Nitrogen Quaternaries

A great number of different heterocycHc residues have been used as the terminal groups of PMDs. Examples appear throughout this article. PMDs containing residues with quaternary nitrogen atoms are traditionally called cyanine dyes (qv). 

These are subdivided into (a) compounds isomeric with aromatic compounds in which the ring contains two double bonds but also an hybridized carbon (7 systems Scheme 6) or a quaternary nitrogen atom (9 systems Scheme 7). 

Scheme 7 Isomers of aromatic compounds with a quaternary nitrogen atom ...

The sorbent of fibrous stmcture has the best kinetic characteristics in relation to noble metals, for which reaching soi ption balance does not exceed 20 minutes. The rate of soi ption balance establishment depends on the form of nitrogen in functional groups of sorbents used and decreases in a line tertiary nitrogen (linear group) > tertiary nitrogen (heterocycle) > quaternary nitrogen. 

Azide, sulfonyl, and quaternary nitrogen groups can also be displaced by this mechanism. 

Replacement by Means of Quaternary Nitrogen and Phosphorus Fluorides... 

The first step of this reaction, decarboxylation of pyruvate and transfer of the acetyl group to lipoic acid, depends on accumulation of negative charge on the carbonyl carbon of pyruvate. This is facilitated by the quaternary nitrogen on the thiazolium group of thiamine pyrophosphate. As shown in (c), this cationic... 

The amination of 2-chloropyridine-A-oxide (53) with potassium amide in liquid ammonia yielded a mixture of 2-(55) and 3-amino-pyridine-A-oxide (56) in 5-10% total yield.This rearrangement might be explained by an aryne mechanism involving 2,3-pyridyne-A-oxide (54). Since the structure of 56, with its quaternary nitrogen atom, is more analogous to that of 3-methoxybenzyne (39) than to that of 2,3-pyridyne (26), an orientation effect directing the amide ion to C-3 can be expected here. 

The exclusion of nitrogen-bridged bicyclic azines is purely arbitrary since the work on such azinoazines with a 10 7r-electron system (and the necessarily accompanying quaternary nitrogen-bridgehead atom) shows the activation expected of other aromatic azinium... 

Just as with cefpimazole, cefepime (54) has a quaternary nitrogen substituent at C-3 whose electron withdrawing character and excellent nucleofugic properties increases the reactivity of the... 

The large activating effect of a methyl group upon the reactivity of aromatic quaternary nitrogen compounds noted above has been confirmed by Utley and Vaughan55, who have measured the second-order rate coefficients and the... 

In compound 76, which has four quaternary nitrogens, a halide ion has been encapsulated without a hydrogen being present on a nitrogen. This ion does not display in-out isomerism. 

O. Ponsati, A. Trius, C. P. Herold, H. Muller, C. Nitsch, and S. von Tapavicza. Use of selected oleophilic compounds with quaternary nitrogen to improve the oil wettability of finely divided clay and their use as viscosity promoters. Patent WO 9219693, 1992. 

Another cyclic boron catalyst K, derived from ra x-2-aminocyclohexanc-methanol, can be prepared with a quaternary nitrogen that enhances activity.101 This particular catalyst is not very stable, but it is highly active. 

Hexafluoroacetone and hydrogen peroxide in buffered aqueous solution can epoxidize alkenes and allylic alcohols.101 N, Af-Dialkylpiperidin-4-one salts are also good catalysts for epoxidation.102 The polar effect of the quaternary nitrogen enhances the... 

The wide latitude of structural variation consistent with bioactivity in this series is illustrated by the observation that antiinflammatory activity is maintained even when the second aromatic group is attached directly to the pyrrole nitrogen rather than to the heterocyclic ring via a carbonyl group as in the previous case. Condensation of p-chloroaniline with hexane-2,5-dione (or its dimethoxy-tetrahydrofuran equivalent) affords pyrrole 7. The acetic acid side chain is then elaborated as above. Thus, Mannich reaction leads to the dimethylaminomethyl derivative 8, which is in turn methylated (9) the quaternary nitrogen replaced by cyanide to afford 10. Hydrolysis of the nitrile then gives clopirac (11). 

