Preparation of new substituted bis(benzoyl) peroxides under aqueous conditions in the presence of stearyltrimethylammonium chloride

Article abstract of DOI:10.1007/s00706-003-0130-1

A series of new substituted bis(benzoyl) peroxides has been synthesised from their corresponding acid chlorides in high yield. The reactions were carried out in aqueous sodium peroxide solution and butanone in the presence of 0.5% stearyltrimethylammonium chloride (STAC) at a temperature below 15°C. STAC improved the purity, and the fast addition improved the yield of the peroxides. Mass spectral analysis of substituted bis(benzoyl) peroxides using EI has been carried out for accurate mass determinations. Springer-Verlag 2003.

Full text of DOI:10.1007/s00706-003-0130-1

Monatshefte f€ur Chemie 135, 397–405 (2004)
DOI 10.1007/s00706-003-0130-1
Preparation of New Substituted
Bis(benzoyl) Peroxides under Aqueous
Conditions in the Presence
of Stearyltrimethylammonium Chloride
Cornelis M. Moorhoff1;ꢀ;# and Carl Braybrook2;z
1
CRC for polymers, Notting Hill, VIC, Australia, 3168
2
CSIRO, Molecular Science, Bag 10, Clayton South, VIC, Australia, 3169
Received September 5, 2003; accepted September 9, 2003
Published online December 30, 2003 # Springer-Verlag 2003
Summary. A series of new substituted bis(benzoyl) peroxides has been synthesised from their corre-
sponding acid chlorides in high yield. The reactions were carried out in aqueous sodium peroxide
solution and butanone in the presence of 0.5% stearyltrimethylammonium chloride (STAC) at a
temperature below 15ꢁC. STAC improved the purity, and the fast addition improved the yield of the
peroxides. Mass spectral analysis of substituted bis(benzoyl) peroxides using EI has been carried out
for accurate mass determinations.
Keywords. Bis(p-alkylbenzoyl) peroxide; Bis(p-n-decylbenzoyl) peroxide; Bis(p-alkoxybenzoyl)
peroxide; Bis(p-n-butoxybenzoyl) peroxide; Stearyltrimethylammonium chloride.
Introduction
Benzoyl peroxides are widely used for the initiation of free radical polymerisations
and in grafting reactions to form copolymers. Their solubility in the reaction me-
dium (solvent, monomers, molten polymer) can be altered by introducing substitu-
ents on the aryl rings and this can affect the course of the polymerisation reactions.
To systematically study the effect of different alkyl substituents of the benzoyl
peroxides, we required efficient synthetic procedures to prepare these compounds.
This paper describes the synthesis of new substituted bis(benzoyl) peroxides by an
adaptation of known methods [1].
ꢀ
Corresponding author. E-mail: cmoorhoff@boronmolecular.com
#
Present address: Boron Molecular Ltd. PO Box 756, Noble Park, VIC, Australia 3174
z
Author to receive any questions about mass spectral analysis

398
C. M. Moorhoff and C. Braybrook
Results and Discussion
Synthesis
Stearyltrimethylammonium chloride (STAC) was added to a little water and then
heated to 55ꢁC to form a micellar solution. This solution was cooled to room
temperature.
A substituted benzoyl chloride in butanone was added dropwise to an aqueous
premixed solution of hydrogen peroxide and sodium hydroxide in the presence of
0.5 to 1 wt% STAC as a surfactant [2, 3]. The temperature was kept below 15ꢁC.
(Scheme 1).
For comparative and reference purposes three known substituted bis(benzoyl)
peroxides, namely bis(p-ethylbenzoyl)- (1), bis(p-t-butylbenzoyl)- (2), and bis(p-
ethoxybenzoyl) peroxide (3), were included in the study. We found that 1, 2, and
bis(p-n-butoxybenzoyl) peroxide (4) formed solid precipitates during the addition.
