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Oxidation of Ethers with Benzyl(triethyl)ammonium Permanganate.

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vantage is that alkylarenes are degraded to arenecarboxylic
acids[']. The advantages of oxidation in organic solvents have
hitherto been exploited only in isolated cases. Olefins can
be cleaved to carboxylic acids with potassium permanganate
in benzene. if the potassium ion is complexed with a crown
etherr3].In pyridine, alcohols and aldehydes can be oxidized
to carboxylic acids with tetrabutylammonium permanganate[4'.
We report here on the oxidation of alkanes with benzyl(triethy1)arnmonium permanganate (1 ) in dichloromethane
or glacial acetic acid (Table 1). ( 1 ) precipitates as a violet
salt on treatment of an aqueous solution of the corresponding
chloride with potassium permanganate[? It is thermally stable
at 100°C. resistant to shock, and readily soluble in dichloromethane and glacial acetic acid (0.3-0.5mol/l), in which it
is relatively stable.
Table I . Product5 of the oxidation of alkanes with henzyl(triethyl)ammonium
permanganate ( I ).
Alkanc
Oxidation products, Yields [a]
Cumene 1 2 ) [b]
2-PhenyI-2-propano1, 28 ",, (98 X ) , acetophenone, I
2-Phenyl-2-butanoI. 12 "4 (61 %,), dcetophenone, 1 "G: propiophenone. 19": ( I methyl-I-phenylpropyl)acetate,2"; ( I 2 ");,
Isobutyrophenone, 26 Yo (51
2-methyl-lphenyl-2-propanol,
3 yo: (3.r-dimethylphenethy1)acetate. 20 'yo (
ri-Butyrophenone, 44 % (
tyl)acetate, 26 (37 %)
3-Pentanone. 12 % (25
tanone, 13 (25 "/;):3-ethyl-3-pentanol, 12 ?lo
(24 %); (1,l-diethylpropy1)aceta
I-Methylcyclohexanol, 23 ":,( 7
ylcyclohexanone. 3 "4
rrrrr1s-9-Decalol. I 1 "/#',(37
rrurwl -decalone, 13 % (43 "i);truris-2-decalone, 3 ",A
<.i.s-9-Decalol.33 7" (67 %)
s"(
-Butylbentene ( 3 J [c]
lsohtitylhenzene ( 4 ) [d
11-Butylbenzene ( S i [e]
3-Ethylpentane (61 [f]
Methylcyclohexane ( 7 ) g]
rruns-Decalin ( X i [h]
cis-Decalin ( Y ) [h]
[a] Chromatographically determined yields, based on original amount of
alkane and (in brackets) on consumed alkane. [b] 50mmol (2). 52mmol
( I ) . 6mmol pyridinr. 3 d at 40°C in CH2C12. [c] 50mmol (31, 50mmol
(1),2dat40"CingIacialaceticacid.[d] 5 0 m m o l ( 4 ) , IOmmol ( I ) , l00mrnol
KMnOl. 4 d at 30°C in glacial acetic acid. [el As in [d] hut only 2d.
[g As in [d] bur at 50°C. [g] As in [d] hut 2d at 60°C. [h] as in [d]
hut only 3 d.
Benzylic methylene groups [ ( 4 ) , ( 5 ) ] are oxidized to the
ketone; cleavage to benzoic acid is suppressed. Tertiary benzylic CH-groups [(2), ( 3 ) ] are smoothly transformed into tertiary alcohols. Some aliphatic methine groups [ ( 4 ) , (6)-(9)]
require higher reaction temperatures and activation of the
permanganate by glacial acetic acid as solvent, whereupon
the alcohol formed is partially dehydrated and/or secondary
methylene groups are also oxidized. Hydroxylation of the
decalins [ ( 8 ) , (911 proceeds stereospecifically with retention
of configuration.
In the oxidation of alkanes with ( I ) the yields obtained
are not as high as those achieved by dry ozonolysis[61;however,
the former method appears to be advantageous for the oxygenation of alkylarenes, which are degraded to alkylcarboxylic
acids by ozone['].
