'Reductive ozonolysis' via a new fragmentation of carbonyl oxides

Article abstract of DOI:10.1016/j.tet.2006.08.092

This account describes the development of methodologies for 'reductive' ozonolysis, the direct ozonolytic conversion of alkenes into carbonyl groups without the intermediacy of 1,2,4-trioxolanes (ozonides). Ozonolysis of alkenes in the presence of DMSO produces a mixture of aldehyde and ozonide. The combination of DMSO and Et₃N results in improved yields of carbonyls but still leaves unacceptable levels of residual ozonides; similar results are obtained using secondary or tertiary amines in the absence of DMSO. The influence of amines is believed to result from conversion to the corresponding N-oxides; ozonolysis in the presence of amine N-oxides efficiently suppresses ozonide formation, generating high yields of aldehydes. The reactions with amine oxides are hypothesized to involve an unprecedented trapping of carbonyl oxides to generate a zwitterionic adduct, which fragments to produce the desired carbonyl group, an amine, and ¹O₂.

Full text of DOI:10.1016/j.tet.2006.08.092

Tetrahedron 62 (2006) 10747–10752
‘Reductive ozonolysis’ via a new fragmentation of carbonyl oxides
*
Chris Schwartz, Joseph Raible, Kyle Mott and Patrick H. Dussault
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, United States
Received 12 June 2006; revised 13 August 2006; accepted 13 August 2006
Available online 28 September 2006
Abstract—This account describes the development of methodologies for ‘reductive’ ozonolysis, the direct ozonolytic conversion of alkenes
into carbonyl groups without the intermediacy of 1,2,4-trioxolanes (ozonides). Ozonolysis of alkenes in the presence of DMSO produces
a mixture of aldehyde and ozonide. The combination of DMSO and Et3N results in improved yields of carbonyls but still leaves unacceptable
levels of residual ozonides; similar results are obtained using secondary or tertiary amines in the absence of DMSO. The influence of amines is
believed to result from conversion to the corresponding N-oxides; ozonolysis in the presence of amine N-oxides efficiently suppresses ozonide
formation, generating high yields of aldehydes. The reactions with amine oxides are hypothesized to involve an unprecedented trapping of
carbonyl oxides to generate a zwitterionic adduct, which fragments to produce the desired carbonyl group, an amine, and 1O2.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
In approaching this problem, it is instructive to overview the
mechanism of alkene ozonolysis (Fig. 1).8 A highly exother-
mic cycloaddition of ozone with an alkene generates a pri-
mary ozonide (1,2,3-trioxolane).9 The primary ozonide has
limited stability, and, under typical reaction conditions
(>À80 ꢀC) undergoes immediate cycloreversion to a car-
bonyl oxide and a carbonyl. The fate of the carbonyl oxide,
which is so short lived as to be undetectable in solution-
phase chemistry, determines the distribution of reaction
products.10 A nearly activationless cycloaddition of the
carbonyl oxide with a reactive dipolarophile, often the co-
generated aldehyde or ketone, produces ozonides or 1,2,4-
trioxolanes.11 Alternatively, trapping of carbonyl oxides by
unhindered alcohols12 and related nucleophiles generates
hydroperoxyacetals and similar addition products.8,10
When neither addition nor cycloaddition pathways are avail-
able, carbonyl oxides can undergo dimerization or oligo-
merization to furnish 1,2,4,5-tetraoxanes or polymeric
peroxides.13 For simplicity, only ozonide formation is
illustrated.
The ozonolysis of alkenes, first reported in 1840, remains
one of the most important methods for oxidative cleavage
of alkenes.1 For example, a SciFinder search for ozone-
related conversion of terminal alkenes to aldehydes returns
thousands of examples. A powerful oxidant directly available
from oxygen, ozone is also an attractive reagent for sustain-
able oxidations. However, whereas alkene cleavage with
high-valent metal oxides typically results in the direct forma-
tion of aldehydes and ketones, ozonolysis initially generates
ozonides and other peroxides, species often capable of
spontaneous and dangerously exothermic decomposition
reactions.2 The formation of energetic intermediates is par-
ticularly problematic for large-scale processes, but even
laboratory-scale reactions must typically be accompanied
by a subsequent work-up reaction, most often a reduction.3,4
The most effective reducing agents can lead to problems with
functional group compatibility (Pt/H2, BH3, Zn/HOAc,
LiAlH4) or product separation (PPh3).5 The use of more se-
lective and easily separated reagents (Me2S) can leave high
concentrations of residual 1,2,4-trioxolane (ozonide), lead-
ing to explosions upon reaction concentration.6 We hoped
to exploit the mechanism of alkene ozonolysis to achieve
the direct production of carbonyl products, avoiding genera-
tion or isolation of peroxidic intermediates. In this account,
we describe the development of a practical methodology
for ‘reductive ozonolysis’ in which trapping and fragmenta-
tion of carbonyl oxides by amine oxides results in the direct
formation of aldehydes and ketones.7
CH2
carbonyl
O3
ozonide
oxide
O
O
O
O
O
O
O
CH2
O
O
separate
reduction
step
primary
ozonide
this
research
O
* Corresponding author. Tel.: +1 402 472 3634; fax: +1 402 472 9402;
e-mail: pdussault1@unl.edu
Figure 1. Overview of alkene ozonolysis.