Without surfactant it became obvious that some substituted bis(benzoyl) peroxides,
namely2and4,formedunwantedlumpsduringtheaddition. Whenthesebis(benzoyl)
peroxides were analysed, they were found to contain up to 30% of the corres-
ponding substituted benzoic acids as coprecipitated impurities. With STAC as a
surfactant, substituted bis(benzoyl) peroxides, for example 1, and especially
those substituted bis(benzoyl) peroxides with longer alkyl groups like bis(p-n-
butylbenzoyl)- (5), bis(p-n-hexylbenzoyl)- (6), and bis(p-n-decylbenzoyl) peroxide
(7) did not precipitate during the addition. These peroxides, when using more
butanone, remained in the butanone layer on top of the aqueous layer. Evaporation
of the butanone layer produced a solid crust of the peroxide with little or no water
present (CAUTION). In the case of 6 a precipitate only formed when all the
butanone had evaporated; the resulting compound had a low melting point. Anhy-
drous 5 and 7 are solids when pure, but they remained oils at room temperature
Scheme 1

Preparation of New Substituted Bis(benzoyl) Peroxides
399
when they contain only little impurities. Peroxides 5 and 7 were better isolated by
extraction from the water layer. This was first cautiously tried with 5 by extraction
with petroleum ether (bp ¼ 30–40ꢁC). After evaporation of the solvent, the product
obtained was surfactant free almost 100% pure 5 with no water (CAUTION).
Bis(p-n-decylbenzoyl) peroxide (7) could not be extracted with petroleum ether
and ethyl acetate was used instead. Again, no STAC was found in the final product.
Less soluble sodium benzoyl peroxides and substituted benzoic acids remained in
the surfactant aqueous solution and gave the water layer a milky to translucent
appearance. When the peroxides were isolated as water-free oils, they usually
solidified at room temperature to form waxes. Extreme caution should be
observed in handling these materials. This method is therefore not recommended
for peroxide isolation.
The active oxygen contents of 5, 6, and 7 are 4.5, 3.9, and 3.1 wt% compared to
bis(benzoyl) peroxide with an active oxygen content of 6.6 wt%. This makes 7 a
fairly safe material, even in pure form without water. Last mentioned three
bis(benzoyl) peroxides were purified by recrystallisation from petroleum ether
(bp ¼ 40–60ꢁC) by dissolving these compounds at room temperature and then
cooling the solution to ꢂ10ꢁC. In general, the peroxide reaction of substituted
benzoyl chlorides with long aliphatic chains (R ¼ p-n-hexyl-, p-n-decyl-) occurred
at a much slower rate and a 24 hour reaction period was required. By comparison,
the bis(alkoxybenzoyl) peroxides formed very rapidly. A 100 gram batch of p-
ethoxybenzoyl chloride was transformed to the desired 3 in less than 30 minutes.
Furthermore, increasing the amount of butanone in the reaction mixture either
during or before the addition of the acid chloride, also curbed lumping and
improved the purity of the precipitated peroxide. Adding an additional amount
of butanone after the addition improved the purity and yield of certain bis(benzoyl)
peroxides that form more slowly, e.g. 6 and 7.
Reducing the excess amount of sodium hydroxide required, minimized cleav-
age of the bis(benzoyl) peroxide. Thus, instead of 15–20% excess NaOH, only
ꢃ5% excess NaOH were used. The hydrogen peroxide excess, on the other hand,
was increased from just 10% to up to 50% (and in some cases twice the amount)
and had no adverse effect on the bis(benzoyl) peroxide purity, provided that the
temperature was kept below 15ꢁC. More importantly, the concentration of hydro-
gen peroxide was not always reliable. It seemed that excess hydrogen peroxide did
not make the reaction more hazardous by forming butanone peroxides since these
peroxides either stayed in the aqueous layer or as liquids in ketone solvents and did
not coprecipitate with the solid bis(benzoyl) peroxides (NMR). With some
bis(benzoyl) peroxide preparations, for example bis(3,4-dimethoxybenzoyl) perox-
ide (8) and bis(n-decyloxybenzoyl) peroxide (9), the reaction did not go to com-
pletion. In such cases the hydrolyses of the acid chloride competed with peroxide
formation and for these compounds low yields were obtained. The corresponding
substituted benzoic acid and an equal amount of HCl had formed. The final reac-
tion mixture reached an acidity level well below pH ¼ 2. Where this problem was
severe, we have found that it was best to work up the reaction immediately to curb
acid catalysed cleavage of the peroxide. Therefore, thirty minutes after the addition
of the acid chloride to the sodium peroxide solution had completed, excess sodium
hydrogencarbonate was added to the mixture to neutralise the aqueous solution.

