US5500059A - Anhydrous 5-aminotetrazole gas generant ...
USA - Anhydrous 5-aminotetrazole gas generant ...
The present application is a continuation-in-part of copending application Ser. No. 08/101,396 now allowed, filed Aug. 2, and entitled "BITETRAZOLEAMINE GAS GENERANT COMPOSITIONS AND METHODS OF USE," which application is incorporated herein by this reference.
FIELD OF THE INVENTIONThe present invention relates to novel gas generating compositions for inflating automobile air bags and similar devices. More particularly, the present invention relates to the use of substantially anhydrous aminotetrazole (5-aminotetrazole) as a primary fuel in gas generating pyrotechnic compositions, and to methods of preparation of such compositions.
BACKGROUND OF INVENTIONGas generating chemical compositions are useful in a number of different contexts. One important use for such compositions is in the operation of "air bags." Air bags are gaining in acceptance to the point that many, if not most, new automobiles are equipped with such devices. Indeed, many new automobiles are equipped with multiple air bags to protect the driver and passengers.
In the context of automobile air bags, sufficient gas must be generated to inflate the device within a fraction of a second. Between the time the car is impacted in an accident, and the time the driver would otherwise be thrust against the steering wheel, the air bag must fully inflate. As a consequence, nearly instantaneous gas generation is required.
There are a number of additional important design criteria that must be satisfied. Automobile manufacturers and others set forth the required criteria which must be met in detailed specifications. Preparing gas generating compositions that meet these important design criteria is an extremely difficult task. These specifications require that the gas generating composition produce gas at a required rate. The specifications also place strict limits on the generation of toxic or harmful gases or solids. Examples of restricted gases include carbon monoxide, carbon dioxide, NOx, SOx, and hydrogen sulfide.
The automobile manufacturers have also specified that the gas be generated at a sufficiently and reasonably low temperature so that the occupants of the car are not burned upon impacting an inflated air bag. If the gas produced is overly hot, there is a possibility that the occupant of the motor vehicle may be burned upon impacting a just deployed air bag. Accordingly, it is necessary that the combination of the gas generant and the construction of the air bag isolates automobile occupants from excessive heat. All of this is required while the gas generant maintains an adequate burn rate. In the industry, burn rates in excess of 0.5 inch per second (ips) at 1,000 psi, and preferably in the range of from about 1.0 ips to about 1.2 ips at 1,000 psi, are generally desired,
Another related but important design criteria is that the gas generant composition produces a limited quantity of particulate materials. Particulate materials can interfere with the operation of the supplemental restraint system, present an inhalation hazard, irritate the skin and eyes, or constitute a hazardous solid waste that must be dealt with after the operation of the safety device. These features are undesirable aspects of the present sodium azide materials, but are presently tolerated in the absence of an acceptable alternative.
In addition to producing limited, if any, quantities of particulates, it is desired that at least the bulk of any such particulates be easily filterable. For instance, it is desirable that the composition produce a filterable, solid slag. If the solid reaction products form a stable material, the solids can be filtered and prevented from escaping into the surrounding environment. This also limits interference with the gas generating apparatus and the spreading of potentially harmful dust in the vicinity of the spent air bag which can cause lung, mucous membrane and eye irritation to vehicle occupants and rescuers.
Both organic and inorganic materials have also been proposed as possible gas generants. Such gas generant compositions include oxidizers and fuels which react at sufficiently high rates to produce large quantities of gas in a fraction of a second.
At present, sodium azide is the most widely used and accepted gas generating material. Sodium azide nominally meets industry specifications and guidelines. Nevertheless, sodium azide presents a number of persistent problems. Sodium azide is relatively toxic as a starting material, since its toxicity level as measured by oral rat LD50 is in the range of 45 mg/kg. Workers who regularly handle sodium azide have experienced various health problems such as severe headaches, shortness of breath, convulsions, and other symptoms.
In addition, sodium azide combustion products can also be toxic since molybdenum disulfide and sulfur are presently the preferred oxidizers for use with sodium azide. The reaction of these materials produces toxic hydrogen sulfide gas, corrosive sodium oxide, sodium sulfide, and sodium hydroxide powder. Rescue workers and automobile occupants have complained about both the hydrogen sulfide gas and the corrosive powder produced by the operation of sodium azide-based gas generants.
Increasing problems are also anticipated in relation to disposal of unused gas-inflated supplemental restraint systems, e.g. automobile air bags in demolished cars, The sodium azide remaining in such supplemental restraint systems can leach out of the demolished car to become a water pollutant or toxic waste. Indeed, some have expressed concern that sodium azide, when contacted with battery acids following disposal, forms explosive heavy metal azides or hydrazoic acid.
Sodium azide-based gas generants are most commonly used for air bag inflation, but with the significant disadvantages of such compositions many alternative gas generant compositions have been proposed to replace sodium azide. Most of the proposed sodium azide replacements, however, fail to deal adequately with each of the selection criteria set forth above.
One group of chemicals that has received attention as a possible replacement for sodium azide includes tetrazoles and triazoles. These materials are generally coupled with conventional oxidizers such as KNO3 and Sr(NO3)2. Some of the tetrazoles and triazoles that have been specifically mentioned include 5-aminotetrazole, 3-amino-1,2,4-triazole, 1,2,4-triazole, 1H-tetrazole, bitetrazole and several others. However, because of poor ballistic properties and/or high gas temperatures, none of these materials has yet gained general acceptance as a sodium azide replacement.
It will be appreciated, therefore, that there are a number of important criteria for selecting gas generating compositions for use in automobile supplemental restraint systems. For example, it is important to select starting materials that are not toxic. At the same time, the combustion products must not be toxic or harmful. In this regard, industry standards limit the allowable amounts of various gases produced by the operation of supplemental restraint systems.
