May dithiophosphoric acid participate in the set process?

Article abstract of DOI:10.1080/10426500212210

Recently we have developed a convenient method for the synthesis of S-thioacyl dithiophosphates 1, excellent thioacylating reagents. When hydroxylamines with one bulky group or two substituents on the nitrogen atom are treated with S-thioacyl dithiophosph

Full text of DOI:10.1080/10426500212210

This article was downloaded by: [Universitat Politècnica de València]
On: 23 October 2014, At: 16:50
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and the Related
Elements
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gpss20
May Dithiophosphoric Acid Participate in the SET
Process?
Leszek Doszczak a , Witold Przychodzen a , Dariusz Witt a & Janusz Rachon a
a Department of Organic Chemistry, Chemical Faculty , Technical University of Gdańsk ,
Gdańsk, Poland
Published online: 27 Oct 2010.
To cite this article: Leszek Doszczak , Witold Przychodzen , Dariusz Witt & Janusz Rachon (2002) May Dithiophosphoric
Acid Participate in the SET Process?, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:6-7, 1851-1854, DOI:
10.1080/10426500212210
To link to this article: http://dx.doi.org/10.1080/10426500212210
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Phosphorus, Sulfur and Silicon, 2002, Vol. 177:1851–1854
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290093225
MAY DITHIOPHOSPHORIC ACID PARTICIPATE
IN THE SET PROCESS?
Leszek Doszczak, Witold Przychodzen, Dariusz Witt,
and Janusz Rachon
Department of Organic Chemistry, Chemical Faculty, Technical
University of Gdan´sk, Gdan´sk, Poland
(Received July 29, 2001; accepted December 25, 2001)
Recently we have developed a convenient method for the synthesis of
S-thioacyl dithiophosphates 1, excellent thioacylating reagents. When
hydroxylamines with one bulky group or two substituents on the ni-
trogen atom are treated with S-thioacyl dithiophosphates 1 O-thioacyl
hydroxylamines 3 are produced exclusively. What is more important,
compounds 3 undergo interesting reaction with dithiophosphoric acid 4
yielding amine and acyl thiophosphoryl disulfide 5. The disulfide 5 can
be formed as a product of thiophilic attack of the dithiophosphate anion
on the thiocarbonyl group in protonated O-thioacyl hydroxylamine 3.
On the other hand, it is well known that dithiophosphate anions easily
undergo one electron oxidation. Hence the dithiophosphate anion can
act as single electron donor and disulfide 5 can be formed as a product
of the SET reaction. The influence of light and radical traps strongly
suggests that the second possibility operates in the reaction in focus.
Keywords: Hydroxylamines; SET; thioacylation; thiohydroxamic acids
We have recently discovered that easily available S-thioacyl dithiophos-
phates 1 are excellent thioacylating agents. Mixed anhydrides of type
1 chemoselectively thioacylate nitrogen or sulfur nucleophiles in the
presence of hydroxyl groups. This property allowed us to obtain hy-
droxythioamides, hydroxydithioesters, or thioxydroxamic acids as well,
from substrates nonprotected on oxygen atom.1 Particularly interest-
ing is the synthesis of thiohydroxamic acids 2 in the reaction of hy-
droxylamines with mixed anhydrides 1. Thiohydroxamic acids are a
very important class of compounds from the technological, theoretical,
We gratefully acknowledge the Polish State Committee for Scientific Research for
financial support (Grant No. 3 T09A 061 16).
Address correspondence to Janusz Rachon, Department of Organic Chemistry, Chem-
ical Faculty, Technical University of Gdan´sk, ul. Narutowicza 11/12, 80-952 Gdan´sk,
Poland. E-mail: dzknt@chem.pg.gda.pl
1851