Enol lactones are assumed to form from iV-methylisoquinolinium salts as a result of a Hofmann-type degradation process. This P elimination is a highly stereospecific reaction in which Z isomers are produced from precursors of erythro configuration and isomers from threo diastereomers(5,97). This fact seems to suggest that syn rather than the more usual anti elimination takes place. Examination of models indicates, however, that there is a preferred conformation in which the C-8 hydrogen is in the syn and coplanar position to the quaternary nitrogen. This hypothesis was proved correct in experiments carried out in vitro (5,14,15,91-94). 

Organic polymers claimed to be effective swelling clay and mineral fine particle stabilizers in the patent literature can be divided into four classes. The polymers of class 1 have the quaternary nitrogen atom as part of the polymer backbone (6-10). Polymers in this class include poly(dimethylamine-co-epichlorohy-drin, abbreviated poly(DMA-co-EPl), and poly(N,N,N, N,-tetramethyl-l,4-l,4-diaminobutane-co-l,4-dichlorobutane), abbreviated poly (TMDAB-co- DCB). These low molecular weights are not surprising since these are condensation polymers. Molecular weights cited range from 800 to 800,000 daltons. 

Results indicated that swelling clay stabilizers such as poly (DMA-co-EPl) which do not possess a quaternary nitrogen atom in a pendant chain may not be very effective at preventing permeability damage due to fines migration in the absence of water-swelling clays. 

Copolymers. Copolymers have also been studied (16-18). While one comonomer contains 1-2 quaternary nitrogen in a flexible pendant chain, the other comonomer was nonionic. Copolymers of the methyl chloride salt of dimethylaminoethyl methacrylate (one quaternary nitrogen atom) and dimethylaminoethyl methacrylate (DMAEMA) and of MDTHD (2 quaternary nitrogen atoms) and DMAEMA, N,N-dimethylacryl-amide (NNDMAm) or dimethylaminopropyl methacrylate (DMAPMA) have been studied and the results summarized in Table VI. 

When the DMAEMA content of NVP - DMAEMA copolymers was reduced from 20% to 8%, the silica fines stabilization effectiveness appeared to improve slightly. When the 80/20 NVP - DMAEMA copolymer was converted to a terpolymer containing 8% DMAEMA (CH SO, silica fines stabilization was substantially unaffected. However, stabilization of silica/kaolinite fines was greatly improved. This suggested that the interaction of polymer quaternary nitrogen atoms with anionic sites on mineral surfaces was important for the stabilization of migrating clays but a different interaction was important for the stabilization of silica fines. Calcite fines stabilization improved while hematite fines stabilization effectiveness decreased. This also indicated the nature of the adsorbed polymer - fine particle complex varied for different minerals. 

The results summarized in Table IX indicated that another copolymer which does not contain quaternary nitrogen atoms, poly (DMAEMA - co - methyl acrylate) was also an effective silica fines stabilizer. 

Results indicate that the effectiveness of quaternary ammonium salt polymers in stabilizing swelling clays and mineral fine particles is dependent on monomer chemical structure and polymer molecular weight. Long flexible pendant sidechains containing quaternary nitrogen atoms appear to be required for these polymers to function as mineral fine particle stabilizers. 

Electrochemical techniques have been utilized for many years to study metal corrosion. Two of these techniques, linear polarization (LP) and cyclic voltammetry (CV), complement each other, LP providing corrosion rates under conditions where the surface is minimally altered and CV furnishing information about the corrosion mechanism. With the advent of impedance spectroscopy (IS), both kinds of information can be gleaned simultaneously and more rapidly, while leaving the surface almost intact. In this paper, we discuss the application of IS to the study of rapid steel corrosion and describe a study we undertook to elucidate the roles played by adsorption and film formation in the inhibition mechanisms of the above-named compounds. For comparison, we also investigated two quaternary nitrogen salts, which appear to adsorb electrostatically and presumably do not form macroscopic films (8). 

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