Process for the production of dinitrate esters

Details Process for the production of dinitrate esters Process for the production of dinitrate esters

1999-03-03

2000-06-06

Ambrose, Michael G.

Organic compounds -- part of the class 532-570 series

Organic compounds

Nitrate esters or chalcogen analogues thereof

558482, 558483, C07C20102, C07C20304

Patent

active

060720719

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of nitrating polyols having either 1,2- or 1,3-diol fragments, which process involves, as an intermediate stage, the use of a 1,3-dioxa-2-borole (boronate ester) protecting group.
A particular problem arises in attempting the nitration of polyols having such diol fragments when they are incorporated into a polymeric chain. Polyols, even when not of high molecular weight dissolve at best only in low concentrations in either water or common organic solvents and in consequence they are difficult to completely nitrate using the common mixed acid (sulphuric
itric acid mixture) or like methods. Even where it is possible to dissolve some of a polymeric polyol into an appropriate solvent the yields of nitrated product obtained are likely to be very low.
A further problem with conventional nitrating procedures based on mixed acids is that they are rather aggressive in character and tend to be somewhat non-specific. There is thus a considerable possibility when dealing with polymeric polyols that attack by the nitrating agent at some other location on the polymer chain will occur.
Protection of the reactive hydroxyl groups of 1,2- and 1,3-diol fragments as a cyclic phenyl boronate is well known. The procedure is shown below for a 1,2-diol which will be used hereafter in the description of the invention as a general term intended to cover the group of polyols containing either 1,2- or 1,3-diol fragments: ##STR1## where n is 0 or 1.
Conventionally, to then obtain the dinitrate ester from the protected diol the protecting group is hydrolytically cleaved to recreate the diol and this is then treated with a conventional nitrating agent, with the disadvantages identified previously.
The applicant has now found that by use of the unconventional nitrating agent dinitrogen pentoxide it is not only possible to achieve nitration in a relatively non-aggressive manner but also without isolation of the diol. Thus it has been found possible to achieve direct nitration effectively and in good yield from a protected diol by treatment with dinitrogen pentoxide.
Accordingly the present invention provides a process for the preparation of 1,2- and 1,3-dinitrate esters from the corresponding polyol having a 1,2- or 1,3-diol fragment which comprises the steps of: of the polyol with an alkyl or aryl boronic acid; under anhydrous conditions in order to form the corresponding dinitrate; and product.
Step (a) of the process may be carried out at any suitable temperature having regard to the stability of the reactants; however the reaction will generally proceed satisfactorily at or not greatly in excess of ambient temperature. The reaction may most conveniently be carried out by mixing equimolar amounts of the diol with the boronic acid and stirring until the formation of water is evident as a separate layer. Extraction and distillation affords the boronate in excellent yield.
In an optional step between steps (a) and (b), the diol may be modified in some other reaction during which the protected hydroxyl groups are unaffected. For example a triol of general formula HO(CH.sub.2).sub.n CHOHCH.sub.2 OH can have the 1,2-diol fragment protected as a cyclic boronate and the free hydroxyl group can be protected as a silyl ether or as an ester such as an acetate. This gives different protecting groups for the different hydroxyl groups and thus different reactivity and the opportunity for selective deprotection.
It will be appreciated that by avoiding the presence of water, cleavage of the protecting groups and creation of the relatively insoluble hydroxyl-bearing compounds is obviated. Thus, provided that other groups sensitive to N.sub.2 O.sub.5 are not present in the protected diol, the problems of unwanted side reactions and of the lack of solubility of the diols in common organic solvents are side-stepped. Furthermore the nitrating procedure according to the present invention requires only a single step whereas conventional methods require two steps.
The corresponding cyclic boronate esters are readily

REFERENCES:
patent: 3549687 (1970-12-01), Bachman et al.

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