Alkylation of peroxyacids as a new method of peroxyester synthesis

Full text of DOI:10.1039/b005192f

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Alkylation of peroxyacids as a new method of peroxyester
synthesis
Stefan Baj* and Anna Chrobok
1
Institute of Organic Chemistry and Technology, Silesian University of Technology,
Krzywoustego 4, 44-100 Gliwice, Poland. E-mail: baj@zeus.polsl.gliwice.pl
Received (in Cambridge, UK) 28th June 2000, Accepted 4th July 2000
Published on the Web 24th July 2000
A
new method for synthesis of short alkyl chain
Peroxyesters easily decompose to give free radicals and there-
fore they find wide application as initiators of free-radical
reactions, cross-linking agents, bleaching or oxidising agents
and pharmaceutical additives.1
Alkyl peroxyesters have been synthesised until now by acyl-
ation of alkyl hydroperoxides only (Schotten–Baumann pro-
peroxyesters has been developed, which involves reaction
of organic peroxyacids with alkyl trifluoromethane-
sulfonates, methyl chlorosulfonate, ethyl toluene-p-
sulfonate, dimethyl sulfate and trialkyloxonium tetra-
fluoroborate performed under phase-transfer conditions.
Table 1 Reactions of peroxyacid (1) with alkylating agent ARЈ (2) in the presence of phase-transfer catalyst leading to formation of alkyl
peroxyester (3)
Peroxyacid 1
Alkylating agent, ARЈ 2
Product 3
Yield (%)
98
60
58
49
73
55
49
37
98
94
90
76
38
DOI: 10.1039/b005192f
J. Chem. Soc., Perkin Trans. 1, 2000, 2575–2576
This journal is © The Royal Society of Chemistry 2000
2575

