Phosphorus pentachloride decomposition

B. Reactions.—This year has seen the publication of a number of papers on the reactions of olefins and acetylenes with phosphorus pentachloride, to produce new phosphorus-carbon bonds. An investigation into the structural requirements of trisubstituted olefins (40) undergoing the above reaction has shown that both steric and electronic factors are important, e.g. an adduct forms with (40 X = CH3) but no reaction occurs for (40 X = Ph). Further examples of the reactions of unsaturated ethers include the formation and decomposition of adducts from a-methoxystyrene... 

The nitrobenzene/phosphorus pentachloride mixture is stable up to 110°C. Above this temperature there is a decomposition that becomes more and more violent. Nitrogen oxides are also released in large quantities. 

This intermediate (or its ethyl homologue), produced dining the preparation of phosphoryl dichloride isocyanate from interaction of phosphorus pentachloride and methyl (or ethyl) carbamate, is unstable. Its decomposition to the required product may be violent or explosive unless moderated by presence of a halogenated solvent. 

The hot material remaining after vacuum stripping of solvent up to 130°C decomposed with evolution of gas and then exploded violently 50 min after heating had ceased. Further attempts to distil the acid chloride even in small amounts at below 1.3mbar caused exothermic decomposition at 110°C. It was, however, possible to flash-distil the chloride in special equipment [1]. Two later similar publications recommend use in solution of the unisolated material [2], Smaller scale distillation of the chloride at 94-95°C/0.03 mbar had been uneventful, but a 1.2 mol scale preparation exploded dining distillation at 128°C/1.2 mbar [3], even in presence of phosphorus pentachloride, previously recommended to reduce the danger of explosion during distillation [4], Many previous explosions had been reported, and the need for adequate purity of intermediates was stressed. It is shock sensitive [5],... 

See Chlorine Nitrogen compounds, or Dimethyl phosphoramidate Phosphorus pentachloride Urea Sodium chloride Nitrogen compounds See other irradiation decomposition incidents... 

Condensed 4-halo-1,2,3-triazines are a virtually unknown class of compounds and are apparently very unstable. Reaction of 1,2,3-benzo-triazin-4-one (10, R = H) with a mixture of phosphorus oxychloride and phosphorus pentachloride, for example, results in formation of o-chlorobenzonitrile, presumably via formation and then decomposition of the 4-chlorotriazine (137) to give the diazonium salt (138), subsequent... 

The halides, GaQs, AlBrs, A1C13, and FeCl3, very probably also exist in dimeric form. With these halides, however, the complexation reaction with the azide is the fast step so that no square-root term is found in the kinetic equation. Arsenic trichloride, arsenic tribromide, phosphorus trichloride, and phosphorus pentachloride were without effect on the rate of decomposition of benzoyl azide. Finally, the authors have observed that the catalytic influence of boron tribromide was much higher than all the other halides. Its rate constant was estimated to be about 18 times larger than that for gallium chloride. 

VI, obtained from stereospecific reactions of the corresponding optically active alcohol (11) with thionyl chloride, phosphorus pentachloride, etc., was not racemized under any of the reaction conditions. Monitoring the carbonyl absorption frequencies in the IR during these decarbonylations showed that the transformations II — III — IV took place during the conversion of V to racemic VI. Thus rearrangement or decomposition or both could be responsible for the racemization. 

The acid chloride is prepared by treating the acid (50 gms.) in a flask, gradually, with phosphorus pentachloride (69 gms.) the reaction may be completed by wanning on the water-bath. To remove phosphorus oxychloride, the liquid is distilled under diminished prossure subsequently the pressure is reduced to below 35 mm. before the /3-pkeuyl-propionyl chloride cau be distilled without decomposition. B.p. 125°—135° at 33 mm. and 117°—119° under 13 mm. Yield, about 90 per cent. 

Recent patents cover the conversion of both isomers of salutaridinol (148 R = Me) into thebaine in 80% yield by the action of thionyl chloride, phosphorus pentachloride, or other acid chlorides, followed by decomposition with bases.180,181 N-Acyl-nor-reticulines have been cyclized by thallium tristrifluoroacetate to the iV-acyl-norsalutaridines [149 R = Ac, F3CCO, cyclo-C3H5CO, EtOCO, or PhCH2OCO), which have been reduced to the corresponding salutaridinols (148) these have been cyclized by sodium hydroxide to the related acyl-northebaines.182... 

The reaction with thionyl chloride affords a chlorosulfite, the decomposition of which may generate an alkyl chloride by the S i (substitution, nucleophilic, internal) mechanism (Scheme 2.16). This reaction, w hich may proceed by an ion pair, can lead to the retention of configuration of an asymmetric secondary alcohol in the conversion to the alkyl chloride. This is in contrast to the inversion of configuration found with the reaction with phosphorus pentachloride and with the nucleophilic displacement of a leaving group. 

---