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.08.092

10748
C. Schwartz et al. / Tetrahedron 62 (2006) 10747–10752
Table 1. Reduction with DMSO
Ozonides possess a dangerous combination of kinetic stabil-
ity and thermochemical instability; they are typically iso-
lable yet often capable of spontaneous and dangerously
exothermic decomposition reactions.2 Our goal was to de-
velop methodology that would avoid generation of ozonides
or other peroxides, and instead directly deliver the desired
carbonyl products. Our approach required a reagent capable
of intercepting the primary ozonide, the carbonyl oxide, or
the ozonide (1,2,4-trioxolane), yet compatible with ozone,
one of the strongest oxidants in organic chemistry. Ozonides
appeared too stable to be the targets of such an approach. Pri-
mary ozonides (1,2,3-trioxolanes) have been generated at
very low temperature and separately reacted with strong
nucleophiles, but this process has not been accomplished
in the presence of ozone.14 This leaves carbonyl oxides, the
most reactive intermediates in an ozonolysis, as the most
logical targets for in situ capture.
O3
CH2
H
O
O
O
CH2Cl2
O
C8H17
DMSO (equiv)
DMSO C8H17
H C8H17
T (ꢀC)
Aldehyde (%)a
Ozonide (%)a
0
2
2
À78 or 0
Trace
52
61
>95%
35
22
À78
0
a
Isolated yield.
Table 2. Competition for carbonyl oxide
O
O
O3
O
OOH
OMe
decene (1.0 equiv)
DMSO (2.0 equiv)
ROH (2.0 equiv)
CH2Cl2
O
-78 °C
H
ROH
Aldehyde (%)a
Ozonide (%)a
Hydroperoxide (%)a
MeOH
i-PrOH
11
34
16
19
31
23
2. Results and discussion
a
Isolated yield.
Our initial approach focused on cycloaddition of carbonyl
oxides with X]O reagents (Fig. 2). An optimal trapping
reagent would be a readily available and reactive dipolaro-
phile containing a central atom (X) in an incompletely oxi-
dized state. The derived heteroozonides would be expected
to undergo internal fragmentation with liberation of
O]X]O and a carbonyl group, achieving net oxidation of
the X]O reagent and net reduction of the carbonyl oxide.
Literature reports suggested that sulfinyl dipolarophiles re-
duce carbonyl oxides, presumably via intermediate 3-thia-
1,2,4-trioxolanes.15 Moreover, electron rich carbonyl oxides
preferentially oxidize sulfoxides (to sulfones), even in the
presence of a sulfide.16 A similar strategy has recently been
applied to the reduction of persulfoxides with aryl
selenoxides.17
The DMSO-mediated reduction was unaffected by the addi-
tion of a proton donor (HOAc), but was actively suppressed
by Sc(OTf)3. Although we had hoped that the Lewis acid
might serve to bring together the reactants, the results
suggest that the Sc+3 is simply sequestering the sulfoxide.
In contrast, ozonolysis at À78 ꢀC in the presence of both
DMSO and Et3N achieved a noticeable improvement in
the yield of aldehyde (Table 3); an even better yield was
obtained upon reaction at 0 ꢀC. The formation of aldehyde
appeared to be enhanced by trace moisture; performing the
reaction with deliberate exclusion of water (including drying
the incoming stream of O3/O2 through a À78 ꢀC U-tube),
resulted in a reduced yield. For reasons that would later be-
come clear, the use of excess Et3N slowed the reaction and
resulted in the isolation of recovered decene (not shown).
Our investigations began with dimethyl sulfoxide (DMSO).
