N205 synthesis

Abstract

The present invention relates to the synthesis of N2O5, for the nitration of energetic materials. There is provided a method of synthesis of N2O5, comprising the steps of reacting, silver ni

Description

Dinitrogen pentoxide (N2O5), the anhydride of nitric acid, was synthesised by Henri Etienne Sainte-Claire Deville in Paris in 1849 using silver nitrate and chlorine gas. SUMMARY Before the present invention is described in further detail, it is to be understood that the invention is not limited to the particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. According to the first aspect of the present invention, there is provided a method of synthesis of N2O5, comprising the steps of reacting, silver nitrate in the presence of dry chlorine gas, at a temperature in the range of 40 °C to 95 °C in the presence of UV radiation, wherein the reaction product is collected via a cooled region less than 10 °C. The reaction may be carried out in a batch or continuous vessel. In a batch process the reaction may be undertaken in a UV transparent sublimator reaction vessel, said sublimator comprising a system with gas / vacuum access through at least one valve; comprising the steps of i) in a reaction chamber in said sublimator, charging with anhydrous silver nitrate, wherein said reaction chamber is caused to be heated in the range of 40 °C to 95 °C, ii) in a cooled region in said sublimator, a condenser arrangement wherein the temperature is caused to be the range of -10 °C to +10 °C, iii) charging the reaction chamber with dry chlorine gas, iv) subjecting said reaction chamber to UV radiation to furnish N2O5. The yield may be increased by removal of moisture from the system, preferably prior to step iii) there is provided the step of evacuating the reaction chamber of the sublimator to create a vacuum, which is held by the valve. The vacuum may then be replaced by the dry chlorine gas, in the substantial absence of air and moisture. The product may be retrieved under a stream of dry inert gas, such as for example nitrogen or argon to avoid moisture reacting with the N2O5. The UV radiation is in the range of from 100 nm to 400 nm, preferably in the range of 300 nm to 400 nm, more preferably in the range of 365 nm to 385 nm. In the prior art methods conducted over 100 years ago the temperature requirement was 95 °C for silver nitrate, the use of UV radiation reduces the necessary reaction temperature and therefore avoids high temperature decomposition of N2O5. Preferably in step i) the reaction chamber is heated in the range of 65-70 °C. Use of UV increases the reaction rate of silver nitrate, therefore lower reaction temperatures are required. According to a further aspect of the invention there is provided a continuous flow method for producing N2O5 comprising a continuous vaporisation system, said system comprising i) a gas supply system for supplying dry chlorine gas, ii) a reactor, operably linked to the gas supply system, which comprises a reaction chamber which comprises silver nitrate, said silver nitrate being heated in the range of 40 °C to 95 °C, wherein the reaction chamber is caused to be in the presence of UV radiation, to furnish gaseous N2O5, iii) a product collecting system, which receives the gaseous N2O5 from the reactor, said product collecting system being operably linked to a cooling system wherein the gaseous N2O5. is collected via a cooled region of less than 10 °C within the product collecting system. In a preferred step, the N2O5 from step iii) is fed into the product storage system, which may be held under vacuum. In a preferred step the reaction chamber is filled with a dry, unreactive gas such as nitrogen or argon, so as to reduce the reaction with moisture in the air. The chlorine gas may be provided at any pressure, preferably greater than 1 atm, to increase rate of the reaction and to decrease the temperature of the reaction. The UV radiation may be in the range of from 100 nm to 400 nm, preferably in the range of 300 nm to 400 nm, more preferably in the range of 365 nm to 385 nm. Experimental prior art: Synthesis of dinitrogen pentoxide (N2O5) at a temperature of 95 °C. The method first proposed by Deville was repeated using modern day equipment, such as a sublimator to allow facile collection of the dinitrogen pentoxide from the other starting materials. AgNOa (Sigma-Aldrich, Reagent Grade), was ground by pestle and mortar into a fine powder and transferred with a magnetic stirrer to a Chemglass sublimator. The sublimator had an inner diameter of 40 mm, an inner volume of 190 mL and was fitted with Viton seals capable of withstanding chlorine and N2O5. The sublimator was assembled and a septum was secured in the sublimator valve. The sublimator with AgNOs was then completely evacuated of air before securing the apparatus on a hotplate with the tip of the sublimator containing the silver nitrate was immersed in sand contained within an aluminium heater block fitted with a thermocouple. The inlet and outlet pipes of the sublimator were secured to a Huber 3000 chiller set at 4 °C. The chiller was then immediately switched on to get to temperature. The chlorine gas system was then prepared. This system consisted of a chlorine cylinder (BOO Material number: 158321-E3, Cylinder size: E3 (980mm x 219mm - 32 liquid litre capacity) Nominal pressure (bar): 4.9 @ 15°C Contents: 39 kg Valve outlet: BS6) and regulator (ERB Gas Solutions Ltd (Nottingham, UK), 0-3 Bar Single Stage Stainless Steel Regulator c / w Inlet Tee Purge -BS6 316L Cylinder Connection -1 / 8 OD Compression) and needle valve (ERB Gas Solutions Ltd, Outlet Stainless Steel Needle Valve). The outlet for the needle valve was connected to a needle via a length of PTFE tubing to allow the delivery of gasses via a septum in the sublimator. The tee connection of the chlorine regulator was connected via a valve tap to a regulator on a dry nitrogen cylinder. The nitrogen was in place to purge the gas system before and after the experiments. At the start of the experiment (prior to charging the reaction chamber), the dry nitrogen was allowed to flow for several minutes to dry the system before switching off the gas flow. The gas was then switched to chlorine and the chlorine was then allowed to flow momentarily into the back of the fume cupboard to ensure an outlet pressure of 1 bar, and to prime the system. The needle valve was set to % - % a turn out to ensure gentle release of gas. The valve closest the delivery needle was then closed. The needle from the needle valve was then inserted into the septum