Reduction of Phosphorus Trifluoride & Phosphoryl Fluoride with Lithium

---- if 'j '.J I Indian Journal of Chemistry I Vol. 23A, October 1984, p. 875 ~ !

Reduction of Phosphorus Trifluoride & Phosphoryl Fluoride with Lithium Table I-Reduction of Phosphorus Trifluoride and Aluminium Hydride Phosphoryl Fluoride by Lithium AluminiumHydride. Amount of Amount (mg) of Amount (mg) of compd taken PH3 formed F - in soln R G KALBANDKERI, D K PADMA & A R VASUDEVA (mg) MURTHY· FpundFound66.3763.8563.1257.6458.4258.8062.8782.2365.5564.7638.7590.0653.6290.2142.9671.2348.0580.9637.8634.2656.9634.9139.3582.5449.0781.3572.74Calc34.8549.2338.0835.0839.5943.3948.5339.1053.81Calc Department of 116.50101.20125.60121.10164.60112.30150.60Inorganic and Physical Chemistry, 99.20107.30 LABLABreductionreductionofofPOF3PF3 Indian Institute of Science, Bangalore 560012 Received 7 May 1984; revised and accepted 5 June 1984

Phosphorus trifluoride and phosphoryl fluoride undergo reduction with lithium aluminium hydride in ether medium to produce phosphine in quantitative yield. The liberated phosphine is estimated iodometrically.

Several sulphur-fluorine compounds 1-4 and phos• phorus trichloride5 have been found to undergo reduction with lithium aluminium hydride (LAB). In order to study the nature of phosphorus-fluorine chloride solution, an excess of potassium iodide (10 g) reduction with LAH, we have presently studied the was added, the solution acidified with 2N acetic acid LAH reduction of phosphorus trifluoride and and treated with a known excess of iodine solution. phosphoryl fluoride in ether medium. The results of The excess of iodine solution was titrated against this investigation are reported in this note. standard sodium thiosulphate solution. The phos• Lithium aluminium hydride (500 mg) in ether (25 ml) phine content was then calculated. The analytical was taken in a glass trap fitted with appropriate results are presented in Table I. ground glass joints and vacuum stopcocks. The From the analytical data (Table I) it is observed that contents were frozen with liquid nitrogen and phosphorus trifluoride and phosphoryl fluoride undissolved gases were pumped out. A known amount undergo quantitative reduction by LAH in ether ('" 100~150mg) of phosphorus trifluoride or phos• medium in accordance with the Eqs(l) and (2) phoryl fluoride was introduced into the reaction vessel. respectively. The coolant was withdrawn and the reaction vesselwas 4PF 3+ 3LiAIH4-+4PH3 + 3LiF + 3AIF3 ••• (1) allowed to attain room temperature and set aside for 4POF 3+4LiAIH4 -+4PH3 +LiOH Ihr. The reactants were frozen again with liquid + AI(OH)3 + 3LiF + 3AIF3 ... (2) nitrogen and contents allowed to warm slowly to room The formation of phosphine in the above reactions is temperature and left overnight. The reaction vessel further confirmed by gas phase IR spectral study was connected to two bubblers BI and B2, BI (reported8; 2421, 2327, 1122, 992cm -I. Found: 2420, containing 20ml of 2N potassium hydroxide (to 2325, 1120, 990cm -I). remove unreacted PF3 or POF3) and B2 containing 100mi of 5% mercuric chloride solution (to absorb References phosphine formed during the reduction)6. The gaseous I Padma D K, Vasudeva Murthy A R, BecherW & MassonneJ, J product was swept off in a current of dry nitrogen Fluorine Chem, 2 (1972) 113. through the bubblers. Phosphine got absorbed into the 2 Padma D K, Subrahmanya Bhat V & Vasudeva Murthy A R, mercuric chloride solution. Indian J Chem, 19A (1980) 471; 20A (1981) 777. 3 Padma D K, Subrabmanya Bhat V & Vasudeva Murthy A R, J The excess of LAH was destroyed by the successive inorg nucl Chem, 43 (1981) 3099. addition of ethyl acetate and water. The mixture was 4 Padma D K, Vijayalakshmi S K & Vasudeva Murthy A R, J then warmed to drive off the remaining traces of Indian Inst of Sci. 59 (1977) 108. phosphine filtered and the filtrate analysed for its 5 Padcock N L, Nature, London, 167 (1951) 1070. 6 Scott W W in Standard methods of chemical analysis, edited by N fluoride content 7• H Furman (Van Nostrand, Princeton) 1962,28". After I hr, when the absorption was complete, 7 Padma D K & Vijayalakshmi S K, J Indian Inst Sci, 58(1976) 280. nitrogen stream was stopped and bubblers were 8 McConaghie V M & Nielson H H, Proc natl Acad Sci US, 34 disconnected. To the bubblers containing mercuric (1968) 455.

875