Weygand/Hilgetag Preparative Organic Chemistry

736 Formation of carbon-phosphorus bonds
propylaluminum give a phosphonate adduct which on hydrolysis provides
diethyl ethylphosphonate in about 70% yield. 340 Alkyl phosphinites are similarly
isomerized to trialkylphosphine oxide adducts by trialkyltin halides. 342
IV. Replacement of other non-metals by phosphorus
1. Replacement of nitrogen by phosphorus
a. Replacement of nitrogen by phosphorus by means of phosphorus halides
Provided moisture is rigidly excluded, phosphorus trichloride or tribromide
and a diazoalkane at low temperatures afford ArPO(OH)2
In spite of the moderate yields (generally 20-50%), the process is of great
interest because, unlike the reaction of PC13/A1C13 with aromatic compounds
(page 711), it gives products that are free from isomers. Small amounts of
diarylphosphinic acids are formed as by-products.
General directions for the preparation of arylphosphonic acids: 343 Phosphorus trichloride
(0.2 mole) and copper© chloride (4 g) are added to a suspension of the dry arenediazonium
tetrafluoroborate (0.2 mole) in ethyl acetate (250 ml, dried over phosphorus pentaoxide)
whilst the mixture is stirred and nitrogen is led in. After initial slight evolution of heat there
is no sign of reaction for a considerable time (15 min to 2 h), then evolution of nitrogen and
rise in temperature occur suddenly; in the latter phase cooling may be necessary; occasionally
the -mixture must be warmed to 50° to induce reaction. When gas evolution ceases, water
(50 ml) is stirred in cautiously and the solvent and volatile by-products are removed by distillation
in steam. When considerable (11) distillate has collected, the residual mixture is concentrated
(to 200 ml) and filtered from the sparingly soluble phosphinic acid (sometimes this
crystallizes only after cooling.) The filtrate is then further evaporated (to about 50 ml), so
that the phosphonic acid separates on cooling. For purification this acid is dissolved in sufficient
20% sodium hydroxide solution to give pH 8, and the mixture is boiled with charcoal,
filtered, and acidified to Congo Red; this precipitates the monosodium salt.
0-Toluenediazonium tetrafluoroborate does not react, although the m- and
/7-compounds give good yields; 344 ethylbenzenediazonium salts give poor
yields. 345 Diazonium fluorosilicates may be used in place of the fluoroborates
340 M. Sander, Angew. Chem., 73, 67 (1961).
341 A. N. Pudovik and co-workers, Zh. Obshch. Khim., 33, 3350 (1963); Chem. Abstr., 60,
4175 (1964).
342 A. Ya. Yakubovich and V. A. Ginsburg, Zh. Obshch. Khim., 22, 1534 (1952); Chem.
Abstr., 47, 9254 (1953).
343 G. O.Doak and L. D. Freedman, /. Amer. Chem. Soc, 73, 5658 (1951); 74, 753
(1952); 75, 683 (1953).
344 E. C. Ashby and G. M. Kosolapoff, J. Amer. Chem. Soc, 75, 4903 (1953).
345 L. D. Freedman and G. O. Doak, /. Amer. Chem. Soc, 77, 173 (1955).