of the sublimator valve. The delivery needle valve partially opened. The sublimator inlet valve was then opened and chlorine was observed immediately filling the sublimator. The sublimator valve was closed and the chlorine flow turned off at the needle valve. The delivery needle was then closed and completely removed from the sublimator septum, leaving the sublimator isolated from the gas lines. The chlorine was then purged from the gas lines with the dry nitrogen until clear of chlorine (0 ppm CI2). The gas system was kept under 2 bar of dry N2 pressure when not in use. The sublimator filled with chlorine (cold finger at 4 °C), was isolated from the main gas lines and with the gas detector at 0 ppm, the stirrer was switched on at 250 rpm and the heat set to 95 °C to ensure full conversion and left to continue at this temperature for up to 96 hours. By this time, the green / yellow colour of the chlorine was being replaced by the red / brown of the decomposition NO2 product of N2O5. Also, the AgNOs / AgCI was much finer and had begun to coat the inside of the sublimator. These observations indicated the reaction was complete. The 95 °C heat was switched off and allowed to return to room temperature. During cooling, small clusters of geometrical translucent N2O5 crystals began forming all over the cold finger of the sublimator. This crystallisation was allowed to continue for 2 hours before the opening the sublimator under an argon atmosphere for crystal recovery for XRD analysis and N2O5 recovery in excellent yield in dry dichloromethane for subsequent yield calculations and nitration synthesis. Other solvents may be used for the recovery. Synthesis of dinitrogen pentoxide (N2O5) with 365 nm UV light and a temperature of 65 °C. hv 4 AgNO3(S) * 2 Ch(g)                    * 2 N2O§(S) Synthesis procedure was that of above, but with the following modifications. The temperature was reduced from 95 °C to 65 °C. The addition of 365 nm UV light facing directly into the lower portion of the sublimator containing the AgNOs which was switched on upon the temperature of the cold finger in the sublimator reaching 4 °C and the hot plate reaching 65 °C. The reaction apparatus was then completely enclosed for safety considerations with UV light. The reaction was complete within 18 hours, which was evident from the chlorine colour becoming being practically translucent, no apparent NO2 formation and the change in powder consistency as discussed above. However, the most obvious indicator of reaction completion was that N2O5 crystals were clearly evident on mainly on the tip of the sublimator. The 30 °C decrease in temperature required for the experiment described above, without UV light, allows for the immediate recrystallisation of the N2O5 in excellent to quantitative yield >95%. Yield was determined from titration against NaOH and phenolphthalein after recovering the N2O5 from the dichloromethane recovery solvent. Synthesis of dinitroqen pentoxide (N2O5) the modified Deville method incorporating AgNOs exposure with 365 nm UV light and a temperature of 50 °C. Synthesis procedure was that of section above, but with a lower temperature of 50°C. The reaction was left to run for 18 hours as above. After this time, there was N2O5 clearly visible on the cold finger, but there was visibly much less (»50% less) and there was more decomposition of the N2O5 evident from the swirling deep red colour of the NO2 gas present inside the sublimator. The reaction did not proceed without UV irradiation at 65 °C. Recovery of the Dinitroqen Pentoxide. N2O5 is a thermally labile translucent crystalline solid that exhibits a half-life of 10 days at 0 °C, and 10 hours at 20 °C. The solid readily sublimes, having a vapour pressure of 51 mm at 0 °C, 200 mm at 15 °C, 279 mm at 20 °C and 1 atm at 32.5 °C. The reaction vessel cannot be placed in a glove box as the N2O5 will rapidly sublime into a gas in a vacuum. Indeed, if the CS is flushed with N2(g) it will rapidly erode the N2O5. Therefore, the following recovery procedure was developed. Once the crystalline solid and contents have cooled and enough time (2 hours) has passed to allow the N2O5 to condense and crystallise, place a funnel attached to an argon gas line directly above the crystalline solid. This will dilute the air which contains moisture that will destroy the anhydride causing it to fume as per this equation: N2O5 (s) + H2O(aq) -> 2 HNO3(I) The samples agreed with literature characterisation. BRIEF DESCRIPTION OF THE FIGURES Embodiments of the invention will now be described by way of example only with reference to the figures, in which: Figure 1 shows a batch sublimator using hv (light); Figure 2 shows a continuous process for the production of N2O5. DETAILED DESCRIPTION Figure 1 without the UV source was used for the prior art experimental, as above. Turning to figure 1 there is provided a sublimator 1, with a valve 2 to allow a vacuum to be achieved in the reaction chamber 5. The valve 2 also allows the flow 3 of dry chlorine gas into the reaction chamber 5. The sublimator has an upper section which comprises the condenser 4, which has a flow in 8 and a flow out 9 of a cooling liquid, such as for example chilled water, to cause the condenser (cold finger) 4 to be below 10°C. The chamber 5 is heated and further subjected to UV light. The silver nitrate is therefore heated and irradiated simultaneously, such that it reacts in the presence of chlorine gas (not shown). The reaction product N2O5 6 collects on the surface of the condenser. The sublimator 1 is of two part construction for easy assembly / disassembly and is 5 held together by clamp 7. Turning to Fig 2, there is provided a schematic for a continuous flow vaporiser. A reactor is primed with silver nitrate, initially under vacuum, the silver nitrate may be replenished and the resultant silver chloride byproduct can be 10 converted back into the silver nitrate using peroxide and concentrated nitric acid. The reactor is charged by a continuous stream of chlorine gas which can be controlled by a valve, to pass over the silver nitrate. The reaction chamber is subjected to both heat and UV light, to cause a reaction to furnish N2O5. The gaseous N2O5 travels to the product collection system, which is held at a 15 temperature to cause condensation and crystallisation of N2O5. The product collection system is operably linked to a cooling system to provide continuous cooling in the product collection system. After collection the product is transferred to product storage, either at a reduced temperature, inert gas, or solvent.

