuran is oxidized to the corre-

sponding α-diol in preference to the trans compound (eqs 57
and 58).

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

MeO

OMe

MeO

OMe

(57)

KMnO

THF, H

fast

MeO

OMe

MeO

OMe

(58)

KMnO

THF, H

slow

Oxidation of poly(vinyl alcohol) by permanganate results in the

formation of poly(vinyl ketone) (eq 59).

(59)

KMnO

Treatment of

-unsaturated steroids with KMnO

/CuSO

O in CH

containing catalytic amounts of t-butyl

alcohol and water results in formation of the corresponding 5β,6β-
epoxide (eq 60).

22,57

AcO

(60)

KMnO

, CuSO

•5H

, t-BuOH, H

92%

The oxidation of

-cholesterol acetate by KMnO

under

neutral or slightly basic conditions results in formation of all-
cis

-epoxydiol (eq 61).

AcO

(61)

KMnO

Aliphatic nitro compounds are converted into the correspond-

ing oxo compounds on treatment with basic permanganate.

59,60

Because these reactions are carried out under basic conditions, it
is likely that anions are intermediates, as suggested in eqs 62–64.

–

(62)

–

83–97%

KMnO

(63)

–

91%

KMnO

NaH

-BuOH

(64)

–

( )

59%

KMnO

NaH

-BuOH

Nitrones can be obtained from the oxidation of imines by

KMnO

in a two-phase CH

O solution containing a

phase-transfer agent (PTA) such as tetrabutylammonium chloride
(eq 65).

-Bu

–

HN t-Bu

KMnO

, PTA

, H

(65)

11%

89%

First Update

María Ribagorda & Javier Adrio
Universidad Autónoma de Madrid, Madrid, Spain

Benzylic and Allylic Oxidations.

Aliphatic side chains of

aromatic compounds are oxidized at the benzylic position in the
presence of potassium permanganate, whereas carboxylic acids
were obtained when KMnO

was used in aqueous solutions.

Higher selectivity was observed when the reaction was performed
under heterogeneous conditions, giving rise to the ketones and
alcohols with little or no overoxidation. Hence, using perman-
ganate adsorbed on moist alumina, or copper sulfate pentahydrate,
excellent yields and selectivities were obtained in the alkylben-
zene aliphatic side chain. The reaction can be carried out under
very mild, neutral conditions (eq 66).

KMnO

/CuSO

⋅5H

, 72 h, 95%

(66)

The use of ultrasonic irradiation permits shorter reaction times

in the heterogeneous oxidation with KMnO

/CuSO

O at

room temperature. Significantly higher yields were accomplished
in sonochemical experiments than in similar silent experiments
(eq 67).

Solvent-free conditions have also been reported using

the copper sulfate pentahydrate solid support.

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

)))), 93%
silent, 17%

KMnO

/CuSO

⋅5H

, rt, 2 h

solvent-free, 5 min, 95%

(67)

Permanganate supported on active manganese dioxide can be

used effectively under solvent-free conditions for the oxidation of
alkylarenes (eq 68). The residue that remains after the extraction
of organic compounds, manganese dioxide, can be recycled.

KMnO

/MnO

solvent-free, 23 h

89%

(68)

The combination of potassium permanganate and an ion

exchange resin (IER) has been described as an efficient ox-
idant system for alkylarenes under heterogeneous conditions
(eq 69).

66,67

KMnO

/IER

, reflux, 5.30 h

86–91%

(69)

Alkyl arenes are oxidized to the corresponding α-ketones in

moderate to good yields under heterogeneous conditions without
the use of solid supports using acetonitrile as the solvent at room
temperature (eq 70). No reaction was observed when R = H.

KMnO

CN, rt, 15–30 h

58–80%

(70)

R = Alkyl, Ar

Convenient syntheses of 7-halo-1-indanones and 8-halo-1-

tetralones have been reported through regioselective oxidation of
4-amidoindans with potassium permanganate (eq 71).

2. KMnO

, acetone

O, MgSO

, 0

°C, 16 h

NHAc O

1. Ac

O, EtOH

X = halogen

overall yield

= 1, 70%

= 2, 66%

(71)

The oxidation of 1,2,3,4-tetrahydroquinolines with potassium

permanganate in acetone at room temperature is a fast exother-
mic reaction leading to the corresponding isoquinoline. How-
ever, when the reaction is carried out in the presence of a
catalytic amount of 18-crown-6 in a CH

solution at room

temperature, the oxidation process became selective, affording
3,4-dihydroisoquinolines in preparative yields (eq 72).

KMnO

, 18-crown-6

, 20 min

MeO

75%

(72)

1,2-Dihydro-[2,7]naphthyridines can be easily oxidized into the

respective naphthyridine-1-ones derivatives in good yields with
potassium permanganate in the presence of 18-crown-6 at room
temperature (eq 73).

KMnO

, 18-crown-6

, 2 h

61–92%

(73)

Using potassium permanganate under basic conditions, the

10-position of the 4,5-epoxymorphinan can be oxidized in good
yield. The reaction can be performed on a large scale (eq 74).

