Thermolysis of N-tetramethylpiperidinyl triphenylacetate: Homolytic fragmentation of a TEMPO ester

Article abstract of DOI:10.1002/poc.655

Thermolysis of N-tetramethylpiperidinyl triphenylacetate (7, Ph ₃CCO₂T, T = 2,2,6,6-tetramethylpiperidinyl) in benzene at 146 °C leads to the formation of triphenylmethane (Ph₃CH, 80%), tetramethylpiperidine (TH, 91%), and tetraphenylmethane (Ph₄C, 9%). First-order rate constants for the decomposition at 132.8 and 150.0 °C were 2.20 × 10^-6 and 2.88 × 10^-5 s^-1, respectively. In benzene-d₆ solvent the triphenylmethane was formed as Ph₃CD to the extent of 20%, as determined by ¹H NMR and mass spectrometry. The results are interpreted as showing that Ph ₃CCC₂T undergoes thermolysis by concerted two-bond scission with formation of Ph₃C^., tetramethylpiperidinyl radicals and CO₂. The formation of Ph₄C occurs by addition of Ph₃C^. to benzene, followed by hydrogen atom abstraction from the resulting adduct. Calculations using DFT methods at the B3LYP/6-311++G** level were used to elucidate the bond fission of HCO₂T (2), and indicate that cleavage to HCO₂^. and T^. is favored by 7.8 kcal mol^-1 relative to cleavage to HC(·)=O and TO^., in agreement with the experimental results. Copyright

Full text of DOI:10.1002/poc.655

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2003; 16: 559–563
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.655
Thermolysis of N-tetramethylpiperidinyl
triphenylacetate: homolytic fragmentation of a
TEMPO estery
Huda Henry-Riyad and Thomas T. Tidwell*
Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
Received 27 October 2002; revised 26 December 2002; accepted 21 March 2003
ABSTRACT: Thermolysis of N-tetramethylpiperidinyl triphenylacetate (7, Ph3CCO2T, T ¼ 2,2,6,6-tetramethylpiper-
epoc
idinyl) in benzene at 146 ꢀC leads to the formation of triphenylmethane (Ph3CH, 80%), tetramethylpiperidine (TH,
91%), and tetraphenylmethane (Ph4C, 9%). First-order rate constants for the decomposition at 132.8 and 150.0 ꢀC
were 2.20 ꢁ 10ꢂ6 and 2.88 ꢁ 10ꢂ5 sꢂ1, respectively. In benzene-d6 solvent the triphenylmethane was formed as
Ph3CD to the extent of 20%, as determined by 1H NMR and mass spectrometry. The results are interpreted as showing
*
that Ph3CCO2T undergoes thermolysis by concerted two-bond scission with formation of Ph3C , tetramethylpiper-
idinyl radicals and CO2. The formation of Ph4C occurs by addition of Ph3C to benzene, followed by hydrogen atom
*
abstraction from the resulting adduct. Calculations using DFT methods at the B3LYP/6–311þþG** level were used
*
*
*
to elucidate the bond fission of HCO2T (2), and indicate that cleavage to HCO2 and T is favored by 7.8 kcal molꢂ1
—
*
relative to cleavage to HC( ) O and TO , in agreement with the experimental results. Copyright # 2003 John Wiley
—
& Sons, Ltd.