400
C. M. Moorhoff and C. Braybrook
It was important though to do this addition in small portions, because the CO2 that
was released caused a foam due to the surfactant.
Analysis of Substituted Bis(benzoyl) Peroxides
Bis(p-alkylbenzoyl) peroxides with long aliphatic chains (namely 5, 6, and 7,
Scheme 1) were all soluble and recrystallised from cold petroleum ether
(bp ¼ 40–60ꢁC) but were less soluble in methanol. However, the bis(alkoxyben-
zoyl) peroxides were soluble in chloroform, but methanol was important to use as a
co-solvent in the recrystallisations to trap excessive amounts of water. Bis(p-eth-
oxybenzoyl) peroxide (3) had the lowest solubility and was purified by recrystallisa-
tion from methanol, but this peroxide could also be recrystallised from chloroform.
The determination of the melting points of anhydrous bis(benzoyl) per-
oxides was carried out on very small samples using a heating block and visually
monitored by optical microscopy rather than a melting tube. Peroxides 2 and 3
decomposed before their melting points were reached, this was typically observed
as a slow fizz, due to the evolution of CO2 and with some liquification or
solidification.
Experimental
Note: Peroxides are shock-sensitive and therefore hazardous and need to be handled with appropriate
care. Peroxide preparations should be carried out in a fumehood behind a safety shield.
The reaction of the substituted benzoic acids with thionyl chloride was carried out at 90ꢁC for
4 h. The process was followed visually. At room temperature the white paste of the mixture of the
substituted benzoic acid and thionyl chloride reacted very slowly. Above 60ꢁC a fast evolution of
HCl and SO2 occurred with the gradual disappearance of the white solid. No noticeable cleavage of
the alkoxy group occurred during the formation of the acid chloride and no obvious formation
of the anhydride was found. High-vacuum distillation was included as a necessary purification step
for the preparation of all distillable substituted benzoyl chlorides. p-n-Decoxybenzoyl chloride could
not easily be distilled and was therefore impure, as a result bis(p-n-decoxybenzoyl) peroxide, which
was prepared, was also very impure. A 13wt% stock solution of STAC was prepared at 55ꢁC and
Fig. 1. Numbering used of compounds 2, 5, 6, and 7 for spectrometric assignments
Fig. 2. Numbering used of compounds 3, 4, 8, and 10 for spectrometric assignments

Preparation of New Substituted Bis(benzoyl) Peroxides
401
cooled to room temperature before addition. Butanone was not redistilled. As a safety precaution
it was important to obtain at least a 20 wt% moisture content in the free-flowing peroxide
powder.
1H and 13C NMR of bis(benzoyl) peroxides were run on a Varian Gemini instrument at 200 and
50MHz. For aromatic coupling constants, Jo ¼ 8.8–9.0Hz, Jm ¼ ꢃ1–2 Hz. For aliphatic coupling
constants J ¼ 6.9–7.1Hz. The NMR analyses of the moisture content was carried out only 24h after
precipitation of the peroxide and was determined in acetone-d6. However, with some compounds it was
necessary to add CDCl3 or DMSO-d6 to the deuterated solvents to facilitate dissolution. For example, 7
was poorly soluble in acetone and some CDCl3 had to be added in such an amount that all H2O was
still dissolved in the deuterated solvent mixture. The mass spectra were obtained with a ThermoQuest
MAT95XL high resolution mass spectrometer in the EI mode at a source temperature of 200ꢁC and a
source pressure of 5.10ꢂ6 mbar. Substituted bis(benzoyl) peroxides were dissolved in acetonitrile and
introduced via a direct insertion probe. The source probe was ramped from room temperature until
sufficient to vaporise the sample. Previously, mass spectra of bis(benzoyl) peroxide and bis(p-toluoyl)
peroxide have been measured using methane chemical ionisation (CI) [5]. To the best of our knowl-
edge, this is the first time that mass spectra of pure bis(benzoyl) peroxides have been determined
utilising electron impact (EI) for accurate mass determinations of molecular ions [6]. IR of 14 asym-
metric- and symmetric sulfo-substituted bis(benzoyl) peroxides (p-RSO2C6H4(CO)OOCOPh) have
been reported and were determined at ꢀꢀ¼ 1790 (C¼O), 1770 (C¼O), 1230 (C–O–), and 1000cmꢂ1
(C–O–O–C) [7].
