A Fundamental Research Study Aimed at the Development of a Novel Benign Technology for the Direct Fixation and Subsequent Re-Utilization of Nitrogen Oxides (NO₂ and N₂O₄)

OUR RESEARCH IS PREDICATED ON A THEORY WHICH WE DEVELOPED and propose as a viable explanation for the observed reactivity of organometallic compounds in general. Our proposed theory has two fundamental tenets which form its foundation: (1) that the evaluation of the mechanisms involving organometallic reagents can better be discerned if the observed dynamic structure reactivity relationship is correlated to the dynamic residual bonding capacity (DRBC) of the reagent under study and (2) that the mechanism for a given general structural family of organometallic reagents will vary along a mechanistic continuum as the dynamic residual bonding capacity of the reagent goes from a maximum to a minimum. The dynamic residual bonding capacity is defined here as a function of available low lying electronic orbitals (pure or hybridized) present on the metal of the organometallic compound, which are in turn influenced by the ligands appended to the metal, the volume in space occupied by the ligands around the metal, external electron donors (such as donor solvents, ligands or other organometallic compounds), etc. as the reagent is used in a given dynamic setting. This theory would predict that mechanistic studies on a given organometallic family of reagents should be undertaken with the most representative structural member (with respect to maximum DRBC) and that the observed structure-reactivity relationships would be different than for any other member of the family of reagents which would have their DRBC either internally or externally decreased.

A perusal of the scientific literature yields a multitude of examples where investigators have not used this approach, but rather have assumed that the structure of a given organometallic reagent with minimal DRBC, for example the so-called Grignard Reagent, was representative of the "true" structure for all organomagnesium compounds, and then carried out structure-reactivity relationship studies where the correlation to single factors, such as electronic and steric effects and use of absolute transition state theory, have led to a mechanism involving a polar transition state with "anomalous" S.E.T. behavior being invoked for those systems which did not yield the expected polar transition state results.

To test the tenets of our theory, we have embarked on both the design and synthesis of metal-containing reagents which we propose possess the maximum innate DRBC. In parallel, we are carrying out physical studies and the development of novel synthetic methods which would not be available via the analogous classical reagents possessing low DRBC.

Among some of the most fundamental results to date are the following: (1) Physical studies concerning the reaction between unstated diorganomagnesium compounds and the analogous externally unsolvated organomagnesium amides (not the minimum DRBC containing so-called Grignard Reagents or Hauser bases which have been used in the past) and carbon monoxide have indicated to us that the fundamental tenets of our theory are valid. A major new theory has resulted from these endeavors and will be communicated to the general scientific community via a manuscript which has been submitted to the Journal of the American Chemical Society.² (2) Using the unsolvated organomagnesium amides ,which we first prepared and characterized,³ we have been able to develop several new synthetic methods which are not available via the analogs of these reagents which have limited DRBC (such as the so-called Hauser Bases). In addition to the new methods which we have described in the primary literature,⁴ we have been able to bring about the fixation of carbon dioxide at room temperature and atmospheric pressure and are continuing to develop this novel reaction for the removal and regeneration of carbon dioxide.⁵ From these latter studies, we have also isolated a new family of reagents with a novel composition of matter. We are exploring the use of this new family of reagents to further test our theory via physical techniques and the development of other new synthetic methods and unprecedented technologies. Because of our fundamental interests, which require that we carry out concurrent research on multiple projects, we do not anticipate committing to the pursuit of that one research endeavor alone. However, we will use the new family of reagents to evaluate the possibility of bringing about chemical transformations of interest in synthetic organic chemistry. We will also use the reagents to develop novel technologies. Among these is a new reaction for the conjugate addition of organoaluminum compounds to a,b-unsaturated.⁶ We have also achieved (and because of the potential of getting either composition of matter or process patent coverage, have as of yet not submitted for publication in the primary literature) the following scientific findings during the further testing of our fundamental premise: (1) a novel method for the formylation of olefins via a tandem carbometalation/carbonylation of a Main-Group bimetallic species; (2) a novel synthesis for formamidines via the direct carbonylation of unsolvated organomagnesium amides; (3) a novel method for the extension of the carbon framework of simple formamides to formamidines; (4) a novel reaction which allows for the direct conversion of nitrites to substituted imidazoles and pyrimidines; (5) a novel method for the cyclotrimerization of alkynes; (6) a novel method for the direct conversion of isocyanates to substituted guanidines; (7) a new reaction for the synthesis of alcohols from CO and ethylene; (8) a novel composition of matter for polymerization of olefins; (9) the preparation and preliminary structure-reactivity relationships studies as well as new synthetic method development, of unsolvated organomagnesium imides; (10) a new synthesis for ureas from CO. The novel reaction, which is the basis of this proposal, is our most recent discovery and is the subject of a formal invention disclosure submitted to the University of Houston System. The current status is that the University of Houston Clear Lake has committed funds and hired external legal counsel to carry out the filing of applications for United States and foreign patents.⁷