It would, therefore, be a significant advancement in the art to provide compositions capable of generating large quantities of gas that would overcome the problems identified in the existing art. It would be a further advancement to provide gas generating compositions which are based on substantially nontoxic starting materials and which produce substantially nontoxic reaction products. It would be another advancement in the art to provide gas generating compositions which produce limited particulate debris and limited undesirable gaseous products. It would also be an advancement in the art to provide gas generating compositions which form a readily filterable solid slag upon reaction.
Such compositions and methods for their use are disclosed and claimed herein.
SUMMARY AND OBJECTS OF THE INVENTIONThe novel solid compositions of the present invention include a non-azide fuel and an appropriate oxidizer. Specifically, the present invention is based upon the discovery that improved gas generant compositions are obtained using substantially anhydrous 5-aminotetrazole, or a salt or a complex thereof, as a non-azide fuel. The compositions of the present invention are useful in supplemental restraint systems, such as automobile air bags.
It will be appreciated that 5-aminotetrazole generally takes the monohydrate form. However, gas generating compositions based upon hydrated tetrazoles have been observed to have unacceptably low burning rates. Accordingly, the present invention is related to the use of 5-aminotetrazole in its anhydrous or substantially anhydrous form.
The methods of the present invention teach manufacturing techniques whereby the processing problems encountered in the past can be minimized. In particular, the present invention relates to methods for preparing acceptable gas generating compositions using anhydrous 5-aminotetrazole. In one embodiment, the method entails the following steps:
(a) obtaining a desired quantity of gas generating material, said gas generating material comprising an oxidizer and hydrated 5-aminotetrazole;
(b) preparing a slurry of said gas generating material in water;
(c) drying said slurried material to a constant weight;
(d) pressing said material into pellets in hydrated form; and
(e) drying said pellets such that the gas generating material is in anhydrous or substantially anhydrous form.
Importantly, the methods of the present invention provide for pressing of the material while still in the hydrated form. Thus, it is possible to prepare acceptable gas generant pellets. If the material is pressed while in the anhydrous form, the pellets are generally observed to powder and crumble, particularly when exposed to a humid environment.
Following pressing of the pellets, the gas generating material is dried until the tetrazole is substantially anhydrous. Generally, the hydrated 5-aminotetrazole composition loses about 3% to 5% of its weight during the drying process. The 5-aminotetrazole itself loses about 17% of its weight (theoretical weight loss is 17.5%). This is found to occur, for example, after drying at 110° C. for 12 hours. A material in this state can be said to be anhydrous for purposes herein. Of course the precise temperature and length of time of drying is not critical to the practice of the invention, but it is presently preferred that the temperature not exceed 150° C. FIG. 1 illustrates a typical 5-aminotetrazole drying curve at 35° C.
Pellets prepared by this method are observed to be robust and maintain their structural integrity when exposed to humid environments. In general, pellets prepared by the preferred method exhibit crush strengths in excess of 10 lb load in a typical configuration (3/8 inch diameter by 0.07 inches thick). This compares favorably to those obtained with commercial sodium azide generant pellets of the same dimensions, which typically yield crush strengths of 5 lb to 15 lb load.
The present compositions are capable of generating large quantities of gas while overcoming various problems associated with conventional gas generating compositions. The compositions of the present invention produce substantially nontoxic reaction products. The present compositions are particularly useful for generating large quantities of a nontoxic gas, such as nitrogen gas. Significantly, the present compositions avoid the use of azides, produce no sodium hydroxide by-products, generate no sulfur compounds such as hydrogen sulfide and sulfur oxides, and still produce a nitrogen containing gas.
The compositions of the present invention also produce only limited particulate debris, provide good slag formation and substantially avoid, if not avoid, the formation of nonfilterable particulate debris. At the same time, the compositions of the present invention achieve a relatively high burn rate, while producing a reasonably low temperature gas. Thus, the gas produced by the present invention is readily adaptable for use in deploying supplemental restraint systems, such as automobile air bags.
BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 is a graph of a drying curve for 5-aminotetrazole at 35° C.
DETAILED DESCRIPTION OF THE INVENTIONThe present invention relates to the use of substantially anhydrous 5-aminotetrazole (sometimes referred to herein as "5-AT"), or a salt or a complex thereof, as the primary fuel in a novel gas generating composition. As used herein, substantially anhydrous 5-aminotetrazole is defined as hydrated 5-AT which has lost not less than about 14% of its weight during drying and more preferably about 17% of its weight during drying. The salts or complexes of 5-aminotetrazole may including, for example, those of transition metals such as copper, cobalt, iron, titanium, and zinc; alkali metals such as potassium and sodium; alkaline earth metals such as strontium, magnesium, and calcium; boron; aluminum; and nonmetallic cations such as ammonium, hydroxylammonium, hydrazinium, guanidinium, aminoguanidinium, diaminoguanidinium, triaminoguanidinium, or biguanidinium.
In the compositions of the present invention, the fuel is paired with an appropriate oxidizer. Inorganic oxidizing agents are preferred because they produce a lower flame temperature and an improved filterable slag. Such oxidizers include metal oxides and metal hydroxides. Other oxidizers include metal nitrates, metal nitrites, metal chlorates, metal perchlorates, metal peroxides, ammonium nitrate, ammonium perchlorate and the like. The use of metal oxides or hydroxides as oxidizers is particularly useful and such materials include for instance, the oxides and hydroxides of copper, cobalt, manganese, tungsten, bismuth, molybdenum, and iron, such as CuO, Co2 O3, Fe20 O3, MoO3, Bi2 MoO6, Bi2 O3, and Cu(OH)2. The oxidizer may also be a mixture of the above-referenced oxidizing agents, or the above-referenced oxidizing agents and other oxidizing agents. For example, the oxide and hydroxide oxidizing agents mentioned above can, if desired, be combined with other conventional oxidizers such as Sr(NO3)2, NH4 ClO4, and KNO3, for a particular application, such as, for instance, to provide increased flame temperature or to modify the gas product yields.
