Microwave-assisted esterification of phosphinic acids by alcohols, phenols, and alkyl halogenides

Article abstract of DOI:10.1080/10426507.2010.499550

Cyclic phosphinic acids undergo direct esterification with alcohols at ca. 200°C under microwave conditions. Copyright Taylor & Francis Group, LLC.

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Microwave-Assisted Esterification of
Phosphinic Acids by Alcohols, Phenols,
and Alkyl Halogenides
György Keglevich a , Nóra Zs. Kiss a , Erika Bálint a , Erzsébet
Jablonkai a , Alajos Grün a , Mátyás Milen a , Dávid Frigyes b & István
Greiner c
a Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Budapest, Hungary
b Laboratory of Physical Organometallic Chemistry, Institute of
Chemistry, Eötvös University, Budapest, Hungary
c Richter Plc, Budapest, Hungary
Published online: 25 Apr 2011.
To cite this article: György Keglevich , Nóra Zs. Kiss , Erika Bálint , Erzsébet Jablonkai , Alajos Grün ,
Mátyás Milen , Dávid Frigyes & István Greiner (2011) Microwave-Assisted Esterification of Phosphinic
Acids by Alcohols, Phenols, and Alkyl Halogenides, Phosphorus, Sulfur, and Silicon and the Related
Elements, 186:4, 802-803, DOI: 10.1080/10426507.2010.499550
To link to this article: http://dx.doi.org/10.1080/10426507.2010.499550
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Phosphorus, Sulfur, and Silicon, 186:802–803, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.499550
MICROWAVE-ASSISTED ESTERIFICATION OF
PHOSPHINIC ACIDS BY ALCOHOLS, PHENOLS,
AND ALKYL HALOGENIDES
Gyo¨rgy Keglevich,1 No´ra Zs. Kiss,1 Erika Ba´lint,1 Erzse´bet
Jablonkai,1 Alajos Gru¨n,1 Ma´tya´s Milen,1
Da´vid Frigyes,2 and Istva´n Greiner3
1Department of Organic Chemistry and Technology, Budapest University
of Technology and Economics, Budapest, Hungary
2Laboratory of Physical Organometallic Chemistry, Institute of Chemistry,
Eo¨tvo¨s University, Budapest, Hungary
3Richter Plc, Budapest, Hungary
Abstract Cyclic phosphinic acids undergo direct esterification with alcohols at ca. 200◦C
under microwave conditions.
Keywords Esterification; green chemistry; microwave; phase transfer catalysis; P-
heterocycles; phosphinic acid
Phosphinic acids do not undergo direct esterification; for this, phosphinates are usually pre-
pared by the reaction of phosphinic chlorides with alcohols. We have found that phenylphos-
phinic acid could be esterified with butanol under microwave (MW) irradiation at 180◦C
to give PhP(O)H(OBu) in 90% yield.1 The MW-assisted direct esterification could be ex-
tended to 1-hydroxy-3-phospholene 1-oxides (1), 1-hydroxy-phospholane 1-oxides (3), and
a 1-hydroxy-1,2,3,4,5,6-hexahydrophosphinine 1-oxide (5) to afford cyclic phosphinates
2, 4, and 6, respectively. Using an excess of butanol or propanol at 180–230◦C, the best
yields amounted to ca. 60% (Scheme 1).
The cyclic phosphinates (2,2 4, and 6) could also be prepared by alkylating esterifi-
cation of the cyclic phosphinic acids (1,2 3, and 5) under MW conditions at 100–120◦C. It
was found that using alkyl halogenides of normal reactivity (e.g., EtI, PrBr, and BuBr), the
presence of triethylbenzylammonium chloride (TEBAC) as the phase transfer catalyst was
synergetic with the MW irradiation. At the same time, applying benzyl chloride, that is, of
increased reactivity, MW irradiation was beneficial without the use of TEBAC (Scheme 1).
It was found that 1-hydroxy-3-phospholene oxides 1 were more reactive than the
phospholane- and the hexahydrophosphinine derivatives (3 and 5, respectively). The reason
for this may be because in the case of a fully saturated ring moiety, both the nucleophilicity
of the P O group and the acidity of the P(O)OH function are decreased.
Received 1 June 2010; accepted 1 June 2010.
Support from the Hungarian Scientific Research Fund (OTKA No. K067679, K83118) is acknowledged.
Address correspondence to Gyo¨rgy Keglevich, Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Budapest, Hungary. E-mail: gkeglevich@mail.bme.hu
802

PHOSPHINIC ACIDS ESTERIFICATION
803
MW
100°C
MW
180–230°C
R2OH
R1
O
Me
R1
O
Me
OH
R1
O
Me
TEBAC
R2X
P
P
P
K2CO3
OR2
OR2
R2 = Bu, Pr
R2 = Bn, Bu, Pr, Et
2
1
2
R1 = H, Me
MW
120°C
TEBAC
BuBr
MW
220°C
BuOH
R1
O
Me
R1
O
Me
OH
R1
O
Me
P
P
P
K2CO3
OBu
OBu
4
3
4
R1 = H, Me
MW
120°C
TEBAC
BuBr
MW
220°C
BuOH
Me
Me
Me
P
P
P
K2CO3
OBu
OH
OBu
O
O
O
6
5
6
Scheme 1
Using phenol derivatives as the reactant in MW-assisted esterification of hydroxy-
phospholene oxide 1 (R1 = Me), the desired ester (7) was formed only in a small quantity
(≤3%); adduct 8 and adduct-ester 9 were also present in the reaction mixture (Scheme 2).
Y
Y
OH
Y
Me
OH
MW
200°C
Me
O
O
Me
Me
+
+
+
P
P
P
P
O
O
O
O
OH
O
O
1 (R1 = H)
Y
Y
Y = H, Me, Cl
7
9
8
Scheme 2
Further studies to explore the possibilities offered by the above reactions are in
progress.
REFERENCES
1. Kiss, N. Zs.; Luda´nyi, K.; Drahos, L.; Keglevich, G. Synth. Commun. 2009, 39, 2392–2404.
2. Ba´lint, E.; Jablonkai, E.; Ba´lint, M.; Keglevich, G. Heteroat. Chem. 2010, 21, 211–214.