Additional material for this paper is available from the epoc website at http://www.wiley.com/epoc
KEYWORDS: free radicals; TEMPO; triphenylmethyl radical; homolysis
INTRODUCTION
The TEMPO ester t-BuCO2T (2) was reported to distill
at 150 ꢀC without apparent decomposition,4a and Studer
and co-workers1b have reported that PhCH2CO2T (3)
reacted at 150 ꢀC in tert-butylbenzene in the presence of
O2 with a rate constant for formation of TEMPO radicals
as measured by ESR estimated as 1.1 ꢁ 10ꢂ9 sꢂ1 at
120 ꢀC for fission of the NO—C bond.1b This rate
constant was a factor of 107 lower than that calculated
from a correlation1d of logkd for dissociation of TEMPO-
derived alkoxyamines ROT (R ¼ a hydrocarbon) forming
The thermal stability of adducts of tetramethylpiperidi-
nyloxyl (TEMPO, TO ) and related aminoxyl radicals
*
plays a prominent role in the trapping of free radicals1
and in living free radical polymerization.2 As part of our
studies of the reactions of ketenes with aminoxyl radi-
cals,3 we have generated a number of esters derived from
the addition of TEMPO as illustrated for the case of
phenylketene, which forms the bis(TEMPO) adduct 1
[Eqn (1)]. The chemistry of such TEMPO adducts is of
great interest,1,3a,b,4,5 but little is known about the reac-
tivity of acyl derivatives, and therefore we have under-
taken computational and experimental studies of their
properties, beginning with a study of esters RCO2T
(T ¼ N-2,2,6,6-tetramethylpiperidinyl).
*
*
R and TO versus the bond dissociation energies for
R—H.1b The difference was attributed to a much greater
strength for the C—O bond in 3 due to interaction with
—
the C O group, so that the correlation with formation of
—
alkyl radicals would not be expected.1b Elucidation of the
mechanism involved in this process appeared desirable,
and we have therefore undertaken computational studies
of model systems and experimental studies of a TEMPO
ester expected to generate readily identifiable radicals as
a first step in this area.
ð1Þ
RESULTS
*Correspondence to: T. T. Tidwell, Department of Chemistry, Uni-
versity of Toronto, Toronto, Ontario M5S 3H6, Canada.
E-mail: ttidwell@chem.utoronto.ca
Computations of the decomposition of the model sys-
tems HCO2NH2 and HCO2T with either C—O or
N—O cleavage were carried out using DFT methods at
the B3LYP/6–311þþG**//B3LYP/6–311þþG** using
yDedicated to Professor Shinjiro Kobayashi.
Contract/grant sponsor: Natural Sciences and Engineering Research
Council of Canada.
Copyright # 2003 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 559–563

560
H. HENRY-RIYAD AND T. T. TIDWELL
Table 1. Energies (hartree) for dissociation of HCO2NH2 and HCO2T (B3LYP/6–31þþG**//B3LYP/6–31þþG**)
Structure
E
ZPVEb
E þ ZPVE
S (cal molꢂ1 Kꢂ1
)
HCO2NH2
HC( )O
ꢂ245.123975
ꢂ113.891332
ꢂ189.142904
ꢂ131.138719
ꢂ55.900417
ꢂ597.834837
ꢂ483.855969
ꢂ408.617140
0.049343
0.012964
0.019575
0.025982
0.018898
0.282024
0.260681
0.255041
ꢂ245.074632
ꢂ113.878368
ꢂ189.123329
ꢂ131.112737
ꢂ55.881519
ꢂ597.552813
ꢂ483.595288
ꢂ408.362099
68.106
53.585
59.992
58.795
46.520
112.678
104.698
100.801
*
*
HCO2
H2NO
H2N
*
*
HCO2Ta
*
TO a
*
a
T
a T ¼ 2,2,6,6-tetramethylpiperidinyl.
b Zero point vibrational energy.
Table 2. Energy changes for dissociation of HCO2NH2 and HCO2T (B3LYP/6–31þþG** //B3LYP/6–31þþG**), with relative
energies in parentheses
Reaction
ÁE
ÁE298
ÁH
(kcal molꢂ1
ÁG
ÁꢂS1
(kcal molꢂ1
)
(kcal molꢂ1
)
)
(kcal molꢂ1
)
(cal mol Kꢂ1
)
*
*
HCO2NH2 ! HC( )O þ H2NO
52.4 (8.6)
43.8 (0.0)
49.7 (7.4)
42.3 (0.0)
53.5 (8.9)
44.6 (0.0)
45.2 (7.8)
37.4 (0.0)
54.1 (8.9)
45.2 (0.0)
45.8 (7.8)
38.0 (0.0)
40.9 (7.2)
33.7 (0.0)
32.2 (8.5)
23.7 (0.0)
44.3
38.4
45.6
48.1
*
*
HCO2NH2 ! HCO2 þ H2N
*
*
HCO2T ! HC( )O þTO
*
*
HCO2T ! HCO2 þ T
Gaussian 98.6 The calculated energies and entropies are
given in Table 1, values of ÁE, ÁE298, ÁH, ÁG and ÁS
for these processes are given in Table 2 and the computed
values of ÁH are shown in Eqns 2 and 3. For all the
comparisons (Table 2) there is a clear prediction that N—
O bond cleavage is favored, by amounts ranging from 7.2
to 8.9 kcal molꢂ1 (1 kcal ¼ 4.184 kJ).
