Alkaline reagents

In 1952, F. Weygand started his studies with trifluoroacetic acid (TFA) in peptide chemistry. TFA-amino acids and TFA-peptides showed themselves to lose the TFA residue by treatment with dilute aqueous hydroxides or with piperidine. The volatility of TFA esters allowing the separation of amino acids and peptides by gas chromatography was mentioned on page 54. 

The principle of the safety-catch can be illustrated very well at the sulfonyl-containing group mentioned above (Fig. 13). In the thioether-analog the readiness for jS-elimination is much less than in the sulfone state. Therefore the unoxidized residue will tolerate alkaline conditions during a peptide synthesis without danger and in order to be removed, must only be oxidized. 

Sulfonyl-containing groups have also been proposed for carboxyl protection, i.e. as esters, readily cleavable by alkali. This principle can be usefully applied in solid phase peptide synthesis where the growing peptide chain is anchored as an ester to the support (p. 108) and finally is split off by means as mild as possible. 

The Fmoc group has proven very valuable during the past decade of peptide chemistry, particularly in the solid phase technique [58]. 

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Extraction of hemiceUulose is a complex process that alters or degrades hemiceUulose in some manner (11,138). Alkaline reagents that break hydrogen bonds are the most effective solvents but they de-estetify and initiate -elimination reactions. Polar solvents such as DMSO and dimethylformamide are more specific and are used to extract partiaUy acetylated polymers from milled wood or holoceUulose (11,139). Solvent mixtures of increasing solvent power are employed in a sequential manner (138) and advantage is taken of the different behavior of various alkaUes and alkaline complexes under different experimental conditions of extraction, concentration, and temperature (4,140). Some sequences for these elaborate extraction schemes have been summarized (138,139) and an experimenter should optimize them for the material involved and the desired end product (102). 

Table 2. Basicity Factors of Common Alkaline Reagents ...

In addition to neutralization, prolonged action of alkaline reagents can effect oxidation—reduction and extensive decomposition. 1,1-Dinitroparaffins and trinitromethane are more stable than are mononitro compounds during neutralization and subsequent regeneration, and therefore more rigorous experimental conditions are permissible. 

Etherification. The reaction of alkyl haUdes with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraaHyl ether is formed on reaction of D-mannitol with aHyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional aHyl bromide, leads to hexaaHyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trim ethyl chi oro s il an e in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

On treatment with alkaline reagents, -toluenesulfonylhydra-zones of aldehydes and ketones yield diazo compounds which decompose in hydroxylic solvents to yield olefinic (or bicylic) compounds and in aprotic solvents to yield olefins and cyclo-propanes. ... 

The reactions of alum with the common alkaline reagents are... 

It has been found " that those derivatives of 3-aminopropan-l-ol react most readily which contain secondary amino and hydroxyl groups as in the original formation of (1). The reaction can be catalyzed by alkaline reagents, e.g., small amounts of potassium hydroxide. 

The Action of Alkaline Reagents on 2 3-1 6- and 3 4-l 6-Dianhydro-3-talose. A Constitutional Synthesis of Chondrosamine and other Amino-Sugar Derivatives, S. P. James, F. Smith, M. Stacey, and L. F. Wiggins, J. Chem. Soc., (1946) 625-628. 

These compounds are much more toxic than chlordan (Table III), and yet are stable toward alkaline reagents (15), being unable to eliminate hydrogen chloride without the formation of a double bond at a bridgehead carbon atom. Thus in this type of compound the conclusion must again be reached that dehydrochlorination with alkali and insecticidal activity have no systematic relationship. 

The process of lactonization and enolization of 2-keto esters under the influence of alkaline reagents has also been applied to the production of analogs of L-ascorbic acid containing a six-membered ring structure.22 For example, methyl 3,4,6-trimethyl-2-keto-D-gluconate (XLI) is treated... 

This 2,3-dimethyl-D-araboascorbic acid (LXXXIII) behaves in precisely the same way as 2,3-dimethyl-L-ascorbic acid when treated with alkaline reagents.46 Saturation of the double bond between C2 and C3 by ring closure between C6 and C3 and transference of a proton to C2 takes place, giving LXXXVI. 

The isomerization of D-mannosaccharodilactone which proceeds under the influence of alkaline reagents can also be brought about by diazomethane and by silver oxide and methyl iodide. In both cases isomerization is accompanied by methylation and there results 2,5-dimethyI-A4-D-mannosaccharo-3,6-lactone methyl ester (Cl).84... 

Ketones and their Behavior toward Alkaline Reagents. J. Amer. chem. Soc. 73, 3831 (1951). 

The action of alkaline reagents on sugars has been the subject of much study since Lobry de Bruyn s researches in 1896. Many complex changes are induced in the sugar molecule by alkaline reagents, as is exemplified by the researches of Evans.Here, however, mention will be made only of the production of lactic acid by the action of alkali on sucrose. 

The scrubbing liquid is controlled to a neutral pH with reagent addition to drive SO2 absorption. Caustic soda (NaOH) is typically used as the alkaline reagent. However, other alkalis, such as soda ash, magnesium hydroxide, and lime have also been utilized with excellent results in terms of performance and reliability. For FCCU applications, however, where a 5-7 year continuous operation is required, the use of lime as a reagent is not recommended. Multiple levels of spray nozzles provide sufficient stages of gas/liquid contact to remove both particulate and SO2. An illustration of the spray tower and the spray nozzles is provided in Figure 16.6. 

Carbohydrate oxetanes have been prepared from deoxyiodo sugars without die use of strongly alkaline reagents. Thus, treatment of 5-deoxy-5-iodo-l,2-0-isopropylidene-a-D-xylofuranose with silver fluoride in cold pyridine afforded 3,5-anhydro-l,2-0-isopropylidene-... 

In the preparation described here, the alkaline reagent of choice is potassium hydroxide because it is more soluble in methanol than is sodium hydroxide. In the final purification of the product, residues of potassium salts and potassium hydroxide are also more easily removed than sodium analogs. Commercially, sodium methoxide is often used as the catalyst for hydrolysis, but handling of this reagent calls for a somewhat more complex procedure. 

Although (SN) t does not react with water or acidic solutions, the sensitivity of this inorganic polymer to alkaline reagents and to oxidation imposes... 

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