Inorganic esters conversion

When proton acids catalyze alcohol dehydration, the mechanism is El. ° The principal process involves conversion of ROH to ROHj and cleavage of the latter to R and H2O, though with some acids a secondary process probably involves conversion of the alcohol to an inorganic ester and ionization of this (illustrated for H2SO4) ... 

Alkyl sulfates, tosylates, and other esters of sulfuric and sulfonic acids can be converted to alkyl halides with any of the four halide ions.979 Neopentyl tosylate reacts with Cl, Br, or I without rearrangement in HMPA.980 Similarly, allylic tosylates can be converted to chlorides without allylic rearrangement by reaction with LiCl in the same solvent.981 Inorganic esters are intermediates in the conversion of alcohols to alkyl halides with SOCl2, PC15, PC13, etc. (0-67), but are seldom isolated. 

Various ways of overcoming the PTA oxidation problem have been incorporated into commercial processes. The predominant solution is the use of high concentrations of manganese and cobalt ions (2,248—254), optionally with various cocatalysts (204,255,256), in the presence of an organic or inorganic bromide promoter in acetic acid solvent. Operational temperatures are rather high (ca 200°C). A lesser but significant alternative involves isolation of intermediate PTA, conversion to methyl/)-toluate, and recycle to the reactor. The ester is oxidized to monomethyl terephthalate, which is subsequentiy converted to DMT and purified by distillation (248,257—264). 

A mixture of dihydroxyacetone and inorganic arsenate can replace DHAP due to the transient formation of a monoarsenate ester which is recognized by the aldolase as a DHAP mimic21. This approach suffers from the high toxicity of arsenate, especially at the relatively high levels (>0.5 M) needed for efficient conversion, and from problems in product isolation. 

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