Bis(4-t-butylbenzoyl) Peroxide (2, [4])
A 60.0 g of 30 wt% aqueous H2O2 (529mmol) in 65 cm3 of H2O solution was added within 20min to a
50.0g of 30wt% aqueous NaOH (375mmol) in 100 cm3 of H2O solution at ꢂ5ꢁC. A 13 wt% solution
of STAC (10 cm3) was added to the reaction mixture. A solution of 65.0 g of p-t-butylbenzoyl chloride
(331 mmol) in 40 cm3 of butanone was added to the reaction mixture within 30min at 5ꢁC. Then,
600 cm3 of H2O were added followed by 10g of NaHCO3. The white precipitate was collected by
filtration and washed with deionised H2O to give 93.17g of wet 2 (38 wt% H2O). Yield of active
compound: 57.9g (99%). Recrystallisation from petroleum ether:chloroform (1:1). Mp 133–138ꢁC
(dec) (Ref. [4] 142–143ꢁC); t1=2 (10 h)¼ 68.3ꢁC; HRMS (CI): m=z ¼ calcd. for C22H26O4 (Mþ)
354.18311, found 354.1830; IR: ꢀꢀ¼ 3080w, 2962s, 2885 s, 1785m, 1759 s, 1607 s, 1572w,
1464 m, 1412 s, 1366m, 1249 s, 1220 s, 1178 s, 1108m, 1030s, 992 s, 908 s, 850 m, 765m, 734s,
1
700 m cmꢂ1; H NMR (CDCl3): ꢁ ¼ 8.04 (d, J ¼ 9 Hz, H-3, H-7), 7.55 (d, J ¼ 9 Hz, H-4, H-6), 1.37
(s, H-9) ppm; 13C NMR (CDCl3): ꢁ ¼ 163.09 (C-1), 122.78 (C-2), 129.69 (C-3, C-7), 125.83 (C-4, C-
6), 158.11 (C-5), 35.26 (C-8), 31.02 (C-9) ppm.
Bis(p-ethoxybenzoyl) Peroxide (3, [4])
A 75.0 g of 30wt% aqueous H2O2 (662mmol) in 100 cm3 of H2O solution was added to a 60.0g of
30wt% aqueous NaOH (450mmol) solution at ꢂ5ꢁC within 20min. At first, a very exothermic
reaction occurred (rapid increase in temperature, CAUTION) with the simultaneous formation of a
white paste which then became transparent after final addition. The reaction mixture was not allowed
to rise above 15ꢁC. The mixture was stirred for a further 20min and then cooled to 5ꢁC. A 13 wt%
solution of STAC (10 cm3) was added to the mixture to suppress lump formation during the peroxide
formation. A solution of 70.0g of p-ethoxybenzoyl chloride (379.1mmol) in 40cm3 of butanone was
slowly added to the cooled aqueous sodium peroxide solution within 45min under stirring whereby
the temperature rose to 15ꢁC. Halfway through the addition, 130cm3 of butanone were added to the
reaction mixture to facilitate stirring. The temperature was kept <15ꢁC for another 2 h. 3.0 g of
NaHCO3 (0.0357 mol) were added to the reaction mixture to raise the pH to ꢃ7. The mixture was

402
C. M. Moorhoff and C. Braybrook
then diluted with H2O to a volume of 1 dm3 to enhanced the peroxide precipitation and the mixture
was kept for 16 h at 4ꢁC. The fine white suspension was filtered and the product was washed with
water to give 81.9g of free flowing but wet 3 (46 wt% H2O). Yield of active compound: 44.5g
(71%). Mp 137–139ꢁC (dec) (Ref. [4] 131–132ꢁC) t1=2 (10 h)¼ 40.5ꢁC; HRMS (CI): m=z ¼ calcd.