Relevance of the Study
One of the key problems faced by humans inhabiting platforms/vehicles while conducting long-duration space activities is the need for the removal of nitrogenous-based materials which hold no further direct potential for the sustainment of life. One example of such types of non-essential nitrogenous-based materials is that percentage of the higher plants which make up the primary air purification systems being developed by the NASA-JSC Advanced Life Support Systems Group (ALSSG). Those plants are deemed to be non-edible and therefore must be removed from the platform/vehicle in the most efficient way possible. One approach being evaluated by the NASA-JSC ALSSG involves the use of pyrolysis and similar high temperature degradation of these non-essential nitrogenous based materials in an on-board pressure reactor. In principle, the reactor's reaction conditions can be set to yield either a mixture of hydrocarbons, CO₂ and H₂O, or, alternatively, the reactor parameters can be set so that the final products will be the products of complete degradation followed by in situ oxidation to yield only CO₂ and H₂O. In the former case, the idea is that the hydrocarbons could then be subsequently used as a combustible source of energy, whose final products would then become CO₂ and H₂O. In the latter case, the intent is to convert the nitrogenous-based materials directly to CO₂ and H₂O. In both instances, the CO₂ and H₂O would then be further processed on-board by proven mature technologies which have been well integrated into the NASA-JSC Advanced Life Support Systems Group's closed loop life support system.

One major problem which must be overcome for this type of approach to be competitive with other technologies which purport to achieve the destruction of nitrogenous-based materials from these environments (such as the technologies based upon the use of microorganisms) is the fact that, however, the reactor parameters are set, there is a real expectation that there will be an undesirable yield of nitrogen oxides from the destruction of any nitrogen-based materials, such as NO₂ and N₂O₄. One solution to this problem is to develop a chemical process which will not only bring about the fixation of NO₂ and N₂O₄ at low temperature and pressure, but which will also allow for the conversion of the products of that chemical fixation process into CO₂ and H₂O without the generation of new waste stream (so-called benign technology). See Scheme 1.

Scheme 1. General scheme of the desired chemical process.

Under partial support from the ISSO Post-Doctoral Aerospace Fellowship Program, we have been carrying out research on several novel reactions which we have discovered in an attempt to lay down the foundation for various new technologies which can be developed and used as closed loop systems to support life during long duration manned space activities. Last year, we reported that we had discovered a heretofore unknown chemical process which allows for the direct fixation and re-utilization of NO₂ and N₂O₄. That finding we considered to have direct and positive relevance to NASA-JSC efforts, which are based on the use of pyrolysis or other high temperature methods, for the degradation of non-edible higher plant life forms which are part of the primary environmental life support system being developed by the NASA-JSC ALSSG. Moreover, we felt that the new reaction could be useful as well for the removal of nitrogen oxides from all sources onboard a platform inhabited by a crew during a long duration space mission.