The oxidation of toluene using aqueous potassium perman-

ganate was studied in the presence of acoustic or hydrodynamic
cavitation (eq 75). The reaction was found to be considerably
accelerated at ambient temperature in the presence of cavitation.
About six times more product would be obtained in the case of
hydrodynamic cavitation than in the case of acoustic (ultrasound)
cavitations at the same energy dissipation.

MeO

OAc

MeO

OAc

KMnO

, MgSO

NaOH,

BuOH, rt

27 h, 74%

(74)

(75)

KMnO

hydrodynamic cavitation

3 h, 44%

Allylic oxidations also can be achieved using potassium

permanganate. Thus, tetrahydropyridines undergo the introduc-

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

tion of an oxo group into the allyl position of the piperidine frag-
ment (eq 76).

Successive permanganate oxidations of the allyllic

carbon atoms in the piperidine ring can be achieved to afford 1-
aminoalkan-3-ones.

KMnO

, CH

rt, 50 min

65%

(76)

Oxidations of Alkenes.

Benzaldehydes can be prepared in

good yields from the oxidative cleavage of styrene and cinnamic
acid derivatives by permanganate oxidation under heterogeneous
conditions. Alumina and Amberlite IR-120 can be used as solid
supports with equally good results (eq 77).

KMnO

/solid support

, overnight

90%

(77)

Rapid and efficient oxidative cleavages of olefins with potas-

sium permanganate in the presence of solid polymeric cation
exchange resins in good yield have been reported (eq 78).

KMnO

, tulsion T42

BuOH, CH

, rt

3 h, 82%

(78)

The potassium permanganate oxidation of the side chain at

C(9) of some labdanic diterpenoids leads to intermediates that
have been transformed into Ambrox

-like compounds (flavor

compounds). The exocyclic double bond at C(8) remains unal-
tered under the oxidizing conditions. While a mixture of triols [at
C(3

′

),C(4

′

), C(5

′

)] and the methyl ketone were obtained using 1.5

equiv of oxidant, the latter compound could be obtained in good
yields using 3 equiv of potassium permanganate (eq 79).

KMnO

(3 equiv)

, 0

ºC, 14 h

68%

(79)

Permanganate oxidation under heterogeneous conditions has

also been applied to the epoxidation of

steroids. The epoxi-

dation takes place from the more hindered side of the molecule.
The best results were achieved with KMnO

/Fe

(SO

)

·n

(eq 80).

AcO

, 0.3−16 h

AcO

KMnO

/solid support

89−92%

(80)

The oxidation of cholesteryl acetate can be achieved as well

with potassium permanganate in the presence of a Lewis acid,
either FeCl

or ZnCl

, to afford the corresponding epoxides in

very good yields (eq 81).

79,80

AcO

acetone, 14 h

AcO

KMnO

/FeCl

80%

(81)

The highly selective dihydroxylation of

-spirotanic olefins

bearing ketone-, α-ketol-, epoxy-, hydroxyl-, and acetoxy func-
tions can be achieved using homogeneous nonaqueous potassium
permanganate (eq 82).

Ultrasound accelerates permanganate oxidations of olefins to

cis-

1,2-diols in aqueous media under neutral conditions (eq 83).

, 90 min

(82)

KMnO

/Et

BnN

−

67%

KMnO

/t-BuOH/H

))), 5−20 min

= H, C

, 4-MeC

, 4-MeOC

= H, Br

55−88%

= 0, 1

(83)

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

The utilization of potassium permanganate in combination with

18-crown-6 provides a versatile procedure for the dihydroxylation
of lactams (eq 84).

EtO

KMnO

, 18-crown-6

EtO

OH OH

, pH 9, 3 h

31%

(84)

An asymmetric phase transfer dihydroxylation of enones using

potassium permanganate and a chiral quaternary ammonium salt
have been recently described.

Moderate to good enantioselec-

tivities were achieved, although large quantities of catalyst are
required (eq 85).

BnO

KMnO

, AcOH

, −30

°C, 7 h

41%, 63% ee

(85)

Potassium permanganate supported on zeolite can be used for

the selective oxidative cleavage of various enamines to the corre-
sponding ketones in good yields (eq 86).

KMnO

/zeolite

1,2-dichloroethane, rt, 6 h

94%

(86)

Oxidation of enamines can also be performed with potassium

permanganate supported on neutral alumina. This reagent system
allows the selective oxidation of enamine carbon-carbon double
bonds in the presence of distal alkenes (eq 87).

KMnO

/Al

(87)

acetone, rt, 4 h

92%

4,5-Diamino-porphirazine systems undergo oxidation with

potassium permanganate at 20

◦

C to give rise to the corresponding

sec

-porphyrazines. These were shown to be efficient sensitizers for

the production of singlet oxygen (eq 88).

87,88

Oxidation of Dienes and Trienes.

Potassium permanganate

adsorbed on alumina has been used to oxidize 1,4-cyclohexadienes
to the corresponding aromatic compounds. These heterogeneous
reactions are an efficient alternative to the synthesis of highly
substituted aromatic systems (eq 89).