A presently preferred oxidizer is cupric oxide. It has been found that gas generant compositions prepared from pyrometallurgical grade cupric oxide produce faster burn rates compared to hydrometallurgical grade cupric oxide. In addition, faster burn rates have been observed with ground cupric oxide compared to unground cupric oxide. An average oxidizer particle size of less than about 4 microns is presently preferred.
The 5-AT fuel is combined, in a fuel-effective amount, with an appropriate oxidizing agent to obtain a gas generating composition. In a typical formulation, the tetrazole fuel comprises from about 10 to about 50 weight percent of the composition and the oxidizer comprises from about 50 to about 90 weight percent thereof. More particularly, a composition can comprise from about 15 to about 35 weight percent fuel and from about 60 to about 85 weight percent oxidizer.
An example of the reaction between the anhydrous tetrazole and the oxidizer is as follows: ##STR1##
The present compositions can also include additives conventionally used in gas generating compositions, propellants, and explosives, such as binders, burn rate modifiers, slag formers, release agents, and additives which effectively remove NOx. Typical binders include lactose, boric acid, silicates including magnesium silicate, polypropylene carbonate, polyethylene glycol, and other conventional polymeric binders. Typical burn rate modifiers include Fe2 O3, K2 B12 H12, Bi2 MoO6, and graphite carbon fibers.
A number of slag forming agents are known and include, for example, clays, talcs, silicon oxides, alkaline earth oxides, hydroxides, oxalates, of which magnesium carbonate, and magnesium hydroxide are exemplary. A number of additives and/or agents are also known to reduce or eliminate the oxides of nitrogen from the combustion products of a gas generant composition, including alkali metal salts and complexes of tetrazoles, aminotetrazoles, triazoles and related nitrogen heterocycles of which potassium aminotetrazole, sodium carbonate and potassium carbonate are exemplary. The composition can also include materials which facilitate the release of the composition from a mold such as graphite, molybdenum sulfide, calcium stearate, or boron nitride.
The present compositions produce stable pellets. This is important because gas generants in pellet form are generally used for placement in gas generating devices, such as automobile supplemental restraint systems. Gas generant pellets should have sufficient crush strength to maintain their shape and configuration during normal use and withstand loads produced upon ignition since pellet failure results in uncontrollable internal ballistics.
The present invention relates specifically to the preparation of anhydrous 5-AT gas generant compositions. Anhydrous 5-AT compositions produce advantages over the hydrated form. For example, a higher (more acceptable) burn rate is generally observed. At the same time, the methods of the present invention allow for pressing the composition in the hydrated form such that pellets with good integrity are produced.
As discussed above, a gas generating composition comprises anhydrous 5-AT coupled with an acceptable oxidizer. At the stage of formulating the composition, the 5-aminotetrazole may be in the hydrated form which is generally available as a monohydrate. The components of the gas generant are mixed, for example by dry blending.
A water slurry of the gas generant composition is then preferably prepared. Generally the slurry comprises from about 3% to about 40% water by weight, with the remainder of the slurry comprising the gas generating composition. Although other materials may be used to prepare the slurry, such as ethanol and methanol, water is presently preferred. The slurry will generally have a paste-like consistency, although under some circumstances a damp powder consistency is desirable.
The mixture is then dried to a constant weight. This preferably takes place at a temperature less than about 110° C., and preferably less than about 45° C. For instance, a 5-AT/CuO composition mixture will generally establish an equilibrium moisture content in the range of from about 3% to about 5%, with the 5-AT being in the hydrated form (typically monohydrated). 5-AT monohydrate has a moisture content of approximately 17%.
Next, the material is pressed into pellet form in order to meet the requirements of the specific intended end use. As mentioned above, pressing the pellets while the 5-AT is hydrated results in a better pellet. In particular, crumbling of the material after pressing and upon exposure to ambient humidities is substantially avoided. It will be appreciated that if the pellet crumbles it generally will not burn in the manner required by automobile air bag systems.
After pressing the pellet, the material is dried such that the composition becomes anhydrous or substantially anhydrous. For instance, the above mentioned 5-AT/CuO material typically loses between 3% and 5% by weight water during this transition to the anhydrous state. It is found to be acceptable if the material is dried for a period of about 12 hours at about 110° C., or until the weight of the material stabilizes as indicated by no further weight loss at the drying temperature. For the purposes of this application, the material in this condition will be defined as "anhydrous."
Following drying it may be preferable to protect the material from exposure to moisture, even though the material in this form has not been found to be unduly hygroscopic at humidities below 20% Rh at room temperature. Thus, the pellet may be placed within a sealed container, or coated with a water impermeable material.
One of the important advantages of the anhydrous 5-AT gas generating compositions of the present invention, is that they are stable and combust to produce sufficient volumes of substantially nontoxic gas products. 5-AT has also been found to be safe when subjected to conventional impact, friction, electrostatic discharge, and thermal tests.
These anhydrous 5-AT compositions also are prone to form slag, rather than particulate debris. This is a further significant advantage in the context of gas generants for automobile air bags.
An additional advantage of an anhydrous 5-AT fueled gas generant composition is that the burn rate performance is good. As mentioned above, burn rates above 0.5 inch per second (ips) are preferred. Burn rates in these ranges are achievable using the compositions and methods of the present invention.
Anhydrous 5-AT compositions compare favorably with sodium azide compositions in terms of burn rate as illustrated in Table 1.
Boraychem supply professional and honest service.
