Brown phosphorus

Colour Tests. Palladium Chloride—brown Phosphorus Test— yellow. 

Colour Tests. Palladium Chloride—orange-brown Phosphorus Test—yellow. 

Colour Tests. Palladium Chloride—brown Phosphorus Test— yellow Sodium Nitroprusside (Method 2)—violet. 

Brown phosphorus has been obtained by condensing phosphorus vapour containing P molecules on to a surface at liquid nitrogen temperatures. Above 0°C it changes to a mixture of red and white. Fibrous red phosphorus is a red-brown form of phosphorus which contains tubes of pentagonal cross section (similar to those in Hittorf s variety) and all of which lie parallel to the fibre direction [39,48]. 

Assemble in a fume-cupboard the apparatus shown in Fig. 67(A). Place 15 g. of 3,5-dinitrobenzoic acid and 17 g. of phosphorus pentachloride in the flask C, and heat the mixture in an oil-bath for hours. Then reverse the condenser as shown in Fig. 67(B), but replace the calcium chloride tube by a tube leading to a water-pump, the neck of the reaction-flask C being closed with a rubber stopper. Now distil off the phosphorus oxychloride under reduced pressure by heating the flask C in an oil-bath initially at 25-30, increasing this temperature ultimately to 110°. Then cool the flask, when the crude 3,5-dinitro-benzoyl chloride will solidify to a brown crystalline mass. Yield, 16 g., i.e,y almost theoretical. Recrystallise from caibon tetrachloride. The chloride is obtained as colourless crystals, m.p. 66-68°, Yield, 13 g Further recrystallisation of small quantities can be performed using petrol (b.p. 40-60°). The chloride is stable almost indefinitely if kept in a calcium chloride desiccator. 

Place a mixture of 30 g. of 3 5-dinitrobenzoic acid (Section IV,168 and 33 g. of phosphorus pentachloride in a Claisen flask fit a reflux condenser into the short neck and cork the other neck and side arm (compare Fig. Ill, 31, 1). Heat the mixture in an oil bath at 120-130° for 75 minutes. Allow to cool. Remove the phosphorus oxychloride by distillation under reduced pressure (25°/20 mm.) raise the temperature of the bath to 110°. The residual 3 5-dinitrobenzoyl chloride solidifies on cooling to a brown mass the yield is quantitative. Recrystallise from carbon tetrachloride the yield is 25 g., m.p. 67-68° and this is satisfactory for most purposes. Further recrystallisation from a large volume of light petroleum b.p. 40-60°, gives a perfectly pure product, m.p. 69 -6°. 

The development of a brown color indicates that sufl cient phosphorus oxytrichloride has been added. If the mixture remains colorless, the final product is likely to be contaminated with unreacted iV-( -tolylsulfonylmethyl)formamide. It is therefore advantageous to add more phosphorus oxjrtrichloride and continue stirring until the brown color is obtained. 

The potassium benzenesulphonate is carefully dried on the water-bath, powdered, and mixed with the phosphorus pentachloride in a flask. A vigorous reaction sets in. When it hats abated, the flask is heated on the water-bath for one hour, and the mass occasionally stirred with a glass rod. The product is poured into a flask containing 200 c.c. cold water and allowed to stand an hour. The sulphonic chloride, which separates as an oil, is then extracted with ether, dehydrated over calcium chloride, decanted, and the ether removed on the water-bath. Yield, 10 grams of a light brown oil. 

Other oxides of phosphorus are less well characterized though the suboxide PO and the peroxide P2O6 seem to be definite compounds. PO was obtained as a brown cathodic deposit when a saturated solution of Et3NHCl in anhydrous POCI3 was electrolysed between Pt electrodes at 0°. Alternatively it can be made by the slow reaction of POBrs with Mg in Et20 under reflux ... 

H. C. Brown (Purdue) and G. Wittig (Heidelberg) for their development of boron and phosphorus compounds, respectively, into important reagents in organic synthesis. 

Herbert C. Brown and Georg Wittig development of boron (H. C. B.) and phosphorus (G. W.) compounds into important reagents in organic synthesis... 

FIGURE B.l Samples of common elements. Clockwise from the red-brown liquid bromine are the silvery liquid mercury and the solids iodine, cadmium, red phosphorus, and copper. 

Switzerland, and prepared according to a literature procedure, were used by the submitters without any noticeable difference. Lead tetraacetate was dried prior to use for at least 12 hours over potassium hydroxide and phosphorus pentoxide in an evacuated desiccator (12 mm.) that was protected from direct light. If well protected from moisture, lead tetraacetate can be kept for weeks in this way. However, after exposure to moisture in the air, lead tetraacetate usually turns brown from hydrolysis to lead hydroxide. The reactivity of such lead tetraacetate is diminished somewhat, but it can still be used. If the lead tetraacetate has turned black, the reagent should be recrystallized from glacial acetic acid and dried prior to use as described above. 

Ferrar WT, Lenhart W, Lippert J, Molaire T, Guistina R, Brown D (1989) Phosphorus Sulfur Silicon 41 147... 

After the reaction mixture has been cooled, the excess phosphorus oxychloride is distilled under reduced pressure (80-100 mm.) (0.5-1.0 hour). Near the end of the distillation the product begins to sublime into the still head. The residual dark-brown oil is poured with stirring into an 800-ml. beaker containing 280-300 g. of crushed ice (Notes 3 and 4). The volume of the ice-water mixture is brought to 600 ml. and allowed to stand at 5° overnight. The crude light-brown product is filtered by suction and washed with water. 

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