KMnO

, 20

°C, 45 min

92%

(88)

KMnO

-Al

acetone, 0

°C, 2 h

70%

(89)

The oxidative cyclization of 1,5-dienes was elegantly used by

Kociénski and co-workers as a key step in the synthesis of the
C(21)–C(30) (salinomycin numbering) lactone fragment of Sali-
nomycin. The success of the oxidation lies in the control of pH.
Use of acetate buffer mixed with acetic acid at pH 5 gave complex
mixtures, but the same reaction conducted at pH 6 and at −35

◦

was quite clean, giving the desired oxidative cyclization product
together with a diastereoisomer (dr 6:1) in 54% yield (eq 90).

cis

-Solamin and its diastereomer have been also synthesized

using the permanganate-promoted oxidative cyclization of 1,5-
dienes to create the tetrahydrofuran diol core (eq 91).

91,92

KMnO

Salinomycin

pH 6 acetate buffer

AcOH, acetone, H

−35

°C, 5 h, 54%

(90)

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

KMnO

, AcOH

Adogen 464, EtOAc

−30 to 0

°C, 55%

(10:1)

(91)

Promising levels of induction have been achieved in the asym-

metric phase-transfer-catalyzed oxidative cyclization of 1,5-dien-
ones by permanganate using a chiral ammonium salt (eq 92).

BnO

Ar = Ph (47%, 58% ee)

Ar = p-FC

(50%, 72% ee)

Ar = p-BrC

(26%, 75% ee)

KMnO

, AcOH

, −30

°C

(92)

The permanganate oxidation of 1,5,9-trienes took place regio-

selectively to afford substituted octahydro-2,2

′

-bifuranyl systems

(eq 93).

94,95

(pH 6.5)

52%

KMnO

, AcOH

acetone, acetate buffer

(93)

1,6-Dienes also undergo permanganate oxidative cyclizations,

affording only the cis-isomers. Good levels of asymmetric
induction have been achieved using a sultam as a chiral auxiliary
(eq 94).

(94)

KMnO

, AcOH

Adogen 464, EtAc

−60

°C, 20%

Oxidation of Alkynes.

Permanganate oxidation is one of the

most attractive methods for the synthesis of 1,2-diketones due
to the availability of starting materials and the ease of work up.
Recently, this method has been extended to alkynes substituted
with heterocycles such as pyridine or thiophene (eq 95).

KMnO

R =

rt, 4 h

(55–96%)

(95)

-Keto esters and derivatives can be easily prepared through

potassium permanganate oxidation of the corresponding substi-
tuted alkynyl ethers. The reaction was accomplished with a great
variety of substrates containing different functionality (eq 96).

KMnO

, pH = 7

(96)

2−5 min, 76−98%

An alternative method for the preparation of α-keto esters from

terminal alkynes via bromination and permanganate oxidation has
been recently reported (eq 97).

KMnO

, NaHCO

, MgSO

OMe

MeOH:H

O 1:1

93%

(97)

Oxidation of Organic Alcohols and Diols.

The classical

oxidation of primary alkyl or benzyl alcohols with potassium
permanganate has been supplemented by a new technique invol-
ving solid supports, such as Montmorillonite K-10,

100

alumina

silicate,

101

Kieselguhr,

102

zirconyl chloride octahydrate,

103

cop-

per sulfate pentahydrate,

or silica sulfuric acid-wet silica

104

to render the corresponding aldehydes without concomitant
oxidation to carboxylic acids. Some examples of the oxidation
of benzyl alcohol with supported potassium permanganate in
heterogeneous or solvent-free conditions are shown in eq 98,
Table 1.

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

Table 1

Entry

Conditions

Solvent

Time

Yield (%)

KMnO

/K10

solvent-free

2 h

KMnO

/aluminum silicate

toluene

70–80

◦

30 min

KMnO

/Kieselguhr

solvent-free

30 min

KMnO

/ZrOCl

·8H

3.5 h

KMnO

/CuSO

·5H

O, )))

1.5 h

KMnO

/SiO

-OSO

H, wet SiO

reflux

30 min

supported-KMnO

(98)

These solid-supported permanganate conditions have also been

used to oxidize secondary alcohols to the corresponding ketones.
For example, acetophenone was obtained using KMnO

/CuSO

after 1 h of sonochemical oxidation (eq 99), while the silent reac-
tion at room temperature gave, after the same time, just 8%. The
process can be performed as well in refluxing CH

, although

ultrasound irradiation significantly decreases the reaction time. A
KMnO

/zeolite reagent converts unsaturated secondary alcohols

to olefinic ketones under mild conditions (eq 100).

In general,

primary alcohols are oxidized more rapidly than secondary
alcohols (eq 101). However, oxidation of primary or secondary
benzylic alcohols in the presence of aliphatic carbinols shows high
selectivity toward the benzylic alcohols. An example is depicted
in eq 102 using zirconyl chloride octahydrate (ZrOCl

O) as

a solid support.

KMnO

/CuSO

⋅5H

rt, ))), 1 h 100%

rt, 1 h 8%

reflux, 70 h 95%

(99)

1,2-dichloroethane

KMnO

/zeolite

rt, 6 h, 87%

(100)

KMnO

/Al

solvent-free

100%

(101)

O, rt, 4 h, 90%

KMnO

/ZrOCl

⋅8H

(102)

1,3-Dialkylimidazolium salts comprise an important class of

ionic liquids and have been of considerable interest as being
environmentally benign. They have been employed as a reaction
media in the oxidation of different benzylic alcohols to the corres-
ponding carbonyl compounds with potassium permanganate
(eq 103).

