Nitrogen adducts

The literature on these structures is sparse, and generally the articles report preparations of several of them in similar ways. These compounds are constituted by oxygen, sulfur, or nitrogen adducts at the silicon atom, thus providing pentacoordinated silicon compounds or structural analogs (Scheme 33). 

The principal feature of the chemical reactivity of QBA is the addition of a nucleophile to the iminium bond C=N (Scheme 1). The carbon atom C-6 displays the lowest 7C-electron density [97,98]. This process is associated with a number of significant alterations in the constitution, physical appearance, solubility, spectral properties, etc. The quaternary cation is a brightly coloured, polar, water-soluble species. The tertiary-nitrogen adduct has lost the colour and is non-polar and water insoluble. In the case of aminoacetal and aminal derivatives (Scheme 1, Nu = OR, NHR), the reaction is essentially reversible, i.e. the action of acid immediately converts the adduct back to the quaternary salt. Viewed from another perspective the emergence of colour is a sensitive indicator of the presence of some acid and ipso facto of deconq)osition of the adduct. 

Resonance line broadening due to chemical exchange and quadrupole-induced relaxation in the H and nB n.m.r. spectra of some boron-nitrogen adducts ArNMe2,BY3 (Y = halogen) has been observed and used to determine the mechanism of amine scrambling in these adducts.165 This is thought to occur via a unimolecular ionization rather than a B—N bond-rupture process. 

The nitrogen chemical shifts of the tetracoordinate boron-nitrogen adducts, R3B - NR3 (Table X, note f)> have been measured. (92) If we compare the data for the corresponding amines (Table VIII) with those for the adducts, high-frequency shifts are observed upon the formation... 

Indoles are usually constructed from aromatic nitrogen compounds by formation of the pyrrole ring as has been the case for all of the synthetic methods discussed in the preceding chapters. Recently, methods for construction of the carbocyclic ring from pyrrole derivatives have received more attention. Scheme 8.1 illustrates some of the potential disconnections. In paths a and b, the syntheses involve construction of a mono-substituted pyrrole with a substituent at C2 or C3 which is capable of cyclization, usually by electrophilic substitution. Paths c and d involve Diels-Alder reactions of 2- or 3-vinyl-pyrroles. While such reactions lead to tetrahydro or dihydroindoles (the latter from acetylenic dienophiles) the adducts can be readily aromatized. Path e represents a category Iley cyclization based on 2 -I- 4 cycloadditions of pyrrole-2,3-quinodimcthane intermediates. 

In Group 15 (V), nitrogen compounds readily form molecular compounds with BF. Phosphoms compounds also form adducts with BF. Inorganic or organic compounds containing oxygen form many adducts with boron trifluoride, whereas sulfur and selenium have been reported to form only a few (41—43). 

The XeF+ cation forms Lewis acid—base adduct cations containing N—Xe—F linkages with nitrogen bases that are resistant to oxidation by the strongly oxidizing XeF+ cation having an estimated electron affinity of the XeF+ cation of 10.9 eV (12). The thermally unstable colorless salt,... 

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

Tertiary amines have been shown to react with isocyanates ia an analogous fashion to form ureas (41—43). Similarly, a2iridines (three-membered rings containing nitrogen) are found to react with isocyanates to yield cycHc ureas. Tertiary amines have also been shown to form labile dipolar 1 1 adducts with isocyanates reminiscent of salt formation. In contrast, formaldehyde acetal aminals form iasertion products with sulfonyl isocyanates (44,45). 

Qu tern iy S Its. The ring nitrogen of quinoline reacts with a wide variety of alkylating and acylating agents to produce useful intermediates like A/-benzoylquinolinium chloride [4903-36-0] (8). The quinoline 1,2-adducts, eg, A/-benzyl-2-cyano-l,2-dihydroquinoline [13721 -17-0] (9), or Reissert compounds (28), formed with potassium cyanide can produce 2-carboxyquinoline [93-10-7] (10) or 2-cyanoquinoline [11436-43-7] (11). 

Sulfamation is the formation (245) of a nitrogen sulfur(VI) bond by the reaction of an amine and sulfur trioxide, or one of the many adduct forms of SO. Heating an amine with sulfamic acid is an alternative method. A practical example of sulfamation is the artificial sweetener sodium cyclohexylsulfamate [139-05-9] produced from the reaction of cyclohexylamine and sulfur trioxide (246,247) (see Sweeteners). Sulfamic acid is prepared from urea and oleum (248). Whereas sulfamation is not gready used commercially, sulfamic acid has various appHcations (see SuLFAMiC ACID AND SULFAMATES) (249—253). 

Addition compounds form with those organics that contain a donor atom, eg, ketonic oxygen, nitrogen, and sulfur. Thus, adducts form with amides, amines, and A/-heterocycles, as well as acid chlorides and ethers. Addition compounds also form with a number of inorganic compounds, eg, POCl (6,120). In many cases, the addition compounds are dimeric, eg, with ethyl acetate, in titanium tetrachloride-rich systems. By using ammonia, a series of amidodichlorides, Ti(NH2) Cl4, is formed (133). 

It melts at 39°C and may be purified by vacuum sublimation. The Hquid boils at 233°C to give a monomeric vapor in which the Ti—Br distance is 231 pm. Titanium tetrabromide is soluble in dry chloroform, carbon tetrachloride, ether, and alcohol. Like titanium tetrachloride, TiBr forms a range of adducts with molecules such as ammonia, amines, nitrogen heterocycles, esters, and ethers. 

Titanium triiodide can be made by direct combination of the elements or by reducing the tetraiodide with aluminum at 280°C in a sealed tube. Til reacts with nitrogen, oxygen, and sulfur donor ligands to give the corresponding adducts (148). 

Amine—borane adducts have the general formula R3N BX where R = H, alkyl, etc, and X = alkyl, H, halogen, etc. These compounds, characterized by a coordinate covalent bond between boron and nitrogen, form a class of reducing agents having a broad spectmm of reduction potentials (5). 

Complex Formation. B-Ttichlorobora2iQe was reported to readily form crystalline adducts of uncertain stmcture with pyridine (131). The Lewis acids aluminum tribromide or gallium trichloride form 1 1 adducts with hexamethylbota2iQe (eq. 36) ia which the metal atom coordinates with a nitrogen with loss of planarity of the ring (132,133). 

The only recorded synthesis of this type from a pyridazine involves the [4 + 2] cycloaddition of the lactim ether (374) with l,2,4,5-tetrazine-3,6-dicarboxylic ester, which proceeds with loss of nitrogen and methanol from the intermediate adduct to give the pyrido[2,3-t/]pyridazine (375) (77AP936). 

The high reactivity of pyrroles to electrophiles is similar to that of arylamines and is a reflection of the mesomeric release of electrons from nitrogen to ring carbons. Reactions with electrophilic reagents may result in addition rather than substitution. Thus furan reacts with acetyl nitrate to give a 2,5-adduct (33) and in a similar fashion an adduct (34) is obtained from the reaction of ethyl vinyl ether with hydrogen bromide. 

A-Carbamoyldiaziridines can open the three-membered ring and recyclize through the carbamoyl nitrogen, as demonstrated in a benzoyl isocyanate adduct (74JOC3198) and in the formation of (140) (79JOC3935). 

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