In situ version of radical-chain substitution reactions

Article abstract of DOI:10.1134/S1070427207090236

Peroxy acetals derived from an ether and a hydroperoxide can be prepared in situ and used without isolation to effect sulfochlorination of n-alkanes or chlorination of toluene to benzyl chloride.

Full text of DOI:10.1134/S1070427207090236

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 9, pp. 1566 1569. Pleiades Publishing, Ltd., 2007.
Original Russian Text A.M. Kurdyukov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 9, pp. 1533 1536.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
In Situ Version of Radical-Chain Substitution Reactions
A. M. Kurdyukov
Volgograd State Technical University, Volgograd, Russia
Received April 27, 2007
Abstract Peroxy acetals derived from an ether and a hydroperoxide can be prepared in situ and used without
isolation to effect sulfochlorination of n-alkanes or chlorination of toluene to benzyl chloride.
DOI: 10.1134/S1070427207090236
The feasibility of initiated radical processes using
activators prepared in situ in the reaction volume is
obvious. The interest in such way of initiating chain
reactions is particularly pronounced in production of
polymers, e.g., of suspension PVC [1]. Acyl peroxides
prepared in a polymerizer from a hydrogen peroxide
salt and an acyl chloride in the monomer water sys-
tem are fairly effective. Peroxydicarbonates and sul-
fonyl peroxides are also used.
tert-butyl hydroperoxide (TBHP) at the -H atom
relative to the ether bond. For example, 1,1-di-tert-
butylperoxyethane (DTBPE) is rapidly formed in a
good yield at the molar ratio Et O : TBHP : SO Cl =
2
2
2
(10 5) : (3 2.3) : 1 by the reaction
CH CH O C H + 2(CH ) COOH + SO Cl
2
3
2
2
5
3 3
2
0 5 C
(
CH ) COO CH OOC(CH ) + C H OH + 2HCl
3 3 3 3 2 5
CH3
Common liquid-phase radical-chain reactions involv-
ing C H substitution, such as chlorination and sulfo-
chlorination of hydrocarbons, are performed in the
bulk of a hydrocarbon or in a nonpolar solvent. The
components of the chemical initiating system should
be readily soluble or uniformly distributed in the hy-
drocarbon (RH). The majority of organic peroxides
described in the literature are used in both polymeri-
zation and substitution reactions [2]. However, there
are virtually no data in the literature on the use of
a reaction mixture of initiator synthesis (without its
isolation) for initiating a chain substitution reaction.
In a sulfochlorinator or a chlorinator, the presence of
oxygen and water, which are frequently used compo-
nents in syntheses of peroxides, is inadmissible.
+
SO2.
There is certain evidence that the reaction occurs
via formation of the monoperoxy acetal, 1-ethoxy-1-
tert-butylperoxyethane.
High yield was attained with a 1 : (1 0.2) mixture
of Cl and SO taken instead of SO Cl . For example,
-tert-butylperoxytetrahydrofuran (TBPTHF) is pre-
pared in >90% yield on the standard equipment of
chlorine plants [3] by passing Cl and SO evaporated
from cylinders through a solution of TBHP in THF
at 5 10 C for 20 min:
2
2
2
2
2
2
2
SO
2
+ (CH ) COOH + Cl
2
OOC(CH3)3
3
3
O
O
Here we consider a version of initiator synthesis
in situ in the reaction volume, followed by an initiated
substitution reaction. As investigation objects we
chose well-known aldehyde derivatives, peroxy ace-
tals.
+
2HCl.
The procedure of synthesis of peroxy acetals fortu-
nately matches the substitution reactions with respect
to reagents, equipment, temperature, and reaction rate,
which opens real prospects for simplifying the step of
chemical initiation of chlorination and sulfochlorina-
tion of hydrocarbons. Indeed, under the conditions
typical for the formation of an alkanesulfonyl chloride
from a liquid alkane and a mixture of SO and Cl at
Of particular practical value is the procedure for
preparing mono- and diperoxy acetals from ethers and
hydroperoxides in the presence of sulfuryl chloride
SO Cl or evaporated Cl (taken separately or in a
2
2
2
2
2
mixture with SO ), described in [3]. It was demon-
2
30 35 C,
strated by numerous examples that aliphatic and cyclic
(unstrained) ethers can be vigorously oxidized with
R H + SO2 + Cl2
RSO Cl + HCl,
2
1566