105

Primary and secondary aliphatic alcohols, however,

required longer reaction times and higher temperatures. Again,
the conversion of benzylic alcohols to the corresponding carbonyl
compounds could be selectively performed in the presence of
aliphatic hydroxy groups (eq 104).

KMnO

[bmim]BF

, rt, 1−2 h

83−97%

= Aryl, heteroaryl

= H, Me

[bmim] = 1-Butyl-3-methylimidazolium

(103)

KMnO

[bmim]BF

, rt, 1 h

85%

(104)

Primary alcohols can also be converted into the corresponding

carboxylic acids in good yield by means of potassium perman-
ganate. Examples using an IER as a solid support are shown in
eqs 105 and 106.

The double bond moiety of α,β-unsaturated

alcohols are preserved during the oxidation. Ketones are obtained
in comparable yields from the oxidation of secondary aliphatic or
aromatic alcohols (eqs 107 and 108.)

MeO

KMnO

/IER

, reflux, 4 h

94%

(105)

KMnO

/IER

, reflux, 4.15 h

95%

(106)

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

KMO

/IER

, reflux, 4.30 h

93%

(107)

KMnO

/IER

, reflux, 4 h

91%

(108)

A mixture of KMnO

and MnO

can be used as an effec-

tive oxidant for alcohols under both heterogeneous and solvent-
free conditions.

Both primary and secondary α,β-unsaturated

alcohols were oxidized to the corresponding carbonyl compounds
without disruption of the double bond. Active MnO

is able to

oxidize alcohols to the corresponding ketones under solvent-free
conditions. However, the time required to complete the reaction
is often a few days instead of hours as is observed when perman-
ganate is present (eqs 109 and 110).

KMnO

/MnO

(109)

Conditions

Yields (%)

, 4 h

solvent-free, 50 min

))), solvent-free, 43 min

KMnO

/MnO

Conditions

Yields (%)

, 5 h

solvent-free, 2 h

))), solvent-free, 1 h 45 min

(110)

Primary and secondary benzylic alcohols are converted into the

corresponding carbonyl compounds in relatively high yields in
MeCN at room temperature (eqs 111 and 112).

KMnO

MeCN, rt, 0.30−3.30 h

70−98%

(111)

KMnO

MeCN, rt, 0.30−3.30 h

40−98%

(112)

A polymer-supported reagent, potassium permanganate/

Amberlyst A-27, has been used to convert trifluoromethyl
aryl carbinols to trifluoromethyl ketones.

106

The oxidation is

performed in refluxing CH

(THF or toluene can also be used

if higher reaction temperatures are required) in the presence of
4 Å molecular sieves as a dehydrating agent. The trifluoromethyl
aryl ketones are obtained in high yields and excellent purities

eq 113. One exception was the p-nitrophenyl-substituted alcohol,
which generates a complex mixture in which no trace of the ketone
could be found.

KMnO

/A-27

Å, CH

, reflux, 2−7 h

74−100%

(113)

Oxidation of α-hydroxyphosphonates to α-ketophosphonates

is performed at room temperature with KMnO

in dry benzene

or under solvent-free conditions supported onto neutral alumina,
providing very good yields of the desired products (eq 114).

107

P(OEt)

KMnO

P(OEt)

A: dry benzene, 3−12 h, 85−98%
B: Al

, solvent-free, 4−15 h, 81−96%

R = Ar, 3-py, Bn

(114)

Allylic spiro-γ-lactones are obtained by the oxidative cycliza-

tion of γ-hydroxyl alkenes with potassium permanganate and
CuSO

O as the solid support in the presence of catalytic

amounts of water and tert-butyl alcohol (eq 115).

108

It is be-

lieved that in these oxidations the tert-butyl alcohol acts as a
phase-transfer catalyst, and both water and tert-butyl alcohol form
a third phase (omega phase) over the inorganic solid. The reaction
takes places on or at the interface.

(115)

KMnO

/CuSO

⋅5H

rt, H

BuOH

, 1 h, 62%

The oxidation of diols under heterogeneous conditions gave

the corresponding ketones. 1,2-Bis(1-hydroxyethyl)benzene was
quantitatively oxidized to 1,2-diacetylbenzene after 1.5 h of sono-
chemical reaction (eq 116).

Reaction of hydroquinone with

potassium permanganate-silica sulfuric in the presence of wet sil-
ica under solvent-free conditions gave p-benzoquinone in very
good yield (eq 117).

109

(116)

KMnO

/CuSO

⋅5H

))), CH

, 1.5 h, 100%

KMnO

/SiO

-OSO

H, wet SiO

solvent-free, rt, 30 min, 95%

(117)

Oxidation of Ethers, Acetals, and Thioacetals.

Trimethyl-

silyl- and tetrahydropyranyl ethers are efficiently deprotected to
the corresponding carbonyl compounds by KMnO

supported

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

on alumina, under solvent-free conditions, in very good yields
(eqs 118 and 119).

