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U.M.R. Kunda et al. / Chinese Chemical Letters 22 (2011) 895–898
versatile catalyst for performing the various functional group transformations and in the general organic synthesis
[10].
We now report a relatively simple synthesis of alkyl phosphonates in good yields using amberlyst-15 as an efficient
and environmentally benign catalyst under solvent-free conditions.
1. Experimental
A mixture of propyl bromide 1a (0.365 mL, 0.004 mol) and triethyl phosphite 2 (0.68 mL, 0.004 mol) and catalytic
amount (0.1 g) of amberlyst-15 was taken in 25 mL round bottomed flask and stirred at room temperature for about
one hour. The reaction was monitored by TLC. After completion of the reaction, the reaction mixture was extracted
with acetone to separate the catalyst and reused for another reaction after 3 to 4 washings with acetone. The solvent
was separated from the filtrate by rotaevaporator. The resulting product was purified by column chromatography on
silica gel (100–200 mesh) using petroleum ether and ethyl acetate in 7:3 ratio as eluent to afford pure alkyl
phosphonate 3a. The other compounds 3b–j were prepared by this procedure (Scheme 1).
Diethyl propyl phosphonate (3a): Semi solid, IR (KBr) cmꢁ1: 1243 (P O, phosphonate), 735 (P–C aliphatic); 1H
NMR (CDCl3): d 3.29–3.41 (m, 4H, 2 ꢂ O–CH2), 1.69–1.78 (m, 2H, P–CH2), 1.52–1.58 (m, 2H), 1.35 (t, 6H,
J = 6.9 Hz, 2 ꢂ O–CH2CH3), 1.05 (t, 3H, J = 7.7 Hz); 13C NMR (CDCl3): d 65.2 (OCH2CH3), 46.4 (P–CH2–), 23.8 (–
CH2–), 19.6 (OCH2CH3), 13.8(–CH3); 31P NMR (DMSO-d6): d 1.54 (P O); LC–MS m/z: 180(Mꢃ+, 100%); anal.
calcd. for C7H17O3P:C, 46.66; H, 9.51; found C, 46.56; H, 9.49.
Dipheyl propyl phosphonate (3b): Semi solid, IR (KBr) cmꢁ1: 1240 (P O, phosphonate), 755 (P–C aliphatic); 1H
NMR (CDCl3): d 6.77–7.35 (m, 10H, Ar–H), 1.76–1.83 (m, 2H, P–CH2), 1.67–1.69 (m, 2H), 1.01 (t, J = 7.2 Hz, 3H);
13C NMR (CDCl3): d 149.22 (C-1 and 10), 120.36 (C-2 and 20), 129.17 (C-3 and 30), 119.6 (C-4 and 40), 129.87 (C-5
and 50), 125.62 (C-6 and 60), 34.2 (P–CH2–), 25.81(–CH2), 11.94 (–CH3); 31P NMR (DMSO-d6): d 1.98 (P O); anal.
calcd. for C15H17O3P:C, 65.21; H, 6.20; found C, 65.14; H, 6.12.
Diethyl sec. butyl phosphonate (3c): Semi solid, IR (KBr) cmꢁ1: 1232 (P O, phosphonate), 729 (P–C aliphatic); 1H
NMR (CDCl3): d 4.06–4.19 (m, 4H, 2 ꢂ O–CH2), 1.79–1.88 (m, 1H, P–CH), 1.68 (d, 3H, J = 4.0 Hz), 1.33–1.41 (m,
2H), 1.33 (t, 6H, J = 6.8 Hz, 2 ꢂ O–CH2CH3), 1.04 (t, 3H, J = 7.6 Hz); 13C NMR (CDCl3): d 61.8 (OCH2CH3), 44.0
(P–CH2–), 25.8 (–CH2–), 17.8 (–CH2–), 19.1 (OCH2CH3), 11.9(–CH3); 31P NMR (DMSO-d6): d 1.64 (P O); LC–MS
m/z: 194(Mꢃ+, 100%); anal. calcd. for C8H19O3P:C, 49.48; H, 9.86; found C, 49.42; H, 9.81.
Dipheyl sec. butyl phosphonate (3d): Semi solid, IR (KBr) cmꢁ1: 1244 (P O, phosphonate), 757 (P–C aliphatic);
1H NMR (CDCl3): d 6.79–7.36 (m, 10H, Ar–H), 1.81–1.90 (m, 2H, P–CH2), 1.54–1.62 (m, 2H), 1.41–1.50 (m, 2H),
1.19 (t, 3H, J = 7.5 Hz); 31P NMR (DMSO-d6): d 2.04 (P O); LC–MS m/z: 290 (Mꢃ+, 100%); anal. calcd. for
C16H19O3P:C, 66.20; H, 6.60; found C, 65.97; H, 6.56.
2. Results and discussion
The conventional method of this two component one pot reaction requires high temperatures and long reaction
times to afford the corresponding phosphonates. A new method is developed for the preparation of alkyl phosphonates
from a mixture of alkyl halide and trialkyl/aryl phosphonates in the presence of amberlyst-15 as catalyst at room
temperature under solvent free conditions.
Reaction of a mixture of alkyl halide and triethyl phosphite, triphenyl phosphite in the presence amberlyst-15 under
solvent free condition at room temperature afforded the desired phosphonates in high yields after a reaction time of
about 20–40 min. The progress of the reaction was followed by analysis of the reaction mixture by TLC on silica gel
using hexane and ethyl acetate (3:1 v/v) at different time intervals. After completion of the reaction the catalyst can be
separated simply by filtration and reused for another 4 to 5 times without losing its activity [11].
[()TD$FIG]
O
P
OR
1
Amberlyst-15
R
R
Br
P(OR )
+
1 3
neat, rt
OR
20-40 min.
1
(1a-j)
(2)
(3a-j)
Scheme 1. Neat synthetic rout of alkyl/aryl/heterocyclic phosphonates.