GB1605333A - Potassium salts of nitrated phenols - Google Patents

Description

(54) POTASSIUM SALTS OF NITRATED PHENOLS 1, THE SECRETARY OF STATE FOR DEFENCE.

London, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed. to be particularly descnbed in and by the following statement: The present invention reiates to salts of nitrated phenols which have explosive properties.

Metal salts of nitrated phenols, especially polynitrated phenols such as picric acid 2. 4, 6trinitrophenol) and styphnic acid (, 4. 6trinitroresorcinol), have found extensive use as primary explosives in, for example, priming compositions. In most cases. the materials used have been heavy metal, especially lead. salts.

Although potassium salts have been noted to have explosive properties. they have been considered only for high explosives and propellants (Urbanski T, Chemistry and Technology of Explosives. Pergamon Press Vol 1 p 525 and Vol 3 p 334) and are not currently used as explosives.

The heavy metal salts currently used as primary explosives are highly sensitive to initiation by shock or electrostatic charges. This is a major disadvantage in handling the materials during the production of the salts and devices using them. It is also undesirable in ammunition which receives considerable physical shock which could cause premature ignitions.

It has now been found that the potassium salts of nitrated phenols especially picric acid.

although relatively insensitive to initiation by mechanical shock and electrostatic charges, are sensitive to thermal initiation by conventional means such as hot wire or flash. They are therefore potentially useful in electrically-fired devices. especially those which must withstand physical shock.

However the physical form of the potassium salt is important in determining its suitability for filling small initiating devices and especially when used in fuse-heads where intimate contact with the heated wire is essential.

For example potassium picrate has previously been prepared only as matted-needles or lathshaped crystals as described by Silberrad & Phillips, J Chem Soc 93 p 474 and in this form is totally unsuitable for use in such devices. it has now been found that the presence of a polysaccharide material, such as dextrin, in the solution from which the potassium salt is precipitated limits acicular growth and promotes the formation of non-acicular. substantially equant (that is having even growth on all faces) crystals possessing good processing propenies and the required combination of mechanical stability and thermal sensitivity. Although both dextrin and cellulose ethers have been described as crystal modifiers for heavy metal salt initiators, they have not been suggested for the preparation of non-acicular potassium salts having the advantages described above.

Thus according to one aspect of the invention.

a process for the production of a potassium salt of a nitrated phenol in the form of free-flowing, non-acicular crystals comprises inducing crystallisation of the said salt from an aqueous solution in the presence of a crystal-modifying polysaccharide material (as herein defined).

Although crystallisation may be induced by cooling a concentrated solution of the potassium salt, it is preferably induced by mixing a solution containing anions of the nitrated phenol with a solution containing potassium cations. the overall concentration of the resulting solution being greater than the solubility of the said potassium salt. In this way higher yields may often be achieved from a given volume of solution whilst the particle size may more readily by controlled by the rate of mixing.

The crystal-modifying polysacchande material used in the process of this invention may be a polysaccharide alone or a substituted polysaccharide, mixtures thereof. or mixtures of polysaccharides with mono- andlor disaccharides. the crystal-modifying polysaccharide material may be a colloidforming polysaccharide such as starch, or preferably a hydrolysis product thereof e.g.

dextrin which is a mixture of glucose, maltose and higher molecular weight saccharides. In either case the polysaccharide material preferably comprises between 2.5 and 25 grms (dry weight) per litre of the total volume of the solution. Other polysaccharide materials which can be used include substituted derivatives, notably cellulose ethers such as methyl cellulose. At typical concentrations of 0.1 to 10 gims/litre these also modify crystal habit but usually result in a wider size distribution of the product and are less preferable. Simple carbohydrates, for example, mono- and disaccharides such as glucose are not suitable.