TABLE 1
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Relative Vol. Gas
Gas Generant
Burn Rate at psi
Per Vol. Generant
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Sodium azide
1.2 ± 0.1 ips
0.97
(baseline)
Sodium azide
1.3 ± 0.2 ips
1.0
low sulfur
Anhydrous 0.75 ± 0.05 ips
1.2
5-AT/CuO
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An inflatable restraining device, such as an automobile air bag system comprises a collapsed, inflatable air bag, a means for generating gas connected to that air bag for inflating the air bag wherein the gas generating means contains a nontoxic gas generating composition which comprises a fuel and an oxidizer therefor wherein the fuel comprises anhydrous S-AT or a salt or complex thereof.
Suitable means for generating gas include gas generating devices which are used in supplemental safety restraint systems used in the automotive industry. The supplemental safety restraint system may, if desired, include conventional screen packs to remove particulates, if any, formed while the gas generant is combusted.
The present invention is further described in the following non-limiting examples.
EXAMPLES EXAMPLE 1Gas generating compositions were prepared utilizing 5-aminotetrazole as the fuel. Commercially obtained 5-aminotetrazole monohydrate was recrystallized from ethanol, dried in vacuo (1 mm Hg) at 170° F. for 48 hours and mechanically ground to a fine powder. Cupric oxide (15.32 g, 76.6%) and 4.68 g (23.4%) of the dried 5-aminotetrazole were slurried in 14 grams of water and then dried in vacuo (1 mm Hg) at 150° F. to 170° F. until the moisture content was approximately 25% of the total generant weight. The resulting paste was forced through a 24 mesh screen to granulate the mixture, which was further dried to remove the remaining moisture. A portion of the resulting dried mixture was then exposed to 100% relative humidity at 170° F. for 24 hours during which time 3.73% by weight of the moisture was absorbed. The above preparation was repeated on a second batch of material and resulted in 3.81% moisture being retained.
Pellets of each of the compositions were pressed and tested for burning rate and density. Burning rates of 0.799 ips at 1,000 psi were obtained for the anhydrous composition, and burning rates of 0.395 ips at 1,000 psi were obtained for the hydrated compositions. Densities of 3.03 g/cc and 2.82 g/cc were obtained for the anhydrous and hydrated compositions respectively. Exposure of pellets prepared from the anhydrous condition to 45% and 60% Rh at 70° F. resulted in complete degradation of pellet integrity within 24 hours.
EXAMPLE 2In this example compositions within the scope of the invention were prepared. The compositions comprised 76.6% CuO and 23.4% 5-aminotetrazole. In one set of compositions, the 5-aminotetrazole was received as a coarse material. In the other set of compositions, the 5-aminotetrazole was recrystallized from ethanol and then ground.
A water slurry was prepared using both sets of compositions. The slurry comprised 40% by weight water and 60% by weight gas generating composition. The slurry was mixed until a homogenous mixture was achieved.
The slurry was dried in air to a stable weight and then pressed into pellets. Four pellets of each formulation were prepared and tested. Two pellets of each composition were dried at 110° C. for 18 hours and lost an average of 1.5% of their weight.
Burn rate was determined at 1,000 psi and the following results were achieved:
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Burn Rate (ips)
Sample (ips @ psi)
Density (gm/cc)
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Coarse 5-AT/no post drying
0.620 2.95
Coarse 5-AT/post drying
0.736 2.94
Fine 5-AT/no post drying
0.639 2.94
Fine 5-AT/post drying
0.690 2.93
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Overall, improved results were observed using the post drying method of the present invention.
EXAMPLE 3Commercially obtained 5-aminotetrazole monohydrate was prepared to be utilized as a fuel for use in gas generant compositions. Approximately five pounds of aminotetrazole monohydrate (Aldrich) was ground in a fluid energy mill. Using a Microtrac Standard Range Particle Analyzer it was determined that 10% of the resulting fuel particles had a diameter less than 2.2 microns and that 50% of the fuel particles had a diameter less than 5.6 microns. The ground aminotetrazole hydrate was dried at 220 F for at least four hours. A weight loss of approximately 14% was observed. The resulting anhydrous aminotetrazole powder was forced through a 60 mesh sieve before use.
EXAMPLE 4Three gas generating compositions were prepared utilizing the anhydrous 5-aminotetrazole powder from Example 3 as the fuel and three different types of cupric oxide as the oxidizer. The three types of cupric oxide were obtained from the American Chemet Corporation. They consisted of a ground cupric oxide of pyrometallurgical origin (grd pyro) with a mean particle size of 3.6 microns, a cupric oxide of hydrometallurgical origin (ungrd hydro) with a mean particle size of 9.5 microns, and a ground cupric oxide of hydrometallurgical origin (grd hydro) with a mean particle size of 3.6 microns. The respective cupric oxide (22.98 g, 76.60%) was stirred into 7.02 g (23.40%) of the aminotetrazole, the composition was shaken in an enclosed container for approximately two minutes and then slurried with 12 g of water. The three compositions were dried overnight at 73° F., and granulated through an 18 mesh sieve. Samples therefrom were pressed into 1/2" diameter cylindrical pellets with a weight of three grams each. The resulting burn rate data are summarized in Table 2. The burn rates were a function of the type of cupric oxide used as the oxidizer and increased in the burn rate as follows: ungrd hydro<<grd hydro<grd pyro.
