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Cade, Joseph A. (1955) Reactions in carboxylic acid-phosphorus trihalide systems. Doctoral thesis, Northern Polytechnic.
A study is made of the interaction of certain carboxylic acids with phosphorus trichloride, or an alkyl phospboro- dichloridite, ROPC12, or a dialkylphosphorochloridite, (RO)2PCl, in the absence or in the presence of pyridine.
With aliphatic acids such as acetic acid, there is no evidence that a chlorine atom attached to tervalent phosphorus can be replaced by an acyloxy group, as it can be by an alkyl group, either in the absence or in the presence of the base, by a primary interaction process. In the absence of base, all three chlorine atoms in the trichloride, cannot be used effectively for the conversion of acid to acyl chloride, and hydrogen chloride is produced concurrently. The nature of the products obtained from interaction of the trichloride or the chloridite, (RO)2P1, and acid, when pyridine is introduced into the systems, have led to the proposal that fruitful dechlorination of the trichloride by acid and spontaneous formation of hydrogen chloride from the intermediate compounds resulting from its partial dechlorination, are competitive simultaneous reactions. From among the products of the reaction between the dichloridite, ROPC12, and an acid of this type in the presence of the base, diacyl alkyl phosphites can be isolated, but the formation of these compounds is considered to be a result of a secondary reaction.
In contrast, aromatic acids such as benzoic acid, form with the trichloride and base, triaroyl phosphites directly. Of aromatic acids examined, the reactions of salicylic acid in these systems provide a subject of special interest, and the structures of the heterocyclic phosphorus compounds formed from this acid are demonstrated.
Probable mechanisms of the individual steps in the reaction sequences are proposed, and discussed in terms of accepted ideas in the electronic theory of organic chemistry. An attempt is made to explain the differences exhibited by different classes of acids in these reactions according to their structures. Comparisons are drawn with acid-thionyl chloride systems, and with corresponding alcohol systems.
Some properties of the acyl and aroyl phosphites are described and discussed.
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