Experimentally, 2,2,6,6-tetramethylpiperidinol (TOH)
was prepared by ascorbic acid (6) reduction of TEMPO
[Eqn (5)].4b The tetramethylpiperidinyl ester 7 was pre-
pared by the reaction of the acyl chloride with 2,2,6,6-
tetramethylpiperidinol as in Eqn (6).4
ð2Þ
ð5Þ
ð3Þ
Esters of TEMPO bear a structural resemblance to
esters RCO3Bu-t of tert-butyl peroxide, which are widely
used as free radical initiators and have a well-studied
chemistry.7 These species undergo thermal decomposi-
tion with cleavage of the O—O bond over a range of
temperatures depending on the structure of R, and in the
ð6Þ
The products of thermolysis of 7 in degassed benzene at
146 ꢀC (Scheme 1) were isolated and identified by compar-
ison with authentic materials as triphenylmethane (8,
84 ꢃ 4%), tetraphenylmethane (9, 8 ꢃ 3%) and tetra-
methylpiperidine (10, TH, 91 ꢃ 3%). Reaction in ben-
zene-d6 gave 8 (75 ꢃ 4%), containing 20% Ph3CD as
determined by 1H NMR and mass spectrometry, 9
(7 ꢃ 3%) and 10 (93 ꢃ 3%) (Scheme 1). Product yields
were determined by vapor-phase chromatography (VPC)
calibrated with authentic samples. In samples which
had been incompletely degassed, the diphenyl ether
PhOCPh2CPh2OPh (12) of benzpinacol was isolated, and
this product could be isolated in high yield when oxygen
was added to the reaction mixture prior to thermolysis.
more reactive cases concerted R—C bond cleavage also
7
*
*
occurs with formation of R , tert-BuO and CO2. One of
the most reactive such peroxy esters is tert-butyl triphe-
nylperacetate (4), which forms triphenylmethyl (5), tert-
*
butoxy radical (t-BuO ) and CO2 in a concerted process
with a rate constant of 1.7 ꢁ 10ꢂ4 at 25 ꢀC [Eqn (4)].7a
Because of the evidence of low reactivity of TEMPO
esters,1b,4a the analogous TEMPO ester derived from
triphenylacetic acid was chosen for study.
ð4Þ
Copyright # 2003 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 559–563

THERMOLYSIS OF N-TETRAMETHYLPIPERIDINYL TRIPHENYLACETATE
561
occurs with concerted breaking of the N—O and Ph3C—
*
C bonds leading to the persistent radical Ph3C . This rate
enhancement may be compared with that of 2.7 ꢁ 103 at
25 ꢀC for the perester Ph3CCO3Bu-t compared with
PhCH2CO3Bu-t, both of which are interpreted as reacting
with concerted cleavage of the C—CO and O—O
bonds.7
The rate constant of 7 at 132 ꢀC of 2.20 ꢁ 10ꢂ6 sꢂ1 may
be compared with the extrapolated rate constant of
102 sꢂ1 for Ph3CCO3Bu-t, indicating that 7 is less reac-
tive by a factor of 108. This large difference shows the
influence of the greater bond dissociation energy for an
N—O compared with an O—O bond.