for C18H18O6 (Mþ) 330.11034, found 330.1106; IR: ꢀꢀ¼ 3090 w, 2992m, 2960 m, 2930w, 2890 w,
1780 s, 1753 s, 1606s, 1577 m, 1508 m, 1459m, 1427m, 1390m, 1311 m, 1275s, 1237 s, 1169m,
1
1123 m, 1045 s, 991 m, 908 s, 843 m, 738 s cmꢂ1; H NMR (CDCl3): ꢁ ¼ 7.95 (d, J ¼ 9 Hz, H-3, H-
7), 7.03 (d, J ¼ 9 Hz, H-4, H-6), 4.12 (q, J ¼ 7 Hz, H-8), 1.40 (t, J ¼ 7 Hz, H-9) ppm; 13C NMR
(CDCl3): ꢁ ¼ 162.33 (C-1), 115.40 (C-2), 130.16 (C-3, C-7), 113.33 (C-4, C-6), 161.01 (C-5), 62.34
(C-8), 12.94 (C-9) ppm.
Bis(p-n-butoxybenzoyl) Peroxide (4, C22H26O6)
A 6.5 g of 30wt% aqueous H2O2 (57.33mmol) in 25cm3 of H2O solution was added to a 15.0g of
30wt% aqueous NaOH (112.5mmol) solution at ꢂ5ꢁC within 15 min and the mixture was stirred for a
further 20min. The temperature was not allowed to rise above 10ꢁC. A 13 wt% solution of STAC
(5cm3) was added to the sodium peroxide at 5ꢁC. Then, a solution of 20.0g of p-n-butoxybenzoyl
chloride (94.04 mmol) in 5 cm3 of butanone was added within 30 min to the cooled reaction mixture at
3ꢁC under stirring whereby the temperature rose to 7ꢁC. The reaction mixture became a white paste
and was then treated with 35 cm3 of butanone and stirred at room temperature. H2O (500 cm3) was
added to the reaction mixture to complete precipitation. The precipitate was filtered and washed with
250 cm3 of deionised water to give 24.65g of wet 4 (28 wt% H2O, 8% impurity due to p-n-but-
oxybenzoic acid). Yield of active compound: 16.46 g (91%). Recrystallisation from petroleum ether:
chloroform (1:1). Mp 110.5ꢁC; t1=2 (10 h)¼ 37.5ꢁC; HRMS (CI): m=z ¼ calcd. for C22H26O6 (Mþ)
386.17294, found 386.1724; IR: ꢀꢀ¼ 2963s, 2930m, 2880w, 1780s, 1753s, 1606s, 1577 w, 1510m,
1
1467 w, 1315w, 1255 m, 1235s, 1168 s, 1019m, 993 m, 909 s, 843 w, 732 s, 650 w cmꢂ1; H NMR
(CDCl3): ꢁ ¼ 8.02 (d, J ¼ 9 Hz, H-3, H-7), 6.96 (d, J ¼ 9 Hz, H-4, H-6), 4.04 (d, J ¼ 7 Hz, H-8), 1.81
(t, J ¼ 7 Hz, H-9), 1.51 (hex, J ¼ 7 Hz, H-10), 0.99 (t, J ¼ 7 Hz, H-11) ppm; 13C NMR (CDCl3):
ꢁ ¼ 163.93 (C-1), 117.31 (C-2), 131.91 (C-3, C-7), 114.57 (C-4, C-6), 162.98 (C-5), 68.03 (C-8),
31.04 (C-9), 19.15 (C-10), 13.78 (C-11) ppm.
