Oxychloride, phosphorus

To 100 grammes of phosphorus trichloride, contained in a large tubulated retort connected with a condenser, add gradually, in small portions of about 2-3 grammes, 

32 grammes of finely pulverised potassium chlorate. After each addition, wait until the liquid bubbles up, before adding a new quantity. If, on the addition of the first portion, no reaction takes place, it is started by a gentle warming. During the addition, no liquid should distil into the receiver, but if this does happen, it is poured back into the retort. After all of the chlorate has been added, the phosphorus oxychloride formed is distilled, by heating the retort in an oil-bath, to 130°, or with a luminous flame. A suction-flask is used as a receiver this is firmly connected with the end of the condenser, by means of a cork. 

The distillate is rectified from a fractionating flask provided with a thermometer. Boiling-point, uc°. Yield, ioo-iio grammes. 

Uses/Sources. In the manufacture of pesticides, pharmaceuticals, plasticizers, gasoline additives, and hydraulic fluid 

Toxicology. Phosphorus oxychloride is strongly irritating to the skin, eyes, and respiratory tract. 

Exposure to the vapors can cause cough, painful inflammation of the eyes, burning in the nose and throat, shormess of breath, and, in severe exposures, death. Both chronic and acute cases of occupational exposures have been reported in the foreign literature.  

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for phosphorus oxychloride is 0.1 ppm (0.63 mg/m ). 

Weeks MH, Musselman NP, Yevich PP, et al Acute vapor toxicity of phosphorus oxychloride, phosphorus trichloride and methyl phos-phonic dichloride. Am Ind Hyg Assoc J 25 470-475, 1964 

Formylation of Aromatic Rings. The Vilsmeier reagent attacks electron-rich aromatic systems to form aryl-methyleneiminium ions which liberate a formylated aromatic compound upon hydrolysis (eq 2). Thio- and selenoaldehydes can be prepared by hydrolysis in the presence of Sodium Hydrogen Sulfide or Sodium Hydrogen Selenide. A wide range of aromatic systems can be formylated in this fashion, including benzene derivatives, polyaromatic hydrocarbons (eq 3), and azulene. Substitution occurs at relatively electron-rich positions. 

Formylation of Heterocycles. Many heterocycles are readily formylated by POCI3/DMF, including pyrroles, thiophenes, furans, indoles, quinolines, pteridines, and purines. Reaction at the 2- and 5-positions of pyrroles, furans, and thiophenes is preferred, and indoles undergo attack at the 3-position (eq 4).  

Solubility sol THF, MeCN, CH2CI2, many other solvents. 

Form Supplied in colorless, fuming liquid commercially available. 

Handling, Storage, and Precautions toxic and corrosive reacts vigorously with alcohols and water, liberating HCl, phosphoric acid, and heat. Protect from water. Use in a fume hood. 

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CH3)2N]3P0. M.p. 4°C, b.p. 232"C, dielectric constant 30 at 25 C. Can be prepared from dimethylamine and phosphorus oxychloride. Used as an aprotic solvent, similar to liquid ammonia in solvent power but easier to handle. Solvent for organolithium compounds, Grignard reagents and the metals lithium, sodium and potassium (the latter metals give blue solutions). 

The oxide dichloride, b.p. 351 K, is separated from the less volatile phosphorus oxychloride by a fractional distillation. 

One disadvantage of this method is that it is sometimes difficult to separate the acid chloride sharply from the phosphorus oxychloride by fractional dis tillation, and unless the boiling oints of these two substances are fairly wide apart, traces of the oxychloride will occasionally pass over in the vapour of the acid chloride. If, however, thionyl chloride is used instead of phosphorus... 

This preparation illustrates the use of phosphorus pentachloride for the preparation of acyl chlorides in this case no difficulty is experienced in separating the 3,5-dinitrobenzoyl chloride from the phosphorus oxychloride formed simultaneously (c/. p. 240), because the former is readily isolated as a crystalline... 

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. 

Method 2. Mix 1 0 g. of 3 5-dinitrobenzoic acid with 1 5 g. of phosphorus pentachloride in a small, dry test-tube. Warm the mixture gently over a small smoky fiame to start the reaction when the reaction has subsided (but not before), boil for 1-2 minutes or until the solid matter has dissolved. Pour the mixture while still liquid on a dry watch glass (CAUTION the fumes are irritating to the eyes). When the product has solidified, remove the liquid by-product (phosphorus oxychloride) by transferring the pasty mixture to a pad of several thicknesses of filter paper or to a small piece of porous tile. Spread the material until the liquid has been absorbed and the residual solid is dry. Transfer the 3 5 dinitrobenzoyl chloride to a test-tube, add 0-5-1 ml. of the alcohol, and continue as in Method 1. 

