Org. Synth. 1951, 31, 33
DOI: 10.15227/orgsyn.031.0033
DIISOPROPYL METHYLPHOSPHONATE
[Phosphonic acid, methyl-, diisopropyl ester]
Submitted by A. H. Ford-Moore and B. J. Perry
1.
Checked by William S. Johnson and James Ackerman.
1. Procedure
A
2-l. round-bottomed flask containing
284 g. (113 ml., 2 moles) of methyl iodide2 is fitted with an
efficient water-cooled condenser and a
dropping funnel which is charged with
416 g. (453 ml., 2 moles) of triisopropyl phosphite (Note 1). A few pieces of porous plate are added to the
methyl iodide, and about
50 ml. of the phosphite is introduced. The mixture is heated over a gauze with a free flame until an exothermic reaction begins. The flame is then withdrawn and the remainder of the phosphite is added at such a rate that the mixture keeps boiling briskly. Towards the end of the addition it may be necessary to reapply heat. After the addition is complete, the mixture is boiled under reflux for 1 hour. The condenser is replaced by a
50–75 cm. Vigreux column attached to a
condenser set for distillation, and the bulk of the
isopropyl iodide is distilled at
85–95° (atmospheric pressure). The residue is transferred to a
pear-shaped flask for distillation through a 75-cm. Vigreux column under reduced pressure. The remainder of the
isopropyl iodide is distilled at water-pump pressure, a
Dry Ice trap being interposed between the
receiver and the pump in order to effect complete condensation. A total of
310 g. (
91%) of
isopropyl iodide is thus recovered. The residue is then fractionated at vacuum-pump pressure. Except for a small fore-run and residue, the product distils almost entirely at
51°/1.0 mm. (
46°/0.8 mm.). The yield of colorless product is
308–325 g. (
85–90%);
nD20 1.4101,
nD25 1.4081;
d424 0.985,
d410 0.997
(Note 2).
2. Notes
1.
The
triisopropyl phosphite is prepared according to the procedure for
triethyl phosphite (p. 955) and should be free from any
diisopropyl hydrogen phosphite. The latter substance does not enter into the reaction but is difficult to remove from the final product. The starting material was supplied to the submitters by Messrs. Albright, Wilson and Company, Oldbury, Birmingham, England.
2.
Diisopropyl ethylphosphonate can be obtained by a similar procedure, using the appropriate amount of
ethyl iodide in place of
methyl iodide.
Ethyl iodide is less reactive, and it is necessary to apply heat during the addition of the phosphite and to allow the mixture to reflux for 7 hours after the addition. On a 2
M scale the yield is
354 g. (
91%), b.p.
61°/0.7 mm.,
nD25 1.4108,
d425 0.968. The recovery of
isopropyl iodide is
317 g. (
93%).
Diethyl ethylphosphonate may be obtained by refluxing 332 g. (348 ml., 2 moles) of triethyl phosphite and 250 g. (1.6 moles) of ethyl iodide, for 3 hours. After distillation of 231 g. (92%) of ethyl iodide, the residue is fractionated under reduced pressure, giving 329 g. (98.5%) of product, b.p. 56°/1 mm. (58.5°/1.8 mm.); nD25 1.4141, nD20 1.4161; d425 1.022.
Diethyl methylphosphonate may be prepared similarly by refluxing one molar equivalent of triethyl phosphite with one mole of methyl iodide, but it is very difficult to separate the product from the small amount of diethyl ethylphosphonate that is formed simultaneously by the interaction of the phosphite with the ethyl iodide liberated in the reaction. The pure substance boils at 51°/1 mm., nD25 1.4117, d425 1.050.
3. Discussion
Diisopropyl methylphosphonate has been prepared from
diisopropylethyl phosphite and
methyl iodide,
3 and by treating
sodium diisopropylphosphonate with
methyl chloride.
4 The method described here for the preparation of
diisopropyl methylphosphonate is a modification of the Arbusov rearrangement.
5
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
methyl chloride (74-87-3)
Methyl iodide (74-88-4)
Ethyl iodide (75-03-6)
isopropyl iodide (75-30-9)
Diisopropyl methylphosphonate,
Phosphonic acid, methyl-, diisopropyl ester (1445-75-6)
triisopropyl phosphite (116-17-6)
phosphite
Triethyl phosphite (122-52-1)
diisopropyl hydrogen phosphite
Diisopropyl ethylphosphonate (1067-69-2)
Diethyl ethylphosphonate (78-38-6)
Diethyl methylphosphonate (683-08-9)
diisopropylethyl phosphite
sodium diisopropylphosphonate
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