1852
L. Doszczak et al.
SCHEME 1 Thioacylation of hydroxylamines with anhydrides 1.
and biological point of view. Thus we decided to study scope and limi-
tations of the new strategy of thioacylation. We treated the set of hy-
droxylamines with anhydrides 1, efficiently isolating thiohydroxamic
acids (see Table I, Entries 2a–l). Surprisingly, from the reaction mix-
ture composed of S-thiopivaloyl dithiophosphate 1d (R = t-Bu) and N-
isopropylhydroxylamine we were not able to isolate desired thiohy-
droxamic acid, but we obtained thiophosphoryl pivaloyl disulfide 5d
(R = t-Bu). In due course we have found that hydroxylamines with one
but bulky group on the nitrogen atom, in the reaction with hindered
S-thioacyl dithiophosphates 1, furnish O-thioacyl hydroxylamines 3,
TABLE I Thioacylation of Hydroxylamines with Anhydrides 1
Entry
R
R0
R00
Yield (%)
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
3a
3b
3c
3d
3e
3f
Ph
Ph
Ph
Pr
Pr
Pr
Pr
Me
i-Pr
CH(Me)Ph
Me
i-Pr
CH(Me)Ph
t-Bu
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
68
73
72
83
80
77
57
91
91
94
82
71
73a
96
95
71
95b
74
MeOCO(CH2)4
MeOCO(CH2)4
MeOCO(CH2)4 CH(Me)Ph
Me
i-Pr
MeOCO(CH2)4
t-Bu
Me
i-Pr
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
Ph
t-Bu
CH(Me)Ph
CH2CH2OCH2CH2
i-Pr
t-Bu
PhCO
H
aProduct not isolated, the yield estimated on isolated disulphide 5.
bThe thioacylation of hydroxamic acid required application of DBU as a
base.

Dithiophosphoric Acid in the Set Process
1853
which are stable under basic conditions and can be isolated with high
yields (Table I, Entries 3a–f). Naturally hydroxylamines possessing
two substituents on the nitrogen atom give the same results. But
what is more important, if dithiophosphoric acid 4 is present in the
reaction mixture, O-thioacylhydroxylamines 3 undergo an interest-
ing process, yielding amine and acyl O,O-dialkylthiophosphoryl disul-
fides 5 (Scheme 2). From the theoretical point of view the first step
SCHEME 2 Reaction of O-thioacyl hydroxylamines 3 with dithiophosphoric
acid 4.
SCHEME 3 Proposed mechanisms of reaction of O-thioacyl hydroxylamines
with dithiophosphoric acids.

1854
L. Doszczak et al.
(Scheme 3, Pathway A) should be the protonation of the nitrogen atom.
In the second step the nucleophilic (thiophilic) attack of dithiophosphate
anion on the sulfur atom of the thiocarbonyl group occurs. However,
dithiophosphoric acid anion easily undergoes one electron oxidation
process, hence disulfide 5 can be formed as a product of the SET reac-
tion (Scheme 3, Pathway B). In pathway B the principal process is the
single-electron transfer from dithiophosphate anion into the protonated
form of O-thioacylhydroxylamines, producing amine and acyl thioradi-
cal. The key step in the mechanism outlined in Scheme 4, Pathway B is
the formation of the disulfide anion radical as a consequence of the re-
action between the monothiocarboxyl radical and dithiophosphate an-
ion. Subsequent electron transfer from the disulfide anion radical to
O-thioacyl hydroxylamine provides chain process. How we can distin-
guish between these two mechanisms? Well, in pathway B radicals are
transient species, thus radical traps should decrease the yield of the
products. Contrary light promotes SET process and thus should influ-
ence the yield as well. Reaction proceeding with pathway A should be
insensitive to both factors. And indeed O-thioacyl hydroxylamine does
not react with dithiophosphoric acid in the darkness, and only irradia-
tion (or daylight exposure) leads to disulfide 5 formation. Consequently,
ionic mechanism (Scheme 3, Pathway A) is excluded. Also, the addition
of radical scavengers like 2,6-dimethylthiophenol prevents the forma-
tion of disulfide 5, confirming proposed SET mechanism (Scheme 3,
Pathway B). On the other hand, at this point one can also argue that
during light irradiation of O-thioacyl hydroxylamines, homolytic cleav-
age of the N O bond can lead to aminyl and monothiocarboxy radi-
cals. These radicals can initiate the radical chain process (Scheme 3,
Pathway C). However thioacylhydroxylamines are resistant to irradia-
tion under the same conditions (or even more drastic one) and no prod-
ucts of homolysis are formed. This fact makes Pathway C doubtful.
REFERENCE
[1] L. Doszczak and J. Rachon, Chem. Comm., 21, 2093 (2000).