IODINE.143 PHOSPHORUS PENTOXIDE

Phenyl isothiocyanate has been prepared from thiocarbanilide by the action of phosphorus pentoxide, hydrochloric acid, iodine, phosphoric acid, acetic anhydride, and nitrous acid. It has also been prepared from ammonium phenyl dithiocarbamate by the action of ethyl chlorocarbonate, copper sulfate lead carbonate, lead nitrate, ferrous sulfate,and zinc sulfate. ... 

When distilled with phosphorus pentoxide, camphor yields cymene, and with iodine, carvacrol. Both of these bodies are para-derivatives of benzene. On oxidation with nitric acid camphor yields many acids, of which the chief are camphoric acid, CjgHjgO, camphanic acid, CjoHj O, and camphoronic acid, CgHj Og. The constitution of these acids has an important bearing on that of camphor. Many formulae have been suggested for camphor during the past few years, but that of Bredt is now universally accepted, and has received complete confirmation by Komppa s synthesis of camphoric acid. This synthesis confirms the formula for camphoric acid as—... 

The compounds may have either the formula H3PO4 (m.p., 40°) or 2H3P04-H20 (m.p., 30°). In a round-bottomed flask of suitable size, place 1 part of white phosphorus and 16 parts of nitric acid of sp. gr. 1.2 together with a few crystals of iodine as a catalyzer. Provide the flask with a reflux condenser, painting the cork with black asphalt paint to protect it from the action of the nitric acid. Heat until all of the phosphorus has dissolved then distill off most of the liquid and pour the residue into an open dish. Evaporate with several additions of concentrated nitric acid to oxidize all lower acids of phosphorus and finally concentrate in a platinum dish until the temperature of the solution reaches 150°. On cooling, if necessary with a freezing mixture, the liquid can be brought to crystallization. The crystals should be dried over phosphorus pentoxide... 

Methylpropene can be removed from the reaction mixture by distillation and easily is made the principal product by appropriate adjustment of the reaction conditions. If the 2-methylpropene is not removed as it is formed, polymer and oxidation products become important. Sulfuric acid often is an unduly strenuous reagent for dehydration of tertiary alcohols. Potassium hydrogen sulfate, copper sulfate, iodine, phosphoric acid, or phosphorus pentoxide may give better results by causing less polymerization and less oxidative degradation which, with sulfuric acid, results in the formation of sulfur dioxide. 

The thiocyanogen solution is standardized by treating with an excess of potassium iodide and titrating the liberated iodine with standard sodium thiosulfate. The burette containing the halogenoid solution is protected against moisture by a tube containing calcium chloride or phosphorus pentoxide. 

Assay Dissolve about 400 mg of sample, previously dried over phosphorus pentoxide for 24 h and accurately weighed, in a mixture of 100 mL of water, recently boiled and cooled, and 25 mL of 2 N sulfuric acid, and titrate with 0.1 N iodine, adding starch TS near the endpoint. Each milliliter of 0.1 N iodine is equivalent to 9.905 mg of C6H7NaOg. 

Acylation of aromatic ethers yields the corresponding keto ethers. Typical examples are found in the conversion of anisole with aluminum chloride and appropriate acyl halide to p-methoxybutyrophenone (85%) and p-methoxyphenyl benzyl ketone (84%). Mild catalysts like iodine and phosphorus pentoxide are also effective. 

Cymene is found in thyme oil, eucalyptus oil, and Roman cummin oil. It is also obtained by heating camphor with phosphorus pentoxide and from turpentine by reduction with iodine. 

In addition to the methods of preparation given in connection with the procedure for the acetylation of thiophene with acetyl chloride in the presence of stannic chloride, 2-acetothienone has been prepared from thiophene and either acetyl chloride or acetic anhydride in the presence of iodine, hydriodic acid, silica-metal oxides, zinc chloride, or inorganic oxyacids. It has also been prepared from thiophene and acetic acid in the presence of hydrogen fluoride or phosphorus pentoxide. The acylation in the presence of phosphorus pentoxide is particularly useful with higher aliphatic acids. ... 

Dehydration Alumina (see also Dihydropyrane, preparation). Boric acid. Boron triSuoride. N-Bromoacetamide-Pyridine-SOj. Dicyclohexylcarbodiimide. Diketene. Dimethylform-amide-Thionyl chloride. Dimethyl sulfoxide. Ethylene chlorophosphite. Florisil. Girard s reagent. Hydrobromic acid. Iodine. Mesyl chloride-Sulfur dioxide. Methyl chlorosulfite. Methylketene diethylacetal. Naphthalene-d-sulfonic acid. Oxalic acid. Phenyl isocyanate. Phosgene. Phosphorus pentoxide. Phosphoryl chloride. Phthalic anhydride. Potassium bisulfate. Pyridine. Thionyi chloride. Thoria. p-Toluenesulfonic acid. p-Toluenesulfonyl chloride. Triphenylphosphine dibromide. 

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