The reaction of 7 in toluene occurs by the same first
step as in Scheme 1, and then the tetramethylpiperidinyl
radical abstracts hydrogen from toluene forming tetra-
methylpiperidine and a benzyl radical. Combination of
the triphenylmethyl and benzyl radicals forms tetraphe-
nylethane [Eqn (8)].
Scheme 1. Thermal decomposition of 7
The kinetics of reaction of 7 in benzene were measured
by an ampoule technique, with IR measurement of
the decrease of the carbonyl peak of the ester with
time. The data were best fit with a first-order dependence
on [Ph3CCO2T] and gave rateꢂc6onstants at 132.8 and
150.0 ꢀC of (2.20 ꢃ 0.15) ꢁ 10
and (2.88 ꢃ 0.80) ꢁ
10ꢂ5 sꢂ1, respectively. Owing to the experimental diffi-
culties of measuring reaction rates at these temperatures,
reliable rate constants over a wider range of temperature
could not be obtained, and the data are of insufficient
precision to warrant calculation of activation parameters.
The products of the reaction of 7 in toluene were
determined as 1,1,1,2-tetraphenylethane (74%) and
tetramethylpiperidine (78%) [Eqn (7)]. The identification
of the isolated 1,1,1,2-tetraphenylethane was confirmed
by comparison of the spectral properties with those
reported.8b
ð8Þ
The ether 12 in the presence of O2 results from the
*
reaction of Ph3C with O2 followed by formation of the
peroxide 13 and Wieland rearrangement8a by cleavage of
the peroxidic O—O bond with formation of oxyl radicals
14 which undergo phenyl migration from C to O and then
combination (Scheme 2). This process is known to occur
at these temperatures.8a Authentic samples of 12 and 13
were prepared to confirm the identifications.
ð7Þ
As noted above, the reaction of PhCH2CO2T (3) at
150 ꢀC occurs with the formation of TEMPO,1b but this
experiment was carried out in the presence of O2, which
could react with initially formed tetramethylpiperidinyl
*
DISCUSSION
radicals T forming TEMPO. This reactivity of 3 and
those of related esters of TEMPOH are under further
investigation.
The products and first-order kinetic behavior of 7 are
consistent with a unimolecular reaction forming CO2 and
In summary, DFT calculations predict that homolysis
of N-formyloxy-2,2,6,6-tetramethylpiperidine (HCO2T)
*
*
the free radicals Ph3C and T (Scheme 1). Preferential
reaction of 7 with cleavage of the O—N bond, rather than
the C—O bond, is also as predicted by the calculated
preference (Table 2) of 6.5–7.8 kcal molꢂ1 for the model
system in Eqn (3). The formation of Ph3CH (8) and
tetramethylpiperidine (TH, 10) would occur by hydrogen
abstraction reactions, while tetraphenylmethane (9,
Ph4C) could be formed by addition of triphenylmethyl
radical to benzene forming the radical 11, which loses a
*
*
favors cleavage of the N—O bond forming HCO2 and T.
In agreement with this prediction, experimental studies of
Ph3CCO2T (7) show that this reacts by concerted thermal
*
*
decomposition at 132–150 ꢀC forming Ph3C , CO2 and T,
with a rate constant at 150 ꢀC that is 2.6 ꢁ 104 times
greater than that of PhCH2CO2T (3).
COMPUTATIONAL STUDIES
*
hydrogen atom to Ph3C or to tetramethylpiperidinyl
radical (T ). The experiment in benzene-d6 forming
*
Computations were carried out at the B3LYP/6–
311þþG**//B3LYP/6–311þþG** level using Gaussian
20% Ph3CD confirms the role of intermediate 11, but
the incomplete deuteration found and the high yield of
TH (10) show that there are other sources of H atoms
available, possibly the piperidine rings or the head-to-tail
*
dimer of Ph3C .