EXAMPLE 5Samples of granules prepared according to the procedure of Example 4 were dried further at 220° F. The accompanying weight losses are summarized in Table 2. Samples of the 5-AT/CuO composition were pressed into 1/2" diameter cylindrical pellets with a weight of three grams each. The resulting burn rate data are summarized in Table 2. The burn rates were a function of the type of cupric oxide used as the oxidizer and increased in burn rate as follows: ungrd hydro<<grd hydro<grd pyro. The burn rates were about twice as high as those obtained for pellets derived from granules dried at 73° F. as described in Example Samples of the granules prepared in Example 4 that were dried at 220° F. were pressed into 1/2" diameter cylindrical pellets with a weight of one gram each. These pellets were placed in a humidity chamber held at 60% humidity. Over a period of 67 hours, the pellets had gained between 3.7 and 4.3% of their original weight and were seriously delaminated with several large circumferential cracks.
EXAMPLE 6Samples of granules prepared according to the procedure of Example 4 were pressed into 1/2" diameter cylindrical pellets with a weight of three grams each. The pellets were dried overnight at 220° F. The accompanying weight losses are reported in Table 2 as well as the resulting burn rate data. The burn rates were a function of the type of cupric oxide used as the oxidizer and increased in burn rate as follows: ungrd hydro<<grd hydro<grd pyro. Furthermore, the burn rates are consistently higher than those of the corresponding pellets prepared as in Example 5. A sample of granules prepared in Example 4 were pressed into 1/2" diameter cylindrical pellets with a weight of one gram each. These pellets were dried at 220° F. and then placed in a humidity chamber held at 60% humidity. Over a period of 67 hours, the pellets gained between 4.2 and 4.5% of their original weight. These pellets appeared to be unchanged and showed no signs of cracking or delamination. Pellets processed by this method appear to be much more robust under conditions of high humidity than those prepared by the method of Example 5.
EXAMPLE 7A gas generating composition was prepared utilizing anhydrous 5-aminotetrazole powder from Example 3 as the fuel. The grd pyro cupric oxide described in Example 4 (22.98 g, 76.60%) was stirred into 7.02 g (23.40%) of the aminotetrazole. The composition was shaken in an enclosed container for approximately two minutes. However, this particular sample was not slurried in water or any other solvent. The resulting powder was pressed into 1/2" diameter cylindrical pellets with a weight of three grams each. The resulting burn rate data are summarized in Table 2. The burn rate of the composition was significantly lower than that of the corresponding grd pyro composition which was slurried in water and dried at 220° F. as pellets. One gram pellets of this material gained 4.7% of their original weight over a period of 67 hours in an atmosphere containing 60% humidity. In addition, pellets of this material delaminated during this humidity aging.
EXAMPLE 8A composition containing aminotetrazole from Example 3 (23.40 g, 23.40%) and the grd pyro cupric oxide described in Example 4 (76.60 g, 76.60%) was mixed and dried as in Example 4. Three gram pellets were produced according to procedures in Examples 4, 5, and 6, respectively. The burn rate data obtained from the 100 g mix are summarized in Table 2. Again, pellets produced from the completely dried granules delaminated, while pellets pressed from slightly moist granules and then dried as pellets remained intact during humidity aging.
EXAMPLE 9A crystalline sample of aminotetrazole hydrate (Dynamit Nobel) was dehydrated at 220° F. losing 17.1% of it original weight (17.5% being theoretical weight loss). A portion of this anhydrous aminotetrazole was recrystallized from methanol and an additional portion was recrystallized from ethanol. The resulting solids were heated at 220° F. to a constant weight. Each type of aminotetrazole was forced through a 60 mesh sieve. Three compositions containing grd pyro cupric oxide (38.30 g, 76.60%) and aminotetrazole (11.70 g, 23.40%) were mixed and processed in the solvent from which the aminotetrazole was last crystallized: water, methanol and ethanol, respectively. The cupric oxide and aminotetrazole were dry blended and mixed by shaking, followed by slurrying in 19 g, 11 g and 13 g of water, methanol an ethanol, respectively. The mixes were dried partially, granulated, dried completely, and then allowed to take up solvent in solvent-saturated air over a three day period. The formulations gained 3.6%, 2.1%, and 1.1% water, methanol and ethanol, respectively. Pellets were pressed from -18 mesh solvated granules. The pellets lost 4.2%, 0.6%, and 0.2% of their weight upon drying at 220° F. Burn rate data are summarized in Table 2. Burn rate for pellets derived from water-processing are significantly higher than those derived from alcohol processing.
TABLE 2
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Cupric Oxide/Aminotetrazole Formulations*
Burn Rate Variations with Processing and Cupric Oxide Grade
Mix Final
Final
Final
Pellets
Example
CuO Size
Slurry
Dry Dry Dry in Rb (in/s) at
Number
Grade (gm)
Media
Form Temp.
Wt. Loss
Humidity
P.sub.ave (psi)
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Ex. 4
grd pyro
30 water
granules
73° F.
NA NA 0.329 at
Ex. 4
grd hydro
10 water
granules
73° F.
NA NA 0.309 at
Ex. 4
ungrd hydro
30 water
granules
73° F.
NA NA 0.229 at
Ex. 5
grd pyro
30 water
granules
220° F.
5.3% crumbled
0.711 at
Ex. 5
grd hydro
30 water
granules
220° F.
6.0% crumbled
0.634 at
Ex. 5
ungrd hydro
30 water
granules
220° F.
7.4% crumbled
0.497 at
Ex. 6
grd pyro
30 water
pellets
220° F.
5.3% intact
0.787 at
Ex. 6
grd hydro
30 water
pellets
220° F.
4.8% intact
0.731 at
Ex. 6
ungrd hydro
30 water
pellets
220° F.
6.0% intact
0.537 at
Ex. 7
grd pyro
30 dry powder
NA NA crumbled
0.565 at
Ex. 8
grd pyro
100
water
granules
73° F.
NA NA 0.325 at
Ex. 8
grd pyro
100
water
granules
220° F.
4.6% crumbled
0.735 at
Ex. 8
grd pyro
100
water
granules
220° F.
