A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1936, 16, 9
DOI: 10.15227/orgsyn.016.0009
Submitted by G. R. Dutton and C. R. Noller.
Checked by John R. Johnson and Anthony Hunt.
1. Procedure
In a 2-l. round-bottomed flask, fitted with a reflux condenser, liquid-sealed mechanical stirrer, dropping funnel (Note 1), and thermometer, are placed 222 g. (274 cc., 3 moles) of dry n-butyl alcohol, 260 g. (265 cc., 3.3 moles) of pyridine, and 275 cc. of dry benzene (Note 2). The solution is stirred and the flask is cooled in an ice-salt mixture until the temperature has fallen to −5°. With efficient stirring (Note 3), 153 g. (91 cc., 1 mole) of phosphorus oxychloride (b.p. 106–107°) is added dropwise at such a rate that the temperature does not exceed 10°. After the addition is completed the reaction mixture is heated slowly to the reflux temperature and held there for two hours. The mixture is cooled to room temperature, and 400–500 cc. of water is added to dissolve the pyridine hydrochloride (Note 4). The benzene layer is separated, washed with 100–150 cc. of water (Note 5), and dried over 20 g. of anhydrous sodium sulfate.
The benzene and other low-boiling materials are removed by distillation at 40–50 mm. pressure until the temperature of the distilling vapor reaches 90°. The n-butyl phosphate fraction is collected at 160–162°/15 mm., or 143–145°/8 mm., and weighs 190–200 g. (71–75 per cent of the theoretical amount) (Note 6).
2. Notes
1. The tip of the funnel should be placed sufficiently high above the surface of the reaction mixture of avoid encrustation with pyridine hydrochloride. It is advantageous to use a thermometer on which the scale above −5° is visible above the stopper; otherwise, the fog in the flask and the pyridine salt may obscure the scale.
2. The reactants and solvent were dried by distillation; fractions boiling over an interval of 1° were used.
3. The first 10–15 cc. of phosphorus oxychloride must be added very slowly to avoid vigorous reaction and overheating. It is essential to avoid an initial temperature so low that unreacted phosphorus oxychloride accumulates and then suddenly reacts with violence. The mechanical stirrer should be of such dimensions and operated at such speeds that the heat of reaction is dissipated rapidly without throwing solid material (and occluded reactants) against the upper walls of the flask.
4. About 50 per cent of the pyridine may be recovered by concentrating this aqueous solution over a steam bath, treating with strong caustic soda solution, and distilling the pyridine layer.
5. The solution should be neutral before distillation. The presence of hydrogen chloride promotes decomposition of phosphoric esters.1 The benzene solution should not be washed with alkaline reagents, such as sodium carbonate solution, since alkaline reagents also cause decomposition during distillation.
6. This is a general method for preparing alkyl phosphates. Using a similar procedure, the n-propyl ester may be obtained in 60–65 per cent yields, the sec.-butyl ester in 40–45 per cent yields, and the n-amyl ester in 60–65 per cent yields.2
3. Discussion
n-Butyl phosphate has been prepared by the action of phosphorus pentachloride or oxychloride on butyl alcohol;3 by the action of phosphorus oxychloride on aluminum butoxide4 or sodium butoxide;5 and by the oxidation of butyl phosphite.6 The procedure described above2 is similar to one which has been used for the preparation of alkyl phosphites.7

References and Notes
  1. Balarev, Z. anorg. allgem. Chem. 101, 227 (1917).
  2. Noller and Dutton, J. Am. Chem. Soc. 55, 424 (1933).
  3. Nicolai, U. S. pat. 1,766,720 [C. A. 24, 4053 (1930)]; Celluloid Corporation, Brit. pat. 455,014 [C. A. 31, 1427 (1937)].
  4. Bannister, U. S. pat. 1,799,349 [C. A. 25, 3014 (1931)].
  5. Evans, Davies, and Jones, J. Chem. Soc. 1930, 1310.
  6. Chemische Fabrik von Heyden A.-G., Brit. pat. 398,659 [C. A. 28, 1362 (1934)]; Ger. pat. 605,174 [C. A. 31, 3066 (1937)].
  7. Milobendski and Sachnowski, Chemik Polski 15, 34 (1917) [C. A. 13, 2865 (1919)].

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

caustic soda

phosphorus pentachloride or oxychloride

n-propyl ester

sec.-butyl ester

n-amyl ester

hydrogen chloride (7647-01-0)

Benzene (71-43-2)

sodium carbonate (497-19-8)

sodium sulfate (7757-82-6)

butyl alcohol,
n-butyl alcohol (71-36-3)

Phosphorus Oxychloride (21295-50-1)

pyridine (110-86-1)

aluminum butoxide

pyridine hydrochloride (628-13-7)

sodium butoxide

butyl phosphite

n-BUTYL PHOSPHATE (12788-93-1)