Phosphorus pentachloride, ammonolysis

Preparation of phosphonitrilechloride trimer. Phosphonitrilechloride trimer is synthesised by partial ammonolysis of phosphorus pentachloride with ammonia chloride in the presence of quinoline as a catalyst ... 

The mechanism of ammonolysis of phosphorus pentachloride is not completely understood. It has been shown (164) that it proceeds in two steps. Initially, the intermediate [C13PNPC13] + [PC16] is formed, probably via PC14NH2 and PC13NH (48, 380). In the second step, this intermediate reacts with NH4C1 to produce cationic phosphazene chains that undergo cyclization by the elimination of [PC14]+ (164, 256). 

The question of whether the phosphonitrilic chlorides have cyclic or linear structures has been frequently discussed in the literature. The structural evidence will be considered in Section lY, where it will be seen that the cyclic formulation is established beyond doubt for the trimer and tetramer, and is highly probable for the higher soluble polymers it will meanwhile be assumed for all compounds of formula (PNX2) . For reasons considered in Section II, C the petrol-insoluble fraction (PNCUln PCls is believed to consist of a mixture of linear polymers. The two series are related, in that the linear compounds of low molecular weight are intermediates in the formation of the cyclics by the ammonolysis of phosphorus pentachloride. 

The linear structure of these polymers is strongly suggested by the conditions required for their formation from the cyclic compounds and phosphorus pentachloride. That the ring is actually broken in the reaction is shown by the fact that a mixture of polymers, not the original cyclic compound, is obtained by the ammonolysis of the reaction product. It is natural, therefore, to formulate these compounds as PCUfNPCla), Cl, the chlorides of the polyimidophosphoric acids. 

The manner in which the linear and cyclic polymers are formed in the ammonolysis of phosphorus pentachloride is not known in detail, but seems likely to involve a series of condensation reactions. The first stage is thought to be the formation of the unstable ammonium hexa-... 

The formation of phosphonitrilic chlorides by ammonolysis of phosphorus pentachloride is considered (Section II, D) to proceed by formation of ammonium hexachlorophosphate, followed by elimination of hydrogen chloride and a series of related condensation processes. Similar reactions are quite common in inorganic chemistry, as will be seen below. 

Phosphonitrilic chlorides were prepared (Stokes, 1895) by the ammonolysis of phosphorus pentachloride dry distillation gives a mixture of (PNCl2)3 and... 

In considering the synthesis of this compound several alternatives are possible. Two will be considered. Aniline may be sulfo-nated to sulfanilic acid, and after acetylation the chloride may be prepared by the action of phosphorus pentachloride. The acyl chloride, on ammonolysis, will give the acetylated sulfonamide. The other possibility is to use chlorosulfonic acid and introduce the sulfo and chloro groups simultaneously. Aniline is acetylated, and the acetanilide is sulfonated with excess of chlorosulfonic acid. The sulfonic acid group is introduced first, and by further reaction the acid chloride is formed ... 

Thus, as shown in Scheme 14.7, the reaction of ethyl formate with ethyl acetate in ether in the presence of sodium metal yielded ethyl sodium formyl acetate. Then, the addition product of ethyl bromide with thiourea was treated with aqueous base and the ethyl sodium formyl acetate was added so that, after standing for a number of hours, acidification with acetic acid yielded 2-ethylmercapto-6-oxypyrimidine. Treatment of the latter with phosphorus pentachloride yielded the corresponding 2-ethylmercapto-6-chloropyrimidine subsequent alcoholic ammonolysis generated 2-ethylmercapto-6-aminopyrimidine and boiling aqueous hydrobromic acid resulted in the production of 6-amino-2-oxypyrimidine (cytosine). 

Reaction of j8-maltotriose hendeca-acetate with phosphorus pentachloride afforded 2, 2",3,3, 3",4",6,6, 6"-nona-0-acetyl-2-(9-trichloroacetyl- -maltotriosyl chloride (42%), which could be isomerized (TiCh in chloroform) to the corresponding a-chloride. 2 Selective ammonolysis of the trichloroacetyl group in the a- and jS-chlorides gave the 2-hydroxy derivatives. 

Ammonolysis of the diacid chloride, obtained from the treatment of C,C -neocarboranecarboxylic acid with phosphorus pentachloride, gives the diacid amide. Pyrolysis of the latter compound does not result in the formation of a cyclic imide, as is observed in the corresponding 1,2-C2B 1 qH 12 derivative (Section III, C, 6) (335). A number of silyl derivatives have been prepared from dilithioneocarborane, and again, in contrast to the isomeric silylcarboranes (Section III, C, 8), they do not tend to form exocyclic derivatives (353). These observations are consistent with the 1,7-arrangement of the carbons in the neocarborane icosahedron. 

The ready availability of 1,2,5-thiadiazole 1,1-dioxides (177) (see above) has provided data for their comparison with the parent aromatic ring system, The NO-, NN-, and OO-dimethylated derivatives are obtained by suitable alkylation procedures. The action of an excess of phosphorus pentachloride gives the 3,4-dichloro-compound (181 X = Cl), which is rapidly hydrolysed back to the dione (177), and which undergoes ammonolysis or aminolysis to give a variety of 3,4-di(substituted amino)- ,2,5-thiadiazole 1,1-dioxides [e.g. (181 X = NR R )]. The amide-like character of the 3,4-diamino-derivative (181 X = NHa) has been noted, as has a pronounced tendency of the 3,4-di-alkoxy-derivatives (181 X = OMe) to transfer their 0-alkyl groups to the ring nitrogen on thermolysis. ... 

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