4.7% intact
0.815 at
Ex. 9
grd pyro
50 water
pellets
220° F.
4.25%
NA 0.757 at
Ex. 9
grd pyro
50 methanol
pellets
220° F.
0.64%
NA 0.537 at
Ex. 9
grd pyro
50 ethanol
pellets
220° F.
0.16%
NA 0.540 at
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*76.60% cupric oxide, 23.40% anhydrous aminotetrazole.
EXAMPLE 10
A gas generating composition consisting of 55.78% (11.16 g) grd pyro cupric oxide as described in Example 4, 26.25% (5.25 g) of the 5.6 micron, partially dehydrated aminotetrazole (AT 0.8H2 O) described in Example 3, and 17.96% (3.59 g) of a ground sample of strontium nitrate was slurried with five grams of water and dried at 135° F. to a constant weight. Pellets were pressed from a portion of this gas generant material exhibiting a pellet density of 2.8 g/cc and a burn rate of 0.886 ips at Pave of psi. Additional generant was dried further at 220° F. with a corresponding weight loss of 2%. The density of pellets therefrom remained at 2.8 g/cc while the burn rate increased to 0.935 ips at a Pave of psi. The theoretical flame temperature of the anhydrous formulation is ° K.
EXAMPLE 11Three gas generating compositions were prepared utilizing the anhydrous 5-aminotetrazole powder prepared in Example 3 as the fuel (21.24%, 10.62 g), the three different types of cupric oxide described in Example 4, as the oxidizer (54.72%, 27.36 g), and ground strontium nitrate as the co-oxidizer (24.04%, 12.02 g). The formulation was mixed, slurried, dried, and granulated according to the procedure in Example 4, with a drying temperature of 122° F. Pellets were formed and processed similarly to those described in Example 4, 5, and 6. The results are summarized in Table 3. As with the cupric oxide/aminotetrazole formulations, burn rate values are dependent on the type of cupric oxide and follow the same trend: ungrd hydro<<grd hydro<grd pyro. Pellets from hydrated granules exhibit a lower burn rate than pellets derived from granules dried at 220° F. or from pellets dried at 220° F. The latter two types of pellets have comparable burn rates. This may be due in part to the fact that the weight loss from the hydrated compositions is much smaller than for the cupric oxide/aminotetrazole series of compositions in Example 4-6. One gram pellets that were formed and processed similarly to those of Examples 4-6, were placed in closed chamber with 60% humidity. After aging for 90 hours, weight gains of 3-4.5% were observed. Furthermore, all of the pellets showed signs of delamination except for the pellets containing the grd pyro cupric oxide that had been dried in the pellet form (See, Table 3). The granules of this particular mix had been pressed with the highest moisture content.
TABLE 3
__________________________________________________________________________
Cupric Oxide/Strontium Nitrate/Aminotetrazole Formulations*
Burn Rate Variations with Processing and Cupric Oxide Grade
Mix Final
Final
Final
Pellets
Example
CuO Size
Slurry
Dry Dry Dry in Rb (in/s) at
Number
Grade (gm)
Media
Form Temp.
Wt. Loss
Humidity
P.sub.ave (psi)
__________________________________________________________________________
Ex. 11
grd pyro
50 water
granules
122° F.
NA NA 0.793 at
Ex. 11
grd hydro
50 water
granules
122° F.
NA NA 0.753 at
Ex. 11
ungrd hydro
50 water
granules
122° F.
NA NA 0.655 at
Ex. 11
grd pyro
50 water
granules
220° F.
1.6% crumbled
0.986 at
Ex. 11
grd hydro
50 water
granules
220° F.
0.7% crumbled
0.758 at
Ex. 11
ungrd hydro
50 water
granules
220° F.
0.6% crumbled
0.736 at
Ex. 11
grd pyro
50 water
granules
220° F.
1.9% intact
0.950 at
Ex. 11
grd hydro
50 water
granules
220° F.
0.9% crumbled
0.772 at
Ex. 11
ungrd hydro
50 water
granules
220° F.
0.7% crumbled
0.678 at
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*54.72% cupric oxide, 24.04 strontium nitrate, 21.24% anhydrous
aminotetrazole.
EXAMPLE 12
A gas generating composition was prepared utilizing anhydrous 5-aminotetrazole powder (9.86%, 0.54 g, Fairmont), 8.7 micron ungrd hydro cupric oxide (55.30%, 3.04 g, Aldrich) as the oxidizer, ground strontium nitrate as the co-oxidizer (24.52%, 1.35 g), and sodium dicyanamide (NaDCA) as a ballistic modifier (10.32%, 0.57 g Aldrich Lot). The formulation was mixed as a water slurry, dried completely and pressed into pellets. The burn rate was 0.567 ips at Pave of psi with a calculated flame temperature of ° K.
EXAMPLE 13A gas generating composition was prepared utilizing anhydrous 5-aminotetrazole powder (12.64%, 1.27 g, Fairmont), 8.7 micron ungrd hydro cupric oxide (31.52%, 3.15 g, Aldrich) as the cooxidizer, ground strontium nitrate as the oxidizer (42.59%, 4.26 g), and sodium dicyanamide as a ballistic modifier (13.23%, 1.32 g, Aldrich Lot). The formulation was mixed as a water slurry, dried completely, and pressed into pellets. The burn rate was 0.817 ips with a Pave of psi. The theoretical flame temperature is ° K. Mixes producing the fastest burn rate are summarized in Table 4 for each of the formulation types described in the above examples.
TABLE 4
__________________________________________________________________________
Cupric Oxide, Aminotetrazole Formulations
Effect of Additives on Burn Rate
Mix
Flame
Example Size
Temp.
Density
Weight %
Rb (in/s) at
Number
Formulation
(gm)
(°K.)