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cedure2). The acylation takes place either in a homogeneous
system in the presence of e.g. pyridine or triethylamine, or in
a heterogeneous system in the presence of alkaline aqueous
solutions. The acylation of primary alkyl hydroperoxides
suffers from the problem of base-catalysed decomposition of
the hydroperoxides. Moreover, few primary hydroperoxides are
available; their preparation is difficult and unsafe. Instead of
the hydroperoxides, under neutral conditions their barium salts
can be employed.3 Also these salts are of low stability, which
limits their wider application. Only primary hydroperoxides
with longer alkyl chains (C4 and higher) react with ketenes4 to
yield peroxyesters.
We present a new approach to primary alkyl peroxyester syn-
thesis involving alkylation of easily available organic peroxy-
acids by strong alkylating agents. It is worth mentioning that
there are literature reports that claim alkylation of peroxyacids
is not a possible process.5,6
The peroxyacid and alkylating agent dissolved in solvent
provided the organic phase, while solid base formed the
other phase. The syntheses were carried out at Ϫ20 ЊC in
the presence of a phase-transfer catalyst (solid–liquid PTC).
The results of the alkylation are shown in Table 1 and clearly
indicate that the use of strong alkylating agents such as
alkyl trifluoromethanesulfonates, methyl chlorosulfonate, ethyl
toluene-p-sulfonate, dimethyl sulfate and trialkyloxonium tetra-
fluoroborate permits preparation of methyl peroxyesters in
good yields. Methyl and ethyl peroxyesters are novel com-
pounds, so far not described in the literature.
In summary, we have elaborated a new, efficient preparative
method for the synthesis of short alkyl chain peroxyesters
that has not been available before. In addition, we have
shown that peroxyacids, in contrast to some earlier reports, can
react with alkylating agents under mild conditions to give
peroxyesters.
The peroxyesters were characterised9 by elemental analysis,
1
mass spectrometry and H and 13C NMR spectroscopic anal-
ysis;8 the active oxygen was determined according to the known
procedure10 by iodometric titration.
Acknowledgements
The authors thank Dr J. Suwinski for useful comments.
Notes and references
1 O. L. Mageli and C. S. Sheppard, Organic Peroxides, ed. D. Swern,
Wiley-Interscience, New York, 1970, vol. 1, p. 81.
2 Y. Sawaki, Organic Peroxides, ed. W. Ando, Wiley-Interscience,
New York, 1992, p. 450.
3 A. Riehe and F. Hitz, Ber. Dtsch. Chem. Ges., 1930, 63, 2505.
4 R. Naylor, J. Chem. Soc., 1945, 244.
5 N. A. Milas and D. M. Surgenov, J. Am. Chem. Soc., 1946, 68, 642.
6 L. A. Singer, Organic Peroxides, ed. D. Swern, Wiley-Interscience,
New York, 1970, vol. 1, p. 271.
7 S. Baj and A. Chrobok, J. Liq. Chromatogr., 2000, 23, 551.
1
8 H NMR and 13C NMR spectra were recorded at 300 MHz in
CDCl3 (Varian Unity Inova plus, internal TMS). Mass spectra (ESI
MS and EI MS) were recorded on a Mariner mass spectrometer
(PerSeptive Biosystems). Elemental analyses were obtained on
Perkin-Elmer analyser. HPLC was performed on a liquid chromato-
graph (Alliance, Waters 2690 system) with a Waters photodiode
array detector and cartridge column (Nova-Pak C18 4 µm); solvent
system included methanol–water (70:30, 1 cm3 minϪ1).
9 Methyl peroxybenzoate: bp 40 ЊC/0.2 mmHg; 1H NMR δ 4.14 (s,
1H), 7.41–7.95 (m, 5H); 13C NMR: δ 64.7, 126.3, 127.7, 128.2, 133.3,
163.9; EI MS: 152 (M, 6%), 136 (2), 122 (4), 105 (99), 77 (100), 51
(64). Anal. calc. for C8H8O3: C 63.16, H 5.26; found: C 63.11, H
5.20%. Active (O) calc.: 21.8; found: 20.8%.
1
Methyl peroxyoctanoate: bp 48 ЊC/0.5 mmHg; H NMR : δ 0.88
(t, J = 7.6 Hz, 3H), 1.30 (m, 8H), 1.66 (q, J = 7.3 Hz, 2H), 2.29 (t,
J = 7.8 Hz, 2H), 4.13 (s, 3H); 13C NMR: δ 13.9, 22.5, 24.6, 28.7, 28.9,
30.4, 31.5, 64.0, 170.1; ESI MS: 175 (MHϩ), 197 (MNaϩ). Anal.
calc. for C9H18O3: C 62.07, H 10.34; found: C 62.00, H 10.20%.
Active (O) calc.: 18.4; found: 18.2%.
Experimental
1
Ethyl peroxybenzoate: H NMR: δ 1.39 (t, J = 7.8 Hz, 3H), 4.41
(q, J = 7.4 Hz, 2H), 7.42–7.96 (m, 5H); 13C NMR: δ 12.9, 72.5, 127.2,
128.5, 129.3, 133.4, 164.2. Anal. calc. for C9H10O3: C 65.06, H 6.02;
found: C 64.88, H 5.89%. Active (O) calc.: 19.2; found: 18.6%.
Into a thermostated three-necked 100 cm3 flask, equipped with
a mechanical stirrer, a solution of peroxyacid (10 mmol) dis-
solved in toluene (30 cm3), tetra-n-butylammonium hydrogen
sulfate (0.2 mmol) and solid NaOH (15 mmol) were introduced
at Ϫ20 ЊC. After stirring for 10 min at this temperature, a
solution of alkylating agent (15 mmol) in toluene (20 cm3) was
added dropwise under nitrogen. Reactions with trialkyloxo-
nium salts as alkylating agents (15 mmol) were carried out in
methylene chloride (50 cm3) and in the presence of solid K2CO3
(30 mmol). After stirring for up to 5 h (in the case of the
butyl peroxybenzoate synthesis the reaction time was 40 h)
at Ϫ20 ЊC the reaction mixture was washed with a solution
of H2O and saturated Na2CO3. The reaction progress was
followed by HPLC.7,8 The organic phase was dried over
magnesium sulfate and evaporated to dryness; the residue was
chromatographed (benzene–acetone, 7:1) to afford the alkyl
peroxyesters.
1
Ethyl peroxycaprylate: H NMR: δ 0.88 (t, J = 7.6 Hz, 3H), 1.29
(m, 11H), 1.67 (quintet, J = 7.3 Hz, 2H), 1.29 (t, J = 7.8 Hz, 2H),
4.27 (quintet, J = 7.4 Hz, 2H); 13C NMR: δ 12.8, 13.7, 22.3, 24.6,
28.6, 28.7, 30.8, 31.3, 72.0, 170.7. Anal. calc. for C10H20O3: C 63.83,
H 10.64%; found: C 63.77, H 10.55%. Active (O) calc.: 17.0; found:
16.0%.
1
Butyl peroxybenzoate: H NMR: δ 0.98 (t, J = 7.6 Hz, 2H), 1.46
(s, J = 7.2 Hz, 2H), 1.72 (quintet, J = 7.3 Hz, 2H), 4.53 (t, J= 7.6,
2H), 7.39–8.06 (m, 5H); 13C NMR: δ 13.6, 19.2, 31.0, 70.28, 128.2,
128.3, 129.4, 132.7, 166.4. Anal. calc. for C11H14O3: C 68.04, H
7.22%; found: C 67.79, H 7.10%. Active (O) calc.: 16.5; found:
15.6%.
10 (a) J. M. Kolthof and A. J. Medalia, J. Am. Chem. Soc., 1949, 71, 22;
(b) J. Zawadiak, D. Gilner, Z. Kulicki and S. Baj, Analyst, 1993, 118,
1081; (c) P. D. Bartlett and R. R. Hiatt, J. Am. Chem. Soc., 1958, 80,
1398.
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J. Chem. Soc., Perkin Trans. 1, 2000, 2575–2576