Since the potassium salt will normally be partially soluble in water, to an extent increasing with temperature, the solutions should be as concentrated as conveniently possible and the reaction temperature relatively low. However very low temperatures will also reduce the solubility of the reagents and hence the maximum reagent concentrations. In generai reagent solutions should be as near saturated as can be handled without possible crystallisation in storage and product separation should be carried out at temperatures towards the lower end of the ambient range, typically about 15"C. although initial mixing may take place at higher temperatures.

The pH at which the reaction is carried out will vary depending on the particular salt being prepared. In panicular. as well known in the art, normal or acid salts may be prepared from polybasic nitrated phenols by arranging the pH of the various solutions to give a desired final pH.

The process may be applied to salts of various mono or poly-nitrated phenols, which may have one or more hydroxyl groups. (The term "polynitrated" as used herein includes di-nitrated).

Whilst all will normally form free-flowing nonacicular crystals, some will be unsuitable for use as initiating explosives due to the presence of water of crystallisation. In addition, use in explosive devices normally requires relatively small particles.

According to a further aspect of the invention.

therefore, there is provided a material suitable for use in an explosive device, said material being a potassium salt of a nitrated phenol in the form of anhydrous. free-tlowing. non-acicular crystals having a mean particle size of less than 100calm.

All mean particle sizes stated in the present specification and claims are. unless clearly stated otherwise. measured as "Manin's diameter" as described, for example. in "Particle Atlas", Edition 2, by W.C. McCrone & J.G. Delly, Vol 1 p 265. published by Ann Arbor Science Publishers Inc. USA.

The term "free-fiowing" is. of course, relative and the freeness will clearly depend on the exact panicle size. As used in the present specification and claims the term denotes material which flows substantially more freely than the acicular crystal forms in which the potassium salts crystallise in the absence of the crystal-modifying polysaccharide materials herein defined.

Polassium salts of nitrophenols which may be produced in the form of anhydrous free flowing crystals by the process of the present invention and are useful as initiatory explosives include salts of 4.6 dinitro-resorcinol, trinitrophloroglucinol, 3:5 dinitrocatechol, 4:6 dinitro-o-cresol and especially picric acid. When the crystallisation is induced by mixing. the solution containing anions derived from the nitrated phenol may be a solution of the nitrated phenol Itself or of a salt which is more soluble than the potassium salt. for example the sodium salt. The solution containing potassium ions will normally be a potassium salt of an inorganic acid or. preferablg. potassium hydroxide.

The mean particle size of the product will depend on various factors as understood in the an. For example slow cooling or addition of the second solution will generally result in larger crystals. In addition rapid agitation of the crystallising solution will induce smaller particles than are produced with gentle stirring.

For example, potassium picrate typical\' crystallises from a stirred solution with a mean particle size of 40-70pm suitable for use in priming compositions whilst a similar precipitation carried out with vigorous agitation gives a produce of mean panicle size 5 to 20pm more suitable for use in fuse-heads.

Although the solution used in processes in accordance with the present invention should be predominantly aqueous. it will be understood that minor proponions of other water-miscible solvents may be added. The term "aqueous solution" as used in the specification and claims includes such predominantly aqueous solvent mixtures.

The products of the present invention may. be used in electrically fired igniferous or gasgenerating devices either alone or admixed with conventional additives. For example priming compositions for use in bridge-uire igniters or similar devices may be prepared by mixing the potassium salts of the present invention with conventional oxidisers such as metal. especially alkali metal, or ammonium. chlorate, perchlorate or nitrate. Other additives such as aluminium powder may be included as well known in the an. Similarly fuse-heads may be prepared with coatings of the potassium salt and a binder, typically 2 to 5g. (w/w) of a cellulose binder such as nitro-cellulose or ethyl cellulose.

Oxidisers may also be included. The fuse-heads may be produced by conventional dipping techniques using a solution of the binder in, for example, amyl alchohol or amyl alcohol/amy acetate, containing the potassium salt in suspension.