(g/cc)
Gas P.sub.ave (psi)
__________________________________________________________________________
Ex. 8
23.40%
AT 100
2.95 39 0.815 at
76.60%
CuO
Ex. 11
21.24%
AT 50
2.86 39 0.950 at
54.72%
CuO
24.04%
Sr(NO.sub.3).sub.2
Ex. 10
23.34%
AT 20
2.83 41 0.935 at
57.99%
CuO
18.67%
Sr(NO.sub.3).sub.2
Ex. 12
9.86%
AT 5.5
3.11 34 0.567 at
55.31%
CuO
24.52%
Sr(NO.sub.3).sub.2
10.31%
NaDCA
Ex. 13
12.64%
AT 10
2.58 45 0.817 at
31.53%
CuO
42.60%
Sr(NO.sub.3).sub.2
13.23%
NaDCA
__________________________________________________________________________
The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description.
A Click Chemistry Approach to Tetrazoles: Recent Advances
1. Introduction
1.1. Chemistry of tetrazoles
1H-Tetrazole (1) is a crystalline light yellow powder and odorless. Tetrazole shows melting point temperature at 155&#;157°C. On heating, tetrazoles decomposed and emit toxic nitrogen fumes. These are burst vigorously on exposed to shock, fire, and heat on friction.
Tetrazoles easily react with acidic materials and strong oxidizers (acidic chloride, anhydrides, and strong acids) to liberate corrosive and toxic gases and heat. It undergoes reaction with few active metals and produces new compounds which are explosives to shocks. It involves exothermic reactions with reducing agents. On heating or burning, it releases carbon monoxide, carbon dioxide, and harmful nitrogen oxide. Tetrazole dissolves in water, acetonitrile, etc. Generally, dilute 1H-tetrazole in acetonitrile is used for DNA synthesis in biochemistry.
The presence of free N-H causes the acidic nature of tetrazoles and forms both aliphatic and aromatic heterocyclic compounds. Heterocycles of tetrazoles can stabilize the negative charge by delocalization and show corresponding carboxylic acid pKa values. Tetrazole nitrogen electron density results in the formation of so many stable metallic compounds and molecular complexes. This compound shows strong negative inductive effect (&#;I electron withdrawing) and weak positive mesomeric effect (+M electron releasing).
The tetrazole is a five-membered aza compound with 6π electrons, and 5-substituted tetrazole reactivity is similar to aromatic compounds. The Huckel 6π electrons are satisfied by four π electrons of ring and one loan pair of electrons of nitrogen. The acidic nature of tetrazole is similar to corresponding carboxylic acids, but there is a difference in annular tautomerism of ring tetrazoles to carboxylic acids. The acidic nature of tetrazole is mainly affected by substitution compound nature at C-5 position. 5-Phenyltetrazole anion shows high acidic nature like benzoate due to resonance stabilization. A simple method to produce tetrazole anion is the reaction of tetrazole with metal hydroxides and can be stable in aqueous and alcoholic solution at high temperature.
1.2. Introduction to click chemistry
Click chemistry is called as tagging in synthesis of chemicals. It is in the category of non-harmful reactions, proposed initially to unite the base materials of choice with certain bimolecular substance. It also can be termed as a non-peculiar reactive process. Indeed it explains a way of generating products that follow examples in nature. At the same time, it can produce the variety of materials by consolidating small compatible units. Usually, click reactions join a biomolecule and a reporter molecule. Click chemistry is not limited to the state of survival. It is the concept of a &#;click&#; reaction that has been used in pharmacological and various biomedical applications. It also can be described as non-single specific reaction etic application. Nevertheless, it is observed to be highly functional in the diagnosis of localization and qualification of bimolecular material.
Click reactions occur in one pot and generally make an evidence of being uninterrupted by water. They produce negligible and innocuous corollary and are spring-loaded. In addition to this, they are distinguished by a high thermodynamic driving force that pushes them rapidly and irrevocably to supply a single reaction product, with high reaction specificity. In few cases, they are created with both regio- and stereospecificity. These click reactions are specifically adaptable in the case of segregating and navigating the molecules in composite biological environments. In such conditions, items in like manner should be physiologically steady, and any side effects should be nonlethal.
Researchers have opened up the likelihood of hitting specific focuses in complex cell lysates, by developing specific and controllable bio-orthogonal reactions. Recently, they have adjusted snap science for use in live cells, for instance, utilizing little atom tests that find and append to their objectives by click reactions. In spite of difficulties of cell porousness, bio-orthogonality, foundation naming, and response effectiveness, click responses have officially demonstrated valuable in another era of pull-down tests and fluorescence spectrometry. All the more as of late, novel strategies have been utilized to fuse click response accomplices onto and into biomolecules, including the joining of unnatural amino acids containing receptive gatherings into proteins and the change of nucleotides. These strategies speak to a piece of the field of compound science, in which click science assumes a central part by deliberately and particularly coupling secluded units to different finishes.
This refresh outlines the developing use of &#;click&#; science in various zones, for example, bioconjugation, sedate disclosure, materials science, and radiochemistry. It additionally talks about snap science responses that continue quickly with high selectivity, specificity, and yield. Two essential qualities make click science so appealing for collecting mixes, reagents, and biomolecules for preclinical and clinical applications. To begin with, click reactions are bio-orthogonal. First of all, they are neither reciprocal nor their functional gatherings of different products connect with functionalized biomolecules. Secondly, the responses continue effortlessly under gentle nontoxic conditions. Example is their reaction at the room temperature and, for the most part, in water. The copper-catalyzed Huisgen cycloaddition, azide-alkyne [3+2] dipolar cycloaddition, Staudinger ligation, and azide-phosphine ligation all have these interesting qualities. These responses can be utilized to change one cell part while leaving others unharmed or untouched.