IN SITU VERSION OF RADICAL-CHAIN SUBSTITUTION REACTIONS
it is absolutely unnecessary to prepare an initiator
1567
Cl , %
h
(e.g., TBPTHF, an effective sulfochlorination initiator
4]) in a separate step.
[
Before feeding the gases, it is sufficient to add
a solution of TBHP in THF to the hydrocarbon and
make sure that the initiator has formed in situ in the
sulfochlorinator and affected the parameters of the
reaction mixture.
The most important reaction parameter is the rate
of accumulation of hydrolyzable chlorine Cl after
h
Volhard. The figure shows the results of experiments
under similar conditions with TBPTHF prepared be-
forehand (curve 3) and in situ (curve 4), and also with
TBHP (curve 2). These data show that the degree of
, min
Accumulation of Cl with time in a dark vessel. (1) No
h
initiator, (2) 0.005 M TBHP, (3) 0.005 M TBPTHF, and
(4) 0.07 g of TBHP (72%) in 1.2 ml of THF ( 0.005 M per-
1
oxide in reaction mixture). Gas supply rate 0.3 g min
sulfochlorination, and also the conversion of Cl and
2
each. RH weight, g: (1, 3) 73 and (2, 4) 72.
RH (evaluated by various procedures) are higher when
the initiator is prepared in situ, compared to the sep-
arate preparation of the initiator or UV initiation [4].
with benzyl chloride, also the unchanged reactants:
toluene (63.4%) and SO Cl (23.8%). Despite consid-
2
2
The idea put forward [4] was indirectly supported
by experiments on revealing effective chemical initi-
ators of toluene chlorination with sulfuryl chloride:
erable differences in the boiling points of the mixture
components, pure benzyl chloride cannot be isolated
by single distillation; repeated distillation, desirably
with a dephlegmator, is required.
C H CH + SO Cl
C H CH Cl + SO + HCl.
6 5 2 2
6
5
3
2
2
When the peroxy acetal is prepared in the chlori-
nator in situ (run nos. 4 6), 98.7% pure (GLC data)
benzyl chloride can be readily isolated by single dis-
tillation (run no. 4).
Benzyl chloride is obtained in a high yield only in
the presence of benzoyl and lauryl peroxides and
AIBN in amounts of 0.001 0.005 mol per mole of
toluene, including experiments with 1 : 1 reactant
ratio and heating for 20 30 min [5]. Without initi-
In the suggested procedure for preparing benzyl
chloride [6], it is possible to attain almost quantitative
conversion of the reactants with 85 90% product
yield. The order of mixing the components exerts
a noticeable influence. When a solution of TBHP in
ators, toluene does not react with SO Cl even under
2
2
refluxing for 6 h. In many books, this transformation
is considered as a particular reaction: The reaction is
.
selective owing to formation of the SO Cl radical in
an ether is added to toluene before adding SO Cl , the
2
2
2
the initiation [2] and chain propagation steps. The
reaction
Yield of benzyl chloride with various initiators
.
.
Inc + SO Cl
IncCl + SO Cl
Initiator
2
2
2
Run
no.
is probable owing to fragmentation of the initially
amount
Yield, %
.
.
formed acyloxy radicals R"COO to R" , followed by
name
.
mmol* 103
g
the reaction of R" with the reagent.
The results of experiments on preparation of benzyl
chloride showed that in situ synthesis of peroxy ace-
tals in the chlorinator ensures higher yield of the final
product compared to the synthesis with the ready
initiator (52 2 C, 30 min; see table). For comparison
we used a protocol of the synthesis of benzyl chloride
by the reaction of RH with SO Cl at the molar ratio
1
2
3
4
5
AIBN, mp 103 C 0.200
1.23
1.25
2.35
1.10
4.36
68.8
Traces
50.4
71.5
88.2
92% TBHP
96% TBPTHF
0.118
0.387
TBPTHF, in situ** 0.122
The same, from 92% 0.343
TBHP
The same, from 92% 0.398
TBHP
6
5.06
77.8
2
2
of the reactants of 1 : 0.5 in the presence of AIBN [5].
Under these conditions (run no. 1), the reaction is
essentially incomplete. By distillation under reduced
pressure, we isolated from the reaction mixture, along
*
Per mole toluene. Toluene amount: 92 g in run nos. 1 4,
74 g in run nos. 5 and 6.
** From 85% TBHP.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 9 2007