Bis(p-n-butylbenzoyl) Peroxide (5, C22H26O4)
A 20g of 30 wt% aqueous H2O2 (176.5mmol) in 25cm3 of H2O solution was added slowly to a 40g of
30wt% aqueous NaOH (300 mmol) solution at ꢂ5ꢁC within 15min and the mixture was stirred for a
further 30 min. The temperature was not allowed to rise above 10ꢁC. Butanone (25 cm3) followed by a
10cm3 of 13 wt% solution of STAC was added to the sodium peroxide. A solution of 54.54g of p-n-
butylbenzoyl chloride (277.3mmol) in 25cm3 of butanone was added within 30min to the cooled
reaction mixture at ꢃ5ꢁC. No precipitation was observed and the reaction mixture separated into two
layers. H2O (500 cm3) was added to the stirred reaction mixture. A viscous oil floated to the top of the
beaker and was left in a draft of the fume hood. No crust developed and the oil was separated to give
nearly 40.08g of anhydrous 5 (3 wt% H2O, CAUTION). This oil solidified on standing at room
temperature (CAUTION). Yield of active compound: 39.1g (80%). This compound was recrystallised
from cold petroleum ether. Mp 30.4ꢁC; t1=2 (10 h) ¼ 71.7ꢁC; HRMS (CI): m=z ¼ calcd. for C22H26O4
(Mþ) 354.18311, found 354.1829; IR: ꢀꢀ¼ 3080 w, 3040 w, 2960s, 2933 s, 2863 s, 1795 s, 1764s,
1691 m, 1610s, 1574 w, 1466 m, 1417 m, 1229s, 1178s, 1028 m, 994 s, 909 m, 846 m, 734s cmꢂ1
;
1H NMR (CDCl3): ꢁ ¼ 7.99 (d, J ¼ 9 Hz, H-3, H-7), 7.32 (d, J ¼ 9 Hz, H-4, H-6), 2.70 (t, J ¼ 6 Hz, H-
8), 1.64 (m, H-9), 1.37 (H, J ¼ 6 Hz, H-10), 0.95 (t, J ¼ 6 Hz, H-11) ppm; 13C NMR (CDCl3):
ꢁ ¼ 163.17 (C-1), 122.94 (C-2), 129.82 (C-3, C-7), 128.89 (C-4, C-6), 150.11 (C-5), 35.81 (C-8),
33.14 (C-9), 22.27 (C-10), 13.87 (C-11) ppm.

Preparation of New Substituted Bis(benzoyl) Peroxides
403
Bis(p-n-hexylbenzoyl) Peroxide (6, C26H34O4)
A 7.5g of 30wt% aqueous H2O2 (66.15 mmol) in 25cm3 of H2O solution was added slowly to a 17.0g
of 30 wt% aqueous NaOH (127.5mmol) solution at 5ꢁC within 25 min and the mixture was stirred for a
further 20 min. The temperature was not allowed to rise above 10ꢁC. Butanone (25 cm3) followed by a
10cm3 of 13 wt% solution of STAC was added to the sodium peroxide solution and the reaction
mixture was cooled to 5ꢁC. A solution of 25.0g of p-n-hexylbenzoyl chloride (111.2mmol) in
25cm3 of butanone was added within 30 min to the cooled reaction mixture at 5ꢁC and the mixture
was stirred overnight at room temperature. Then, 500 cm3 of H2O were added to the reaction mixture.
Extraction with 2ꢄ 400 cm3 of EtOAc followed by washing the organic extract with 2 ꢄ 100 cm3 of
H2O gave, after drying with MgSO4 and solvent evaporation on a cold rotavaporator (CAUTION),
24.3g of 6 as an oil (4wt% H2O, 4 wt% impurity). Yield of active compound: 22.3g (98%). Product
6 was recrystallised from cold petroleum ether. Mp 38.3ꢁC; t1=2 (10 h) ¼ 72.6ꢁC; HRMS (CI):
m=z ¼ calcd. for C26H34O4 (Mþ) 410.24571, found 410.2457; IR: ꢀꢀ¼ 2965 m, 2932 s, 2885 m,
1795 m, 1764s, 1686 s, 1610 m, 1465w, 1420m, 1289 m, 1229 s, 1178m, 1029 s, 995 s, 858 w,
1
755 w cmꢂ1; H NMR (CDCl3): ꢁ ¼ 7.99 (d, J ¼ 9 Hz, H-3, H-7), 7.32 (d, J ¼ 9 Hz, H-3, H-7), 2.69
(t, J ¼ 6 Hz, H-8), 1.65 (m, H-9), 1.32 (m, H-10–H-12), 0.89 (t, J ¼ 6 Hz, H-13) ppm; 13C NMR
(CDCl3): ꢁ ¼ 163.19 (C-1), 122.94 (C-2), 129.82 (C-3, C-7), 128.88 (C-4, C-6), 150.14 (C-5), 36.12
(C-8), 31.61 and 30.99 (C-9 and=or C-10), 28.85 (C-11), 22.54 (C-12), 14.04 (C-13) ppm.