In addition to this focused application, we feel that our discovery of this new chemical reaction process may also be developed into an even more "general use technology" for use by the general private sector and other government agencies of the United States. The work at that time had shown that, indeed, we could fix nitrogen oxides at room temperature and atmospheric pressure by use of what we call unsolvated diorganomagnesium compounds, [(R₂N)₂Mg]_n. Those preliminary results are depicted, in general, by Eqs. (1) and (2) below.

Even though we had already discovered how to convert certain structures to the corresponding N-nitrosamines after the fixation of nitrogen oxides, that procedure would need subsequent chemical steps to arrive at the point where we could then envision the process which removes nitrogen oxides taking those intermediates to the final desired product methane, oxygen and water. We decided to see if by structure modification [(R₂N)₂Mg]_n we could get to the desired hydrocarbon or alcohols directly from the fixation without need for additional processes to convert N-nitrosoamines to suitable products. This, of course, is based on the fact that the relevance of the new reaction to the NASA-JSC ALSSG endeavors described above is predicated on the fact that any new technology which is eventually developed for the specified use should allow for the conversion of the nitrogen oxides into methane, carbon dioxide and water as depicted in general by Scheme 1. We concentrated our efforts over the last funding cycle on evaluating the generality of the process for the yield of products which can be taken via mature technologies to the desired end. This effort prompted us to look at the reactivity of reagents which could primarily yield alcohols, and other hydrocarbons, which could then be directly converted to carbon dioxide and water and subsequently to methane, oxygen and hydrogen.

Summary of Research Accomplishments
The major part of the research has focused on evaluating the reactivity of starting materials which would yield non nitroso compounds from the reaction between unstated diorganomagnesium amides and NO₂ and N₂O₄. From our earlier work, we concluded that this task would involve evaluating various carbon frameworks appended to the nitrogen of the unsolvated diorganomagnesium as potential sources of the desired alcohols or hydrocarbons after the fixation of nitrogen oxide. Since, to our knowledge, there exists no cited literature precedence for the reaction which we have developed, we needed to carry out a systematic cursory set of experiments to see which [(R₂N)₂Mg]_n might hold the potential for further study. After a series of experiments with a host of structurally disparate [(R₂N)₂Mg]_n reagents, we have now concluded that the following generalizations provide a basis for use in further studies which we now will be initiating.

1. Unsolvated [(RNH)₂Mg]_n compounds which contain R groups which are either cyclic or acyclic aliphatic groups give, predominately, mixtures of alcohols and saturated and unsaturated hydrocarbons, with relatively small amounts of the N-nitrosoamine.
2. Unsolvated [(RNH)₂Mg]_n, which have R groups which are either bicyclic or tricyclic saturated frameworks, such as the adamantyl group, give an even larger percent of the non-N-nitrosoamines than do their saturated open-chained or mono-cyclic analogous.
3. Unsolvated bis(Naphtylamino)Magnesium gives almost exclusively, napthalene as the major product from the reaction with NO₂ and N₂O₄.

In light of these results, our plans are to focus exclusively on the evaluation of strained multi-cyclic and bis(Naphtylamino)Magnesium compounds as we attempt to optimize the reaction conditions for the new chemical process which we have discovered.

