Hexamine complexes

Somewhat unanticipated applications can arise. For example, a process for the production of ultrapure hydrogen peroxide for the electronics industry has been patented recently,1425 which uses the macrobicyclic hexamine complex (29) supported on an inert material for dioxygen... 

All the above considerations impose substantial restrictions on the use of the data obtained by molecular mechanics to compare different types of hexamine complexes. Moreover, the comparison may be reasonable only for isomers with a similar number and mode of interaction exhibiting identical electronic effects [230],... 

Figure 5.6 Infrared spectra of metal hexamine complexes. From Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 5th Edn. Copyright (1997 John Wiley Sons, Inc.). This material is used by permission of John WUey Sons, Inc.

The spectra presented in Figure 5.6 show a trend in the wavenumber shifts for the three hexamine complexes the N H bands shift to lower wavenumbers from Co to Cr to Ni. This indicates that the N-H bond order (bond strength) decreases as the metal-N bond order increases in the stability order mentioned. 

Figure 8.18 Schematic view of the structure of the cobalt hexamine complex.

Heating of the hexamine complex leads to eUminatimi of one ammonia molecule ... 

The Bachmann process, used in the United States and in some European countries, is a simplification of a series of complex reactions. In this process, a solution of one part hexamine in 1.65 parts acetic acid, and a solution of 1.50 parts ammonium nitrate dissolved in 2.0 parts nitric acid and 5.20 parts acetic anhydride are used. The reaction may be summarized as ... 

The macrocyclic hexamine [18]aneN6 was further found to recognize catechol, catecholamines and biologically relevant compounds (see Chart II)64). It interacts with all of these donor compounds in neutral pH solutions to form 1 1 complexes, which were determined polarographically. The stability constants pL are summarized in Table 6. 

The chemistry of the prepn of RDX is highly complex and remains not fully understood. What follows is a synthesis of the views of British and Canadian investigators (Refs 37a 41a) as summarized by Urbanski (Ref 82, pp88-89). The following reactions presumably occur when hexamine is treated with nitric add to produce RDX ... 

Tracer Studies on the Nitro lysis of Hexamine to RDX and HMX. The formation of RDX and/or HMX molecules from the nitration or nitrolysis of Hexamethylenetetramine (Hexamine) is a complex process and has been postulated to take place via two separate paths. One involves the selective cleavage of the Hexamine molecule to the appropriate cyclic nitramine (RDX, HMX or both) depending on the specific... 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

Recent years, the authors have innovatively proposed a method by using the aqueous ammonia liquor containing hexamine cobalt (II) complex to scrub the NO-containing flue gases[6-9], since several merits of this complex have been exploited such as (1) activation of atmospheric O2 to a peroxide to accelerate the O2 solubility, (2) coordination of NO, as NO is a stronger ligand than NH3 and H2O of Co( II) complexes to enhance the NO absorption and (3), catalysis of NO oxidation to further improve the absorption both of O2 and NO. Thus, a valuable product of ammonium nitrate can be obtained. 

This paper presents the experimental results, with a focus on studies of the regeneration of the hexamine cobalt complex additive by using the activated carbon in a laboratory packed-bed absorber. 

The ligand 6,13-dimethyl-l,4,8,ll-tetra-azacyclotetradecane-6,13-diamine coordinates as a hexadentate ligand to zinc in neutral aqueous solution. Potentiometric titrations were used to determine the stability constant for formation. The pXa values were determined for five of the six possible protonation steps of the hexamine (2.9, 5.5, 6.3, 9.9 and 11.0).697 Studies of the syn and anti isomers of 6,13-dimethyl-1,4,8, ll-tetraazacyclotetradecane-6,13-diamine reveal that they offer different shapes for metal binding, which is reflected in the stability constants for 1 1 zinc ligand ratio complexes. The selectivity of binding to the zinc ion compared to the cadmium(II) ion by both isomers is significant.698... 

The hexamine-iodine complex deflagrates at 138°C. See other IODINE compounds... 

Theory The solution of potassium alum is heated with an excess of disodium edetate to ensure complete formation of aluminium-edetate complex. Hexamine serves as a buffer thereby stabilizing the pH between 5 and 6, the ideal pH for the titration of the disodium edetate not required by the A1 with 0.05 M lead nitrate employing xylenol orange as indicator. The various reactions involved may be represented by the following equations ... 

Procedure Weigh accurately 1.7 g of potassium alum and dissolve it in sufficient DW in a flask. Heat the contents of flask over a water-bath for 10 minutes to allow completion of complexation and cool to ambient temperature. Now, add 1 g hexamine to act as buffer and titrate with 0.05 M lead nitrate employing 0.4 ml of xylenol orange solution as an indicator. The colour shall change from that of the indicator (yellow at the pH of the titration) to the corresponding reddish purple, the colour of the lead complex of the indicator. Each ml of 0.05 M disodium edetate is equivalent to 0.02372 g of KA1(S04)2, 12H20. 

The replacement of amine and amide hydrogen with a nitro group via direct nitration is an important route to A-nitro functionality. However, the cleavage of other bonds is also important. In the case of C-N bond cleavage the process is known as nitrolysis and is an invaluable route to many energetic materials (Section 5.6). The nitrolysis of hexamine and the syntheses of the important explosives HMX and RDX are discussed in Section 5.15. This area of chemistry could easily demand a separate chapter of its own and is the most complex and diverse in the field of nitramine chemistry. 

In this method, first established by Herz and later studied by Hale, hexamine is introduced into fuming nitric acid which has been freed from nitrous acid. The reaction is conducted at 20-30 °C and on completion the reaction mixture is drowned in cold water and the RDX precipitates. The process is, however, very inefficient with some of the methylene and nitrogen groups of the hexamine not used in the formation of RDX. The process of nitrolysis is complex with formaldehyde and some other fragments formed during the reaction undergoing oxidation in the presence of nitric acid. These side-reactions mean that up to eight times the theoretical amount of nitric acid is needed for optimum yields to be attained. 

Fenton, D. E. Kitchen, S. J. Spencer, . M. Tamburini, S. Vigato, P. A. Complexes of ligands providing endogenous bridges. Part 5. Solution studies on a novel 3 + 3 hexamine Schiff-base macrocyclic complex of lanthanum. J. Chem. Soc., Dalton Trans. 1988, 685-690. 

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