Whereas ozonolysis of decene provides a nearly quantitative
yield of isolated ozonide (3-octyl-1,2,4-trioxolane),18 the
same reaction in the presence of 2.0 equiv of DMSO gener-
ated a mixture of aldehyde and ozonide in which the former
was predominant (Table 1). While these results were intrigu-
ing, we were unable to find conditions able to effectively
suppress ozonide formation. For example, the use of 5 equiv
of DMSO offered little improvement in yield of aldehyde,19
while attempts to employ even larger amounts of reagent
resulted in phase separation or freezing.
The combination of DMSO and Et3N provides a useful
protocol for syntheses of aldehydes and ketones (Table 4).
To our surprise, a control reaction investigating ozonolysis
in the presence of Et3N furnished better yields of nonanal
than had been obtained with DMSO (Table 5). The amine-
promoted reduction appeared general for secondary and
tertiary amines; primary amines, which react with carbonyl
oxides to form oxaziridines, were not investigated.20 The
use of anhydrous conditions again resulted in a decreased
yield of aldehyde.
The addition of protic nucleophiles provided an opportunity
to test the role of the carbonyl oxide in the DMSO-promoted
reductions (Table 2). The presence of methanol resulted in
the formation of hydroperoxyacetal at the expense of alde-
hyde. The same effect was observed to a lesser extent for iso-
propanol, as would be expected based upon the reported
rates of trapping by primary and secondary alcohols.10,12
Table 3. Reaction with DMSO and Et3N
O3/O2, CH2Cl2,
DMSO (2 eq)
O
O
CH2
O
Et3N (1 eq)
H
O
C8H17
O
T (ꢀC)
Wet/dry
Aldehyde (%)a
Ozonide (%)a
O-
CH2O
X=O
O
O
+O
À78
À78
0
Dry
Wetb
Wet
43
65
84
17
29
12
O
O
O
XO2
X
O
a
Isolated yield.
H2O (0.05%) in CH2Cl2.
b
Figure 2. Capture by reductive dipolarophile.

C. Schwartz et al. / Tetrahedron 62 (2006) 10747–10752
10749
Table 4. Application to other substrates
furnish both N-oxides and products of side chain cleavage,
the latter process accounting for our observation of
acetaldehyde in the crude products from reactions employ-
ing Et3N.23 Furthermore, the ratio of N-oxide formation to
side chain cleavage is enhanced in the presence of a proton
donor, accounting for the influence of moisture on the reac-
tions involving amines.
a
O3
carbonylb
ozonideb
Alkene
CH2
O
O
O
Ph
Ph
H
Ph
O
93%
trace
O
O
CH2
O
O
The role of N-oxides was explicitly tested by ozonolysis of
1-decene in the presence of commercial N-methylmorpho-
line-N-oxide (NMMO). Reaction proceeded without fuming
to furnish exclusively nonanal (Table 6).24 Predominant for-
mation of aldehyde was also observed for reactions in the
presence of DABCO-N-oxide and pyridine N-oxide. The
latter reduction, while complicated by the formation of
intensely colored byproducts, is noteworthy given the very
limited amount of reduction observed in the presence of
pyridine.
Bu
Bu
Bu
65%
Bu
28%
Bu
Bu
O
O
O
O
O
64%
7%
CH2
a
b
O3, DMSO (2 equiv), Et3N (1 equiv), wet CH2Cl2, 0 °C.
Isolated yield.
The intermediacy of carbonyl oxides in these reactions was
supported by a simple set of competition reactions. The
products obtained from ozonolysis of a CH2Cl2 solution of
decene were compared under three sets of conditions: (1)
no additives; (2) addition of stoichiometric MeOH; and (3)
addition of stoichiometric amounts of both MeOH and
NMMO (Table 7). The results demonstrate competition
between the amine oxide and the alcohol for capture of the
intermediate nonanal-O-oxide.25 Furthermore, 1-methoxy-
decene, which generates the same carbonyl oxide but cannot
easily form an ozonide, also produces nonanal as the major
product in the presence of NMMO.10
The sole precedent for this process was a report describing
isolation of adipaldehyde upon ozonolysis of cyclohexene
in the presence of Et3N.21 The reduction of carbonyl oxides
by pyridine has been reported and later refuted.22 However,
several observations led us to question the role of the amines.