Bis(p-n-decylbenzoyl) Peroxide (7, C34H50O4)
A 14.0 g of 30 wt% aqueous H2O2 (123.5mmol) in 50cm3 of H2O solution was added within 15 min to a
25.0g of 30 wt% aqueous NaOH (188 mmol) solution at 0ꢁC and then stirred for a further 20min. The
temperature was not allowed to rise above 15ꢁC. Butanone (25 cm3) was added to the aqueous sodium
peroxide solution followed by a 10 cm3 of 13 wt% solution of STAC. A solution of 50.0g of p-n-
decylbenzoyl chloride (178mmol) in 25 cm3 of butanone was then added within 30min to the cooled
sodium peroxide solution at 5ꢁC and the mixture was stirred for 15h at room temperature. H2O
(500 cm3) was added to the reaction mixture to facilitate workup. Extraction with 2 ꢄ 400 cm3 of EtOAc
followed by washing of the organic extract with 2 ꢄ 100 cm3 of water gave, after solvent evaporation on
a cold rotavaporator, an oil that slowly crystallised at room temperature (CAUTION) to give 46.7g of 7
(3wt% H2O, 15wt% impurities). Yield of active compound: 38.6g (83%). Compound 7 was recrys-
tallised from petroleum ether at 0ꢁC. Mp 25–26ꢁC; t1=2 (10 h)¼ 71.9ꢁC; HRMS (CI): m=z ¼ calcd. for
C34H50O4 (Mþ) 522.37089, found 522.3699; IR: ꢀꢀ¼ 3050 w, 2927 s, 2857 s, 1787 m, 1763 s, 1691 m,
1610 s, 1466m, 1417 m, 1228 s, 1178 m, 1028m, 997 s, 909 m, 851w, 735 s cmꢂ1; 1H NMR (CDCl3):
ꢁ ¼ 7.94 (d, J ¼ 9 Hz, H-3, H-7), 7.31 (d, J ¼ 9 Hz, H-4, H-6), 2.69 (t, J ¼ 6 Hz, H-8), 1.65 (m, H-9), 1.27
(m, H-10–H-16), 0.89 (t, J ¼ 6 Hz, H-17) ppm; 13C NMR (CDCl3): ꢁ ¼ 163.18 (C-1), 122.94 (C-2),
129.82 (C-3, C-7), 128.88 (C-4, C-6), 150.15 (C-5), 36.13 (C-8), 31.88 (C-9), 31.05 (C-10), 29.57,
29.53, 29.43, 29.30, 29.20 (C-11–C-15), 22.67 (C-16), 14.10 (C-17) ppm.
Note: Known substituted bis(benzoyl) peroxides, namely bis(p-toluoyl) peroxide, bis(m-toluoyl) per-
oxide, bis(o-toluoyl) peroxide, and bis(p-ethylbenzoyl) peroxide [4], have also been prepared in an
identical manner.
Bis(3,4-dimethoxybenzoyl) Peroxide (8, C18H18O8)
A75.0 gof30wt%aqueousH2O2 (662mmol)in100 cm3 ofH2Osolutionwasaddedtoa 60.0 gof30wt%
aqueous NaOH (450 mmol) solution at ꢂ5ꢁC within 20min. The temperature was not allowed to rise
above 15ꢁC. The mixture was stirred for a further 20min, then cooled to 5ꢁC. A 13wt% solution of STAC
(10 cm3)wasaddedtothemixture. Asolutionof380.0 gof4-dimethoxybenzoylchloride(398.7mmol)in
300 cm3 of butanone was added within 45min to the cooled, stirred reaction mixture whereby the
temperature roseto15ꢁC. Stirring was continuedfor another 30min. Then15.0g of NaHCO3 (178 mmol)

404
C. M. Moorhoff and C. Braybrook
were added to the solution and the reaction mixture was diluted with H2O to 1 dm3. The fine white
suspension was filtered and the product was washed with water to give 28.00 g of wet 8 (38 wt% H2O).
