Angewandte
Chemie
Keywords: alcohols · green chemistry · homogeneous catalysis ·
.
phosphoric acid monoesters · rhenium
[1] a) T. F. Tadros, Applied Surfactants: Principles and Applications,
Wiley,Weinheim, 2005; b) A. D. F. Toy,E. N. Walsh, Phosphorus
Chemistry in Everyday Living,2nd ed.,American Chemical
Society,Washington,DC, 1987.
[2] For reviews of the synthesis of phosphoric acid esters,see: a) Y.
Hayakawa in Comprehensive Organic Synthesis, Vol. 6 (Eds.:
B. M. Trost,I. Fleming,E. Winterfeldt),Pergamon,Oxford,
1991,pp. 601 – 630; b) C. B. Reese, Org. Biomol. Chem. 2005, 3,
3851 – 3868.
[3] A. Matsunaga,A. Fujiu,S. Tsuyutani,T. Nozaki,M. Ueda,PCT
International Application WO 96/17852, 1996.
[4] M. Sprecher,R. Breslow,R. Philosof-Oppenheimer,E. Chavet,
Tetrahedron 1999, 55,5465 – 5482.
Scheme 1. Proposed mechanism for the dehydrative condensation of
phosphoric acid with alcohols catalyzed by perrhenic acid.
[5] P. T. Anastas,J. C. Warner, Green Chemistry: Theory and
Practice,Oxford University Press,Oxford, 1998.
[6] J. Otera, Esterification,Wiley,Weinheim, 2003.
phosphoric acid (pKa1 = 2.1),[21] nucleophilic substitution of 3
by alcohols occurs preferentially at the phosphorus atom to
produce the phosphoric acid monoester 4. Phosphoric acid
mono- and diesters are stronger acids than phosphoric acid
itself. For example,the p Ka values of MeOPO(OH)2 and
(MeO)2PO(OH) are 1.54 and 1.29,respectively. Therefore,
the nucleophilic substitution of 1 or 2 with phosphoric acid
monoester 4 should be slower than with phosphoric acid.
Thus,phosphoric acid monoesters are selectively produced by
the present condensation. Alternatively,the active species 3
might react with phosphoric acid to produce pyrophosphoric
acid (5),which could easily react with alcohols to give 4.[22]
In conclusion,we have achieved the direct catalytic
condensation of phosphoric acid with an equimolar amount
of an alcohol and have synthesized several useful phosphoric
acid monoesters. This catalytic condensation can be readily
applied to large-scale processes with high efficiency. The
present method should be useful for the environmentally and
industrially important synthesis of phosphoric acid mono-
esters. Studies on the recyclability of the catalyst using
oxorhenium(VII) complexes immobilized on secondary
amine resins are in progress.
[7] For our recent contributions to catalytic direct condensations of
carboxylic acids,see: a) K. Ishihara,S. Ohara,H. Yamamoto, J.
Org. Chem. 1996, 61,4196 – 4197; b) K. Ishihara,S. Ohara,H.
Yamamoto, Science 2000, 290,1140 – 1142; c) K. Ishihara,S.
Nakagawa,A. Sakakura, J. Am. Chem. Soc. 2005, 127,4168 –
4169; d) A. Sakakura,S. Nakagawa,K. Ishihara, Tetrahedron
2006, 62,422 – 433.
[8] We have reported that nucleophilic bases such as N-butylimida-
zole promote the condensation of phosphoric acid and alcohols
in the presence of tributylamine. However,the catalytic
activities of the nucleophilic bases were such that 2 equiv of
phosphoric acid and 2 equiv of tributylamine were needed to
give phosphoric acid monoesters in good yield: A. Sakakura,M.
Katsukawa,K. Ishihara, Org. Lett. 2005, 7,1999 – 2002.
[9] Honjo and coworkers have reported the condensation of
phosphoric acid with 2’,3’-O-isopropylidene ribonucleosides in
the presence of tributylamine. In this work,a large excess of
phosphoric acid (5 equiv) and tributylamine (10 equiv) was
required. The reactions were conducted at reflux in DMF (b.p.
1538C),and the yields were low (38–58%). Since DMF
decomposes gradually at its boiling point,the obtained crude
products must be highly contaminated with impurities produced
by the decomposition of DMF: M. Honjo,Y. Furukawa,K.
Kobayashi, Chem. Pharm. Bull. 1966, 14,1061 – 1065.
[10] The esterification of monosubstituted phosphonic acids has been
reported. Monosubstituted phosphonic acids are less acidic than
phosphoric acid: Y. R. Dumond,R. L. Baker,J.-L. Montchamp,
Org. Lett. 2000, 2,3341 – 3344.
[11] For a review of oxorhenium(VII) complexes,see: a) C. C.
Experimental Section
Rom¼o,F. E. Kühn,W. A. Herrmann,
Chem. Rev. 1997, 97,
In a typical procedure (Table 2),a 30-mL single-necked round-
bottomed flask containing a Teflon-coated magnetic stirring bar and
equipped with a 5-mL pressure-equalized addition funnel containing
a cotton plug and about 2 g of 4 molecular sieves (pellets) and a
reflux condenser was charged with phosphoric acid (2.2 mmol),the
alcohol (2.0 mmol),dibutylamine (0.4 mmol),and a 65–75 wt%
aqueous solution of perrhenic acid (3.5 mL,ca. 1 mol%) in NMP/ o-
xylene (1:1,10 mL). The mixture was heated for 12 h under
azeotropic reflux with the removal of water. After the reaction
mixture had cooled to ambient temperature the solvents were
removed under vacuum. The resulting crude product was purified
on an ion-exchange resin (DOWEX 50WX2-200) to give the
corresponding phosphoric acid monoester. The small excess of
phosphoric acid could be removed by ion-exchange purification.
3197 – 3246; b) G. S. Owens,J. Arias,M. M. Abu-Omar, Catal.
Today 2000, 55,317 – 363; c) F. E. Kühn,A. Scherbaum,W. A.
Herrmann, J. Organomet. Chem. 2004, 689,4149 – 4164.
[12] For recent studies on catalysis by oxorhenium(VII) complexes,
see: a) C. Morrill,R. H. Grubbs, J. Am. Chem. Soc. 2005, 127,
2842 – 2843; b) P. Paraskevopoulou,N. Psaroudakis,S. Koinis,P.
Stavropoulos,K. Mertis, J. Mol. Catal. A 2005, 240,27 – 32;
c) F. E. Kühn,A. M. Santos,W. A. Herrmann, Dalton Trans.
2005,2483 – 2491; d) B. Royo,C. C. Rom¼o, J. Mol. Catal. A
2005, 236,107 – 112; e) F. M. Pedro,S. Hirner,F. E. Kühn,
Tetrahedron Lett. 2005, 46,7777 – 7779.
[13] J. Emsley, The Elements,3rd ed.,Clarendon,Oxford,
1998,
pp. 172 – 173.
[14] K. Ishihara,Y. Furuya,H. Yamamoto, Angew. Chem. 2002, 114,
3109 – 3112; Angew. Chem. Int. Ed. 2002, 41,2983 – 2986.
[15] A. Sakakura,R. Kondo,K. Ishihara, Org. Lett. 2005, 7,1971 –
1974.
Received: October 23,2006
Published online: January 17,2007
Angew. Chem. Int. Ed. 2007, 46, 1423 –1426
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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