First, as had been previously observed during the experi-
ments with DMSO/Et3N, the use of excess amine slowed
consumption of alkene. Second, directing the gaseous
stream of O3/O2 onto or into a CH2Cl2 solution of alkene
and amine resulted in intense fuming, which persisted for
a period proportional to the amount of amine. Similar fum-
ing was observed for ozonolysis of solutions of Et3N or
N-methylmorpholine (NMM); in contrast, no fuming was
observed when a stream of ozone was directed onto or into
a solution of decene. Moreover, monitoring (TLC or NMR
of quenched aliquots) of the ozonolysis of mixtures of amine
and alkene detected very little formation of aldehyde or
ozonide until after fuming had ceased. Third, ozonolysis
of a solution of amine, followed by addition of decene
and continued ozonolysis, produced a mixture of aldehyde
and ozonide. These results suggested the intermediacy of
N-oxides. The ozonolysis of tertiary amines is known to
Table 6. Reduction by amine oxides
O3
CH2Cl2
O
O
O
O
amine oxide
C8H17
C8H17
H C8H17
Amine oxide (equiv)
T (ꢀC)
RCHO (%)a
Ozonide (%)a
NMMO (1.0)
NMMO (3.0)
À78 or 0
88
94
80
68
62
58
0
0
0
0
0
0
0
Et3NOb (1.0)
Trace
12
10
9
Me3NOc (1.0)
DABCO-N-oxide (1.0)
Pyridine N-oxide (1.0)
Table 5. Ozonolysis in presence of amines
a
Isolated yields.
Generated in situ.
Poor solubility.
O3/O2,
CH2Cl2
b
CH2
O
O
c
O
C8H17
C8H17
H
C8H17
O
amine
T (ꢀC) Wet/dry Aldehyde (%) Ozonide (%)
Table 7. Competition for the carbonyl oxidea
Amine
Et3N
Et3N
Et3N
Et3N (2 equiv)
NMM
NMM
Morpholine
Morpholine
EtNi-Pr2
(C12H25)2NMe
DABCO
Pyridine
À78
Weta
Dry
Wet
Wet
Wet
Dry
Wet
Dry
Dry
Wet
Dry
Dry
79
50
75
64b
68
57
62
56
58
55
48
16
13
30
14
14
12
10
10
18
9
O3/O2,
X
O
O
CH2Cl2
O
OOH
OMe
À78
0
0
0
0
0
0
0
0
additives
O
H
C8H17
aldehyde hydroperoxide ozonide
(A)
(B)
(C)
X
Additive
A
B
C
15
10
11
H
H
H
OMe
None
MeOH
MeOH+NMMO
MeOH+NMMO
—
—
Major
0
Trace
Major
Major
Major
Minor
Trace
Minor
Trace
Trace
a
H2O (0.05%) in CH2Cl2.
Unreacted alkene also recovered.
Ratios assessed by 1H NMR of reaction mixtures.
b
a

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C. Schwartz et al. / Tetrahedron 62 (2006) 10747–10752
2.1. Role of base-promoted fragmentation
O-oxide, allowing more time for side reactions such as tau-
tomerization or polymerization.10 We continue to investigate
this process in the hope of identifying optimal conditions for
ketone synthesis.
Amines and pyridines are known to cleave terminal ozonides
to a 1:1 mixture of aldehyde and formate through a Korn-
blum-type E1CB fragmentation (Fig. 3).26–28 Although
amine oxides are less basic than amines,29 we were curious
as to whether the putative reductions might also result from
base-promoted fragmentation. In fact, treatment of a CH2Cl2
solution of purified decene ozonide with NMMO did gener-
ate a 1:1 mixture of nonanal and formate. However, the
reaction was slower than the in situ reductions described
above. More convincingly, analysis of the crude reaction
mixtures from ozonolysis of decene in the presence of
NMMO consistently found ratios of aldehyde/formate
greater than 4:1, indicating that the base-promoted fragmen-
tation is a minor contributor to the direct formation of alde-
hyde in the ozonolysis medium.
2.3. Mechanism
There is no mechanistic precedent for ‘reductive’ ozonolysis
in the presence of amine oxides. Our hypothesis is that the
process is not actually a reduction, but instead a fragmenta-
tion driven by the reactivity of carbonyl oxides (Fig. 5).