110

The rates and yields of the reactions in

the absence of Al

are lower.

TMS

R = H, Me

KMnO

/Al

rt, 3−20 min

75−99%

(118)

THP

(119)

KMnO

/Al

rt, 5−20 min

75−95%

Oxidation of benzyl methyl ether with permanganate combined

with iron(III) chloride in acetone solution gave the corresponding
esters in 86% yield, together with a 10% yield of benzaldehyde
(eq 120).

OMe

KMnO

/FeCl

acetone, −78

°C to rt, 15 h

86%

10%

(120)

Cyclic ethers are also converted into lactones under alumina-

supported potassium permanganate in the presence of copper sul-
fate pentahydrate (eq 121).

When the α-carbons are tertiary,

the product is a dione, formed presumably by dehydration of the
corresponding intramolecular bis(hemiacetal) (eq 122).

KMnO

/Al

/CuSO

⋅5H

rt, 6 h, 65%

(121)

KMnO

/Al

/CuSO

⋅5H

rt, 8 h, 60%

(122)

Ethylene acetals are oxidized as well to the carbonyl com-

pounds using solvent-free alumina-supported potassium perman-
ganate (eq 123). Overoxidation of the products was not observed.
Cinnamaldehyde acetal was not converted to its correspond-
ing α,β-unsaturated aldehyde, giving rise instead to many by-
products.

110

KMnO

/Al

rt, 5−15 min

75−98%

(123)

= Aryl, alkyl

= H, aryl, alkyl

Potassium permanganate and silica chloride provides an

effective oxidizing system for selective oxidations of aromatic
or aliphatic cyclic thioacetals (1,3-dithiolanes and 1,3-dithiones),
and conversion of silyl- or tetrahydropyranyl ethers into their car-
bonyl compounds in dry MeCN at room temperature (eqs 124 and

125).

111

Oxidation of cinnamyl derivatives proceeded with the

cleavage of the carbon-carbon double bond to give benzaldehyde.
Overoxidation of the regenerated aldehydes was not observed.

KMnO

/silica Cl

MeCN, rt, 5−35 min

75−98%

(124)

= Aryl, alkyl

= H, aryl, alkyl

n =

1, 2

(125)

KMnO

/silica Cl

MeCN, rt, 5−150 min

70−92%

X = TMS, TBDMS, THP
R = H, Me, Et, Ph

Alumina-supported permanganate also promotes the dethioac-

etalization of acyclic and cyclic thioacetals, under solvent-free
conditions, to the corresponding carbonyl compounds in good
yields (eqs 126 and 127).

112

The method proved to be particularly

effective with C-3 and C-20 dithiolane and dithiane derivatives
of steroidal ketones such as 5-cholesten-3-one and pregnenolone
(eqs 128 and 129), which are usually removed under vigorous
conditions.

KMnO

/Al

solvent-free, rt, 5−25 min

85−99%

(126)

= Aryl, alkyl

= H, aryl, alkyl

n =

1,2

SMe

MeS

KMO

/Al

solvent-free, rt, 20 min

88%

(127)

KMnO

/Al

solvent-free, rt, 25 min

(128)

91%

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

AcO

KMnO

/Al

solvent-free, rt, 25 min

(129)

93%

The N,O-acetal, present in the 3-phenylhexahydro-5H-[1,3]-

oxazolo[3,2-a]pyridine-5-carbonitrile, can be regarded as the
precursor of a lactam function after oxidation with KMnO

(eq 130).

113

Neither degradation nor racemization at the CN group

was observed, leading to the 2-substituted-piperidin-6-one in an
80% yield. Presumably, the permanganate ion oxidized the α-
amino ether function to produce an iminium intermediate. The
reduction of the permanganate ion to manganese dioxide, in aque-
ous medium, liberated hydroxy ions, which could trap the iminium
species. Subsequent opening of the oxazoline afforded the lactam
function.

KMnO

acetone/H

O, rt

80%

(130)

Oxidation of Aldehydes.

Potassium permanganate has been

successfully used in the synthesis of 4-amino-3-carboxy-β-carbo-
line derivatives. In one of the final steps, treatment of the
corresponding aldehyde with potassium permanganate in acetone-
water afforded the 4-carboxylic acid in 84% yield (eq 131).

114

−

KMnO

acetone/H

3 h, 84%

(131)

A similar reaction has been used in the conversion of norditer-

penoid alkaloids into aconane-type diterpenes. In this case, in
addition to the aldehyde being oxidized to a carboxylic acid,
the pendant oxaziridine group was transformed to a formamide
(eq 132).

115

OMe

AcO

OHC

MeO

OMe

MeO

OAs

OAc

OMe

AcO

MeO

OMe

MeO

OAs

OAc

OCH

KMnO

/acetone

10% H

30%

(132)

As =

The utilization of potassium permanganate in aqueous sodium

hydroxide allows the oxidation of phenylboronic aldehydes to the
corresponding acids, without affecting the boronic acid group, in
preparative yield (eq 133).