Yield of active material: 17.4 g (24%). Compound 8 was recrystallised from chloroform. (CAUTION,
this peroxide decomposes at room temperature). t1=2 (10 h) <35ꢁC; IR: ꢀꢀ¼ 3105w, 3040w, 2960m,
2940 w, 2843w, 1753 s, 1685 s, 1601s, 1516 s, 1465m, 1420m, 1348 w, 1295m, 1270s, 1220 m, 1173m,
1024 m,909 s,734 scmꢂ1;1H NMR(CDCl3):ꢁ ¼ 7.51(d, J ¼ 2.0 Hz, H-3), 6.92(d, J ¼ 8.5 Hz, H-6)7.72
(dd, J ¼ 8.5, 2.0Hz, H-7), 3.24 (s, H-8, H-80) ppm; 13C NMR (CDCl3): ꢁ ¼ 162.93 (C-1), 117.51 (C-2),
111.78 (C-3), 148.90 (C-4), 154.00 (C-5), 110.54 (C-6), 124.08 (C-7), 56.00 (C-8, C-80) ppm.
Bis(p-n-propoxybenzoyl) Peroxide (10, C20H22O6)
A 40.0g of 30 wt% aqueous H2O2 (352mmol) in 60cm3 of H2O solution was added to a 37.0 g of
30wt% aqueous NaOH (278 mmol) solution at ꢂ5ꢁC within 10min and then stirred for a further
20min. A 13 wt% solution of STAC (7cm3) was added to the sodium peroxide at 5ꢁC. A solution of
50.0g of p-n-propoxybenzoyl chloride (252mmol) in 20cm3 of butanone was added within 30min to
the cooled, stirred reaction mixture whereby the temperature rose to 15ꢁC. The reaction mixture
became a white suspension and was then treated with 30cm3 of butanone to further enhance stirring
at room temperature. H2O (800 cm3) was added to facilitate complete precipitation, the mixture was
filtered, and the product was washed with H2O to give 62.6g of wet 10 (26 wt% H2O, 28% impurity
due to 4-n-propoxybenzoic acid). Yield of active compound: 32.6g (72%). Compound 10 was purified
by recrystallisation from petroleum ether:chloroform (1:1). t1=2 (10 h)¼ 38ꢁC; HRMS (CI):
m=z ¼ calcd. for C20H22O6 (Mþ) 358.14164, found 358.1415; IR: ꢀꢀ¼ 2970m, 2960m, 2870w,
1
1783 m, 1753s, 1670 s, 1508 s, 1473m, 1426m, 1317 m, 1252 s, 1167m, 1065m, 970m cmꢂ1; H
NMR (CDCl3): ꢁ ¼ 8.06 (d, J ¼ 9 Hz, H-3, H-7), 6.94 (d, J ¼ 9 Hz, H-4, H-6), 4.00 (t, J ¼ 7 Hz, H-8),
1.85 (hex, J ¼ 7 Hz, H-9), 1.056 (t, J ¼ 7 Hz, H-10) ppm; 13C NMR (CDCl3): ꢁ ¼ 163.67 (C-1), 117.98
(C-2), 132.34 (C-3, C-7), 114.18 (C-4, C-6), 162.8 (C-5), 69.74 (C-8), 22.44 (C-9), 10.46 (C-10) ppm.
Determination of t1=2 (10 h) of Substituted Bis(benzoyl) peroxides
To relatively compare the individual half life of bis(benzoyl)peroxides, it is typical to quote the
temperature (in ꢁC) at which half of the compound has decomposed after 10 h (t1=2(10 h)). The method
that we used for determining the temperature of t1=2(10 h) involved the analyses of the amount of
peroxide in a 0.5 to 1 mM methanolic solution remaining after exactly 10h at different temperatures. A
plot of concentration versus temperature (10 h) gave the precise temperature at which half of the
peroxide had decomposed. The methanolic solution (10ꢂl) was injected and analysed by reverse phase
HPLC. A 250 ꢄ 10 mm ALLTIMA C18 column was used and the suitable mobile phase was 80%
MeOH – 20% H2O. The UV-detector was set at ꢃ ¼ 254 and 280 nm to detect the peroxide. The main
decomposition products encountered were the substituted benzoic acid and the corresponding methyl
ester, both compounds had retention times quite different from the peroxide.
Acknowledgements
We thank Basell, the CRC for polymers, and the CSIRO for financial and instrumental assistance. The
HPLC expertise of N. Hart (CSIRO) is gratefully acknowledged.
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Preparation of New Substituted Bis(benzoyl) Peroxides
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