Nucleophilic addition of the amine oxides generates an
unstable zwitterionic peroxyacetal, which undergoes de-
composition to generate aldehyde or ketone, amine, and
dioxygen. The proposed mechanism bears a topological re-
semblance to the Grob fragmentations of diol monosulfo-
nates30 and to the conversion of ketones to dioxiranes.31
However, the base-promoted fragmentation may serve a use-
ful role as a scavenging reaction. For example, if the solution
resulting from ozonolysis of a mixture of decene and NMMO
(1.0 equiv) is quenched into pH 6 buffer prior to concentra-
tion, a small amount of ozonide (up to 7%) is isolated; in the
absence of an acidic quench, no ozonide is present after con-
centration. If the reaction is conducted with three or more
equivalents of NMMO, no ozonide is observed regardless
of work-up, suggesting that capture of the carbonyl oxide
is complete at the higher reagent concentration. For more
substituted systems such as the ozonides of methyl oleate
(vida infra), the base-promoted fragmentation is much
slower, and even less likely to play a significant role in the
formation of aldehydes during ozonolysis.
Verification of the mechanism may prove challenging.
Quantification of the liberated amine will be complicated
by rapid oxidation by ozone. Decomposition of a ground
state zwitterion would be expected to liberate dioxygen in
1
the singlet state; however, detection of O2 will be con-
strained by the compatibility of probe molecules with ozone.
Although an alternative route to carbonyl oxides is available
through photosensitized oxidation of diazoalkanes,32 the
amine produced by the predicted mechanism would quench
1O2 and suppress the photooxidation. The extent of transfer
of 18O from a labeled amine oxide to the carbonyl products
would provide unambiguous evidence for the proposed
mechanism. However, no preparation of a labeled amine
oxide has been reported and we were unable to find a method
for oxidation of tertiary amines that would be practical for
use of 18O-labeled reagents.
2.2. Other substrates
In situ reduction was successfully applied to the ozonolysis
of a 1,2-disubstituted alkene, methyl oleate; the disparity in
the isolated yields of the two products appears to result from
the volatility of nonanal (Fig. 4). Application of the same
protocol to 2-methylundecene provided a moderate yield
of 2-undecanone as well as a number of unidentified minor
byproducts; similar results were obtained for other 1,1-di-
substituted alkenes (not shown). The lower yield observed
for a ketone compared with aldehydes could result from
a lower efficiency of nucleophilic addition to the ketone
The success of the reductive ozonolysis reflects attributes of
both carbonyl oxides and amine oxides. Carbonyl oxides are
highly reactive species typically represented as either zwit-
terions or diradicals.10 Although calculations suggest that
the diradical is more representative of gas phase structure,
our previous work demonstrated the ability to exploit the
zwitterionic character to enhance additions of nucleo-
philes.33 Amine oxides are not only nucleophilic but also
contain an easily fragmented N–O bond, characteristics
that form the basis of a conversion of activated halides to
aldehydes.34 In addition, the coordinative saturation of the
O
H
O
O
:base
O
-
O
O
-
O
H
H
O
O3
O
O
O+
R2
T> -80°C
C8H17
H
C8H17
R2
R1
R2
R1
R1
Figure 3. Base-promoted fragmentation.
O
N+
-
O2
-
O
O
R1
O3, NMO,
(3.0 equiv)
C8H17CHO
(74%)
O
O N+
R2
C8H17
R2
R1
0 °C
MeO2C(CH2)7CHO
(96%)
:N
(CH2)7CO2Me
CH2
O
as above
Grob fragmentation
OSO2Ar
dioxirane synthesis
-
C9H21
C9H21
54%
Me
Me
O OSO3
O
O
Figure 4. Other substrates.
Figure 5. Proposed mechanism.

C. Schwartz et al. / Tetrahedron 62 (2006) 10747–10752
10751
2. Kula, J. Chem. Health Saf. 1999, 6, 21; Gordon, P. M. Chem.
Eng. News 1990, 68, 2.
3. For an overview of ozonide reduction, see: Kropf, H. Houben–
Weyl Methoden Der Organische Chemie; Kropf, H., Ed.; Georg
Thieme: Stuttgart, 1988; Vol. E13/2, p 1111.
ammonium leaving group blocks heteroozonide formation,
leaving fragmentation as the most favorable option. The suc-
cessful reductions in the presence of morpholine (Table 5)
suggests that either hydroxylamines or nitrones may also
promote a similar fragmentation.35
4. Ozonolysis of electron-poor alkenes in methanolic base results
in the direct formation of methyl esters: Marshall, J. A.;
Garofalo, A. W.; Sedrani, R. C. Synlett 1992, 643.