References and Notes
¹See for example: (a) S. Sun, D. L. Henninger, J. Sager, and T. O. Trio. "NASA's Approach to Integrated System Testing of Regenerative Life Support Systems," Int'l Conf. on Environmental Systems, Paper No. 951494, 1995 and references therein; (b) D. L. Henninger, T. O. Trio, D. J. Barta, and R. S. Stahl. "Johnson Space Center's Regenerative Life Support Systems Test Bed," NASA Report, NASA-TM-107943, 1991; (c) B. L. Robertson and C. S. Lemay. "Investigating Pyrolysis/lncineration as A Method of Resource Recovery From Solid Waste," reported in NASA/ASEE Summer Faculty Fellowship Program, SEE-N94-2536706-99, 2 (1993).
²R. Sanchez, E. Tsilingiridis, and M. Anderson. "A Residual Bonding Capacity Based Variable Transition States Theory For The Reactivity of The Carbon-Magnesium Bond Based Upon the Comparative Uncatalyzed Carbonylation of Unsolvated Diorganomagnesium Compounds," J. Amer. Chemical Soc. (1997). (Submitted for publication.)
³R. Sanchez, T. Ratham, R. Morrison, and V. J. Mehta. "Ether-Free Organometallic Amide Compositions," U.S. Patent, 4,944,894, (1990).
⁴See for example: (a) R. Sanchez and W. Scott. "Unsolvated Magnesium Diisopropylamide (MDA) in Organic Synthesis. The Reduction of Aldehydes and Ketones to Alcohols," Tetrahedron Letters 29 (1988): 139; (b) R. Sanchez, G. Vest, W. Scott, and P. S. Engel. "The Reduction of Nitro, Nitroso, and Azoxy Compounds with Unsolvated MDA," J. Org. Chem. 54 (1989): 4026; (c) R. Sanchez, G. Vest, and L. Despres. "The Direct Conversion of Carboxylic Acids to Carboxamides via Unsolvated Magnesium Amides," Synth. Comm. 19 (1989): 2909; (d) R. Sanchez, C. Arrington, and C. A. Arrington. "Reaction of Trimethylaluminum with Carbon Monoxide in Low Temperature Matrices," J. Am. Chem. Soc. 111 (1989): 9110.
⁵R. Sanchez and O. Felan. "Unsolvated Bis(N,N-Diorganocarbamoxy) Magnesium Compounds: A Novel Family of Reagents For The Storage and Transfer of Carbon Dioxide and the Facile Preparation and Transfer of The N,N'-Substituted Carbamoxy Structural Unit," Main Group Metal Chemistry 18.4 (1995): 225.
⁶R. Sanchez and M. Anderson. "The Use of a New Family of Reagents, Unsolvated Bis(N,N'-Diorganocarbamoxy)Magnesium Compounds, to Effect the Uncatalyzed Conjugate Addition of Organoaluminum Compounds," Synthetic Letters (1997). (Submitted for publication.)
⁷R. Sanchez, G. Lubertino and D. Henninger. "A Novel Reaction for the Direct Fixation and Conversion of Nitrogen Dioxide to N-Nitrosoamines, Alcohols, and Ketones," Invention Disclosure formally to be presented to the Univ. of Houston System and NASA-JSC, 1997.
⁸See for Example: (a) A. L. Fridman, F. M. Mukhametshin, and S. S. Novikov. Russian Chemical Rev. 40.1 (1971): 34; (b) P. Beak and W. Zajdel. Chem. Rev. 84 (1984): 471 and references therein.
⁹E. Lorz and Baltzly. J. Am. Chem. Soc. 73 (1951): 93; (b) M. Harfenist and S. Magnilu. Ibid. 79 (1957): 2215, and references therein.
¹⁰R. Sanchez, G. Vest, W. Scott, and P. S. Engel. J. Org. Chem. 54 (1989): 4026.
¹¹R. Sanchez and W. Scott. Tetrahedron Lett. 29 (1988): 139.
¹²(a) E. Fischer. Lieb. Ann. 199 (1879): 308; (b) L. Knorr. Ibid. 221 (1883): 297; (c) R. Stroermer and V. Von Lepel. Ber. 29 (1896): 2110.

Patent Application
Sanchez, R. and G. Lubertino. "A Novel Chemical Process for the Benign Direct Fixation and Conversion of Nitrogen Oxides (NO_x) at Atmospheric Pressure and Room Temperature." (Patent application preparation in progress.)

Contents
ISSO -- Institute for Space Systems Operations
1997-1998 Annual Report