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Herbst, Henry (1955) Reactions in alcohol-phosphorous tribomide systems. Doctoral thesis, Northern Polytechnic.
The alkoxylation of phosphorus in phosphorus tribromide has been shown to be quick. In order to accomplish this it was necessary to prepare some dibromidites ROPBr2 and bromidites (RO)2PBr. These were prepared by the direct reaction of phosphorus tribromide with the corresponding alcohol in the case of the dibromidites, and by the reaction of dibromidites with alcohol in the presence of pyridine in the ease of bromiditea. A novel method of preparation has also been explored where an alkoxytrimethylsilane has been used as the alkoxylating agent.
The "dealkylation" of the intermediate bromo-esters by hydrogen bromide has been investigated. An interesting feature of these "dealkylation" experiments lias been the formation of phosphorus tribromide.
The thermal stability of the esters has been studied in the presence and absence of pyridine hydrobromide. In both cases alkyl bromide and phosphorus tribromide were obtained. From the use of optically active materials it appeared that the alkyl bromide was formed by a mechanism which gave inversion with considerable loss of activity.
Some values for the rate of dealkylation by hydrogen bromide of the n-, sec.-, and isobutyl hydrogen phosphites have been obtained, with ether and carbon tetrachloride as solvents. The reactions have been shewn to be competitive consecutive second order reactions. Evidence that the first step in the reaction is the protonisation of the ester has been obtained. Attempts to use hydrocarbon solvents, such as n-pentane, were frustrated by the precipitation of the entity (RO)2PHBr.
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