While the oxidative regeneration of the amine oxide would
seem to offer the possibility of catalytic reactions, the need
to competitively capture the carbonyl oxide sets a realistic
lower threshold on the concentration of reagent. Moreover,
the lower yields of aldehyde obtained for ozonolyses in the
presence of stoichiometric NMM (Table 5) versus NMMO
(Table 6) may reflect not only the competing formation of
ozonide during early stages of the reaction (when amine
oxide concentration is necessarily low) but also the fact
that the ozonolysis of amines furnishes amine oxides in less
than quantitative yields.36 However, regeneration of amine
oxides may hold promise in batch reactions and for regener-
ation of supported reagents.
5. The use of more effective reducing agents such as PPh3
(Griesbaum, K.; Kiesel, G. Chem. Ber. 1989, 122, 145; Clive,
D. L. J.; Postema, M. H. D. J. Chem. Soc., Chem. Commun.
1994, 235); BH3 (Flippin, L. A.; Gallagher, D. W.; Jalali-
Araghi, K. J. Org. Chem. 1989, 54, 1430); LiAlH4
(Greenwood, F. L. J. Org. Chem. 1955, 20, 803); NaBH4
(Witkop, B.; Patrick, J. B. J. Am. Chem. Soc. 1952, 74,
3855); and Mg/MeOH or Zn/HOAc (Dai, P.; Dussault, P. H.;
Trullinger, T. K. J. Org. Chem. 2004, 69, 2851) can lead to
problems with separation of byproducts or functional group
compatibility.
6. Chen, L.; Wiemer, D. F. J. Org. Chem. 2002, 67, 7561;
ꢀ
Lavallee, P.; Bouthillier, G. J. Org. Chem. 1986, 51, 1362,
footnote 27.
Finally, the observed fragmentation of carbonyl oxides could
be the first example of a new class of reactions. The key
structural feature in the amine oxides, a nucleophilic center
weakly bonded to a leaving group, is found in other a-nucleo-
philes, suggesting that a similar fragmentation may be pos-
sible with reagents such as hypohalites and peroxysulfates
(Fig. 6). Along these lines, it is interesting to note that reac-
tion of amine oxides with dioxiranes generates amines and
1O2, presumably via an intermediate peroxyammonium
zwitterion.37
7. Schwartz, C.; Raible, J.; Mott, K.; Dussault, P. H. Org. Lett.
2006, 8, 3199.
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X = NR3+: Proposed (this work)
X = Cl or OSO3-: Adducts from
ClO- or peroxymonosulfate
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J. Chem. Soc., Perkin Trans. 1 1980, 1950.
O-
O
O
X
Figure 6. Alternative fragmentation precursors.
3. Conclusion
The ozonolysis of alkenes in the presence of amine oxides
directly generates aldehydes and ketones through an unprec-
edented mechanism involving nucleophilic trapping of car-
bonyl oxides and fragmentation of the derived zwitterionic
peroxides. The methodology, which avoids formation of
ozonides or related energetic intermediates, offers a safer al-
ternative to traditional ozonolyses and may expand the syn-
thetic applications of an already versatile oxidative cleavage.
17. Sofikiti, N.; Rabalakos, C.; Statakis, M. Tetrahedron Lett.
2004, 45, 1335.
18. Any work involving peroxides should follow standard precau-
tions: Medard, L. A. Accidental Explosions: Types of Explosive
Substances; Ellis Horwood: Chichester, UK, 1989; Vol. 2;
Patnaik, P. A Comprehensive Guide to the Hazardous
Properties of Chemical Substances; Van Nostrand Reinhold:
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19. Based upon 1H NMR of crude reaction mixtures.
20. Schulz, M.; Rieche, A.; Becker, D. Chem. Ber. 1966, 99,
3233.
21. Pokrovskaya, I. E.; Ryzhankova, A. K.; Menyailo, A. T.;
Mishina, L. S. Neftekhimiya 1971, 11, 873.
22. See: Slomp, G., Jr.; Johnson, J. L. J. Am. Chem. Soc. 1958, 80,
915; and, Griesbaum, K. J. Chem. Soc., Chem. Commun. 1966,
920.
Acknowledgements
We are grateful for support from the Petroleum Research
Fund, and for technical assistance from Paul Unverzagt
and Fred Zinnel. We thank Dennis Schilling for pointing
out Ref. 22 (Slomp et al.) NMR spectra were acquired, in
part, on spectrometers purchased with support from NSF
(MRI 0079750 and CHE 0091975). A portion of this re-
search was conducted in facilities remodeled with support
from NIH (RR016544-01).
References and notes
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