Typical processes for the production of some anhydrous potassium salts of nitrated phenols, the resulting products and use of those products in accordance with the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure i shows a bridge-wire igniter cap suitable for firing compositions containing a potassium salt of the present invention, and Figure 2 shows a fuse-head having an ignitable coating containing a potassium salt of the present invention.

Referring to Figure 1 the igniter cap comprises a cylindrical metal sleeve 1 rebated at one end to receive an insulating plug 2 closing one end of the sleeve to form a cup. Two conductors 3 pass through insulating plug and terminate on its inner face 4 which forms the base of the cup. A heating wire 5 passing across the inner face 4 of the plug connects the ends of the two conductors 3.

A priming composition 6 is packed into the cup, formed by the sleeve 1 and p]ug 2, in contact with the heating wire 5. A firing current passed through the heating wire 5 via the conductors 3 causes the wire to heat up and thus ignites the priming composition.

In an alternative embodiment (not shown) the heating wire 5 may be replaced by an electrically conducting composition such as lead styphnate/graphite. Referring to Figure 2, the fuse-head comprises a sheet 11 of electrically insulating material, such as phenolic resin. coated on each side with an electrically conducting layer 12, 13 normally of copper. The electrically conducting layers are connected across one end of the sheet ] I by a wire 14. A coating 15 of explosive material with a binder is applied over the wire 14 by spraying, painting. or, more usually. dipping the fuse-head in a suspension of explosive containing dissolved binder and drying by evaporation of the solvent.

To fire the fuse-head, a voltage is applied between the two conducting layers 12. 13 and the resulting current through the wire 14 generates heat to ignite the explosive. The explosion may be used to fire further exp]osives or as a means of generating gas to move a control piston.

In an alternative embodiment (not shown) multiple layer coatings may be used in p]ace of the single layer coating shown.

Example 1 24 litres of a solution of sodium picrate in a concentration equivalent to 34.4 grms/litre picric acid with < 0.5g/l free acid) was measured into a precipitation pan. Whilst stirring at 80 + 3 rev/mn, 6 litres of 50 grms (dry weight)llitre dextrin solution was added and the temperature adjusted to 1 5 C. This temperature was then maintained throughout. 1.8 litres of a 126 grm/litre nitric acid solution was then added at a regular rate over I 10 minutes. After a further .5 minutes stirring, 1.8 litres of a 112.2 grm/litre solution of potassium hydroxide was added at a regular rate over 20 minutes followed by a further 5 minutes stirring to comp]ete the precipitation.

After 5 minutes settling. the pan was tilted to decant off the mother liquor through a cambric lined filter box. The precipitate from the pan and filter box was then transferred to a gutta percha drying pot and washed twice with 5(X)ml portions of water, and twice with 25()ml portions o industrial methylated spirit. The precipitate was then dried bv passing at least 1 X() cubic feet of dry air through the pot at 15-2O cu ft per hour (alternatively' the precipitate may be sucked drv on a filter funnel and oven dried at 5() C).

The dried mass of potassium picrate was sieved at 60% relative humidity through a hO BSS stainless steel sieve to remove any oversize aggregates (normally no more than (1. Cr by weight).

The product (e 70() grms) comprised anhydrous potassium picrate in the fonn of free flowing, yellow rhombic. predominantly single crystals containing about 84.5Cr (w/w) combined picric acid and less than 0.01% (w/w) free picric acid. All the material passed a 355pm sieve and microscopic analysis showed all particles less than 150pm and greater than 8pm with about 80% (by number) between 25 and 120pm. On analysis the mean particle size was found to be 50pm. The crystal density at 15"C measured by a liquid (p-xylene) displacement method was about 1.95grim cm-3. It had a temperature of ignition of 31 00C when heated at 50C/Min and a mechanical sensitivity in terms of Figure of Insensitiveness (F of I) as measured by a Rotter impact machine of 67 (BDX = 80. lead styphnate = 20).