The rate constant of 7 at 150 ꢀC of 2.88 ꢁ 10ꢂ5 sꢂ1
exceeds that of 1.1 ꢁ 10ꢂ9 sꢂ1 reported1b for
PhCH2CO2T (3) by a factor of 2.6 ꢁ 104, and this large
rate enhancement is strong evidence that the reaction of 7
Scheme 2. Reaction of triphenylmethyl oxygen
J. Phys. Org. Chem. 2003; 16: 559–563
Copyright # 2003 John Wiley & Sons, Ltd.

562
H. HENRY-RIYAD AND T. T. TIDWELL
986 with a computer cluster from Velocet Communica-
tions (Toronto, Canada). The calculated energies and
entropies are given in Table 1 and the energy changes
in Table 2.
poules were heated for 26 h (for C6H6) or 48 h (for C6D6)
and the products analyzed by gas chromatography. The runs
in C6H6 gave Ph3CH (82 ꢃ 3%), tetramethylpiperidine
(92 ꢃ 3%) and Ph4C (9 ꢃ 3%), and runs in C6D6 gave
Ph3CH(D) (76 ꢃ 4%, containing 20% D by MS), tetra-
methylpiperidine (93 ꢃ 3%) and Ph4C (7 ꢃ 3%). The com-
position of Ph3CD was confirmed by HREIMS: m=z calc.
for C13H15D, 245.13095; found, 245.13148.
EXPERIMENTAL
Gas chromatography. GC analysis was carried out using a
flame ionization detector and a Simplicity 5 column (poly-
5% diphenyl-95% dimethylsiloxane). Authentic samples
were used to calibrate the response for quantitative product
analysis.
Products of N-triphenylacetoxy-2,2,6,6-tetramethylpiperi-
dine (7) thermolysis in toluene. A solution of 7 (20 mg,
0.046 mmol) in 1 ml of toluene in a flame-dried ampoule
was degassed by four freeze–thaw cycles and heated for 40 h
at 146 ꢀC. The products were analyzed by gas chromato-
graphy as tetramethylpiperidine (78 ꢃ 4%) and Ph3CCH2Ph.
The latter product was isolated in 74% yield and identified
by comparison of its spectral properties with those repor-
ted.8b 1H NMR (400 MHz, CDCl3), ꢀ 3.96 (s, 2, CH2), 6.64
(d, 2, J ¼ 7.1 Hz, o-H), 7.0–7.1 (m, 4, m- and p-H), 7.16–7.36
(m, 15, 3Ph). 13C NMR (100 MHz, CDCl3), ꢀ 46.5, 58.7,
58.7, 126.1, 127.5, 127.8, 128.2, 130.0, 131.4, 142.7, 146.8.
EIMS, m=z 333 (Mþ ꢂH), 243 (Ph3Cþ ), 165, 91. HREIMS,
m=z calc. for C26H21, 333.16438; found, 333.16433.
Preparation of 1-hydroxy-2,2,6,6-tetramethylpiperidine
(TOH).4 A suspension of TEMPO (1 g, 6.4 mmol) in a
solution of sodium ascorbate (2.1 g, 10.6 mmol) prepared
from 1.87 g of ascorbic acid and 0.42 g of NaOH in water
(18 ml) was stirred vigorously until completely decolorized
with the appearance of a white precipitate (ca 5 min). The
resulting suspension was extracted with diethyl ether and
the ether extracts were washed with water and brine, dried
over anhydrous sodium sulfate and evaporated under re-
1
duced pressure to provide TOH (0.94 g, 94%). H NMR
(400 MHz, CDCl3), ꢀ 1.20 (s, 12), 1.55 (s, 6). 13C NMR
(100 MHz, CDCl3), ꢀ 12.1, 34.5, 53.7. IR (pentane),
Kinetics of N-triphenylacetoxy-2,2,6,6-tetramethylpiperi-
dine (7 ) thermolysis. Aliquots (0.2 ml) of a solution of 7
(50 mg in 5 ml of benzene) were sealed in 20 ampoules,
which were divided into two batches that were heated in an
oil-bath. Ampoules were withdrawn at intervals and the
residual substrate was determined from the change in the
integrated IR signal at 1754 cmꢂ1, which was fit to first-
order kinetics. Duplicate runs gave first-order rate constants
1
3590 cmꢂ1. EIMS, m/z 157, 156, 142, 109, 83, 69, 55. H
NMR (500 MHz, CDCl3, ꢂ60 ꢀC), ꢀ 1.10 (s, 6), 1.18 (s, 6),
1.40 (m, 4), 1.56 (m, 2), 2.26 (s, 1). 13C NMR (500 MHz,
CDCl3, ꢂ60 ꢀC), ꢀ 16.8, 18.9, 32.2, 39.1, 58.7.