Click chemistry has discovered expanding applications in all parts of medication revelation in restorative science, for example, for producing lead mixes through combinatorial strategies. Through bioconjugation click chemistry is thoroughly utilized in proteomics and nucleic exploration. In radiochemistry, specific radiolabeling of biomolecules in cells and living creatures for imaging and treatment has been acknowledged by this innovation. Bifunctional chelating operators for a few radionuclides are valuable for positron discharge tomography and single-photon emanation processed tomography. They have additionally been set up by click chemistry. This survey reasons that click chemistry is not the ideal conjugation, and gathering innovation for all applications, however, gives a capable, appealing another option to ordinary science. This science has turned out to be prevalent in fulfilling numerous criteria, e.g., biocompatibility, selectivity, yield, stereospecificity, etc. In this way, one can expect that it will subsequently turn into a more normal procedure soon for an extensive variety of uses.
1.3. Introduction to molecular docking
Molecular docking (hereafter, MD) is the study of fitting together by two or more molecular components (e.g., drug and enzyme or protein). It is something like a problem of &#;lock and key&#; (Figure 1). It is an optimization issue which clearly explains how best a ligand and protein bind based on orientation. As both ligand and protein are flexible, a &#;hand-in-glove&#; word suit more effective compared to &#;lock and key&#; model. Both ligand and protein adapt their confirmation for overall binding, known as &#;induced effect.&#;
MD research depends mostly on computationally simulating the molecular recognition process by decreasing the free energy of overall system. Basic awareness on the preferred orientation in turn may be used to predict the binding affinity between two molecules used. Molecular docking is an invaluable tool in the field of molecular biology, computational structural biology, computer-aided drug designing, and pharmacogenomics.
There are two ways of docking approaches, namely, the first matching methodology which explains ligand-enzyme as complementary surfaces and the other simulated docking methodology of protein and ligand pairwise interaction energies. The application of docking in a targeted drug-delivery system is a huge benefit. One can study the size, shape, charge distribution, polarity, hydrogen bonding, and hydrophobic interactions of both ligand (drug) and receptor (target site).
1.4. Aims and significance
The investigation of tetrazoles centers the most imperative organic exercises like antihypertensive, against inflammatory, antibacterial, antifungal, anticancer, antidiabetic, and hypoglycemic activity. Different strategies for synthesis and characterization techniques were discussed.
Throughout the previous couple of years, investigation of tetrazole chemistry has been rapidly expanded in view of its huge applications, for the most part because of the pretended by this heterocyclic usefulness in restorative chemistry. This provides more support to pharma field and metabolically stable swap for carboxylic acid functionalities, particularly, joining of the tetrazole exercises into angiotensin II rival structures, sartans (2&#;4) [1, 2, 3, 4].
Irbesartan (5), one of the essential tetrazole subsidiaries, has a place with the sort of medication called angiotensin II receptor enemy antihypertensives. This medication is utilized for the treatment of high blood pressure (hypertension) and for kidney issues because of Type 2 diabetes (noninsulin-dependent).
Tetrazolo quinoline has an imminent and empowering new structure for the novel against the anti-inflammatory (6) and antibacterial (7) agents [3, 4].
Piperidine-substituted tetrazoles (8) showed antifungal activity.
Tetrazole derivatives (9) have been chosen and enhanced for their anticancer action on the majority of various human tumor cell lines separated from nine neoplastic disease sorts. The capable anticancer compound was observed to be dynamic with specific impact on ovarian cancer [1, 2, 3, 4].
The 2,4 thiazolidinedione by-products (10) comprise tetrazole loop for their antidiabetic movement. The greater part of the mixes indicated great antidiabetic action when contrasted to glibenclamide [1, 2, 3, 4].
The in vivo hypoglycemic action of tetrazole bears N-glycosides as SGLT2 inhibitors. A progression of 5-[(5-aryl-1H-pyrazol-3-yl)methyl]-1H-tetrazoles (11&#;13) has been assessed for their in vivo antihyperglycemic action. A portion of the mixture have indicated critical glucose bringing down the movement [1, 2, 3, 4].
1.5. Motivation of the chapter
Powerful drugs in opposition to hypertension, cancer, and bacterial and fungal infections have to fulfill a number of requirements like toxicity to tumor cells and are capable of being dissolved for efficient delivery. This makes necessary full-fledged characterization of drug position, comprising achieved synthetic strategies. In this chapter we directed on tetrazole biological activities. As a consequence, the need of synthetic routes to prepare tetrazole derivatives that are selective toward specific malfunctioning enzyme connects with illness. The study of good approaches of tetrazoles and medicinal applications will definitely allow to propose more useful drugs.
1.6. History of tetrazoles
Since , regular synthesis of 5-switched-1H-tetrazoles (16) has been accounted for to continuation of [3+2] cycloaddition of azide (14) with nitriles (15). This strategy experiences various disadvantages including utilization of costly and poisonous metal natural azide, exceedingly dampness touchy response conditions, solid Lewis corrosive, and hydrazoic corrosive. The &#;click&#; chemistry approach using metal catalysis in fluid arrangement is an outstanding evolution over last strategies, however every so often still requires the monotonous and tedious expulsion of metal salts from the acidic items.
Tetrazoles as a gathering of heterocyclic compounds are accounted for having an expansive range of organic exercises, for example, antibacterial, antifungal, antiviral, pain-relieving, mitigating, antiulcer, and antihypertensive exercises. Likewise, 5-substituted-1H-tetrazoles can work as lipophilic spacers and carboxylic corrosive surrogates, forte explosives and data recording frameworks in materials ligands, and forerunners of an assortment of nitrogen-containing heterocycles in coordination science.
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