Exprrimenfal
Preparation of benzyl(triethy1)ammonium permanganate
( I ) [ 5 1 : A solution of benzyl(triethy1)ammonium chloride
(227.8 g, 1.00mol) in 200ml water is added dropwise and
slowly to a solution of potassium permanganate (1 58.0g,
1.00 mol) in 4.7 1 water. The violet crystals are recovered by
filtration and dried at 4OaC/0.2 torr. Yield of ( 1 ) 294.8g
(0.947 mol, 95 XI; over 99 '%I pure (iodometrically)); m. p.
(decomp.) 127-1 29°C.
Received: November 6, 1978 [Z 123a IE]
German version: Angew. Chem. YI. 77 (1979)
D. G . Lee in R. L. A i r y u s t i w Oxidation. Marcel Dekker, New York
1969. Val. 1. p. 3.
R. S r r i w r r in K . 5.Wibrrg. Oxidation in Organic Chemistry. Academic
Press, New York 1965, Part A, p. 39; C. F . Cullia, J . W Ludhury.
J. Chem. Soc. 1955, 2850.
D. J . Sum, H . E. Sirnmnrrs, J. Am. Chem. Soc. 94. 4024 (1972); G. W
Gokrl, H . D. Dvrsr, Synthesis 1976. 168.
7: Sulu, M . K Surgerlr. J. Chem. Soc. Chem. Commun. IY78, 253.
1 Cluirsseii, Diplomarbeit, UniversitPt Munster 1977.
Z . Cohen, E. Keiriun. Y .Uuzur, 7: H . Vrrrkori?., J. Org. Chem. 4 0 . 2141
( I 975).
H . Kleiri, A . Stt!i!irnefz, Tetrahedron Lett. 1975, 4249.
[I]
[2]
[3]
[4]
[5]
[6]
[7]
Oxidation of Ethers with Benzyl(triethy1)arnmonium
Permanganate
By H.-Jiirgen Schmidt and Huns J . Schufer[*]
Ruthenium tetraoxide has long been known to be a particularly suitable reagent for the oxidation of alkyl ethers"]. Other
oxidizing agents have also been used. For example, chromium
trioxide''] and trichloroisocyanuric acidr3]oxidize ethers to
esters and lactones, respectively. Reaction with
uranium hexaflu~ride[~],
lead tetraacetatec6I or
as
well as anodic oxidation[*], leads via oxidative cleavage of
the ethers to carboxylic acids, ketones and alcohols. Ruthenium tetroxide is, of course. only suitable for the oxidation
of dialkyl ethers, since aryl groups are oxidatively degraded.
This disadvantage is overcome on oxidation with benzyl(triethy1)ammonium permanganate ( I ),which oxidizes ethers cleanly
and chemoselectively to esters (Table 1).
Table I. Products of the oxidation of ethers with benzyl(triethy1)ammonium
perrnanganate ( I ).
Ether
Oxidation products. Yields [a]
Dibutyl ether ( 2 ) [b]
Dibenzyl ether ( 3 ) [c]
Butyl hutyrate, 58 y,, (80 %)
Benzyl benzoate, 80 ',<, (84
methylene dibenzoate, X"%
Butyl benzoate, 90 '?
Methyl butyrate, 23
Benzyl butyl ether ( 4 ) [d]
Butyl methyl ether (5) [el
Methyl octyl ether (6)
Benzyl (I-ethylpropyl) ether ( 7 ) [g]
[fl
Benzyl methyl ether ( X I [g]
(85 'yo)
Methyl benzoate. 83 '4(84 "")
Bntyl (I-ethylpropyl) ether ( 9 ) [h]
Benzyl (I-phenylethyl) ether ( I O ) [i]
Benzyl phenyl ether ( I I ) h]
Butyl (I-phenylethyl) ether ( 1 2 ) [k]
Butyl phenyl ether ( 1 3 ) [fl
(83 "~:,); acetophenone. 6 'k
Phenyl benzoate, 42 '',<,(94 "6)
Acetophenone,
38",,
(67
(I-phenylethyl)hutyrate.3~~,:
butyl
benzoate, 2 "<,
Phenyl butyrate. I I ",,, (92 "<,)
[a] Yields based on initial amount o l ether and (in brackets) amounts of
ether consumed: determined by gas-chromatography. [h] 30 mmol ( 2 ) ,
IOmmol ( I ) , 50nimol KMnO, in lO0mi H 2 0 , IOOml CH2CI2, 14d at
30°C. [c] 30mmol ( 3 ) . 60mmol ( I ) in Ch2C12. 6 d at - 5 t o 20°C. [d]
As in [c], but 8 d at 0°C. [el As in [b], hut IOd at 42°C. [f] As in [h].