The product was used as a component of a priming composition consisting of (by weight) potassium picrate 425F potassium perchlorate 48go, aluminium powder 106 The composition had a F of I of 40, but when filled into a conventional bridge-wire igniter cap as shown in Figure 1 was readily ignited by a standard electrical pulse.

Example 2.

229grms (1.0 mol) of picric acid was suspended by stirring in 1 litre of water warmed to 55"C. 500 ml of 2N caustic soda (1.0 mol) was added followed by 5()0ml of a 1% solution of methyl cellulose in water. The mixture was heated to 600C and 1.2 litres of a 100grm/litre aqueous potassium nitrate solution (1.2 mol) was added slowly with stirring over 24 minutes with the temperature held at 59-62 C. The mixture was stirred for a further 2 minutes and then cooled to 20"C over 15 minutes. The precipitate was filtered off and washed twice by resuspension in 1.5 litres of water.

The yield comprised 210grms of substantially equant crystals of potassium picrate having a particle size range (by visual estimation) of 40 to 400pm (average about 200pm.

Evaniple 3 4 litres of a solution of sodium picrate (in a concentration equivalent to 34.4grm/Iitre picric acid with < 0.5 g/l free acid) was measured into a 10 litre precipitation pan. The solution was vigorously mixed with a high speed emulsifier (comprising an impeller rotating at several thousand rpm within a fixed cage) whilst 1 litre of 50grm (dry weight) per litre dextrin solution was added and the temperature adjusted to 150C.

This temperature was maintained throughout. 0.3 litres of a I 26grm/litre nitric acid solution was then added at a regular rate over 10 minutes.

After a further 5 minutes mixing. 0.3 litres of a 112.2grm/litre solution of potassium hydroxide was added at a regular rate over 20 minutes followed by a further 5 minutes mixing.

The precipitate was filtered off and washed with 2()0ml of water followed by 20()ml of industrial methylated spirit. The dried yield was 1 5()grms of fine equant crystals having a particle range of 2 to 50pm with a mean particle size of 12cm.

The product was suspended in a solution of ethyl cellulose (3% by weight of the potassium picrate used) in amyl alchohol and used to coat standard fuse-heads as shown in Figure 2 by a conventional dipping technique. The fuse-heads as shown in Figure 2 by a conventional dipping technique. The fuse-heads were successfully fired by a standard 0.8 amp ]0 m sec terminated D.C. pulse.

Example 4 114.5grms (0.5 mol) of picric acid was suspended at 1 SOC in 250ml of water and 50ml of 50grm/litre (dry weight) dextrin solution were added. The mixture was then agitated by a highspeed, low amplitude reciprocating mixer whilst 250my of 2N potassium hydroxide (0.5 mol) was added gradually over 15 minutes. Agitation was continued for a further 5 minutes after which the precipitate was filtered off and washed with 200my of water followed bv 200m1 of industrial methylated spirit. Drying at 50"C in air yielded 125grms of potassium picrate crystals having a panicle size range of 5 to 30pom with most particles about 10pm. The potassium picrate in either the methylated spirit-washed or the dried form was successfully used for the production of fuseheads, as described in Example 3.

Example 5 8.58g (0.033 mole) of trinitrophloroglucinol was suspended in 50m1 of water at 250C. 66ml of N sodium hydroxide solution (0.066 mole) was added and stirred until dissolved. The solution was filtered and the volume made up to 180my by the addition of water.

45ml of 50g/] dextrin solution was then added and the temperature adjusted to 20"C. Whilst briskly agitating, 33ml 2N potassium nitrate solution (0.066 mole) was added over 5 minutes.

Stirring was continued for a further 2 minutes after which the precipitate was filtered off and washed on the filter with two 25ml portions of water, followed by 50m1 of methylated spirit.

Drying at 50"C in air yielded 7.5g of dipotassium trinitrophloroglucinate in a free flowing crystalline form consisting of near square platish panicles. It had a temperature of ignition of 285"C.