Alkyl phosphates. From phosphorus oxychloride and the alcohol in the presence of p3u-idine, for example ... 

An equivalent result may be obtained by treating excess of sodium acetate with phosphorus oxychloride acetyl chloride is an intermediate product and the final result is ... 

The phosphorus oxychloride formed in the reaction is a dehydrating agent also. 

The liquid phosphorus oxychloride, b.p. 107°, is a by-product and is removed by fractional distillation under normal pressure. Unless the b.p. of the acid chloride differs very considerably (say, <] 100°) from that of the phosphorus oxychloride, the acyl halide is liable to contain traces of the latter. In such circumstances it is preferable to use thionyl chloride for the preparation of the acid chloride. 

Alternatively a mixture of 90 g. of sodium benzenesulphonate and 60 g. (36 ml.) of phosphorus oxychloride may be used. The experimental procedure is identical with that for phosphorus pentachloride, but the yield is slightly better. 

The preparation of 4-methylcoumarin is an example of the Pechmann reaction, which consists in the interaction of a phenol with a 3-ketonic ester In the presence of a condensing agent (sulphuric acid, aluminium chloride, phosphorus oxychloride or pho.sphoric oxide) ... 

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°. 

Crystal violet is an example of a triphenylmethane dye. Its preparation in the laboratory may be illustrated by the condensation of 4 4 -tetramethyl-diaminobenzophenone (Michler s ketone) and dimethylaiiiliue in the presence of phosphorus oxychloride ... 

In a 1 htre round-bottomed flask, provided with an air condenser, place a mixture of 25 g. (26 ml.) of pure dimethylanihne, 10 g. of Michler s ketone (4 4 tetramethyldiaminobenzophenone) and 10 g. (6 ml.) of phosphorus oxychloride. Heat on a boding water bath for 5 hours. Add about 150 ml. of water and sufificient sodium hydroxide solution to render the solution alkaline. Calculate the quantity of sodium hydroxide required upon the basis of the hydrolysis product derived from the phosphorus oxychloride ... 

The reaction is again most successful with phenol and indole derivatives. Reaction con-litions are also quite mild. Phosphorus oxychloride may be used in refluxing chloroform or ligher boiling hydrocarbons. Duration of the reaction is usually less than 6 hours (T. Kameta-li, 1977 A E.E. van Tamelen, 1969). 

Alkoxy and 2-methyl derivatives of A-2-thiazoline-4-one (182) react with phosphorus oxychloride to yield the thiazolylphosphoric esters (183), which have insecticidal uses (Scheme 95) (428-430). 

Hydroxythiazoles give 2-chIorothiazole derivatives almost quantitatively upon treatment with phosphorus oxychloride (221, 229, 428). This constitutes a convenient synthesis method for these compounds when the conversion of 2-aminothiazoles to 2-chlorothiazole derivatives fails. Esters of thiocarbamic acid or thiourethanes also react with a-halocarbonyl compounds to give the corresponding 2-alkoxythiazoles (50, 68, 209, 272). 

Thiazole carboxamides are readily dehydrated to nitriles in good yields by heating with phosphorus oxychloride (91), phosphorus pentoxide (87, 71), or phosphoryl chloride (16) (Scheme 19). 

Treatment of thiazole-4,5-dicarboxamides (26) with phosphorus oxychloride in the presence of pyridine afforded 4,5-dicyanOthiazoles (27) (Scheme 20) (91). 

Phosphorus oxychloride content and impurities are determined by gas chromatography analyses. 

Treatment of pyridazine 1-oxides with phosphorus oxychloride results in a-chlorination with respect to the N-oxide group, with simultaneous deoxygenation. When the a-position is blocked, substitution occurs at the y-position. 3-Methoxypyridazine 1-oxide, for example, is converted into 6-chloro-3-methoxypyridazine and 3,6-dimethylpyridazine 1-oxide into 4-chloro-3,6-dimethylpyridazine. 

The second most important nucleophilic substitution in pyridazine A-oxides is the replacement of a nitro group. Nitro groups at the 3-, 4-, 5- and 6-position are easily substituted thermally with a chlorine or bromine atom, using acetyl chloride or hydrobromic acid respectively. Phosphorus oxychloride and benzoyl chloride are used less frequently for this purpose. Nitro groups in nitropyridazine A-oxides are easily replaced by alkoxide. The... 

Pyridazinecarboxamides are prepared from the corresponding esters or acid chlorides with ammonia or amines or by partial hydrolysis of cyanopyridazines. Pyridazinecarboxamides with a variety of substituents are easily dehydrated to nitriles with phosphorus oxychloride and are converted into the corresponding acids by acid or alkaline hydrolysis. They undergo Hofmann degradation to give the corresponding amines, while in the case of two ortho carboxamide groups pyrimidopyridazines are formed. 

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