116

(HO)

KMnO

(HO)

(133)

NaOH aq.

overnight

90%

Oxidation of Organic Sulfur Compounds.

Aliphatic and

aromatic thiols are converted into the corresponding disulfides
in good yields under very mild conditions, using solvent-free
solid-supported potassium permanganate. No overoxidations to
sulfonic acids were observed in any case. Sulfides can be
converted to the sulfoxides or to the sulfones. Alumina-supported
permanganate affords the corresponding disulfides upon treat-
ment with thiols in good to excellent yields (eq 134).

117

The

optimum molar ratio between the thiol and the oxidant is found
to be 1:1, but in the case of heterocyclic thiols an increase of the
thiol to permanganate ratio is required to complete the reaction.
Sulfoxides are selectively obtained by oxidation of the sulfides
with KMnO

-Al

(eq 135).

S R

R = Aryl, heterocyclic, alkyl

KMnO

/Al

rt, 15−30 min

75−90%

(134)

S R

KMnO

/Al

rt, 10−30 min

75−90%

(135)

R = Aryl, alkyl

The reaction of thiols with potassium permanganate adsorbed

on Montmorillonite K-10

100

gave the corresponding disulphides

in good yields (eq 136). Alkyl- and aryl sulfides are oxidized to the
corresponding sulfones in a few hours at rt with no concomitant
formation of sulfoxides (eq 137).

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

S R

KMnO

/K-10

rt, 25−70 min

74−96%

(136)

R = Aryl, alkyl

KMnO4/K-10

rt, 2−6 h

75−85%

(137)

R = Aryl, alkyl

Similar results are obtained with potassium permanganate

mixed with MnO

65,118

or hydrated salts of transition metals,

such as copper sulfate pentahydrate (eqs 138 and 139),

as pro-

moters of heterogeneous permanganate oxidation. Sulfones are
more rapidly obtained when the reaction is assisted by microwave
irradiation.

S R

R = Aryl, alkyl

KMnO

/CuSO

⋅5H

rt, 7−15 min

95−100%

(138)

KMnO

/CuSO

⋅5H

rt, 5–15 min

85–90%

(139)

R = Aryl, alkyl

Oxidation of thiols and sulfides with KMnO

in the presence

of IER Rexyn 101H in refluxing CH

gave disulfides and sul-

fones, respectively, in excellent yields (eqs 140 and 141).

Alkyl-

and aryl sulfides are converted into the corresponding sulfones.
The observation that benzyl phenyl sulfide and dibenzyl sulfide
gave the related sulfones indicated that the reaction proceeds by
way of an oxygen transfer mechanism, instead of the electron
transfer which would have formed substantial amounts of ben-
zaldehyde.

S R

R = Bn, alkyl

KMnO

/IER

94−96%

(140)

reflux, 2−2.45 h

KMnO

/IER

85−95%

(141)

R = Aryl, alkyl

, reflux, 4−7 h

Treatment of benzyl phenyl sulfide with permanganate and

iron(III) chloride in either acetone or MeCN gave the correspond-
ing sulfone in excellent yield (eq 142).

79,80

Since the ultimate

product is a sulfone, the initially formed sulfoxide must undergo
a subsequent rapid oxidation. This conclusion is consistent with
competitive experiments in which incompounds containing both
sulfide and sulfoxide functionalities, the latter is preferentially
oxidized (eqs 143 and 144).

(142)

KMnO

, FeCl

acetone, 0

°C

98%

KMnO

, FeCl

acetone

(143)

KMnO

, FeCl

acetone

(144)

Heterogeneous oxidations of aromatic and aliphatic sulfides in

acetonitrile solution give rise to the corresponding sulfones in
good yields (eqs 145 and 146).

KMnO

, rt

CN, 55 h, 95%

, 72 h, 25%

(145)

Alkyl

KMnO

, rt

CN, 5−7 h, 85−93%

(146)

Reaction of thiazolines with KMnO

under phase-transfer

catalysis conditions gave the corresponding thiazoles (eq 147).
However, addition of 1 equiv of benzoic acid resulted in a com-
plete change in favor of S-oxidation, affording the thiazoline S,S-
dioxides in 85–93% yield.

119

The oxidation was carried out in an

aqueous solution of KMnO

(2 equiv) and benzyltriethylammo-

nium chloride (0.1 equiv) at rt in CH

(eq 148).

KMnO

, BnEt

NCl

, rt, 85−93%

(147)

KMnO

, BnEt

NCl, PhCO

, rt, 85−93%

(148)

This reagent system gave excellent results in converting the

exocyclic C=S of thiazolidine-2-thines into C = O (eq 149).
Moreover this procedure is suitable for a variety of simple
sulfides, dibenzylsulfoxide, thiazolidines, and thiaxolidin-2-ones
(eqs 150–153).

KMnO

, BnEt

NCl, PhCO

, rt, 3 h, 70%

(149)

S R

R = Aryl, alkyl

KMnO

, BnEt

NCl, PhCO

, rt, 3 h, 52−82%

(150)

KMnO

, BnEt

NCl, PhCO

, rt, 3 h, 75%

(151)

KMnO

, BnEt

NCl, PhCO

, rt, 3 h, 50−95%

(152)

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

KMnO

, BnEt

NCl, PhCO

, rt, 3 h, 72%

(153)

Amine Oxidation.