N-triphenylacetoxy-2,2,6,6-tetramethylpiperidine (7 ). Tri-
phenylacetyl chloride (520 mg, 1.7 mmol) prepared from the
reaction of triphenylacetic acid (0.5 g, 1.7 mmol) and oxalyl
chloride (0.36 ml, 4.25 mmol) with 2 drops of DMF was
added to a stirred solution of 1-hydroxy-2,2,6,6-tetramethyl-
piperidine (270 mg, 1.7 mmol) and n-BuLi (1 ml, 1.6 mmol)
in 50 ml of CH2Cl2. The reaction mixture was stirred for
20 min and 40 ml of 10% HCl were added. The organic layer
was washed with 3 ꢁ 20 ml of brine, dried over MgSO4, and
concentrated. Column chromatography (silica gel with
CH2Cl2) gave 7 as white crystals, m.p. 139–142 ꢀC
of (2.20 ꢃ 0.20) ꢁ 10ꢂ6 sꢂ1 at 132.8 C and (2.88 ꢃ 0.80) ꢁ
ꢀ
10ꢂ5 sꢂ1 at 150.0 ꢀC.
Tetraphenylmethane. Phenylazotriphenylmethane (0.70 g,
2.0 mmol) in 10 ml of benzene was refluxed for 2 h, giving
a dark red solution which changed to yellow on cooling. The
solvent was evaporated and the residue chromatographed
(silica gel, CH2Cl2) to give tetraphenylmethane (0.11 g,
10%).8c 1H NMR (400 MHz, CDCl3), ꢀ 7.28 (s, 20, 4Ph).
13C NMR (400 MHz, CDCl3), ꢀ 127.5, 128.2, 128.5, 130.3,
132.7, 147.1. EIMS, m=z 320 (Mþ ), 243 (Ph3Cþ ), 165,
105. HREIMS, m=z calc. for C25H20, 320.15595; found,
320.15650.
1
(470 mg, 1.2 mmol, 65%). H NMR (100 MHz, CDCl3), ꢀ
0.86 (s, 6, 2CH3), 0.98 (s, 6, 2CH3), 1.1–1.7 (m, 6, 3 CH2),
7.23–7.34 (m, 15, 3Ph). 13C NMR (100 MHz, CDCl3), ꢀ
17.4, 21.4, 32.3, 39.9, 60.8, 65.7, 127.0, 127.7, 130.8, 142.7.
IR (CDCl3), 1749 cmꢂ1; (toluene), 1754 cmꢂ1. EIMS, m/z
427 (Mþ ), 271 (Mþ ꢂTO), 243 (PhCþ ), 165, 97, 82, 69,
56. HREIMS, m/z calc. for C29H34NO2, 428.25899; found,
428.25896.
Trityl peroxide.8a,d–f Zinc dust (0.5 g, 7.5 mmol) and triphe-
nylmethyl chloride (1 g, 3.6 mmol) in 20 ml of cyclohexane
were stirred for 30 min open to the atmosphere. Filtration
gave solid trityl peroxide (71%), which was recrystallized
from toluene. 1H NMR (400 MHz, CDCl3), ꢀ 7.24–7.32 (m,
30, 6 Ph). 13C NMR (100 MHz, CDCl3), ꢀ 128.2, 128.3,
128.4, 130.2, 145.7. EIMS, m=z 259 (Ph3COþ, 100), 243
(Ph3Cþ, 90), 165, 105, 77; lit.8e 259 (100), 243 (73). Upon
Products of N-triphenylacetoxy-2,2,6,6-tetramethylpiperi-
dine (7) thermolysis in benzene. A solution of 7 (20 mg,
0.046 mmol) in 1 ml of benzene in a flame-dried ampoule
was degassed by either 15 min of bubbling in N2 or by four
freeze–thaw cycles. Duplicate runs were carried out with
each degassing method, with the same results. The am-
1
heating melting begins at 110 ꢀC, and H NMR shows
partial rearrangement at this point, which is complete on
heating to 190 ꢀC.