Claims

1. A method of synthesis of N2O5, comprising the steps of reacting, silver nitrate in the presence of dry chlorine gas, at a temperature in the range of 40 °C to 95 °C in the presence of UV radiation, wherein the reaction product is collected via a cooled region less than 10 °C.

2. A method according to claim 1, wherein the reaction is undertaken in a UV transparent sublimator reaction vessel, said sublimator comprising a system with gas / vacuum access through at least one valve;i) in a reaction chamber in said sublimator, charging with anhydrous silver nitrate, wherein said reaction chamber is caused to be heated in the range of 40 °C to 95 °C,ii) in a cooled region in said sublimator, a condenser arrangement wherein the temperature is caused to be the range of -10 °C to +10 °C,iii) charging the reaction chamber with dry chlorine gas,iv) subjecting said reaction chamber to UV radiation to furnish N2O5.

3. The method according to claim 1, wherein prior to step iii) evacuating the reaction chamber of the sublimator to create a vacuum, which is held by the valve.

4. The method according to claim 1 or claim 2, wherein the UV radiation is in the range of 300 nm to 400 nm.

5. The method according to claim 4 wherein the UV radiation is in the range of 365 nm to 385 nm.

6. The method according to any one of the preceding claims, wherein in step i) the reaction chamber is heated in the range of 65-70°C.

7. A continuous flow method for producing N2O5 comprising a continuous vaporisation system, said system comprisingi) a gas supply system for supplying dry chlorine gas,ii) a reactor, operably linked to the gas supply system, which comprises a reaction chamber which comprises silver nitrate, said silver nitrate being heated in the range of 40 °C to 95 °C, wherein the reaction chamber is caused to be in the presence of UV light, to furnish gaseous N2O5iii) a product collecting system, which receives the gaseous N2O5 from the reactor, said product collecting system being operably linked to a cooling system wherein the gaseous N2O5, is collected via a cooled region of less than 10°C within the product collecting system.

8. A method according to claim 7, wherein the N2O5 from step iii) is fed into product storage system, which is held under vacuum or under inert gas.

9. A method according to claim 7 or 8 comprising the step of evacuating the reaction chamber to create a vacuum.

10. A method according to claim 7 to 9, wherein the UV radiation is in the range of from 300 nm to 400 nm.10

Images