Vide supra

The impurities usually found in raw hydrogen are CO2, CO, N2, H2O, CH, and higher hydrocarbons. Removal of these impurities by shift catalysis, H2S and CO2 removal, and the pressure-swing adsorption (PSA) process have been described (vide supra). Traces of oxygen in electrolytic hydrogen are usually removed on a palladium or platinum catalyst at room temperature. 

Where larger quantities (upwards of Ig) are required, most of the impurities should be removed by preliminary treatments, such as solvent extraction, liquid-liquid partition, or conversion to a derivative (vide supra) which can be purified by crystallisation or fractional distillation before being reconverted to the starting material. The substance is then crystallised or distilled. If the final amounts must be in excess of 25g, preparation of a derivative is sometimes omitted because of the cost involved. In all of the above cases, purification is likely to be more laborious if the impurity is an isomer or a derivative with closely similar physical properties. 

Liquid amines can be further purified via their acetyl or benzoyl derivatives (vide supra). Solid amines can be recrystallised from water, alcohol, toluene or toluene-petroleum ether. Care should be taken in handling large quantities of amines because their vapours are harmful (possibly carcinogenic) and they are readily absorbed through the skin. 

Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulfite, semicarbazone or oxime derivatives (vide supra). The bisulfite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Fig. 10 shows the radial particle densities, electrolyte solutions in nonpolar pores. Fig. 11 the corresponding data for electrolyte solutions in functionalized pores with immobile point charges on the cylinder surface. All ion density profiles in the nonpolar pores show a clear preference for the interior of the pore. The ions avoid the pore surface, a consequence of the tendency to form complete hydration shells. The ionic distribution is analogous to the one of electrolytes near planar nonpolar surfaces or near the liquid/gas interface (vide supra). 

As expected, the TgS of the hybrid sulfanuric-phosphazene polymers are much closer to the values reported for poly(phosphazenes) than those of sulfanuric polymers (vide supra). The values for the polymers 14.10a... 

Four isomeric menthones may exist, with eight corresponding isomeric menthols (vide supra). But whichever menthone is converted into menthol, natural laevo-menthol is the predominating resulting compound. 

S.O., abbrev. (siehe oben) see above, vide supra. sobald, conj, as soon as. 

As shown in Figure 3.6-1, GC and Pt exhibit anodic and cathodic potential limits that differ by several tenths of volts. However, somewhat fortuitously, the electrochemical potential windows for both electrodes in this ionic liquid come out to be 4.7 V. What is also apparent from Figure 3.6-1 is that the GC electrode exhibits no significant background currents until the anodic and cathodic potential limits are reached, while the Pt working electrode shows several significant electrochemical processes prior to the potential limits. This observed difference is most probably due to trace amounts of water in the ionic liquid, which is electrochemically active on Pt but not on GC (vide supra). 

The thermolabile, unsubstituted 3-benzothiepin (3) can be synthesized by a double Wittig reaction, in analogy to the Knoevenagel condensation (vide supra). This is achieved by condensation of phthalaldehyde with the bis(triphenylphosphonium) salt of bis(bromomethyl) sulfide in the presence of lithium methoxide as base at — 30"C.68... 

The C —C double bonds of 3-benzothiepins do not react with bromine (vide supra), nor with phenyl azide or diazoacetate however, one or two equivalents of diazomethane do add to 3-benzothiepins, e.g. 4, to yield crystals which melt with quantitative loss of nitrogen.65... 

There are very few examples of naturally occurring, fully unsaturated azepines.100 Surprisingly, in view of the relative stabilities of the azepine tautomers (vide supra), the 2/7-azepine, chal-ciporone (24) and the related propanoate ester, norchalciporyl propanoate (25), are the pungent components of the peppery mushroom, Chalciporus piperatus,40... 

Subsequently it was found140 that ethyl 2-alkyl-1//-azepine-1-carboxylates can be isolated from a mixture of isomeric 1//-azepines by stirring the mixture with potassium hydroxide in ethanol at room temperature. Apparently, this method, which is limited to 2-alkylated azepines, depends on the slower rate of hydrolysis (and subsequent decomposition of the resulting 1H-azepine-l-carboxylic acid) of the sterically hindered 1-(ethoxycarbonyl) group. Although the yields of l//-azepines are poor (4-7%, vide supra), the method provides access to otherwise difficult to obtain, isomerically pure 2-alkyl-1//-azepines. Under the basic hydrolysis conditions aryl 2-alkyl-l//-azepine-1-carboxylates undergo transesterification to the l-(ethoxycarbonyl) derivatives. 

Attempts to prepare 2-butoxy-3//-azepines by heating nitro compounds with tris(di-ethylamino)phosphane in /m-butyl alcohol failed, as diethylamine, liberated by alcoholysis of the aminophosphane, reacts in preference with the alcohol (vide supra) to give the Ar,/V-di-ethyl-3//-azepin-2-amine in good yield.176 However, the deoxygenation of nitroarenes with tributylphosphane in the presence of primary and secondary alcohols furnishes 2-alkoxy-3//-azepines 98 in practicable yields.79... 