Copyright # 2003 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 559–563

THERMOLYSIS OF N-TETRAMETHYLPIPERIDINYL TRIPHENYLACETATE
563
3. (a) Allen AD, Fenwick MH, Henry-Riyad H, Tidwell TT. J. Org.
Chem. 2001; 66: 5759–5765; (b) Huang W, Henry-Riyad H,
Tidwell TT. J. Am. Chem. Soc. 1999; 121: 3939–3943; (c) Allen
AD, Cheng B, Fenwick MH, Huang W, Missiha S, Tahmassebi D,
Tidwell TT. Org. Lett. 1999; 1: 693–696; (d) Allen AD, Cheng B,
Fenwick MH, Givehchi B, Henry-Riyad H, Nikolaev VA, Shikova
EA, Tahmassebi D, Tidwell TT, Wang S. J. Org. Chem. 2001; 66:
2611–2617; (e) Carter J, Fenwick MH, Huang W, Popik VV,
Tidwell TT. Can. J. Chem. 1999; 77: 806–809; (f) Allen AD,
Porter J, Tahmassebi D, Tidwell TT. J. Org. Chem. 2001; 66:
7420–7426; (g) Fenwick MH, Tidwell TT. Eur. J. Org. Chem.
2001; 3415–3419; (h) Allen AD, Rangwalla H, Saidi K, Tidwell
TT, Wang J. Russ. Chem. Bull. 2001; 2130–2133; (i) Sung K,
Tidwell TT. J. Org. Chem. 1998; 63: 9690–9697; (j) Allen AD,
Fenwick MH, Jabri A, Rangwala H, Saidi K, Tidwell TT. Org.
Lett. 2001; 3: 4095–4098; (k) Saidi K, Tidwell TT. ARKIVOC
2001; 2: 100–107.
Thermolysis of trityl peroxide: formation of 1,2-diphenoxy-
1,1,2,2-tetraphenylethane.8a Trityl peroxide (100 mg, 0.019
mmol) in 5 ml of benzene was degassed under nitrogen for
15 min and heated for 6 h at 150 ꢀC. The solvent was
evaporated and the product 12 identified by the spectral
properties. 1H NMR (400 MHz, CDCl3), ꢀ 7.21–7.33 (m, 20,
4 Ph), 7.49–7.54 (m, 4, m-H), 7.60–7.62 (m 2, p-H), 7.82 (d,
4, J ¼ 8.5 Hz, o-H). 13C NMR (100 MHz, CDCl3), ꢀ 127.4,
127.8, 127.9, 128.1, 128.4, 129.8, 130.2, 132.5, 145.3.
EIMS, m=z 260 [Ph2C(OPh)Hþ , 46], 243 (Ph3Cþ , 44),
183, 165, 154, 105, 77.
Supplementary material
4. (a) Anderson JE, Corrie JET. J. Chem. Soc., Perkin Trans. 2 1992;
1027–1031; (b) Anderson JE, Casarini DJ, Corrie JET, Lunazzi L.
Chem. Soc., Perkin Trans. 2 1993; 1299–1304.
Rate plots for 7 and a table of computed thermodynamic
properties are available at the epoc website at http://
www.wiley.com/epoc.
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Acknowledgement
Financial support by the Natural Sciences and Engine-
ering Research Council of Canada is gratefully acknow-
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Copyright # 2003 John Wiley & Sons, Ltd.
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