The heterogeneous oxidation of primary

aliphatic- and aromatic amines using potassium permanganate ad-
sorbed onto hydrated copper sulfate gives rise to ketones and azo
compounds, respectively, in nearly quantitative yields (eqs 154
and 155).

120

No oxidation of the benzylic positions are observed

in the case of alkylanilines. Other solid supports such as iron(II)
sulfate heptahydrate have been used (eqs 156 and 157).

121

KMnO

/CuSO

⋅5H

, rt or reflux, 1−2 d

87−100%

(154)

Ar NH

KMnO

/CuSO

⋅5H

, rt or reflux, 1−2 d

78−100%

Ar N N Ar

(155)

Ar NH

= Aniline, 2- and 4-butylaniline, 2- and 4- isopropylaniline,

2- and 4- sec -butylaniline, 4-iodoaniline, 4-chloroaniline

KMnO

, FeSO

⋅7H

N N

95%

(156)

, reflux, 5 h

KMnO

, FeSO

⋅7H

80%

(157)

, reflux, 5 h

Primary aromatic amines are also oxidatively coupled under

mild conditions using alumina and copper sulfate pentahydrate as
a solid support (eq 158).

The presence of an electron-withdra-

wing substituent such as a chloro group decreased the reaction
rate but not the yield.

KMnO

/Al

/CuSO

⋅5H

Me,

N Ar

rt, 5−20 h

70−85%

Ar = Ph,

(158)

Oxidation of 5-hydroxyaminopyridine-2-sulfonic acid to 5-

nitropyridine-2-sulfonic acid may be performed selectively by
sodium perborate in acetic acid, bleach in water, or potassium
permanganate in water, with the latter being preferred. By

NMR this process appeared to provide quantitative conversion to
product, but high isolated yields were difficult to achieve, proba-
bly due to inorganic impurities present even after treatment with
acidic ion exchange resin. Isolated yields were in the range of
60–65% (eq 159).

122

KMnO

, H

(159)

rt, 20 h

60−65%

Cleavage of Carbon–Nitrogen Double Bonds.

Potassium

permanganate supported on a solid support regenerates carbonyl
compounds from oximes. No overoxidation of the correspond-
ing carbonyl compounds to carboxylic acids was observed. The
deoximation reaction with KMnO

-Al

proceeded under

solvent-free conditions at 50

◦

C in good to excellent yields

(eq 160).

123

In addition, α,β-unsaturated oximes were selec-

tively oxidized to the corresponding enone. The carbon-carbon
double bond remained unaltered (eq 161). Under these reac-
tion conditions, ketoximines can be exclusively cleaved in the
presence of aldoximes. Organic solvents, such as acetone or ether,
can also be used to perform the oxidative cleavage of ketoximines
to ketones.

124

KMnO

/Al

°C, 15−40 min

= Aryl, naphthyl, alkyl

= H, Me, Ph

78−99%

(160)

KMnO

/Al

°C, 10–40 min

87–92%

R = H, Me, Ph

(161)

Oxidation using KMnO

in the presence of montmorillonite

K-10 occurs under solvent-free conditions in good yields
(eq 162).

125

Semicarbazones, phenylhydrazones, and azines were

also transformed to their corresponding carbonyl compounds in
80–96% yields (eqs 163–165). However, 2,4-dinitrophenylhydra-
zones are resistant to this reagent system and remained intact in
the reaction mixture.

KMnO

/K-10

rt, 5–60 min

85–97%

= H, Me, Ph

= Aryl or alkyl

(162)

NHCONH

KMnO

/K-10

rt, 15–20 min

80–96%

(163)

NHPh

KMnO

/K-10

rt, 10–20 min

82–96%

= H, Me

(164)

A list of General Abbreviations appears on the front Endpapers

POTASSIUM PERMANGANATE

KMnO

/K-10

rt, 25–30 min

83–95%

= H, Me

(165)

Other solid supports such as wet silica promote the KMnO

oxidative cleavage of semicarbazones and phenylhydrazones
under solvent-free conditions at rt (eq 166).

126

This procedure

is fairly effective also for sterically hindered semicarbazones
(eq 167). Molecules bearing acid-sensitive as well as base-sensi-
tive functional groups as tert-butoxycarbonyl, tetrahydropyranyl
ether, and aliphatic or aromatic hydroxyl or sulfide groups re-
main intact under the reaction conditions. Cinnamaldehyde semi-
carbazone underwent oxidative cleavage without affecting the
double bond moiety.

KMnO

/wet SiO

rt, 15–45 min

72–98%

= Aryl, alkyl

= H, Me

X = NHCONH

, NHPh

(166)

N NHCONH

rt, 30 min

80%

KMnO

/wet SiO

(167)

Miscellaneous Oxidations.

Oxidation of secondary α-hydro-

xysilanes to acylsilanes is performed by a mild procedure using
permanganate supported on neutral alumina. Due to the lability of
the acylsilane to oxidizing reagents, a biphasic mixture of hexane-
water was used as solvent to limit contact between the inorganic
reagent and the product (eq 168).