hut at 42°C. [g] A5 in [ c ] , hut 7 d at -5°C. [h] As in [h]. but 30 to
42°C. [i] As in [ c ] . but 9 d at 5°C. b] As in [c], but Yd a t 0°C [k]
As i n [b]. hut 8 d at 25°C.
_ _
[*I
-
Pro[. Dr. H. J. Schlfer, DipLChem. H.-J. Schmidt
Organisch-Chernisches lnstitut der UniversitBt
OrIednS-Ring 23, D-4400 Munster (Germany)
69
The esters formed from the unsymmetrical ethers and the
reaction times and temperatures indicate the following reactivity sequence for the individual CH-bonds: benzyl > phenylalkyl > primary-alkyl > secondary-alkyl, methyl > phenyl.
In phenyl ethers the phenyl group deactivates the CH-group
of the alkyl residue.
Received: November 6, 1978 [Z I23 b [El
German version. Angew. Chem. 91. 78 (1Y79)
[l] L. M . Brrkowitz, P . N . Rylander, J. Am. Chem. SOC.80, 6682 (1958);
M. E. WoljJ, J . K . Kerwien, F. F. Ow,ings, B. B. Lewis, 8. Blank, 1.
Org. Chem. 28, 2729 (1963); D. G. Lee, M . c'an den Engh in W S.
Truhunousk): Oxidation in Organic Chemistry. Academic Press, New
York 1973, Part B, p. 222.
[2] I . 7: Harrison, S. Hurrison, J. Chem. Soc. Chem. Commun. 1966. 752;
W Huckel, H . Bretschneidrr, J . Prakt. Chem 11, 61 (1938); H. B. Henbesr,
B. Nicholls, J . Chem. SOC.1959, 227.
131 E . C . Juenge, M . D. Core), D. A. B e d , Tetrahedron 27, 2671 (1971);
E . C . Juetige. D . A. B e d , Tetrahedron Lett. 1968, 5819.
[4] N. C. Deno, N . H . Potter. J. Am. Chem. SOC.89, 3550 (1967).
[5] G. A . Oluh, J . Welch, 7: L. Ho, J . Am. Chem. Soc. 98, 6717 (1976).
[6] !-!F r a n z m , R. Edens, Justus Liebigs Ann. Chem. 735, 47 (1970).
[7] K. A. Pollart, R. E. Mdler., J. Org. Chem. 27, 2392 (1962).
[8] ?: Shono, Y Matsumura, J . Am. Chem SOC.91, 2803 (1969).
Intermolecular Ene Reactions in a High-Pressure/HighTemperature Flow A p p a r a t u s [ * * ]
By Jiirgen Metzger and Peter KOll[*]
In the thermal degradation of chitin in supercritical acetone['I we were able to demonstrate the presence of large
amounts ofdiacetamide (1 1,which can be formed by dimerization of the acetamide molecules in the sense of an ene reaction.
This finding encouraged us to investigate some ene reactions['], as example of the numerous types of thermal pericyclic
reactions[31, in the same high-pressure/high-temperature
apparatus ("HP-HT" apparatus)['], which enables relatively
unproblematical operation at pressures of up to cu. 500bar
and temperatures of up to ca. 700K, and is readily built
from commercially available HPLC and G C equipment. The
apparatus offers all the advantages of a flow reactor, such
as exceptionally rapid withdrawal of sensitive products from
the reaction zone and the possibility of quickly changing
the reaction parameters with slightest consumption of substances.