Example 6 l5g (0.075 mole) of 4:6 dinitroresorcinol was suspended in 50m1 of water at 450C and 75ml of 2N KOH (0.15 mole) was added and stirred until dissolved. The solution was filtered and the volume made up to I 80m1 by the addition of water.

ISmI of 50 g dextrin solution was added and the temperature adjusted to 15 C. Whilst briskly agitating, 37.5m1 of 2N acetic acid (0.075 mole) was added during 30 minutes. Stirring was continued for a further 5 minutes after which the precipitate was filtered off and washed on the filter with two 25ml portions of water followed by 50ml of methylated spirit. Drying at 500C in air yielded 15.8g of robust tablet type, free flowing crystals of monopotassium 4:6 dinitroresorcinate having a temperature of ignition of 262"C and an F of 1 of 43.

Example 7 100ml of a 0.4 molar solution of dipotassium 3:5 dinitrocatechate together with 50ml of a 1% (w/v) solution of methyl cellulose solution was stirred vigorously and the temperature adjusted to 15 C. 20ml of 2N acetic acid was then added during 15 minutes.

Stirring was continued for a further 5 minutes after which the precipitate was filtered off, washed with two 25ml portions of water, followed by 50ml of methylated spirit. Drying at 500C in air yielded 6.7g of small equant crystals of monopotassium dinitrocatechate suitable for fusehead manufacture and having a temperature of ignition of 280"C.

Claims (20)

WHAT I CLAIM IS:

1. A process for the production of a potassium salt of a nitrated phenol in the form of free-flowing, non-acicular crystals comprising inducing crystallisation of the said salt from an aqueous solution in the presence of a crystal modifying polysacchoride material as herein defined.

2. A process according to claim 1 wherein the crystallisation is induced by mixing a solution containing anions of the nitrated phenol with a solution containing potassium cations.

3. A process according to either claim 1 or claim 2 wherein the nitrated phenol is picric acid.

4. A process according to either claim 1 or claim 2 wherein the nitrated phenol is 4:6 dinitroresorcinol, trinitrophloroglucinol or 3:5 dinitrocatechot.

5. A process according to either claim 1 or claim 2 wherein the nitrated phenol is 4:6 dinitroo-cresol.

6. A process according to any one of the preceding claims wherein the polysaccharide material consists of a colloid-forming polysaccharide or hydrolysis product thereof.

7. A process according to claim 6 wherein the polysaccharide material consists of dextrin.

8. A process according to any one of the preceding claims wherein the polysaccharide material is present in a concentration of 2.5 to 25grms per litre of the said aqueous solution.

9. A process according to any one of claims 1 to 5, wherein the polysaccharide material is a cellulose ether.

10. A process according to claim 9 wherein the polysaccharide material Is present in a concentration of 0.1 to I 0grms per litre of the said aqueous solution.

I I. A process for the production of a potassium salt of a nitrated phenol substantially as hereinbefore described in any of the examples.

12. A potassium salt of a nitrated phenol when produced by a process according to any preceding claim.

13. A potassium salt of a nitrated phenol in the form of anhydrous. free-flowing, nonacicular crystals having a mean panicle size of less than 100cm.

14. A potassium salt according to claim 13 wherein the nitrated phenol is 4:6 dinitroresorcinol, trinitrophloroglucinol, 3:5 dinitrocatechol or 4:6 dinitro-o-cresol.

15. A potassium salt according to claim 13 wherein the nitrated phenol is picric acid.

16. A potassium salt according to claim 15 having a mean particle size within the range 40pm to 70pom.

17. A potassium salt according to claim 15 having a mean particle size within the range Sltm to 20lem.

18. A potassium salt according to any one of claims 13 to 17 substantially as hereinbefore described.

19. A priming composition comprising a potassium salt according to any one of claims 14 to 18 mixed with an oxidiser.

20. A fuse-head coating comprising a potassium salt according to claim 17 mixed with a binder.