Phenyldibenz[r/,/][l,3]oxazepine (3) is obtained in 25% yield by treatment of the dibenzo-pyrylium perchlorate 1 with sodium azide, followed by heating the resulting azide 2 (vide supra).2 5... 

The monothione 2 (vide supra) is converted into the (methylsulfanyl)benzoxazepinone 3a by sodium hydride/iodomethane an analogous reaction with ethyl bromoacetate gives the ester 3b.37... 

Aroyl-1 H-1,2-diazepin-3(2//)-ones 27 are obtained80 by demethylation90 of 3-methoxy-l H-1,2-diazepines (vide supra) with chlorotrimethylsilane/sodium iodide. 

Methylsulfanyl)-37/-l,5-benzodiazepines 11 (vide supra) react with amines by replacement of the methylsulfany group to yield derivatives 12 of 3//-l,5-benzodiazepin-2-amine. Selected examples are given.283... 

Dimethoxy-2- 1 -[2-(tetrahydropyran-2-yloxy)ethyl]vinyl -l, 3.6-oxadiazepine (4 vide supra) isomerizes to an imidazole 1 or 2 in aqueous methanol.320... 

Monocyclic 2-methoxyazocines 1 (see Section 1.1.1.1.1.) can be hydrolyzed to the corresponding lactams with anhydrous hydrogen bromide, but only in low yield. NMR spectroscopy reveals that, in contrast to the benzannulated systems (vide supra), the products mainly exist as their bicyclic tautomers 3.28... 

The chloro groups of 4,7-dichloro-l,2-diazocines (vide supra) can be sequentially substituted by O-, S- or W-nucleophiles.25 27 The reaction most likely proceeds via an elimination-addition mechanism utilizing the valence tautomeric diazabicyclo[4.2.0]octatriene forms. 

Hexaphenyl-l,5-diazocine (4) can also be generated by irradiation of the substituted triazine 5. After initial elimination of nitrogen, the reaction proceeds by the same mechanism as the triphenyltriazafulvenes vide supra).48,49... 

Diazocines are isolated, as byproducts, in another photochemical reaction which starts from fluorinated pyridazines. On irradiation of 6 a Dewar diazabenzene derivative is formed, via an electrocyclic ring closure, which looses a fluorinated nitrile to give the azacyclobutadiene system 7. This reactive intermediate then leads vide supra) to the 1,5-diazocine 8.50... 

Dichlorodibenzo[/>,/][l,5]diazocine (4, vide supra) can be used for the synthesis of several other derivatives by substitution reactions. 

Dimethyl 4,8-diphenyl-l,2,5,6-tetrazocine-3,7-dicarboxylate (3, vide supra) can be saponified and dccarboxylated in excellent yield.18... 

Ethyl azonine-l-carboxylate (3) can be used to prepare the parent 1//-azonine12 (1, R = H). as well as a number of substituted systems via its anion 213 (vide supra). 

In marked contrast to what is usually observed with porphinoid macrocycles under these oxidation conditions and therefore surprisingly, the rosarins are obtained as 2471 cyclically conjugated, but nonaromatic species, an observation which was also made in the amethyrin series vide supra). 

The synthesis of aziridines through reactions between nitrenes or nitrenoids and alkenes involves the simultaneous (though often asynchronous vide supra) formation of two new C-N bonds. The most obvious other alternative synthetic analysis would be simultaneous formation of one C-N bond and one C-C bond (Scheme 4.26). Thus, reactions between carbenes or carbene equivalents and imines comprise an increasingly useful method for aziridination. In addition to carbenes and carbenoids, ylides have also been used to effect aziridinations of imines in all classes of this reaction type the mechanism frequently involves a stepwise, addition-elimination process, rather than a synchronous bond-forming event. 

Although several interesting nitrogen-centered nucleophiles have been developed with ARO reactions of epoxides (vide supra), kinetic resolutions with such reagents are unlikely to be of practical value for the recovery of enantioenriched terminal epoxides. This is due to the fact that these nucleophiles are too valuable to be discarded in a by-product of the resolution, are generally not atom-economical, and, particularly in the case of azide, may represent safety hazards. 

L-Amino adds could be produced from D,L-aminonitriles with 50% conversion using Pseudomonas putida and Brembacterium sp respectively, the remainder being the corresponding D-amino add amide. However, this does not prove the presence of a stereoselective nitrilase. It is more likely that the nitrile hydratase converts the D,L-nitrile into the D,L-amino add amide, where upon a L-spedfic amidase converts the amide further into 50% L-amino add and 50% D-amino add amide. In this respect the method has no real advantage over the process of using a stereospecific L-aminopeptidase (vide supra). 

In contrast to the results obtained with the jS-alkoxy-a-alkyl-y-lactol 16 (vide supra), a chelation-directed, anti-Cram selective nucleophilic addition to the a-methyl-y-lactol 1 was not only observed with methyllithium and methylmagnesium bromide but also with (triisopropoxy)methyl-titanium72. In fact, the highest diastereoselectivity (> 98 % de) was observed with the titanium reagent in dichloromethane as reaction solvent. A seven-membered chelate 3 with the a-methyl substituent in a pscudoequatorial position has been postulated in order to explain the stereochemical outcome. 

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