Whereas numerous intramolecular ene reactions, even with
nonactivated enophiles, have already been reported[41,intermolecular ene reactions generally require active enophiles[21. It
was predicted, however, that if the latter reactions were to
be carried out at high pressures, besides the usual conditions
employed for ene reactions, namely high temperatures and
long reaction times, then intermolecular ene reactions with
nonactivated enophiles should also be possible. Thus, the reactions carried out at high temperatures under pressure by
Nemtsov et al.''' in 1938 with the aim of polymerizing olefins
[*] Prof. Dr. P. KOII, Dr. J . Metzger
Fachbereich 4 (Naturwissenschaften) der Universitat
Ammerlinder Heerstr. 67--99, D-2900 Oldenburg (Germany)
[**I Part 2 of High-Pressure/High-Temperature Reactions in a Flow Reactor.-Part 1 : [t].
70
may be regarded as ene reactions. The reaction of acetylene
as moderately active enophile with olefins at 623 K and 170
bar to give 1,4-dienes-likewise in a flow reactor--also
demonstrates the influence of pressure in such reactions''!
In all the examples so far investigated by us (cf. Table 1)
the expected products were seen to be formed in the overall
main reaction. Even toluene was found to react as "deactivated" ene component with non-activated enophiles; reaction
with cyclohexene afforded o-cyclohexyltoluene (2).
The yields quoted in Table 1 are not optimized and might
easily be increased to preparatively satisfactory values by
increasing the residence time of the reactants (incorporation
Table 1 Some intermolecular ene reactions with non-activdted enophiles
Reaction conditions 673 K, 450 bar, 10 min residence time, ene enophile
=10 1, conversion based on enophile Characterization of the products
by GC-MS
Ene
Enophile
Reaction product(s)
ConverSlOll[
UO]
~
I-Hexene
Cyclohexene
Acetone
Toluene
Toluene
1 -Hexene
Cyclohexene
Cyclohexene
Cyclohexene
Tolan
Mixture of isomeric dodecenes
3-Cyclohexylcyclohexene
Cyclohexyldcetone
o-Cyclohexyltoluene
1,2-Diphenyl-l-tolylethylene
5
45
05
12
15
of a longer reaction capillary or reduction in the rate of flow
of reactants). A typical example here is the synthesis of 3-cyclohexylcyclohexene from cyclohexene (see Experimental). Such
a dimerization apparently proceeds regiospecifically, corresponding to the expected pericyclic mechanism. (With longer
residence times, however, about 5 % of the primary product
isomerizes to 1-cyclohexylcyclohexene.) Thus, the thermal olefin-dimerization and the alkylation of toluene described here
are superior to the catalytic methods, at least as far as regioselectivity is concerned.
Experimental
Synthesis of 3-cyclohexylcyclohexene: Cyclohexene (20 g)
is pumped through the "HP-PT" apparatus['] at 673 K and
460bar at a flow-rate of 0,12ml/min and with a residence
time of ca. 50min. A 15-m long stainless steel capillary (0.D.
1.6mm, I.D. 0.7mm) can be used as reactor. Unreacted cyclohexene (16g) is removed by distillation. The residue (3.4g,
17 %) mainly consists of pure 3-cyclohexylcyclohexene,which
is further purified by distillation: b.p. 98"C/10 torr,
n ~ o = l . 4 9 1 2(b.p. 224"C/760 torr, nio= 1.4941['1). The IR,
NMR, and mass spectra are consistent with the given structure.
Received: September 29, 1978 [ Z 13O;t IE]
German version: Angew. Chem. 91.74 (1979)
[l] P. K611, J . M e t z g e r , Angew. Chem. YO, 802 (1978); Angew. Chem Int.
Ed. Engl. 17, 754 ( I 978).
[Z] H. M. R. Hofjmann, Angew. Chem. 81, 597 (1969); Angew. Chem. Int.
Ed. Engl. 8, 566 (1969).
[3] J. B. Hendrickton, Angew. Chem. 86, 71 (1974); Angew. Chem. Int.
Ed. Engl. 13, 47 ( I 974).
Aiigew Chem. I n t . Ed. Engl. 18 11979) N O . 1
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