Alkali cyclic

In their reactions with aldehydes in the presence of alkali cyclic ketones such as cyclopentanone and cyclohexanone generally give only the dialkylidene or diarylidene compounds, and not the monosubstituted derivatives, since the two methylene groups vicinal to the carbonyl group are equally activated. Monosubstituted cyclanones can be obtained in this way only when about a six-fold excess of the ketone and special precautions are used.949 On the other hand, Birkofer and his co-workers showed monoalkylidenecycloalkanones to be easily obtained starting from enamines 950 yields are between 30% and 90% ... 

The commercial polymers are stabilized directly by additives in the polymerizing mixture, and this is in contrast to polymerization from formaldehyde, where the polymer is first produced and then subsequently stabilized. Here, a distinction is made between thermal degradation stabilization and stabilization against degradation induced by alkali. Cyclic ethers such as ethylene oxide are thermal stabilizers, that is, they stabilize against a depolymerization starting from the chain ends. They are quantitatively incorporated into the chain as comonomers at small yields ... 

Simplest examples are prepared by the cyclic oligomerization of ethylene oxide. They act as complexing agents which solubilize alkali metal ions in non-polar solvents, complex alkaline earth cations, transition metal cations and ammonium cations, e.g. 12—crown —4 is specific for the lithium cation. Used in phase-transfer chemistry. ... 

Ring-opening reactions are best known in the pyridazine ring. For example, the N-aryl cyclic hydrazides (321) undergo ring opening with alkali to give the N-aminoimides (322),... 

Vinylidene chloride-vinyl chloride polymers are also self-extinguishing and possess very good resistance to a wide range of chemicals, including acids and alkalis. They are dissolved by some cyclic ethers and ketones. 

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

DNA is not susceptible to alkaline hydrolysis. On the other hand, RNA is alkali labile and is readily hydrolyzed by dilute sodium hydroxide. Cleavage is random in RNA, and the ultimate products are a mixture of nucleoside 2 - and 3 -monophosphates. These products provide a clue to the reaction mechanism (Figure 11.29). Abstraction of the 2 -OH hydrogen by hydroxyl anion leaves a 2 -0 that carries out a nucleophilic attack on the phosphorus atom of the phosphate moiety, resulting in cleavage of the 5 -phosphodiester bond and formation of a cyclic 2, 3 -phosphate. This cyclic 2, 3 -phosphodiester is unstable and decomposes randomly to either a 2 - or 3 -phosphate ester. DNA has no 2 -OH therefore DNA is alkali stable. 

Solutions of alkali metals in liquid ammonia have been developed as versatile reducing agents which effect reactions with organic compounds that are otherwise difficult or impossible/ Aromatic systems are reduced smoothly to cyclic mono- or di-olefins and alkynes are reduced stereospecifically to frani-alkenes (in contrast to Pd/H2 which gives cA-alkenes). 

Organometallic reagents and alkali metal amides can react via a cyclic transition state (Section II, B, 5) beginning with electrophilic attack at the most basic ring-nitrogen. As a result, sodamide (in dimethylaniline, 145°, 2 hr) yields the 4-amino derivatives (40% yield S)) methyl- or phenyl-magnesium iodides give the 4-adduct quantitatively.s ... 

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

This class of aziridine-forming reaction includes the first reaction reported to afford aziridines. In 1888 Gabriel reported that aziridines could be prepared in a two-step process, by chlorination of ethanolamines with thionyl chloride, followed by alkali-induced cyclization [75]. Wenker subsequently reported that heating of 600 g of ethanolamine with more than 1 kg of 96 % sulfuric acid at high temperature produced P-aminoethyl sulphuric acid 282 g of it was distilled from aqueous base to give 23 g of aziridine itself, the first preparation of the parent compound in a pure condition [76]. Though there is no evidence to substantiate the hypothesis, the intermediate in these reactions is perhaps a cyclic sulfamidate (Scheme 4.51). 

Both of these compds yield expls on nitration. It is claimed that these expis have a high detonation velocity, can be pouted at temps below 100°, and are stable when stored at 50° The same investigators proposed the use of nitrates of other cyclic keto-alcohols, such as tetramethylolcyclohexanone, tetramethylolcyclo-pentanone, etc, as expls. All of these alcohols can be prepd by condensing cyclic ketones with formaldehyde in the presence of alkalies or al-... 

RNA can be hydrolyzed by alkali to 2 3 cyclic diesters of the mononucleotides, compounds that cannot be formed from alkah-treated DNA because of the absence of a 2 -hydroxyl group. The alkali lability of RNA is useful both diagnostically and analytically. 

H2O may be replaced by any acid, HA, and a cyclic mechanism for the breakdown of the ester is quite feasible. For oxidation in alkali the fractional order in hydroxide ion, the low kjkjy and low degree of oxygen-transfer from oxidant are taken as symptomatic of a free-radical chain reaction of the type... 

Hydrolysis of RNA by alkali or pancreatic RNase leads initially to fragments which terminate in 2, 3 -cyclic phosphodiesters. Micrococcal nuclease, on the other hand, gives rise to fragments terminating in 3 -phos-phomonoester groups which facilitate their isolation, and this enzymic hydrolysis has been used to prepare 3 -ribodinucleotides. ... 

Scheme 5-47 Asymmetric hydrophosphonylation of a cyclic imine catalyzed by heterobimetallic rare earth/alkali metal/BI-NOL complexes or by chiral titanium alkoxide complexes...

Chesniuk et al. studied the transfer of alkali and alkaline-earth cations across phospholipid monolayers at water-1,2-DCE macrointerfaces by cyclic voltammetry. These authors considered the effect of the cation nature, the concentration of the transferring ion, and the applied potential (at the positive end of the polarization window), and noticed either an enhancement of the current or a blocking of the transfer process [13,14]. The enhancement factors observed were very much larger than in other studies, especially at... 

Especially sensitive and selective potassium and some other ion-selective electrodes employ special complexing agents in their membranes, termed ionophores (discussed in detail on page 445). These substances, which often have cyclic structures, bind alkali metal ions and some other cations in complexes with widely varying stability constants. The membrane of an ion-selective electrode contains the salt of the determined cation with a hydrophobic anion (usually tetraphenylborate) and excess ionophore, so that the cation is mostly bound in the complex in the membrane. It can readily be demonstrated that the membrane potential obeys Eq. (6.3.3). In the presence of interferents, the selectivity coefficient is given approximately by the ratio of the stability constants of the complexes of the two ions with the ionophore. For the determination of potassium ions in the presence of interfering sodium ions, where the ionophore is the cyclic depsipeptide, valinomycin, the selectivity coefficient is Na+ 10"4, so that this electrode can be used to determine potassium ions in the presence of a 104-fold excess of sodium ions. 

Summary Many cyclic and linear transition metal-silicon compounds have been obtained by the elimination of alkali halides. The structures of these complexes were determined by INEPT and INEPT-INADEQUATE NMR spectroscopy. 

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