127

hexane, 1–4 h

80%

KMnO

/Al

-H

SiMe

MeO

(168)

A simple and efficient decarboxylation of aromatic carboxylic

acids can be performed by KMnO

in nonaqueous media. No vig-

orous conditions or catalysts were required. The reaction is carried
out in CH

or CHCl

at room temperature. No overoxidation

of the aldehydes was observed. Some examples are depicted in
(eqs 169–171).

128

, rt, 20 h

80%

COOH

KMnO

(2 equiv)

(169)

, rt, 20 h

75%

COOH

KMnO

(2 equiv)

COOH

(170)

, rt, 20 h

90%

KMnO

(1.5 equiv)

COOH

(171)

2,5-Disubstituted 1,3,4-oxadiazoles were prepared by oxidation

of 1-aroyl-2-arylidene hydrazines with KMnO

on the surface of

silica gel or montmorillonite K-10, or with mixtures of acetone
and water under microwave (MW) irradiation (eq 172).

129

KMnO

SiO

, MW, 8−25 min, 61−96%

acetone/water, MW, 8−22 min, 64−96%

(172)

= Ph, Me, 4-ClC

= Ar, Me, CH=CHCH

Various types of 2-imidazolines can be efficiently oxidized

to the corresponding imidazoles using potassium permanganate
supported on silica gel under mild conditions at room temper-
ature. Chemoselective oxidation in the present of other oxidiz-
able functional groups was also accomplished by this reagent sys-
tem (eq 173).

130

Selective oxidation of 2-alkylimidazolines in the

presence of 2-arylimidazolines was achieved using alumina-
supported potassium permanganate.

131

N
H

KMnO

/SiO

CN, rt, 2 h

85%

(173)

Oxidation of α-amido nitro derivatives with permanganate

potassium in phosphate buffer (pH = 11) lead, after acidic work up,
to the corresponding N-protected α-amino acids in good yield.

132

When a secondary nitro group is present in the framework it is
also oxidized to the parent carbonyl derivative affording the keto
amino acid or aminodicarboxylic acid (eqs 174–176). Alkenes are
incompatible with this reaction conditions.

COOH

1. KMnO

/phosphate buffer

2. H

(174)

Avoid Skin Contact with All Reagents

POTASSIUM PERMANGANATE

COOH

1. KMnO

/phosphate buffer

2. H

(175)

COOH

1. KMnO

/phosphate buffer

2. H

(176)

Trimethylsilyl chloride and benzyltriethylammonium perman-

ganate, easily prepared with KMnO

and the phase-transfer

reagent benzyltriethylammonium chloride, chemo- and stereo-
selectively dichlorinate alkenes, cleave epoxides, and oxidize
sulfides to sulfoxides in high yields (eqs 177–181).

133

The

emerald-green manganese complex, KMnO

/BnNEt

Cl/TMSCl,

reacts with alkenes at 0

◦

C in CH

exclusively by anti-dichlori-

nation, with the exception of the aromatic olefins which gave a
mixture of syn- and anti-dichlorides. Reaction with epoxides takes
place with an excess of TMSCl. In benzylic oxiranes, ring opening
to form benzylic chlorides is preferred, while in alkyl epoxides,
chloride insertion is performed at the less sterically hindered
position (eqs 179 and 180). Sulfoxides are obtained by inverse
addition of the manganese reagent (1–2 equiv) to the sulfide.
Alkenyl sulfides display excellent chemoselectivity, with only
traces of dichlorinated olefin (eq 181).

KMnO

/BnNEt

Cl/TMSCl

, 0

°C to rt

95%

(177)

KMnO

/BnNEt

Cl/TMSCl

, 0

°C to rt

60%

(178)

(1:4)

(179)

KMnO

/BnNEt

Cl/TMSCl

, 20

°C, 50 min

89%

(6:1)

(180)

KMnO

/BnNEt

Cl/TMSCl

, 20

°C, 50 min

85%

(181)

KMnO

/BnNEt

Cl/TMSCl

, −78 to 25 °C

80%

KMnO

in liquid ammonia can be used as an efficient oxidant

for the oxidation of σ

-adducts formed in the addition of car-

banions to nitroarenes (eq 182).

134−136

In these oxidative nucle-

ophilic aromatic substitution of hydrogen reactions (ONASH), the
permanganate anion presumably attacks the adduct at the addition
site of the nucleophile.

KMnO

/NH

(liq)

87%

(182)

−

Similarly, the direct coupling of amines, amides, and ketones

with nitroarenes and nitronaphthalenes is reported through ox-
idative activated nucleophilic aromatic substitution promoted by
fluoride anions as the nucleophilic activating agent and KMnO

as the oxidant (eq 183).

137

KMnO

, DMF

NuH, TBAF·3H

Nu =

PrNH

, PhNH

, PhCONH

, MeCOEt

42−75%

(183)

Related Reagents.

Potassium Permanganate–Copper(II) Sul-

fate; Sodium Periodate–Potassium Permanganate.

Stewart, R. In Oxidation in Organic Chemistry; Wiberg, K. B., Ed.;
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A list of General Abbreviations appears on the front Endpapers

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