1568
KURDYUKOV
product yield is always 5 10% higher than when a
solution of TBHP in an ether is added to the reactant
mixture (run no. 6, as in run no. 1).
EXPERIMENTAL
Freshly prepared peroxides with a high content of
available oxygen (O ; iodometric titration) were used.
Thus, the mechanism of the effect of peroxides
prepared in situ in the reaction vessel should not differ
from the mechanism of the effect of pure peroxides
a
In all the cases the initiator was added into the hydro-
carbon, after which the chlorinating agents were
added. The initiator concentration is given counting
on 100% purity.
(
as sources of alkoxy radicals) on the system with
predominance of RH:
Sulfochlorination of a liquid paraffin was per-
formed in a round-bottomed vessel equipped with a
bubbler for feeding gases, a stirrer, a reflux condenser,
and a thermometer. The chlorinating mixture compo-
nents, SO and Cl , were evaporated from cylinders,
dried, and fed in 1.1 : 1 ratio, using rheometers, to the
reaction mixture at 30 2 C. As alkane we used syn-
thine, TU (Technical Specification) 602-953 77, used
in production of ionic surfactants, alkanesulfonates.
.
0
.5R"OOR" + RH
R"OH + R .
The dissociation of the O O bond in mono- or
diperoxy acetals should not be considered separately
from the escape ot the resulting radicals into the bulk
of solution. It is improbable, e.g., that the tert-butoxy
radical would react with a chlorinating agent (includ-
2
2
ing SO Cl ) in the presence of RH (irrespective of
2
2
whether RH is toluene or n-alkane).
Synthine (synthetic paraffin) is a mixture of C12
The procedure suggested in [6] for preparing ben-
zyl chloride is also very selective (the content of ben-
zal chloride is as low as 0.25%), compared to chlori-
C
n-alkanes with the mean molecular weight of 198;
1
8
20
d
0.764 0.768, flash point 85 C, bp 290 65 C.
4
With TBPTHF prepared in situ from TBHP and
THF in the sulfochlorinator, the reaction mixture
nation of toluene with elemental Cl in the presence
2
of known initiators [2]. Presumably, the considerable
differences between the results obtained with different
chlorinating agents (Cl or SO Cl ) are associated
with the structure and energy of the transition state in
the chain propagation step involving these agents,
at least provided that the benzyl radical C H CH is
formed in the chain initiation step under the action of
peroxides as generators of alkoxy radicals.
parameters (figure, curve 4) after blowing-off are as
follows: d2 0.8627, nD 1.4458, Cl 5.65%, weight
0
20
4
h
2
2
2
gain 1.15 g per gram of RH. The conversion evaluated
from Cl is 100% for Cl and 34.89% for RH. In
h
2
.
experiments described by curves 1 3, the conversion
6
5
2
and weight gain were lower.
Chlorination of Toluene with Sulfuryl Chloride
in the Presence of Initiator Prepared in situ
in the Chlorinator
The initial component of the initiating system we
suggest is TBHP, one of the most readily available
organic peroxides whose commercial production is
well mastered. At 30 50 C, the O O bond in TBHP
in hydrocarbon solutions does not noticeably dissoci-
ate. Experiments (figure, curve 2; table, run no. 2)
show that straight TBHP, irrespective of purity (chem-
ically pure or technical grade), shows no promise for
intensification of radical substitution reactions. The
hydroxy derivative may react with SO Cl as acid
Synthesis of benzyl chloride using TBPTHF
prepared in situ from TBHP and THF (table, run
no. 5). A reactor equipped with a stirrer, a reflux con-
denser, and a thermometer was charged with 74.0 g
0.8 mol) of toluene [analytically pure grade, GOST
State Standard) 5789 78], after which a solution of
(
(
0
2
2
.343 g of TBHP (92% pure according to iodometric
chloride or be reduced with SO . The latter process
2
titration data) in 1.8 ml of THF was added. This
amount corresponds to 0.004359 mol of TBPTHF per
mole of toluene. Then 54.0 g (0.4 mol) of SO Cl
(
at a high SO Cl concentration) is, apparently, re-
2 2
sponsible for the low yield of the product when the
chlorination is performed in the presence of TBPTHF
2
2
20
(
bp 69 C, d4 1.667) was added. The mixture warmed
(table, run no. 3) or when the initiating system is
up to spontaneously to 37 C, and, before the tempera-
ture started to decrease, it was heated to 54 4 C and
kept at this temperature for 30 min. The resulting
mixture (89.0 g) was distilled from a Claisen flask.
The following fractions were obtained: unchanged
added to the reactants mixed beforehand (run no. 6).
Activation of the hydroperoxide with an ether or,
more precisely, use of a mixture of TBHP with an
ether for in situ preparation of a peroxy acetal (with-
out its isolation) in the reaction volume is a simple
way of effective initiation of substitution reactions.
2
0
toluene (46.7 g, bp 54 56 C/100 mm Hg, n 1.4963,
D
2
0
d
0.864) and benzyl chloride (33.1 g, bp 92 93 C/
4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 9 2007

IN SITU VERSION OF RADICAL-CHAIN SUBSTITUTION REACTIONS
1569
4
3 mm Hg, n20 1.5392, d 24 0 1.102, in agreement with
79.5% based on converted sulfuryl chloride. This is
good agreement taking into account possible loss of
D
reference data). According to GLC, the benzyl chlo-
ride was 99.35% pure (which is similar to the purity
of a commercial sample after fractional distillation
low-boiling SO Cl .
2
2
[
6]). The residue was a dark tar (1.4 g). The yield of
CONCLUSION
benzyl chloride was 88.24% (based on converted tolu-
ene, without taking into account the residue).
A mixture of tert-butyl hydroperoxide with an ali-
phatic or cyclic ether was suggested for in situ genera-
tion of peroxy acetals in a chlorinator or a sulfochlo-
rinator with the aim of effective initiation of radical-
chain C H substitution reactions in hydrocarbons.
Synthesis of benzyl chloride with DTBPE
prepared in situ from TBHP and diethyl ether.
A stirred reactor was charged in succession with
4
8
sponds to 0.00206 mol of DTBPE per mole of tolu-
ene), and 27.1 g (0.2 mol) of sulfuryl chloride. The
mixture warmed up virtually immediately, and vigor-
ous gas evolution started. Although at 52 2 C visual-
ly observed gas evolution practically ceased 15 min
after the start of the reaction, the reaction was per-
formed for 30 min. By simple distillation of the mix-
ture (55.3 g), 29.0 g (33.5 ml) of unchanged toluene
6.1 g (0.5 mol) of toluene, a solution of 0.22 g of
5% TBHP in 1.5 ml of diethyl ether (which corre-
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1
2
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4
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(bp 60 62 C/96 mm Hg) was obtained. Further dis-
2
0
. RF Patent 2231524.
tillation gave 20.1 g of a product with d 1.104, bp
7
with the reference data for pure benzyl chloride. Yield
of benzyl chloride 85% based on converted toluene or
4
1 74 C/17 18 mm Hg, n1 1.5411, which agrees
5
5. Weygand Hilgetag, Organisch-chemische Experimen-
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D
6. RF Patent 2291144.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 9 2007